Alumina nanoparticles-induced effects on wastewater nitrogen and phosphorus removal after short-term and long-term exposure

Abstract

Alumina nanoparticles (Al2O3 NPs) have been widely used in many fields, which causes a growing concern about their potential health and environmental risks. However, their possible impacts on wastewater nitrogen and phosphorus removal have not yet been reported. In this study, both short-term and long-term effects of Al2O3 NPs on wastewater nutrient removal were investigated. Scanning electron microscope (SEM) analysis showed that most of Al2O3 NPs were adsorbed onto activated sludge, but these NPs had no adverse effects on the surface integrity and viability of activated sludge. It was found that short-term exposure to 1 and 50 mg/L Al2O3 NPs induced marginal influences on wastewater nitrification, denitrification and phosphorus removal. Nevertheless, the prolonged exposure to 50 mg/L Al2O3 NPs was observed to decrease the total nitrogen (TN) removal efficiency from 80.4% to 62.5% due to the suppressed denitrification process, although biological phosphorus removal and the transformations of intracellular polyhydroxyalkanoates and glycogen were not affected. Quantitative PCR assays indicated that compared with the control, 50 mg/L Al2O3 NPs decreased the abundance of denitrifying bacteria in activated sludge. Further enzyme activity tests showed that the activities of key denitrifying enzymes (nitrate reductase and nitrite reductase) were inhibited, which might be responsible for the negative effects of 50 mg/L Al2O3 NPs on wastewater nitrogen removal after long-term exposure.