Enhanced biological phosphorus removal systems adapting to seawater intrusion: Impacts of varying carbon source on metabolic adaptation in Candidatus Accumulibacter phosphatis

Abstract

In enhanced biological phosphorus removal (EBPR) systems, seawater intrusion may introduce uncertainty into the metabolism of Polyphosphate Accumulating Organisms (PAOs), especially when volatile fatty acid (VFA) profiles derived from fermentation liquids serves as the carbon source. This study investigated the impacts of varying sea salt salinity levels on the metabolism of Accumulibacter with different VFA as carbon sources. As sea salt salinity increased from 0.5 % to 3.5 %, catabolism (phosphorus release, glycogen and PHA biodegradation) was inhibited to a much lower degree compared to anabolism (phosphorus uptake, glycogen and PHA synthesis). Under seawater conditions, the intracellular free Mg2+ was partially excreted, leading to a subsequent reduction in glycogen metabolism and PHA synthesis. The decrease in PHA synthesis resulted in the diminished aerobic metabolic activity and polyphosphatase (PPX) enzyme activity, collectively causing decreased phosphorus uptake. Moreover, additional energy consumption was used to alleviate osmotic stress, which limited the energy used for esterase activity, translation activity, and phosphorus and glycogen metabolism, resulting in a decrease in growth activity. When using butyrate as a carbon source, Accumulibacter exhibited the highest metabolic activity (49.8 %), making it more adaptable to seawater conditions. The clade IIF was the dominant Accumulibacter in seawater conditions and could synthesize more PHA with butyrate, isobutyrate and valerate as a carbon source, respectively, stabilizing aerobic metabolism. Therefore, fermentation liquid containing high concentrations of butyrate and the activated sludge dominated by clade IIF have the potential to enhance the stabilization of EBPR systems in wastewater treatment plants infiltrated by seawater.