The present invention provides a biological process for reducing the levels of nitrogen and phosphorous in wastewater, wherein said wastewater comprises at least 100mg/L total nitrogen wherein said process comprises feeding said wastewater into a reaction vessel in at least two steps, wherein said reaction vessel comprises an active biomass comprising nitrifying and denitrifying organisms and polyphosphate accumulating organisms (PAOs), wherein at least the first feed step is followed by a non-aerated period of sufficient duration to result in sufficiently low concentrations of NO<SUB>x </SUB>species in the wastewater to allow for accumulation of polyhydroxyalkanoates in the PAOs, and at least the first non-aerated period is followed by an aerated period of sufficient duration to allow for ammonium oxidation by the nitrifying organisms and assimilation by the PAOs of at least a portion of the phosphorous in the wastewater.
