Evaluation of simultaneous organic matters and nutrients removal from municipal wastewater using a novel bioreactor...

A novel bioreactor, the divisional influent dual-anaerobic-anoxic/oxic (D-A²O) system, was applied to treat municipal wastewater. This new system improved the removal efficiency of simultaneous organic matters and nutrients, and provided a reduction in the system's energy costs and sludge yield. Results from the reactor's 18 months of operation demonstrated the following optimal conditions for the 4 key parameters of the system: (1) a divisional ratio (DR) of 8:2 between the influent flow volumes fed into the anaerobic and anoxic tanks, (2) a hydraulic retention time (HRT) of 6 h, (3) a R:r ratio of 200%:100% between the mixed liquor return ratio (R) and the return activated sludge ratio (r), and (4) an alternative operating time (t_A/B) of 1 h for the A/B anaerobic-anoxia series. Under optimal conditions, the system showed a high removal efficiency for the chemical oxygen demand (COD), total nitrogen (TN), ammonia nitrogen (NH₃-N), and total phosphorus (TP) removals, with the average removal efficiencies (with a standard deviation of less than 3%) being 95.23%, 80.64%, 90.42%, and 90.03%, respectively. The final concentration ranges of COD, TN, NH₃-N, and TP in the effluent were 26-48 mg L^-1, 6.11-11.03 mg L^-1, 2.93-4.04 mg L^-1, and 0.21-0.45 mg L^-1, respectively. The concentrations of the pollutants in the effluent from the D-A²O system were lower than those required for Level 1A (Chinese quality of wastewater discharge standard GB18918-2002). According to the results, we concluded that the divisional influent dual-anaerobic-anoxic system (which integrated the A²O and sequencing batch reactor (SBR) process) was successfully provided sufficient carbon sources for denitrification and phosphorus uptake without external carbon addition. Compared to the conventional anaerobic-anoxic/oxic (A²O) process, the D-A²O system offers a high removal efficiency, simple operation, and significant energy saving of about 0.276 kWh m^-3 based on the volume of the treated water. Therefore, the new D-A²O system has a strong potential for use in treatment plants.