@article{deviney_classen_bruce_2024, title={Pathways to sustainable transitions in a complex agricultural system: a case study of swine waste management in North Carolina}, volume={7}, ISSN={["2571-581X"]}, url={http://dx.doi.org/10.3389/fsufs.2023.1292326}, DOI={10.3389/fsufs.2023.1292326}, abstractNote={North Carolina has a high density of swine farms with nearly half of the commercial operations located in two eastern counties. Lagoon and sprayfield (LS) is the dominant method of swine manure management despite pressure to transition to environmentally superior technologies. LS is an efficient and cost-effective method of waste management but has negatively impacted the environment and local communities from both discreet events (breeches, flooding) and ongoing issues (odor, disease vectors). The Multilevel Perspective Theory (MLP) is a frame for understanding the relationships between a sociotechnical regime, its surrounding landscape, and emerging niches for sustainable technology development to help align these different levels of perspective and support transitioning toward more sustainable practices. Here, a farm level is added to represent the user perspective of regime technology in complex agriculture systems (MLP + F). We demonstrate how change may influence the North Carolina swine waste management (NC SWM) system through alternative scenarios applied to a conceptual model developed with the MLP + F frame in a methodology for analyzing complex agricultural systems with input from a diverse panel of experts. This case study demonstrates how the methodology can be applied through two NC SWM model scenarios analyzed with fuzzy cognitive mapping techniques. The first scenario explores whether panel recommended changes generate a shift toward sustainable manure management. Inference results suggest that experts have a broad understanding of how these goals may be achieved, but strategies are needed to enhance the specificity of proposed changes. Testing scenarios with more targeted interventions within specific subsystems could provide greater guidance with regard to policy, economic factors, farm practices, or societal demands. The second scenario considers the systemic effect of introducing a manure dewatering process on swine operations, with and without landscape support. Results from this scenario indicate that the more landscape support is engaged, the greater the impact on desirable outcomes. However, contradictions emerged between different versions of this scenario such as increased negative public perceptions despite positive community outcomes. This may require further investigation to tease out potential misalignment between perceptions of a complex system and actual system behaviors.}, number={1292326}, journal={FRONTIERS IN SUSTAINABLE FOOD SYSTEMS}, author={Deviney, Alison V. and Classen, John J. and Bruce, Jacklyn A.}, year={2024}, month={Jan} }
 @article{deviney_classen_bruce_2023, title={A methodology for using a multilevel perspective framework to analyze complex systems}, volume={3}, ISSN={2059-7991 2059-7991}, url={http://dx.doi.org/10.1177/20597991231160280}, DOI={10.1177/20597991231160280}, abstractNote={ Misalignment between the different levels of complex societal systems (e.g. socio-technical, socio-ecological) are often a barrier to transitioning these systems toward more sustainable behavior. One way to understand alignment is through the Multilevel Perspective Theory of sustainable transitions in sociotechnical systems (MLP) which posits that when a regime (the current “ways of doing” something) exhibits behavior that negatively impacts its surrounding economic, social and environmental landscape, that landscape will exert pressure on the regime to change. This in turn opens the window of opportunity for niche developments such as novel technology adoption or policy changes. Therefore, understanding the relationships between the landscape, the regime and emerging niches can help align these different levels of perspective to facilitate a successful transition toward more sustainable practices. This paper describes a methodology for mapping complex systems such as agricultural systems based on MLP theory, and incorporates a fourth “user” level (e.g. the farm) into this multilevel framework (MLP+ F). The methodology is illustrated with a case study example of North Carolina’s lagoon and sprayfield swine waste management regime. By integrating well-established techniques for data collection and analysis, the case study engages a diverse panel of local experts through a modified Delphi approach to identify the relevant concepts and their cause-effect relationships for the current regime. These concepts and relationships are then categorized and organized into a multilevel, multi-perspective conceptual model using fuzzy cognitive maps. The conceptual model identifies how stakeholder groups align in their perception of the system, and provides a foundation for future qualitative, semi-quantitative, and visual analyses of the system and how it can be changed through alternative scenarios. Although this methodology was initially developed for agricultural applications, it has potential for application to other complex societal issues where understanding stakeholder alignment and the potential for sustainability transitions through change are needed. }, journal={Methodological Innovations}, publisher={SAGE Publications}, author={Deviney, Alison V and Classen, John J and Bruce, Jacklyn A}, year={2023}, month={Mar}, pages={205979912311602} }
 @article{deviney_grieger_merck_classen_marshall_2023, title={Phosphorus sustainability through coordinated stakeholder engagement: a perspective}, volume={2}, ISSN={2194-5403 2194-5411}, url={http://dx.doi.org/10.1007/s10669-023-09896-0}, DOI={10.1007/s10669-023-09896-0}, abstractNote={AbstractIn this Perspective we take an in-depth look at what coordinated stakeholder engagement could entail for phosphorus sustainability. The element phosphorus is critical to life on Earth and to the continued functioning of society as we know it. Yet, how society uses phosphorus is currently unsustainable, both as a resource in support of global food production where inequitable distribution creates food security challenges, but also from an environmental aspect, where mismanagement has led to negative impacts on the quality of agricultural soils, human health, and freshwater and marine ecosystems. A number of initiatives and cross-sector consortia have come together to address sustainable phosphorus management at either global or regional scales. However, these efforts could benefit from a more coordinated approach to stakeholder engagement to identify the diversity of needs and perspectives involved in this complex challenge. Herein we examine some examples of different approaches to developing such coordinated stakeholder engagement in other areas of environmental sustainability. We consider how to apply the lessons learned from those efforts toward stakeholder coordination in the realm of phosphorus sustainability. Particularly, we discuss the value of a coordinating body to manage the communications and knowledge sharing necessary to develop trust and cooperation among diverse stakeholder groups and to transition society to more sustainable phosphorus use.}, journal={Environment Systems and Decisions}, publisher={Springer Science and Business Media LLC}, author={Deviney, Alison and Grieger, Khara and Merck, Ashton and Classen, John and Marshall, Anna-Maria}, year={2023}, month={Feb} }
 @misc{sharara_kolesch_cortus_larson_classen_janni_2022, title={ADDRESSING NUTRIENT IMBALANCES IN ANIMAL AGRICULTURE SYSTEMS}, volume={65}, ISSN={["2769-3287"]}, DOI={10.13031/ja.14661}, abstractNote={HighlightsAnimal agriculture intensification has greatly affected nutrient cycling and circularity in food production systems.Various nutrient balance methods are developed to improve nutrient management at various spatial scales.Balance-derived thresholds for action are identified using real-life examples in dairy production.Outreach and knowledge exchange are critical for development, adoption, and improvement of nutrient balance methods.Abstract. Animal agriculture is a major consumer and generator of both macro- and micronutrients. Intensification and regional concentration of animal production, due to economic and logistical advantages, have altered nutrient fluxes in agriculture systems, causing increased stock of nutrients in soils and, consequently, their emission to air and transport to surface water and groundwater. Established nutrient and manure planning frameworks, while effective in addressing nutrient point sources and using manure to enhance fertility and soil quality, have not been wholly successful in addressing farm- and region-scale challenges with nutrient concentrations. This review article addresses nutrient management issues associated with modern animal agriculture by advancing the use of nutrient budgets and balances. This is accomplished by establishing core concepts for nutrient budgets and balances as they apply to animal agriculture. Relevant spatial scales for these budgets are reviewed, including field, whole-farm, and watershed scales, along with proposed methodologies and data sources for each. This study also identifies existing region- and commodity-specific metrics (when available) for use as thresholds for corrective action toward more balanced nutrient budgets. Finally, recommendations for the community of practitioners, researchers, and educators are provided to address nutrient imbalance in animal agriculture systems. At farm and region scale, nutrient balance investments will be needed to strengthen accounting methodologies, develop appropriate data sources for measurements, identify thresholds for action, and apply the methods in appropriate settings and decisions. Data availability and uncertainty are recognized as key limitations facing wider adoption of these concepts, particularly considering data ownership and privacy concerns. The lack of transparent datasets that capture current animal production practices and their impact on manure composition and nutrient cycling is a gap facing these methodologies. The lack of engagement by practitioners and producers in the development phase of such tools greatly affects their adoption and utility. The need for continued engagement in establishing accepted methodologies, training, data collection, and education are crucial to establish farm- and region-scale methods and measure their value to nutrient planning over time.  Keywords: Farm scale, Livestock, Manure nutrients, Nutrient budget, Poultry, Regional scale.}, number={2}, journal={JOURNAL OF THE ASABE}, author={Sharara, Mahmoud and Kolesch, Richard K. and Cortus, Erin L. and Larson, Rebecca A. and Classen, John J. and Janni, Kevin A.}, year={2022}, pages={235–249} }
 @article{akter_cheng_west_liu_qian_zou_classen_cordova_oviedo_wang-li_2022, title={Impacts of Air Velocity Treatments under Summer Condition: Part I—Heavy Broiler’s Surface Temperature Response}, volume={12}, ISSN={2076-2615}, url={http://dx.doi.org/10.3390/ani12030328}, DOI={10.3390/ani12030328}, abstractNote={Heavy broilers exposed to hot summer conditions experience fluctuations in surface temperatures due to heat stress, which leads to decreased performance. Maintaining a bird’s homeostasis depends on several environmental factors (temperature, relative humidity, and air velocity). It is important to understand the responses of birds to environmental factors and the amount of heat loss to the surrounding environment to create thermal comfort for the heavy broilers for improved performances and welfare. This study investigates the variation in surface temperatures of heavy broilers under high and low air velocity treatments. Daytime, age and bird location’s effect on the surface temperature variation was also examined. The experiment was carried out in the poultry engineering laboratory of North Carolina State University during summers of 2017, 2018, and 2019 as a part of a comprehensive study on the effectiveness of wind chill application to mitigate heat stress on heavy broilers. This live broiler heat stress experiment was conducted under two dynamic air velocity treatments (high and low) with three chambers per treatment and 44 birds per chamber. Surface temperatures of the birds were recorded periodically through the experimental treatment cycles (flocks, 35–61 d) with infrared thermography in the morning, noon, evening, and nighttime. The overall mean surface temperature of the broilers under two treatments was found to be 35.89 ± 2.37 °C. The variation in surface temperature happened due to air temperature, thermal index, air velocity, bird’s age, daytime, and position of birds inside the experimental chambers. The surface temperatures were found lower under high air velocity treatment and higher under low air velocity treatment. During the afternoon time, the broilers’ surface temperatures were higher than other times of the day. It was also found that the birds’ surface temperature increased with age and temperature humidity indices. Based upon the experimental data of five flocks, a simple linear regression model was developed to predict surface temperature from the birds’ age, thermal indices, and air velocity. It will help assess heavy broilers’ thermal comfort under heat stress, which is essential to provide a comfortable environment for them.}, number={3}, journal={Animals}, publisher={MDPI AG}, author={Akter, Suraiya and Cheng, Bin and West, Derek and Liu, Yingying and Qian, Yan and Zou, Xiuguo and Classen, John and Cordova, Hernan and Oviedo, Edgar and Wang-Li, Lingjuan}, year={2022}, month={Jan}, pages={328} }
 @article{akter_liu_cheng_classen_oviedo_harris_wang-li_2022, title={Impacts of Air Velocity Treatments under Summer Conditions: Part II—Heavy Broiler’s Behavioral Response}, volume={12}, ISSN={2076-2615}, url={http://dx.doi.org/10.3390/ani12091050}, DOI={10.3390/ani12091050}, abstractNote={Broiler chickens exposed to heat stress adapt to various behavioral changes to regulate their comfortable body temperature, which is critical to ensure their performance and welfare. Hence, assessing various behavioral responses in birds when they are subjected to environmental changes can be essential for assessing their welfare under heat-stressed conditions. This study aimed to evaluate the effect of two air velocity (AV) treatments on heavy broilers’ behavioral changes from 43 to 54 days under summer conditions. Two AV treatments (high and low) were applied in six poultry growth chambers with three chambers per treatment and 44 COBB broilers per chamber from 28 to 61 days in the summer of 2019. Three video cameras placed inside each chamber (2.44 m × 2.44 m × 2.44 m in dimension) were used to record the behavior of different undisturbed birds, such as feeding, drinking, resting, standing, walking, panting, etc. The results indicate that the number of chickens feeding, drinking, standing, walking, sitting, wing flapping, and leg stretching changed under AV treatments. High AV increased the number of chickens feeding, standing, and walking. Moreover, a two-way interaction with age and the time of day can affect drinking and panting. This study provides insights into heavy broilers’ behavioral changes under heat-stressed conditions and AV treatments, which will help guide management practices to improve birds’ performance and welfare under commercial conditions in the future.}, number={9}, journal={Animals}, publisher={MDPI AG}, author={Akter, Suraiya and Liu, Yingying and Cheng, Bin and Classen, John and Oviedo, Edgar and Harris, Dan and Wang-Li, Lingjuan}, year={2022}, month={Apr}, pages={1050} }
 @article{patil_sharara_shah_kulesza_classen_2023, title={Impacts of utilizing swine lagoon sludge as a composting ingredient}, volume={327}, ISSN={0301-4797}, url={http://dx.doi.org/10.1016/j.jenvman.2022.116840}, DOI={10.1016/j.jenvman.2022.116840}, abstractNote={Lagoon sludge, a byproduct of swine operations in the Southeast United States, poses a management challenge due to its high mineral and metal content. Composting is a low-cost, scalable technology for manure management. However, limited information is available on composting swine lagoon sludge in terms of recipes, greenhouse gas emissions and end-product quality. Moreover, due to its high Zn and Cu content, high inclusion of sludge in composting recipes can potentially inhibit the process. To address these knowledge gaps, in-vessel aerated composting (0.4 m3each) was carried out to evaluate impacts of sludge inclusion, at 10% (Low Sludge, LS-Recipe) and 20% (High sludge, HS-Recipe) wet mass-basis, on composting process and end-product quality. Comparable maximum temperatures (74 ± 2.7 °C, 74.9 ± 2.9 °C), and organic matter loss were observed in both recipes. Similarly, sludge inclusion ratio had no significant impact on cumulative GHG emissions. The global warming potential (20-year GWP) for swine lagoon sludge composting using LS and HS recipes was observed to be 241.9 (±13.3) and 229.9 (±8.7) kg CO2-e/tDM respectively. Both recipes lost 24–28% of initial carbon (C) and 4–15% of nitrogen (N) respectively. Composting and curing did not change water-extractable (WE) phosphorus (P) concentrations while WE Zn and Cu concentrations decreased by 67–74% and 55–59% respectively in both recipes. End compost was stable (respiration rates <2 mgCO2-C/g OM/day) with germination index >93 for both recipes.}, journal={Journal of Environmental Management}, publisher={Elsevier BV}, author={Patil, Piyush and Sharara, Mahmoud and Shah, Sanjay and Kulesza, Stephanie and Classen, John}, year={2023}, month={Feb}, pages={116840} }
 @article{bird_nichols_garay_nowatzke_essary_post_deviney_welles_alao_dorbu_et al._2022, title={Means, motive, and opportunity}, volume={10}, ISSN={2325-1026}, url={http://dx.doi.org/10.1525/elementa.2021.00066}, DOI={10.1525/elementa.2021.00066}, abstractNote={Wicked problems are inherent in food–energy–water systems (FEWS) due to the complexity and interconnectedness of these systems, and addressing these challenges necessitates the involvement of the diverse stakeholders in FEWS. However, successful stakeholder engagement requires a strong understanding of the relationships between stakeholders and the specific wicked problem. To better account for these relationships, we adapted a means, motive, and opportunity (MMO) framework to develop a method of stakeholder analysis that evaluates the agency of stakeholders related to a wicked problem in FEWS. This method involves two key components: (1) identification of a challenge at the FEWS nexus and (2) evaluation of stakeholder agency related to the challenge using the dimensions of MMO. This approach provides a method for understanding the characteristics of stakeholders in FEWS and provides information that could be used to inform stakeholder engagement in efforts to address wicked problems at the FEWS nexus. In this article, we present the stakeholder analysis method and describe an example application of the MMO method by examining stakeholder agency related to the adoption of improved swine waste management technology in North Carolina, USA.}, number={1}, journal={Elementa: Science of the Anthropocene}, publisher={University of California Press}, author={Bird, Kate I. T. and Nichols, Virginia A. and Garay, Eduardo S. and Nowatzke, Matthew and Essary, Ch’Ree and Post, Kimberly K. and Deviney, Alison V. and Welles, Jacqueline S. and Alao, Mumuni O. and Dorbu, Freda Elikem and et al.}, year={2022} }
 @article{cheng_wang-li_classen_bloomfield_2022, title={Performance of a Thermodynamic Model for Predicting Inorganic Aerosols in the Southeastern U.S.}, volume={13}, ISSN={2073-4433}, url={http://dx.doi.org/10.3390/atmos13121977}, DOI={10.3390/atmos13121977}, abstractNote={Fine particulate matter (i.e., PM2.5) has gained intensive attention due to its adverse health and visibility degradation effects. As a significant fraction of atmospheric PM2.5, secondary inorganic PM2.5 may be formed through the gas-phase ammonia (NH3) and particle-phase ammonium (NH4+) partitioning. While partitioning of NH3-NH4+ may be simulated using a thermodynamic equilibrium model, disagreement between model predictions and measurements have been realized. In addition, the applicability of the model under different conditions has not been well studied. This research aims to investigate the applicability of a thermodynamic equilibrium model, ISORROPIA II, under different atmospheric conditions and geographic locations. Based upon the field measurements at the Southeastern Aerosol Research and Characterization (SEARCH) network, the performance of ISORROPIA II was assessed under different temperature (T), relative humidity (RH), and model setups in urban and rural locations. The impact of organic aerosol (OA) on the partitioning of NH3-NH4+ was also evaluated. Results of this research indicate that the inclusion of non-volatile cations (NVCs) in the model input is necessary to improve the model performance. Under high T (>10 °C) and low RH (<60%) conditions, ISORROPIA II tends to overpredict nitric acid (HNO3) concentration and underpredict nitrate (NO3−) concentration. The predominance of one phase of semi-volatile compound leads to low accuracy in the model prediction of the other phase. The model with stable and metastable setups may also perform differently under different T-RH conditions. Metastable model setup might perform better under high T (>10 °C) and low RH (<60%) conditions, while stable model setup might perform better under low T (<5 °C) conditions. Both model setups have consistent performance when RH is greater than 83%. Future studies using ISORROPIA II for the prediction of NH3-NH4+ partitioning should consider the inclusion of NVCs, the under/over prediction of NO3−/HNO3, the selection of stable/metastable model setups under different T-RH conditions, and spatiotemporal variations of inorganic PM2.5 chemical compositions.}, number={12}, journal={Atmosphere}, publisher={MDPI AG}, author={Cheng, Bin and Wang-Li, Lingjuan and Classen, John and Bloomfield, Peter}, year={2022}, month={Nov}, pages={1977} }
 @article{cheng_wang-li_meskhidze_classen_bloomfield_2021, title={Partitioning of NH3-NH4+ in the Southeastern U.S.}, volume={12}, ISSN={2073-4433}, url={http://dx.doi.org/10.3390/atmos12121681}, DOI={10.3390/atmos12121681}, abstractNote={The formation of inorganic fine particulate matter (i.e., iPM2.5) is controlled by the thermodynamic equilibrium partitioning of NH3-NH4+. To develop effective control strategies of PM2.5, we aim to understand the impacts of changes in different precursor gases on iPM2.5 concentrations and partitioning of NH3-NH4+. To understand partitioning of NH3-NH4+ in the southeastern U.S., responses of iPM2.5 to precursor gases in four seasons were investigated using field measurements of iPM2.5, precursor gases, and meteorological conditions. The ISORROPIA II model was used to examine the effects of changes in total ammonia (gas + aerosol), total sulfuric acid (aerosol), and total nitric acid (gas + aerosol) on iPM2.5 concentrations and partitioning of NH3-NH4+. The results indicate that reduction in total H2SO4 is more effective than reduction in total HNO3 and total NH3 to reduce iPM2.5 especially under NH3-rich condition. The reduction in total H2SO4 may change partitioning of NH3-NH4+ towards gas-phase and may also lead to an increase in NO3− under NH3-rich conditions, which does not necessarily lead to full neutralization of acidic gases (pH < 7). Thus, future reduction in iPM2.5 may necessitate the coordinated reduction in both H2SO4 and HNO3 in the southeastern U.S. It is also found that the response of iPM2.5 to the change in total H2SO4 is more sensitive in summer than winter due to the dominance of SO42− salts in iPM2.5 and the high temperature in summer. The NH3 emissions from Animal Feeding Operations (AFOs) at an agricultural rural site (YRK) had great impacts on partitioning of NH3-NH4+. The Multiple Linear Regression (MLR) model revealed a strong positive correlation between cation-NH4+ and anions-SO42− and NO3−. This research provides an insight into iPM2.5 formation mechanism for the advancement of PM2.5 control and regulation in the southeastern U.S.}, number={12}, journal={Atmosphere}, publisher={MDPI AG}, author={Cheng, Bin and Wang-Li, Lingjuan and Meskhidze, Nicholas and Classen, John and Bloomfield, Peter}, year={2021}, month={Dec}, pages={1681} }
 @article{welles_soriano_dorbu_pereira_rubeck_timmermans_ndayambaje_deviney_classen_koziel_et al._2021, title={Socio-Economic and Governance Conditions Corresponding to Change in Animal Agriculture: South Dakota Case Study}, volume={13}, ISSN={2071-1050}, url={http://dx.doi.org/10.3390/su131910682}, DOI={10.3390/su131910682}, abstractNote={Understanding sustainable livestock production requires consideration of both qualitative and quantitative factors in a temporal and/or spatial frame. This study adapted Qualitative Comparative Analysis (QCA) to relate conditions of social, economic, and governance factors to changes in livestock inventory across several counties and over time. This paper presents an approach that (1) identified factors with the potential to relate to a change in livestock inventory and (2) analyzed commonalities within these factors related to changes spatially and temporally. This paper illustrates the approach and results when applied to five counties in eastern South Dakota. The specific response variables were periods of increasing, no change, or decreasing beef cattle, dairy cattle, and swine inventories in the specific counties for five-year census periods between 1992 and 2017. In the spatial analysis of counties, stable beef inventories and decreasing dairy inventories related to counties with increasing gross domestic products. The presence of specific social communities related to increases in county swine inventories. In the temporal analysis of census periods, local governance and economic factors, particularly market price influences, were more prevalent. Swine inventory showed a stronger link to cash crop markets than to livestock markets, whereas cattle market price increases associated with stable inventories for all animal types. Local governance tools had mixed effects for the different animal types across space and time. The factors and analysis results are context-specific. However, the process considers the various socio-economic processes in livestock production and community development applicable to agricultural sustainability questions in the Midwest and beyond.}, number={19}, journal={Sustainability}, publisher={MDPI AG}, author={Welles, Jacqueline S. and Soriano, Noelle Cielito T. and Dorbu, Freda Elikem and Pereira, G. M. and Rubeck, Laura M. and Timmermans, Erica L. and Ndayambaje, Benjamin and Deviney, Alison V. and Classen, John J. and Koziel, Jacek A. and et al.}, year={2021}, month={Sep}, pages={10682} }
 @article{cheng_wang-li_classen_meskhidze_bloomfield_2021, title={Spatial and temporal variations of atmospheric chemical condition in the Southeastern U.S.}, volume={248}, ISSN={0169-8095}, url={http://dx.doi.org/10.1016/j.atmosres.2020.105190}, DOI={10.1016/j.atmosres.2020.105190}, abstractNote={Animal feeding operations (AFOs) are the largest ammonia (NH3) emission sources in the United States (U.S.). However, the impact of NH3 emissions from AFOs on the formation of secondary inorganic PM2.5 (iPM2.5) has not been well understood and systematically assessed. Under the Southeastern Aerosol Research and Characterization (SEARCH) Network, the hourly concentrations of iPM2.5 chemical compositions and its precursor gases as well as meteorological data were measured at eight urban/nonurban sites labeled as JST/YRK, BHM/CTR, GFP/OAK, and PNS/OLF during 1998–2016. Using the SEARCH data, this research investigated the spatiotemporal variations of atmospheric chemical conditions in those rural and urban areas. The spatiotemporal variations of atmospheric chemical conditions at the eight sites are characterized by four parameters, including (1) gas ratio (GR), (2) gas-phase NH3 molar fraction (NH3/NHx), (3) total available NH3 (gaseous ammonia + aerosol ammonium) to sulfate (SO42−) molar ratio (TA/TS), and (4) PM2.5 ammonium + nitrate to total PM2.5 mass ratio (AN/PM2.5). Results indicate that the NH3 emissions from AFOs may explain the greater values of GR, NH3/NHx, and TA/TS in the wind directions coming from AFOs at YRK and OAK rural sites than the other wind directions. In the wind directions coming from AFOs at YRK and OAK, NH3 was in excess of fully neutralizing acidic gases, more NH3 stayed in gas phase than those in other wind directions, and both ammonium sulfate and ammonium nitrate existed in iPM2.5. The upward trend in NH3/NHx indicates that gas-particle partitioning ofNH3–NH4+shifted toward gas phase, while the downward trend in AN/PM2.5 may implicate that smaller fraction of PM2.5 was directly NH3 sensitive. Understanding of the spatiotemporal variations of atmospheric chemical condition provides insights to improve our understanding of iPM2.5 formation under rural and urban conditions, the reduction in sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions resulted in the reduction of iPM2.5 formation despite the increase in NH3 emissions in the Southeastern U.S.}, journal={Atmospheric Research}, publisher={Elsevier BV}, author={Cheng, Bin and Wang-Li, Lingjuan and Classen, John and Meskhidze, Nicholas and Bloomfield, Peter}, year={2021}, month={Jan}, pages={105190} }
 @article{deviney_classen_bruce_sharara_2020, title={Sustainable Swine Manure Management: A Tale of Two Agreements}, volume={13}, ISSN={2071-1050}, url={http://dx.doi.org/10.3390/su13010015}, DOI={10.3390/su13010015}, abstractNote={Intensification and concentration of swine farming has provided economic benefit to rural communities but also negative environmental and human health impacts, particularly from the use of the lagoon-sprayfield system for manure management. Although cost effective, this system is susceptible to poor management, unpleasant odor and other emissions, and inundation during extreme weather events. Competition for manure-spreading acres with other livestock or encroaching development can also pose a problem. This study examines two agreements between industry and government designed to develop and implement improved manure management technologies for swine farms: a voluntary agreement between the attorney general of North Carolina and Smithfield Foods and a consent judgment between the State of Missouri and Premium Standard Farms. Individuals involved in executing these agreements were interviewed to gain insight from their perspective on those processes and lessons they learned from their experience. Common themes among participant responses to support transition processes included the need to involve multiple stakeholder groups, clearly define goals, understand the system, allow time for incremental change, and provide adequate “protected space” for technology development and implementation. Viewing these themes through the lens of multi-level perspective theory identifies leverage points throughout the system to support transitioning farms to a more sustainable path of manure management.}, number={1}, journal={Sustainability}, publisher={MDPI AG}, author={Deviney, Alison and Classen, John and Bruce, Jackie and Sharara, Mahmoud}, year={2020}, month={Dec}, pages={15} }
 @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{kolar_classen_hall_2019, title={Physicochemical data of p-cresol, butyric acid, and ammonia}, volume={26}, ISSN={2352-3409}, url={http://dx.doi.org/10.1016/j.dib.2019.104356}, DOI={10.1016/j.dib.2019.104356}, abstractNote={There is a renewed interest in treating odorous contaminants such as butyric acid, p-cresol, and ammonia that are emitted from animal farming operations. However, developing newer treatment technologies require quantitative information regarding the properties of the target pollutants. Therefore, in this communication, baseline data related to physicochemical and thermodynamic properties of butyric acid, p-cresol, and ammonia were predicted using computational chemistry. Density functional theory was employed via B3LYP functional coupled with polarized 6-31G (d) basis set without any solvent effects using Gaussian 16W and GaussView6. The predicted baseline properties collected here are expected to be useful to scientists and engineers working in environmental mitigation technologies in developing treatment processes and make the animal agricultural industry environmental friendly and sustainable.}, journal={Data in Brief}, publisher={Elsevier BV}, author={Kolar, Praveen and Classen, John and Hall, Steven G.}, year={2019}, month={Oct}, pages={104356} }
 @article{cheng_wang-li_meskhidze_classen_bloomfield_2019, title={Spatial and temporal variations of PM2.5 mass closure and inorganic PM2.5 in the Southeastern U.S.}, volume={26}, ISSN={0944-1344 1614-7499}, url={http://dx.doi.org/10.1007/s11356-019-06437-8}, DOI={10.1007/s11356-019-06437-8}, abstractNote={Fine particulate matter (i.e., PM 2.5 ) has gained extensive attention owing to its adverse effects. The impacts of PM 2.5  may vary in time and space due to the spatiotemporal variations of PM 2.5  number size distribution and chemical compositions. This research analyzed the latest PM 2.5  chemical compositions measurements with an aim to better understand the dynamic changes of PM 2.5  in response to emission reductions due to the new regulations. The particulate measurements from the Southeastern Aerosol Research and Characterization (SEARCH) network between 2001 and 2016 were analyzed for the spatiotemporal variations of PM 2.5  and inorganic PM 2.5  (iPM 2.5  = SO 4 2-  + NH 4 +  + NO 3 - ) chemical compositions in the Southeastern United States (U.S.). It was discovered that PM 2.5  and iPM 2.5  mass concentrations exhibited significant downward trends in 2001-2016. Both PM 2.5  and iPM 2.5  mass concentrations were higher at urban and inland sites than rural/suburban and coastal sites. The higher iPM 2.5  concentrations at agricultural sites were attributed to the influences of ammonia (NH 3 ) emissions from animal feeding operations (AFOs). The iPM 2.5  was the dominant contributor to PM 2.5  in 2001-2016 at the coastal sites, whereas organic carbon matter (OCM) was the major contributor to PM 2.5  after 2011 at the inland sites. Our data analysis suggests that significant decrease of PM 2.5  concentrations is attributed to the reductions in nitrogen oxides (NO x ) and sulfur dioxide (SO 2 ) emissions in 2001-2016. Findings from this research provide insights into the development of effective PM 2.5  control strategies and assessment of air pollutants exposure.}, number={32}, journal={Environmental Science and Pollution Research}, publisher={Springer Science and Business Media LLC}, author={Cheng, Bin and Wang-Li, Lingjuan and Meskhidze, Nicholas and Classen, John and Bloomfield, Peter}, year={2019}, month={Sep}, pages={33181–33191} }
 @article{rodríguez_marshall_cotton_koelsch_koziel_meyer_steward_heemstra_padmanabahn_classen_et al._2019, title={The Development of the INFEWS-ER: A Virtual Resource Center for Transdisciplinary Graduate Student Training at the Nexus of Food, Energy, and Water}, volume={7}, ISSN={2296-665X}, url={http://dx.doi.org/10.3389/fenvs.2019.00038}, DOI={10.3389/fenvs.2019.00038}, abstractNote={Problems at the nexus of Food, Energy and Water Systems (FEWS) are among the most complex challenges we face. Spanning simple to complex temporal, geographic, social, and political framings, the questions raised at this nexus require multi-disciplinary if not transdisciplinary approaches. Answers to these questions must draw from engineering, the physical and biological sciences, and the social sciences. Practical solutions depend upon a wide community of stakeholders, including industry, policy-makers, and the general public. Yet there are many obstacles to working in a transdisciplinary environment: unfamiliar concepts, specialized terminology, and countless 'blind' spots. Graduate education occurs in disciplinary 'silos', often with little regard for the unintended consequences of our research. Existing pedagogical models do not usually train students to understand neighboring disciplines, thus limiting student learning to narrow areas of expertise, and obstructing their potential for transdisciplinary discourse over their careers. Our goal is a virtual resource center—the INFEWS-ER—that provides educational opportunities to supplement graduate students, especially in their development of transdisciplinary competences. Addressing the grand challenges at the heart of the FEWS nexus will depend upon such competence. Students and scholars from diverse disciplines are working together to develop the INFEWS-ER. To date, we have sponsored both a workshop and a symposium to identify priorities to design the initial curriculum. We have also conducted surveys of the larger community of FEWS researchers. Our work confirms a widespread interest in transdisciplinary training and helps to identify core themes and promising pedagogical approaches. Our curriculum now centers upon several 'Cohort Challenges', supported by various 'Toolbox Modules' organized around key themes (e.g., communicating science). We plan to initiate the first cohort of students in October of 2018. Students who successfully complete their Cohort Challenges will be certified as the FEW Graduate Scholars. In this paper, we describe the development of this curriculum. We begin with the need for training in transdisciplinary research. We then describe the workshop and symposium, as well as our survey results. We conclude with an outline of the curriculum, including the current Cohort Challenges and Toolbox Modules.}, journal={Frontiers in Environmental Science}, publisher={Frontiers Media SA}, author={Rodríguez, Luis F. and Marshall, Anna-Maria and Cotton, Dan and Koelsch, Richard and Koziel, Jacek and Meyer, Deanne and Steward, Dan and Heemstra, Jill and Padmanabahn, Anand and Classen, John and et al.}, year={2019}, month={Apr} }
 @article{lentz_kolar_classen_2019, title={Valorization of Swine Manure into Hydrochars}, volume={7}, ISSN={2227-9717}, url={http://dx.doi.org/10.3390/pr7090560}, DOI={10.3390/pr7090560}, abstractNote={There is a significant interest in valorizing swine manure that is produced in enormous quantities. Therefore, considering the high moisture content in swine manure, the objective of this research was to convert manure slurry into hydrochars via hydrothermal carbonization and analyze the yields, pH, energy contents, and thermal and oxidation kinetic parameters. Experiments were performed in triplicate in 250 mL kettle reactors lined with polypropylene at 180 °C, 200 °C, 240 °C, 220 °C, and 260 °C for 24 h. Analyses of the results indicated that the process temperature affected the hydrochar yields, with yield generally decreasing with increasing temperature, but it had little effect on the composition of the hydrochar. The hydrochars were found to have higher volatile contents and H/C and O/C ratios and about 85% of the energy compared to coal. However, the presence of high fraction (35–38%) of ash in hydrochars is a serious concern and needs to be addressed before the complete utilization of hydrochars as fuels. The surface characterization of hydrochars coupled with wet chemistry experiments indicated that hydrochars were equipped with nitrogen functional groups with points of zero charges between 6.76 and 7.85, making them suitable as adsorbents and soil remediation agents and energy storage devices.}, number={9}, journal={Processes}, publisher={MDPI AG}, author={Lentz, Zac and Kolar, Praveen and Classen, John J.}, year={2019}, month={Aug}, pages={560} }
 @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} }
 @article{l. kick_zering_classen_2017, title={Approaches to agricultural innovation and their effectiveness}, volume={2}, ISSN={2471-2086}, url={http://dx.doi.org/10.3934/agrfood.2017.4.370}, DOI={10.3934/agrfood.2017.4.370}, abstractNote={Citation: Edward L. Kick, Kelly Zering, John Classen. Approaches to agricultural innovation and their effectiveness[J]. AIMS Agriculture and Food, 2017, 2(4): 370-373. doi: 10.3934/agrfood.2017.4.370}, number={4}, journal={AIMS Agriculture and Food}, publisher={American Institute of Mathematical Sciences (AIMS)}, author={L. Kick, Edward and Zering, Kelly and Classen, John}, year={2017}, pages={370–373} }
 @article{das_kolar_sharma-shivappa_classen_osborne_2017, title={Oxidative Depolymerization of Lignin Using Supported Niobium Catalysts}, volume={1}, ISSN={2305-7084}, url={http://dx.doi.org/10.3390/chemengineering1020017}, DOI={10.3390/chemengineering1020017}, abstractNote={Valorization of lignin into aromatics has driven researchers for decades. In this research, niobium was deposited on oyster shells (OSNC) and carbon rods (CRNC) and tested as a catalyst for depolymerization of lignin. Catalysts (2%, 5%, and 8% loading) were synthesized via wet impregnation. Batch experiments were performed at 95 °C, using 8 g of lignin, and 1 g of catalyst. Our research indicates that niobium supported catalysts are effective in partial oxidation of lignin. Maximum vanillin concentration for OSNC was found to be 86.25 mg L−1 (0.1 wt%) at 5% niobium whereas, as for CRNC, maximum vanillin concentration was found to be 139.40 mg L−1 (0.17 wt%) at 2% niobium loading. Addition of hydrogen peroxide into the batch reactor decreased the concentration of vanillin production.}, number={2}, journal={ChemEngineering}, publisher={MDPI AG}, author={Das, Lalitendu and Kolar, Praveen and Sharma-Shivappa, Ratna and Classen, John and Osborne, Jason}, year={2017}, month={Nov}, pages={17} }
 @article{lentz_classen_kolar_2017, title={THERMOCHEMICAL CONVERSION: A PROSPECTIVE SWINE MANURE SOLUTION FOR NORTH CAROLINA}, volume={60}, ISSN={["2151-0040"]}, DOI={10.13031/trans.12074}, abstractNote={Abstract. The growth of North Carolina’s swine industry in recent decades has led to a subsequent increase in the production of swine manure. This manure represents a potential threat to environmental and human health, as well as an opportunity to add value to pork production. Technologies for treating swine manure safely while generating products to offset costs are part of an expanding field of research centered on sustainable food production for our growing population. Thermochemical conversion processes use heat to degrade organic feedstocks and drive chemical reactions, which generate valuable products. The high moisture content of swine manure is prohibitive for most thermochemical processes, but gasification and hydrothermal carbonization may be more accommodating. Gasification, a time-tested thermochemical conversion process, yields a combustible gas through a series of endothermic reactions, and hydrothermal carbonization yields a solid, coal-like char that can be used as a fuel or chemical precursor. Advances in thermochemical conversion processes have indicated the potential for yielding valuable products from swine manure, but viable scalable processes are still under development, requiring further research to apply these processes to swine manure management and evaluate the usefulness of their products. This review (1) describes, generally, thermochemical conversion via both hydrothermal gasification (HTG) and hydrothermal carbonization (HTC), (2) shows the usefulness of each conversion process for biomass, and (3) discusses the potential of HTG and HTC of swine manure to enhance the value of pork production. Keywords: Energy, Gases, Hydrothermal carbonization, Hydrothermal gasification, Pig manure, Pigs, Sustainable.}, number={3}, journal={TRANSACTIONS OF THE ASABE}, author={Lentz, Z. and Classen, J. and Kolar, P.}, year={2017}, pages={591–600} }
 @article{das_kolar_sharma-shivappa_classen_osborne_2017, title={Catalytic Valorization of Lignin Using Niobium Oxide}, volume={8}, ISSN={["1877-265X"]}, DOI={10.1007/s12649-016-9717-8}, number={8}, journal={WASTE AND BIOMASS VALORIZATION}, author={Das, Lalitendu and Kolar, Praveen and Sharma-Shivappa, Ratna and Classen, John J. and Osborne, Jason A.}, year={2017}, month={Dec}, pages={2673–2680} }
 @article{lu_yuan_cheng_rose_classen_simmons_2016, title={Modeling the Growth of Archaeon Halobacterium halobium Affected by Temperature and Light}, volume={181}, ISSN={0273-2289 1559-0291}, url={http://dx.doi.org/10.1007/s12010-016-2270-x}, DOI={10.1007/s12010-016-2270-x}, abstractNote={The objective of this study was to develop sigmoidal models, including three-parameter (Quadratic, Logistic, and Gompertz) and four-parameter models (Schnute and Richards) to simulate the growth of archaeon Halobacterium halobium affected by temperature and light. The models were statistically compared by using t test and F test. In the t test, confidence bounds for parameters were used to distinguish among models. For the F test, the lack of fit of the models was compared with the prediction error. The Gompertz model was 100 % accepted by the t test and 97 % accepted by the F test when the temperature effects were considered. Results also indicated that the Gompertz model was 94 % accepted by the F test when the growth of H. halobium was studied under varying light intensities. Thus, the Gompertz model was considered the best among the models studied to describe the growth of H. halobium affected by temperature or light. In addition, the biological growth parameters, including specific growth rate, lag time, and asymptote changes under Gompertz modeling, were evaluated.}, number={3}, journal={Applied Biochemistry and Biotechnology}, publisher={Springer Science and Business Media LLC}, author={Lu, Hao and Yuan, Wenqiao and Cheng, Jay and Rose, Robert B. and Classen, John J. and Simmons, Otto D.}, year={2016}, month={Oct}, pages={1080–1095} }
 @article{selective oxidation of lignin into aromatic aldehydes using niobium oxalate_2016, volume={59}, ISSN={2151-0032 2151-0040}, url={http://dx.doi.org/10.13031/trans.59.10908}, DOI={10.13031/trans.59.10908}, abstractNote={Abstract. There is a strong interest in using lignin as a precursor for synthesis of value-added chemicals such as aromatic aldehydes. Among the existing processes for converting lignin into aromatic aldehydes, catalytic oxidation appears to be most promising. In this research, we explored niobium oxalate as a selective oxidation catalyst and hydrogen peroxide as an oxidant for oxidizing lignin into vanillin and syringaldehyde. Research objectives were to (1) determine the effect of catalyst mass, lignin concentration, and H 2 O 2 concentration on synthesis of aromatic aldehydes; (2) study the effect of reaction temperature; and (3) optimize the reaction parameters. Batch experiments were performed via central composite design at 95°C using 4 to 12 g of lignin per 100 mL, 3 to 7 mL of H 2 O 2 per 100 mL, and 0.5 to 1.0 g of catalyst per 100 mL. Results indicated that under optimum conditions (3 mL of H 2 O 2 , 0.5 g of catalyst, and 7.26 g of lignin), 65.58 mg g -1 of vanillin and 23.12 mg g -1 of syringaldehyde were produced. In addition, production of aldehydes showed dependency on temperature in the range of 85°C to 100°C, with 100°C producing the highest product concentrations. It is theorized that perhydroxyl anion (HOO - ), being a strong nucleophile and the most active agent in alkaline hydrogen peroxide, breaks the I± and I²-aryl ether bonds of lignin to produce corresponding aldehydes. It is suggested that niobium is a potential catalyst for selective oxidation of lignin.}, number={2}, journal={Transactions of the ASABE}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, year={2016}, month={Apr}, pages={727–735} }
 @article{hu_wang-li_simmons_classen_osborne_2016, title={Size Distributions of Bioaerosols in an Egg Production Facility and Its Vicinity}, volume={33}, ISSN={["1557-9018"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-84964715430&partnerID=MN8TOARS}, DOI={10.1089/ees.2015.0220}, abstractNote={Abstract Air emissions from animal feeding operations may cause elevated concentrations of bioaerosols in surrounding areas, posing adverse health effects to the people working on or living near the farm. Concentrations of nonselective airborne bacteria and fungi in various size ranges were measured by the Andersen six-stage viable samplers in an egg production house and at four ambient stations surrounding the farm in winter, spring, and summer. It was discovered that in-house bacterial particle size distributions (PSDs) were different among seasons. Under higher temperature and lower relative humidity conditions, more bacteria were associated with the small size ranges. Seasonal variations of in-house fungal PSDs were not significant. On average, 60–80% of in-house bacteria were in respirable size range (≤4.7 μm), whereas 60–70% of in-house fungi were in respirable size range. Bacterial PSDs at ambient locations were different among stations in winter but not in spring and summer. There were significant...}, number={4}, journal={ENVIRONMENTAL ENGINEERING SCIENCE}, author={Hu, Di and Wang-Li, Lingjuan and Simmons, Otto D. and Classen, John J. and Osborne, Jason A.}, year={2016}, month={Apr}, pages={215–223} }
 @article{kick_balcazar tellez_thompson_classen_2016, title={World geography and power, national capitals, and inequality as cross-national causes of food security and environmental outcomes}, volume={1}, ISSN={2471-2086}, url={http://dx.doi.org/10.3934/agrfood.2016.4.419}, DOI={10.3934/agrfood.2016.4.419}, abstractNote={Treatments of sustainability outcomes such as food security, economic development and environmental degradation typically have adopted monocausal approaches. Many have argued for substantial increases in world meat production as the panacea to global food insecurity. We use global and national synthetic explanations and path analytic approaches to examine sustainability outcomes for 200 nations. Both strong direct or indirect links are found among global geography, global power and national capitals, as well as warfare and military expenditures, and economic development. These factors are differentially predictive of the other key measures of sustainability.}, number={4}, journal={AIMS Agriculture and Food}, publisher={American Institute of Mathematical Sciences (AIMS)}, author={Kick, Edward and Balcazar Tellez, Maria and Thompson, Gretchen and Classen, John}, year={2016}, pages={419–438} }
 @article{hu_wang-li_simmons iii_classen_osborne_2015, title={Spatiotemporal Variations of Bioaerosols  in the Vicinity of an Animal Feeding  Operation Facility in the US}, volume={06}, ISSN={2152-2197 2152-2219}, url={http://dx.doi.org/10.4236/jep.2015.66056}, DOI={10.4236/jep.2015.66056}, abstractNote={Bioaerosol emissions from animal feeding operation (AFO) facilities are of increasing interest due to the magnitude of the emissions and their potential health effect on local communities. There is limited information about fate and transport of AFO bioaerosol emissions. In this study, concentrations of airborne bacteria and fungi were measured at four ambient stations in four wind directions surrounding an egg production farm through winter, spring and summer using Andersen six-stage samplers. Mean concentrations of ambient bacteria and fungi ranged from 8.7 × 102 CFU m-3 to 1.3 × 103 CFU m-3 and from 2.8 × 102 CFU m-3 to 1.4 × 103 CFU m-3, respectively. Ambient bacterial concentrations were not significantly different over the seasons, while ambient fungal concentrations were the highest in summer and the lowest in winter. There were significant differences between downwind and upwind bacterial concentrations (p < 0.0001). Downwind bacterial and fungal concentrations responded differently to the influencing factors. Bacterial concentrations were quadratically correlated with wind vector (combined effects of wind speed and direction) and emission rate, were positively correlated with temperature, and were negatively correlated with solar radiation. Fungal concentrations were positively correlated with temperature, RH, and emission rate, and were negatively correlated with wind vector.}, number={06}, journal={Journal of Environmental Protection}, publisher={Scientific Research Publishing, Inc.}, author={Hu, Di and Wang-Li, Lingjuan and Simmons III, Otto D. and Classen, John J. and Osborne, Jason A.}, year={2015}, pages={614–627} }
 @article{hu_wang-li_simmons_classen_osborne_byfield_2014, title={Bioaerosol concentrations and emissions from tunnel-ventilated high-rise layer houses in North Carolina}, volume={57}, number={3}, journal={Transactions of the ASABE}, author={Hu, D. and Wang-Li, L. and Simmons, O. D. and Classen, J. J. and Osborne, J. A. and Byfield, G. E.}, year={2014}, pages={915–925} }
 @article{liang_shah_classen_sharma-shivappa_2014, title={Drying temperature - duration impacts on moisture, carbon, and nitrogen losses from broiler litter}, volume={16}, number={4}, journal={Agricultural Engineering International: CIGR Journal}, author={Liang, Weizhen and Shah, Sanjay B. and Classen, John and Sharma-Shivappa, Ratna}, year={2014}, pages={16–23} }
 @article{fitzgerald_kolar_classen_boyette_das_2015, title={Swine Manure Char as an Adsorbent for Mitigation of p-Cresol}, volume={34}, ISSN={["1944-7450"]}, DOI={10.1002/ep.11972}, abstractNote={There is a significant interest in synthesizing inexpensive adsorbents for mitigating pollutants emitted from animal agriculture industry such as p‐cresol. Biochar, a byproduct obtained from thermochemical biomass processing is one such source of adsorbent materials. However, presently there is not enough quantitative information on adsorption of p‐cresol on biochar. Hence, the goal of this research is to investigate swine manure char as an inexpensive adsorbent for removal of p‐cresol from an aqueous system. Swine manure was gasified for 15 min at 704°C to obtain gasified manure char. The char was characterized using physical and chemical techniques. Batch experiments were performed in duplicates at 25°C, 35°C, and 45°C to determine the adsorption isotherms and kinetics. Results indicated that gasification enhanced surface area and acid value of manure from 11.42 ± 0.20 to 49.12 ± 0.79 m2 g−1 and 7.81 ± 0.05 to 8.57 ± 0.01, respectively. The enhanced basicity of the resultant char promoted chemisorption of p‐cresol on char surface with maximum adsorption capacities of 7.63 mg g−1 (25°C), 14.99 mg g−1 (35°C), and 14.84 mg g−1 (45°C). Langmuir and Freundlich models suggested that adsorption of p‐cresol on char was favorable. Kinetic analysis of the data also confirmed chemisorption of p‐cresol while the analysis of transport processes suggested that internal diffusion of p‐cresol within the pores was the rate‐limiting step. Use of biochar as an adsorbent for p‐cresol will add value to gasification byproducts and simultaneously reduce water and air pollution associated with swine farming operations. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 125–131, 2015}, number={1}, journal={ENVIRONMENTAL PROGRESS & SUSTAINABLE ENERGY}, author={Fitzgerald, Sterling and Kolar, Praveen and Classen, John and Boyette, Mike and Das, Lalitendu}, year={2015}, month={Jan}, pages={125–131} }
 @article{classen_chandler_huie_osborne_2013, title={A centrifuge-based procedure for suspended solids measurements in lagoon sludge}, volume={56}, number={2}, journal={Transactions of the ASABE}, author={Classen, J. J. and Chandler, W. J. and Huie, R. S. and Osborne, J. A.}, year={2013}, pages={747–752} }
 @article{das_kolar_classen_osborne_2013, title={Adsorbents from pine wood via K2CO3-assisted low temperature carbonization for adsorption of p-cresol}, volume={45}, ISSN={["1872-633X"]}, DOI={10.1016/j.indcrop.2012.12.010}, abstractNote={A low-temperature carbonization process was evaluated to synthesize an inexpensive adsorbent from pine wood to mitigate p-cresol from aqueous system. Surface response experiments using carbonization time, impregnation ratio (IR), and carbonization temperature as variables indicated that optimum adsorbent yield and adsorption were 63.22% and 5.40 mg g−1, respectively at carbonization temperature of 266 °C, IR of 2, and carbonization time of 2 h. The equilibrium adsorption data agreed with Langmuir's model and maximum theoretical adsorption of 6.97 mg g−1 was obtained at temperature 25 °C, unadjusted pH and adsorbent dose of 10 g L−1. The kinetic analysis combined with desorption study revealed that p-cresol chemisorbed on the adsorbent surface. Additionally, adsorption of p-cresol was found to be exothermic and inhibited by presence of surface acidic oxygen groups.}, journal={INDUSTRIAL CROPS AND PRODUCTS}, author={Das, Lalitendu and Kolar, Praveen and Classen, John J. and Osborne, Jason A.}, year={2013}, month={Feb}, pages={215–222} }
 @article{liang_classen_shah_sharma-shivappa_2013, title={Ammonia Fate and Transport Mechanisms in Broiler Litter}, volume={225}, ISSN={0049-6979 1573-2932}, url={http://dx.doi.org/10.1007/s11270-013-1812-x}, DOI={10.1007/s11270-013-1812-x}, number={1}, journal={Water, Air, & Soil Pollution}, publisher={Springer Science and Business Media LLC}, author={Liang, Wei-zhen and Classen, John J. and Shah, Sanjay B. and Sharma-Shivappa, Ratna}, year={2013}, month={Dec} }
 @article{liang_shah_classen_sharma-shivappa_2013, title={Modeling Ammonium Adsorption on Broiler Litter and Cake}, volume={224}, ISSN={["0049-6979"]}, DOI={10.1007/s11270-012-1405-0}, number={2}, journal={WATER AIR AND SOIL POLLUTION}, author={Liang, Wei-zhen and Shah, Sanjay B. and Classen, John J. and Sharma-Shivappa, Ratna}, year={2013}, month={Feb} }
 @article{das_kolar_osborne_classen_2012, title={Adsorption of p-cresol on granular activated carbon}, volume={14}, number={4}, journal={Agricultural Engineering Institute: CIGR Journal}, author={Das, L. and Kolar, P. and Osborne, J.A. and Classen, J.J.}, year={2012}, pages={37–49} }
 @inbook{classen_lal_2012, title={Agricultural Waste Management Systems and Software Tools}, url={http://dx.doi.org/10.5772/50484}, DOI={10.5772/50484}, abstractNote={As the demand for animal products such a milk, meat, etc. has increased, producers have found ways to increase productivity and decrease the unit cost of production. Fossil fuels, inorganic fertilizer, pesticides, improved genetics of production species, better management techniques, and mechanization allowed productivity to increase to meet these demands. This has also meant concentration of more animals at each location. Confining some types of animals to houses or barns through all or most of their life cycle protects them from the weather and from predators and facilitates feeding, animal movement, and materials handling. Producers have benefited from economies of scale and product uniformity to provide the consumer with low-cost, high-quality meat and animal products.}, booktitle={Waste Management - An Integrated Vision}, publisher={InTech}, author={Classen, J.J. and Lal, Harbans}, editor={Marmolejo Rebellon, uis FernandoEditor}, year={2012}, month={Oct} }
 @article{love_kolar_classen_das_2011, title={Adsorption of ammonia on ozonated activated carbon}, volume={54}, DOI={10.13031/2013.39834}, abstractNote={In this theoretical research, we investigated ozonated granular activated carbon (OGAC) as an ammonia adsorbent in aqueous systems. Research objectives were to determine the (1) effectiveness of ozone loading on adsorption capacity of activated carbon in aqueous ammonia solutions, (2) kinetics and adsorption isotherms of ammonia adsorption, and (3) effect of volatile organic compounds on adsorption of ammonia from the aqueous phase. Batch experiments indicated that ozonation for 30 min enhanced the adsorption capacity of granular activated carbon from 0.47 ±0.065 mg g-1 to 1.02 ±0.099 mg g-1 due to increased surface oxygen species on activated carbon. These results suggested that activated carbon could be chemically modified to enhance the adsorption of ammonia from aqueous systems. Analysis of the rate data suggested that the adsorption of ammonia on OGAC followed an Elovich model with initial adsorption rate (a) and desorption constants (s) between 0.146 and 1.06 mg g-1 min-1 and 5.5 and 7.75 g mg-1, respectively (25°C to 45°C). The effect of temperature (25°C to 45°C) on adsorption was not found to be significant, suggesting that adsorption on OGAC was non-activated. However, presence of volatile organic compounds (VOCs) such as p-cresol and acetic acid inhibited adsorption of ammonia on OGAC. Future research is needed to synthesize activated carbon that can absorb ammonia and VOCs simultaneously.}, number={5}, journal={Transactions of the ASABE}, author={Love, C. D. and Kolar, P. and Classen, John and Das, L.}, year={2011}, pages={1931–1940} }
 @article{classen_rice_mcneill_simmons_2011, title={Design and evaluation of a discreet sampler for waste treatment lagoons}, volume={27}, DOI={10.13031/2013.40621}, abstractNote={A lagoon sampler was designed to collect 300-mL samples from depths up to 2.82 m at 15.2-cm intervals. Design parameters required the device to collect discrete samples through the entire lagoon column without cross contamination during raising or lowering of the device through the lagoon and to leave the liquid column undisturbed so subsequent samples could be taken from lower depths at the same location. An evaluation protocol was developed to test the device in a 55.9-cm diameter, 3.35-m tall PVC test column. This test column was of sufficient depth to be representative of lagoons and of sufficient diameter to avoid interference, or edge effects, associated with the sampling device. The evaluation protocol used dissolved solids (sodium chloride) as the test parameter in 30.5-cm deep layers of sodium chloride of decreasing concentrations to fill the test column from the bottom and simulated different solids concentrations that may be found in a lagoon. Samples were collected at six depths from 122 to 198 cm. Based on electrical conductivity measurements, samples collected with the device were slightly more dilute than the expected value at all sample depths. Further tests showed that operation of the device did not cause mixing of the layered salt solutions. The sampler was used to collect samples from various depths in a lagoon; results suggested there was little interference among samples taken at specific locations through subsequent depths.}, number={6}, journal={Applied Engineering in Agriculture}, author={Classen, John and Rice, J. M. and McNeill, J. P. and Simmons, O. D.}, year={2011}, pages={1007–1014} }
 @article{guerdat_losordo_classen_osborne_delong_2011, title={Evaluating the effects of organic carbon on biological filtration performance in a large scale recirculating aquaculture system}, volume={44}, ISSN={["1873-5614"]}, DOI={10.1016/j.aquaeng.2010.10.002}, abstractNote={Studies evaluating the impact of organic carbon on biological filters at the large scale for aquaculture production are lacking. Understanding the performance characteristics of different biofilters under actual production conditions will be the only means by which recirculating system designers may properly select and size biological filters for commercial production use. Previous studies have determined the impact of organic carbon on biofilter performance at the small lab scale often using artificial waste nutrients in the evaluation. Evaluations under actual production conditions using real wastewater produce vastly different results than previous lab scale studies using artificial nutrients. As such, this study is a preliminary step in evaluating the impact of organic carbon on three different commercially available biological filters at the large scale under actual recirculating aquaculture production conditions. The study was conducted at the North Carolina State University Fish Barn—a commercial scale research and demonstration recirculating aquaculture facility operated by the Biological and Agricultural Engineering department. The study was based on a 60 m3 Tilapia system with average daily feed rates of 45 kg using a 40% protein feed and an average biomass of 6750 kg. The system was dosed with sucrose (C12H22O11) to increase the concentration of biodegradable organic carbon in the system. The effect of elevated organic carbon concentrations on total ammoniacal nitrogen (TAN) removal rates was evaluated and determined based on biofilter media volume. Variability increased substantially in the volumetric TAN removal rate (VTR) for all three filters. VTR for all three filter types was reduced by approximately 50% as compared to normal production conditions. The results demonstrate the importance of controlling the concentration of biologically available organic carbon in a recirculating aquaculture system.}, number={1}, journal={AQUACULTURAL ENGINEERING}, author={Guerdat, Todd C. and Losordo, Thomas M. and Classen, John J. and Osborne, Jason A. and DeLong, Dennis}, year={2011}, month={Jan}, pages={10–18} }
 @article{guerdat_losordo_classen_osborne_delong_2010, title={An evaluation of commercially available biological filters for recirculating aquaculture systems}, volume={42}, ISSN={["0144-8609"]}, DOI={10.1016/j.aquaeng.2009.10.002}, abstractNote={Three different commercially available biological filters were evaluated in triplicate on a 60 m3 tank-based Tilapia system under commercial warmwater growout conditions. The study was performed at the North Carolina State University Fish Barn—a commercial scale research and demonstration recirculating aquaculture facility operated by the department of Biological and Agricultural Engineering. Total ammoniacal nitrogen (TAN) removal rates were determined for the three types of biofilters for a range of concentrations ranging from 0.13 to 1.20 g TAN m−3. TAN concentrations were varied by feed rates and ammonium chloride additions, and limited by fish feeding response. Maximum feed rates were 65 kg feed d−1 using a 40% protein diet at a maximum biomass of 5500 kg. Average observed TAN removal rates (in g TAN m−3 of unexpanded media d−1 ± standard deviation) for the three filters were 267 ± 123, 586 ± 284, and 667 ± 344 for the moving bed bioreactor, floating bead filter, and fluidized sand filter, respectively. These results are considerably lower than results previously published at the laboratory scale using artificial waste nutrients. This study highlights the need for future biofilter evaluations at the commercial scale using real aquaculture waste nutrients.}, number={1}, journal={AQUACULTURAL ENGINEERING}, author={Guerdat, Todd C. and Losordo, Thomas M. and Classen, John J. and Osborne, Jason A. and DeLong, Dennis P.}, year={2010}, month={Jan}, pages={38–49} }
 @article{classen_rice_sherman_2007, title={The effects of vermicompost on field turnips and rainfall runoff}, volume={15}, DOI={10.1080/1065657x.2007.10702308}, abstractNote={Vermicompost made from separated swine waste solids (0, 10, or 20% by volume of soil) was applied to turnips in small field plots during four growing seasons to determine the effect on plant growth, runoff volume and nutrients in runoff. The effect of nitrogen fertilizer was controlled by supplementing half the plots with inorganic nitrogen to balance the nitrogen fertilizer recommendations for turnips. Vermicompost addition increased fresh weight of fruit and foliage by a factor of two to five and increased dry weight by a factor of three with no increase in nitrogen but higher phosphorus in runoff. Runoff volume was lower in plots that received vermicompost compared to control plots.}, number={1}, journal={Compost Science & Utilization}, author={Classen, John and Rice, J. M. and Sherman, R.}, year={2007}, pages={34–39} }
 @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} }
 @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} }
 @article{cheng_bergmann_classen_stomp_howard_2002, title={Nutrient recovery from swine lagoon water by Spirodela punctata}, volume={81}, ISSN={["0960-8524"]}, DOI={10.1016/S0960-8524(01)00098-0}, abstractNote={Spirodela punctata 7776, the best duckweed strain in total protein production selected from in vitro screening experiments with synthetic swine lagoon water medium was examined for N and P recovery. It has shown a capability to grow in and to remove N and P from synthetic swine lagoon water with high N (240 mg NH4–N/l) and P (31.0 mg PO4–P/l) levels. A lag period of approximately 96 h was observed before the duckweed started to grow. During the lag period, utilization of N and P by the duckweed was very slow. The rates of N and P uptake, and duckweed growth increased with the increase of the initial N and P concentrations in the medium. The highest rates of N and P uptakes, and duckweed growth observed in this study were 0.955, 0.129 mg/l-h, and 1.33g/m2-h (or 31.92g/m2-day), respectively. The N:P ratio in swine lagoon water is adequate for growing the duckweed.}, number={1}, journal={BIORESOURCE TECHNOLOGY}, author={Cheng, JY and Bergmann, BA and Classen, JJ and Stomp, AM and Howard, JW}, year={2002}, month={Jan}, pages={81–85} }
 @article{cheng_landesman_bergmann_classen_howard_yamamoto_2002, title={Nutrient removal from swine lagoon liquid by Lemna minor 8627}, volume={45}, DOI={10.13031/2013.9953}, abstractNote={Nitrogen and phosphorus removal from swine lagoon liquid by growing Lemna minor 8627, a promising duckweed 
identified in previous studies, was investigated under in vitro and field conditions. The rates of nitrogen and phosphorus 
uptake by the duckweed growing in the in vitro system were as high as 3.36 g m–2 day–1 and 0.20 g m–2 day–1, respectively. 
The highest nitrogen and phosphorus removal rates in the field duckweed system were 2.11 g m–2 day–1 and 0.59 g m–2 day–1, 
respectively. The highest observed duckweed growth rate was close to 29 g m–2 day–1 in both conditions. 
Wastewater concentrations and seasonal climate conditions had direct impacts on the duckweed growth and nutrient 
removal in outdoor tanks. The rate of duckweed production in diluted swine lagoon liquid increased as the dilution rate 
increased. Duckweed assimilation was the dominant mechanism for nitrogen and phosphorus removal from the swine lagoon 
liquid when the nutrient concentration in the wastewater was low, but became less important as nutrient concentration 
increased. Reasonably high light intensity and a longer period of warm temperature could result in a higher growth rate for 
the duckweed. Pre–acclimation of the duckweed with swine lagoon liquid could accelerate the start–up of a duckweed system 
to remove nutrients from the wastewater by preventing the lag phase of duckweed growth.}, number={4}, journal={Transactions of the ASAE}, author={Cheng, J. and Landesman, L. and Bergmann, Ben and Classen, John and Howard, J. W. and Yamamoto, Y. T.}, year={2002}, pages={1003–1010} }
 @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{price_classen_payne_2001, title={Aspergillus niger absorbs copper and zinc from swine wastewater}, volume={77}, ISSN={["1873-2976"]}, DOI={10.1016/S0960-8524(00)00135-8}, abstractNote={Wastewater from swine confined-housing operations contains elevated levels of copper and zinc due to their abundance in feed. These metals may accumulate to phytotoxic levels in some agricultural soils of North Carolina due to land application of treated swine effluent. We evaluated fungi for their ability to remove these metals from wastewater and found Aspergillus niger best suited for this purpose. A. niger was able to grow on plates amended with copper at a level five times that inhibitory to the growth of Saccharomyces cerevisiae. We also found evidence for internal absorption as the mechanism used by A. niger to detoxify its environment of copper, a property of the fungus that has not been previously exploited for metal bioremediation. In this report, we show that A. niger is capable of removing 91% of the copper and 70% of the zinc from treated swine effluent.}, number={1}, journal={BIORESOURCE TECHNOLOGY}, author={Price, MS and Classen, JJ and Payne, GA}, year={2001}, month={Mar}, pages={41–49} }
 @inproceedings{smith_cheng_classen_2001, title={Duckweed harvesting and mat control}, volume={1}, DOI={10.13031/2013.4128}, abstractNote={The release of excessive amounts of nutrients into the environment by North 
Carolina’s hog industry has become a major concern in the state. Research is being done on 
the use of duckweed, a floating aquatic plant, in the removal of nutrients from anaerobically 
treated swine wastewater. The plant must be harvested in order to remove the accumulated 
nutrients and to obtain the plant biomass, which may be useful as a protein source. This paper 
describes work towards the design of a system that harvests the plant by skimming it from the 
surface of the wastewater. Specifically, a system was constructed in a concrete tank to test the 
skimming concept. Two qualitative experiments took place: one involved the harvesting of the 
plant under ideal conditions for skimming in which the mat was thin and no clumping of the 
plants had occurred, and the other under very unfavorable conditions in which the plants had 
formed into clumps. It was found that a standard funnel skimmed very effectively under ideal 
conditions, requiring very small amounts of water. The same funnel was much less effective 
when conditions were unfavorable. The experiments showed that skimming could work very 
well in a controlled environment, yet not in a typical agricultural environment. Adjustments must 
be made that can allow the system to work well in all cases.}, booktitle={ASAE 94th annual international meeting : 2001, an engineering odyssey : July 29-August 1, 2001, Sacramento, California}, author={Smith, R. A. and Cheng, J. and Classen, John}, year={2001}, pages={2277} }
 @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} }
 @article{classen_engler_kenerley_whittaker_2000, title={A logistic model of subsurface fungal growth with application to bioremediation}, volume={35}, ISSN={["1093-4529"]}, DOI={10.1080/10934520009376982}, abstractNote={Abstract The goal of this research was to determine the potential of the fungal sterol ergosterol as an indicator of fungal biomass and to determine the growth response of the transformed strain of T. virens (GvT6) to added substrate and changes in temperature. Experiments in liquid culture and agar plates containing a rich medium of glucose, yeast extract, and casein (GYEC), or a soil extract medium supplemented with maltose (SE) showed that the ergosterol content of GvT6 was greatest when grown on GYEC agar plates (14.02 mg/g dry biomass). For both media, plate cultures produced higher specific ergosterol values than liquid cultures. Changes in specific ergosterol values over time were generally not significant. A value of 5.41 mg ergosterol / g dry biomass, determined for SE plate cultures, was used to convert ergosterol values to biomass values in growth experiments in soil bioreactors. Data from experiments in soil bioreactors treated with different levels of substrate (0.5–8 mg maltose / g dry soil) at three different temperatures (22, 27, 32°C) showed subsurface growth of GvT6 can be described by the logistic equation. Culture conditions of 32°C and 8 mg/g substrate produced the highest levels of biomass, but growth at 32°C and 4 mg/g substrate was somewhat faster than at the higher substrate level.}, number={4}, journal={JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH PART A-TOXIC/HAZARDOUS SUBSTANCES & ENVIRONMENTAL ENGINEERING}, author={Classen, JJ and Engler, CR and Kenerley, CM and Whittaker, AD}, year={2000}, pages={465–488} }
 @article{classen_young_bottcher_westerman_2000, title={Design and analysis of a pilot scale biofiltration system for odorous air}, volume={43}, DOI={10.13031/2013.2675}, abstractNote={Three pilot-scale biofilters and necessary peripheral equipment were built to clean odorous air from the pit of a swine gestation building at North Carolina State University. A computer measured temperatures, flow rates, and pressure drops. It also controlled and measured the moisture content of a biofilter medium comprised of a 3:1 mixture of yard waste compost to wood chips mixture (by volume). The system was evaluated to ensure that the biofilters would be useful for performing scientific experiments concerning the reduction of swine odor on future research projects. The capability of the biofilters to remove odor was measured using a cotton swatch absorption method and an odor panel. The average odor reductions measured by odor intensity, irritation intensity, and unpleasantness for five tests were 61%, 58%, and 84%, respectively. No significant differences in odor reduction performance were found between the biofilters.}, number={1}, journal={Transactions of the ASAE}, author={Classen, John and Young, J. S. and Bottcher, R. W. and Westerman, P. W.}, year={2000}, pages={111–117} }
 @article{bergmann_cheng_classen_stomp_2000, title={In vitro selection of duckweed geographical isolates for potential use in swine lagoon effluent renovation}, volume={73}, ISSN={["1873-2976"]}, DOI={10.1016/S0960-8524(99)00137-6}, abstractNote={Plant-based systems for nutrient sequestration into valuable biomass have the potential to help avoid the environmental problems associated with the disposal of large volumes of animal waste. The objective of this study was to select superior duckweed (Lemnaceae) genotypes for the utilization of nutrients in animal wastes. A two-step protocol was used to select promising duckweed geographic isolates to be grown on swine lagoon effluent. Forty-one geographic isolates from the worldwide germplasm collection were used in an in vitro screening test, because they were noted to be fast-growing genotypes during routine collection maintenance. In vitro screening was accomplished by growing geographic isolates on a synthetic medium that approximated swine lagoon effluent in terms of nutrient profile, total ionic strength, pH, and buffering capacity. Large differences among geographic isolates were observed for wet weight gain during the 11-day growing period, percent dry weight, and percent protein in dry biomass. Total protein production per culture jar differed 28-fold between the most disparate of the 41 geographic isolates and was the variable used for selection of superior geographic isolates. The challenge of eight of the 41 geographic isolates with full-strength swine lagoon effluent in the greenhouse led to the selection of three that are promising as genotypes to be grown on lagoon effluent.}, number={1}, journal={BIORESOURCE TECHNOLOGY}, author={Bergmann, BA and Cheng, J and Classen, J and Stomp, AM}, year={2000}, month={May}, pages={13–20} }
 @inproceedings{classen_cheng_bergmann_stomp_2000, title={Lemna gibba growth and nutrient uptake in response to different nutrient levels}, ISBN={1892769115}, booktitle={Animal, agricultural, and food processing wastes : proceedings of the Eighth International Symposium, October 9-11, 2000, Des Moines, Iowa}, author={Classen, J. J. and Cheng, J. and Bergmann, B. A. and Stomp, A. M.}, 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{cheng_stomp_classen_barker_bergmann_2000, title={Nutrient removal from swine lagoon effluent by duckweed}, volume={43}, DOI={10.13031/2013.2701}, abstractNote={ABSTRACT. Three duckweed geographic isolates were grown on varying concentrations of swine lagoon effluent in a 
greenhouse to determine their ability to remove nutrients from the effluent. Duckweed biomass was harvested every other 
day over a 12-day period. Duckweed biomass production, nutrient loss from the swine lagoon effluent, and nutrient 
content of duckweed biomass were used to identify effluent concentrations/geographic isolate combinations that are 
effective in terms of nutrient utilization from swine lagoon effluent and production of healthy duckweed biomass. When 
Lemna minor geographic isolate 8627 was grown on 50% swine lagoon effluent, respective losses of TKN, NH 3 -N, TP, 
OPO 4 -P, TOC, K, Cu, and Zn were 83, 100, 49, 31, 68, 21, 28, and 67%.}, number={2}, journal={Transactions of the ASAE}, author={Cheng, J. and Stomp, A-M and Classen, John and Barker, J. C. and Bergmann, Ben}, year={2000}, pages={263–269} }
 @inproceedings{cheng_bergmann_classen_stomp_howard_2000, title={Nutrient removal from swine wastewater by duckweed - Spirodela punctata}, volume={1}, ISBN={1900222681}, booktitle={Industrial wastewater and envrironmental contaminants : proceedings of the 1st World Water Congress of the International Water Association, held in Paris, France, 3-7 July 2000}, author={Cheng, J. and Bergmann, B. A. and Classen, J. J. and Stomp, A. M. and Howard, J. W.}, year={2000} }
 @article{bicudo_classen_goldsmith_smith_1999, title={Effects of aeration cycles and hydraulic retention time on the sequencing batch treatment of flushed swine manure}, volume={3}, number={1}, journal={Advances in Environmental Research}, author={Bicudo, J. R. and Classen, J. J. and Goldsmith, C. D. and Smith, T.}, year={1999}, pages={U5–73} }
 @article{classen_liu_kenerley_whittaker_1996, title={Fractal analysis of subsurface growth of a genetically modified strain of Gliocladium virens and its parental strain}, volume={39}, DOI={10.13031/2013.27736}, abstractNote={The structure of a fungal colony growing on an agar surface has been shown to follow a fractal model. This report investigates the fractal dimensions of subsurface colonies of a transformed strain of Gliocladium virens (GvT6) and the unaltered strain (Gv29-8). Strain GvT6 contains the opd gene from Flavobacterium sp. Fractal analysis of GvT6 and Gv29-8 should indicate changes in the branching character of a fungus due to genetic modification.}, number={6}, journal={Transactions of the ASAE}, author={Classen, John and Liu, W.-S. and Kenerley, C. M. and Whittaker, A. D.}, year={1996}, pages={2271} }
 @article{classen_siebenmorgen_griffis_1993, title={Vegetable processing energy requirements}, volume={42}, number={2}, journal={Arkansas Farm Research}, author={Classen, John J. and Siebenmorgen, Terry J. and Griffis, Carl L.}, year={1993}, pages={8–9} }
 @article{classen_siebenmorgen_griffis_young_1992, title={Technical Notes: Processing Energy Requirements for Several Vegetables}, volume={35}, ISSN={2151-0059}, url={http://dx.doi.org/10.13031/2013.28689}, DOI={10.13031/2013.28689}, abstractNote={Energy usage was measured at a vegetable processing plant during the canning of several different vegetables. The plant capacity was nominally 100 000 kg per day, depending on the product being processed; usually multiple products were handled each day. Process energy of spinach, pork and beans, baked beans, and hominy was calculated to be 2.7, 3.9, 4.7, and 6.6 MJ/kg, respectively.}, number={3}, journal={Transactions of the ASAE}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, author={Classen, J. and Siebenmorgen, T. J. and Griffis, C. L. and Young, J. C.}, year={1992}, pages={973–974} }
 @article{classen_siebenmorgen_griffis_young_1991, title={ANAEROBIC DIGESTION OF HOMINY WASTE}, volume={34}, ISSN={2151-0059}, url={http://dx.doi.org/10.13031/2013.31752}, DOI={10.13031/2013.31752}, abstractNote={ABSTRACT The production of hominy results in a waste stream with a very high chemical oxygen demand (COD) as well as a very high pH. This research evaluated anaerobic digestion as a means of treating this wastewater. Results indicated that COD could be reduced by approximately 90% with little or no additional alkalinity required..}, number={3}, journal={Transactions of the ASAE}, publisher={American Society of Agricultural and Biological Engineers (ASABE)}, author={Classen, J. and Siebenmorgen, T. J. and Griffis, C. L. and Young, J. C.}, year={1991}, pages={0937–0943} }