The comparison of treatability of raw and anaerobically pre-treated domestic sewage by a sequencing batch reactor system

In this study, the treatability of raw and anaerobically pre-treated domestic sewage in sequencing batch reactor systems was compared. In this context, two sequencing batch reactors, the first one (SBR1) fed with raw domestic sewage and the second one (SBR2) fed with anaerobically pre-treated domestic sewage, were operated at six cycles per day operation. The feeding was introduced into the reactor by pumping for 30 min (the last 15 min with mixing), mixed and aerated for 180 min, followed by 20 min of settling. The effluent COD concentrations of SBRs were 50-70 mgL^-1. The effluent orthophosphate concentrations of SBR 1 and SBR 2 were 4-1.5 mgL^-1 and 5.5-3 mgL^-1, respectively. Experimental results showed that in both SBR1 and SBR 2 the removal efficiency of NH₄-N was about 100%, and nitrification rates in SBR1 and SBR2 were 12.2 mg g^-1 VSS h ^-1 and 21.8 mg g^-1 VSS h^-1, respectively. Activated sludge samples for microscopic and microbiological examinations have been collected from both reactors. The SBR1 activated sludge system showed better and richer microbial diversity structure, and the filamentous bacteria abundances have frequently reached high values in the SBR2 system. On the other hand, because of macrostructure failure and loose floc structure, the effluent quality and treatment efficiency of the SBR2 system was not so good as in SBR1 system.