Effect of cerium dioxide, titanium dioxide, silver, and gold nanoparticles on the activity of microbial communities intended in wastewater treatment

► Toxicity of TiO2, CeO2, Ag and Au nanoparticles (NP) has been studied. ► NP were synthesized in the lab and stabilized to prevent agglomeration. ► Toxicity was studied in all the communities used for the wastewater treatment. ► Heterotrophic, nitrifying and anaerobic organisms were studied for nanotoxicology. ► Au and TiO2 NP were not toxic, but Ag and CeO2 NP were inhibitory.