Anaerobic-anoxic-aerobic sequential degradation of synthetic wastewaters

This study was conducted in a continuous three-stage system of anaerobic (R1)--anoxic (R2)--aerobic (R3) reactors with synthetic wastewater containing phenol (1000 mg/L), chemical oxygen demand (COD) (3000 mg/L), CN- (30 mg/L), SCN- (400 mg/L), and NH4+-N (600 mg/L) as principal pollutants and well-acclimated heterogeneous microbial cultures. The final effluent was partially returned to R2 with a recycle ratio of 1. Anaerobic stage served to detoxify the feed by removing up to 80% of cyanide. Complete SCN- removal and denitrification could be achieved in the anoxic stage by utilizing phenol as an internal source of carbon. Nitrification efficiency of 93% was obtained in the aerobic reactor. The results demonstrated that the three-stage system can give the desired final treated effluent quality (0 mg/L of phenol, 0.2 mg/L of CN-, 210 mg/L of COD, and 20 mg/L of NH4+-N) and that the NO3(-)-N concentration can be lowered by a higher recycle ratio.