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This project assessed the potential of woodchip bioreactors to remove multiple water quality contaminants, including nitrogen, phosphorus and bacteria, which are especially important in agricultural landscapes with integrated livestock and cropping systems. While much emphasis in Iowa has been focused on nitrate removal, it is equally important to consider removal of phosphorous and bacteria to meet the goals of the nutrient reduction strategy and to address impaired waters across the state. We addressed this goal by monitoring several field bioreactors located on private land and also by conducting laboratory experiments. Our field results generally showed reduction of fecal indicator bacteria concentrations, but we found mixed results for phosphorus removal. New studies are suggesting that materials designed to sorb phosphorus such as steel slag need to be added to bioreactors for consistent phosphorus removal to be achieved. Both our field monitoring and laboratory experiments show that woodchip bioreactors have potential to remove bacteria.
The second phase of the project addressed a new method to increase nitrate removal in woodchip bioreactors through electrical stimulation. As this practice has not been previously studied in a woodchip environment, our work was conducted in the laboratory. From our work we have shown that the electrical stimulation does indeed lead to increased nitrate removal and we also identified design parameters under which the electrical stimulation is likely to be most cost effective. The NO3-N removal cost ($4.49/kg-N) using electrically stimulated woodchip bioreactors is still within the range of other BMPs costs ($0.12 to $36.00), and thus we conclude that this treatment is a viable alternative when nutrient removal is of high priority.