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

Law, J.Y., Soupir, M.L., Raman, D.R., Moorman, T.B.
Ecological engineering 2018 v.120 pp. 146-153
best management practices, bioreactors, denitrification, electrical treatment, models, nitrate nitrogen, nitrates, pollution control, surface water, tile drainage, water pollution, wood chips, Iowa
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, 4–8 h 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 37–72% annual NO₃-N load than a traditional woodchip bioreactor, but at the expense of higher NO₃-N removal costs, which were increased by 138–194%.