Absence of nitrogen and phosphorus in activated sludge: Impacts on flocculation characteristics and the microbial community

A sequencing batch reactor operated in anoxic/aerobic mode was used to investigate the effects of simultaneous nitrogen (N) and phosphorus (P) absence in activated sludge. Through controlling the N and P content in the influent water, we investigated changes in sludge concentration, settling performance, morphological structure, surface properties, extracellular polymer content, and microbial community structure and function. When N and P were simultaneously absent, the relative hydrophobicity of the activated sludge and the sludge concentration decreased. The specific oxygen uptake rate also decreased, the activated sludge did not bulk, and the flocs were larger and more concentrated. The content of extracellular polysaccharides did not significantly change. An increase in the concentration of extracellular proteins, particularly loose-binding layer proteins, improved activated sludge aggregation. The structure and function of the activated sludge microbial community changed significantly in the absence of both N and P, with a significant decrease in the relative abundance of species related to N and P metabolism. Tax4Fun analysis showed that the absence of both N and P decreased metabolism and genetic information processing of the microbial community. These results elucidate the effects of simultaneous N and P absence on activated sludge from the perspective of microbial community structure and function. These results will be useful for treatment of N and P deficient wastewater by the activated sludge method.