Although anoxic phosphorus uptake has been demonstrated, the conditions that stimulate or inhibit the anoxic uptake are not fully understood. In this study, the possibility of achieving biological excess phosphorus removal in sequencing batch reactors using nitrate as an electron acceptor without including an aerobic phase has been confirmed. The use of an anaerobic/anoxic/aerobic sequencing batch reactor allows anoxic phosphorus uptake to be achieved, in spite of the low fraction of denitrifying phosphorus accumulating organisms present in the inoculum. Biomass characterisation was carried out to determine the denitrifying fraction of the phosphorus accumulating organisms in sequencing batch reactors operating at different operational conditions. With an anaerobic/anoxic/aerobic cycle, it was demonstrated that the disadvantage of denitrifying phosphorus accumulating organisms due to the lower substrate utilisation efficiency in anoxic conditions relative to aerobic conditions, is not so effective to cause the "strictly aerobic" phosphorus accumulating organisms to dominate in the system.

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