Comparison between aerobic and anoxic metabolism of denitrifying-EBPR sludge: effect of biomass poly-hydroxyalkanoates content.

Biomass with denitrifying phosphate uptake ability was tested under sequencing anaerobic-aerobic and anaerobic-anoxic conditions. The initial dose of acetate, under anaerobic conditions varied to achieve different PHA (poly-hydroxyalkanoates) saturation of PAO (polyphosphate accumulating organisms) cells. Increased acetate dosage under anaerobic conditions led to higher phosphate release and increased PHA storage by PAOs and, also, to greater phosphate uptake rates under the following aerobic and/or anoxic conditions. The experimental results also indicated that when organic carbon is limited under anaerobic conditions, more internal glycogen supplementary to polyphosphate cleavage is utilized by the biomass, resulting in less phosphate release and more PHA stored per acetate taken up. In the subsequent aerobic and/or anoxic phase PAOs demonstrate an improved EBPR (enhanced biological phosphorus removal) performance, with regard to PHA consumption per phosphate taken up, for reduced initial biomass PHA content under both aerobic and anoxic conditions. The examination of EBPR biomass under controlled operational conditions, where experimental analysis of the relevant compounds in the bulk phase (PO(4)(3-), NO(3)(-) and/or O(2)) in conjunction with the biomass intracellular products (PHA, glycogen), contributes to an improved understanding of the PAOs metabolic behavior, with regard to organic substrate availability.