Impacts of different nanoparticles on functional bacterial community in activated sludge

•Silver and ZnO nanoparticles exert different impacts on functional bacterial community.•Denitrifying bacteria were inhibited by high dosage of silver and ZnO nanoparticles.•Sludge bulking, heavy metal resistant and biosorption bacteria enriched by both nanoparticles.•Increase of bulking related bacteria may help to maintain functional redundancy of the community.