Aerobic phosphorus release linked to acetate uptake: influence of PAO intracellular storage compounds

The mechanisms of polyphosphate accumulating organisms (PAO) are not fully established yet under conditions that differ from the classical anaerobic/aerobic conditions. Recently, some research in the field of biological phosphorus removal has been focused on studying systems where the electron donor (substrate) and the electron acceptor (nitrate or oxygen) are present simultaneously. The aim of this study was to assess the influence of the levels of intracellular storage compounds in the net phosphorus removal process occurring under continuous aerobic conditions. An enhanced biological phosphorus removal (EBPR) system was enriched in a sequencing batch reactor working under alternating anaerobic/aerobic conditions and the percentage of “Candidatus Accumulibacter phosphatis” (the PAO in this study) was 45%. Three different batch experiments were performed to obtain a better insight of this process: one under standard anaerobic–aerobic conditions and two experiments under strictly aerobic conditions. One of the aerobic experiments was developed with the EBPR biomass withdrawn at the end of the anaerobic period and the other one with biomass withdrawn at the end of the aerobic period of the standard process. Although net phosphorus removal was achieved in both aerobic experiments, the ratios of phosphorus released and glycogen degraded versus acetate taken up were higher when the sludge was withdrawn at the end of the aerobic period, where higher levels of polyphosphate and glycogen were present in the biomass