Microbiology of a membrane aerated biofilm reactor upgrade in a municipal wastewater treatment facility.

Novel wastewater treatment biotechnologies, including membrane aerated biofilm reactors (MABR), aim to reduce energy consumption, and improve nitrogen removal and nitrification in cold weather conditions. A municipal wastewater treatment plant (WWTP) in Southern Ontario was upgraded with a large-scale MABR system in 2022, which was installed upstream of the existing conventional activated sludge (CAS) system. Here we evaluated how the MABR upgrade impacted mixed liquor and MABR biofilm microbial communities spatially and temporally, which previously has not been done in large-scale hybrid MABR-CAS systems. Microbial communities were characterized using 16S rRNA gene amplicon sequencing, with selected MABR biofilm samples analyzed with metagenomics to evaluate the functional potential of the biofilm for nitrification and denitrification. The CAS mixed liquor before the upgrade included ammonia-oxidizing bacteria (AOB; Nitrosomonas) and nitrite-oxidizing bacteria (NOB; Nitrotoga), which exhibited seasonal abundance and activity patterns. Following the upgrade, seeding from the MABR biofilm increased diversity of the mixed liquor, including nitrifiers. Along with AOB, Nitrospira NOB and comammox Nitrospira were present in the MABR biofilm, representing upwards of 10 % of microbial community profiles. Metagenomic sequencing showed that biofilm microbial communities were equipped to perform nitrification and denitrification in the system. Overall, characterization of microbial communities in the WWTP showed that the MABR installation increased microbial diversity, concomitant with increased representation of nitrifier groups and coinciding with reductions in plant effluent nitrogen concentrations.