Advanced treatment of low-pollution and poor biodegradability sewage by combined process

Abstract

A system was developed for the treatment of low-pollution sewage with poor biodegradability and a low ratio of chemical oxygen demand (CODCr) to nitrate-nitrogen (COD/NO3−-N (C/N)) ratio to achieve high efficiency. This system combines the anaerobic-oxic (AO) process with the biological aerated filter (BAF) and introduces the Fenton advanced oxidation process. A pilot test system was established, and feasibility investigations were conducted using a continuous flow of 500 L/h. The results showed that the optimal conditions for removing nitrate from sewage were achieved with a C/N ratio of 5.5–6 and a hydraulic retention time (HRT) of 4 h. Under these conditions, the average nitrate removal efficiency was 83.36%, and the average concentration of total nitrogen (TN) in the effluent was reduced to 6.68 mg/L. Additionally, the Fenton oxidation treatment was effective in reducing the COD content of sewage, with an average removal efficiency of 82.47% and a decrease in CODCr from 55.24 mg/L to 9.68 mg/L. The combined process successfully met the stringent discharge standards after advanced treatment. Microbial community analysis revealed that the dominant genera in anoxic BAFs were Trichococcus, Comamonadaceae, Lentimicrobium, and Thauera, while the dominant genera in aerobic BAFs were mainly Acinetobacter, Thiothrix, Gemmobacter, and Caldilineaceae. The synergistic effect of various nitrifying and denitrifying bacteria in BAFs effectively removed nitrate from the sewage. Furthermore, GC-MS analysis indicated that the Fenton oxidation significantly reduced the concentration of refractory organic compounds in the sewage, including long-chain organic compounds and acrylic acid maleic acid copolymer (MA/AA). After upgrading and renovating the factory's sewage treatment facilities, the impact of the discharged effluent on the receiving drainage basin will be minimized.