Side-stream phosphorus famine selectively strengthens glycogen accumulating organisms (GAOs) for advanced nutrient removal in an anaerobic-aerobic-anoxic system

Endogenous denitrification (ED) is an effective approach to achieve advanced nitrogen removal for low COD/N (C/N) municipal wastewater, in which internal carbon sources are used for denitrification. However, phosphorus-accumulating organisms (PAOs) and denitrifying ordinary heterotrophic organisms (DOHOs) outcompeting glycogen-accumulating organisms (GAOs) for carbon sources decreases total inorganic nitrogen (TIN) removal efficiency. This study proposed a novel side-stream sludge treatment strategy, i.e., through phosphorus famine, to selectively strengthen GAOs. Two sequencing batch reactors (SBR) were used, with one served as an anaerobic/aerobic/anoxic SBR (AOA-SBR) and the other as a side SBR. Side-stream phosphorus famine treatment was conducted three times during 140 days' experiment, of which 20-30% of the sludge collected from the AOASBR was imposed to phosphorus famine condition in the side SBR for 4 days (24 cycles). Results showed that the average TIN and phosphorus removal efficiencies were 88.76% and 95.31%, and the average TIN and phosphorus in the effluent were 8.01 and 0.30 mg/L, respectively, treating low C/N (similar to 3.25) municipal wastewater in the AOA-SBR. The relative abundance of PAOs decreased from 3.23% to 2.15% and that of DOHOs reduced by 62.78%. In contrast, the abundance of GAOs increased from 3.09% to18.25%, which should be the key reason for the improvement of the ED efficiency. Moreover, the enrichment of GAOs promoted ED simultaneously using glycogen and poly-beta-hydroxyalkanoates (PHA) as carbon sources. The strategy of side-stream treatment proved the potential of rapid proliferation of GAOs while achieving improved nitrogen removal.