Anaerobic sequencing batch reactors in pilot-scale for domestic sewage treatment

The comparative performance of three pilot-scale anaerobic sequencing batch reactors treating domestic sewage from the University of Sao Paulo (Sao Carlos City, Brazil) was evaluated. Physical, chemical and physicochemical variables were accessed in the influent and in the effluent for performance evaluation. The three ASBR reactor with 1.2 m(3) (total volume) each had different geometric characteristics (ratio L-length/D-diameter) and mixing type (mechanical mixer or liquor recirculation) and were designed for the treatment of 1.95 m(3).d(-1) of domestic sewage. The reactors were operated at 8-h sequential batch cycles during 70 days (loading rate: 0.6-1.2 kgCOD.m(-3).d(-1)) and inoculated with anaerobic granular sludge. The two ASBR (ASBR1 and ASBR3) reactors operated under mixed liquor recirculation showed non-satisfactory results, attaining mean values of COD and TSS removals efficiencies of 40% and 65%, respectively. The mean effluent values were of 320 mgCOD l(-1) and 85 mgTSS l(-1). The ASBR2 operated under mechanical mixing showed better results with average removal efficiencies of 60% and 80% for COD and TSS, respectively. The mean values of effluent COD and TSS were 215 mg l(-1) and 50 mg l(-1), respectively.