Enhanced treatment of coke plant wastewater using an anaerobic–anoxic–oxic membrane bioreactor system

A laboratory-scale anaerobic–anoxic–oxic membrane bioreactor (A1/A2/O-MBR) system was used to treat heavily loaded and toxic coke plant wastewater and operated for more than 500 d. Treatment performance, acute toxicity assessment, and dissolved organic characteristics of the A1/A2/O-MBR system were investigated. The present (A1/A2/O-MBR) system was more efficient and reliable in pollutants and acute toxicity reduction than the conventional anaerobic–anoxic–oxic system tested in parallel as control especially at high and varying loading rates. When the total hydraulic retention times of the A1/A2/O-MBR system was 40 h, the average effluent COD, phenol, NH3-N, TN concentrations and acute toxicity were 264 ± 36 mg/L, 0.2 ± 0.1 mg/L, 0.8 ± 1.0 mg/L, 112 ± 47 mg/L and 0.17 ± 0.01 mg/L (Zn2+ toxicity reference), with removals of 89.8 ± 1.2%, >99.9%, 99.5 ± 0.7%, 71.5 ± 7.8% and 98.3 ± 0.3%, respectively. Hydrophobic/hydrophilic fractionation indicated that the hydrophobic acids were the most abundant fraction of dissolved organic matters in influent and effluent, accounting for 70.3%, 67.2% of total dissolved organic carbon, and 75.0%, 76.2% of total colour intensity, respectively. The hydrophilic substances of the oxic supernatant could be rejected effectively by the membrane. Fluorescence excitation–emission matrix (EEM) analysis suggested that humic substance-like matters were potentially refractory and colour causing matters in coke plant wastewater.