Fate of CeO₂ nanoparticles during laboratory-scale activated sludge treatment

The semiconductor industry is a major consumer of engineered nanoparticles since slurries containing silica, alumina, and ceria oxides are utilized extensively for the chemical-mechanical planarization (CMP) of wafers. Little is known about the fate of abrasive CMP nanoparticles during conventional wastewater treatment. With the objective to get a better understanding of the behavior of nanoparticles during biological treatment of wastewater, a laboratory-scale aerobic activated sludge treatment was set up to evaluate the fate of cerium oxide nanoparticles. The results obtained show that only a small fraction of the cerium oxide nanoparticles entering the treatment system escaped with the treated effluent (< 4.5%). Mechanisms contributing to the removal of the ceria included partitioning onto the microbial sludge floccules as well as destabilization of the nanoparticle dispersions by constituents present in the wastewater.