Impacts Of Zinc Oxide Nanoparticles On Sewage Biological Phosphorus Removal And Microbial Community

Nanoparticles(NPs) are widely applied in many commercial industrial and consumer products such as semiconductors and cosmetics, which leads to a great number of NPs discharging into industrial and domestic waste water and waste water treatment plant(WWTP). It is well known that many NPs have antibacterial abilities, such as Zn O-NPs, Ag-NPs, Ti O2-NPs.Concern whether the NPs in wastewater treatment plant shall negatively impact the function of WWTP can be therefore raised. Therefore, the experiment investigated the impacts of Zn O nanopartcles with different doses on biological phosphorus removal and the functional bacterial community in SBR to predict the possible harm to WWTP.In this study, 1, 5, 10, 20 mg/L was chosen as the investigated concentrations to assess the adverse impacts of Zn O-NPs on biological phosphorus removal system after short-term(8 h) and long-term exposure(10 d). Activated sludge was cultured in the anaerobic-aerobic parent SBR, which was operated to achieve biological phosphorus remova. No obvious influence was observed at the short-term exposure experiments of 1, 5 mg/L Zn O-NPs, however, when dosing Zn O-NPs concentrations at 10 and 20 mg/L, the biological phosphorus removal effects were negatively affected. In the presence of 10 and 20 mg/L of Zn O-NPs, the average anaerobic SOP releases were lower than the control test, and.the rate of aerobic SOP uptakes declined. Besides, the removal efficiencies decreased obviously. 1mg/L Zn O-NPs didn’t cause inhibitory effect on the transformations of intracellular PHA and glycogen. However, compared with the control test, activated sludge exposed to 5,10 and 20 mg/L of Zn O-NPs showed greater variations of total PHA and glycogen in both anaerobic and aerobic stages.1, 5 mg/L Zn O-NPs were observed no obvious influence to total phosphorus removal efficiency after long-term exposure(10 d), at the same time, they has no adverse influence on the activities of PPX and PPK, respiration rate, EPS production,plasma membrane integrity, and biomass. In the presence of 10 and 20 mg/L of Zn O-NPs, the average anaerobic SOP releases were lower than the control test, and the effluent phosphorus concentrations did not meet drainage standards. What is more, compared with the control test, 10, 20 mg/L Zn O-NPs caused inhibitory effect on PPX, PPK, respiration rate and EPS production, increased the LDH activity unit,declined the biomass to lower than 3000 mg/L.The impacts of Zn O-NPs on microbial community were characterized by using high-throughput sequencing. The experiment results showed that the addition of 10mg/L Zn O-NPs increased the biological community diversity, which indicated thatthe activated sludge have the ability of self adjusting to resist the toxicity of Zn O-NPs. But the shock of 20mg/L Zn O-NPs is too large for microorganism to endure, thus the biological community diversity is the lowest when exposed to20mg/L Zn O-NPs. The results of microbial community diversity indicated that the systems were affected by Zn O-NPs, and the system with 20 mg/L Zn O-NPs existed the most obvious difference with the control. Microbial communities showed differences at the phylum, class, order and genus levels. There was a shift in the abundance of the dominant phylum(Proteobacteria, Bacteroidetes and Actinobacteria). That the decrease of phosphorus accumulating organism(Rhodocyclales) and the increase of glycogen accumulating organism(Alphaproteobacteria and Gammaproteobacteria) lead to the failure of biological phosphorus removal. Besides, the bacteria related to heavy metal resistant(Zoogloea)increased and the bacteria related to sludge bulking(Haliscomenobacter) declined.