Evaluation of simultaneous organic matters and nutrients removal from municipal wastewater using a novel bioreactor (D-A2O) system

Abstract

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 (tA/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.