Investigation of the mechanism of anammox granules alleviating the inhibition of organic matter in pharmaceutical wastewater

In current study, the reactor performance, granular characteristics and microbial community succession were investigated in an anaerobic ammonium oxidation (anammox) granular system treating pharmaceutical wastewater under varying COD/N ratios. The results showed that the optimal nitrogen removal performance was achieved with COD/N of 0.63, indicating the feasibility of anammox granular system to treat pharmaceutical wastewater. As the COD/N ratio increased to 1.31, the nitrogen removal efficiency declined to 49.2%. However, the reactor recovered rapidly after 60 days, because that stable granular structure retained high biomass. It was found that AnAOB secreted more extracellular protein, especially a specific humic acid-like substance to form fine and coarse granules as response to the inhibitory conditions. The population of anammox species has shifted significantly. Besides, the key genera and the symbiotic genera with AnAOB were confirmed by molecular ecological networks analysis. •Good performance was obtained in anammox system treating pharmaceutical wastewater.•Humic acid-like substance was secreted to form fine and coarse anammox granules.•Pseudofulvimonas, Frateuria and Curvibacter were considered as keystone microbes.•The anammox species shift to Planctomycetes_bacterium.•RDA revealed that the main factors on community were COD/N and PN/PS.