Fate of cerium dioxide (CeO2) nanoparticles in municipal wastewater during activated sludge treatment

► Nano-ceria (CeO2) is highly removed by activated sludge treatment (96.6% total Ce). ► Extensive removal of CeO2 <200 nm was also attained. ► Nano-CeO2 interaction with wastewater components caused CeO2 aggregation and settling. ► Sorption onto sludge biomass also contributed to CeO2 removal. ► Nano-CeO2 shows low inhibition towards O2 uptake by activated sludge.