A²O-MBR-BAF-O₃ process for treating fractory domestic sewage mixed with industrial sewage

The seriously polluted water environment leads to a high level of refractory organic matter in the water intake of some sewage treatment plants.To solve the vexed water pollution, the anaerobic-anoxic-aerobic (A²O)—membrane bioreactor (MBR)—biological aerated filter (BAF) -ozone(O₃) process was used for treating degradation-resistant domestic sewage mixed with industrial sewage to provide reference for the upgrading. The hydraulic retention time (HRT), internal reflux ratio of the intermixture and O₃ contact time were optimized. At the same time, chemical oxygen demand (COD), ammonia nitrogen (NH₄⁺-N), total nitrogen (TN) and chroma were degraded. The results showed that the optimal operating conditions are as follows: HRT = 10 h, reflux ratio = 250% and O₃ contact time = 10 min. On this basis, the removal rates of COD, NH₄⁺-N, TN, total organic carbon (TOC), UV₂₅₄, and chroma were 94.14%, 99.00%, 81.75%, 95.20%, 94.70%, and 83.31%, respectively. It showed that the process can effectively degrade refractory organic matters and chroma. The water quality indexes of the effluent met the Class IV surface water standard in the "Surface water Environmental Quality Standard" (GB3838-2002). Graphical abstract: (Figure presented.)