Texture and type of polymer fiber carrier determine bacterial colonization and biofilm properties in wastewater treatment

•Biofilm properties were studied in a cascade system treating municipal wastewater.•Carrier type and wastewater matrix both affected biofilm structure and activity.•In the first 2–3weeks, bacterial taxonomic diversity of biofilm reached its maximum.•Proteobacteria, Synergistetes, Bacteroidetes and Firmicutes dominated the biofilm.