Short CommunicationInsight into the impact of ZnO nanoparticles on aerobic granular sludge under shock loading

•Environmental risks of ZnO NPs to aerobic granular sludge was explored for the first time.•ZnO NPs caused acute toxicity to both nitrification and denitrification processes.•The COD and phosphorus removal remained unaffected by exposure to 10-100 mg/L ZnO NPs.•The activities of respiration was improved while both nitrogen and phosphorus rates were inhibited.•The over-produced EPS (mainly PN) helped relieve the toxicity of ZnO NPs.

The increasing use of zinc oxide nanoparticles (ZnO NPs) has raised concerns about the environmental threats to the wastewater treatment systems. Shock loading of 10, 50 and 100 mg/L ZnO NPs was conducted to evaluate impacts on reactor performance, microbial activities and extracellular polymeric substances (EPS) in parent aerobic/oxic/anoxic (A/O/A) granular sequencing batch reactors (SBRs). The results showed that ZnO NPs caused inhibition to nitrogen transformations due to acute toxicity to nitrification and denitrification. However, phosphorus removal remained unaffected by the exposure to ZnO NPs. Besides, ZnO NPs significantly enhanced the oxygen respiration rate and caused acute toxicity to ammonia oxidizing rate (10.40-35.21%), phosphorus release rate (37.79-19.80%), aerobic phosphorus uptake rate (36.95-20.69%) and total phosphorus uptake rate (32.77-16.91%) of aerobic granules. ZnO NPs stimulated the secretion of EPS, especially the content of protein (PN), which could relieve the toxicity of ZnO NPs.

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