THE EFFECTS OF DRAINAGE DITCH FILTER COMPOSITION ON HYDRAULIC PROPERTIES AND P SORPTION

Phosphorus (P) in agricultural runoff is considered a primary contributor to waterway eutrophication. Currently filters made with P-sorbing materials (PSMs) in drainage ditches have been shown to effectively remove P in some situations, but further optimization is necessary. Sorption isotherms were used to determine PSM and temperature effects on P sorption. No effect was found due to temperature, although significant differences were found among the materials used. The different mechanisms of P sorption suggest the retention time used was not suitable for this study. A mesocosm experiment was set up to maximize the flow through filters by mixing gypsum with sand to increase the hydraulic conductivity without sacrificing P sorption. The mixture containing 90% mined gypsum and 10% sand had the highest hydraulic conductivity without a reduction in total P sorption. The mixture containing 80% mined gypsum and 20% sand could have potential as an alternate mixture