Improving Denitrifying Bioreactor Performance By Adding a Post-Bed Processing Chamber.

Higher nitrate-nitrogen (N) removal rates (NRR) can be achieved using corn cobs (CC) as a denitrifying bioreactor medium rather than wood chips; however, CC tend to release additional total organic carbon (TOC).  This study was conducted to investigate the potential to remove additional nitrate-N and to reduce TOC at snowmelt (2 degC) and growing season (16 degC) temperatures by adding a chamber of plastic biofilm carrier (PBC) after the primary chamber containing the CC.  Corn cobs were packed into six 15-cm dia. by 50-cm long PVC columns.  Onto three of these columns, a 25-cm long chamber packed with PBC was added (CC+PBC).  Water (50 mg/L nitrate-N) was pumped through the columns for six months at 16 degC at a 12-h primary-chamber hydraulic residence time.  The columns were disassembled, media sampled for microbial analysis, repacked with fresh media and the experiment repeated at 2 degC.  The nitrate-N load reductions were elevated for the CC+PBC treatment at both temperatures.  The NRR, expressed in units of (gN/m³/d) was lower for CC+PBC when the volume of the non-carbon-contributing plastic medium was included.  The effluent TOC concentrations were not different for CC and CC+PBC; however, nitrous oxide production was significantly and consistently lower in CC+PBC compared with CC.  The promising findings demonstrate that adding a compartment filled with a non-consumable medium with high specific surface area to the outlet end of a denitrifying bioreactor can improve denitrifying bioreactor performance.