Two bench-scale activated sludge Sequencing Batch Reactors(SBR's), with working volumes of 100 liters each, operated onsynthetic wastewater at sludge retention times (SRT) of 7 days(Reactor 1) and 15 days (Reator 2) respectively. Biologicalphosphorus and nitrogen removals were applied in the systems to studynitrification, denitrification, and phosphorus removal kineticsduring the start-up phase. Excellent enhanced biological phosphorusremoval was achieved in both reactors within 21 days. The maximumphosphorus release rate in each reactor was 10-mg PO_4-P/g. MLSS.h at20 deg C and phosphorus contents of about 5/100 dry weight of biomasswere achieved. In Reactor 2, very good nitrificaiton was achievedwith 100/100 ammonia removla within initial two weeks of operation.The maximum nitrificaiton rate was 3.0 mg NO_3-Ng. MLSS.h, but laterphosphorus release rates continued to decline, due to the elevatedremaining nitrate concentrations from preceding cycles in the initialfill and mix phase. Remaining nitrate consume sinfluent organicduring the fill and mix phase, decreasing the availability of organicmatter for phosphorus removing bacteria, thus deteriorating theiractivity. For SBR 1, phoshorus release rates didnt shows any decline,as incomplete nitrification led to much lower nitrate during theinitial fill and mix phase. The present study implied that higher SRTis beneficial for phosphorus removal. But later, SRT should bereduced to decrease the nitrification activity, if the target isphosphorus removal, otherwise remaining elevated nitrateconcentration dimi
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