Exploring multiple operating scenarios to identify low-cost, high nitrate removal strategies for electrically-stimulated woodchip bioreactors

Authors: LAW, JI YEOW - Iowa State University; SOUPIR, MICHELLE - Iowa State University; RAMAN, D. RAJ - Iowa State University; Moorman, Thomas

Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2018
Publication Date: 5/1/2018
Publication URL: http://handle.nal.usda.gov/10113/6363795
Citation: Law, J., Soupir, M.L., Raman, D., Moorman, T.B. 2018. Exploring multiple operating scenarios to identify low-cost, high nitrate removal strategies for electrically-stimulated woodchip bioreactors. Ecological Engineering. 120:146-153. https://doi.org/10.1016/j.ecoleng.2018.05.001.
DOI: https://doi.org/10.1016/j.ecoleng.2018.05.001

Interpretive Summary: The Midwestern United States is dominated by agricultural production on lands with artificial subsurface drainage which is an important source of nitrate pollution. Woodchip bioreactors are being implemented for the removal of nitrate in tile water drainage. 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. We explored the potential of using electrically stimulated woodchip bioreactors to achieve greater NO3-N removal and estimated the costs of this approach. Batch experiments were conducted to determine the denitrification efficiency of electrically stimulated and traditional woodchip bioreactors at different hydraulic residence times (HRT) and electrical current densities. The resulting data was used to model costs and denitrification efficiency in 75 scenarios, covering a range of bioreactor volumes, HRTs, current densities, and annual durations of electrical stimulation. We found that electrically stimulated woodchip bioreactors may remove an additional 37 to 72% annual NO3-N load than a traditional woodchip bioreactor, but at the expense of higher NO3-N removal costs, which were increased by 138 to 194%. This work informs engineers and conservationists on the design of electrically-stimulated woodchip bioreactors to obtain optimal and economic nitrate removal.

Technical Abstract: Woodchip bioreactors are recognized as an effective best management practice in the Iowa Nutrient Reduction Strategy. This edge-of-field practice intercepts and removes NO3-N, thereby reducing the NO3-N concentration in tile drainage before being discharged into surface water. Actual NO3-N load reductions realized by woodchip bioreactors are impacted by bioreactor size, hydraulic retention time (HRT), and denitrification efficiency. A typical woodchip bioreactor in Iowa may have 0.07% bioreactor area with respect to treatment area, 4 to 8 hour HRT, and 43% mean denitrification efficiency. Here, we explored the potential of using electrically-stimulated woodchip bioreactors to achieve greater NO3-N removal and estimated the costs of this approach. Batch experiments were conducted to determine the denitrification efficiency of electrically-stimulated and traditional woodchip bioreactors at different HRTs and current densities. The resulting data was used to model costs and denitrification efficiency in 75 scenarios, covering a range of bioreactor volumes, HRTs, current densities, and annual durations of electrical stimulation periods. For each scenario, we reported the estimated annual NO3-N load reduction and NO3-N removal cost. We found that electrically stimulated woodchip bioreactors may remove an additional 37 to 72% annual NO3-N load than a traditional woodchip bioreactor, but at the expense of higher NO3-N removal costs, which were increased by 138 to 194%.