Christine Lepine Philip Sibrell Chad J. Penn Steven T. Summerfelt Laura E. Christianson 2017 <p><span>Pairing denitrifying woodchip bioreactors and phosphorus-sorbing filters provides a unique, engineered approach for dual nutrient removal from waters impaired with both nitrogen (N) and phosphorus (P). This column study aimed to test placement of two P-filter media (acid mine drainage treatment residuals and steel slag) relative to a denitrifying system to maximize N and P removal and minimize pollution swapping under varying flow conditions (i.e., woodchip column hydraulic retention times (HRTs) of 7.2, 18, and 51&nbsp;h; P-filter HRTs of 7.6–59&nbsp;min). Woodchip denitrification columns were placed either upstream or downstream of P-filters filled with either medium. The configuration with woodchip denitrifying systems placed upstream of the P-filters generally provided optimized dissolved P removal efficiencies and removal rates. The P-filters placed upstream of the woodchip columns exhibited better P removal than downstream-placed P-filters only under overly long (i.e., N-limited) retention times when highly reduced effluent exited the woodchip bioreactors. The paired configurations using mine drainage residuals provided significantly greater P removal than the steel slag P-filters (e.g., 25–133 versus 8.8–48&nbsp;g&nbsp;P removed m</span>⁻³<span> filter media d</span>⁻¹<span>, respectively), but there were no significant differences in N removal between treatments (removal rates: 8.0–18&nbsp;g&nbsp;N removed m</span>⁻³<span> woodchips d</span>⁻¹<span>; N removal efficiencies: 18–95% across all HRTs). The range of HRTs tested here resulted in various undesirable pollution swapping by-products from the denitrifying bioreactors: nitrite production when nitrate removal was not complete and sulfate reduction, chemical oxygen demand production and decreased pH during overly long retention times. The downstream P-filter placement provided a polishing step for removal of chemical oxygen demand and nitrite.</span></p> application/pdf 10.1016/j.watres.2017.05.026 en Elsevier Denitrifying woodchip bioreactor and phosphorus filter pairing to minimize pollution swapping article