The effects of GAOs abundance to the systemmatic phosphorus enrichment performance and the metabolic characteristics in phosphorus-accumulating biofilm

In this study, the activated sludge from an oxidation ditch was used as the inoculated sludge for culturing poly-phosphate biofilm enrichment in a sequencing batch reactor with alternating anaerobic/aerobic operation. The effects on the phosphorus enrichment performance of the system and on the metabolic characterization of the microbial community can be analyzed by examining the effects of changes in the abundance of glycogen-accumulating organisms (GAOs) in the biofilm. The results indicated that GAOs became the dominant bacteria during the enrichment of phosphorus-accumulating biofilm, but did not negatively impact the phosphorus removal and enrichment effect of the biofilm system. The overall biofilm community was dominated by the phosphorus accumulating metabolism (PAM) due to the significant enhancement of both PHA metabolizing activity and poly-P metabolic activity of individual cells of phosphorus-accumulating organisms (PAOs). As a dominant genus in the system, GAOs may obtain the reducing power (NADH) required for synthesizing PHA through the EMP metabolic pathway, which provides sufficient energy reserve for PAOs to absorb phosphorus under aerobic conditions, thus stimulating the up-regulation of the expression of the inorganic phosphorus transport system (pst) and the poly-P synthesis metabolism genes (ppk) . This enables the biofilm system to exhibit a good capacity of phosphorus removal and enrichment. Additionally, GAOs (Candidatus Competibacter) as a potential denitrifying functional bacteria make the biofilm phosphorus enrichment system have synchronized aerobic nitrogen removal.