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 (A²O)–membrane bioreactor (MBR)–biological aerated filter (BAF)–O₃ combination process was studied. The ultrafiltration membrane was placed inside the A²O reactor to form an integrated reactor. The experimental water was sequentially degraded by A²O–MBR, BAF, and O₃ 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.