Strategies and relative mechanisms to attenuate the bioaccumulation and biotoxicity of ceria nanoparticles in wastewater biofilms

Inhibitory effects of ceria nanoparticles (CeO2 NPs) on biofilm were investigated individually and in combination with phosphate (P), ethylene diamine tetraacetic acid (EDTA), humic acid (HA) and citrate (CA) to further explore the toxicity alleviating solutions. Exposure to 20 mg/L CeO2 NPs significantly decreased the performance of biofilm in nutrients removal. Distribution experiments suggested > 98% of the CeO2 NPs retained in microbial aggregates, leading to 51.26 mu g/L Ce ions dissolution. The dissolved Ce-IV and its further being reduced to Ce-III stimulated the formation of O-2(center dot-) and (OH)-O-center dot, which increased lipid peroxidation level to 130.93% in biofilms. However, P/EDTA/CA captured or precipitated Ce ions, whereas EDTA/HA/CA shielded NPs-bacteria direct contacts, both disturbing the NPs adsorption, intercepting the redox transition between Ce-IV and Ce-III, reducing the generation of O-2(center dot-) and (OH)-O-center dot, thus mitigating the toxicity of CeO2 NPs. These results illustrate the main drivers of CeO2 NPs biotoxicity and provide safer-by-design strategies.