Enhanced Biological Phosphorus Removal at low Sludge Retention Time in view of its integration in A-stage systems

The two-stage A/B WWTP configuration is being studied as a possible wastewater treatment with low energy consumption or even with a net energy generation. The first phase, A-stage, is designed to remove organic matter at very short Sludge Retention Time (SRT), while the B-stage is based on autotrophic nitrogen removal. However, P-removal in the A/B process usually only relies on precipitation. This work studies the potential inclusion of Enhanced Biological Phosphorus Removal (EBPR) in the A-stage phase. For this aim, the long-term operation of three different Sequencing Batch Reactors (SBR) enriched in Accumulibacter at low SRT was thoroughly monitored for more than three months each one. This work shows that EBPR can be sustained with a minimal SRT of 3.6 d at 25 °C. Lower values, SRT = 3 d, led to the PAO washout because of a reduction in P-release and P-uptake, an increase of the VSS/TSS ratio and a decrease of the P/C ratio. The Y_obs could be related to the SRT with the parameters Y = 0.39 ± 0.05 gCOD_X·g^-1COD_S and k_D = 0.06 ± 0.04 d^-1 which leads to a 24% increase of biomass yield when SRT was reduced from 10 to 4 d.