Removal of a mixture of metal nanoparticles from natural surface waters using traditional coagulation process

Abstract

Engineered nanoparticles (ENPs) present in natural water systems and wastewater treatment plants, due to their wide use in industrial products and consumer goods, represent a hazard to human health, especially if occur in surface waters used for human consumption. Different nanoparticles may co-exist in the natural waters and until now no works have been developed on the impact of the co-existing nanoparticles on water treatment processes. Thus, this work evaluates the removal of different co-existing metal-based ENPs (TiO2, Ag and CuO) from natural surface waters applying the most used water treatment process, coagulation/flocculation/sedimentation (C/F/S). Results showed that C/F/S is effective in the removal of the co-existing ENPs from the studied hydrophilic natural waters (low/medium turbidity and moderate/moderate-high natural organic matter content) with efficiencies above 93% for TiO2, Ag and CuO nanoparticles. The formation of destabilised nanoparticle-organic matter aggregates in C/F promoted their precipitation. For the lowest turbidity and organic content water, Ti presented the lowest concentration, followed by Ag and Cu, because of titanium properties. For the highest turbidity and organic content water, the residual Cu concentration was the lowest and Ag the highest, due to the natural water characteristics. Water characteristics played an important role on the coagulant demand and removal of ENPs mixture by C/F/S. Results also demonstrated that ENPs mixture did not hampered the treated water quality for turbidity and natural organic matter. For the lowest turbidity and natural organic matter water, ENPs appear to contribute to a higher removal of these parameters.