Paired Woodchip Bioreactors and P-Filters for Combined Nutrient Removal from Agricultural Effluents.

Accelerating use of woodchip-based denitrification technologies to remediate nitrogen (N) contaminated water provides the potential to also capture and treat other pollutants through more advanced designs. Phosphorus (P) in agricultural effluents and runoff waters is of increasing concern in many watersheds that are also impaired by N. Anecdotal evidence that woodchips may leach P creates a critical opportunity to combine woodchip bioreactors and P-sorbing filters into a paired end-of-pipe technology.  A column experiment at The Conservation Fund’s Freshwater Institute (Shepherdstown, WV, USA) pairing woodchips with either acid mine drainage treatment residuals or steel slag assessed the effectiveness of P-filter placement relative to woodchips as well as the impact of varying hydraulic loadings on both N and P removal. Plastic columns packed with woodchips (15 cm diameter; 60 cm length) were placed either upstream or downstream of columns containing one of the two P-filter media (2.5 cm diameter; approximately 40-60 cm bed depth). Water samples were collected prior to, between, and following each of the paired columns and analyzed for parameters including nitrate-N and dissolved reactive P.  It was thought that placing the P filter media downstream of the woodchips would help mitigate any potential P leaching from the woodchips. Expected results will help improve the design of paired nutrient removal technologies, and preliminary results will be presented.