Abstract：Community structures and population dynamics of nitrifying bacteria determine biological nitrogen removal from municipal wastewater. The population structures and dynamics of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) in four full-scale wastewater treatment plants (WWTPs) were investigated in this study. Quantitative real-time PCR results showed that the abundance of AOB was in a range of 8.56×106~4.46×107cells/gMLSS, while NOB was varying in 3.37×108~1.53×109cells/gMLSS. In each process Nitrospira was the dominant species of NOB. Nitrospira abundance was obviously higher than Nitrobacter, accounting for 88% of total NOB. In the A2O process the abundances of AOB and Nitrospira in winter were less than those in summer, leading to decline of biological nitrogen removal. The phylogenetic analysis of AOB amoA genes indicated that all the sequences were affiliated with genera Nitrosomonas, among which Nitrosomonas oligotropha cluster was the dominant species, accounting for 60% of the clone libraries. The pre-dominant AOB were Nitrosomonas-like cluster and Nitrosomonas europaea cluster, accounting for 29.6% and 9.1% of the clone libraries, respectively. N. europaea cluster was only found in A2O process, and reached 44.7% of total AOB in summer sample, which was a main reason causing high nitrite accumulation during summer operation of A2O process. The outcomes verified that the dominant AOB and NOB in WWTPs was Nitrosomonas and Nitrospira, respectively. Nitrifying bacteria accounted for 1%~7% of total bacteria. The abundances, relative distributions and community structures of nitrifying bacteria significantly influence the performance of biological nitrogen removal.
