Diverse microbial communities colonize biofilm carriers in moving bed and intermittent cleaning reactors for municipal and industrial wastewater treatment.

Conventional biofilm reactors are widely used for the removal of organic constituents and nutrients (i.e., nitrogen and phosphorus) in municipal and industrial wastewater treatment. Moving bed biofilm reactor (MBBR) and continuously flow intermittent cleaning reactor (CFIC) have been developed as more compact, small footprint, and highly efficient biofilm-based systems for wastewater treatment. However, despite the advancements in reactor technology, there is limited scientific information on the microbial composition of the biofilms in these systems. This study aimed to characterize and provide early insights into the microbial diversity of biofilms grown on biofilm carriers and liquid suspensions of the biofilm-based wastewater treatment systems. Microbial samples were collected from biofilm carriers and liquid suspension in four full-scale MBBR plants and two CFIC plants in Norway, all treating municipal and industrial wastewater. DNA was extracted from the samples and subjected to meta-barcode sequencing for taxonomic classification of microbial communities in each treatment plant. The results revealed significant variation in microbial compositions across treatment plants, influenced by wastewater characteristics, biofilm carrier types, and reactor operational characteristics. On the biofilm carriers, the dominant bacterial taxa included TM7-1 (Saccharibacteria), Burkholderiales, Clostridiales, Actinomycetales, Pseudomonadales, Rickettsiales, and Rhodobacteriales. In liquid suspensions, the dominant groups were Clostridiales, Methanosarcinales, Pseudomonadales, Flavobacteriales, and Rhodobacteriales. In conclusion, this study highlights the diverse microbial populations on biofilm carriers and liquid suspensions, which collectively contribute to the enhanced treatment efficiency of both MBBR and CFIC systems.