Succession of the Activated Sludge Microbial Community and Phosphorus Removal Performance in a Sequencing Batch Reactor During Transition from an Anoxic/Aerobic System to EBPR

Enhanced biological phosphorus removal (EBPR) technologies, which are widely applied in wastewater treatment, are based on the activity of polyphosphate-accumulating organisms (PAOs). However, the transition from conventional systems to EBPR remains poorly understood. In this study, phosphorus removal performance and the succession of an activated sludge microbial community were investigated in a sequencing batch reactor during transition from the anoxic/aerobic process to the anaerobic/aerobic EBPR configuration. Reactor performance data combined with molecular analyses revealed that community development proceeded through three distinct stages. During the first 15–20 days, a community with a pronounced PAO phenotype was formed, in which representatives of the genus Azonexus predominated (up to 23.8%). From 15–20 days to 2 months, a pseudo-steady state was achieved, with stable phosphorus removal (36–51%) and sustained dominance of Azonexus (up to 23–18%). Then a shift in community structure occurred, marked by a decline of Azonexus (<1%) and an increase in Accumulibacter (up to 8.3%) and other potential PAOs (Comamonadaceae and Thiotrichaceae); however, phosphorus removal efficiency decreased to 27–31%. These results highlight the importance of considering microbial succession at the EBPR start-up to develop operational strategies that ensure sustainable phosphorus removal.