@misc{kruzic_liehr_2008, title={Natural treatment and onsite systems}, volume={80}, number={10}, journal={Water Environment Research}, author={Kruzic, A. P. and Liehr, S. K.}, year={2008}, pages={1206–1224} }
 @misc{liehr_kruzic_2007, title={Natural treatment and onsite processes}, volume={79}, number={10}, journal={Water Environment Research}, author={Liehr, S. K. and Kruzic, A.}, year={2007}, pages={1451–1473} }
 @article{liehr_kruzic_2006, title={Natural treatment and onsite processes}, volume={78}, DOI={10.2175/106143006X119233}, abstractNote={Natural treatment systems for wastewater can be divided into three broad categories: soil-based systems, which include subsurface infiltration, rapid infiltration/soil aquifer treatment, overland flow, and slow rate systems; wetland systems, which include free water surface and submerged flow systems; and aquatic systems, which include pond and floating aquatic plant systems. Many, but not all, on-site wastewater treatment systems are natural systems using septic tanks as a pretreatment.}, number={10}, journal={Water Environment Research}, author={Liehr, S. K. and Kruzic, A.}, year={2006}, pages={1386–1405} }
 @article{chaiprapat_cheng_classen_liehr_2005, title={Role of internal nutrient storage in duckweed growth for swine wastewater treatment}, volume={48}, DOI={10.13031/2013.20088}, abstractNote={The objective of this study was to investigate the relationship of the nutrient content of duckweed biomass to 
duckweed growth in swine wastewater. Batch tests of Spirodela punctata 7776, the selected strain for highest total protein 
production, were conducted in an environment-controlled growth chamber at 24°C and 16 h of light per day. A prolonged 
growth period was observed after the nutrients in the medium were exhausted, indicating that duckweed could use its stored 
nutrients for growth. Prediction of growth using medium concentration as an independent variable was deemed unsuitable 
to describe this growth. Throughout the 30-day growing period, nitrogen and phosphorus content in the biomass varied from 
59.7 to 19.7 mgN/gbiomass and from 14.8 to 6.8 mgP/gbiomass (dry weight basis), respectively. The relationship between biomass 
nitrogen content and specific growth rate of Spirodela punctata 7776 was found to follow Monod-type kinetics with .max of 
0.24 gN/gbiomass/day and KN of 28.8 mgP/gbiomass. Reduced growth rate was observed in the duckweed culture with high 
duckweed density (mass per unit area). Effects of the duckweed density on growth rate and nutrient uptake are modeled and 
discussed.}, number={6}, journal={Transactions of the ASAE}, author={Chaiprapat, S. and Cheng, J. J. and Classen, J. J. and Liehr, S. K.}, year={2005}, pages={2247–2258} }
 @misc{liehr_rubin_tonning_2004, title={Natural treatment and onsite processes}, volume={76}, ISSN={["1061-4303"]}, DOI={10.2175/106143004X142059}, abstractNote={Tonning This review includes many types of physical and biological treatment technologies, with the common feature of utilizing primarily natural processes or components for the treatment function, whether the system is aquatic or}, number={6}, journal={WATER ENVIRONMENT RESEARCH}, author={Liehr, SK and Rubin, AR and Tonning, B}, year={2004}, pages={1191–1237} }
 @article{chaiprapat_cheng_classen_ducoste_liehr_2003, title={Modeling Nitrogen Transport in Duckweed Pond for Secondary Treatment of Swine Wastewater}, volume={129}, ISSN={0733-9372 1943-7870}, url={http://dx.doi.org/10.1061/(asce)0733-9372(2003)129:8(731)}, DOI={10.1061/(asce)0733-9372(2003)129:8(731)}, abstractNote={A mathematical model was developed to describe nitrogen transport in duckweed-covered static ponds for nutrient recovery from swine lagoon water. A finite difference technique was used to solve the partial differential equations describing the ammonia transport and concentration in the pond. The key parameters in the model include the diffusion coefficient of ammonium in the medium (D) and kinetic constant of nitrogen uptake by duckweed (k). Using one order of magnitude parameter variations, the simulations showed that the model was clearly much more sensitive to D than to k, indicating the process of nitrogen removal in a static pond by duckweed is diffusion limited. Laboratory testing was conducted with Spirodela punctata 7776, a duckweed strain, to calibrate the model. The calibration of the model with experimental data yielded a new ammonium transport coefficient (T) that is 85 times of D value. Model results showed good agreement with depth-wise experimental ammonium concentration and the model also ...}, number={8}, journal={Journal of Environmental Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Chaiprapat, Sumate and Cheng, Jiayang and Classen, John J. and Ducoste, Joel J. and Liehr, Sarah K.}, year={2003}, month={Aug}, pages={731–739} }
 @inproceedings{cheng_liehr_lyerly_2003, title={Swine wastewater treatment in an integrated system of anaerobic digestion and duckweed nutrient removal}, DOI={10.13031/2013.13893}, abstractNote={Organics destruction and nutrient uptake in an integrated pilot system of anaerobic digestion and 
duckweed nutrient removal for swine wastewater treatment were monitored under field conditions. Raw swine 
wastewater of 100 gallons/day was first treated in a 1,000-gallon anaerobic digester with floating ballast rings. 
Organic compounds in the wastewater were digested to produce biogas. Many nutrients including nitrogen and 
phosphorus remain in the effluent of the anaerobic digester. Duckweed (Lemna gibba 8678) was grown in 
three 1,000-gallon tanks to recover nutrients from the anaerobic effluent. The duckweed was periodically 
harvested and can be used as animal, poultry, and fish feed. This research provides an initial understanding of 
the attached-growth anaerobic digester and the characteristics exhibited by Lemna gibba in the treatment of 
swine wastewater under conditions similar to those found in North Carolina. Both the anaerobic digester and 
the duckweed tanks were run as completely mixed systems. The performance of the system was monitored by measuring chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), ammonia nitrogen, total phosphorus 
(TP), ortho-phosphate-phosphorus, and pH in the influent and effluent of each treatment unit.}, booktitle={ASAE annual International Meeting 2003, Las Vegas : The Riviera Hotel, July 27-30, 2003}, author={Cheng, Jay and Liehr, S. and Lyerly, C.}, year={2003} }
 @inproceedings{chaiprapat_cheng_classen_liehr_2002, title={Role of internal nutrient storage in duckweed for secondary swine wastewater treatment}, volume={2}, booktitle={Paper, 2002 ASAE annual international meeting/CIGR XVth world congress : Hyatt Regency Chicago, Chicago, Illinois, USA, July 28 - July 31, 2002}, author={Chaiprapat, S. and Cheng, J. and Classen, J. J. and Liehr, S. K.}, year={2002}, pages={4130} }
 @article{wynn_liehr_2001, title={Development of a constructed subsurface-flow wetland simulation model}, volume={16}, number={4}, journal={Ecological Engineering}, author={Wynn, T. M. and Liehr, S. K.}, year={2001}, pages={519–536} }
 @inproceedings{chaiprapat_cheng_classen_liehr_2001, title={Modeling nitrogen transfer in duckweed covered pond for secondary treatment of swine wastewater}, ISBN={0966977017}, booktitle={Proceedings of the International Symposium Addressing Animal Production and Environmental Issues}, author={Chaiprapat, S. and Cheng, J. and Classen, J. J. and Liehr, S. K.}, year={2001} }
 @book{liehr_kozub_rash_sloop_doll_rubin_house_hawes_burks_2000, title={Constructed wetlands treatment of high nitrogen landfill leachate}, ISBN={1893664082}, publisher={Alexandria, VA : Water Environment Research Foundation}, author={Liehr, S. K. and Kozub, D. D. and Rash, J. K. and Sloop, G. M. and Doll, B. and Rubin, A. R. and House, C. H. and Hawes, S. and Burks, D.}, year={2000} }
 @article{jones_liehr_classen_robarge_2000, title={Mechanisms of dinitrogen gas formation in anaerobic lagoons}, volume={4}, DOI={10.1016/s1093-0191(00)00016-2}, abstractNote={Anaerobic lagoons have been widely used to treat agricultural waste and waste from small municipalities for many years. Oxidation of ammonia is generally assumed to not occur in such lagoons because of their anaerobic environment. Nitrification, the most likely process that would lead to ammonia oxidation, has not been considered a significant process in anaerobic lagoons because of the negligible concentrations of dissolved oxygen measured in these systems. Therefore observed nitrogen losses are usually assumed to be due to ammonia volatilization. However, in field studies of primary swine waste lagoons in the south-eastern US Coastal Plain, rates of dinitrogen (N2) gas production have been observed to be much greater than rates of NH3 volatilization. This paper discusses possible mechanisms that could explain observations of N2 gas generation in anaerobic waste lagoons. Chemical and microbial reactions have been documented that combine ammonia with nitrite, or nitrous acid, to form N2 under anaerobic conditions. Nitrification and denitrification reactions have also been observed under microaerobic conditions. Each of these reactions requires low levels of oxygen for the initial nitrification of ammonia to nitrite. Diffusion rates of oxygen through the lagoon surface appear to be adequate to allow enough nitrite formation to explain observed N2 fluxes.}, number={2}, journal={Advances in Environmental Research}, author={Jones, M. L. and Liehr, S. K. and Classen, John and Robarge, W.}, year={2000}, pages={133–139} }
 @article{kozub_liehr_1999, title={Assessing denitrification rate limiting factors in a constructed wetland receiving landfill leachate}, volume={40}, ISSN={["0273-1223"]}, DOI={10.1016/S0273-1223(99)00459-X}, abstractNote={The focus of this research was to investigate denitrification in constructed wetlands to improve the nitrogen treatment capabilities of these systems. A free water surface flow constructed wetland located at the New Hanover County Solid Waste Management Facility, near Wilmington, North Carolina, USA, was used for this research. Field water sampling in conjunction with a laboratory acetylene block method was used to quantify nitrogen removals in the wetland. Background denitrification rates as well as potential denitrification rates using sodium acetate and sodium phosphate were measured in the laboratory. According to field measurements, average nitrate nitrogen loading and removal rates in the constructed wetland during 1997 were 11.1 ± 3.4 g N/m3/d and 4.5 ± 2.2 g N/m3/d, respectively. Denitrification rates measured in the laboratory with the addition of sodium acetate were higher than background denitrification rates while the addition of sodium phosphate had no effect on the denitrification rates. Results suggested denitrification in the wetland was limited by the availability of easily degradable sources of organic carbon. Background denitrification rates measured using the laboratory method were comparable to the nitrate nitrogen removal rates measured by field water sampling.}, number={3}, journal={WATER SCIENCE AND TECHNOLOGY}, author={Kozub, DD and Liehr, SK}, year={1999}, pages={75–82} }
 @article{hilger_liehr_barlaz_1999, title={Exopolysaccharide control of methane oxidation in landfill cover soil}, volume={125}, DOI={10.1061/(asce)0733-9372(1999)125:12(1113)}, abstractNote={An examination takes place as to whether a relationship exists between the accumulation of exopolymeric substances (EPS) in landfill cover soil and the gradual decline in biotic methane oxidation observed in laboratory soil columns sparged with synthetic landfill gas. A mathematical model that combined multicomponent gas diffusion along the vertical axis of the columns with biotic methane oxidation was used to predict vertical gas gradients in the columns. An initial trial assumed methane oxidizers were embedded in a thin base layer of biofilm coating the soil, and the model predictions fit experimental data from soil columns early in their operating period. A second trial modeled the same system with a thick EPS layer coating the base biofilm and limiting diffusion of gases into and out of the cells. Predictions from the latter trials fit experimental data from soil columns later in their operating period when lower methane consumption rates were observed. The model results suggest that EPS accumulation may regulate methane oxidation rates in landfill covers.}, number={12}, journal={Journal of Environmental Engineering (New York, N.Y.)}, author={Hilger, H. A. and Liehr, S. K. and Barlaz, Morton}, year={1999}, pages={1113–1123} }
 @article{rash_liehr_1999, title={Flow pattern analysis of constructed wetlands treating landfill leachate}, volume={40}, DOI={10.1016/S0273-1223(99)00450-3}, abstractNote={Three series of tracer studies were performed on three constructed wetlands at the New Hanover County Landfill near Wilmington, North Carolina, USA. One vegetated free water surface wetland (FWS-R), one vegetated subsurface flow wetland (SSF-R), and one unvegetated control subsurface flow wetland (SSF-C) were studied. A conservative tracer, lithium chloride, was used to study the chemical reactor behavior of these wetlands under normal operating conditions. Results indicated that short-circuiting is quite common in SSF wetlands, while FWS wetlands are well-mixed and not as subject to short-circuiting. These results were obtained from and reinforced with tracer measurements at interior points in these wetlands, analysis of residence time distributions from two different formulations, and the construction of residence volume distributions. The short-circuiting in the SSF wetlands can be attributed to the following: (1) Vertical mixing is inhibited by a combination of physical barriers and density gradients caused by rainfall and runoff dilution of the upper layer; and (2) Leachate is drawn from the bottom of the wetland, causing it to further prefer a flow path along the bottom.}, number={3}, journal={Water Science and Technology}, author={Rash, J. K. and Liehr, S. K.}, year={1999}, pages={309–315} }
 @article{borden_dorn_stillman_liehr_1998, title={Effect of in-lake water quality on pollutant removal in two ponds}, volume={124}, DOI={10.1061/(asce)0733-9372(1998)124:8(737)}, abstractNote={An extensive field study examined pollutant removal in two regional wet detention ponds near High Point, N.C. Substantial differences in influent pollutant concentrations between the ponds caused significant differences in pond water quality and pollutant removal efficiency. In Davis Pond, influent fecal coliform and nutrient concentrations were high because of several large dairy farms in the watershed, resulting in hypereutrophic conditions as evidenced by high chlorophyll-a concentrations, high midday pH values and supersaturated midday oxygen concentrations. In Piedmont Pond, influent fecal coliform and nutrient concentrations were much lower, resulting in mesotrophic to slightly eutrophic conditions. Both ponds thermally stratified and developed an anaerobic hypolimnion. In Davis Pond, annual pollutant removal efficiencies for total suspended solids, volatile suspended solids, total organic carbon, total phosphorus, dissolved phosphorus, nitrate/nitrite, total ammonia nitrogen, and total nitrogen were 56%, 32%, 15%, 41%, 54%, 16%, 2%, and 11%, respectively. In Piedmont Pond, annual pollutant removal efficiencies were 20%, 30%, 27%, 40%, 15%, 66%, -64%, and 36%, respectively.}, number={8}, journal={Journal of Environmental Engineering (New York, N.Y.)}, author={Borden, R. C. and Dorn, J. L. and Stillman, J. B. and Liehr, S. K.}, year={1998}, pages={737–743} }
 @inproceedings{kozub_liehr_1998, title={Measurement of denitrification rates in a constructed wetlands receiving municipal solid waste landfill leachate}, booktitle={Engineering approaches to ecosystem restoration: Protecting, restoring and managing the world's water resources: Proceedings of the Wetlands Engineering & River Restoration Conference 1998, American Society of Civil Engineers, March 22-27, 1998, Denver CO}, author={Kozub, D. D. and Liehr, S. K.}, year={1998} }
 @book{borden_dorn_stillman_liehr_1997, title={Evaluation of wet ponds for protection of public water supplies}, number={311}, journal={Report (Water Resources Research Institute of the University of North Carolina)}, institution={Raleigh, NC: University of North Carolina Water Resources Research Institute}, author={Borden, R. C. and Dorn, J. L. and Stillman, J. B. and Liehr, S. K.}, year={1997} }
 @inproceedings{liehr_kozub_rash_1997, title={Nitrogen removal in constructed wetlands treating high nitrogen landfill leachate}, number={1997 Oct.}, booktitle={Proceedings WEFTEC '97: Water Environment Federation 70th Annual Conference & Exposition, Chicago, Illinois, October 18-22, 1997}, author={Liehr, S. K. and Kozub, D. D. and Rash, J. K.}, year={1997} }
 @article{liehr_1995, title={Effect of pH on metals precipitation in denitrifying biofilms}, volume={32}, ISSN={["0273-1223"]}, DOI={10.1016/0273-1223(96)00023-6}, abstractNote={The objective of this paper is to present evidence for the possibility of enhanced metal precipitation inside denitrifying biofilms. The pH environment surrounding microorganisms growing in biofilms is frequently different than the environment of the bulk liquid because products of metabolic reactions are limited in their ability to diffuse out of the biofilm. In the case of denitrifying biofilms, the interior pH will be higher than the pH in the bulk liquid, creating conditions that favor precipitation of heavy metals. A theoretical model was used to predict pH inside denitrifying biofilms. Copper and nickel solubities were calculated as a function of pH and alkalinity. Results provide evidence to support the theory that higher internal pH can result in greater metal removal by the biofilms.}, number={8}, journal={WATER SCIENCE AND TECHNOLOGY}, author={Liehr, SK}, year={1995}, pages={179–183} }
 @article{liehr_chen_lin_1994, title={Metals removal by algal biofilms}, volume={30}, number={11}, journal={Water Science and Technology}, author={Liehr, S. K. and Chen, H. J. and Lin, S. H.}, year={1994}, pages={59} }