New insight into the effect of short-term exposure to polystyrene nanoparticles on activated sludge performance

Microplastics have become a global concern because of their adverse effects on ecosystems. Although wastewater treatment plants (WWTPs) are considered a potential source of microplastics in the environment, the effect of polystyrene nanoparticles on activated sludge performance is not clear. In this study, the effect of short-term exposure to polystyrene nanoparticles (PS-NPs) on activated sludge activity and sedimentation was investigated, and the mechanism behind the effect was analysed. At 5 g/L, the PS-NPs could be adsorbed completely by activated sludge (2.8 g VSS/L) and could be transferred from the aqueous phase to the sludge phase in a short period. At a low concentration (0.1 g/L), the PS-NPs significantly inhibited the endogenous respiration in the sludge by causing bacterial death and affecting the mass transfer in the sludge. Changes in the zeta potential of the sludge surface and in the components of extracellular polymeric substance (EPS) resulted in low sludge aggregation. PS-NPs also caused sludge disintegration, so that when the PS-NP concentration reached 5 g/L, the sludge sedimentation decreased by approximately 50%. Short-term PS-NP exposure has a significant effect on the activity and sedimentation of activated sludge, which could affect the WWTP effluent quality. The findings of this study provide new insight for evaluating the potential risks posed by nanoplastics in WWTPs.