@article{cheng_meng_knappe_2025, title={Removal of Per- and Polyfluoroalkyl Substances (PFAS) in fixed bed anion exchange reactors: Factors determining PFAS uptake capacity and models predicting PFAS breakthrough}, volume={268}, ISSN={["1879-2448"]}, url={https://doi.org/10.1016/j.watres.2024.122629}, DOI={10.1016/j.watres.2024.122629}, journal={WATER RESEARCH}, author={Cheng, Lan and Meng, Pingping and Knappe, Detlef R. U.}, year={2025}, month={Jan} }
 @article{li_zhi_weed_broome_knappe_duckworth_2024, title={Commercial compost amendments inhibit the bioavailability and plant uptake of per- and polyfluoroalkyl substances in soil-porewater-lettuce systems}, volume={186}, ISSN={["1873-6750"]}, DOI={10.1016/j.envint.2024.108615}, abstractNote={Compost is widely used in agriculture as fertilizer while providing a practical option for solid municipal waste disposal. However, compost may also contain eight per- and polyfluoroalkyl substances (PFAS), potentially impacting soils and leading to PFAS entry into food chains and ultimately human exposure risks via dietary intake. This study examined how compost affects the bioavailability and uptake of eight PFAS (two ethers, three fluorotelomer sulfonates, and three perfluorosulfonates) by lettuce (Lactuca sativa) grown in commercial organic compost-amended, PFAS spiked soils. After 50 days of greenhouse experiment, PFAS uptake by lettuce decreased (by up to 90.5 %) with the increasing compost amendment ratios (0–20 %, w/w), consistent with their decreased porewater concentrations (by 30.7–86.3 %) in compost-amended soils. Decreased bioavailability of PFAS was evidenced by the increased in-situ soil-porewater distribution coefficients (Kd) (by factors of 1.5–7.0) with increasing compost additions. Significant negative (or positive) correlations (R2 ≥ 0.55) were observed between plant bioaccumulation (or soil-porewater distribution coefficient) and soil organic carbon content, suggesting that compost amendment inhibited plant uptake of PFAS mainly by increasing soil organic carbon and enhancing PFAS sorption. However, short-chain PFAS alternatives (i.e., Perfluoro-2-methoxyacetic acid (PFMOAA)) were effectively translocated to shoots with translocation factors > 2.9, increasing their risks of contamination in leafy vegetables. Our findings underscore the necessity for comprehensive risk assessment of compost-borne PFAS when using commercial compost products in agricultural lands.}, journal={ENVIRONMENT INTERNATIONAL}, author={Li, Yuanbo and Zhi, Yue and Weed, Rebecca and Broome, Stephen W. and Knappe, Detlef R. U. and Duckworth, Owen W.}, year={2024}, month={Apr} }
 @article{dodds_kirkwood-donelson_boatman_knappe_hall_schnetzer_baker_2024, title={Evaluating Solid Phase Adsorption Toxin Tracking (SPATT) for passive monitoring of per- and polyfluoroalkyl substances (PFAS) with Ion Mobility Spectrometry-Mass Spectrometry (IMS-MS)}, volume={947}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2024.174574}, abstractNote={Detection and monitoring of per- and polyfluoroalkyl substances (PFAS) in aquatic environments has become an increasingly higher priority of regulatory agencies as public concern for human intake of these chemicals continues to grow. While many methods utilize active sampling strategies ("grab samples") for precise PFAS quantitation, here we evaluate the efficacy of low-cost passive sampling devices (Solid Phase Adsorption Toxin Tracking, or SPATTs) for spatial and temporal PFAS assessment of aquatic systems. For this study, passive samplers were initially deployed in North Carolina along the Cape Fear River during the summer and fall of 2016 and 2017. These were originally intended for the detection of microcystins and monitoring potentially harmful algal blooms, though this period also coincided with occurrences of PFAS discharge from a local fluorochemical manufacturer into the river. Additional samplers were then deployed in 2022 to evaluate changes in PFAS fingerprint and abundances. Assessment of PFAS showed legacy compounds were observed across almost all sampling sites over all 3 years (PFHxS, PFOS, PFHxA, etc.), while emerging replacement PFAS (e.g., Nafion byproducts) were predominantly localized downstream from the manufacturer. Furthermore, samplers deployed downstream from the manufacturer in 2022 noted sharp decreases in observed signal for replacement PFAS in comparison to samplers deployed in 2016 and 2017, indicating mitigation and remediation efforts in the area were able to reduce localized fluorochemical contamination.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Dodds, James N. and Kirkwood-Donelson, Kaylie I. and Boatman, Anna K. and Knappe, Detlef R. U. and Hall, Nathan S. and Schnetzer, Astrid and Baker, Erin S.}, year={2024}, month={Oct} }
 @article{jensen_genereux_solomon_knappe_gilmore_2024, title={Forecasting and Hindcasting PFAS Concentrations in Groundwater Discharging to Streams near a PFAS Production Facility}, volume={9}, ISSN={["1520-5851"]}, url={https://doi.org/10.1021/acs.est.4c06697}, DOI={10.1021/acs.est.4c06697}, abstractNote={Per- and polyfluoroalkyl substances (PFAS) are known to be highly persistent in groundwater, making it vital to develop new approaches to important practical questions such as the time scale for future persistence of PFAS in contaminated groundwater. In the approach presented here, groundwater from beneath streambeds was analyzed for PFAS and age-dated using SF}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Jensen, Craig R. and Genereux, David P. and Solomon, D. Kip and Knappe, Detlef R. U. and Gilmore, Troy E.}, year={2024}, month={Sep} }
 @article{guelfo_ferguson_beck_chernick_doria-manzur_faught_flug_gray_jayasundara_knappe_et al._2024, title={Lithium-ion battery components are at the nexus of sustainable energy and environmental release of per- and polyfluoroalkyl substances}, volume={15}, ISSN={["2041-1723"]}, url={https://doi.org/10.1038/s41467-024-49753-5}, DOI={10.1038/s41467-024-49753-5}, abstractNote={Abstract Lithium-ion batteries (LiBs) are used globally as a key component of clean and sustainable energy infrastructure, and emerging LiB technologies have incorporated a class of per- and polyfluoroalkyl substances (PFAS) known as bis-perfluoroalkyl sulfonimides (bis-FASIs). PFAS are recognized internationally as recalcitrant contaminants, a subset of which are known to be mobile and toxic, but little is known about environmental impacts of bis-FASIs released during LiB manufacture, use, and disposal. Here we demonstrate that environmental concentrations proximal to manufacturers, ecotoxicity, and treatability of bis-FASIs are comparable to PFAS such as perfluorooctanoic acid that are now prohibited and highly regulated worldwide, and we confirm the clean energy sector as an unrecognized and potentially growing source of international PFAS release. Results underscore that environmental impacts of clean energy infrastructure merit scrutiny to ensure that reduced CO 2 emissions are not achieved at the expense of increasing global releases of persistent organic pollutants.}, number={1}, journal={NATURE COMMUNICATIONS}, author={Guelfo, Jennifer L. and Ferguson, P. Lee and Beck, Jonathan and Chernick, Melissa and Doria-Manzur, Alonso and Faught, Patrick W. and Flug, Thomas and Gray, Evan P. and Jayasundara, Nishad and Knappe, Detlef R. U. and et al.}, year={2024}, month={Jul} }
 @article{koyama_fasaee_berglund_knappe_2024, title={Machine Learning Models to Predict Early Breakthrough of Recalcitrant Organic Micropollutants in Granular Activated Carbon Adsorbers}, volume={9}, ISSN={0013-936X 1520-5851}, url={http://dx.doi.org/10.1021/acs.est.4c01316}, DOI={10.1021/acs.est.4c01316}, abstractNote={Granular activated carbon (GAC) adsorption is frequently used to remove recalcitrant organic micropollutants (MPs) from water. The overarching aim of this research was to develop machine learning (ML) models to predict GAC performance from adsorbent, adsorbate, and background water matrix properties. For model calibration, MP breakthrough curves were compiled and analyzed to determine the bed volumes of water that can be treated until MP breakthrough reaches ten percent of the influent MP concentration (BV10). Over 400 data points were split into training, validation, and testing sets. Seventeen variables describing MP, background water matrix, and GAC properties were explored in ML models to predict log}, journal={Environmental Science & Technology}, publisher={American Chemical Society (ACS)}, author={Koyama, Yoko and Fasaee, Mohammad A. K. and Berglund, Emily Z. and Knappe, Detlef R. U.}, year={2024}, month={Sep} }
 @article{kotlarz_mccord_wiecha_weed_cuffney_enders_strynar_knappe_reich_hoppin_2024, title={Measurement of Hydro-EVE and 6:2 FTS in Blood from Wilmington, North Carolina, Residents, 2017-2018}, volume={132}, ISSN={["1552-9924"]}, url={https://doi.org/10.1289/EHP14503}, DOI={10.1289/EHP14503}, number={2}, journal={ENVIRONMENTAL HEALTH PERSPECTIVES}, author={Kotlarz, Nadine and McCord, James and Wiecha, Nate and Weed, Rebecca A. and Cuffney, Michael and Enders, Jeffrey R. and Strynar, Mark and Knappe, Detlef R. U. and Reich, Brian J. and Hoppin, Jane A.}, year={2024}, month={Feb} }
 @article{hopkins_knappe_2024, title={Predicting per- and polyfluoroalkyl substances removal in pilot-scale granular activated carbon adsorbers from rapid small-scale column tests}, volume={6}, ISSN={["2577-8161"]}, url={https://doi.org/10.1002/aws2.1369}, DOI={10.1002/aws2.1369}, abstractNote={AbstractPer‐ and polyfluoroalkyl substances (PFAS) occur widely in drinking water, and consumption of contaminated drinking water is an important human exposure route. Granular activated carbon (GAC) adsorption can effectively remove PFAS from water. To support the design of GAC treatment systems, a rapid bench‐scale testing procedure and scale‐up approach are needed to assess the effects of GAC type, background water matrix, and empty bed contact time (EBCT) on GAC use rates. The overarching goal of this study was to predict PFAS breakthrough curves obtained at the pilot‐scale from rapid small‐scale column test (RSSCT) data. The scale‐up protocol was developed for pilot data obtained with coagulated/settled surface water (TOC = 2.3 mg/L), three GACs, and two EBCTs. Between 7 and 11 PFAS breakthrough curves were available for each pilot column. RSSCT designs were investigated that assumed intraparticle diffusivity is independent of GAC particle size (i.e., constant diffusivity [CD]) or linearly dependent on GAC particle size (i.e., proportional diffusivity [PD]). CD‐RSSCTs effectively predicted the bed volumes of water that could be treated at the pilot‐scale to reach 50% breakthrough (BV50%) of individual PFAS. In contrast, PD‐RSSCTs overpredicted BV50% obtained at the pilot‐scale by a factor of ~2–3. The shape of PFAS breakthrough curves obtained with CD‐RSSCTs deviated from those obtained at the pilot‐scale, indicating that intraparticle diffusivity was dependent on GAC particle diameter (dp). Using the pore surface diffusion model (PSDM), intraparticle diffusivity was found to be proportional to (dp)0.25 when considering data up to about 70% PFAS breakthrough. This proportionality factor can be used to design RSSCTs or scale up existing CD‐RSSCT data using the PSDM. Using pilot‐scale data obtained with groundwater and wastewater‐impacted groundwater as well as with additional GACs, the developed RSSCT scale‐up approach was validated for PFAS breakthrough percentages up to 70%. The presented methodology permits the rapid prediction of GAC use rates for PFAS removal.}, number={2}, journal={AWWA WATER SCIENCE}, author={Hopkins, Zachary R. and Knappe, Detlef R. U.}, year={2024}, month={Mar} }
 @article{kotlarz_mccord_wiecha_weed_cuffney_enders_strynar_knappe_reich_hoppin_2024, title={Reanalysis of PFO5DoA Levels in Blood from Wilmington, North Carolina, Residents, 2017-2018}, volume={132}, ISSN={["1552-9924"]}, url={https://doi.org/10.1289/EHP13339}, DOI={10.1289/EHP13339}, abstractNote={,}, number={2}, journal={ENVIRONMENTAL HEALTH PERSPECTIVES}, author={Kotlarz, Nadine and McCord, James and Wiecha, Nate and Weed, Rebecca A. and Cuffney, Michael and Enders, Jeffrey R. and Strynar, Mark and Knappe, Detlef R. U. and Reich, Brian J. and Hoppin, Jane A.}, year={2024}, month={Feb} }
 @article{cheng_knappe_2024, title={Removal of Per- and Polyfluoroalkyl substances by anion exchange resins: Scale-up of rapid small-scale column test data}, volume={249}, ISSN={["1879-2448"]}, url={https://doi.org/10.1016/j.watres.2023.120956}, DOI={10.1016/j.watres.2023.120956}, abstractNote={Anion exchange (IX) is a readily implementable water treatment method that can effectively remove per- and polyfluoroalkyl substances (PFAS). The overarching objective of this research was to predict PFAS removal in full- or pilot-scale packed-bed IX resin contactors from rapid small-scale column test (RSSCT) data. Specific objectives were to (1) assess the effects of IX resin crushing on total anion exchange capacity and packed bed density, (2) determine the effects of initial PFAS concentration on PFAS uptake capacity, (3) determine the rate-limiting step controlling PFAS uptake kinetics, (4) determine the effects of hydraulic loading rate on PFAS uptake capacity, and (5) link constant diffusivity RSSCT data to pilot test data to develop a scale-up protocol. Experiments were conducted with two single-use IX resins and three water matrices, including coagulated surface water and groundwater. Crushing IX resin did not substantially change the bed density and total anion exchange capacity, but the morphology of particles changed from almost perfectly spherical to irregularly shaped. PFAS uptake capacity was independent of influent PFAS concentrations in the 30-300 ng/L range. This finding facilitated the development of an RSSCT scale-up approach because influent PFAS concentrations in RSSCTs and corresponding pilot tests often differ. Biot number values and data from interrupted RSSCTs demonstrated that film diffusion or a combination of film diffusion and intraparticle diffusion controls the rate of PFAS uptake by IX resins. From RSSCTs with identical empty bed contact times but different hydraulic loading rates (v}, journal={WATER RESEARCH}, author={Cheng, Lan and Knappe, Detlef R. U.}, year={2024}, month={Feb} }
 @article{weaver_alexander_cubeta_knappe_aziz_2023, title={Degradation of imidacloprid by Phanerodontia chrysosporium on wood chips for stormwater treatment}, volume={9}, ISSN={["2053-1419"]}, url={https://doi.org/10.1039/D3EW00545C}, DOI={10.1039/d3ew00545c}, abstractNote={The white-rot fungus Phanerodontia chrysosporium degraded more than 50% of imidacloprid in synthetic stormwater in one week, demonstrating the potential of fungal bioremediation for improved contaminant removal in stormwater infrastructure.}, number={12}, journal={ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY}, author={Weaver, Leah M. M. and Alexander, Nancy Lee and Cubeta, Marc A. and Knappe, Detlef R. U. and Aziz, Tarek N.}, year={2023}, month={Nov}, pages={3333–3343} }
 @article{wallis_kotlarz_knappe_collier_lea_reif_mccord_strynar_dewitt_hoppin_2023, title={Estimation of the Half-Lives of Recently Detected Per- and Polyfluorinated Alkyl Ethers in an Exposed Community}, volume={57}, ISSN={["1520-5851"]}, url={https://doi.org/10.1021/acs.est.2c08241}, DOI={10.1021/acs.est.2c08241}, abstractNote={To estimate half-lives for novel fluoroethers, the GenX Exposure Study obtained two serum measurements for per- and polyfluoroalkyl substances (PFAS) for 44 participants of age 12-86 years from North Carolina, collected 5 and 11 months after fluoroether discharges into the drinking water source were controlled. The estimated half-lives for these compounds were 127 days (95% confidence interval (95% CI) = 86, 243 days) for perfluorotetraoxadecanoic acid (PFO4DA), 296 days for Nafion byproduct 2 (95% CI = 176, 924 days), and 379 days (95% CI = 199, 3870 days) for perfluoro-3,5,7,9,11-pentaoxadodecanoic acid (PFO5DoA). Using these estimates and the literature values, a model was built that predicted PFAS half-lives using structural properties. Three chemical properties predicted 55% of the variance of PFAS half-lives based on 15 PFAS. A model with only molecular weight predicted 69% of the variance. Some properties can predict the half-lives of PFAS, but a deeper understanding is needed. These fluoroethers had biological half-lives longer than published half-lives for PFHxA and PFHpA (30-60 days) but shorter than those for PFOA and PFOS (800-1200 days). These are the first and possibly only estimates of human elimination half-lives of these fluoroethers.}, number={41}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Wallis, Dylan J. and Kotlarz, Nadine and Knappe, Detlef R. U. and Collier, David N. and Lea, C. Suzanne and Reif, David and McCord, James and Strynar, Mark and DeWitt, Jamie C. and Hoppin, Jane A.}, year={2023}, month={Oct}, pages={15348–15355} }
 @article{cuffney_wilkie_kotlarz_knappe_lea_collier_dewitt_hoppin_2023, title={Factors associated with per- and polyfluoroalkyl substances (PFAS) serum concentrations in residents of New Hanover County, North Carolina: The GenX exposure study}, volume={237}, ISSN={["1096-0953"]}, url={https://doi.org/10.1016/j.envres.2023.117020}, DOI={10.1016/j.envres.2023.117020}, abstractNote={In 2017, people living in New Hanover County, North Carolina, learned that for ∼40 years they were unknowingly exposed to per- and polyfluoroalkyl substances (PFAS) through drinking water sourced by the Cape Fear River. Using data from the GenX Exposure Study, which measured serum PFAS levels in county residents, we aimed to understand questionnaire-measured factors associated with serum PFAS levels. Because most residents were served by the same municipal water source, we focused on surrogate factors of drinking water exposure that may contribute to variability in PFAS levels. Our analysis included 335 participants aged 6 and older. We included seven chemicals detected in ≥75% of the study population: four well-studied perfluoroalkyl acids (PFOA, PFOS, PFNA, PFHxS) and three understudied fluoroethers (Nafion byproduct 2, PFO4DA, PFO5DoA). For each PFAS, we evaluated associations of variables with serum PFAS levels adjusting for key demographic characteristics. Additionally, we developed predictive models for each PFAS. We used years of residence in the lower Cape Fear Region as a surrogate for water consumption. Duration of drinking water exposure was associated with higher serum levels of all seven PFAS. Drinking municipal water treated by home filters or other sources of water (non-city) were associated with lower PFAS concentrations for all seven PFAS compared to drinking municipal water without additional filtration. Males had higher levels of well-studied PFAS, but there was no difference for fluoroethers. For six PFAS, the predictive models explained ≥30% of the variance in serum PFAS levels. While some factors were significantly associated with levels of individual PFAS, their relative importance to overall prediction was low, such as microwave popcorn consumption. Consistently, water consumption-related variables were important for both the association and predictive investigations. These analyses provide additional evidence that drinking water is a primary source for serum PFAS concentrations among New Hanover County residents.}, journal={ENVIRONMENTAL RESEARCH}, author={Cuffney, Michael and Wilkie, Adrien A. and Kotlarz, Nadine and Knappe, Detlef and Lea, C. Suzanne and Collier, David N. and Dewitt, Jamie and Hoppin, Jane A.}, year={2023}, month={Nov} }
 @article{ruyle_pickard_schultes_fredriksson_heffernan_knappe_lord_meng_mills_ndungu_et al._2023, title={Interlaboratory Comparison of Extractable Organofluorine Measurements in Groundwater and Eel (<i>Anguilla rostrata</i>): Recommendations for Methods Standardization}, volume={57}, ISSN={["1520-5851"]}, url={https://doi.org/10.1021/acs.est.3c04560}, DOI={10.1021/acs.est.3c04560}, abstractNote={Research on per- and polyfluoroalkyl substances (PFAS) frequently incorporates organofluorine measurements, particularly because they could support a class-based approach to regulation. However, standardized methods for organofluorine analysis in a broad suite of matrices are currently unavailable, including a method for extractable organofluorine (EOF) measured using combustion ion chromatography (CIC). Here, we report the results of an international interlaboratory comparison. Seven laboratories representing academia, government, and the private sector measured paired EOF and PFAS concentrations in groundwater and eel (Anguilla rostrata) from a site contaminated by aqueous film-forming foam. Among all laboratories, targeted PFAS could not explain all EOF in groundwater but accounted for most EOF in eel. EOF results from all laboratories for at least one replicate extract fell within one standard deviation of the interlaboratory mean for groundwater and five out of seven laboratories for eel. PFAS spike mixture recoveries for EOF measurements in groundwater and eel were close to the criterion (±30%) for standardized targeted PFAS methods. Instrumental operation of the CIC such as replicate sample injections was a major source of measurement uncertainty. Blank contamination and incomplete inorganic fluorine removal may introduce additional uncertainties. To elucidate the presence of unknown organofluorine using paired EOF and PFAS measurements, we recommend that analysts carefully consider confounding methodological uncertainties such as differences in precision between measurements, data processing steps such as blank subtraction and replicate analyses, and the relative recoveries of PFAS and other fluorine compounds.}, number={48}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Ruyle, Bridger J. and Pickard, Heidi M. and Schultes, Lara and Fredriksson, Felicia and Heffernan, Amy L. and Knappe, Detlef R. U. and Lord, Heather L. and Meng, Pingping and Mills, Marc A. and Ndungu, Kuria and et al.}, year={2023}, month={Nov}, pages={20159–20168} }
 @article{zhang_tang_knappe_2023, title={Oxidation of Per- and Polyfluoroalkyl Ether Acids and Other Per- and Polyfluoroalkyl Substances by Sulfate and Hydroxyl Radicals: Kinetic Insights from Experiments and Models}, volume={5}, ISSN={["1520-5851"]}, url={https://doi.org/10.1021/acs.est.3c00947}, DOI={10.1021/acs.est.3c00947}, abstractNote={Per- and polyfluoroalkyl substances (PFAS) are widely used anthropogenic chemicals. Because of the strength of the carbon-fluorine bond, PFAS are not destroyed in typical water treatment processes. Sulfate (SO4•-) and hydroxyl (•OH) radicals can oxidize some PFAS, but the behavior of per- and polyfluoroalkyl ether acids (PFEAs) in processes involving SO4•- and •OH is poorly understood. In this study, we determined second-order rate constants (k) describing the oxidation of 18 PFAS, including 15 novel PFEAs, by SO4•- and •OH. Among the studied PFAS, 6:2 fluorotelomer sulfonate reacted most readily with •OH [k•OH = (1.1-1.2) × 107 M-1 s-1], while polyfluoroalkyl ether acids containing an -O-CFH- moiety reacted more slowly [k•OH = (0.5-1.0) × 106 M-1 s-1]. In the presence of SO4•-, polyfluoroalkyl ether acids with an -O-CFH- moiety reacted more rapidly [kSO4•- = (0.89-4.6) × 106 M-1 s-1] than perfluoroalkyl ether carboxylic acids (PFECAs) and a chloro-perfluoro-polyether carboxylic acid (ClPFPECA) [kSO4•- = (0.85-9.5) × 104 M-1 s-1]. For homologous series of perfluoroalkyl carboxylic acids, linear and branched monoether PFECAs, and multiether PFECAs, PFAS chain length had little impact on second-order rate constants. SO4•- reacted with the carboxylic acid headgroup of perfluoroalkyl carboxylic acids and PFECAs. In contrast, for polyfluoroalkyl ether carboxylic and sulfonic acids with an -O-CFH- moiety, the site of SO4•- attack was the -O-CFH- moiety. Perfluoroalkyl ether sulfonic acids were not oxidized by SO4•- and •OH under the conditions evaluated in this study.}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Zhang, Chuhui and Tang, Tiffany and Knappe, Detlef R. U.}, year={2023}, month={May} }
 @article{mcelroy_ogles_hyman_knappe_2023, title={Pilot-scale biofiltration of 1,4-dioxane at drinking water-relevant concentrations}, volume={231}, ISSN={["1879-2448"]}, url={https://doi.org/10.1016/j.watres.2023.119652}, DOI={10.1016/j.watres.2023.119652}, abstractNote={1,4-Dioxane is a drinking water contaminant of emerging concern. Because conventional and many advanced drinking water treatment technologies are ineffective for 1,4-dioxane removal, cost-effective technologies for the removal of 1,4-dioxane at drinking water-relevant concentrations are needed. In this research, a gravity-fed, cometabolic biofiltration system was developed to degrade 1,4-dioxane that was spiked into coagulated, settled surface water at a concentration of ∼10 µg/L. Objectives were to determine whether cometabolic degradation of trace levels of 1,4-dioxane can be sustained using n-butane as primary substrate and whether filter media properties and empty bed contact time (EBCT) affect biofiltration efficiency. A mixed culture of bacteria derived from the Cape Fear River basin and previously enriched using isobutane served as inoculum for biologically active filters. Two granular activated carbons (GACs) with different grain sizes and one carbonaceous resin were used as attachment media, and n-butane served as the primary substrate for biologically active filters. Non-inoculated controls with the same media were evaluated in parallel to distinguish between biological and adsorptive removals of 1,4-dioxane. For the duration of the pilot study (>3 months), 1,4-dioxane was degraded in inoculated biofilters receiving n-butane. In control filters containing larger and smaller grain GAC, 1,4-dioxane broke through completely within 750 and 1250 bed volumes, respectively, corresponding to 15 to 30 days of operation at an EBCT of 30 min. 1,4-Dioxane removal increased with increasing EBCT in all biologically active filters. At an EBCT of 30 min, the biologically active GAC filter containing the larger-grain GAC removed on average 87% of 1,4-dioxane at pseudo steady-state. When the hydraulic loading rate was decreased to achieve an overall EBCT of 60 min, 1,4-dioxane was removed to <1 µg/L in the biologically active GAC filter containing the larger-grain GAC. Activity-based labeling showed the presence of catalytically active monooxygenases in backwash water from biologically active filters that degraded 1,4-dioxane. Amplicon sequencing results showed that while taxa shifted after the initial inoculation of biologically active filters, taxa in biologically active filters remained more similar to the inoculum than those in the non-inoculated control filters. Overall, results of this research demonstrate that cometabolic degradation of 1,4-dioxane at trace levels is possible for extended periods of time in inoculated biofilters that receive n-butane as primary substrate.}, journal={WATER RESEARCH}, author={McElroy, Amie C. and Ogles, Matthew E. and Hyman, Michael R. and Knappe, Detlef R. U.}, year={2023}, month={Mar} }
 @article{stults_choi_rockwell_schaefer_nguyen_knappe_illangasekare_higgins_2023, title={Predicting Concentration- and Ionic-Strength-Dependent Air-Water Interfacial Partitioning Parameters of PFASs Using Quantitative Structure-Property Relationships (QSPRs)}, volume={3}, ISSN={["1520-5851"]}, url={https://doi.org/10.1021/acs.est.2c07316}, DOI={10.1021/acs.est.2c07316}, abstractNote={Air-water interfacial retention of poly- and perfluoroalkyl substances (PFASs) is increasingly recognized as an important environmental process. Herein, column transport experiments were used to measure air-water interfacial partitioning values for several perfluoroalkyl ethers and for PFASs derived from aqueous film-forming foam, while batch experiments were used to determine equilibrium Kia data for compounds exhibiting evidence of rate-limited partitioning. Experimental results suggest a Freundlich isotherm best describes PFAS air-water partitioning at environmentally relevant concentrations (101-106 ng/L). A multiparameter regression analysis for Kia prediction was performed for the 15 PFASs for which equilibrium Kia values were determined, assessing 246 possible combinations of 8 physicochemical and system properties. Quantitative structure-property relationships (QSPRs) based on three to four parameters provided predictions of high accuracy without model overparameterization. Two QSPRs (R2 values of 0.92 and 0.83) were developed using an assumed average Freundlich n value of 0.65 and validated across a range of relevant concentrations for perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), and hexafluoropropylene oxide-dimer acid (i.e., GenX). A mass action model was further modified to account for the changing ionic strength on PFAS air-water interfacial sorption. The final result was two distinct QSPRs for estimating PFAS air-water interfacial partitioning across a range of aqueous concentrations and ionic strengths.}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Stults, John F. and Choi, Youn Jeong and Rockwell, Cooper and Schaefer, Charles E. and Nguyen, Dung D. and Knappe, Detlef R. U. and Illangasekare, Tissa H. and Higgins, Christopher P.}, year={2023}, month={Mar} }
 @article{guelfo_ferguson_beck_chernick_doria-manzur_faught_flug_gray_jayasundara_knappe_et al._2023, title={The dirty side of clean energy: Lithium ion batteries as a source of PFAS in the environment}, url={https://doi.org/10.21203/rs.3.rs-3150504/v1}, DOI={10.21203/rs.3.rs-3150504/v1}, abstractNote={Abstract
        Lithium ion batteries (LiBs) are used globally as a key component of clean and sustainable energy iinfrastructure1,2. Emerging LiB technologies have incorporated a novel class of per- and polyfluoroalkyl substances (PFAS, i.e., "forever chemicals") known as bis-perfluoroalkyl sulfonimides (bis-FASIs)3–8. PFAS are recognized internationally as recalcitrant, mobile, and toxic environmental contaminants9.  Despite this, virtually nothing is known about environmental impacts of bis-FASIs released during LiB manufacture, use, and disposal.  Here we demonstrate that occurrence, ecotoxicity, and treatability of this novel class of PFAS are comparable to PFAS that are now prohibited and highly regulated worldwide10–15 and confirm the clean energy sector as an unrecognized and growing source of global PFAS release. U.S. and European surface water, soil, and sediment measurements confirmed bis-FASI release internationally at concentrations as high as 2,437 parts per trillion (ppt). Toxicity data demonstrated effects on swimming behavior in Daphnia magna at bis-FASI exposures of 10 ppt and swimming behavior and metabolic process changes in Danio rerio resulting from exposures of 25 ppt. Occurrence of up to 881 ppt of bis-FASIs in landfill leachates highlights current impacts of LiB disposal. Although fully recalcitrant to advanced oxidation processes, select bis-FASIs were removed from water during adsorptive treatment with similar or better efficiency as more hydrophobic PFAS such as perfluorooctane sulfonate (PFOS).  LiB use is anticipated to increase globally over the next decade, and 8 million tons of LiB waste are projected by 2040 as a result of low recycling rates16. This suggests that environmental exposure to this novel, unregulated class of PFAS will increase with time and will be relevant to the majority of the world's population.  Results underscore that environmental impacts of clean energy infrastructure merit scrutiny to ensure that reduced CO2 emissions are not achieved at the expense of increasing global releases of persistent organic pollutants.}, author={Guelfo, Jennifer and Ferguson, P. and Beck, Jonathan and Chernick, Melissa and Doria-Manzur, Alonso and Faught, Patrick and Flug, Thomas and Gray, Evan and Jayasundara, Nishad and Knappe, Detlef and et al.}, year={2023}, month={Aug} }
 @article{pétré_genereux_koropeckyj-cox_knappe_duboscq_gilmore_hopkins_2022, title={Correction to “Per- and Polyfluoroalkyl Substance (PFAS) Transport from Groundwater to Streams near a PFAS Manufacturing Facility in North Carolina, USA”}, volume={56}, url={https://doi.org/10.1021/acs.est.2c03111}, DOI={10.1021/acs.est.2c03111}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to "Per- and Polyfluoroalkyl Substance (PFAS) Transport from Groundwater to Streams near a PFAS Manufacturing Facility in North Carolina, USA"Marie-Amélie Pétré*Marie-Amélie PétréMore by Marie-Amélie Pétréhttps://orcid.org/0000-0001-7975-7476, David P. Genereux*David P. GenereuxMore by David P. Genereux, Lydia Koropeckyj-CoxLydia Koropeckyj-CoxMore by Lydia Koropeckyj-Cox, Detlef R. U. KnappeDetlef R. U. KnappeMore by Detlef R. U. Knappehttps://orcid.org/0000-0003-1315-1791, Sandrine DuboscqSandrine DuboscqMore by Sandrine Duboscq, Troy E. GilmoreTroy E. GilmoreMore by Troy E. Gilmore, and Zachary R. HopkinsZachary R. HopkinsMore by Zachary R. HopkinsCite this: Environ. Sci. Technol. 2022, 56, 12, 9145Publication Date (Web):June 1, 2022Publication History Published online1 June 2022Published inissue 21 June 2022https://pubs.acs.org/doi/10.1021/acs.est.2c03111https://doi.org/10.1021/acs.est.2c03111correctionACS PublicationsCopyright © 2022 American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views1330Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (484 KB) Get e-Alertsclose Get e-Alerts}, number={12}, journal={Environmental Science & Technology}, publisher={American Chemical Society (ACS)}, author={Pétré, Marie-Amélie and Genereux, David P. and Koropeckyj-Cox, Lydia and Knappe, Detlef R. U. and Duboscq, Sandrine and Gilmore, Troy E. and Hopkins, Zachary R.}, year={2022}, month={Jun}, pages={9145–9145} }
 @article{hosseini_mcelroy_knappe_gabr_pour-ghaz_2022, title={Diffusion of benzene and tetrachloroethylene through saturated cement paste}, volume={329}, ISSN={0950-0618}, url={http://dx.doi.org/10.1016/j.conbuildmat.2022.127196}, DOI={10.1016/j.conbuildmat.2022.127196}, abstractNote={Diffusion of highly volatile organic compounds (VOCs) through buried concrete infrastructure components, such as pipes and culverts, can occur if these components come in contact with contaminated groundwater or soil. Among various VOCs, benzene and tetrachloroethylene (PCE), are the most common contaminants. This paper aims at measuring the effective diffusion coefficients of benzene and PCE in cement paste. The free diffusion coefficients of VOCs in simulated pore solution were also measured and used in empirical models. Results show that VOCs diffusion coefficients decreased with decreasing w/c because of reduced porosity and increased tortuosity of the pore network as well as increased ionic strength of the pore solution. The increased ionic strength of the pore solution reduced the solubility limit of VOCs in the pore solution and decreased the free diffusion coefficient of VOCs in the pore solution. Also, among all models, phenomenological model provided the most accurate estimates.}, journal={Construction and Building Materials}, publisher={Elsevier BV}, author={Hosseini, Payam and McElroy, Amie and Knappe, Detlef R.U. and Gabr, Mohammed and Pour-Ghaz, Mohammad}, year={2022}, month={Apr}, pages={127196} }
 @article{rosen_kotlarz_knappe_lea_collier_richardson_hoppin_2022, title={Drinking Water-Associated PFAS and Fluoroethers and Lipid Outcomes in the GenX Exposure Study}, volume={130}, ISSN={["1552-9924"]}, url={https://doi.org/10.1289/EHP11033}, DOI={10.1289/EHP11033}, abstractNote={Background: Residents of Wilmington, North, Carolina, were exposed to drinking water contaminated by fluoroethers and legacy per- and polyfluoroalkyl substances (PFAS), such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), with fluoroether exposure occurring from 1980 to 2017. PFOA and PFOS have previously been associated with metabolic dysfunction; however, few prior studies have examined associations between other PFAS and lipid levels. Objectives: We measured the association between serum fluoroether and legacy PFAS levels and various cholesterol outcomes. Methods: Participants in the GenX Exposure Study contributed nonfasting blood samples in November 2017 and May 2018 that were analyzed for 20 PFAS (10 legacy, 10 fluoroethers) and serum lipids [total cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglycerides] and calculated non-HDL cholesterol. We estimated covariate-adjusted associations between quartiles of exposure to each of the PFAS measures (as well as the summed concentrations of legacy PFAS, fluoroethers, and all 10 targeted PFAS) and lipid outcomes by fitting inverse probability of treatment weighted linear regressions. Results: In this cross-sectional study of 326 participants (age range 6–86 y), eight PFAS were detected in >50% of the population. For PFOS and perfluorononanoic acid (PFNA), non-HDL cholesterol was approximately 5mg/dL higher per exposure quartile increase: [PFOS: 4.89; 95% confidence interval (CI): 0.10, 9.68 and PFNA: 5.25 (95% CI: 0.39, 10.1)], whereas total cholesterol was approximately 6mg/dL higher per quartile [PFOS: 5.71 (95% CI: 0.38, 11.0), PFNA: 5.92 (95% CI: 0.19, 11.7)]. In age-stratified analyses, associations were strongest among the oldest participants. One fluoroether was associated with higher HDL, whereas other fluoroether compounds were not associated with serum lipid levels. Discussion: PFNA and PFOS were associated with higher levels of total and non-HDL cholesterol, with associations larger in magnitude among older adults. In the presence of these legacy PFAS, fluoroethers appeared to be associated with HDL but not non-HDL lipid measures. https://doi.org/10.1289/EHP11033}, number={9}, journal={ENVIRONMENTAL HEALTH PERSPECTIVES}, author={Rosen, Emma M. and Kotlarz, Nadine and Knappe, Detlef R. U. and Lea, C. Suzanne and Collier, David N. and Richardson, David B. and Hoppin, Jane A.}, year={2022}, month={Sep} }
 @article{meng_destefano_knappe_2022, title={Extraction and Matrix Cleanup Method for Analyzing Novel Per- and Polyfluoroalkyl Ether Acids and Other Per- and Polyfluoroalkyl Substances in Fruits and Vegetables}, volume={70}, ISSN={["1520-5118"]}, url={https://doi.org/10.1021/acs.jafc.1c07665}, DOI={10.1021/acs.jafc.1c07665}, abstractNote={Per- and polyfluoroalkyl ether acids (PFEAs) are a subclass of per- and polyfluoroalkyl substances (PFAS) that are detected with increasing frequency in environmental matrices. Diet can be an important route of PFEA exposure, but the presence of PFEAs in food is poorly understood. Extraction methods for food samples exist for traditionally studied PFAS, but their suitability for PFEAs and other novel PFAS remains unknown. In this study, an extraction and matrix cleanup method was developed to quantify 45 PFAS, including 13 PFEAs, 3 perfluoroalkane sulfonamides, and 6 fluorotelomer carboxylic acids in 10 types of fruits and vegetables. Homogenized samples were extracted with basic methanol, and resulting extracts were diluted with water and cleaned up using solid-phase extraction with weak anion-exchange cartridges. The method was validated by performing spike-recovery experiments at spike levels of 1 ng/g in all 10 matrices and 0.1 ng/g in 2 matrices. For PFAS without a corresponding isotopically labeled internal standard (IS), adopting an IS with a similar chromatographic retention time generated the most accurate recoveries. Dependent upon the matrix, recoveries of 38-44 PFAS (including 10-13 PFEAs) fell within 50-150% for samples spiked at 1 ng/g. Recoveries of 40 and 38 PFAS in blueberries and corn, respectively, fell within 50-150% for samples spiked at 0.1 ng/g. Method quantification limits (MQLs) of PFAS in pure solvents were determined as the lowest calibration level with an accuracy between 70 and 130%. To compensate for matrix effects, a matrix factor was applied on the basis of the analyte response in different matrices relative to the pure solvent. The MQLs of 45 PFAS (including 13 PFEAs) in 10 matrices ranged from 0.025 to 0.25 ng/g. Overall, this method is capable of sensitively quantifying 45 PFAS in many fruits and vegetables.}, number={16}, journal={JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Meng, Pingping and DeStefano, Noelle J. and Knappe, Detlef R. U.}, year={2022}, month={Apr}, pages={4792–4804} }
 @article{kempisty_arevalo_spinelli_edeback_dickenson_husted_higgins_summers_knappe_2022, title={Granular activated carbon adsorption of perfluoroalkyl acids from ground and surface water}, url={https://doi.org/10.1002/aws2.1269}, DOI={10.1002/aws2.1269}, abstractNote={AbstractAdsorption of perfluoroalkyl acids (PFAAs) by granular activated carbon (GAC) was evaluated in bench‐, pilot‐, and full‐scale studies to determine effects of PFAA characteristics and background organic matter on carbon use rates. Rapid small‐scale column tests (RSSCTs) were conducted according to the proportional diffusivity (PD) design to assess their suitability to predict full‐ or pilot‐scale GAC performance. PFAA removal from groundwater (GW) and coagulated surface water (SW) was studied with two sub‐bituminous coal‐based GACs. In batch tests conducted with pulverized GAC, the GACs performed similarly in GW, but the GAC with the larger mesopore volume was more effective for PFAA removal from SW. In column tests, carbon use rates decreased with increasing PFAA chain length and were lower for GW (total organic carbon [TOC] = 0.7 mg/L) than for SW (TOC = 2.0–2.7 mg/L). The volume of SW that could be treated to 10% or 50% PFAA breakthrough was about 50–60% of the volume of GW that could be treated when comparing pilot‐scale data for SW with full‐scale data for GW. Consistent differences in PFAA adsorption capacity were not observed for empty bed contact times of 13 and 26 min in full‐scale adsorbers treating GW. The PD‐RSSCT simulating PFAA removal from GW consistently overpredicted full‐scale adsorption capacity, on average by ~70%. Using a carbon use rate of <25 mgGAC/Lwater treated) as a criterion for the feasibility of GAC treatment, full‐ and pilot‐scale GAC adsorber data suggest that GAC is a viable treatment option (carbon use rate < 25 mgGAC/Lwater treated) for perfluoroalkylcarboxylic acids with six or more carbon atoms in SW and five or more carbon atoms in GW. For perfluoroalkyl sulfonic acids, GAC treatment is viable for compounds containing four or more carbons based on results obtained with both SW and GW.}, journal={AWWA Water Science}, author={Kempisty, David M. and Arevalo, Elisa and Spinelli, Allison M. and Edeback, Viking and Dickenson, Eric R. V. and Husted, Courtney and Higgins, Christopher P. and Summers, R. Scott and Knappe, Detlef R. U.}, year={2022}, month={Jan} }
 @article{vatankhah_tajdini_milstead_clevenger_murray_knappe_remucal_bellona_2022, title={Impact of ozone-biologically active filtration on the breakthrough of Perfluoroalkyl acids during granular activated carbon treatment of municipal wastewater effluent}, volume={223}, ISSN={["1879-2448"]}, url={https://doi.org/10.1016/j.watres.2022.118988}, DOI={10.1016/j.watres.2022.118988}, abstractNote={The presence of perfluoroalkyl acids (PFAAs) in municipal wastewater has highlighted the need to develop PFAA treatment approaches for wastewater effluent and potable reuse applications. Ozone (O3) and biologically active filtration (BAF) were investigated as standalone and combined pretreatment processes to improve the performance of granular activated carbon (GAC) for PFAA removal from wastewater effluent. As individual processes, ozonation at all three investigated doses (0.35, 0.75, 1.0 mg O3/mg DOC) and BAF at both tested empty bed contact times (EBCT; 15 and 20 min) led to significant improvement in PFAA removal by subsequent GAC treatment. With respect to standalone ozonation, the specific O3 dose of 0.75 mg O3/mg DOC was proven to be the optimum operating condition as further increase of the specific ozone dose to 1.0 mg O3/mg DOC did not provide considerable additional improvement. Extending the EBCT during standalone BAF from 15 to 20 minutes significantly improved the efficacy of GAC for the removal of tested PFAAs. Pretreatment with O3-BAF (0.75 mg O3/mg DOC; 20 min EBCT) in tandem outperformed both standalone ozonation and BAF for the removal of PFAA by GAC. Characterization of effluent organic matter (EfOM) by size exclusion chromatography (SEC) and Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR-MS) before and after pretreatments suggest that among multiple co-occurring phenomena, the shift towards smaller and more polar EfOM may have predominantly alleviated pore constriction/blockage without having adverse impact on direct site competition. This observation is supported by SEC and FT-ICR-MS results indicating reduced EfOM molecular size through O3 and BAF pretreatment as well as transition to more hydrophilic byproducts.}, journal={WATER RESEARCH}, author={Vatankhah, Hooman and Tajdini, Bahareh and Milstead, Reid P. and Clevenger, Erica and Murray, Conner and Knappe, Detlef and Remucal, Christina K. and Bellona, Christopher}, year={2022}, month={Sep} }
 @article{nickels_genereux_knappe_2023, title={Improved Darcian streambed measurements to quantify flux and mass discharge of volatile organic compounds from a contaminated aquifer to an urban stream}, volume={253}, ISSN={["1873-6009"]}, DOI={10.1016/j.jconhyd.2022.104124}, abstractNote={Quantifying VOC transport from contaminated groundwater to streams is challenging and important for understanding off-site migration of VOCs, cross-media contamination (groundwater to surface water and eventually air), and potential impacts on downstream ecosystems and human populations. A streambed point sampling approach was used to quantify fluxes of water and 14 VOCs from groundwater to an urban stream in North Carolina, USA, during summer (June 2015) and winter (January 2016). The approach is unique in coupling measurements of vertical hydraulic conductivity, vertical hydraulic head gradient, and groundwater VOC concentration at each individual sampling point, reducing or eliminating some potential concerns with other Darcian methods for quantifying VOC inputs to streams. Most results were consistent with discharge of two main VOC plumes on opposite sides of the stream. Plume 1 from the west side was dominated by cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) at mean concentrations of 19 and 11 μg L−1, respectively. Plume 2 from the east side was dominated by benzene (mean concentration 56 μg L−1). Plume 2 was not previously known, and the improved sampling approach allowed VOC discharge from both plumes to be quantified simultaneously. For 13 of the 14 detected VOCs, the mean VOC flux from groundwater to the stream (fVOC) was higher in January 2016 than in June 2015, mainly because groundwater flux was higher in January. The only exception was cDCE, the most abundant VOC in Plume 1, which had mean fVOC values of 9.8 and 9.5 mg m−2 d−1 in June 2015 and January 2016, respectively. Benzene was the most abundant VOC in Plume 2 and had mean fVOC values of 11 and 37 mg m−2 d−1 in June 2015 and January 2016, respectively. High groundwater flux drove almost all the occurrences of high VOC flux. For a given VOC, the flow-weighted mean concentration (with each VOC concentration weighted by the upward groundwater flux at the VOC sampling point) was generally larger than the unweighted mean concentration. Thus, flow-weighting of concentrations gave a more accurate indication of the average VOC concentration in net groundwater discharge to the stream. An estimate of total VOC mass discharge from groundwater to the study reach of the stream, 3.6 kg of VOC per year, was based on the fVOC results and streambed area in the reach. The bulk of this discharge was due to benzene, cDCE, and VC, with individual mass discharges of 2.1, 0.83, and 0.40 kg yr−1, respectively. Estimates of maximum potential VOC degradation in the streambed suggest that the 3.6 kg yr−1 estimate of mass discharge was not sensitive to potential degradation of VOCs in the streambed sediments above the groundwater sampling depth.}, journal={JOURNAL OF CONTAMINANT HYDROLOGY}, author={Nickels, J. L. and Genereux, D. P. and Knappe, D. R. U.}, year={2023}, month={Feb} }
 @article{zhi_paterson_call_jones_hesterberg_duckworth_poitras_knappe_2022, title={Mechanisms of orthophosphate removal from water by lanthanum carbonate and other lanthanum-containing materials}, volume={820}, ISSN={["1879-1026"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85123356200&partnerID=MN8TOARS}, DOI={10.1016/j.scitotenv.2022.153153}, abstractNote={Removing phosphorus (P) from water and wastewater is essential for preventing eutrophication and protecting environmental quality. Lanthanum [La(III)]-containing materials can effectively and selectively remove orthophosphate (PO4) from aqueous systems, but there remains a need to better understand the underlying mechanism of PO4 removal. Our objectives were to 1) identify the mechanism of PO4 removal by La-containing materials and 2) evaluate the ability of a new material, La2(CO3)3(s), to remove PO4 from different aqueous matrices, including municipal wastewater. We determined the dominant mechanism of PO4 removal by comparing geochemical simulations with equilibrium data from batch experiments and analyzing reaction products by X-ray diffraction and scanning transmission electron microscopy with energy dispersive spectroscopy. Geochemical simulations of aqueous systems containing PO4 and La-containing materials predicted that PO4 removal occurs via precipitation of poorly soluble LaPO4(s). Results from batch experiments agreed with those obtained from geochemical simulations, and mineralogical characterization of the reaction products were consistent with PO4 removal occurring primarily by precipitation of LaPO4(s). Between pH 1.5 and 12.9, La2(CO3)3(s) selectively removed PO4 over other anions from different aqueous matrices, including treated wastewater. However, the rate of PO4 removal decreased with increasing solution pH. In comparison to other solids, such as La(OH)3(s), La2(CO3)3(s) exhibits a relatively low solubility, particularly under slightly acidic conditions. Consequently, release of La3+ into the environment can be minimized when La2(CO3)3(s) is deployed for PO4 sequestration.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, publisher={Elsevier BV}, author={Zhi, Yue and Paterson, Alisa R. and Call, Douglas F. and Jones, Jacob L. and Hesterberg, Dean and Duckworth, Owen W. and Poitras, Eric P. and Knappe, Detlef R. U.}, year={2022}, month={May} }
 @article{crimi_speth_chowdhury_dickenson_knappe_liu_2022, title={PFAS Challenges and Novel Research A Conversation With the Editorial Board of the AWWA Water Science Topical Collection on PFAS Analytics and Treatment}, volume={114}, ISSN={["1551-8833"]}, DOI={10.1002/awwa.1956}, abstractNote={Key TakeawaysPer‐ and polyfluoroalkyl substances, “forever chemicals” commonly known as PFAS and used in countless products, have become a significant environmental and public health concern.Among especially alarming PFAS issues are their pervasive presence, the low concentrations at which they are found to be hazardous, and the challenges and limitations of remediation.A roundtable interview with water industry experts—guest editors of an AWWA Water Science article collection—presents their candid, comprehensive take on the PFAS picture.}, number={7}, journal={JOURNAL AWWA}, author={Crimi, Michelle and Speth, Thomas F. and Chowdhury, Zaid K. and Dickenson, Eric R. V. and Knappe, Detlef R. U. and Liu, Jinxia}, year={2022}, month={Sep}, pages={13–22} }
 @article{speth_crimi_chowdhury_dickenson_guelfo_knappe_liu_leeson_2022, title={PFAS are forever? The state of the science and research needs for analyzing and treating PFAS‐laden water}, url={https://doi.org/10.1002/aws2.1276}, DOI={10.1002/aws2.1276}, abstractNote={This juxtaposition of factors combined with a lack of standardized analytical methods, health effects data, and treatment options for the vast majority of PFAS identified in the environment have created a complex regulatory and social dynamic. Without a firm regulatory framework, impacted water utilities and other entities can be pressured into making difficult choices. Ideally, any management approach chosen would be flexible enough to account for future health protection requirements along with changes in other factors, such as increased knowledge of additional PFAS because of advances in analytical techniques or changing influent PFAS concentrations. This flexibility ideally would include both the treatment of the water for its intended use, but also for handling any residual streams that would be disposed of in a managed system or via discharge to the environment. However, any built-in flexibility must be economically, managerially, technically, and environmentally sustainable. To develop a sound management approach, more guidance is needed. This includes general information to set the stage for what PFAS need to be removed, including}, journal={AWWA Water Science}, author={Speth, Thomas and Crimi, Michelle and Chowdhury, Zaid and Dickenson, Eric and Guelfo, Jennifer and Knappe, Detlef and Liu, Jinxia and Leeson, Andrea}, year={2022}, month={Mar} }
 @article{petre_salk_stapleton_ferguson_tait_obenour_knappe_genereux_2022, title={Per- and polyfluoroalkyl substances (PFAS) in river discharge: Modeling loads upstream and downstream of a PFAS manufacturing plant in the Cape Fear watershed, North Carolina}, volume={831}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2022.154763}, abstractNote={The Cape Fear River is an important source of drinking water in North Carolina, and many drinking water intakes in the watershed are affected by per- and polyfluoroalkyl substances (PFAS). We quantified PFAS concentrations and loads in river water upstream and downstream of a PFAS manufacturing plant that has been producing PFAS since 1980. River samples collected from September 2018 to February 2021 were analyzed for 13 PFAS at the upstream station and 43-57 PFAS downstream near Wilmington. Frequent PFAS sampling (daily to weekly) was conducted close to gauging stations (critical to load estimation), and near major drinking water intakes (relevant to human exposure). Perfluoroalkyl acids dominated upstream while fluoroethers associated with the plant made up about 47% on average of the detected PFAS downstream. Near Wilmington, Σ43PFAS concentration averaged 143 ng/L (range 40-377) and Σ43PFAS load averaged 3440 g/day (range 459-17,300), with 17-88% originating from the PFAS plant. LOADEST was a useful tool in quantifying individual and total quantified PFAS loads downstream, however, its use was limited at the upstream station where PFAS levels in the river were affected by variable inputs from a wastewater treatment plant. Long-term monitoring of PFAS concentrations is warranted, especially at the downstream station. Results suggest a slight downward trend in PFAS levels downstream, as indicated by a decrease in flow-weighted mean concentrations and the best-fitting LOADEST model. However, despite the cessation of PFAS process wastewater discharge from the plant in November 2017, and the phase-out of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in North America, both fluoroethers and legacy PFAS continue to reach the river in significant quantities, reflecting groundwater discharge to the river and other continuing inputs. Persistence of PFAS in surface water and drinking water supplies suggests that up to 1.5 million people in the Cape Fear watershed might be exposed.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Petre, M-A and Salk, K. R. and Stapleton, H. M. and Ferguson, P. L. and Tait, G. and Obenour, D. R. and Knappe, D. R. U. and Genereux, D. P.}, year={2022}, month={Jul} }
 @misc{evich_davis_mccord_acrey_awkerman_knappe_lindstrom_speth_tebes-stevens_strynar_et al._2022, title={Per- and polyfluoroalkyl substances in the environment}, volume={375}, ISSN={["1095-9203"]}, url={https://doi.org/10.1126/science.abg9065}, DOI={10.1126/science.abg9065}, abstractNote={Over the past several years, the term PFAS (per- and polyfluoroalkyl substances) has grown to be emblematic of environmental contamination, garnering public, scientific, and regulatory concern. PFAS are synthesized by two processes, direct fluorination (e.g., electrochemical fluorination) and oligomerization (e.g., fluorotelomerization). More than a megatonne of PFAS is produced yearly, and thousands of PFAS wind up in end-use products. Atmospheric and aqueous fugitive releases during manufacturing, use, and disposal have resulted in the global distribution of these compounds. Volatile PFAS facilitate long-range transport, commonly followed by complex transformation schemes to recalcitrant terminal PFAS, which do not degrade under environmental conditions and thus migrate through the environment and accumulate in biota through multiple pathways. Efforts to remediate PFAS-contaminated matrices still are in their infancy, with much current research targeting drinking water.}, number={6580}, journal={SCIENCE}, author={Evich, Marina G. and Davis, Mary J. B. and McCord, James P. and Acrey, Brad and Awkerman, Jill A. and Knappe, Detlef R. U. and Lindstrom, Andrew B. and Speth, Thomas F. and Tebes-Stevens, Caroline and Strynar, Mark J. and et al.}, year={2022}, month={Feb}, pages={512-+} }
 @article{fang_meng_schaefer_knappe_2023, title={Removal and destruction of perfluoroalkyl ether carboxylic acids (PFECAs) in an anion exchange resin and electrochemical oxidation treatment train}, volume={230}, ISSN={["1879-2448"]}, DOI={10.1016/j.watres.2022.119522}, abstractNote={Perfluoroalkyl ether carboxylic acids (PFECAs) are a group of emerging recalcitrant contaminants that are being developed to replace legacy per- and polyfluoroalkyl substances (PFAS) in industrial applications and that are generated as by-products in fluoropolymer manufacturing. Here, we report on the removal and destruction of four structurally different PFECAs using an integrated anion exchange resin (AER) and electrochemical oxidation (ECO) treatment train. Results from this work illustrated that (1) flow-through columns packed with PFAS-selective AERs are highly effective for the removal of PFECAs and (2) PFECA affinity is strongly correlated with their hydrophobic features. Regeneration of the spent resin columns revealed that high percentage (e.g., 80%) of organic cosolvent is necessary for achieving 60-100% PFECA release, and regeneration efficiency was higher for a macroporous resin than a gel-type resin. Treatment of spent regenerants showed (1) >99.99% methanol removal was achieved by distillation, (2) >99.999% conversion of the four studied PFECAs was achieved during the ECO treatment of the still bottoms after 24 hours with an energy per order of magnitude of PFECA removal (EE/O) <1.03 kWh/m3 of total groundwater treated, and (3) >85% of the organic fluorine was recovered as inorganic fluoride. Trifluoroacetic acid (TFA), perfluoropropionic acid (PFPrA), and perfluoro-2-methoxyacetic acid (PFMOAA) were confirmed via high-resolution mass spectrometry as transformation products (TPs) in the treated still bottoms, and two distinctive degradation schemes and four reaction pathways are proposed for the four PFECAs. Lastly, dissolved organic matter (DOM) inhibited uptake, regeneration, and oxidation of PFECAs throughout the treatment train, suggesting pretreatment steps targeting DOM removal can enhance the system's treatment efficiency. Results from this work provide guidelines for developing effective separation-concentration-destruction treatment trains and meaningful insights for achieving PFECA destruction in impacted aquatic systems.}, journal={WATER RESEARCH}, author={Fang, Yida and Meng, Pingping and Schaefer, Charles and Knappe, Detlef R. U.}, year={2023}, month={Feb} }
 @article{wallis_barton_knappe_kotlarz_mcdonough_higgins_hoppin_adgate_2023, title={Source apportionment of serum PFASs in two highly exposed communities}, volume={855}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2022.158842}, abstractNote={Per- and polyfluoroalkyl substances (PFASs) are synthetic chemicals that are ubiquitous in environmental and biological systems, including human serum. PFASs are used in many products and industrial processes and are tied to numerous health effects. Due to multiple sources and exposure pathways, methods are needed to identify PFAS sources in communities to develop targeted interventions. We assessed effectiveness of three source apportionment methods (UNMIX, positive matrix factorization [PMF], and principal component analysis - multiple linear regression [PCA-MLR]) for identifying contributors to human serum PFAS concentrations in two highly exposed populations in Colorado and North Carolina where drinking water was contaminated via upstream sources, including a Space Force base and a fluorochemical manufacturing plant. UNMIX and PMF models extracted three to four potential PFAS exposure sources in the Colorado and North Carolina cohorts while PCA-MLR classified two in each cohort. No sources were characterized in NHANES (National Health and Nutrition Examination Study). Results suggest that these three methods can successfully identify sources in highly exposed populations. Future PFAS exposure research should focus on analyzing serum for an expanded PFAS panel, identifying cohorts with other distinct point source exposures, and combining biological and environmental data to better understand source apportionment results in the context of PFAS toxicokinetic behavior.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Wallis, Dylan J. and Barton, Kelsey E. and Knappe, Detlef R. U. and Kotlarz, Nadine and McDonough, Carrie A. and Higgins, Christopher P. and Hoppin, Jane A. and Adgate, John L.}, year={2023}, month={Jan} }
 @article{parker_knappe_titaley_wanzek_field_2022, title={Tools for Understanding and Predicting the Affinity of Per- and Polyfluoroalkyl Substances for Anion-Exchange Sorbents br}, volume={56}, ISSN={["1520-5851"]}, url={https://doi.org/10.1021/acs.est.1c08345}, DOI={10.1021/acs.est.1c08345}, abstractNote={Anion-exchange (AE) sorbents are gaining in popularity for the remediation of anionic per- and polyfluoroalkyl substances (PFAS) in water. However, it is unclear how hydrophobic and electrostatic interactions contribute to anionic PFAS retention. The goal of this study was to understand the effects of PFAS chain length and head group on electrostatic interactions between PFAS and an aminopropyl AE phase. Liquid chromatography-mass spectrometry (LC-MS) was used with an aminopropyl AE guard column to find relative retention times. The average electrostatic potential (EPavg) of each PFAS was calculated, which correlated positively with the PFAS chromatographic retention time, demonstrating the value of EPavg as a proxy for predicting electrostatic interactions between PFAS and the aminopropyl AE phase. The order of greatest to lowest PFAS AE affinity for an aminopropyl column based on chromatographic retention times and electrostatic interactions was n:3 fluorotelomer carboxylic acids (n:3 FtAs) > n:2 fluorotelomer carboxylic acids (n:2 FtAs) > perfluoroalkyl carboxylates (PFCAs) > perfluoroalkyl sulfonamides (FASAs) ∼ n:2 fluorotelomer sulfonates (n:2 FtSs) > perfluoroalkyl sulfonates (PFSAs). This study introduces a methodology for qualitatively characterizing electrostatic interactions between PFAS and AE phases and highlights that electrostatic interactions alone cannot explain the affinity of PFAS for AE resins in water treatment/remediation scenarios.}, number={22}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Parker, Bethany A. and Knappe, Detlef R. U. and Titaley, Ivan A. and Wanzek, Thomas A. and Field, Jennifer A.}, year={2022}, month={Nov}, pages={15470–15477} }
 @article{zhi_call_grieger_duckworth_jones_knappe_2021, title={Influence of natural organic matter and pH on phosphate removal by and filterable lanthanum release from lanthanum-modified bentonite}, volume={202}, ISSN={0043-1354}, url={http://dx.doi.org/10.1016/j.watres.2021.117399}, DOI={10.1016/j.watres.2021.117399}, abstractNote={Lanthanum modified bentonite (LMB) has been applied to eutrophic lakes to reduce phosphorus (P) concentrations in the water column and mitigate P release from sediments. Previous experiments suggest that natural organic matter (NOM) can interfere with phosphate (PO4)-binding to LMB and exacerbate lanthanum (La)-release from bentonite. This evidence served as motivation for this study to systematically determine the effects of NOM, solution pH, and bentonite as a La carrier on P removal. We conducted both geochemical modeling and controlled-laboratory batch kinetic experiments to understand the pH-dependent impacts of humic and fulvic acids on PO4-binding to LMB and La release from LMB. The role of bentonite was studied by comparing PO4 removal obtained by LMB and La3+ (added as LaCl3 salt to represent the La-containing component of LMB). Our results from both geochemical modeling and batch experiments indicate that the PO4-binding ability of LMB is decreased in the presence of NOM, and the decrease is more pronounced at pH 8.5 than at 6. At the highest evaluated NOM concentration (28 mg C L−1), PO4-removal by La3+ was substantially lower than that by LMB, implying that bentonite clay in LMB shielded La from interactions with NOM, while still allowing PO4 capture by La. Finally, the presence of NOM promoted La-release from LMB, and the amount of La released depended on solution pH and both the type (i.e., fulvic/humic acid ratio) and concentration of NOM. Overall, these results provide an important basis for management of P in lakes and eutrophication control that relies on LMB applications.}, journal={Water Research}, publisher={Elsevier BV}, author={Zhi, Yue and Call, Douglas F. and Grieger, Khara D. and Duckworth, Owen W. and Jones, Jacob L. and Knappe, Detlef R.U.}, year={2021}, month={Sep}, pages={117399} }
 @article{mulhern_bynum_liyanapatirana_destefano_knappe_gibson_2021, title={Longitudinal assessment of point‐of‐use carbon filters for removal of per‐ and polyfluoroalkyl substances from private well water}, volume={3}, url={https://doi.org/10.1002/aws2.1262}, DOI={10.1002/aws2.1262}, abstractNote={AbstractEighteen private well users in North Carolina were recruited to test the performance of under‐sink, activated carbon block water filters to remove per‐ and polyfluoroalkyl substances (PFAS). Monthly sampling was conducted for 8 months. Filters were certified for removal of perfluorooctanoic acid and perfluorooctanesulfonic acid under NSF International certification P473, but not for additional short‐chain perfluoroalkyl acids or perfluoroalkyl ether acids (PFEAs) evaluated in this study. Out of 47 targeted analytes, 17 PFAS were detected in filter influent samples (influent ∑PFAS 4.7–131 ng/L). Mixed‐effects Tobit regression models showed that the filters effectively removed 97%–99% of all influent PFAS, including short‐chain PFEAs, for the entire manufacturer‐recommended lifetime of the device. The prevalence of PFAS above the minimum reporting limits was reduced by 99.5%, and the prevalence of any PFAS above the method detection limits was reduced by 92%. The results provide increased confidence in NSF P473‐certified filters for the removal of PFAS from private well water.}, number={6}, journal={AWWA Water Science}, publisher={Wiley}, author={Mulhern, Riley and Bynum, Nichole and Liyanapatirana, Chamindu and DeStefano, Noelle J. and Knappe, Detlef R. U. and Gibson, Jacqueline MacDonald}, year={2021}, month={Nov} }
 @article{petre_genereux_koropeckyj-cox_knappe_duboscq_gilmore_hopkins_2021, title={Per- and Polyfluoroalkyl Substance (PFAS) Transport from Groundwater to Streams near a PFAS Manufacturing Facility in North Carolina, USA}, volume={55}, ISSN={["1520-5851"]}, url={https://doi.org/10.1021/acs.est.0c07978}, DOI={10.1021/acs.est.0c07978}, abstractNote={We quantified per- and polyfluoroalkyl substance (PFAS) transport from groundwater to five tributaries of the Cape Fear River near a PFAS manufacturing facility in North Carolina (USA). Hydrologic and PFAS data were coupled to quantify PFAS fluxes from groundwater to the tributaries. Up to 29 PFAS were analyzed, including perfluoroalkyl acids and recently identified fluoroethers. Total quantified PFAS (ΣPFAS) in groundwater was 20–4773 ng/L (mean = 1863 ng/L); the range for stream water was 426–3617 ng/L (mean = 1717 ng/L). Eight PFAS constituted 98% of ΣPFAS; perfluoro-2-(perfluoromethoxy)propanoic acid (PMPA) and hexafluoropropylene oxide dimer acid (GenX) accounted for 61%. For PFAS discharge from groundwater to one tributary, values estimated from stream water measurements (18 ± 4 kg/yr) were similar to those from groundwater measurements in streambeds (22–25 ± 5 kg/yr). At baseflow, 32 ± 7 kg/yr of PFAS discharged from groundwater to the five tributaries, eventually reaching the Cape Fear River. Given the PFAS emission timeline at the site, groundwater data suggest the abundant fluoroethers moved through the subsurface to streams in ≪50 yr. Discharge of contaminated groundwater may lead to long-term contamination of surface water and impacts on downstream drinking water supplies. This work addresses a gap in the PFAS literature: quantifying PFAS mass transfer between groundwater and surface water using field data.}, number={9}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, publisher={American Chemical Society (ACS)}, author={Petre, Marie-Amelie and Genereux, David P. and Koropeckyj-Cox, Lydia and Knappe, Detlef R. U. and Duboscq, Sandrine and Gilmore, Troy E. and Hopkins, Zachary R.}, year={2021}, month={May}, pages={5848–5856} }
 @article{baker_knappe_2021, title={Per- and polyfluoroalkyl substances (PFAS)-contaminants of emerging concern}, volume={12}, ISSN={["1618-2650"]}, DOI={10.1007/s00216-021-03811-9}, journal={ANALYTICAL AND BIOANALYTICAL CHEMISTRY}, author={Baker, Erin S. and Knappe, Detlef R. U.}, year={2021}, month={Dec} }
 @article{kwiatkowski_andrews_birnbaum_bruton_dewitt_knappe_maffini_miller_pelch_reade_et al._2021, title={Response to “Comment on Scientific Basis for Managing PFAS as a Chemical Class”}, volume={8}, url={https://doi.org/10.1021/acs.estlett.1c00049}, DOI={10.1021/acs.estlett.1c00049}, abstractNote={O recent publication titled, “Scientific Basis for Managing PFAS as a Chemical Class”, concludes that the combination of high persistence, accumulation potential, mobility, and known and potential harm of the thousands of PFAS (perand polyfluoroalkyl substances) identified to date justifies managing them as a single class of chemicals. Classbased approaches have been applied to other chemicals as a more efficient and effective alternative to the traditional approach of addressing one chemical at a time that is timeconsuming and costly. Regulatory work in the European Union has recently begun to apply this framework to PFAS in its Chemicals Strategy for Sustainability. Here we are responding to the comment by Singh and Papanastasiou (DOI: 10.1021/acs.estlett.0c00765) who disagree with a class-based approach to PFAS and build their argument around hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), and hydrofluoroolefins (HFOs), which are fluorinated gases used in refrigeration, air conditioning, and other applications. It is worth noting that the authors work for Honeywell International Inc., a major manufacturer of PFAS refrigerant gases and other fluorinated products, as they disclosed. We are grateful for this opportunity to expand the public discourse regarding specific uses of PFAS and to provide examples demonstrating the importance of managing the entire class of PFAS. First, as an overall approach, we disagree with Singh and Papanastasiou’s suggestion that societies should pursue “an extensive scientific evaluation of each PFAS subgroup and compounds within”. While such in-depth information for each compound would be ideal for scientific understanding, it is not necessary for regulating or managing PFAS. Most importantly, it leads to undue and harmful delays in protecting human and ecological health. Second, Singh and Papanastasiou state that the majority of HCFCs, HFCs, and HFOs degrade fully in the environment or transform into trifluoroacetic acid (TFA), which they claim is persistent but does not bioaccumulate and is therefore not problematic. Such claims are not supported by evidence; quite the opposite. TFA has been found in high levels in human blood and can cause severe skin burns and eye damage, as well as harm to aquatic life, with long-lasting effects. The wide use of HCFCs, HFCs, and HFOs has resulted in significant environmental accumulation of TFA, as reflected by the >10fold increase in the level of Arctic deposition since implementation of the Montreal Protocol and the 17-fold increase in the level of TFA in Beijing waters from 2002 to 2012. As TFA is persistent and highly mobile in the environment, the continued use of HCFCs, HFCs, and HFOs will result in increased and widespread accumulation of TFA, and thus increased risks of chronic exposure for humans and other biota. Due to the long degradation half-lives of many HCFCs, HFCs, and HFOs, even with an immediate cessation of their use, they would continue to break down in the environment for years, even decades, resulting in increasing levels of accumulated TFA. Other scientists have argued, and we agree, that high environmental persistence alone is a sufficient basis for managing PFAS as a single class of chemicals and that mobility is of equivalent concern to bioaccumulation. Third, Singh and Papanastasiou argue that although perfluorocarboxylic acids (PFCAs) are of great regulatory interest, the contribution of PFCA precursors is responsible for a small fraction of environmental PFCA contamination. This statement is not accurate. In fact, references they cite demonstrate the opposite, particularly that a large, overlooked environmental reservoir of various side chain fluorinated polymers, one group of PFCA precursors among many others, has built up, and PFCA releases from their slow (bio)degradation can be significant in the long term. With regard to their example of fluorotelomer alcohols (FTOHs), these specific precursors have long been known to degrade into other toxic PFAS. Concern over FTOHs is growing as some metabolites of FTOHs have been shown to be more toxic than PFCAs, and recently, a toxic metabolite of the short chain 6:2 FTOH (5:3 fluorotelomer carboxylic acid) was demonstrated to bioaccumulate. When it comes to concern over environmental and human exposure to PFAS, it matters little whether harm comes from the precursor or the degradation product. The identities and sources of the wide range of PFAS to which we are exposed are often unknown. Extractable organic fluorine (EOF) analyses of environmental matrices, biota, and human serum show that in numerous cases ≪50% of organofluorines could be identified, with a proportion of compounds coming from PFCA precursors. These examples support the idea that the current scientific evidence is sufficient to move forward with a class-based}, number={2}, journal={Environmental Science & Technology Letters}, publisher={American Chemical Society (ACS)}, author={Kwiatkowski, Carol F. and Andrews, David Q. and Birnbaum, Linda S. and Bruton, Thomas A. and DeWitt, Jamie C. and Knappe, Detlef R.U. and Maffini, Maricel V. and Miller, Mark F. and Pelch, Katherine E. and Reade, Anna and et al.}, year={2021}, month={Feb}, pages={195–197} }
 @article{zhang_mcelroy_liberatore_alexander_knappe_2022, title={Stability of Per- and Polyfluoroalkyl Substances in Solvents Relevant to Environmental and Toxicological Analysis br}, volume={56}, ISSN={["1520-5851"]}, url={https://doi.org/10.1021/acs.est.1c03979}, DOI={10.1021/acs.est.1c03979}, abstractNote={Per- and polyfluoroalkyl substances (PFASs) are widely used anthropogenic chemicals. For environmental and toxicological analysis, it is important to understand the stability of PFASs, including novel per- and polyfluoroalkyl ether acids (PFEAs), in commonly used solvents. In this study, we investigated the effects of PFAS characteristics, solvent type, water-to-organic solvent ratio, and temperature on the stability of 21 PFASs including 18 PFEAs. None of the studied PFASs showed measurable degradation in deionized water, methanol, or isopropyl alcohol over 30 days; however, nine PFEAs degraded in the polar aprotic solvents acetonitrile, acetone, and dimethyl sulfoxide (DMSO). PFEA degradation followed first-order kinetics, and first-order rate constants increased with increasing temperature and with decreasing water-to-organic solvent ratio. Monoethers with a carboxylic acid functional group adjacent to a tertiary carbon (>CF-COOH) degraded more rapidly than multiethers in which the carboxylic acid moiety was adjacent to repeating -CF2O- groups. In contrast, monoethers with a carboxylic acid moiety adjacent to a secondary carbon (-CF2-COOH) were stable in all tested solvents. Using high-resolution mass spectrometry, we determined that PFEAs with a >CF-COOH group were stoichiometrically decarboxylated in aprotic solvents and formed products with a >CFH group; e.g., hexafluoropropylene oxide-dimer acid (HFPO-DA or GenX), HFPO-trimer acid, and HFPO-tetramer acid were stoichiometrically converted to Fluoroethers E-1, E-2, and E-3, respectively. PFEA degradation results highlight the importance of solvent choice when preparing dosing solutions and performing extractions for environmental and toxicological assessments of PFEAs.}, number={10}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, publisher={American Chemical Society (ACS)}, author={Zhang, Chuhui and McElroy, Amie C. and Liberatore, Hannah K. and Alexander, Nancy Lee M. and Knappe, Detlef R. U.}, year={2022}, month={May}, pages={6103–6112} }
 @article{herkert_merrill_peters_bollinger_zhang_hoffman_ferguson_knappe_stapleton_2020, title={Assessing the Effectiveness of Point-of-Use Residential Drinking Water Filters for Perfluoroalkyl Substances (PFASs)}, volume={7}, ISSN={["2328-8930"]}, url={https://doi.org/10.1021/acs.estlett.0c00004}, DOI={10.1021/acs.estlett.0c00004}, abstractNote={Per- and polyfluoroalkyl substances (PFASs) have come under increased scrutiny due to concerns about their potential toxicity and prevalence in the environment, particularly drinking water. PFASs a...}, number={3}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS}, publisher={American Chemical Society (ACS)}, author={Herkert, Nicholas J. and Merrill, John and Peters, Cara and Bollinger, David and Zhang, Sharon and Hoffman, Kate and Ferguson, P. Lee and Knappe, Detlef R. U. and Stapleton, Heather M.}, year={2020}, month={Mar}, pages={178–184} }
 @article{merle_knappe_pronk_vogler_hollender_gunten_2020, title={Assessment of the breakthrough of micropollutants in full-scale granular activated carbon adsorbers by rapid small-scale column tests and a novel pilot-scale sampling approach}, volume={6}, ISSN={["2053-1419"]}, url={https://doi.org/10.1039/D0EW00405G}, DOI={10.1039/d0ew00405g}, abstractNote={This study aimed to compare three approaches for predicting the service life of full-scale GAC adsorbers for the removal of micropollutants.}, number={10}, journal={ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY}, publisher={Royal Society of Chemistry (RSC)}, author={Merle, Tony and Knappe, Detlef R. U. and Pronk, Wouter and Vogler, Bernadette and Hollender, Juliane and Gunten, Urs}, year={2020}, month={Oct}, pages={2742–2751} }
 @article{kearns_dickenson_aung_joseph_summers_knappe_2021, title={Biochar Water Treatment for Control of Organic Micropollutants with Ultraviolet A Surrogate Monitoring}, volume={38}, ISSN={["1557-9018"]}, DOI={10.1089/ees.2020.0173}, abstractNote={Biochar adsorbent can be produced in low-resource settings using local materials and simple pyrolysis technology, and it has shown promise for uptake of micropollutants (MPs) such as pesticides, pharmaceuticals, industrial compounds, and chemicals released from consumer goods present in water at ng/L to μg/L levels. Accordingly, the use of biochar in water treatment applications where granular activated carbon (GAC) is economically or logistically infeasible is gaining interest. Monitoring treatment systems for individual MPs require laboratory analytical techniques that are typically cost-prohibitive and impractical for low-resource settings. Therefore, identification of surrogate parameters(s) for adsorbent bed life that can be measured inexpensively and in the field is a high priority. Background dissolved organic matter (DOM) is ubiquitous in natural and anthropogenic waters at concentrations typically 1,000 to 100,000 that of MPs. Some constituents of DOM foul the adsorbent and reduce bed life for removal of target contaminants. Aromatic DOM foulants absorb ultraviolet light at a wavelength of 254 nm (UVA254). Because DOM fouling directly affects MP adsorption capacity and DOM is a bulk water parameter that can be quantified using relatively inexpensive and portable instruments, it could be exploited as a surrogate for monitoring biochar adsorber bed life under field conditions. The objective of this study was to quantify removal of MPs from waters containing different types and concentrations of background DOM (surface water, wastewater, dump leachate) and thus exhibiting different UVA254 breakthrough profiles in bench-scale column experiments. Breakthrough profiles of weakly to moderately adsorbing MPs, including herbicides, pharmaceuticals and personal care products, and perfluoroalkyl acids, were collected using biochars generated under different pyrolysis conditions and a commercial GAC as a performance benchmark. Optimal conditions for biochar water treatment include using biochar produced from wood at ≥850°C under slightly aerobic conditions, empty bed contact times of ≥30 min, and upstream treatment processes to reduce DOM. Relative UVA254 breakthrough (C/C0) up to 0.6–0.9 corresponded to ≥90% MP removal for most MP-water combinations studied.}, number={5}, journal={ENVIRONMENTAL ENGINEERING SCIENCE}, author={Kearns, Joshua and Dickenson, Eric and Aung, Myat Thandar and Joseph, Sarangi Madhavi and Summers, Scott R. and Knappe, Detlef}, year={2021}, month={May}, pages={298–309} }
 @article{hosseini_alhomair_faeli_pour-ghaz_gabr_knappe_parker_2020, title={Degradation Model for the Tensile Strength of PVC and Rubber Gasket Materials Exposed to Benzene and PCE-Saturated Aqueous Solutions}, volume={2674}, ISSN={["2169-4052"]}, DOI={10.1177/0361198120906126}, abstractNote={ In this paper, a tensile strength degradation model is developed for polyvinyl chloride (PVC) pipe and three rubber gasket materials commonly used in stormwater drains and wet utilities; the degradation model considers exposure to a single contaminant at its saturation level. The contaminant considered included benzene and tetrachloroethylene (PCE) because of their prevalence. The materials considered are unplasticized Polyvinyl chloride (u-PVC) utilized as the pipe material, and three types of rubber gaskets: Polychloroprene (Neoprene-CR), Acrylonitrile (nitrile) butadiene rubber (Buna-N), and fluoroelastomer rubber (FKM—Grade A VitonTM). First, the degradation rates of these materials are experimentally quantified using accelerated testing; then using the experimental results and Williams–Landel–Ferry (WLF) method a degradation model is developed. Finally, a simplified method is introduced to relate the tensile strength degradation of PVC to the penetration rate of the contaminants. }, number={2}, journal={TRANSPORTATION RESEARCH RECORD}, author={Hosseini, Payam and Alhomair, Sultan and Faeli, Zahra and Pour-Ghaz, Mohammad and Gabr, Mohammed and Knappe, Detlef and Parker, Cyrus}, year={2020}, month={Feb}, pages={274–283} }
 @article{guillette_mccord_guillette_polera_rachels_morgeson_kotlarz_knappe_reading_strynar_et al._2020, title={Elevated levels of per- and polyfluoroalkyl substances in Cape Fear River Striped Bass (Morone saxatilis) are associated with biomarkers of altered immune and liver function}, volume={136}, ISSN={["1873-6750"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85079172705&partnerID=MN8TOARS}, DOI={10.1016/j.envint.2019.105358}, abstractNote={Per- and polyfluoroalkyl substances (PFAS) are anthropogenic chemicals of concern that persist in the environment. Environmental monitoring revealed high concentrations of hexafluoropropylene oxide dimer acid (HFPO-DA) and other novel PFAS in the lower Cape Fear River; however, there is limited information on PFAS exposures and effects of this contamination on aquatic biota. Serum concentrations of 23 PFAS in Striped Bass (Morone saxatilis) from the Cape Fear River (n = 58) and a reference population from an aquaculture laboratory on the Pamlico/Tar watershed (n = 29) were quantified using liquid chromatography and high-resolution mass spectrometry, and correlations between PFAS concentrations and health-related serum biomarkers were evaluated. Perfluorooctane sulfonate, the predominant PFAS in Cape Fear River Striped Bass serum, was detectable in every sample with serum concentrations reaching 977 ng/mL. Perfluorononanoic and perfluorodecanoic acid were also detected in all samples, with perfluorohexanesulfonic acid present in >98% of the samples. HFPO-DA (range <0.24-5.85 ng/mL) and Nafion byproduct 2 (range <0.2-1.03 ng/mL) were detected in 48% and 78% of samples, respectively. The mean total PFAS concentration found in domestic Striped Bass raised in well-water under controlled aquaculture conditions was 40 times lower, with HPFO-DA detected in 10% of the samples, and Nafion byproduct 2 was not detected. The elevated PFAS concentrations found in the Cape Fear River Striped Bass were associated with biomarkers of alterations in the liver and immune system.}, journal={ENVIRONMENT INTERNATIONAL}, author={Guillette, T. C. and McCord, James and Guillette, Matthew and Polera, M. E. and Rachels, Kyle T. and Morgeson, Clint and Kotlarz, Nadine and Knappe, Detlef R. U. and Reading, Benjamin J. and Strynar, Mark and et al.}, year={2020}, month={Mar} }
 @misc{zhi_zhang_hjorth_baun_duckworth_call_knappe_jones_grieger_2020, title={Emerging lanthanum (III)-containing materials for phosphate removal from water: A review towards future developments}, volume={145}, ISSN={["1873-6750"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85090951095&partnerID=MN8TOARS}, DOI={10.1016/j.envint.2020.106115}, abstractNote={The last two decades have seen a rise in the development of lanthanum (III)-containing materials (LM) for controlling phosphate in the aquatic environment. >70 papers have been published on this topic in the peer-reviewed literature, but mechanisms of phosphate removal by LM as well as potential environmental impacts of LM remain unclear. In this review, we summarize peer-reviewed scientific articles on the development and use of 80 different types of LM in terms of prospective benefits, potential ecological impacts, and research needs. We find that the main benefits of LM for phosphate removal are their ability to strongly bind phosphate under diverse environmental conditions (e.g., over a wide pH range, in the presence of diverse aqueous constituents). The maximum phosphate uptake capacity of LM correlates primarily with the La content of LM, whereas reaction kinetics are influenced by LM formulation and ambient environmental conditions (e.g., pH, presence of co-existing ions, ligands, organic matter). Increased La solubilization can occur under some environmental conditions, including at moderately acidic pH values (i.e., < 4.5–5.6), highly saline conditions, and in the presence of organic matter. At the same time, dissolved La will likely undergo hydrolysis, bind to organic matter, and combine with phosphate to precipitate rhabdophane (LaPO4·H2O), all of which reduce the bioavailability of La in aquatic environments. Overall, LM use presents a low risk of adverse effects in water with pH > 7 and moderate-to-high bicarbonate alkalinity, although caution should be applied when considering LM use in aquatic systems with acidic pH values and low bicarbonate alkalinity. Moving forward, we recommend additional research dedicated to understanding La release from LM under diverse environmental conditions as well as long-term exposures on ecological organisms, particularly primary producers and benthic organisms. Further, site-specific monitoring could be useful for evaluating potential impacts of LM on both biotic and abiotic systems post-application.}, journal={ENVIRONMENT INTERNATIONAL}, publisher={Elsevier BV}, author={Zhi, Yue and Zhang, Chuhui and Hjorth, Rune and Baun, Anders and Duckworth, Owen W. and Call, Douglas F. and Knappe, Detlef R. U. and Jones, Jacob L. and Grieger, Khara}, year={2020}, month={Dec} }
 @article{kearns_dickenson_knappe_2020, title={Enabling Organic Micropollutant Removal from Water by Full-Scale Biochar and Activated Carbon Adsorbers Using Predictions from Bench-Scale Column Data}, volume={37}, ISSN={["1557-9018"]}, DOI={10.1089/ees.2019.0471}, abstractNote={Organic micropollutants (MPs), such as pesticides, pharmaceuticals, industrial compounds, and waste breakdown products occurring in waters at ng/L-μg/L levels are a threat to ecosystems and human h...}, number={7}, journal={ENVIRONMENTAL ENGINEERING SCIENCE}, author={Kearns, Joshua and Dickenson, Eric and Knappe, Detlef}, year={2020}, month={Jul}, pages={459–471} }
 @misc{dodds_alexander_kirkwood_foster_hopkins_knappe_baker_2021, title={From Pesticides to Per- and Polyfluoroalkyl Substances: An Evaluation of Recent Targeted and Untargeted Mass Spectrometry Methods for Xenobiotics}, volume={93}, ISSN={["1520-6882"]}, url={https://doi.org/10.1021/acs.analchem.0c04359}, DOI={10.1021/acs.analchem.0c04359}, abstractNote={Environmental analysis of xenobiotics is a challenging yet necessary undertaking to characterize pollution levels, assess the effectiveness of remediation interventions, and prevent adverse environmental and health outcomes. Xenobiotics are concerning from an environmental perspective due to their chemical persistence, toxicity to humans and wildlife, and prolific use in agricultural and industrial applications.1 Many xenobiotics are persistent organic pollutants (POPs), and the number of POPs listed in the Stockholm Convention is}, number={1}, journal={ANALYTICAL CHEMISTRY}, publisher={American Chemical Society (ACS)}, author={Dodds, James N. and Alexander, Nancy Lee M. and Kirkwood, Kaylie I and Foster, MaKayla R. and Hopkins, Zachary R. and Knappe, Detlef R. U. and Baker, Erin S.}, year={2021}, month={Jan}, pages={641–656} }
 @article{cuthbertson_kimura_liberatore_knappe_stanford_summers_dickenson_maness_glover_selbes_et al._2020, title={GAC to BAC: Does it make chloraminated drinking water safer?}, volume={172}, ISSN={["0043-1354"]}, DOI={10.1016/j.watres.2019.115432}, abstractNote={Biological activated carbon (BAC) is widely used as a polishing step at full-scale drinking water plants to remove taste and odor compounds and assimilable organic carbon. BAC, especially with pre-ozonation, has been previously studied to control regulated disinfection by-products (DBPs) and DBP precursors. However, most previous studies only include regulated or a limited number of unregulated DBPs. This study explored two full-scale drinking water plants that use pre-chloramination followed by BAC and chloramine as the final disinfectant. While chloramine generally produces lower concentrations of regulated DBPs, it may form increased levels of unregulated nitrogenous and iodinated DBPs. We evaluated 71 DBPs from ten DBP classes including haloacetonitriles, haloacetamides, halonitromethanes, haloacetaldehydes, haloketones, iodinated acetic acids, iodinated trihalomethanes, nitrosamines, trihalomethanes, and haloacetic acids, along with speciated total organic halogen (total organic chlorine, bromine and iodine) across six different BAC filters of increasing age. Most preformed DBPs were well removed by BAC with different ages (i.e., operation times). However, some preformed DBPs were poorly removed or increased following treatment with BAC, including chloroacetaldehyde, dichloronitromethane, bromodichloronitromethane, N-nitrosodimethylamine, dibromochloromethane, tribromomethane, dibromochloroacetic acid, and tribromoacetic acid. Some compounds, including dibromoacetaldehyde, bromochloroacetamide, and dibromoacetamide, were formed only after treatment with BAC. Total organic halogen removal was variable in both plants and increases in TOCl or TOI were observable on one occasion at each plant. While calculated genotoxicity decreased in all filters, decreases in overall DBP formation did not correlate with decreases in calculated cytotoxicity. In three of the six filters, calculated toxicity increased by 4-27%. These results highlight that DBP concentration alone may not always provide an adequate basis for risk assessment.}, journal={WATER RESEARCH}, author={Cuthbertson, Amy A. and Kimura, Susana Y. and Liberatore, Hannah K. and Knappe, Detlef R. U. and Stanford, Benjamin and Summers, R. Scott and Dickenson, Eric R. and Maness, J. Clark and Glover, Caitlin and Selbes, Meric and et al.}, year={2020}, month={Apr} }
 @article{kotlarz_mccord_collier_lea_strynar_lindstrom_wilkie_islam_matney_tarte_et al._2020, title={Measurement of Novel, Drinking Water-Associated PFAS in Blood from Adults and Children in Wilmington, North Carolina}, volume={128}, ISSN={["1552-9924"]}, DOI={10.1289/EHP6837}, abstractNote={Background: From 1980 to 2017, a fluorochemical manufacturing facility discharged wastewater containing poorly understood per- and polyfluoroalkyl substances (PFAS) to the Cape Fear River, the primary drinking water source for Wilmington, North Carolina, residents. Those PFAS included several fluoroethers including HFPO-DA also known as GenX. Little is known about the bioaccumulation potential of these fluoroethers. Objective: We determined levels of fluoroethers and legacy PFAS in serum samples from Wilmington residents. Methods: In November 2017 and May 2018, we enrolled 344 Wilmington residents ≥6 years of age into the GenX Exposure Study and collected blood samples. Repeated blood samples were collected from 44 participants 6 months after enrollment. We analyzed serum for 10 fluoroethers and 10 legacy PFAS using liquid chromatography–high-resolution mass spectrometry. Results: Participants’ ages ranged from 6 to 86 y, and they lived in the lower Cape Fear Region for 20 y on average (standard deviation: 16 y). Six fluoroethers were detected in serum; Nafion by-product 2 and PFO4DA were detected in >99% of participants. PFO3OA and NVHOS were infrequently detected. Hydro-EVE was present in a subset of samples, but we could not quantify it. GenX was not detected above our analytical method reporting limit (2 ng/mL). In participants with repeated samples, the median decrease in fluoroether levels ranged from 34% for Nafion byproduct 2 to 65% for PFO4DA in 6 months due to wastewater discharge control. Four legacy PFAS (PFHxS, PFOA, PFOS, PFNA) were detected in most (≥97%) participants; these levels were higher than U.S. national levels for the 2015–2016 National Health and Nutrition Examination Survey. The sum concentration of fluoroethers contributed 23% to participants’ summed PFAS (median: 25.0 ng/mL). Conclusion: Poorly understood fluoroethers released into the Cape Fear River by a fluorochemical manufacturing facility were detected in blood samples from Wilmington, North Carolina, residents. Health implications of exposure to these novel PFAS have not been well characterized. https://doi.org/10.1289/EHP6837}, number={7}, journal={ENVIRONMENTAL HEALTH PERSPECTIVES}, author={Kotlarz, Nadine and McCord, James and Collier, David and Lea, C. Suzanne and Strynar, Mark and Lindstrom, Andrew B. and Wilkie, Adrien A. and Islam, Jessica Y. and Matney, Katelyn and Tarte, Phillip and et al.}, year={2020}, month={Jul} }
 @article{rodowa_knappe_chiang_pohlmann_varley_bodour_field_2020, title={Pilot scale removal of per- and polyfluoroalkyl substances and precursors from AFFF-impacted groundwater by granular activated carbon}, volume={6}, ISSN={["2053-1419"]}, DOI={10.1039/c9ew00936a}, abstractNote={The US military, municipal fire stations, airports, and the petroleum-processing industry have used aqueous film forming foam (AFFF) to extinguish hydrocarbon-based fires.}, number={4}, journal={ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY}, author={Rodowa, Alix E. and Knappe, Detlef R. U. and Chiang, Sheau-Yun Dora and Pohlmann, Dirk and Varley, Catharine and Bodour, Adria and Field, Jennifer A.}, year={2020}, month={Apr}, pages={1083–1094} }
 @article{dodds_hopkins_knappe_baker_2020, title={Rapid Characterization of Per- and Polyfluoroalkyl Substances (PFAS) by Ion Mobility Spectrometry-Mass Spectrometry (IMS-MS)}, volume={92}, url={https://doi.org/10.1021/acs.analchem.9b05364}, DOI={10.1021/acs.analchem.9b05364}, abstractNote={Per- and polyfluoroalkyl substances (PFAS) are an ensemble of persistent organic pollutants of global interest because of their associations with adverse health outcomes. Currently, environmental PFAS pollution is prolific as a result of the widespread manufacturing of these compounds and their chemical persistence. In this work, we demonstrate the advantages of adding ion mobility spectrometry (IMS) separation to existing LC-MS workflows for PFAS analysis. Using a commercially available drift tube IMS-MS, we characterized PFAS species and isomeric content both in analytical standards and wastewater samples. Molecular trendlines based on intrinsic mass and structural relationships were also explored for the PFAS subclasses (e.g. PFSA, PFCA, etc.). Results from rapid IMS-MS analyses provided a link between mass and collision cross sections (CCS) for specific PFAS families and are linked to compositional differences in molecular structure. In addition, CCS values provide additional confidence of annotating prioritized features in untargeted screening studies for potential environmental pollutants. Results from this study show that the IMS separation provides novel information to support traditional LC-MS PFAS analyses and will greatly benefit the evaluation of unknown pollutants in future environmental studies.}, number={6}, journal={Analytical Chemistry}, publisher={American Chemical Society (ACS)}, author={Dodds, J.N. and Hopkins, Z.R. and Knappe, D.R.U. and Baker, E.S.}, year={2020}, month={Feb}, pages={4427–4435} }
 @article{kwiatkowski_andrews_birnbaum_bruton_dewitt_knappe_maffini_miller_pelch_reade_et al._2020, title={Scientific Basis for Managing PFAS as a Chemical Class}, volume={7}, ISSN={["2328-8930"]}, url={https://doi.org/10.1021/acs.estlett.0c00255}, DOI={10.1021/acs.estlett.0c00255}, abstractNote={This commentary presents a scientific basis for managing as one chemical class the thousands of chemicals known as PFAS (per- and polyfluoroalkyl substances). The class includes perfluoroalkyl acids, perfluoroalkylether acids, and their precursors; fluoropolymers and perfluoropolyethers; and other PFAS. The basis for the class approach is presented in relation to their physicochemical, environmental, and toxicological properties. Specifically, the high persistence, accumulation potential, and/or hazards (known and potential) of PFAS studied to date warrant treating all PFAS as a single class. Examples are provided of how some PFAS are being regulated and how some businesses are avoiding all PFAS in their products and purchasing decisions. We conclude with options for how governments and industry can apply the class-based approach, emphasizing the importance of eliminating non-essential uses of PFAS, and further developing safer alternatives and methods to remove existing PFAS from the environment.}, number={8}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS}, publisher={American Chemical Society (ACS)}, author={Kwiatkowski, Carol F. and Andrews, David Q. and Birnbaum, Linda S. and Bruton, Thomas A. and DeWitt, Jamie C. and Knappe, Detlef R. U. and Maffini, Maricel V and Miller, Mark F. and Pelch, Katherine E. and Reade, Anna and et al.}, year={2020}, month={Aug}, pages={532–543} }
 @article{zhang_maness_cuthbertson_kimura_liberatore_richardson_stanford_sun_knappe_2020, title={Treating water containing elevated bromide and iodide levels with granular activated carbon and free chlorine: impacts on disinfection byproduct formation and calculated toxicity}, volume={6}, ISSN={["2053-1419"]}, url={https://doi.org/10.1039/D0EW00523A}, DOI={10.1039/d0ew00523a}, abstractNote={Granular activated carbon effectively controlled disinfection byproduct formation and calculated toxicity, especially at high influent bromide levels.}, number={12}, journal={ENVIRONMENTAL SCIENCE-WATER RESEARCH & TECHNOLOGY}, publisher={Royal Society of Chemistry (RSC)}, author={Zhang, Chuhui and Maness, J. Clark and Cuthbertson, Amy A. and Kimura, Susana Y. and Liberatore, Hannah K. and Richardson, Susan D. and Stanford, Benjamin D. and Sun, Mei and Knappe, Detlef R. U.}, year={2020}, month={Dec}, pages={3460–3475} }
 @article{mcelroy_hyman_knappe_2019, title={1,4-Dioxane in drinking water: emerging for 40 years and still unregulated}, volume={7}, ISSN={2468-5844}, url={http://dx.doi.org/10.1016/j.coesh.2019.01.003}, DOI={10.1016/j.coesh.2019.01.003}, abstractNote={The likely human carcinogen 1,4-dioxane was first detected in drinking water more than 40 years ago, and a recent analysis suggests that almost 30 million people in the United States receive drinking water with 1,4-dioxane levels above the health-based reference concentration of 0.35 μg/L. The widespread occurrence of 1,4-dioxane has exposed the need for developing and implementing management and treatment approaches that protect drinking water sources and prevent human exposure to 1,4-dioxane through drinking water. In this review, we highlight recent advances in analytical methods, understanding of occurrence, and treatment processes. Findings are discussed in the context of managing 1,4-dioxane as a drinking water contaminant, and recommendations are made to address important knowledge gaps.}, journal={Current Opinion in Environmental Science & Health}, publisher={Elsevier BV}, author={McElroy, Amie C. and Hyman, Michael R. and Knappe, Detlef R.U.}, year={2019}, month={Feb}, pages={117–125} }
 @article{cuthbertson_kimura_liberatore_summers_knappe_stanford_maness_mulhern_selbes_richardson_2019, title={Does Granular Activated Carbon with Chlorination Produce Safer Drinking Water? From Disinfection Byproducts and Total Organic Halogen to Calculated Toxicity}, volume={53}, ISBN={1520-5851}, DOI={10.1021/acs.est.9600023}, number={10}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Cuthbertson, Amy A. and Kimura, Susana Y. and Liberatore, Hannah K. and Summers, R. Scott and Knappe, Detlef R. U. and Stanford, Benjamin D. and Maness, J. Clark and Mulhern, Riley E. and Selbes, Meric and Richardson, Susan D.}, year={2019}, pages={5987–5999} }
 @article{cuthbertson_kimura_liberatore_summers_knappe_stanford_maness_mulhern_selbes_richardson_2019, title={Does Granular Activated Carbon with Chlorination Produce Safer Drinking Water? From Disinfection Byproducts and Total Organic Halogen to Calculated Toxicity}, volume={53}, ISSN={["1520-5851"]}, DOI={10.1021/acs.est.9b00023}, abstractNote={Granular activated carbon (GAC) adsorption is well-established for controlling regulated disinfection byproducts (DBPs), but its effectiveness for unregulated DBPs and DBP-associated toxicity is unclear. In this study, GAC treatment was evaluated at three full-scale chlorination drinking water treatment plants over different GAC service lives for controlling 61 unregulated DBPs, 9 regulated DBPs, and speciated total organic halogen (total organic chlorine, bromine, and iodine). The plants represented a range of impacts, including algal, agricultural, and industrial wastewater. This study represents the most extensive full-scale study of its kind and seeks to address the question of whether GAC can make drinking water safer from a DBP perspective. Overall, GAC was effective for removing DBP precursors and reducing DBP formation and total organic halogen, even after >22 000 bed volumes of treated water. GAC also effectively removed preformed DBPs at plants using prechlorination, including highly toxic iodoacetic acids and haloacetonitriles. However, 7 DBPs (mostly brominated and nitrogenous) increased in formation after GAC treatment. In one plant, an increase in tribromonitromethane had significant impacts on calculated cytotoxicity, which only had 7-17% reduction following GAC. While these DBPs are highly toxic, the total calculated cytotoxicity and genotoxicity for the GAC treated waters for the other two plants was reduced 32-83% (across young-middle-old GAC). Overall, calculated toxicity was reduced post-GAC, with preoxidation allowing further reductions.}, number={10}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Cuthbertson, Amy A. and Kimura, Susana Y. and Liberatore, Hannah K. and Summers, R. Scott and Knappe, Detlef R. U. and Stanford, Benjamin D. and Maness, J. Clark and Mulhern, Riley E. and Selbes, Meric and Richardson, Susan D.}, year={2019}, month={May}, pages={5987–5999} }
 @article{hess_kolar_classen_knappe_cheng_2019, title={Effects of Co-occurring Species Present in Swine Lagoons on Adsorption of Copper on Eggshell}, volume={13}, ISSN={["2008-2304"]}, DOI={10.1007/s41742-019-00203-x}, number={4}, journal={INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH}, author={Hess, Brianna J. and Kolar, Praveen and Classen, John J. and Knappe, Detlef and Cheng, Jay J.}, year={2019}, month={Aug}, pages={613–622} }
 @article{zhang_hopkins_mccord_strynar_knappe_2019, title={Fate of Per- and Polyfluoroalkyl Ether Acids in the Total Oxidizable Precursor Assay and Implications for the Analysis of Impacted Water}, volume={6}, ISSN={2328-8930 2328-8930}, url={http://dx.doi.org/10.1021/acs.estlett.9b00525}, DOI={10.1021/acs.estlett.9b00525}, abstractNote={Per- and polyfluoroalkyl substances (PFASs) are widely used anthropogenic chemicals. The PFAS class includes almost 5000 registered compounds, but analytical methods are lacking for most PFASs. The total oxidizable precursor (TOP) assay was developed to indirectly quantify unknown PFASs that are precursors to commonly measured perfluoroalkyl acids. To understand the behavior of recently identified per- and polyfluoroalkyl ether acids (PFEAs), including fluorinated replacements and manufacturing byproducts, we determined the fate of 15 PFEAs in the TOP assay. Ten perfluoroalkyl ether acids and a chlorinated polyfluoroalkyl ether acid (F-53B) were stable in the TOP assay and represent terminal products that are likely as persistent as historically used PFASs. Adding perfluoroalkyl ether acids and F-53B to the target analyte list for the TOP assay is recommended to capture a higher percentage of the total PFAS concentration in environmental samples. In contrast, polyfluoroalkyl ether acids with a -O-CFH- moiety were oxidized, typically to products that could not be identified by liquid chromatography and high-resolution mass spectrometry. Application of the TOP assay in its proposed enhanced form revealed high levels of PFEAs, the presence of precursors that form perfluoroalkyl carboxylic acids, and the absence of precursors that form PFEAs in surface water impacted by PFAS-containing wastewater discharges.}, number={11}, journal={Environmental Science & Technology Letters}, publisher={American Chemical Society (ACS)}, author={Zhang, Chuhui and Hopkins, Zachary R. and McCord, James and Strynar, Mark J. and Knappe, Detlef R. U.}, year={2019}, month={Oct}, pages={662–668} }
 @article{kearns_shimabuku_knappe_summers_2019, title={High Temperature Co-pyrolysis Thermal Air Activation Enhances Biochar Adsorption of Herbicides from Surface Water}, volume={36}, ISSN={["1557-9018"]}, DOI={10.1089/ees.2018.0476}, abstractNote={Abstract Recent interest has arisen in the use of biochar as a low-cost adsorbent for control of organic micropollutants in water. However, compared with activated carbon (AC), biochar adsorption c...}, number={6}, journal={ENVIRONMENTAL ENGINEERING SCIENCE}, author={Kearns, Joshua P. and Shimabuku, Kyle K. and Knappe, Detlef R. U. and Summers, R. Scott}, year={2019}, month={Jun}, pages={710–723} }
 @article{hess_kolar_classen_knappe_cheng_2018, title={Evaluation of Waste Eggshells for Adsorption of Copper from Synthetic and Swine Wastewater}, volume={61}, ISSN={2151-0040}, url={http://dx.doi.org/10.13031/trans.12599}, DOI={10.13031/trans.12599}, abstractNote={Abstract. Biomass-derived adsorbents are an attractive alternative to conventional water treatment methods. This study evaluated eggshells produced by the liquid egg and food processing industry for the adsorption of copper from aqueous systems. Research objectives were to (1) determine copper adsorption mechanisms and (2) evaluate copper adsorption by eggshells for the treatment of wastewater. Batch experiments were performed by contacting eggshells with copper solutions to obtain equilibrium, kinetic, and thermodynamic data to determine removal mechanisms and maximum adsorption capacity. Results suggested that the adsorption of copper followed a second-order kinetic model with a theoretical maximum adsorption capacity of 4.3 mg g-1 (20°C). In addition, eggshell adsorption was found to be a favorable process, with an activation energy of approximately 27 to 29 kJ mol-1, and followed similar mechanisms as its calcite analog. Data indicated that slightly acidic (pH = 6) to near-neutral pH conditions enhanced adsorption of copper. Additional experiments were performed using swine lagoon wastewater to evaluate the efficacy of eggshells to treat copper from lagoon wastewater. The data suggested that unmodified eggshells were effective for application in swine lagoon systems only under acidic conditions (pH = 4). Further research is needed to modify eggshells that can adsorb copper in lagoon wastewater at neutral and alkaline pH. Keywords: Adsorption, Copper, Eggshell, Swine lagoon, Water.}, number={3}, journal={Transactions of the ASABE}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, author={Hess, Brianna J. and Kolar, Praveen and Classen, John J. and Knappe, Detlef and Cheng, Jay J.}, year={2018}, pages={967–976} }
 @book{cotton_collins_knappe_linden_brown_upadhyaya_ponturo_2018, place={Denver, Colorado}, title={Evaluation of cVOC Removal Efficiencies by Various Technologies}, number={4492}, institution={Water Research Foundation}, author={Cotton, C. and Collins, J. and Knappe, D.R.U. and Linden, K. and Brown, J. and Upadhyaya, G. and Ponturo, P.}, year={2018} }
 @article{hopkins_sun_dewitt_knappe_2018, title={Recently Detected Drinking Water Contaminants: GenX and Other Per- and Polyfluoroalkyl Ether Acids}, volume={110}, ISSN={0003-150X}, url={http://dx.doi.org/10.1002/awwa.1073}, DOI={10.1002/awwa.1073}, abstractNote={For several decades, a common processing aid in the production of fluoropolymers was the ammonium salt of perfluorooctanoic acid (PFOA). Because PFOA is persistent, bioaccumulative, and toxic, its production and use are being phased out in the United States. In 2009, the US Environmental Protection Agency stipulated conditions for the manufacture and commercial use of GenX, a PFOA replacement. While GenX is produced for commercial purposes, the acid form of GenX is also generated as a byproduct during the production of fluoromonomers. The discovery of high concentrations of GenX and related perfluoroalkyl ether acids (PFEAs) in the Cape Fear River and in finished drinking water of more than 200,000 North Carolina residents required quick action by researchers, regulators, public health officials, commercial laboratories, drinking water providers, and consulting engineers. Information about sources and toxicity of GenX as well as an analytical method for the detection of GenX and eight related PFEAs is presented. GenX/PFEA occurrence in water and GenX/PFEA removal by different drinking water treatment processes are also discussed.}, number={7}, journal={Journal - American Water Works Association}, publisher={Wiley}, author={Hopkins, Zachary R. and Sun, Mei and DeWitt, Jamie C. and Knappe, Detlef R.U.}, year={2018}, month={Jun}, pages={13–28} }
 @article{kennedy_reinert_knappe_summers_2017, title={Prediction of Full-Scale GAC Adsorption of Organic Micropollutants}, volume={34}, ISSN={["1557-9018"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85024364062&partnerID=MN8TOARS}, DOI={10.1089/ees.2016.0525}, abstractNote={Abstract The principal goal of this research was to develop a new scale-up procedure with which the adsorption of organic micropollutants (MPs) by granular activated carbon (GAC) can be predicted from bench-scale tests. To develop scale-up approaches, the adsorption of 29 environmentally relevant MPs was studied in both pilot-scale GAC adsorbers and rapid small-scale column tests that were based on the proportional diffusivity design (PD-RSSCT). Four surface waters with different dissolved organic carbon (DOC) concentrations were spiked with MPs at ng/L levels and tested in PD-RSSCTs simulating full-scale empty bed contact times of 7 and 15 min. Corresponding pilot-scale tests showed MP breakthrough occurred earlier than in PD-RSSCTs, and MP-specific differences between the PD-RSSCT and pilot column breakthrough curves were described by fouling parameters. On average, the PD-RSSCT overpredicted pilot-scale MP breakthrough by a factor of 3.0 ± 1.2 (n = 101). Two approaches were developed for predicting bed...}, number={7}, journal={ENVIRONMENTAL ENGINEERING SCIENCE}, author={Kennedy, Anthony M. and Reinert, Allison M. and Knappe, Detlef R. U. and Summers, R. Scott}, year={2017}, month={Jul}, pages={496–507} }
 @article{wu_wu_zhang_knappe_2017, title={Study on adsorption process and mechanism of p-nitroaniline on bamboo charcoal}, volume={11}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85014384902&partnerID=MN8TOARS}, DOI={10.12030/j.cjee.201509119}, number={1}, journal={Chinese Journal of Environmental Engineering}, author={Wu, G. and Wu, G. and Zhang, Q. and Knappe, D.R.U.}, year={2017}, pages={251–259} }
 @article{sun_lopez-velandia_knappe_2016, title={Determination of 1,4-Dioxane in the Cape Fear River Watershed by Heated Purge-and-Trap Preconcentration and Gas Chromatography-Mass Spectrometry}, volume={50}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84959513702&partnerID=MN8TOARS}, DOI={10.1021/acs.est.5b05875}, abstractNote={Recent U.S. Environmental Protection Agency data show that 1,4-dioxane is frequently detected in U.S. drinking water derived from both groundwater and surface water. 1,4-Dioxane is a likely human carcinogen, and an excess 10(-6) cancer risk is associated with a drinking water concentration of 0.35 μg/L. To support 1,4-dioxane occurrence investigations, source identification and exposure assessment, a rapid and sensitive analytical method capable of quantifying 1,4-dioxane over a wide concentration range in a broad spectrum of aqueous matrices was developed. The fully automated method is based on heated purge-and-trap preconcentration and gas chromatography/mass spectrometry with selected-ion storage and has a reporting limit of 0.15 μg/L. Quantification of 1,4-dioxane was accomplished by isotope dilution using mass-labeled 1,4-dioxane-d8 as internal standard. Matrix spikes yielded recoveries of 86-115% in drinking water, groundwater, surface water, and wastewater treatment plant (WWTP) effluent. Also, 1,3-dioxane can be distinguished from 1,4-dioxane. The method was applied to investigate 1,4-dioxane occurrence and sources in the Cape Fear River watershed of North Carolina. 1,4-Dioxane concentrations ranged from <0.15 μg/L in nonimpacted surface water to 436 μg/L downstream of a WWTP discharge. In WWTP effluent, 1,4-dioxane concentrations varied widely, with a range of 1.3-2.7 μg/L in one community and 105-1,405 μg/L in another. Discharges from three municipal WWTPs were primarily responsible for elevated 1,4-dioxane concentrations in the Cape Fear River watershed.}, number={5}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Sun, Mei and Lopez-Velandia, Catalina and Knappe, Detlef R. U.}, year={2016}, month={Mar}, pages={2246–2254} }
 @article{thompson_shimabuku_kearns_knappe_summers_cook_2016, title={Environmental Comparison of Biochar and Activated Carbon for Tertiary Wastewater Treatment}, volume={50}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84991829573&partnerID=MN8TOARS}, DOI={10.1021/acs.est.6b03239}, abstractNote={Micropollutants in wastewater present environmental and human health challenges. Powdered activated carbon (PAC) can effectively remove organic micropollutants, but PAC production is energy intensive and expensive. Biochar adsorbents can cost less and sequester carbon; however, net benefits depend on biochar production conditions and treatment capabilities. Here, life cycle assessment was used to compare 10 environmental impacts from the production and use of wood biochar, biosolids biochar, and coal-derived PAC to remove sulfamethoxazole from wastewater. Moderate capacity wood biochar had environmental benefits in four categories (smog, global warming, respiratory effects, noncarcinogenics) linked to energy recovery and carbon sequestration, and environmental impacts worse than PAC in two categories (eutrophication, carcinogenics). Low capacity wood biochar had even larger benefits for global warming, respiratory effects, and noncarcinogenics, but exhibited worse impacts than PAC in five categories due to larger biochar dose requirements to reach the treatment objective. Biosolids biochar had the worst relative environmental performance due to energy use for biosolids drying and the need for supplemental adsorbent. Overall, moderate capacity wood biochar is an environmentally superior alternative to coal-based PAC for micropollutant removal from wastewater, and its use can offset a wastewater facility's carbon footprint.}, number={20}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Thompson, Kyle A. and Shimabuku, Kyle K. and Kearns, Joshua P. and Knappe, Detlef R. U. and Summers, R. Scott and Cook, Sherri M.}, year={2016}, month={Oct}, pages={11253–11262} }
 @book{knappe_ingham_moreno-barbosa_sun_summers_dougherty_2016, place={Denver, Colorado}, title={Evaluation of Henry’s Law Constants and Freundlich Adsorption Constants for VOCs}, number={4462}, institution={Water Research Foundation}, author={Knappe, D.R.U. and Ingham, R.S. and Moreno-Barbosa, J. and Sun, M. and Summers, R.S. and Dougherty, T.}, year={2016} }
 @article{sun_arevalo_strynar_lindstrom_richardson_kearns_pickett_smith_knappe_2016, title={Legacy and Emerging Perfluoroalkyl Substances Are Important Drinking Water Contaminants in the Cape Fear River Watershed of North Carolina}, volume={3}, ISSN={["2328-8930"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85006081776&partnerID=MN8TOARS}, DOI={10.1021/acs.estlett.6b00398}, abstractNote={Long-chain per- and polyfluoroalkyl substances (PFASs) are being replaced by short-chain PFASs and fluorinated alternatives. For ten legacy PFASs and seven recently discovered perfluoroalkyl ether carboxylic acids (PFECAs), we report (1) their occurrence in the Cape Fear River (CFR) watershed, (2) their fate in water treatment processes, and (3) their adsorbability on powdered activated carbon (PAC). In the headwater region of the CFR basin, PFECAs were not detected in raw water of a drinking water treatment plant (DWTP), but concentrations of legacy PFASs were high. The U.S. Environmental Protection Agency’s lifetime health advisory level (70 ng/L) for perfluorooctanesulfonic acid and perfluorooctanoic acid (PFOA) was exceeded on 57 of 127 sampling days. In raw water of a DWTP downstream of a PFAS manufacturer, the mean concentration of perfluoro-2-propoxypropanoic acid (PFPrOPrA), a replacement for PFOA, was 631 ng/L (n = 37). Six other PFECAs were detected, with three exhibiting chromatographic peak ar...}, number={12}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS}, author={Sun, Mei and Arevalo, Elisa and Strynar, Mark and Lindstrom, Andrew and Richardson, Michael and Kearns, Ben and Pickett, Adam and Smith, Chris and Knappe, Detlef R. U.}, year={2016}, month={Dec}, pages={415–419} }
 @book{chowdhury_porter_collins_francis_sriboonlue_cornwell_brown_knappe_2016, place={Denver, Colorado}, title={Survey of Existing VOC Treatment Installations}, number={4453}, institution={Water Research Foundation}, author={Chowdhury, Z. and Porter, K.L. and Collins, J. and Francis, C. and Sriboonlue, S. and Cornwell, D. and Brown, R. and Knappe, D.R.U.}, year={2016} }
 @article{kearns_knappe_summers_2015, title={Feasibility of Using Traditional Kiln Charcoals in Low-Cost Water Treatment: Role of Pyrolysis Conditions on 2,4-D Herbicide Adsorption}, volume={32}, ISSN={["1557-9018"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84946830926&partnerID=MN8TOARS}, DOI={10.1089/ees.2015.0243}, abstractNote={Abstract Prior research has established that pyrolysis temperature during charcoal production is the primary variable influencing adsorption capacity. The first objective of this work was to monitor thermal conditions during charcoal production within three common traditional kiln models. Then, a programmable laboratory furnace pyrolyzer was used to generate chars from eucalyptus, pine, and longan woods and bamboo under a similar range of thermal conditions as identified in the field study. Using chars produced from the furnace, the second objective of this study was to investigate the influence of biomass feedstock and grain size, peak pyrolysis temperature, and duration of thermal treatment on 2,4-D herbicide sorption capacity. A third objective was to determine if chars produced in the laboratory furnace using thermal profiles similar to those observed in the horizontal drum kiln would exhibit similar adsorbent characteristics to kiln charcoals. Field observations revealed significant variability in te...}, number={11}, journal={ENVIRONMENTAL ENGINEERING SCIENCE}, author={Kearns, Joshua P. and Knappe, Detlef R. U. and Summers, R. Scott}, year={2015}, month={Nov}, pages={912–921} }
 @article{kearns_shimabuku_mahoney_knappe_summers_2015, title={Meeting multiple water quality objectives through treatment using locally generated char: improving organoleptic properties and removing synthetic organic contaminants and disinfection by-products}, volume={5}, ISSN={["2043-9083"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84940023189&partnerID=MN8TOARS}, DOI={10.2166/washdev.2015.172}, abstractNote={A variety of natural and anthropogenic contaminants can compromise the safety and esthetics of surface water collected for drinking and disinfected using chlorine by households in developing communities. While household chlorination is effective against most microbial pathogens, many users find the taste and odor of chlorine unacceptable and revert to drinking untreated water. Moreover, reactions between chlorine and the dissolved organic matter form harmful disinfection by-products (DBPs) such as trihalomethanes (THMs). Char adsorbers have been used to treat drinking water for thousands of years and are still widely used today. Results obtained here demonstrate that locally produced biomass chars (biochars) exhibit removal capacities comparable to those of activated carbon for removal of THMs, synthetic organic chemicals (SOCs) such as warfarin (WFN) (anticoagulant pharmaceutical, rodenticide), and naturally occurring trace organics such as the taste-and-odor compound 2-methylisoborneol (cyanobacterial metabolite). Results show chars can be used effectively to remove objectionable tastes and odors related to chlorine and cyanobacteria, DBPs, and SOCs. The use of char may lead to microbial risk reduction through greater acceptance of chlorine-based disinfection due to improved water esthetics, as well as chemical risk reduction associated with DBP and SOC exposure.}, number={3}, journal={JOURNAL OF WATER SANITATION AND HYGIENE FOR DEVELOPMENT}, author={Kearns, Joshua P. and Shimabuku, Kyle K. and Mahoney, Ryan B. and Knappe, Detlef R. U. and Summers, R. Scott}, year={2015}, pages={359–372} }
 @book{dudley_arevalo_knappe_2015, place={Denver, Colorado}, title={Removal of perfluoroalkyl substances by PAC adsorption and anion exchange}, number={4344}, institution={Water Research Foundation}, author={Dudley, L.A. and Arevalo, E.C. and Knappe, D.R.U.}, year={2015} }
 @book{summers_kempisty_daugherty_knappe_2015, place={Denver, Colorado}, title={Removal of volatile organic contaminants (VOCs) from drinking water via granular activated carbon treatment}, number={4440}, institution={Water Research Foundation}, author={Summers, R.S. and Kempisty, D. and Daugherty, T. and Knappe, D.}, year={2015} }
 @article{kearns_wellborn_summers_knappe_2014, title={2,4-D adsorption to biochars: Effect of preparation conditions on equilibrium adsorption capacity and comparison with commercial activated carbon literature data}, volume={62}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84902245682&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2014.05.023}, abstractNote={Batch isotherm experiments were conducted with chars to study adsorption of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). Chars generated from corncobs, bamboo and wood chips in a laboratory pyrolyzer at 400–700 °C were compared with traditional kiln charcoals collected from villages in S/SE Asia and with activated carbons (ACs). 2,4-D uptake by laboratory chars obtained from bamboo and wood chips after 14 h of pyrolysis at 700 °C, from wood chips after 96 h of pyrolysis at 600 °C, and one of the field-collected chars (basudha) was comparable to ACs. H:C and O:C ratios declined with pyrolysis temperature and duration while surface area increased to >500 m2/g. Increasing pyrolysis intensity by increasing temperature and/or duration of heating was found to positively influence adsorption capacity yield (mg2,4-D/gfeedstock) over the range of conditions studied. Economic analysis showed that high temperature chars can be a cost-effective alternative to ACs for water treatment applications.}, journal={WATER RESEARCH}, author={Kearns, J. P. and Wellborn, L. S. and Summers, R. S. and Knappe, D. R. U.}, year={2014}, month={Oct}, pages={20–28} }
 @inproceedings{lindsay_byrns_knappe_shannon_2015, title={Characterization of atmospheric pressure rf discharges with aqueous plasma facing surfaces}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84923050875&partnerID=MN8TOARS}, DOI={10.1109/PLASMA.2014.7012279}, abstractNote={Summary form only given. Plasma modification of liquids has opened a broad range of new applications ranging from wound treatment to water purification to agricultural fertigation and herbicide. Two of the primary challenges facing systems designed to modify liquid chemistry through plasma treatment have been throughput and efficient introduction of liquid species in the active plasma region. In this presentation, we present novel pathways for both source scale up and liquid incorporation that can make plasma treatment of liquids more economically viable.}, booktitle={ICOPS/BEAMS 2014 - 41st IEEE International Conference on Plasma Science and the 20th International Conference on High-Power Particle Beams}, author={Lindsay, A. and Byrns, B. and Knappe, D. and Shannon, S.}, year={2015} }
 @book{summers_kennedy_knappe_reinert_fotta_mastropole_corwin_roccaro_2014, place={Denver, Colorado}, title={Evaluation of Available Scale-up Approaches for the Design of GAC Contactors}, number={4235}, institution={Water Research Foundation}, author={Summers, R.S. and Kennedy, A.M. and Knappe, D.R.U. and Reinert, A.M. and Fotta, M.E. and Mastropole, A.J. and Corwin, C.J. and Roccaro, J.}, year={2014} }
 @article{lindsay_byrns_king_andhvarapou_fields_knappe_fonteno_shannon_2014, title={Fertilization of Radishes, Tomatoes, and Marigolds Using a Large-Volume Atmospheric Glow Discharge}, volume={34}, ISSN={0272-4324 1572-8986}, url={http://dx.doi.org/10.1007/s11090-014-9573-x}, DOI={10.1007/s11090-014-9573-x}, number={6}, journal={Plasma Chemistry and Plasma Processing}, publisher={Springer Science and Business Media LLC}, author={Lindsay, Alex and Byrns, Brandon and King, Wesley and Andhvarapou, Asish and Fields, Jeb and Knappe, Detlef and Fonteno, William and Shannon, Steven}, year={2014}, month={Aug}, pages={1271–1290} }
 @article{kennedy_reinert_knappe_ferrer_summers_2015, title={Full- and pilot-scale GAC adsorption of organic micropollutants}, volume={68}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84908518266&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2014.10.010}, abstractNote={Granular activated carbon (GAC) adsorption of 30 environmentally relevant micropollutants (MP) from four surface waters was investigated at the pilot-scale with empty bed contact times (EBCTs) of 7 and 15 min. An increase in background dissolved organic matter resulted in more and earlier MP breakthrough. Compared to an EBCT of 7 min, MP breakthrough at an EBCT of 15 min demonstrated 52% later breakthrough on average for five MPs on a throughput basis. A regression model was developed with data from three waters to predict MP throughput in bed volumes to 10% breakthrough (BV10%) based on the influent dissolved organic carbon concentration and the MP pH-dependent octanol–water partition coefficient, polarizability, and molecular volume. The regression model over predicted full-scale BV10% values when applied to a wastewater-water impacted water source and to GAC with a larger particle diameter, for which a particle size adjustment was able to account for most of the difference.}, journal={WATER RESEARCH}, author={Kennedy, Anthony M. and Reinert, Allison M. and Knappe, Detlef R. U. and Ferrer, Imma and Summers, R. Scott}, year={2015}, month={Jan}, pages={238–248} }
 @article{kearns_bentley_mokashi_redmon_levine_2014, title={Synthetic organic water contaminants in developing communities: an overlooked challenge addressed by adsorption with locally generated char}, volume={4}, ISSN={["2043-9083"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84907209565&partnerID=MN8TOARS}, DOI={10.2166/washdev.2014.073}, abstractNote={Chemical contamination of drinking water sources is a worldwide problem. However, few locally managed, sustainable, and low-cost on-site treatment technologies are available in rural, remote, and emergency/disaster relief/humanitarian crisis situations. Char filter-adsorbers have been used to treat drinking water for thousands of years and are still widely used today. Our studies show that some chars produced by traditional means from a range of feedstocks develop favorable sorption properties for uptake of 2,4-dichlorophenoxyacetic acid (2,4-D), a prevalent herbicide and water contaminant. However, more energy efficient, environmentally sustainable and scalable production of consistent highly sorptive chars can be accomplished with biomass gasification. Our laboratory studies demonstrate that locally produced char adsorbents derived from surplus agricultural and forestry biomass are effective for adsorbing 2,4-D. A year-long study of field-scale application of chars in Thailand is also presented. Based on these studies we present design recommendations for integrating char adsorbers into low-cost, multi-barrier treatment trains for on-site water provision.}, number={3}, journal={JOURNAL OF WATER SANITATION AND HYGIENE FOR DEVELOPMENT}, author={Kearns, J.P. and Bentley, M.J. and Mokashi, P. and Redmon, J.H. and Levine, K.}, year={2014}, pages={422–436} }
 @book{dunn_knappe_2013, place={Denver, Colorado}, title={DBP Precursor and Micropollutant Removal by Powdered Activated Carbon}, number={4294}, institution={Water Research Foundation}, author={Dunn, S.E. and Knappe, D.R.U.}, year={2013} }
 @article{kovalova_knappe_lehnberg_kazner_hollender_2013, title={Removal of highly polar micropollutants from wastewater by powdered activated carbon}, volume={20}, ISSN={["0944-1344"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84878111191&partnerID=MN8TOARS}, DOI={10.1007/s11356-012-1432-9}, abstractNote={Due to concerns about ecotoxicological effects of pharmaceuticals and other micropollutants released from wastewater treatment plants, activated carbon adsorption is one of the few processes to effectively reduce the concentrations of micropollutants in wastewater. Although aimed mainly at apolar compounds, polar compounds are also simultaneously removed to a certain extent, which has rarely been studied before. In this study, adsorption isotherm and batch kinetic data were collected with two powdered activated carbons (PACs) to assess the removal of the polar pharmaceuticals 5-fluorouracil (5-Fu) and cytarabine (CytR) from ultrapure water and wastewater treatment plant effluent. At pH 7.8, single-solute adsorption isotherm data for the weak acid 5-Fu and the weak base CytR showed that their adsorption capacities were about 1 order of magnitude lower than those of the less polar endocrine disrupting chemicals bisphenol A (BPA) and 17-α-ethinylestradiol (EE2). To remove 90 % of the adsorbate from a single-solute solution 14, 18, 70, and 87 mg L(-1) of HOK Super is required for EE2, BPA, CytR, and 5-Fu, respectively. Effects of solution pH, ionic strength, temperature, and effluent organic matter (EfOM) on 5-Fu and CytR adsorption were evaluated for one PAC. Among the studied factors, the presence of EfOM had the highest effect, due to a strong competition on 5-Fu and CytR adsorption. Adsorption isotherm and kinetic data and their modeling with a homogeneous surface diffusion model showed that removal percentage in the presence of EfOM was independent on the initial concentration of the ionizable compounds 5-Fu and CytR. These results are similar to neutral organic compounds in the presence of natural organic matter. Overall, results showed that PAC doses sufficient to remove >90 % of apolar adsorbates were able to remove no more than 50 % of the polar adsorbates 5-Fu and CytR and that the contact time is a critical parameter.}, number={6}, journal={ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH}, author={Kovalova, Lubomira and Knappe, Detlef R. U. and Lehnberg, Kai and Kazner, Christian and Hollender, Juliane}, year={2013}, month={Jun}, pages={3607–3615} }
 @inproceedings{kempisty_summers_knappe_2013, title={The effect of background matrix and competition of GAC Adsorption of Carcinogenic VOCs in Natural Waters}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84890544639&partnerID=MN8TOARS}, booktitle={2013 Water Quality Technology Conference and Exposition, WQTC 2013}, author={Kempisty, D.M. and Summers, R.S. and Knappe, D.}, year={2013} }
 @inproceedings{kennedy_reinert_knappe_summers_2013, title={Understanding and predicting the adsorption of trace organic micropollutants by granular activated carbon}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84890451391&partnerID=MN8TOARS}, booktitle={2013 Water Quality Technology Conference and Exposition, WQTC 2013}, author={Kennedy, A. and Reinert, A. and Knappe, D. and Summers, R.S.}, year={2013} }
 @article{matsui_yoshida_nakao_knappe_matsushita_2012, title={Characteristics of competitive adsorption between 2-methylisoborneol and natural organic matter on superfine and conventionally sized powdered activated carbons}, volume={46}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84864061060&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2012.06.002}, abstractNote={When treating water with activated carbon, natural organic matter (NOM) is not only a target for adsorptive removal but also an inhibitory substance that reduces the removal efficiency of trace compounds, such as 2-methylisoborneol (MIB), through adsorption competition. Recently, superfine (submicron-sized) activated carbon (SPAC) was developed by wet-milling commercially available powdered activated carbon (PAC) to a smaller particle size. It was reported that SPAC has a larger NOM adsorption capacity than PAC because NOM mainly adsorbs close to the external adsorbent particle surface (shell adsorption mechanism). Thus, SPAC with its larger specific external surface area can adsorb more NOM than PAC. The effect of higher NOM uptake on the adsorptive removal of MIB has, however, not been investigated. Results of this study show that adsorption competition between NOM and MIB did not increase when NOM uptake increased due to carbon size reduction; i.e., the increased NOM uptake by SPAC did not result in a decrease in MIB adsorption capacity beyond that obtained as a result of NOM adsorption by PAC. A simple estimation method for determining the adsorbed amount of competing NOM (NOM that reduces MIB adsorption) is presented based on the simplified equivalent background compound (EBC) method. Furthermore, the mechanism of adsorption competition is discussed based on results obtained with the simplified EBC method and the shell adsorption mechanism. Competing NOM, which likely comprises a small portion of NOM, adsorbs in internal pores of activated carbon particles as MIB does, thereby reducing the MIB adsorption capacity to a similar extent regardless of adsorbent particle size. SPAC application can be advantageous because enhanced NOM removal does not translate into less effective removal of MIB. Molecular size distribution data of NOM suggest that the competing NOM has a molecular weight similar to that of the target compound.}, number={15}, journal={WATER RESEARCH}, author={Matsui, Yoshihiko and Yoshida, Tomoaki and Nakao, Soichi and Knappe, Detlef R. U. and Matsushita, Taku}, year={2012}, month={Oct}, pages={4741–4749} }
 @inproceedings{reinert_kennedy_scott summers_ferrer_thurman_knappe_2012, title={Comparing scale-up approaches to predict granular activated carbon absorber performance for micropollutant removal}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84871574489&partnerID=MN8TOARS}, booktitle={American Water Works Association Annual Conference and Exposition 2012, ACE 2012}, author={Reinert, A.M. and Kennedy, A. and Scott Summers, R. and Ferrer, I. and Thurman, M. and Knappe, D.}, year={2012}, pages={1025–1056} }
 @inproceedings{fotta_roccaro_knappe_2012, title={Effect of activated carbon type on scale-up of adsorbers for volatile organic compound removal from groundwater}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84871553369&partnerID=MN8TOARS}, booktitle={American Water Works Association Annual Conference and Exposition 2012, ACE 2012}, author={Fotta, M. and Roccaro, J. and Knappe, D.R.U.}, year={2012}, pages={3188–3218} }
 @inproceedings{dudley_lindstrom_strynar_mcmillan_knappe_2012, title={Removal of perfluorinated compounds by powdered activated carbon: Effects of adsorbent and background water characteristics}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84871533789&partnerID=MN8TOARS}, booktitle={American Water Works Association Annual Conference and Exposition 2012, ACE 2012}, author={Dudley, L.-A. and Lindstrom, A. and Strynar, M. and Mcmillan, L. and Knappe, D.R.U.}, year={2012}, pages={961–1003} }
 @inproceedings{fotta_roccaro_knappe_2012, title={Scale-up of granular activated carbon adsorbers for volatile organic compound removal from groundwater: Effect of carbon type}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84890744863&partnerID=MN8TOARS}, booktitle={Water Quality Technology Conference and Exposition 2012}, author={Fotta, M. and Roccaro, J. and Knappe, D.R.U.}, year={2012} }
 @inproceedings{kennedy_reinert_summers_ferrer_thurman_knappe_2012, title={Scale-up of the GAC adsorption of trace organic compounds}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84890579082&partnerID=MN8TOARS}, booktitle={Water Quality Technology Conference and Exposition 2012}, author={Kennedy, A. and Reinert, A. and Summers, R.S. and Ferrer, I. and Thurman, M. and Knappe, D.R.U.}, year={2012} }
 @article{chen_knappe_barlaz_2013, title={The effect of aging on the bioavailability of toluene sorbed to municipal solid waste components}, volume={90}, ISSN={["1879-1298"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84869886366&partnerID=MN8TOARS}, DOI={10.1016/j.chemosphere.2012.06.062}, abstractNote={Past practice of co-disposing priority pollutants with municipal solid waste (MSW) has led to the placement of more than 150 MSW landfills in the US on the National Priorities List of Superfund. Interactions between organic contaminants and MSW constituents and the effects of these interactions on contaminant fate are poorly understood. The objective of this study was to evaluate the effects of sorbate–sorbent aging time and sorbent decomposition on toluene bioavailability and fate. The bioavailability of 14C-toluene sorbed to individual MSW constituents [office paper, newsprint, model food and yard waste, high density polyethylene (HDPE), and poly(vinyl chloride) (PVC)] was evaluated after aging times of 1, 30, and 180 d. Biodegradable sorbents were tested in both fresh and anaerobically degraded forms to evaluate the effect of sorbent decomposition. At the termination of bioavailability tests, the distribution of 14C that was not converted to 14CO2 was measured by sequential lipophilic solvent and base extractions of sorbents followed by combustion of extracted sorbents. Increasing the toluene-sorbent aging time reduced the rate of toluene biodegradation for all MSW components except for HDPE. 14C remaining in sorbents at the completion of bioavailability tests was physically sequestered within and/or covalently bound to sorbent organic matter, and this fraction increased with increasing aging time. Up to 18.6% of 14C was associated with humic matter (humic and fulvic acids, humin) at the completion of bioavailability tests.}, number={2}, journal={CHEMOSPHERE}, author={Chen, Ye and Knappe, Detlef R. U. and Barlaz, Morton A.}, year={2013}, month={Jan}, pages={251–259} }
 @inproceedings{chowdhury_shaw_knappe_roccaro_randazzo_roberson_2012, title={What are the impacts of a cVOC group regulation? Questions answered with a case study at Suffolk County Water Authority}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84890729349&partnerID=MN8TOARS}, booktitle={Water Quality Technology Conference and Exposition 2012}, author={Chowdhury, Z. and Shaw, J. and Knappe, D. and Roccaro, J. and Randazzo, K. and Roberson, A.}, year={2012} }
 @inbook{summers_knappe_snoeyink_2011, place={New York, NY}, edition={6th}, title={Adsorption of Organic Compounds by Activated Carbon}, ISBN={9780071630115 9780070016590}, booktitle={Water quality & treatment : a handbook on drinking water}, publisher={McGraw-Hill}, author={Summers, R.S. and Knappe, D.R.U. and Snoeyink, V.L.}, editor={Edzwald, J.K.Editor}, year={2011} }
 @article{velten_knappe_traber_kaiser_gunten_boller_meylan_2011, title={Characterization of natural organic matter adsorption in granular activated carbon adsorbers}, volume={45}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79959345067&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2011.04.047}, abstractNote={The removal of natural organic matter (NOM) from lake water was studied in two pilot-scale adsorbers containing granular activated carbon (GAC) with different physical properties. To study the adsorption behavior of individual NOM fractions as a function of time and adsorber depth, NOM was fractionated by size exclusion chromatography (SEC) into biopolymers, humics, building blocks, and low molecular weight (LMW) organics, and NOM fractions were quantified by both ultraviolet and organic carbon detectors. High molecular weight biopolymers were not retained in the two adsorbers. In contrast, humic substances, building blocks and LMW organics were initially well and irreversibly removed, and their effluent concentrations increased gradually in the outlet of the adsorbers until a pseudo-steady state concentration was reached. Poor removal of biopolymers was likely a result of their comparatively large size that prevented access to the internal pore structure of the GACs. In both GAC adsorbers, adsorbability of the remaining NOM fractions, compared on the basis of partition coefficients, increased with decreasing molecular size, suggesting that increasingly larger portions of the internal GAC surface area could be accessed as the size of NOM decreased. Overall DOC uptake at pseudo-steady state differed between the two tested GACs (18.9 and 28.6 g-C/kg GAC), and the percent difference in DOC uptake closely matched the percent difference in the volume of pores with widths in the 1–50 nm range that was measured for the two fresh GACs. Despite the differences in NOM uptake capacity, individual NOM fractions were removed in similar proportions by the two GACs.}, number={13}, journal={WATER RESEARCH}, author={Velten, Silvana and Knappe, Detlef R. U. and Traber, Jacqueline and Kaiser, Hans-Peter and Gunten, Urs and Boller, Markus and Meylan, Sebastien}, year={2011}, month={Jul}, pages={3951–3959} }
 @inproceedings{dunn_yuncu_ged_knappe_2011, title={Combined disinfectant byproduct precursor and micropollutant removal with superfine powdered activated carbon}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84873509681&partnerID=MN8TOARS}, booktitle={Water Quality Technology Conference and Exposition 2011}, author={Dunn, S. and Yuncu, B. and Ged, E. and Knappe, D.R.U.}, year={2011}, pages={2529–2539} }
 @inproceedings{dunn_knappe_2011, title={Effect of powdered activated carbon base material and size on disinfection by-product precursor removal}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84871624478&partnerID=MN8TOARS}, booktitle={American Water Works Association Annual Conference and Exposition 2011, ACE 2011}, author={Dunn, S. and Knappe, D.R.U.}, year={2011}, pages={966–992} }
 @book{ducoste_knappe_alpert_2011, place={Denver, Colorado}, title={Evaluation of Computational Fluid Dynamics for Modeling UV-Initiated Advanced Oxidation Processes}, number={3176}, institution={Water Research Foundation}, author={Ducoste, J.J. and Knappe, D.R.U. and Alpert, S.M.}, year={2011} }
 @article{saquing_knappe_barlaz_2012, title={Fate and transport of phenol in a packed bed reactor containing simulated solid waste}, volume={32}, ISSN={["0956-053X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-82655173775&partnerID=MN8TOARS}, DOI={10.1016/j.wasman.2011.09.017}, abstractNote={An assessment of the risk to human health and the environment associated with the presence of organic contaminants (OCs) in landfills necessitates reliable predictive models. The overall objectives of this study were to (1) conduct column experiments to measure the fate and transport of an OC in a simulated solid waste mixture, (2) compare the results of column experiments to model predictions using HYDRUS-1D (version 4.13), a contaminant fate and transport model that can be parameterized to simulate the laboratory experimental system, and (3) determine model input parameters from independently conducted batch experiments. Experiments were conducted in which sorption only and sorption plus biodegradation influenced OC transport. HYDRUS-1D can reasonably simulate the fate and transport of phenol in an anaerobic and fully saturated waste column in which biodegradation and sorption are the prevailing fate processes. The agreement between model predictions and column data was imperfect (i.e., within a factor of two) for the sorption plus biodegradation test and the error almost certainly lies in the difficulty of measuring a biodegradation rate that is applicable to the column conditions. Nevertheless, a biodegradation rate estimate that is within a factor of two or even five may be adequate in the context of a landfill, given the extended retention time and the fact that leachate release will be controlled by the infiltration rate which can be minimized by engineering controls.}, number={2}, journal={WASTE MANAGEMENT}, author={Saquing, Jovita M. and Knappe, Detlef R. U. and Barlaz, Morton A.}, year={2012}, month={Feb}, pages={327–334} }
 @inproceedings{corwin_kennedy_cardenas_summers_mastropole_knappe_2011, title={Impact of DOC, EBCT and pretreatment on the GAC adsorption of trace organic contaminants}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84873497558&partnerID=MN8TOARS}, booktitle={Water Quality Technology Conference and Exposition 2011}, author={Corwin, C.J. and Kennedy, A. and Cardenas, J. and Summers, R.S. and Mastropole, A. and Knappe, D.}, year={2011}, pages={1038–1043} }
 @inproceedings{dudley_strynar_lindstrom_mcmillan_knappe_2011, title={Removal of perfluorinated compounds by powdered activated carbon: Effect of base material and particle size}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84873499923&partnerID=MN8TOARS}, booktitle={Water Quality Technology Conference and Exposition 2011}, author={Dudley, L.-A. and Strynar, M. and Lindstrom, A. and McMillan, L. and Knappe, D.}, year={2011} }
 @article{baeza_knappe_2011, title={Transformation kinetics of biochemically active compounds in low-pressure UV Photolysis and UV/H2O2 advanced oxidation processes}, volume={45}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-79960557307&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2011.05.039}, abstractNote={Factors controlling photolysis and UV/H2O2 photooxidation rates of the biochemically active compounds (BACs) sulfamethoxazole, sulfamethazine, sulfadiazine, trimethoprim, bisphenol A, and diclofenac were determined. Experiments were conducted with a quasi-collimated beam apparatus equipped with low-pressure UV lamps. The effects of pH, H2O2 concentration, and background water matrix (ultrapure water, lake water, wastewater treatment plant effluent) on BAC transformation rates were evaluated. For the sulfa drugs, solution pH affected direct photolysis rates but had little effect on the hydroxyl radical oxidation rate. For sulfamethoxazole, the neutral form photolyzed more easily than the anionic form while the reverse was the case for sulfamethazine and sulfadiazine. For trimethoprim, the hydroxyl radical oxidation rate was higher for the cationic form (pH 3.6) than for the neutral form (pH 7.85). Quantum yields and second order rate constants describing the reaction between the hydroxyl radical and BACs were determined and used together with background water quality data to predict fluence-based BAC transformation rate constants (k′). For both the lake water and wastewater treatment plant effluent matrices, predicted k′ values were generally in good agreement with experimentally determined k′ values. At typical UV/H2O2 treatment conditions (fluence = 540 mJ cm−2, H2O2 dose = 6 mg L−1), BAC transformation percentages in North Carolina lake water ranged from 43% for trimethoprim to 98% for diclofenac. In wastewater treatment plant effluent, BAC transformation percentages were lower (31–97%) at the same treatment conditions because the hydroxyl radical scavenging rate was higher.}, number={15}, journal={WATER RESEARCH}, author={Baeza, Carolina and Knappe, Detlef R. U.}, year={2011}, month={Oct}, pages={4531–4543} }
 @article{saquing_saquing_knappe_barlaz_2010, title={Impact of Plastics on Fate and Transport of Organic Contaminants in Landfills}, volume={44}, ISSN={["0013-936X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77956547698&partnerID=MN8TOARS}, DOI={10.1021/es101251p}, abstractNote={Factors controlling organic contaminant sorption to common plastics in municipal solid waste were identified. Consumer plastics [drinking water container, prescription drug bottle, soda bottle, disposable cold cup, computer casing, furniture foam, carpet, vinyl flooring, formica sheet] and model polymers [high-density polyethylene (HDPE), medium-density polyethylene, low-density polyethylene, poly(vinyl chloride) (PVC)] were characterized by X-ray diffractometry, differential scanning calorimetry, and elemental analysis. The material characterization was used to interpret batch isotherm and kinetic data. K(p) values describing toluene sorption to rubbery or "soft" polymers could be normalized by the amorphous polymer fraction (f(amorphous)) but not by the organic carbon fraction (f(oc)). Diffusion coefficients (D) describing the uptake rate of toluene by rubbery plastics (HDPE, drinking water container, prescription drug bottle) were similar (D approximately 10(-10) cm(2)/s), indicating that pure HDPE can be used as a model for rubbery plastics. Toluene diffusivity was similar among glassy or "hard" plastics (PVC, soda bottle, computer casing, disposable cold cup; D approximately 10(-12) cm(2)/s) but lower than for rubbery plastics. Plastics in landfills are potential sinks of hydrophobic organic contaminants (HOCs) because of their higher affinity for HOCs compared to lignocellulosic materials and the slow desorption of HOCs from glassy plastics.}, number={16}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Saquing, Jovita M. and Saquing, Carl D. and Knappe, Detlef R. U. and Barlaz, Morton A.}, year={2010}, month={Aug}, pages={6396–6402} }
 @book{knappe_yuncu_deng_2010, place={Denver, Colorado}, title={Removal of 2-Methylisoborneol and Geosmin by High-Silica Zeolites and Zeolite-Enhanced Ozonation}, number={Project #3169}, institution={Water Research Foundation}, author={Knappe, D.R.U. and Yuncu, B. and Deng, Q.}, year={2010} }
 @inproceedings{yuncu_knappe_2010, title={Removal of 2-methylisoborneol and geosmin by zeolite enhanced ozonation}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84871413753&partnerID=MN8TOARS}, booktitle={American Water Works Association Annual Conference and Exposition 2010, ACE 2010, Papers}, author={Yuncu, B. and Knappe, D.R.U.}, year={2010} }
 @inproceedings{dunn_deng_ohno_matsui_knappe_2010, title={Removal of natural organic matter and trace organic pollutants by superfine powdered activated carbon}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84873492183&partnerID=MN8TOARS}, booktitle={Water Quality Technology Conference and Exposition 2010}, author={Dunn, S. and Deng, Q. and Ohno, K. and Matsui, Y. and Knappe, D.R.U.}, year={2010}, pages={2156–2170} }
 @inproceedings{kearns_wellborn_summers_knappe_2010, title={Removal of pesticides from drinking water using indigenous charcoal adsorbents}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84873507968&partnerID=MN8TOARS}, booktitle={Water Quality Technology Conference and Exposition 2010}, author={Kearns, J.P. and Wellborn, L.S. and Summers, R.S. and Knappe, D.R.U.}, year={2010}, pages={1401–1408} }
 @inproceedings{deng_ohno_knappe_2010, title={Removal of pharmaceuticals by powdered activated carbon adsorption: Effect of particle size and point of addition}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84871451325&partnerID=MN8TOARS}, booktitle={American Water Works Association Annual Conference and Exposition 2010, ACE 2010, Papers}, author={Deng, Q. and Ohno, K. and Knappe, D.}, year={2010} }
 @article{rosenfeldt_baeza_knappe_2009, title={Effect of Free Chlorine Application on Microbial Quality of Drinking Water in Chloraminated Distribution Systems}, volume={101}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-73249126255&partnerID=MN8TOARS}, DOI={10.1002/j.1551-8833.2009.tb09974.x}, abstractNote={The potential for bacterial regrowth and the formation of disinfection by‐products in distribution systems are issues of concern for many drinking water utilities. The principal objective of this study was to examine bacterial growth/regrowth in two chloraminated distribution systems before, during, and after a free chlorine flush. Raw water for both systems was of similar quality, but treatment trains differed, primarily in their use of ozone. To avoid culture‐based technique biases, cell counts were measured directly by nucleic acid staining and subsequent analysis by flow cytometry. During the free chlorine flush period, lower cell counts were obtained at all sampled locations in one distribution system, but only at long detention times in the second distribution system. Assimilable organic carbon levels were generally greater in the second distribution system, where ozonation was used in the treatment train. At an intermittent‐use facility, nitrification was mitigated after hydrant flushing led to the appearance of a free chlorine residual. However, without additional hydrant flushing, the free chlorine residual decayed and led to elevated levels of chloroform. In comparing tap water from both distribution systems with several commercially available bottled waters, bacteria levels were found to be higher in more than half of the bottled waters tested.}, number={10}, journal={Journal AWWA}, author={Rosenfeldt, E.J. and Baeza, C. and Knappe, D.R.U.}, year={2009}, pages={60–70} }
 @article{saquing_mitchell_wu_wagner_knappe_barlaz_2010, title={Factors Controlling Alkylbenzene and Tetrachloroethene Desorption from Municipal Solid Waste Components}, volume={44}, ISSN={["0013-936X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-75749108559&partnerID=MN8TOARS}, DOI={10.1021/es9030672}, abstractNote={Desorption rates of toluene, o-xylene and tetrachloroethene from individual municipal solid waste components [high-density polyethylene (HDPE); poly(vinyl chloride) (PVC); office paper; newsprint; and rabbit food, a model food and yard waste] were determined. Effects of sorbent and sorbate properties, solvent composition (ultrapure water, acidogenic and methanogenic leachates), and contact time ("aging") on desorption rates were evaluated. Hydrophobic organic contaminant (HOC) desorption from PVC and HDPE could be described with a single-parameter polymer diffusion model. In contrast, a three-parameter, biphasic polymer diffusion model was required to describe HOC desorption rates from biopolymer composites. In general, HOC desorption rates from plastics were rapid for HDPE (D = 10(-10) cm(2)/s), a rubbery polymer, but slower for PVC (D = 10(-13)-10(-14) cm(2)/s), a glassy polymer. For biopolymer composites, a large fraction of sorbed HOCs was rapidly released (D(r) = 10(-9)-10(-10) cm(2)/s) while the remaining fraction desorbed slowly (D(s) = 10(-11)-10(-16) cm(2)/s). The toluene desorption rate from PVC was 1 order of magnitude faster in acidogenic leachate than in either ultrapure water or methanogenic leachate, a result that was primarily attributed to the plasticizing effect of volatile fatty acids in acidogenic leachate. For biopolymer composites, small increases in the slowly desorbing HOC fraction were observed with increasing aging time.}, number={3}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Saquing, Jovita M. and Mitchell, Lisa A. and Wu, Bingyan and Wagner, Travis B. and Knappe, Detlef R. U. and Barlaz, Morton A.}, year={2010}, month={Feb}, pages={1123–1129} }
 @article{alpert_knappe_ducoste_2010, title={Modeling the UV/hydrogen peroxide advanced oxidation process using computational fluid dynamics}, volume={44}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77149163483&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2009.12.003}, abstractNote={The use of numerical models for the design and optimization of UV/H2O2 systems must incorporate both reactor design (hydrodynamics, lamp orientation) and chemical kinetics (reaction mechanisms, kinetic rate constants). This study was conducted to evaluate the performance of comprehensive CFD/UV/AOP models for the degradation of an indicator organic contaminant. The combination of turbulence sub-models, fluence rate sub-models, and kinetic rate equations resulted in a comprehensive and flexible design tool for predicting the effluent chemical composition from a UV-initiated AOP reactor. The CFD model tended to under predict the percent removal of methylene blue compared to pilot reactor trials under the same operating conditions. In addition, the percent difference between the pilot and the CFD results increased with increasing flow rates. The MSSS fluence rate sub-model predicted higher contaminant removal values than the RAD-LSI sub-model while the different two-equation turbulence sub-models did not significantly impact the predicted removal for methylene blue in the tested reactor configuration. The overall degradation of methylene blue was a strong function of the second-order kinetic rate constant describing the reaction between methylene blue and the hydroxyl radical. In addition, the removal of methylene blue was sensitive to the concentration of dissolved organic carbon in the water matrix since DOC acts as a scavenger of hydroxyl radicals.}, number={6}, journal={WATER RESEARCH}, author={Alpert, Scott M. and Knappe, Detlef R. U. and Ducoste, Joel J.}, year={2010}, month={Mar}, pages={1797–1808} }
 @article{rossner_snyder_knappe_2009, title={Removal of emerging contaminants of concern by alternative adsorbents}, volume={43}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-67651091719&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2009.06.009}, abstractNote={The effective removal of emerging contaminants of concern (ECCs) such as endocrine-disrupting chemicals, pharmaceutically active compounds, personal care products, and flame retardants is a desirable water treatment goal. In this study, one activated carbon, one carbonaceous resin, and two high-silica zeolites were studied to evaluate their effectiveness for the removal of an ECC mixture from lake water. Adsorption isotherm experiments were performed with a mixture of 28 ECCs at environmentally relevant concentrations (∼200–900 ng/L). Among the tested adsorbents, activated carbon was the most effective, and activated carbon doses typically used for taste and odor control in drinking water (<10 mg/L) were sufficient to achieve a 2-log removal for most of the tested ECCs. The carbonaceous resin was less effective than the activated carbon because this adsorbent had a smaller volume of pores in the size range required for the adsorption of many ECCs (∼6–9 Å). For the removal of ECC mixture constituents, zeolites were less effective than the carbonaceous adsorbents. Because zeolites contain pores of uniform size and shape, a few of the tested ECCs with matching pore size/shape requirements were well removed, but the adsorptive removal of others was negligible, even at zeolite doses of 100 mg/L. The results of this study demonstrate that effective adsorbents for the removal of a broad spectrum of ECCs from water should exhibit heterogeneity in pore size and shape and a large pore volume in the 6–9 Å size range.}, number={15}, journal={WATER RESEARCH}, author={Rossner, Alfred and Snyder, Shane A. and Knappe, Detlef R. U.}, year={2009}, month={Aug}, pages={3787–3796} }
 @article{teuten_saquing_knappe_barlaz_jonsson_björn_rowland_thompson_galloway_yamashita_et al._2009, title={Transport and release of chemicals from plastics to the environment and to wildlife}, volume={364}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-67650784197&partnerID=MN8TOARS}, DOI={10.1098/rstb.2008.0284}, abstractNote={
            Plastics debris in the marine environment, including resin pellets, fragments and microscopic plastic fragments, contain organic contaminants, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons, petroleum hydrocarbons, organochlorine pesticides (2,2′-bis(
            p-
            chlorophenyl)-1,1,1-trichloroethane, hexachlorinated hexanes), polybrominated diphenylethers, alkylphenols and bisphenol A, at concentrations from sub ng g
            –1
            to µg g
            –1
            . Some of these compounds are added during plastics manufacture, while others adsorb from the surrounding seawater. Concentrations of hydrophobic contaminants adsorbed on plastics showed distinct spatial variations reflecting global pollution patterns. Model calculations and experimental observations consistently show that polyethylene accumulates more organic contaminants than other plastics such as polypropylene and polyvinyl chloride. Both a mathematical model using equilibrium partitioning and experimental data have demonstrated the transfer of contaminants from plastic to organisms. A feeding experiment indicated that PCBs could transfer from contaminated plastics to streaked shearwater chicks. Plasticizers, other plastics additives and constitutional monomers also present potential threats in terrestrial environments because they can leach from waste disposal sites into groundwater and/or surface waters. Leaching and degradation of plasticizers and polymers are complex phenomena dependent on environmental conditions in the landfill and the chemical properties of each additive. Bisphenol A concentrations in leachates from municipal waste disposal sites in tropical Asia ranged from sub µg l
            –1
            to mg l
            –1
            and were correlated with the level of economic development.
          }, number={1526}, journal={Philosophical Transactions of the Royal Society B: Biological Sciences}, author={Teuten, E.L. and Saquing, J.M. and Knappe, D.R.U. and Barlaz, M.A. and Jonsson, S. and Björn, A. and Rowland, S.J. and Thompson, R.C. and Galloway, T.S. and Yamashita, R. and et al.}, year={2009}, pages={2027–2045} }
 @misc{teuten_saquing_knappe_barlaz_jonsson_bjorn_rowland_thompson_galloway_yamashita_et al._2009, title={Transport and release of chemicals from plastics to the environment and to wildlife}, volume={364}, number={1526}, journal={Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences}, author={Teuten, E. L. and Saquing, J. M. and Knappe, D. R. U. and Barlaz, M. A. and Jonsson, S. and Bjorn, A. and Rowland, S. J. and Thompson, R. C. and Galloway, T. S. and Yamashita, R. and et al.}, year={2009}, pages={2027–2045} }
 @article{bartelt-hunt_knappe_barlaz_2008, title={A Review of Chemical Warfare Agent Simulants for the Study of Environmental Behavior}, volume={38}, ISSN={1064-3389 1547-6537}, url={http://dx.doi.org/10.1080/10643380701643650}, DOI={10.1080/10643380701643650}, abstractNote={There is renewed interest in the environmental fate of chemical warfare agents attributable to the intensified threat of chemical weapons use in a terrorist attack. Knowledge of processes that influence the fate of agents such as distilled mustard, lewisite, tabun, sarin, soman, and VX in the environment is important for development of disposal strategies and for risk and exposure assessments. However, it is often necessary to conduct studies examining chemical agent behavior using simulants due to the toxicity of the agents and usage restrictions. The objective of this study was to review the physical–chemical properties and mammalian toxicity of compounds that can be used to simulate chemical agents and to identify the most appropriate compounds to simulate specific environmental fate processes, including hydrolysis, sorption, bioavailability, and volatilization.}, number={2}, journal={Critical Reviews in Environmental Science and Technology}, publisher={Informa UK Limited}, author={Bartelt-Hunt, Shannon L. and Knappe, Detlef R. U. and Barlaz, Morton A.}, year={2008}, month={Jan}, pages={112–136} }
 @inproceedings{summers_dani_zachman_corwin_blute_mcguire_knappe_2008, title={MTBE adsorption: Evaluating EBCT, competition and fouling in the microgram/liter range}, volume={48}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77955619742&partnerID=MN8TOARS}, number={1}, booktitle={ACS National Meeting Book of Abstracts}, author={Summers, R.S. and Dani, D. and Zachman, B. and Corwin, C. and Blute, N. and McGuire, M. and Knappe, D.}, year={2008}, pages={45–49} }
 @inproceedings{knappe_yuncu_2008, title={Use of high-silica zeolites for the targeted removal of taste and odor compounds from drinking water}, volume={48}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85025618087&partnerID=MN8TOARS}, number={1}, booktitle={ACS, Division of Environmental Chemistry - Preprints of Extended Abstracts}, author={Knappe, D.R.U. and Yuncu, B.}, year={2008}, pages={65–69} }
 @book{knappe_rossner_snyder_strickland_2007, place={Denver, Colorado}, title={Alternative Adsorbents for the Removal of Polar Organic Contaminants}, number={Project #2905}, institution={American Water Works Association Research Foundation}, author={Knappe, D.R.U. and Rossner, A. and Snyder, S.A. and Strickland, C.}, year={2007} }
 @inproceedings{alpert_knappe_ducoste_2007, title={Incorporation of micromixing models within CFD simulations describing UV-initiated advanced oxidation processes}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84871662252&partnerID=MN8TOARS}, booktitle={American Water Works Association - AWWA Annual Conference and Exposition, ACE 2007}, author={Alpert, S.M. and Knappe, D. and Ducoste, J.}, year={2007}, pages={388–401} }
 @inproceedings{rossner_knappe_2007, title={MTBE adsorption kinetics on alternative adsorbents and packed bed adsorber performance}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-37349024315&partnerID=MN8TOARS}, booktitle={ACS National Meeting Book of Abstracts}, author={Rossner, A. and Knappe, D.R.U.}, year={2007} }
 @article{rossner_knappe_2008, title={MTBE adsorption on alternative adsorbents and packed bed adsorber performance}, volume={42}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-41949096645&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2007.12.009}, abstractNote={Widespread use of the fuel additive methyl tertiary-butyl ether (MTBE) has led to frequent MTBE detections in North American and European drinking water sources. The overall objective of this research was to evaluate the effectiveness of a silicalite zeolite, a carbonaceous resin, and a coconut-shell-based granular activated carbon (GAC) for the removal of MTBE from water. Isotherm and short bed adsorber tests were conducted in ultrapure water and river water to obtain parameters describing MTBE adsorption equilibria and kinetics and to quantify the effect of natural organic matter (NOM) on MTBE adsorption. Both the silicalite zeolite and the carbonaceous resin exhibited larger MTBE adsorption uptakes than the tested GAC. Surface diffusion coefficients describing intraparticle MTBE mass transfer rates were largest for the GAC and smallest for the carbonaceous resin. Pilot tests were conducted to verify MTBE breakthrough curve predictions obtained with the homogeneous surface diffusion model and to evaluate the effect of NOM preloading on packed bed adsorber performance. Results showed that GAC was the most cost-competitive adsorbent when considering adsorbent usage rate only; however, the useful life of an adsorber containing silicalite zeolite was predicted to be ∼5–6 times longer than that of an equally sized adsorber containing GAC. Pilot column results also showed that NOM preloading did not impair the MTBE removal efficiency of the silicalite zeolite. Thus, it may be possible to regenerate spent silicalite with less energy-intensive methods than those required to regenerate GAC.}, number={8-9}, journal={WATER RESEARCH}, author={Rossner, Alfred and Knappe, Detlef R. U.}, year={2008}, month={Apr}, pages={2287–2299} }
 @article{chen_tayebali_knappe_2006, title={A  procedure to quantify organic antistrip additives in asphalt binders and mixes}, volume={34}, DOI={10.1520/jte12733}, abstractNote={Stripping is a phenomenon of loss of bond or adhesion between the asphalt binder and the aggregate in asphalt mixes. Stripping frequently results from the presence of water, and most agencies require the use of antistrip additive to control moisture damage. However, there is no simple and quick method for detecting the presence and the amount or percentage of organic antistrip additive in asphalt binders or mixes. This paper presents a procedure based on solid-state spectrophotometry to detect qualitatively and quantitatively the presence of amine-based antistrip additive in asphalt binders and mixes. The developed procedure gives results that are quantifiable and reproducible with low coefficients of variation.}, number={4}, journal={Journal of Testing and Evaluation}, author={Chen, C. and Tayebali, A. A. and Knappe, D. R. U.}, year={2006}, pages={269–274} }
 @article{chun_tayebali_knappe_2006, title={A procedure to quantify organic antistrip additives in asphalt binders and mixes}, volume={34}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33845239692&partnerID=MN8TOARS}, number={4}, journal={Journal of Testing and Evaluation}, author={Chun, C. and Tayebali, A.A. and Knappe, D.R.U.}, year={2006}, pages={269–274} }
 @article{bartelt-hunt_barlaz_knappe_kjeldsen_2006, title={Fate of chemical warfare agents and toxic industrial chemicals in landfills}, volume={40}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33746709349&partnerID=MN8TOARS}, DOI={10.1021/es052400y}, abstractNote={One component of preparedness for a chemical attack is planning for the disposal of contaminated debris. To assess the feasibility of contaminated debris disposal in municipal solid waste (MSW) landfills, the fate of selected chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) in MSW landfills was predicted with a mathematical model. Five blister agents [sulfur mustard (HD), nitrogen mustard (HN-2), lewisite (L), ethyldichloroarsine (ED), and phosgene oxime (CX)], eight nerve agents [tabun (GA), sarin (GB), soman (GD), GE, GF, VX, VG, and VM], one riot-control agent [CS], and two TICs [furan and carbon disulfide] were studied. The effects of both infiltration (climate) and contaminant biodegradability on fate predictions were assessed. Model results showed that hydrolysis and gas-phase advection were the principal fate pathways for CWAs and TICs, respectively. Apart from CX and the TICs, none of the investigated compounds was predicted to persist in a landfill for more than 5 years. Climate had little impact on CWA/TIC fate, and biodegradability was only important for compounds with long hydrolysis half-lives. Monte Carlo simulations were performed to assess the influence of uncertainty in model input parameters on CWA/TIC fate predictions. Correlation analyses showed that uncertainty in hydrolysis rate constants was the primary contributor to variance of CWA fate predictions, while uncertainty in the Henry's Law constant and landfill gas-production rate accounted for most of the variance of TIC fate predictions. CWA hydrolysates were more persistent than the parent CWAs, but limited information is available on abiotic or biotic transformation rates for these chemicals.}, number={13}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Bartelt-Hunt, Shannon L. and Barlaz, Morton A. and Knappe, Detlef R. U. and Kjeldsen, Peter}, year={2006}, month={Jul}, pages={4219–4225} }
 @article{chun_tayebali_knappe_2006, title={Quantitative Determination of and Effect of Prolonged Heating on Amine-Based Antistrip Additive Contents in Asphalt Binders and Mixes}, volume={75}, journal={Journal of the Association of Asphalt Paving Technologists}, author={Chun, C. and Tayebali, A.A. and Knappe, D.R.U.}, year={2006}, pages={1095–1119} }
 @inproceedings{baeza_knappe_2006, title={Removal of sulfonamides and associated antimicrobial activity by UV photolysis and UV/H2O2 processes}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84871626879&partnerID=MN8TOARS}, booktitle={American Water Works Association - AWWA Annual Conference and Exposition, ACE 2006: The World's Water Event}, author={Baeza, C. and Knappe, D.R.U.}, year={2006}, pages={285–289} }
 @inbook{knappe_2006, title={Surface chemistry effects in activated carbon adsorption of industrial pollutants}, volume={10}, ISBN={9780120883806}, ISSN={1573-4285}, url={http://dx.doi.org/10.1016/s1573-4285(06)80078-5}, DOI={10.1016/s1573-4285(06)80078-5}, abstractNote={This chapter describes the effects of activated carbon surface chemistry on the adsorption of industrial pollutants from water. Fundamental interactions controlling the adsorption of aqueous pollutants on activated carbon are reviewed and the characteristics of activated carbons and representative industrial pollutants are described. The effects of activated carbon surface chemistry on the adsorption of industrial pollutants from ultrapure water and from solutions containing natural organic matter (NOM) is also discussed. The chapter emphasizes the solution conditions that apply to the treatment of drinking water. In potable water sources, industrial pollutants are typically present at trace concentrations that are well below the pollutant's aqueous solubility limit. When adsorbing industrial pollutants from very dilute solutions, the effects of activated carbon surface chemistry on adsorption capacity are more pronounced as surface coverages are low. The total micropore volume or the commonly measured BET surface area primarily determine the adsorption capacity of activated carbon for a pollutant at higher surface coverages, which may be achieved in the treatment of highly contaminated waters or in solvent recovery operations.}, number={C}, booktitle={Interface Science and Technology}, publisher={Elsevier}, author={Knappe, D.R.U.}, year={2006}, pages={155–177} }
 @book{knappe_campos_2005, title={Effectiveness of high-silica zeolites for the adsorption of methyl tertiary-butyl ether from natural water}, volume={5}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-31144448170&partnerID=MN8TOARS}, number={5}, journal={Water Science and Technology: Water Supply}, author={Knappe, D.R.U. and Campos, A.A.R.}, year={2005}, pages={83–91} }
 @article{knappe_campos_2005, title={Effectiveness of high-silica zeolites for the adsorption of methyl tertiaty-butyl ether from natural water}, volume={5}, ISBN={["1-84339-560-6"]}, ISSN={["1606-9749"]}, DOI={10.2166/ws.2005.0042}, abstractNote={MTBE adsorption isotherm data were collected for a matrix of high-silica zeolites with different pore sizes (ZSM-5/silicalite, mordenite, beta, Y), exchangeable cations (H+, Na+, NH4+), and hydrophobicities (SiO2/Al2O3 ratios). MTBE adsorption capacities of high-silica zeolites were compared with those of one coconut-shell-based and two coal-based granular activated carbons (GACs) as well as a carbonaceous resin. Isotherm experiments were conducted in ultrapure water buffered at pH 7.2 and in Tar River water (Greenville, NC) to determine the effects of co-adsorbing and preloaded natural organic matter (NOM) on MTBE adsorption. The results of this study showed that (1) high-silica zeolites with small pores (ZSM-5/silicalite, mordenite) exhibit higher MTBE adsorption capacities than GACs, (2) NOM has little or no effect on MTBE adsorption capacities of ZSM-5/silicalite zeolites, and (3) equilibrium model results suggest that silicalite-based adsorption systems are cost-competitive with activated-carbon-based adsorption systems while offering operational advantages such as longer adsorber life and possibly greater ease of regeneration.}, number={5}, journal={Leading-Edge Technology 2005 - Water Treatment}, author={Knappe, DRU and Campos, AAR}, year={2005}, pages={83–91} }
 @article{quinlivan_li_knappe_2005, title={Effects of activated carbon characteristics on the simultaneous adsorption of aqueous organic micropollutants and natural organic matter}, volume={39}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-18144421582&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2005.01.029}, abstractNote={The overall objective of this research was to determine the effects of physical and chemical activated carbon characteristics on the simultaneous adsorption of trace organic contaminants and natural organic matter (NOM). A matrix of 12 activated carbon fibers (ACFs) with three activation levels and four surface chemistry levels (acid-washed, oxidized, hydrogen-treated, and ammonia-treated) was studied to systematically evaluate pore structure and surface chemistry phenomena. Also, three commercially available granular activated carbons (GACs) were tested. The relatively hydrophilic fuel additive methyl tertiary-butyl ether (MTBE) and the relatively hydrophobic solvent trichloroethene (TCE) served as micropollutant probes. A comparison of adsorption isotherm data collected in the presence and absence of NOM showed that percent reductions of single-solute TCE and MTBE adsorption capacities that resulted from the presence of co-adsorbing NOM were not strongly affected by the chemical characteristics of activated carbons. However, hydrophobic carbons were more effective adsorbents for both TCE and MTBE than hydrophilic carbons because enhanced water adsorption on the latter interfered with the adsorption of micropollutants from solutions containing NOM. With respect to pore structure, activated carbons should exhibit a large volume of micropores with widths that are about 1.5 times the kinetic diameter of the target adsorbate. Furthermore, an effective adsorbent should possess a micropore size distribution that extends to widths that are approximately twice the kinetic diameter of the target adsorbate to prevent pore blockage/constriction as a result of NOM adsorption.}, number={8}, journal={WATER RESEARCH}, author={Quinlivan, PA and Li, L and Knappe, DRU}, year={2005}, month={Apr}, pages={1663–1673} }
 @inproceedings{knappe_2005, title={Effects of sorbent structure and chemistry on organic contaminant sorption: Activated carbon perspective}, volume={45}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-32244435339&partnerID=MN8TOARS}, number={2}, booktitle={ACS, Division of Environmental Chemistry - Preprints of Extended Abstracts}, author={Knappe, D.R.U.}, year={2005}, pages={426–432} }
 @article{li_quinlivan_knappe_2005, title={Predicting adsorption isotherms for aqueous organic micropollutants from activated carbon and pollutant properties}, volume={39}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-18344362134&partnerID=MN8TOARS}, DOI={10.1021/es048816d}, abstractNote={A method based on the Polanyi-Dubinin-Manes (PDM) model is presented to predict adsorption isotherms of aqueous organic contaminants on activated carbons. It was assumed that trace organic compound adsorption from aqueous solution is primarily controlled by nonspecific dispersive interactions while water adsorption is controlled by specific interactions with oxygen-containing functional groups on the activated carbon surface. Coefficients describing the affinity of water for the activated carbon surface were derived from aqueous-phase methyl tertiary-butyl ether (MTBE) and trichloroethene (TCE) adsorption isotherm data that were collected with 12 well-characterized activated carbons. Over the range of oxygen contents covered by the adsorbents (approximately 0.8-10 mmol O/g dry, ash-free activated carbon), a linear relationship between water affinity coefficients and adsorbent oxygen content was obtained. Incorporating water affinity coefficients calculated from the developed relationship into the PDM model, isotherm predictions resulted that agreed well with experimental data for three adsorbents and two adsorbates [tetrachloroethene (PCE), cis-1,2-dichloroethene (DCE)] that were not used to calibrate the model.}, number={9}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Li, L and Quinlivan, PA and Knappe, DRU}, year={2005}, month={May}, pages={3393–3400} }
 @book{knappe_2004, title={Algae detection and removal strategies for drinking water treatment plants}, ISBN={1583213074}, publisher={Denver Colo.: AWWA Research Foundation and American Water Works Association}, author={Knappe, D. R. U.}, year={2004} }
 @article{chen_nanny_knappe_wagner_ratasuk_2004, title={Chemical characterization and sorption capacity measurements of degraded newsprint from a landfill}, volume={38}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-3042751476&partnerID=MN8TOARS}, DOI={10.1021/es0305914}, abstractNote={Newsprint samples collected from 12-16 ft (top layer (TNP)), 20-24 ft (middle layer (MNP)), and 32-36 ft (bottom layer (BNP)) below the surface of the Norman Landfill (NLF) were characterized by infrared (IR) spectroscopy, cross-polarization, magic-angle spinning 13C nuclear magnetic resonance (CP-MAS 13C NMR) spectroscopy, and tetramethylammonium hydroxide (TMAH) thermochemolysis gas chromatography/mass spectrometry (GC/MS). The extent of NLF newsprint degradation was evaluated by comparing the chemical composition of NLF newsprint to that of fresh newsprint (FNP) and newsprint degraded in the laboratory under methanogenic conditions (DNP). The O-alkyl/alkyl, cellulose/lignin, and lignin/resin acid ratios showed that BNP was the most degraded, and that all three NLF newsprint samples were more degraded than DNP. 13C NMR and TMAH thermochemolysis data demonstrated selective enrichment of lignin over cellulose, and TMAH thermochemolysis further exhibited selective enrichment of resin acids over lignin. In addition, the crystallinity of cellulose in NLF newsprint samples was significantly lower relative to that of FNP and DNP as shown by 13C NMR spectra. The yield of lignin monomers from TMAH thermochemolysis suggested that hydroxyl groups were removed from the propyl side chain of lignin during the anaerobic decomposition of newsprint in the NLF. Moreover, the vanillyl acid/aldehyde ratio, which successfully describes aerobic lignin degradation, was not a good indicator of the anaerobic degradation of lignin on the basis of the TMAH data. The toluene sorption capacity increased as the degree of newsprint degradation increased or as the O-alkyl/alkyl ratio of newsprint decreased. The results of this study further verified that the sorbent O-alkyl/ alkyl ratio is useful for predicting sorption capacities of natural organic materials for hydrophobic organic contaminants.}, number={13}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Chen, LX and Nanny, MA and Knappe, DRU and Wagner, TB and Ratasuk, N}, year={2004}, month={Jul}, pages={3542–3550} }
 @article{chen_knappe_barlaz_2004, title={Effect of cellulose/hemicellulose and lignin on the bioavailability of toluene sorbed to waste paper}, volume={38}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-3042787671&partnerID=MN8TOARS}, DOI={10.1021/es035286x}, abstractNote={Paper constitutes about 38% of municipal solid waste, much of which is disposed of in landfills. Sorption to such lignocellulosic materials may limit the bioavailability of organic contaminants in landfills. The objective of this study was to identify the effect of individual biopolymers in paper on toluene sorption and bioavailability by subjecting fresh and anaerobically degraded office paper and newsprint to enzymatic hydrolysis and acid hydrolysis. Enzymatic degradation of cellulose and hemicellulose had no effect on toluene bioavailability. In contrast, acid-insoluble lignin controlled toluene sorption and bioavailability for both fresh and degraded newsprint. Acid-insoluble lignin could explain only 54% of the toluene sorption capacity of degraded office paper however, suggesting that crude protein and/or lipophilic organic matter were also important sorbent phases. Toluene sorbed to degraded office paper was also less bioavailable than toluene sorbed to an equivalent mass of lignin extracted from this sorbent. The latter result suggests that a fraction of toluene sorbed to degraded office paper may have been sequestered by lipophilic organic matter. The sorption and bioavailability data indicate that the preferential decomposition of cellulose and hemicellulose relative to lignin in landfills should not decrease the overall toluene sorption capacity of paperwaste or increase the bioavailability of sorbed toluene.}, number={13}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Chen, Y and Knappe, DRU and Barlaz, NA}, year={2004}, month={Jul}, pages={3731–3736} }
 @article{badruzzaman_westerhoff_knappe_2004, title={Intraparticle diffusion and adsorption of arsenate onto granular ferric hydroxide (GFH)}, volume={38}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-4544343747&partnerID=MN8TOARS}, DOI={10.1016/j.watres.2004.07.007}, abstractNote={Porous iron oxides are being evaluated and selected for arsenic removal in potable water systems. Granular ferric hydroxide, a typical porous iron adsorbent, is commercially available and frequently considered in evaluation of arsenic removal methods. GFH is a highly porous (micropore volume ∼0.0394±0.0056 cm3 g−1, mesopore volume ∼0.0995±0.0096 cm3 g−1) adsorbent with a BET surface area of 235±8 m2 g−1. The purpose of this paper is to quantify arsenate adsorption kinetics on GFH and to determine if intraparticle diffusion is a rate-limiting step for arsenic removal in packed-bed treatment systems. Data from bottle-point isotherm and differential column batch reactor (DCBR) experiments were used to estimate Freundlich isotherm parameters (K and 1/n) as well as kinetic parameters describing mass transfer resistances due to film diffusion (kf) and intraparticle surface diffusion (Ds). The pseudo-equilibrium (18 days of contact time) arsenate adsorption density at pH 7 was 8 μg As/mg dry GFH at a liquid phase arsenate concentration of 10 μg As/L. The homogeneous surface diffusion model (HSDM) was used to describe the DCBR data. A non-linear relationship (DS=3.0−9×Rp1.4) was observed between Ds and GFH particle radius (RP) with Ds values ranging from 2.98×10−12 cm2 s−1 for the smallest GFH mesh size (100×140) to 64×10−11 cm2 s−1 for the largest GFH mesh size (10×30). The rate-limiting process of intraparticle surface diffusion for arsenate adsorption by porous iron oxides appears analogous to organic compound adsorption by activated carbon despite differences in adsorption mechanisms (inner-sphere complexes for As versus hydrophobic interactions for organic contaminants). The findings are discussed in the context of intraparticle surface diffusion affecting packed-bed treatment system design and application of rapid small-scale column tests (RSSCTs) to simulate the performance of pilot- or full-scale systems at the bench-scale.}, number={18}, journal={WATER RESEARCH}, author={Badruzzaman, M and Westerhoff, P and Knappe, DRU}, year={2004}, month={Nov}, pages={4002–4012} }
 @article{hepplewhite_newcombe_knappe_2004, title={NOM and MIB, who wins in the competition for activated carbon adsorption sites?}, volume={49}, ISSN={["1996-9732"]}, DOI={10.2166/wst.2004.0584}, abstractNote={The adsorption of an odour compound common in drinking water, 2-methylisoborneol (MIB), was studied on two activated carbons in the presence of 13 well-characterised natural organic matter (NOM) solutions. It was found that, although the carbons and the NOM solutions had a wide range of characteristics, the major competitive mechanism was the same in all cases. The low molecular weight NOM compounds were the most competitive, participating in a direct competition with the MIB molecule for adsorption sites. Equivalent background concentration (EBC) calculations indicated a relatively low concentration of directly competing compounds in the NOM. Some evidence of pore restriction was also seen, with microporous carbons most affected by low molecular weight NOM, and mesoporous carbons impacted by the higher molecular weight compounds.}, number={9}, journal={WATER SCIENCE AND TECHNOLOGY}, author={Hepplewhite, C and Newcombe, G and Knappe, DRU}, year={2004}, pages={257–265} }
 @book{hepplewhite_newcombe_knappe_2004, title={NOM and MIB, who wins in the competition for activated carbon adsorption sites?}, volume={49}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-3042814758&partnerID=MN8TOARS}, number={9}, journal={Water Science and Technology}, author={Hepplewhite, C. and Newcombe, G. and Knappe, D.R.U.}, year={2004}, pages={257–265} }
 @book{knappe_li_quinlivan_wagner_2003, place={Denver, Colorado}, title={Effects of Activated Carbon Surface Chemistry and Pore Structure on the Adsorption of Trichloroethene and Methyl Tertiary-Butyl Ether from Natural Water}, institution={American Water Works Association Research Foundation}, author={Knappe, D.R.U. and Li, L. and Quinlivan, P.A. and Wagner, T.B.}, year={2003} }
 @article{li_quinlivan_knappe_2003, title={Erratum: Effects of activated carbon surface chemistry and pore structure on the adsorption of organic contaminants from aqueous solution (Carbon (2002) 40 (2085-2100) PII: S0008622302000696)}, volume={41}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0038617285&partnerID=MN8TOARS}, DOI={10.1016/S0008-6223(03)00121-0}, number={8}, journal={Carbon}, author={Li, L. and Quinlivan, P.A. and Knappe, D.R.U.}, year={2003}, pages={1693} }
 @article{newcombe_hepplewhite_knappe_2003, title={NOM and MIB, who wins in the competition for activated carbon adsorption sites?}, volume={30}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0037294576&partnerID=MN8TOARS}, number={1}, journal={Water}, author={Newcombe, G. and Hepplewhite, C. and Knappe, D.}, year={2003}, pages={33–36} }
 @article{briley_knappe_2003, title={Optimizing ferric sulfate coagulation of algae with streaming current measurements}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-40349083675&partnerID=MN8TOARS}, number={341}, journal={Water Resources Research Institute News of the University of North Carolina}, author={Briley, D.S. and Knappe, D.R.U.}, year={2003} }
 @article{li_quinlivan_knappe_2002, title={Effects of activated carbon surface chemistry and pore structure on the adsorption of organic contaminants from aqueous solution}, volume={40}, ISSN={["1873-3891"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0036042422&partnerID=MN8TOARS}, DOI={10.1016/S0008-6223(02)00069-6}, abstractNote={The objective of this research was to develop activated carbon selection criteria that assure the effective removal of trace organic contaminants from aqueous solution and to base the selection criteria on physical and chemical adsorbent characteristics. To systematically evaluate pore structure and surface chemistry effects, a matrix of activated carbon fibers (ACFs) with three activation levels and four surface chemistry levels was prepared and characterized. In addition, three granular activated carbons (GACs) were studied. Two common drinking water contaminants, relatively polar methyl tertiary-butyl ether (MTBE) and relatively nonpolar trichloroethene (TCE), served as adsorbate probes. TCE adsorbed primarily in micropores in the 7–10 Å width range while MTBE adsorbed primarily in micropores in the 8–11 Å width range. These results suggest that effective adsorbents should exhibit a large volume of micropores with widths that are about 1.3 to 1.8 times larger than the kinetic diameter of the target adsorbate. Hydrophobic adsorbents more effectively removed both TCE and MTBE from aqueous solution than hydrophilic adsorbents, a result that was explained by enhanced water adsorption on hydrophilic surfaces. To assure sufficient adsorbent hydrophobicity, the oxygen and nitrogen contents of an activated carbon should therefore sum to no more than about 2 to 3 mmol/g.}, number={12}, journal={CARBON}, author={Li, L and Quinlivan, PA and Knappe, DRU}, year={2002}, pages={2085–2100} }
 @article{newcombe_morrison_hepplewhite_knappe_2002, title={In the (adsorption) competition between NOM and MIB, who is the winner, and why?}, volume={2}, ISSN={1606-9749 1607-0798}, url={http://dx.doi.org/10.2166/ws.2002.0046}, DOI={10.2166/ws.2002.0046}, abstractNote={The adsorption of an odour compound common in drinking water, 2-methylisoborneol (MIB), was studied on four activated carbons in the presence of six well characterised natural organic matter (NOM) solutions. It was found that, although the carbons and the NOM solutions had a wide range of characteristics, the major competitive mechanism was the same in all cases. The low molecular weight NOM compounds were the most competitive, participating in a direct competition with the MIB molecule for adsorption sites. Equivalent background concentration (EBC) calculations indicated a relatively low concentration of directly competing compounds in the NOM. Some evidence of pore blockage, and or restriction was also seen, with microporous carbons most affected by low molecular weight NOM, and mesoporous carbons impacted by the higher molecular weight compounds.}, number={2}, journal={Water Science and Technology: Water Supply}, publisher={IWA Publishing}, author={Newcombe, G. and Morrison, J. and Hepplewhite, C. and Knappe, D.R.U.}, year={2002}, month={Apr}, pages={59–67} }
 @article{briley_knappe_2002, title={Optimizing ferric sulfate coagulation of algae with streaming current measurements}, volume={94}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0036477973&partnerID=MN8TOARS}, DOI={10.1002/j.1551-8833.2002.tb09409.x}, abstractNote={This study sought to determine ferric sulfate coagulation conditions that lead to effective removal of algae by conventional gravity sedimentation. Using laboratory‐cultured Anabaena flos‐aquae spiked into natural water, charge titrations and jar tests were conducted to evaluate the effects of streaming current value, coagulation pH, and initial algae concentration on the removal of algae, turbidity, and natural organic matter. At pH 6, ferric sulfate doses corresponding to the point of zero charge (PZC), as determined by streaming current measurements, consistently produced low settled water algae concentrations when an anionic flocculant aid was added. In contrast, ferric sulfate coagulation at pH 7.0 and 7.5 was not effective for algae removal because the algae's surface charge could not be sufficiently neutralized. At pH 6 and the PZC, settled water algae concentrations, turbidity, and ultraviolet absorbance at 254 nm were similar for tests conducted at initial algae concentrations of 10,000 and 50,000 cells/mL, but a larger coagulant dose was required to reach the PZC at the higher initial algae concentration. Thus, adjusting coagulant doses based on streaming current value should be effective for maintaining settled water quality in plants that treat waters with rapidly varying influent algae concentrations and/or background water quality. Experiments conducted with a natural algae bloom sample confirmed that ferric sulfate coagulation at pH 6 and the PZC was effective for algae removal.}, number={2}, journal={Journal / American Water Works Association}, author={Briley, D.S. and Knappe, D.R.U.}, year={2002}, pages={80–90} }
 @article{matsui_knappe_takagi_2002, title={Pesticide adsorption by granular activated carbon adsorbers. 1. Effect of natural organic matter preloading on removal rates and model simplification}, volume={36}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0036667663&partnerID=MN8TOARS}, DOI={10.1021/es0113652}, abstractNote={The adsorptive removal of periodic spikes of the trace synthetic organic chemicals (SOCs) simazine and asulam from water containing natural organic matter (NOM) was studied in pilot-scale granular activated carbon (GAC) adsorbers over a period of nearly 3 years. The SOC removal percentage obtained at any preloading time and bed depth was independent of the liquid-phase SOC concentration, and equations derived from the ideal adsorbed solution theory and a pore surface diffusion model validated this observation. The pseudo-steady-state SOC removal rate, (dC/dz), at each preloading time and bed depth was therefore first order with respectto the liquid-phase SOC concentration, C. Furthermore, the removal modulus, k, in the resulting SOC removal rate expression was a reflection of the solid-phase concentration of the NOM fraction that interfered with the adsorption of SOCs. Analysis of the removal modulus values indicated that the mass transfer zone of the NOM fraction competing with asulamtraveled more rapidlythrough the GAC adsorber than that competing with simazine. Given the similar molecular sizes of the targeted SOCs, this result was primarily explained by differences in SOC adsorbabilities, where the more weakly adsorbing asulam was less capable of displacing preloaded NOM. Consequently, the NOM fraction competing with asulam constituted a larger percentage of the total NOM than that competing with simazine.}, number={15}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Matsui, Y and Knappe, DRU and Takagi, R}, year={2002}, month={Aug}, pages={3426–3431} }
 @article{matsui_knappe_iwaki_ohira_2002, title={Pesticide adsorption by granular activated carbon adsorbers. 2. Effects of pesticide and natural organic matter characteristics on pesticide breakthrough curves}, volume={36}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0036667665&partnerID=MN8TOARS}, DOI={10.1021/es011366u}, abstractNote={The principal objective of this study was to elucidate mechanisms by which NOM affects the adsorption of a nonpolar (simazine) and a polar (asulam) herbicide on activated carbon. Experiments were carried out in microcolumns that were continuously fed solutions containing NOM with different molecular weight (MW) distributions and intermittently solutions containing the same NOM plus simazine or asulam. The MW distributions of a groundwater NOM were altered by coagulation and ultrafiltration, which resulted in the preferential removal of high-MW, UV260-absorbing NOM. At a given NOM loading, the simazine removal efficiency was higher in the column that was preloaded with raw groundwater than in columns receiving coagulated or ultrafiltered water. In contrast, the asulam removal efficiency was similar for all three NOM solutions at a given NOM loading. Therefore, the results suggested that low-MW, UV260-absorbing NOM molecules competed directly with strongly adsorbing pesticides, such as simazine, for adsorption sites. For more weakly adsorbing pesticides, such as asulam, direct competition for adsorption sites originated not only from the strongly adsorbing, low-MW NOM, but also from more weakly adsorbing, higher-MW NOM. Consequently, the competing NOM fraction increases as the adsorbability of the SOC decreases, a result that was confirmed by adsorption data for additional pesticides of similar size. However, a smaller pesticide competed more effectively for adsorption sites than a larger pesticide of similar polarity, suggesting that the concentration of competing NOM decreases as the MW of the SOC decreases.}, number={15}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Matsui, Y and Knappe, DRU and Iwaki, K and Ohira, H}, year={2002}, month={Aug}, pages={3432–3438} }
 @article{newcombe_morrison_hepplewhite_knappe_2002, title={Simultaneous adsorption of MIB and NOM onto activated carbon - II. Competitive effects}, volume={40}, ISSN={["0008-6223"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0036047185&partnerID=MN8TOARS}, DOI={10.1016/S0008-6223(02)00098-2}, abstractNote={The adsorption of an odour compound common in drinking water, 2-methylisoborneol (MIB), was studied on six activated carbons in the presence of six well-characterised natural organic matter (NOM) solutions. It was found that, although the carbons and the NOM solutions had a wide range of characteristics, the major competitive mechanism was the same in all cases. The low-molecular-weight NOM compounds were the most competitive, participating in direct competition with MIB for adsorption sites. Equivalent background compound calculations indicated a relatively low concentration of directly competing compounds in the NOM. Some evidence of pore blockage and/or restriction was also seen, with microporous carbons being the most affected by low-molecular-weight NOM and mesoporous carbons impacted by the higher-molecular-weight compounds.}, number={12}, journal={CARBON}, author={Newcombe, G and Morrison, J and Hepplewhite, C and Knappe, DRU}, year={2002}, pages={2147–2156} }
 @article{jun_lee_lee_knappe_2001, title={Effectiveness of coagulants and coagulant aids for the removal of filter-clogging Synedra}, volume={50}, ISSN={["0003-7214"]}, DOI={10.2166/aqua.2001.0013}, abstractNote={The occurrence of Synedra spp. in the source water of the CheongJu water treatment plant (South Korea) decreased filter run times of rapid sand filters to below 5 hours. During the filter-clogging episode, full-scale Synedra removal by coagulation with polyaluminium hydrogen chloride silicate (PAHCS), flocculation and sedimentation ranged from 20 to 70%. To reduce filter clogging, strategies needed to be developed to improve the coagulation of Synedra . Jar test results showed that alum was more effective for Synedra removal than polyaluminium chloride (PACl), PAHCS and ferric chloride. At the optimum alum dose, Synedra removal in jar tests reached 88%. The addition of flocculant aids (Na- and Mg-alginate; nonionic and anionic polymers) in conjunction with alum did not improve Synedra removal. In contrast, the addition of cationic polymer in conjunction with alum improved Synedra removal to 99%. Analysis of floc with scanning electron microscopy (SEM) and light microscopy showed that the cationic polymer addition led to the formation of larger, stronger, and denser floc. More effective charge neutralization and the formation of interparticle bridges as a result of the cationic polymer addition can explain the improved incorporation of Synedra cells into settleable floc.}, number={3}, journal={JOURNAL OF WATER SUPPLY RESEARCH AND TECHNOLOGY-AQUA}, author={Jun, HB and Lee, YL and Lee, BD and Knappe, DRU}, year={2001}, month={Jun}, pages={135–148} }
 @article{jun_lee_lee_knappe_2001, title={Effectiveness of coagulants and coagulant aids for the removal of filter-clogging synedra}, volume={50}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0034986285&partnerID=MN8TOARS}, number={3}, journal={Journal of Water Supply: Research and Technology - AQUA}, author={Jun, H.-B. and Lee, Y.-J. and Lee, B.-D. and Knappe, D.R.U.}, year={2001}, pages={135–148} }
 @inproceedings{li_quinlivan_knappe_2001, title={Effects of activated carbon surface chemistry and pore structure on the adsorption of MTBE from natural water}, volume={41}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-23844487615&partnerID=MN8TOARS}, number={2}, booktitle={ACS Division of Environmental Chemistry, Preprints}, author={Li, L. and Quinlivan, P.A. and Knappe, D.R.U.}, year={2001}, pages={448–453} }
 @article{wu_taylor_knappe_nanny_barlaz_2001, title={Factors controlling alkylbenzene sorption to municipal solid waste}, volume={35}, ISSN={["1520-5851"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0035890552&partnerID=MN8TOARS}, DOI={10.1021/es010893a}, abstractNote={The sorption of toluene and o-xylene to individual municipal solid waste (MSW) constituents [office paper, newsprint, model food and yard waste, high density polyethylene, and poly(vinyl chloride) (PVC)] was evaluated. Effects of sorbent decomposition and solvent composition on alkylbenzene sorption were studied by evaluating biodegradable sorbents in both fresh and anaerobically decomposed form and by complementing single-solute isotherm tests with experiments conducted in acidogenic and methanogenic leachate. Alkylbenzene sorption to plastics was greaterthan to biopolymer composites, and differences in sorbate/sorbent solubility parameter compatibility explained this observation. Alkylbenzene sorption to biopolymer composites yielded linear isotherms, and sorption capacities [log(Koc/Kow)] decreased linearly with increasing sorbent polarity as expressed by the O-alkyl/alkyl ratio. Leachate composition had little effect on alkylbenzene sorption with one exception; volatile fatty acids in acidogenic leachate appeared to convert PVC from a glassy to a rubbery polymer. The results of this study showed that sorbent organic matter affinity for hydrophobic organic contaminants (HOCs) increases with increasing extent of MSW decomposition because of the recalcitrance of plastics and the preferential degradation of polar biopolymers. Furthermore, the plasticizing effect of volatile fatty acids in acidogenic leachate may enhance the bioavailability of HOCs sorbed to glassy organic matter in MSW or in soils contaminated with acidogenic leachate.}, number={22}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Wu, BY and Taylor, CM and Knappe, DRU and Nanny, MA and Barlaz, MA}, year={2001}, month={Nov}, pages={4569–4576} }
 @article{sanin_knappe_barlaz_2000, title={The fate of toluene, acetone and 1,2-dichloroethane in a laboratory-scale simulated landfill}, volume={34}, ISSN={0043-1354}, url={http://dx.doi.org/10.1016/s0043-1354(00)00084-1}, DOI={10.1016/S0043-1354(00)00084-1}, abstractNote={The objective of this research was to study the fate of toluene, acetone and 1,2-dichloroethane (DCA) in refuse excavated from a municipal solid waste landfill contaminated with organic solvents. Refuse excavated from the landfill was used to fill multiple 8-l simulated landfill reactors that were operated with and without moisture addition to simulate the absence and presence of an engineered cover, respectively. An average of 31.3% of the added 14C-toluene was converted to 14CH4 and 14CO2 in reactors that received water additions, while only 12% was mineralized in the absence of water addition. Up to 30% of the added 14C was recovered in humic and fulvic acid fractions and up to 12% of the 14C was not extractable with dichloromethane (DCM) followed by 0.5 N NaOH. The non-extractable fraction may represent strongly sorbed toluene or toluene metabolites covalently bound to humins. From 21.6 to 40.3% of the added 14C-acetone was converted to 14CH4 and 14CO2 although there was no consistent effect associated with water. This is likely explained by the high solubility of acetone as considerably more acetone was present in the reactor leachate relative to toluene. Reductive dehalogenation of 1,2-DCA to ethylene was measured in all reactors. This study suggests that remediation activities designed to reduce moisture infiltration could adversely affect contaminant biodegradation at the source and that moisture infiltration must be balanced against the potential increase in contaminant release due to leaching. Further, the association with humic matter in decomposed refuse may represent an alternative mechanism for contaminant sequestration.}, number={12}, journal={Water Research}, publisher={Elsevier BV}, author={Sanin, F and Knappe, Detlef R. U. and Barlaz, Morton A.}, year={2000}, month={Aug}, pages={3063–3074} }
 @article{knappe_snoeyink_roche_prados_bourbigot_1999, title={Atrazine removal by preloaded GAC}, volume={91}, ISSN={["0003-150X"]}, DOI={10.1002/j.1551-8833.1999.tb08719.x}, abstractNote={Utilities can use predictions of remaining GAC life to develop a GAC regeneration or replacement schedule.The effect of granular activated carbon (GAC) service time on the remaining life of GAC adsorbers that are exposed to periodic pollutant episodes was evaluated. Equilibrium and kinetic parameters describing the adsorption of atrazine were determined for GAC that had been preloaded with background organic matter (BOM) for as long as 25 months. Furthermore, atrazine removal was measured in pilot tests employing GAC that had been preloaded for five and 20 months. Isotherm data showed that (1) preloaded BOM sharply reduced the remaining adsorption capacity of GAC for atrazine, (2) competitive adsorption was not important on the tested preloaded GAC samples, and (3) use of pulverized preloaded GAC led to an overestimate of remaining adsorption capacity. Preloading had the greatest effect on GAC capacity; adsorption kinetics were not affected as severely. The homogeneous surface diffusion model was used to predict atrazine removal in pilot tests and to predict remaining GAC life. For the given adsorbent and background water, remaining life predictions for atrazine removal are presented for scenarios that may be typical for utilities in the midwestern United States and in western Europe.}, number={10}, journal={JOURNAL AMERICAN WATER WORKS ASSOCIATION}, author={Knappe, DRU and Snoeyink, VL and Roche, P and Prados, MJ and Bourbigot, MM}, year={1999}, month={Oct}, pages={97–109} }
 @article{knappe_snoeyink_röche_prados_bourbigot_1999, title={Atrazine removal by preloaded GAG}, volume={91}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032620092&partnerID=MN8TOARS}, number={10}, journal={Journal / American Water Works Association}, author={Knappe, D.R.U. and Snoeyink, V.L. and Röche, P. and Prados, M.J. and Bourbigot, M.-M.}, year={1999}, pages={97–109} }
 @inproceedings{briley_knappe_1998, title={Optimization of coagulation conditions for the removal of algae}, volume={90}, number={1998 June}, booktitle={Proceedings of the American Water Works Association Annual Conference, Dallas, TX, June 21-25, 1998}, author={Briley, D. S. and Knappe, D. R. U.}, year={1998} }
 @article{knappe_matsui_snoeyink_roche_prados_bourbigot_1998, title={Predicting the capacity of powdered activated carbon for trace organic compounds in natural waters}, volume={32}, ISSN={["0013-936X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0032101736&partnerID=MN8TOARS}, DOI={10.1021/es970833y}, abstractNote={The purpose of this research was to develop a simple method for predicting the powdered activated carbon (PAC) capacity for micropollutants in natural water. The herbicide atrazine and the odor-causing compound 2-methyl- isoborneol served as target compounds. Isotherm data from experiments conducted with a constant initial adsorbate concentration and varying adsorbent doses exhibited nonlinearity in both single- and multi-solute systems. However, at any given adsorbent dose, the PAC capacity for the micropollutant in multi-solute systems was directly proportional to the initial micropollutant concentration. Using the ideal adsorbed solution theory (IAST), an equation was derived that validated the experimentally observed direct proportionality between PAC capacity and initial micropollutant concentration at a given adsorbent dose. The results of this study show that the PAC dose to remove any amount of micropollutant from natural waters can be estimated without the use of mathematical models from a single...}, number={11}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Knappe, DRU and Matsui, Y and Snoeyink, VL and Roche, P and Prados, MJ and Bourbigot, MM}, year={1998}, month={Jun}, pages={1694–1698} }
 @inproceedings{knappe_briley_rastogi_1998, title={Strategies for algae removal in conventional treatment}, volume={90}, number={1998 June}, booktitle={Proceedings of the American Water Works Association Annual Conference, Dallas, TX, June 21-25, 1998}, author={Knappe, D.R.U. and Briley, D.S. and Rastogi, N.}, year={1998} }
 @book{knappe_1998, title={Strategies for algae removal in drinking water treatment}, number={1998 Apr. 1}, journal={Report (Water Resources Research Institute of the University of North Carolina)}, institution={Raleigh, NC: University of North Carolina Water Resources Research Institute}, author={Knappe, D.}, year={1998} }
 @inproceedings{sanin_barlaz_knappe_1998, title={Toluene sorption, humification and biodegradation in excavated refuse: A high organic carbon sorbent}, number={1998 May}, booktitle={1998 Spring Meeting, American Geophysical Union, Boston, MA, May 26-29, 1998}, author={Sanin, F. D. and Barlaz, M. A. and Knappe, D. R. U.}, year={1998} }
 @inproceedings{knappe_snoeyink_roche_prados_bourbigot_1997, title={The effect of GAC service time on the adsorption of periodic episodes of atrazine}, volume={89}, number={1997 June}, booktitle={Proceedings of the American Water Works Association Annual Conference, Atlanta, GA, June 15-19, 1997}, author={Knappe, D. R. U. and Snoeyink, V. L. and Roche, P. and Prados, M. J. and Bourbigot, M. M.}, year={1997} }
 @article{knappe_snoeyink_roche_prados_bourbigot_1997, title={The effect of preloading on rapid small-scale column test predictions of atrazine removal by GAC adsorbers}, volume={31}, ISSN={["0043-1354"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0031281636&partnerID=MN8TOARS}, DOI={10.1016/S0043-1354(97)00148-6}, abstractNote={Rapid small-scale column tests (RSSCTs) were evaluated for their ability to predict atrazine removal in pilot-scale granular activated carbon (GAC) adsorbers. The performance of both virgin and preloaded GACs was tested. Atrazine removal by virgin GAC was studied in post-filter adsorbers at Toulouse, France, and Choisy-le-Roi, France, using empty-bed contact times (EBCTs) of 10.3 and 14 min, respectively. For virgin GAC, RSSCTs successfully simulated atrazine removal over large-scale operating times of about 3.5–7 months. However, RSSCTs significantly overestimated atrazine removal at longer operating times. Atrazine removal by preloaded GAC was studied in pilot-scale post-filter adsorbers at Choisy-le-Roi, France, after preloading times of 5 months and 20 months. EBCTs were approximately 8.5 min. To describe the performance of pilot-scale adsorbers containing preloaded GAC, RSSCTs were initiated with virgin activated carbon, and preloading was simulated prior to the spiking of atrazine. For a pilot-scale adsorber containing GAC that had been preloaded for 5 months, the RSSCT data effectively described atrazine removal. However, the RSSCT was not successful in predicting atrazine removal by GAC after a preloading time of 20 months. Discrepancies between RSSCT and pilot data for long service times or after extended preloading periods may have been due to enhanced adsorption of background organic matter in the presence of oxygen. Overall, RSSCTs were judged to be most useful for predicting the initial performance of adsorbers containing virgin GAC.}, number={11}, journal={WATER RESEARCH}, author={Knappe, DRU and Snoeyink, VL and Roche, P and Prados, MJ and Bourbigot, MM}, year={1997}, month={Nov}, pages={2899–2909} }
 @article{knappe_snoeyink_matsui_prados_bourbigot_1996, title={Determining the remaining life of a granular activated carbon (GAC) filter for pesticides}, volume={14}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0029657394&partnerID=MN8TOARS}, number={2}, journal={Water Supply}, author={Knappe, D.R.U. and Snoeyink, V.L. and Matsui, Y. and Prados, M.J. and Bourbigot, M.-M.}, year={1996}, pages={1–14} }
 @article{knappe_dagois_dewolfe_1992, title={Effect of Calcium on Thermal Regeneration of GAC}, volume={84}, ISSN={0003-150X}, url={http://dx.doi.org/10.1002/j.1551-8833.1992.tb07414.x}, DOI={10.1002/j.1551-8833.1992.tb07414.x}, abstractNote={Calcium commonly accumulates on granular activated carbon (GAC), and when it is chelated by natural organic matter (NOM), it is drawn into the pores of the GAC. Internally loaded calcium greatly catalyzes regeneration reactions, leading to accelerated internal mass loss. Optimal conditions for the regeneration of a GAC not loaded with calcium lead to severe overregeneration if applied to a calcium‐loaded GAC. The pore structure and capacity of the GAC are adversely affected by this overregeneration. The authors of this article found that calcium‐loaded GACs could be regenerated to yield a GAC with the properties of the virgin GAC by reducing the regeneration time or temperature.}, number={8}, journal={Journal - American Water Works Association}, publisher={Wiley}, author={Knappe, Detlef R. U. and Dagois, Gérard and DeWolfe, James R.}, year={1992}, month={Aug}, pages={73–80} }
 @article{knappe_snoeyink_dagois_dewolfe_1992, title={Effect of calcium on thermal regeneration of GAC}, volume={84}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0026909410&partnerID=MN8TOARS}, number={8}, journal={Journal / American Water Works Association}, author={Knappe, Detlef R.U. and Snoeyink, Vernon L. and Dagois, Gerard and DeWolfe, James R.}, year={1992}, pages={73–80} }