Long-term effects of zinc oxide nanoparticles on wastewater treatment in a membrane bioreactor (MBR) process

Abstract

Long-term effects of ZnO nanoparticles on the system performance of an MBR were investigated together with their removal behaviour in the system. Continuous operation over 242 days showed that ZnO NPs at both 1.0 and 10.0 mg/L caused moderate deterioration in the removal of COD, nitrogen and phosphorus. Denitrification was affected upon the exposure but recovered subsequently. Although no significant acute effect was observed on ammonia-oxidization, permanent inhibition occurred after long-term. Nitrite-oxidization was not affected even with 10.0 mg/L ZnO NPs. Significant changes were observed in activated sludge properties which resulted in more severe membrane fouling. ZnO NPs caused changes in the bacteria community structure, however with the diversity remain unchanged. ZnO NPs was removed effectively in the MBR (>98%) with biosorption being a major removal pathway. Membrane filtration also played an important role (20% of total the removal) especially at high ZnO NPs concentrations (10 mg/L).