Optimization of A2O-MBR-BAF-O3 combination process for domestic wastewater

In order to remove pollutants in domestic wastewater more completely, the anaerobic-anoxic-oxic (A(2)O)-membrane bioreactor (MBR)-biological aerated filter (BAF)-O-3 combination process was studied. The ultrafiltration membrane was placed inside the A(2)O reactor to form an integrated reactor. The experimental water was sequentially degraded by A(2)O-MBR, BAF, and O-3 reactor. The three operating parameters of hydraulic retention time (HRT), reflux ratio, and ozone contact time were optimized. The optimal conditions were found in the experiment: HRT was 10 h, reflux ratio was 200%, and ozone contact time was 15 min. Under these optimal conditions, the removal rates of chemical oxygen demand (COD), ammonia nitrogen, total nitrogen (TN), total organic carbon (TOC), UV254, and chroma were 96.00, 99.43, 82.46, 96.6, 93.20, and 79.00%, respectively. The effluent quality satisfied standard of Class IV surface water in China. The ultraviolet-visible and excitation-emission matrix spectra of water samples during the ozone oxidation were analyzed. It showed that the reaction was effective in removing chroma and humic acid-like substances in the wastewater.