Reclamation of Tile Effluent: Denitrifying Woodchip Bioreactors

Tile drainage systems transfer leached nitrate to bodies of water and contribute to hypoxia in the Gulf of Mexico. Performance of denitrification of woodchip bioreactors was conducted through column experiments at various retention times. Field tile water (10–11 mg/L NO₃—N) was pumped through columns packed with wood chips at three different retention time (8, 6.3, and 4.2 hours). Soil was used to amend the column media to test if additional bacteria would enhance denitrification. Synthetic tile water was prepared (12 mg/L NO₃—N) and used to test for the presence of denitrifying bacteria in wood chips. Effluent nitrate concentrations were found to be dependent on the retention time. Removal efficiencies were found to be of 39, 76 and 96% at 4.2, 6.3 and 8 hours of retention time, respectively. Based on the results of this experiment, effluent nitrate concentrations below the EPA's MCL requirements of 10 mg/L NO₃—N are possible with longer retention times. Additionally, these results suggest that utilization of denitrifying bioreactors could be feasible to reclaim California groundwater if the nitrate content is above MCL's and the water is not intended for drinking.