Post‐treatment of UASB reactor effluent by coagulation and flocculation process

Exploratory experiments were performed to test the feasibility of coagulation and flocculation as a post-treatment process for the effluent of an Upflow Anaerobic Sludge Blanket (UASB) reactor treating domestic sewage. Commonly used coagulants [alum, polyaluminium chloride (PAC), ferric chloride, and ferric sulphate] were utilized in a series of jar tests to determine the optimum coagulant dose. The total and fecal coliforms in the effluent were less than 100,000 MPN/100 mL and 10,000 MPN/100 mL, respectively. It was found that all the tested coagulants were effective in reducing the effluent BOD and SS to less than 20 mg/L and 50 mg/L, respectively. The optimum chemical dosage was 20 mg/L (as Al) for alum 24 mg/L (as Al) for PAC, and 39.6 mg/L (as Fe) for FeCl3 and 17.6 mg/L (as Fe) for FeSO4, respectively. Coagulation–flocculation alone was not sufficient to reduce the fecal coliforms concentration to a permissible limit (1000 MPN/100 mL) for unrestricted irrigation. Thus, it would be necessary to disinfect the coagulated effluent. It was found out that after coagulation, a chlorine dose of 1–2 mg/L can reduce the fecal coliforms to less than 1000 MPN/100 mL. © 2007 American Institute of Chemical Engineers Environ Prog, 2007.