Release of ZrO₂ nanoparticles from ZrO₂/Polymer nanocomposite in wastewater treatment processes

The widespread use of nano-enabled water treatment composites (NWTCs) can result in the release of nanoparticles (NPs) into environmental waters. Studying the release of NPs from NWTCs is of great significance for evaluating the material stability, and environment and biological safety. This work evaluated the amount and species of Zr released from a NWTC, a ZrO₂/polymer composite (HZO@D201), during the treatment of electroplating wastewater. About 5 g of the HZO@D201 particles, consisting of porous spheres (0.8 mm in diameter) loaded with ZrO₂ NPs, were packed into a glass column (130 mm in length and 20 mm in diameter) and treated with wastewater at a flow rate of 25 mL/hr. The release of Zr occurred mainly in the initial stages of water treatment, decreased with the increase of treatment volume, and approached an equilibrium value of approximately 3.79 μg/L at the treatment volume of about 800 bed volumes. The total amount of Zr released in the effluent was in the range of 2.62-140 μg/L, which was mainly present in the form of ZrO₂ NPs. The amounts of Zr released under acidic and alkaline conditions were markedly higher than that under neutral conditions, while the presence of humic acid significantly inhibited the release of Zr. Our study implied that the NWTCs could be a source of engineered NPs in environmental waters, and should be considered in evaluating the safety of ZrO₂/polymer composites in water treatment.