Microbial community structures in different wastewater treatment plants as revealed by 454-pyrosequencing analysis

► Sixteen wastewater treatment systems were investigated by 454-pyrosequencing. ► The structures of microbial communities in different samples were not the same. ► The Simpson’s diversity index and evenness index of MBR samples were the lowest. ► Treatment processes might have effects on the structure of microbial communities. In this study, 454-pyrosequencing technology was employed to investigate the microbial communities in 12 municipal wastewater treatment plants (WWPTs) with different treatment processes. In total, 202,968 effective sequences of the 16S rRNA gene were generated from 16 samples that widely represented the diversity of the microbial communities. While Proteobacteria was found to be the dominant phylum in some samples, in other samples it was Bacteroidetes. The Simpson’s diversity index and evenness index were lowest in samples from membrane bioreactors (MBRs), possibly due to the long sludge retention time (SRT) and low food/microorganism ratio (F/M). For one WWTP which had two disparate treatment processes operating in parallel, the structures of microbial communities in the two systems were compared. The differences found between the two indicated that the treatment process likely had effects on the structure of microbial communities.