Effects of beneficial microorganisms on nutrient removal and excess sludge production in an anaerobic-anoxic/oxic (A2O) process for municipal wastewater treatment

[Display omitted] •Beneficial microorganisms lead differences in microbial community composition.•A2O-B is more effective for removal of organic materials and nutrients than A2O-C.•A2O-B exhibited lower MLSS and MLVSS concentrations compared to A2O-C.•Decomposition of EPS governs compressibility and settleability of activated sludge.•Elevated DHA in A2O-B contributes to reduction of excessive sludge production. The performances of anaerobic-anoxic-oxic processes with (A2O-B) and without (A2O-C) beneficial microorganisms were compared to provide valuable insights on how they are affected by changes in the microbial biomass and community composition. Although the A2O-B process showed lower concentrations of mixed liquor suspended solids and mixed liquor volatile suspended solids than the A2O-C process under identical operating conditions, the A2O-B process was more effective for the removal of organic materials and nutrients compared with the A2O-C process. Furthermore, the compressibility and settleability of the activated sludge were significantly better in the A2O-B process than in the A2O-C process due to the enhanced decomposition of extracellular polymeric substances. These results indicated that the inoculation of beneficial microorganisms may increase the proportions of microorganisms in relation to the removal of organic materials, nutrients (i.e., Zoogloea, Dechloromonas, Nitrospira, and Nitrosomonas) and the reduction of the excess sludge (i.e., Proteobacteria and Bacteroidetes).