Nutrient removal, microbial community and sludge settlement were examined in two 3-litre laboratory-scale anaerobic/aerobic sequencing batch reactors (SBRs). One SBR was operated at 10°C and the other SBR at 20°C. Different from conventional enhanced biological phosphorus removal, most of the soluble sodium acetate was removed in the aerobic phase and no organic carbon uptake or biological phosphorus release occurred in the anaerobic phase. In this type of anaerobic/aerobic SBR, the phosphorus removal and sludge settlement seemed to be unstable, and the dominant microorganism was Zoogloea sp. Although no excess biological phosphorus removal occurred, extracellular phosphorus precipitation contributed a significant proportion to total phosphorus removed. Sludge volume index decreased with increasing phosphorus contents in the biomass under all conditions. The functions of extracellular polymeric substances in sludge settlement and phosphorus removal depended on the environmental conditions applied.

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