Phosphorous removal from agricultural tile drainage effluent with activated alumina in novel adsorption

Subsurface tile drains under agricultural field crops are a major source of phosphorus (P) discharge to aquatic ecosystems, contributing to the eutrophication of surface waters. Adsorption reactors for P removal from drainage water (P-reactors) could reduce P outflow from agricultural land but were rarely studied in cold, temperate climates. In our study, four low-cost P-reactors were installed in agricultural fields in south-central Québec, Canada. Activated alumina (AA) beads were used as P-adsorptive material, and the reactors were connected to tile drain outlets. Paired water samples (39 events) from reactor inlets and outlets were analyzed for P species and other physicochemical parameters during one calendar year to assess the P removal from tile drain effluent in the P-reactors. Collectively, the P-reactors retained approximately half (48%) of the total mass of P flowing through the tile drains, mostly (92%) as particulate P. The mass of AA beads adsorbed 11% of the dissolved-P fractions. Results are interpreted in the context of the field drainage area and will require adjustments to the P-reactor design to accommodate larger fields. The P-reactors remained structurally intact throughout all four seasons in a cold temperate climate, showing the potential of simple, inexpensive P-reactors to reduce P concentration in tile drain effluent. .Water draining from agricultural fields contains phosphorus in dissolved and suspended forms. As we need to minimize the phosphorus transported from agricultural fields to rivers and lakes, the authors designed a filter system to retain the phosphorus at the end of the field. These filters, called phosphorus adsorption reactors, removed almost half of the phosphorus from water leaving the drainage pipe. Suspended phosphorus was more efficiently retained than dissolved phosphorus within the filter system. Design modifications are proposed to increase the efficiency of the filter. It was simple and inexpensive to build the filter, which functioned year-round, even in the winter when the field was covered by a thick layer of snow. We recommend installing filters at the end of the field to reduce the phosphorus losses in agricultural drainage water.