Simultaneous organic carbon and nitrogen removal from refractory petrochemical dry-spun acrylic fiber wastewater by hybrid A/O-MBR process

Abstract

To improve the efficiency of the existing plant for refractory petrochemical dry-spun acrylic fiber (DAF) wastewater treatment, a pilot-scale hybrid anoxic/oxic-membrane bioreactor (A/O-MBR) system with multi-cell section was designed and tested. The operation parameters, alkalinity and carbon source demands in nitrification/denitrification and removal performance of typical pollutants were investigated, and the results were compared with those from the existing wastewater treatment plant (WWTP) of DAF factory. It showed that at hydraulic retention time >32 h, recycle ratio of 80 % and pH 7.2–7.8 in nitrification stage, the average removal efficiency of COD, NH4 +–N and TN in the hybrid A/O-MBR could reach 56.5, 86.6 and 45.9 %, respectively, which had been significantly higher than those of the existing WWTP. The deficiency of alkalinities and carbon sources hindered further nitrogen removal; therefore, Na2CO3 and NaAc were supplemented to improve the performance of nitrification and denitrification, and the recycle ratio was optimized from 80 to 200 %. Then, under the conditions of 200 % recycle ratio, 97.8–148.5 mg/L of alkalinity addition to oxic tank and 107.4–149.6 mg/L of carbon source addition to anoxic tank, the nitrification and denitrification performance in the hybrid A/O-MBR was clearly enhanced, and the NH4 +–N and TN removal efficiency could be improved from 64.3 and 45.9 to 86.9 and 60.5 %, respectively. Meanwhile, the removal efficiency of typical pollutants SO3 2−, CN−, AN, DMF, BOD and TOC reached 99.3, 91.3, 100, 100, 92.5 and 53.5 %, respectively. Compared with the existing WWPT, the tested hybrid A/O-MBR process had a better treatment performance for nitrification and denitrification, and the effluent could meet the Grade I requirements of the National Discharge Standard of Acrylic Fiber Industry.