Treatment of produced water from polymer flooding in oil production by the combined method of hydrolysis acidification-dynamic membrane bioreactor–coagulation process

In order to treat produced water from polymer flooding (PWPF), a new treatment method of combining hydrolysis acidification-dynamic membrane bioreactor (DMBR)–coagulation process was developed. The experimental results demonstrated that the highest acidification efficiency in hydrolysis acidification reactor (HAR) was 10.98% under hydraulic retention time (HRT) of 12 h. During the stable stage of dynamic membrane, the average concentration of ammonia nitrogen (NH3–N) and chemical oxygen demand (COD) in effluent from DMBR was 1.50 and 476.63 mg/L, respectively, while the concentration of oil was too low to be detected. In coagulation process, when the effluent from DMBR at pH 9.0 was treated directly, the COD removal efficiency could reach 89.41% with Aluminum sulfate (Al2(SO4)3) under the dosage of 140 mg/L. However, the dosage of Al2(SO4)3 would decrease to 80 mg/L with the same COD removal efficiency (88.37%) under the optimal pH 5.0. The combined process operated continuously for 30 days and the final effluent could meet the class I National Wastewater Discharge Standard of China. (GB 8978-1996).