Inhibition Of ZnO NPs On Enhanced Biological Phosphorus Removal System:from Macro To Micro

Zinc oxide nanoparticles(ZnO NPs )are widely applied in many fields,such as semiconductor,plastic additives,pigments and cosmetic.ZnO NPs will be released into the environment.It was investigated that lots of ZnO NPs existed in wastewater treatment plant(WWTP)which have not been treated.Those can seriously affect the microorganisms in WWTP.The mature activated sludge was taken as the seed sludge in this experiment.The steady and excellent performance was achieved after enrichment of 112 days.Poly-phosphate accumulating organisms(PAOs)received 65.37%and glycogen accumulating organisms(GAOs)accounted for 34.63%.The process of activated sludge granulation has been also realized.The inhibitive test concentration was set as 2 mg/L,6 mg/L,and 10 mg/L.Non-filamentous bulking was observed in reactors,operation efficiency failed with phosphorus removal efficiency decreased to 0.It was not difficult to find that ZnO NPs could effectively inhibit of procedure of polyhydroxyalkanoates(PHAs)synthesis and consumption.Meanwhile,protein and polysaccharides in extracellular polymeric substances(EPS)declined due to the presence of ZnO NPs ,leading to the structure of sludge loose,which did not relaunch after recovery experiment.High-throughput sequencing technology was applied to study the proportion variation of PAOs(53.13%to 0.29%),with the reduction of species and community diversity.Furthermore,it was suggested that toxicity of ZnO NPs was dependent on the species of bacteria.ZnO NPs remarkably caused the significant growth inhibition of Proteobacteria whereas promotion to Bacteroidetes,which was beneficial to screen the certain bacteria.The inhibitive experiment was operated at the concentration of 10 mg/L,50 mg/L,and 90 mg/L.The performance deteriorated when the concentration exceeded 50 mg/L.PHAs and EPS were also seriously affected by ZnO NPs ,however,better tolerability was observed.It was indicated that the percentage of PAOs declined from 51.98%to 14.39%,3.90%and 7.43%at various concentration.Negative correlation was found between ZnO NPs concentration and recovery capability.Additionally,Candidatus_Accumulibacte,Nitrosomonas were severely inhibited which resulted in the decreased proportion.It was interesting that non filamentous bulking had been acknowledged with the increasing Zoogloea.