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Woodchip bioreactors are being implemented for the removal of nitrates in groundwater and tile water drainage. However, low nitrate removals in denitrifying woodchip bioreactors have been observed for short hydraulic retention time (HRT) and low water temperature (°C). One potential approach to improve woodchip bioreactor performance is to provide an alternative and readily available electron source to the denitrifying microorganisms through electrical stimulation. Previous work has demonstrated the capability of bio-electrochemical reactors (BER) to remove a variety of water contaminants, including nitrate, in the presence of a soluble carbon source. The objective of this study was to evaluate the denitrification efficiency of electrically augmented woodchip bioreactors and conduct a simple techno-economic analysis (TEA) to understand the possibilities and limitations for full-scale BER implementation for treatment of agricultural drainage. Up-flow column woodchip bioreactors were studied included two controls (non-energized, and without electrodes), two electrically enhanced bioreactors, each using a single 316 stainless steel anode coupled with graphite cathodes, and two electrically enhanced bioreactors, each with graphite for both anode and cathodes. Both pairs of electrically enhanced bioreactors demonstrated higher denitrification efficiencies than controls when 500 mA of current was applied. While this technology appeared promising, the technoeconomic analysis showed that the normalized N removal cost ($/kg N) for BERs was 2-10 times higher than the base cost with no electrical stimulation. With our current reactor design, opportunities to make this technology cost effective require denitrification efficiency of 85% at 100 mA. This work informs the process and design of electrically stimulated woodchip bioreactors with optimized performance to achieve lower capital and maintenance costs, and thus lower N removal cost. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. A B S T R A C TWoodchip bioreactors are being implemented for the removal of nitrates in groundwater and tile water drainage. However, low nitrate removals in denitrifying woodchip bioreactors have been observed for short hydraulic retention time (HRT) and low water temperature (< 10°C). One potential approach to improve woodchip bioreactor performance is to provide an alternative and readily available electron source to the denitrifying microorganisms through electrical stimulation. Previous work has demonstrated the capability of bio-electrochemical reactors (BER) to remove a variety of water contaminants, including nitrate, in the presence of a soluble carbon source. The objective of this study was to evaluate the denitrification efficiency of electrically augmented woodchip bioreactors and conduct a simple techno-economic analysis (TEA) to understand the possibilities and limitations for full-scale BER im...

Woodchip denitrification bioreactors are an important edge-of-field practice for treating agricultural drainage; however, their ability to filter microbial pollutants has primarily been explored in the context of wastewater treatment. Upflow column reactors were constructed and tested for E. coli, Salmonella, NO3-N, and dissolved reactive phosphorus (DRP) at hydraulic retention times (HRTs) of 12 and 24 h and at controlled temperatures of 10 and 21.5 °C. Influent solution was spiked to 30 mg L−1 NO3-N, 2-8 × 105 E. coli and Salmonella, and 0.1 mg L−1 DRP. Microbial removal was consistently observed with removal ranging from 75 to 78% reduction at 10 °C and 90-96% at 21.5 °C. The concentration reduction ranged from 2.75 to 9.03 × 104 for both organisms. HRT had less impact on microbial removal than temperature and thus further investigation of removal under lower HRTs is warranted. Nitrate concentrations averaged 96% reduction (with load removal of 14.6 g N m−3 d−1) from 21.5 °C columns at 24 HRT and 29% reduction (with load removal of 8.8 g N m−3 d−1) from 10 °C columns at 12 HRT. DRP removal was likely temporary due to microbial uptake. While potential for removal of E. coli and Salmonella by woodchip bioreactors is demonstrated, system design will need to be considered. High concentrations of these microbial contaminants are likely to occur during peak flows, when bypass flow may be occurring. The results of this study show that woodchip bioreactors operated for nitrate removal have a secondary benefit through the removal of enteric bacteria.

Best management practices (BMPs) are effective in reducing nutrient and sediment export, but further understanding of the benefits of the stacked BMPs is needed. This catchment-scale study was established to evaluate the impact of hydrology and BMPs on phosphorus (P) and sediment losses. Two adjacent catchments, one with a lower level of BMP adoption (Low-BMP #11) and one with a higher level (High-BMP #12), were compared for total P (TP) and total suspended solids (TSS) export. The BMPs include nutrient management plans, reduced tillage, grassed waterways, terraces, and perennial vegetation. The TP event-flow-weighted (EFW) concentration was significantly higher at Low-BMP #11 (0.293 mg L −1) than at High-BMP #12 (0.069 mg L −1). There was no significant difference in TP base-flow-weighted (BFW) concentrations between Low-BMP #11 (0.035 mg L −1) and High-BMP #12 (0.037 mg L −1). The TSS-EFW (148.0 vs. 18.6 mg L −1) and TSS-BFW (13.3 vs. 6.9 mg L −1) concentrations were also higher at Low-BMP #11 than at High-BMP #12. High-BMP #12 had lower TP (0.36 vs. 0.59 kg ha −1 yr −1) and TSS (253 vs. 1,961 kg ha −1 yr −1) loading than Low-BMP #11. The lower TP export at High-BMP #12 was likely attributed to the effectiveness of stacked erosion control BMPs and nutrient management plans. Overall, lower P and sediment loading was observed when a greater areal extent of stacked practices was implemented at the catchment level. This finding provides vital information to encourage wider BMP adoption at the watershed scale.

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