Post-treatment of effluent from UASB reactor by surface aerator

Abstract

Effluent from full-scale and bench-scale upflow anaerobic sludge blanket reactors (UASBRs) was aerated by surface aerator. The monitoring parameters used for process were oxidation reduction potential (ORP), dissolved oxygen (DO), chemical oxygen demand (COD) and biochemical oxygen demand (BOD). Experiments were conducted on effluents of bench-scale 56-L UASB reactor as well as on the effluents from four UASB-based sewage treatment plants (STPs) of capacities ranging from 34 to 70 ML/d (million liters per day). The linear relationship between DO and ORP indicates the sensitivity of ORP. The rate of DO transfer depends on ORP, DO deficit, nature and concentration of BOD or COD. The ORP values increased with aeration time indicating improvement in redox status. The oxygen demand of anaerobically treated effluent proceeds in three-stage initial S-BOD exertion followed by CBOD exertion and subsequently NBOD exertion. The optimum condition for BOD, COD and sulfide removal was 120–140 min characterized by DO content of 4–5 mg/L. Sulfides removal rate of 80% and BOD of 30 mg/L desired discharge standards were obtained.