Key microbial groups of MBBR systems at Wellington's sewage treatment plants

Moving Bed Biofilm Reactor (MBBR) systems are used in more than 400 wastewater treatment plants (WWTP) worldwide but little is known about the microbial communities on which these systems rely. This study aimed to address this issue by characterizing the microbial community composition at Wellington’s Moa Point (MP) and Western WWTPs. Monthly samples comprising biofilm carriers and mixed liquor were collected from MBBR reactors at each plant. DNA-based molecular methods were used to determine the bacterial and archaeal community composition of biofilms scraped from the carriers and from suspended material. Differences in microbial community structure and abundance were observed between WWTPs and between biofilm versus suspended fractions Biofilms generally showed a dominance of anaerobic sulphate-reducing bacteria (SRBs) including Desulfobacteriales and Clostridia. In contrast, the suspended communities were more diverse, including aerobes. Archaea were found in low diversity and abundance (<5%). These results suggest that the MBBR process differs from a conventional AS system by selecting for two distinctive bacterial communities. A higher abundance of SRBs in the MP biofilms raises the question of whether sea water infiltration influences this microbial community and requires further investigation.