Selection of denitrifying phosphorous accumulating organisms in IFAS systems: Comparison of nitrite with nitrate as an electron acceptor

- DPAO and AOB were selected in two IFAS systems working with nitrate or nitrite.
- DPAO did not show adaptation to the provided electron acceptor and preferred nitrite.
- Type of electron acceptor did not affect PAO distribution in IFAS system.
- AOB could compete with PAO for oxygen in both suspended and attached forms.
- DO-limited condition in biofilm could maintain nitritation in long term operation.

Nitrite and nitrate were compared as electron acceptors to select for denitrifying phosphorous accumulating organisms (DPAO) in two integrated fixed film activated sludge (IFAS 1 and IFAS 2) systems operated as sequencing batch reactors. The bench-scale experiment lasted one year and synthetic wastewater was used as feed. During anoxic conditions 20 mg NO3−-N L−1 were dosed into IFAS-1 and 20 mg NO2−-N L−1 were dosed into IFAS-2. Long term phosphorous and ammonia removal via nitritation were achieved in both systems and both attached and suspended biomass contributed to phosphorous and ammonia removal. DPAO showed no specific adaptation to the electron acceptor as evidenced by short term switch of feeding with nitrate or nitrite. Anoxic phosphorus uptake rate was significantly higher with nitrite than with nitrate. Results showed that DPAO activity with nitrite could be integrated into attached and suspended biomass of IFAS systems in long term operation.