Nitrate Removal from Drinking Water in a Packed-Bed Bioreactor Coupled by a Methanol-Based Electrochemical Gas Generator

Removal of nitrate from drinking water by a coupling of methanol-based electrochemical hydrogen and carbon dioxide generator and a packed-bed bioreactor was investigated. The major goal was to study the performance of this integrated system for simultaneous, economical, in situ, and on-demand electron donor and carbon source production for hydrogenotrophic denitrification of drinking water in actual scales. The ability of system has been evaluated for treatment of natural underground water up to 120 mg NO3-/L (threefold of the drinking water limit) nitrate concentration. Removal efficiencies above 95% were achieved for more than 150 days of operation at a 2-5 h retention time. Furthermore, the system was operated only by injection of two harmless gases (produced by electrolysis of methanol) and without any chemical addition (solid or liquid). In the electrolysis process, H-2 and CO2 (H-2 as an electron donor and CO2 as a carbon source for denitrifier bacteria) was produced cheaply and simultaneously by applying a very low DC voltage (4-6 V) to a solution that includes an easily oxidizable organic substance (methanol) and electrolyte solution comprised water and a base. In situ and under control generation of H-2 and CO2 by an efficient, cost-effective way showed that this process can be an acceptable and reliable system for treatment of nitrate contaminated drinking water in actual scales. Additionally, convenient process operation without need of high pressure and explosive gas cylinders and only by voltage adjustment is other advantage of the process. (C) 2009 American Institute of Chemical Engineers Environ Prog, 29: 278-285, 2010