Post-Treatment of UASB Reactor Effluent by Coagulation and Flocculation Process K. Jaya Prakash, V.K. Tyagi, A.A. Kazmi, and Arvind Kumar Department of Civil Engineering, Indian Institute of Technology, Roorkee 247667, India; kazmifce@iitr.ernet.in (for correspondence) Published online 7 March 2007 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ep.10192 Exploratory experiments were performed to test the feasibility of coagulation and flocculation as a post- treatment process for the effluent of an Upflow Anaer- obic Sludge Blanket (UASB) reactor treating domestic sewage. Commonly used coagulants [alum, polyalu- minium chloride (PAC), ferric chloride, and ferric sulphate] were utilized in a series of jar tests to deter- mine 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 chemi- cal dosage was 20 mg/L (as Al) for alum 24 mg/L (as Al) for PAC, and 39.6 mg/L (as Fe) for FeCl 3 and 17.6 mg/L (as Fe) for FeSO 4 , respectively. Coagula- tion–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 coagu- lated effluent. It was found out that after coagula- tion, a chlorine dose of 1–2 mg/L can reduce the fecal coliforms to less than 1000 MPN/100 mL. Ó 2007 American Institute of Chemical Engineers Environ Prog, 26: 164–168, 2007 Keywords: chlorination, coagulation, jar test, post- treatment, UASB reactor INTRODUCTION The Upflow Anaerobic Sludge Blanket (UASB) pro- cess for the treatment of municipal wastewater is a pro- ven technology. Many full-scale UASB reactors have been built and are operating in India, Brazil, Colombia, and Egypt. However, the treatment of municipal waste- water by UASB alone cannot produce an effluent that meets the discharge standards of these countries [1]. In India, to discharge the effluent into rivers or streams the limits are; SS (100 mg/L), BOD (30 mg/L), COD (250 mg/L), total coliforms (10,000 MPN/100 mL), and Fecal coliforms (2500 MPN/100 mL). The UASB effluent does not achieve these concentrations. Therefore, this effluent cannot be used for irrigation. However, com- bined with a proper post-treatment process, anaerobic treatment can provide a good quality effluent when treating domestic sewage. Post-treatment may be performed by utilizing vari- ous processes such as a polishing pond, aeration, etc., to meet effluent discharge standards [2]. Recently, the use of several post-treatment systems has been described. The processes include, Rotating Biologi- cal Contractor (RBC), Expanded Granular Sludge Bed (EGSB), Downflow Hanging Sponge (DHS), Waste Stabilization Ponds (WSP), and Constructed Wetlands [3]. Post-treatment in a combined duckweed and algae pond system was able to remove (60 6 32)% of UASB effluent BOD while removal of fecal coliforms was *(99.60–99.95)%, thus raising the overall effi- ciency of BOD and fecal coliforms of combined sys- tem (UASB reactor and pond system) to 90% and 99.90–99.99% respectively [4]. The combination of UASB and Biofilter has been shown to be useful in tropical and subtropical areas due to low production of sludge while at the same time producing a better effluent. Removal efficiencies of 88% and 85% for SS and COD removal, respectively, were achieved. How- ever, the combination of these treatment processes did not produce a bacteriologically acceptable efflu- ent. Disinfection is still necessary [5]. From the above discussion, it can be concluded that none of the treatment technologies for post-treatment Ó 2007 American Institute of Chemical Engineers 164 July 2007 Environmental Progress (Vol.26, No.2) DOI 10.1002/ep