The ability of PAOs to conserve their storage-driven phosphorus uptake activities during prolonged aerobic starvation conditions

A post-denitrification process, known as enhanced biological phosphorus removal and recovery (EBPR-r), was recently developed to facilitate phosphorus (P) recovery from municipal wastewater. This process utilises a biofilm containing phosphate-accumulating organisms (PAOs) to capture P from wastewater and then release the captured P into a separate smaller stream for recovery. The addition of external carbon in the EBPR-r process is expected to be a main operating cost. Hence, it is important to ensure that the added carbon, which is stored internally as poly-β-hydroxy-alkanoates (PHA) within PAOs, is predominately used for P uptake. This study explored the ability of PAOs to conserve their storage-driven P uptake activities following exposure of the biofilm to oxidising and P-deficient conditions for extended periods (up to 7 days). Even after 2 days of exposure the biofilm retained a similar ability to up take P (1.20 ± 0.09 mg-P/g total solids). Beyond 2 days of exposure, a decline in P uptake activity was noted, with only 15% activity remaining by day 7. This study provides the first evidence of the ability of PAOs to conserve their storage-driven P uptake activities. This unique behaviour of PAOs may enable flexible operational strategies, such as infrequent carbon replenishment, to be implemented (i.e. facilitate multiple P uptake phases before an anaerobic carbon replenishment). Such flexibility may reduce the capital and operational costs of the EBPR-r process, increasing the economic incentive for P recovery from wastewater.