The main goal of this study was to provide information on the nitrate and phosphorus removal efficiencies of woodchip, biochar, and corn cobs. Woodchip bioreactors have proven effective in removing nitrate-nitrogen (NO3-N) from agriculturally drained water in the Midwest USA region. Both nitrate and phosphorus can lead to hypoxia and algal blooms in the receiving surface waters and degrade the water quality. This study explored the effectiveness of bioreactor technology in removing NO3-N and orthophosphate, and the emission of N2O from different media. Three types of media were examined in a pilot-scale lab experiment: deciduous mixed hardwood chips, biochar chips (created from the same type of woodchip), and corn cobs. Chemically formulated water was fed through each system using a residence time of 24 hours, and later on, 8 hours.
NO3-N reduction occurred in all three media, although biochar showed a relatively longer lag time. An average of 9.26g N/d/m3 NO3-N total loading reduction was observed from the 24 hours retention time when the total input was 588.82g. An average of 0.35g orthophosphate/d/m3 of the orthophosphate loading was reduced while the input phosphorus was 6.10g, with the biochar media providing the most reduction in outflow orthophosphate concentration. A lower reduction rate and higher nitrate output was observed from the 8 hours retention time. However, corn cobs showed the highest total nitrate removal rate of 22.40g N/d/m3 while the total input was 1156.70g. The orthophosphate reduction rates were not significantly different among the three media (ranging from 0.67g orthophosphate/d/m3 to 0.86g orthophosphate/d/m3) with a total input of 11.10g. Given the recent development of state-wide nutrient management plans to reduce nutrient concentrations in surface water, study results of these technologies will help the row-crop producer community manage nutrient export to surface water.