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Wednesday, Oct. 17, 2018

Volstorff Ballroom, University Student Union South ��ֱ���� State University

• 8 a.m.: Registration Opens
• 8:30–8:40 a.m.:  Welcome by John Killefer
• 8:40–9 a.m.: John McMaine, "Water in South ��ֱ����, Stakeholder Guided Strategies for Moving Forward"
• 9–9:45 a.m.: Francois Birgand, "High Frequency Sensors: Do We Even Have The Choice Of Not Using Them In Drainage?"
• 9:45 a.m.: Poster Judging starts (judges report to posters)
• 9:45–10 a.m.: Matt Hummel, "Rapid On-Site Microbial Source-Tracking in Water Quality"
• 10–10:15 a.m.: Srinivas Janaswamy, "Agriculture materials as novel cost-effective and sustainable tools to capture and recycle water nutrients"
• 10:15–11 a.m.: Poster session/networking break
• 11–11:20 a.m.: Brian Dougherty, "International perspectives on agricultural nutrient management and water quality"
• 11:20–11:40 a.m.: Ryan Thompson, "Mapping and Quantification of Lower Brule Shoreline Erosion"
• 11:40 a.m.–noon: Laura Edwards, "Climate Trends and Projections in the Northern Plains region"
• 12–12:45 p.m.: Lunch
• 1–1:45 p.m.: Jane Frankenberger, "Managing Water For Tomorrow's Agriculture"
• 1:45–2:05&�Բ�����;��.��.: Jim Ristau and Matt Morlock, "​Teaming Up to Address Salinity in South ��ֱ���� - A Win/Win"
• 2:05–2:25&�Բ�����;��.��.: Bruce Schmidt,  "North ��ֱ���� Soil Conservation and Watershed Leadership Academy"
• 2:25–3 p.m.: Networking break
• 3–3:30 p.m.: Mark Imerman Regional Strategic, Ltd (Des Moines), "Linking Nutrient Reduction to Flood Control - Examples from Iowa"
• 3:30–3:50 p.m.: Drew Kessler, "Addressing Water Quality and Quantity through Targeted Conservation Efforts"
• 3:50–4:30 p.m.: Jeff Zimprich, "Answers to South ��ֱ����’s Water Quality and Water Quantity Issue: Soil Health is a key component"
• 4:30 p.m.: Closing Remarks

Purification of Nutrient Pollutants in drinking water (Nitrates and Phosphates) for a sustainable clean water provision using Nanofiltration

Olumuyiwa Babalola, Department of Agriculture and Environmental Science, Lincoln University Missouri

The problem of water eutrophication has become a global environmental menace in recent years. It is caused by the high concentration of nutrients in water, mainly Nitrates and Phosphates, which is due to the fertilizers runoff from agricultural areas, as well as poorly disposal of industrial and domestic wastewater into the environments.

The consumption of high concentration of these pollutants from drinking water can lead to health problems such as Methemoglobinemia also known as blue-baby syndrome.

Considering the negative influence that these nutrient pollutants manifest in our health and environment, numerous studies has been conducted to efficiently remove nutrient pollutants from water, such as chemical method (Electrocoagulation, MAP, chemical precipitation technique), Physio-chemical method (Crystallization, Polymer hydrogels technique) and Bio-electrochemical denitrification method. It was discovered that the electrocoagulation technique was the best method applied for the removal of Nitrate and Phosphate, however it had its downsides such as high electricity usage and high cost of operation. For this reason, this research plans to investigate the possibility of application of nanofiltration in the removal of Nitrate and Phosphate in drinking water.

Keywords: Eutrophication, Nutrient pollution, Nanofiltration

Disinfection Byproducts Removal during Water Reuse Using Natural Solar Photo-Fenton Process

Ibrahim Abusallout, South ��ֱ���� State University

Water scarcity has become a serious issue facing our communities due to the population growth and many others. In the US, water shortage has forced many cities to consider reusing municipal treated wastewater to augment the drinking water. The formation of disinfection byproducts (DBPs) in the wastewater effluent during the chlorination process, can affect the quality of the source water for drinking water supplies. This has raised concerns about the potential impact of those DBPs on water reuse practices. Solar Photo-Fenton process has emerged as a promising energy-efficient process for degradation of a variety of toxic organic compounds present in wastewater. The primary objective of this research was to investigate the kinetics of photocatalytic degradation of DBPs by photo-Fenton process using natural solar irradiation.

In this study, we used outdoor photolysis experiments to investigate the solar photo-Fenton process on the degradation of total organic halogen and specific DBPs. Commercial organic extract and several municipal wastewaters were used as precursors to produce DBPs using chlorine and chloramines. Ethylenediamine-N, N′-disuccinic acid was used as a chelating agent to allow the process to be conducted under neutral conditions. The impact of Fe(III), H2O2, EDDS and pH on the degradation of DBPs were evaluated. In addition, chloride, sulfate, nitrate, humic acid and alkalinity were varied during the experiments.

The results of this study suggest that DBPs can be effectively degraded by EDDS-modified solar photo-fenton. The degradation rates of specific DBPs increased with increasing number of halogens and size of the substituted halogens. Monoiodoacetic acid, was rapidly degraded by the solar-fenton process with a half-life of 13 min. Overall, this study demonstrates that this process is highly effective treatment technology for removing DBPs in water and reducing the health risks associated with it during water reuse.

Biochar amended rain gardens for urban stormwater management

Farhana Akhter, Department of Agricultural and Biosystems Technology, South ��ֱ���� State University

Due to the urbanization, the area of impervious surfaces such as roads, roofs, parking lots increases. Impervious surfaces prevent the precipitation from infiltrating into the ground which leads to an increased volume of stormwater runoff which causes frequent flooding, stream bank erosion and introduces new pollutants to streams. The primary objectives of sustainable stormwater management are reducing runoff volume, removing pollutants from water, reducing streambank erosion, protecting floodplains and wetlands and reestablishing pre-development hydrology. Rain gardens are a simple stormwater management technology consisting of a shallow depression that catches, stores and infiltrates stormwater. This can reduce the volume and rate of stormwater runoff and can also help to restore the watershed pre-development hydrology. In some cases, rain garden soils are amended to increase infiltration of stormwater. Biochar can be used as a potential filter media amendment for better infiltration of stormwater through the soil and for enhanced pollutant removal. However, these technologies have not been tested in South ��ֱ����. Biochar is rich in carbon with a high surface area and made from pyrolysis of biomass. Recently, a rain garden was installed in Sioux Falls with a biochar-soil mixture as a filter bed and an underdrain. The rain garden is divided into two cells. One cell is without amended soil, and the other cell is amended with biochar. Inflow and outflow will be measured to investigate the water quality and water quantity of both cells to determine the biochar’s effect on pollutant removal and water quantity. A column test will be carried out in the lab using a biochar-soil mixture to determine the optimal amount of biochar for pollutant removal and desired hydraulic conductivity. These results will be compared with the results of the field experiment.

Develop an effective biochar-based nanocomposite for removal of nitrogen and phosphorus from waste water

Zhisheng Cen, Department of Agricultural and Biosystems Engineering, South ��ֱ���� State University

Large amounts of nitrogen and phosphorus fertilizers are required to increase the yield of crop production. Due to overuse, run off and leaching loss, low efficiency of fertilizer has resulted in high crop production costs and serious environmental impacts, such as eutrophication of river and lake water as well as groundwater systems with extravagant nitrogen and phosphorous. The goal of this research is to develop an effective biochar-based nanocomposite to remove nitrogen and phosphorus from agricultural waste water. Activated carbon has been proven to be able to efficiently absorb nitrogen and phosphorous from water. Biochar produced from biomass pyrolysis, torrefaction and gasification will be converted into activated carbon and thus combined with cellulose nanofibers or cellulose nanocrystals to produce effective nanocomposites for removal of nitrogen and phosphorus from agricultural waste water. The absorption, desorption and diffusion efficiencies of biomass-derived activated carbon will be investigated for developing the nanocomposites. The spent activated carbon can be used as controlled release fertilizers for recycling nitrogen and phosphorus back to crop production. Successfully developing such nanocomposite is likely to improve quality of agricultural waste water and increase profitability of crop production while minimizing the environmental impacts caused by crop production.

Addressing Water Quality and Quantity through Targeted Conservation Efforts

Drew Kessler, Houston Engineering, Inc.

Historically, conservation efforts are targeted to improve water quality or to manage water quantity, but rarely are both considered simultaneously to assess multiple benefits of conservation efforts. The presentation will highlight a new technique for targeting conservation efforts that provide water quality and quantity benefits to downstream resources that is built upon the Prioritize, Target and Measure Application (PTMApp). The targeting method utilizes LiDAR data to target where conservation can go on the landscape, and then estimate the water quality benefits (i.e., reduction in sediment, total nitrogen, total phosphorus) and water quantity benefits (i.e., changes in hydrographs at downstream resources) of implementing the targeted conservation efforts. Case studies from several watersheds across the Northern Great Plains will be highlighted. 

State of the Art Watershed Management Technique for Peak Discharge Prediction

Philip Adalikwu, Civil and Environmental Engineering Department, South ��ֱ���� State University

The integration of computers and Geographic Information System (GIS) technology in watershed modeling processes has gained ground in recent years. This means that the ubiquity and complexity in landscapes and hydrologic phenomena of the watershed are more easily analyzed. A common practice in watershed modeling is to subdivide the watershed into subbasins. The objective of this study was to use geospatial information and the US Army Corps of Engineering Hydrologic Engineering Centre Hydrologic Modeling System (HEC-HMS) to investigate the effect of watershed subdivision on peak discharge from the Wolf Butte Creek Watershed (23.696 square miles) located in Perkins County, South ��ֱ����. Results of simulations showed that peak discharge is affected by the number of watershed subdivisions. Increasing or decreasing the number of subdivisions results in either overestimation or underestimation of the peak discharge. For example, when the whole watershed was modeled as a single subbasin, the peak discharge was 322.4 cfs. Peak discharge was 315.6 cfs, 344.3 cfs, 342.7 cfs, 140.1 cfs and 132.2 cfs for two, five, 10, 20 and 50 subbasins respectively, for a design storm of 1 inch. For proper and effective application of the HEC-HMS model in watershed management, it is important to identify an appropriate number of watershed subdivisions.

Keywords: watershed management, modeling, geospatial, subdivision, peak discharge

South ��ֱ���� Farmer's Sense of Place in Relationship to the Land They Farm

Emireth Cancino, South ��ֱ���� State University

Sense of place (SOP) focuses on how the biophysical features of a place affect a person’s feelings towards it. Given increasing interest in how SOP relates to conservation behavior and problems with existing SOP measures, our study focuses on how farmers from the eastern part of South ��ֱ���� feel about the land they farm, using revised measures of sense of place, including dimensions of place attachment, identity (place and social) and dependence (place and economic). We use mail survey methodology to examine commodity crop farmers’ sense of place in 34 counties in the eastern part of South ��ֱ���� (see map to the right). Participants were randomly selected from a list of operators provided by the Farm Service Agency. 3,000 letters were sent out in the initial mailing and the final response rate was 30% after four waves of contact (see below for details). We excluded 639 operations with land but not farming or incorrect addresses from the final response rate calculations.

Effects of Disturbance on Soil Hydrology in Northern Great Plains Grasslands

¹Jacob Comer, ²Laurent Ahiablame, ¹Lora Perkins

¹Natural Resource Management, South ��ֱ���� State University, Brookings, SD

²University of California Cooperative Extension, Agriculture and Natural Resources, San Diego, CA

Disturbances, such as grazing and fire, in Northern Great Plains grasslands can influence soil hydrologic processes. This study assessed the impact of intense winter grazing and wildfire on infiltration rates and soil moisture in the western South ��ֱ���� grasslands compared to non-burned and non-winter grazed grasslands. Nine pastures (three winter grazed, three burned and three control) were monitored over two growing seasons after the disturbances (burn and intense winter grazing) occurred. All the pastures were under low-intensity season-long continuous grazing prior to the disturbances. Preliminary data indicate that the control pastures have higher soil moisture content than that of the burned and intense grazed treatments, with notable differences at greater soil depths. There was no statistically significant difference in soil temperature across the treatment pastures. While infiltration in burned and winter grazed pastures were statistically similar, pastures under burned treatments displayed significantly higher infiltration (p < 0.05) than infiltration in the intense winter grazed and burned pastures.

Keywords: Infiltration, Field Hydrology, Grazing, Fire.

Evaluation of Woodchip Bioreactor Denitrification Kinetics

Abdoul Aziz Kouanda, Department of Civil and Environmental Engineering, South ��ֱ���� State University

Agricultural subsurface drainage is a water management practice used to remove excess water in poorly drained soil. The use of fertilizers combined with subsurface drainage practice affects negatively surface water quality due to nitrate loss. Woodchip bioreactors have been used as a method for removing nitrate from agricultural tile drainage. Understanding the mechanism that governs nitrate removal in woodchips bioreactor is crucial for field bioreactor design. The objective of this project is to determine woodchip bioreactor denitrification kinetics parameters, using different types of woodchips (fresh, weathered and aged), under different temperatures. The impact of hydraulic retention time (HRT) was also briefly studied in this project.

Column experiment was conducted with influent nitrate concentrations varying from 50 mg N/L to 3 mg N/L at a HRT of 12 hours. The integrated Michaelis Menten equation was used to determine the denitrification kinetics parameters. At 22 degree Celsius, fresh, weathered and aged woodchips had a half saturation constants of 2.05 mg N/L, 2.60 mg N/L and 2.01 mg N/L respectively. The maximum removal rates were found to be 0.86 mg N/L/H, 2.09 mg N/L/H and 0.3 mg N/L/H respectively for fresh, weathered and aged woodchip at 22 degree Celsius. At 5 degree Celsius, we had a half saturation constants of 0.50 mg N/L and 1.77 mg N/L for fresh and weathered woodchips respectively. Fresh and weathered woodchips had a maximum removal rate of 0.04 mg /L/H and 0.25 mg/L/H respectively at 5 degree Celsius. At HRT of 24 hours with influent nitrate concentration of 10 mg N/L, a 98.70 % and 100% percentage removal were achieved respectively for fresh and weathered woodchips. Fresh and weathered woodchips achieved a nitrate removal percentage of 29.40 % and 99.7 % respectively at HRT of 6 hours.

The results of this study brought a significant contribution in better understanding denitrification kinetics in Woodchip bioreactor.

The effect of bioreactors on transporting E. coli in subsurface drainage systems under different media (Laboratory study).

Sara Mardani, Department of Agricultural and Biosystems Engineering, South ��ֱ���� State University

Nitrate, phosphorous and fecal indicator organisms (e.g. E. coli) transport from agricultural fields to surface waters through surface runoff and subsurface drainage systems (SDSs). The export of associated pollutants to surface water through SDSs should be managed and controlled due to their potential effect on both terrestrial and aquatic health. Woodchip bioreactors (WBs) are a promising strategy to reduce the amount of Nitrate transport in SDSs. Along with woodchip media, phosphorus adsorption media (such as steel shaving and Biochar) are also used to remove phosphorous in areas with high phosphorus concentration. Although these systems are quite effective in removing Nitrate and phosphorous, not much is known regarding the potential impact of these systems on transporting bacteria from SDSs. Therefore, the main objective of this study is to quantify and compare the change in E. coli concentrations from the inlets to the outlets by using different media. To reach this objective, a laboratory study is conducting by using four laboratory-scale bioreactors. The reactors are labeled with 1, 2, 3 and 4 and filled with woodchips, woodchips + steel shavings, steel shavings and a mixture of woodchips and biochar, respectively receiving the same synthetic water by four separate peristaltic pumps in a constant rate (down-flow), allowing a hydraulic retention time equal to 6 hours. The synthetic water is continuously passing through the reactors for 60 days and water samples are taking 10 times over this course of experiment. All water samples have been collected from both the inlets and outlets on the sampling days and processed for E. coli concentrations. So far, the results (for 5 samplings) represent a reduction of E. coli in the reactors under all media. E. coli removal were 75%, 64%, 63% and 53% for columns 4, 2, 1 and 3, respectively, providing some evidence for the broader capability of media to improve water quality from SDSs. 

Monitoring the seasonal variability of E. coli levels in streambed sediment and the evaluation of the effect of Seasonal Riparian Area Management (SRAM)

Sadia Salam, Department of Agricultural and Biosystems Engineering, South ��ֱ���� State University

Streambed sediment considered as a reservoir for microorganism as sediment provides more favorable condition to bacterial growth. Literatures observed fecal indicator bacteria such as, E. coli persists in streambed sediment and contains 100 to 1000 folds higher loadings than water column. One of the many reasons of higher E. coli levels in streambed is change of season. Because past researchers observed E. coli levels in streambed sediment increased in wet season and decreased in dry season. The reason of seasonal change affecting the E. coli levels could be the change of streamflow, livestock grazing or recreational activities throughout the season. The goal of this study is to monitor seasonal variability of E. coli in streambed sediment as well as evaluate the impact of SRAM, which is a unique best management practices that has been used in Skunk Creek among other areas in South ��ֱ����. The study was conducted in Skunk Creek (Sk), a tributary to the Big Sioux River located in Eastern South ��ֱ����. There are four monitoring sites in Sk where samples were collected, abbreviated as Sk1, Sk2, Sk3 and Sk4. The sediment samples have collected throughout the season, started from May to October in 2017-2018. Last year data shows the Sk1 has highest variation of E. coli levels observed of 20 CFU g-1 and 2700 CFU g-1 in June and August, respectively where all other three sites showed similar variation throughout the season. The study also monitors the impact of SRAM, which has implemented in site Sk2, Sk3 and Sk4. For evaluation of SRAM, statistical analysis has done between early season when the cattle are initially left off, and the end of the season. Last year data shows that although there is a significant difference between the early season vs. late season in site Sk1, but three other sites do not show any significant difference as well as three downstream sites (Sk2, Sk3, Sk4) had lower E. coli levels than Sk1 showing positive impact of SRAM.

Biodegradable Biopolymers are Effective to Capture Water Nutrients: A Step towards Developing Renewable Water Treatment Technologies

Most-Farzana Yesmin¹, Srinivas Janaswamy¹, Laurent Ahiablame²

¹Department of Dairy and Food Science, South ��ֱ���� State University, Brookings, SD

²Agriculture & Natural Resources, University of California Cooperative Extension, San Diego, CA

The presence of excess nutrients in agricultural water leads to algal blooms and hypoxia. Conventional technologies such as ion exchange, distillation, reverse osmosis and bioreactors aid immensely in removing nutrients; however, are expensive to implement. Given the deleterious consequences of excessive water nutrients, there is an unmet need for developing low-cost and sustainable protocols. Herein, we demonstrate a novel opportunity based on food-grade polysaccharides (e.g. alginate and carrageenan) to remove nitrate and phosphate from surface and sub-surface agricultural water, leading to downstream water quality improvement. Alginate beads were prepared in the presence of divalent (Ca2+, Fe2+, Ni2+, Cu2+, Zn2+ and Sr2+) and trivalent (Al3+ and Fe3+) cations and treated the 25 mg/L nitrate water at room temperature. Results suggest that alginate beads are effective to gather nitrate and ion type has influence on the total absorbed amount. Around 39% of nitrate could be pulled out by the Fe3+ alginate beads. The capacity of the rest reaches to 30% excepting Ni2+ - and Zn2+-alginate that could only attract 17% of nitrate. The outcome could be extended to phosphorous removal as well and to a variety of biopolymers. These beads are biodegradable and with nutrient enrichment, they gain the required potential to serve as fertilizers with safe and efficient land applications.

Entrepreneurial Aspirations of South ��ֱ���� Commodity Crop Producers

Abdelrahim Abulbasher, South ��ֱ���� State University

This study examines the entrepreneurial aspirations of South ��ֱ���� (SD) commodity crop producers, especially whether producers who adopt best management practices and engage in frequent training and building social networks, as important factors in their business success, are motivated to think more entrepreneurially. It also examines the socio-demographic characteristics of farmers such as age, education level and farm size as they relate to entrepreneurial aspirations and farmers and their attitudes toward adoption of best management practices. We argue that the need for adoption of entrepreneurship and sustainable agriculture in the broader rural context is increasing and the market demands are changing, thus more SD crop farmers need to adopt agricultural entrepreneurship and conservation practices. Theory of Planned Behavior and Networks Theory are two conceptual frameworks used to inform the study. TPB, while Network Theory. Surveys were sent to 3,000 SD farmers between January and March 2018. We found that the majority of SD crop producers are constantly seeking ways to grow and improve their businesses but also taking measures to protect the land they farm from weather variability. Three out of four farmers agreed that they are often looking for ways to diversify their farm operations and remain competitive. Further, the findings show that age, education and farm significantly contribute to farmers’ adoption of entrepreneurship. They also influence the motivation of farmers to build social networks and seek training opportunities to become more innovative, increase their access to business opportunities and maintain economic and environmental sustainability. No significant difference by age, education and farm size was found on whether producers believe that adopting conservation practices reduces natural and environmental challenges with regards to watersheds.

Changes in phosphorus concentrations leaving plots through tile drainage systems after planting rye cover crop

Arun Bawa, South ��ֱ���� State University

Tile drainage systems are widely implemented through the upper Mississippi River Basin (MRB) to keep soils free of excess water to ensure optimal crop growth. However, these systems are also a major pathway for nutrients (nitrogen, N and phosphorus, P) to leave agricultural fields. Nutrients washed off fields fertilize the MRB downstream river networks which in turn enriches the northern Gulf of Mexico’s waters. Elevated nutrient levels in the Gulf’s waters contribute to the occurrence of a hypoxic zone that triggers serious and undesirable environmental effects. Therefore, best management practices that reduce nutrient loses to receiving water bodies have been suggested as potential control measures for preventing downstream waters enrichment. In this study, we quantified changes in phosphorus (total phosphorus, TP and ortho-phosphate, ortho-P) concentrations leaving plots through tile drainage systems after planting rye cover crop. The experimental site was divided into 14 plots, under a randomized complete block design (2 treatments) with 7 replications. The treatments included the control plots (without cover crops) and rye cover crop plots (with cover crop). Water quality sampling at the tile drainage discharge occurred every week starting on April 24, 2018 and samples were analyzed for TP and ortho-P using an AQ1 discrete analyzer. Samples collected from tile drainage at plots planted with rye cover crop showed lower TP concentration than samples collected from tile drainage at the control plots. Unlike TP, ortho-P concentration was higher in samples collected from the pipes at plots planted with rye cover crop. Preliminary results suggest that rye cover crop might have a direct influence on reducing sediments through which TP is transported, possibly due to enhanced soil structure.

The Fargo Project: Understanding urban water quality in a community based green infrastructure design

Jesse Riley, North ��ֱ���� State University

The goal of the Fargo Project is to design a green infrastructure amenity in a stormwater detention basin using community input. Urban detention basins typically serve one purpose, they retain water and slowly release it back to the river to reduce flash flow issues. The objective of this research was to analyze water quality at the Fargo Project as it passes through the basin from inlet to outlet and as it enters and recedes from the basin during storm events. Samples were taken monthly in 2016 and 2017 and during three major storm events. Results indicate that E.coli is high in the storm water at the basin, particulates settle in the basin during storm events and while removing concrete from the basin is aesthetically pleasing, there is currently minimal impact on water quality. If successful the Fargo project may serve as a model for other municipalities to meet economic, natural and social demands of residents while treating water.

Municipal Water Use: A Comprehensive Study of Water Consumption across the State of North ��ֱ����

Nicole Ellingson, North ��ֱ���� State University

Little is known about municipal water use in communities across the state of North ��ֱ����. Typically, the only data reported is to the North ��ֱ���� State Water Commission regarding the total amount of water used as part of a municipal water permit. The goal of this study is to expand current knowledge on water use in the state. Specifically, the study looks at how water use information is stored around the state and what can be learned from it. The project is also attempting to classify water-use data into categories and sub-categories to determine per capita coefficients and normal commerce for different size municipalities. All municipalities in the state with populations greater than 1,000 residents were eligible to participate. A total of twenty-five municipalities participated by providing water-use data. Data was classified to the lowest level possible, into over fifty water use sub-categories. Cities were arranged into three groups based on population size and averages from all categories were compared between different size municipalities to determine if population size influences the average amount of water used per category. The results from this study will provide valuable information for planning purposes across the state of North ��ֱ���� and beyond.

Individual and synergistic effect of heavy metals on bacteria performance in activated sludge.

Sepideh Sadeghi, Civil Engineering Department, South ��ֱ���� State University

Biological treatment methods are the basis of waste water treatment worldwide. The control of the treatment process is complicated due to the large number of parameters that can affect it. Heavy metals in the wastewater influent can be stimulatory, inhibitory or even toxic in biochemical reactions depending on their concentrations. The toxic impact of selenium (Se) and hexavalent chromium (Cr6+) salts on activated sludge of Brookings wastewater treatment facilities has been studied with the help of respiration inhibition tests. The inhibitory doses of Se were found above 500 mg/L and the inhibitory doses of Cr6+ were above 0.05 mg/L. Activated sludge was much more resistant to Se than Cr6+. The combination effect of Se and Cr6+ on activated sludge was found to be stimulatory; the combination of 100, 200, and 500 mg/L Se with 0.05 mg/L Cr6+ negatively affected the activated sludge process, however 50 mg/L Se with 0.05 mg/L Cr+6 could enhance the microorganism performance in the activated sludge. Structure of microbial communities in activated sludge has also been investigated using Biolog plates (Eco-plates). The results showed that activated sludge microbial community fed with Se developed faster on the Biolog plates than the activated sludge microbial community fed with Cr6+.

Key words: biodegradation, selenium, hexavalent chromium, Biolog plate