Biological Removal of Nitrate from Drinking Water in Anoxic Bioreactor - Membrane Bioreactor Hybrid System

The main aim of the present study was evaluating the performance of a biological hybrid system comprising anoxic bioreactor and aerobic membrane bioreactor (MBR) with immersed micro-filter membrane for the nitrate removal from drinking water during 34 days of operation. Operational conditions were constant hydraulic retention time equal to 17 h and 36 h for anoxic bioreactor and MBR, respectively, influent nitrate-N concentration of 33.9 mg NO3-N/L, and C/N ratio equal to 2. The results demonstrated that nitrate removal efficiency in anoxic bioreactor was in the range of 73-97%. The effluent nitrite-N concentration from the hybrid system was in the range of 0.01-0.02 mg NO2-N/L. Both nitrate and nitrite concentrations in the effluent of system were always below the the World Health Organization (WHO) limit. The effluent chemical oxygen demand (COD) of the hybrid system was always less than 15 mg/L and COD removal efficiency of the system was 92.8±0.1 %. The effluent turbidity was also less than 2 NTU that represented membrane efficacy in preventing microbial mixture washout. The results of this research show that hybrid biological system of anoxic bioreactor-MBR has a very good potential for removing nitrate from drinking water.