Effect Of AgNps On Phosphorus Removal Performance And Microbial Population In EBPR System

With the large-scale application of silver nanoparticles(Ag NPs),the ecological and environmental effects caused by it have attracted people’s attention.The content of Ag NPs in the influent of wastewater treatment plants is increasing year by year,and the bacteriostatic properties of Ag NPs may affect the functional microorganisms of wastewater biological treatment,thereby affecting the efficient operation of wastewater treatment plants.In order to explore the effect of Ag NPs on the phosphorus removal efficiency and microbial population structure of the enhanced biological phosphorus removal(EBPR)system,the study took artificially simulated wastewater as the research object to construct an EBPR system.The study selected different concentrations of Ag NPs(0 mg/L,0.5 mg/L,1 mg/L,2 mg/L,3 mg/L,4 mg/L,6 mg/L,8 mg/L and 10 mg/L)for batch testing of short-term exposure(6 h)affecting the EBPR system.According to the test results,4 concentrations of Ag NPs(0 mg/L,2 mg/L,4 mg/L and 8 mg/L)were selected,and 0.8 mg/L Ag~+were used as the toxicity comparison to investigate the effect of long-term exposure(104 d)of Ag NPs on the EBPR system.Finally,based on 16S r RNA high-throughput sequencing technology,the microbial population structure of the long-running EBPR system was deeply analyzed,and the activated sludge was characterized by SEM and TEM.The main results are as follows:Based on the batch test of the effect of short-term exposure of Ag NPs on the phosphorus removal efficiency of EBPR system,the study found that:Ag NPs can significantly inhibit the anaerobic phosphorus release rate,anaerobic COD degradation rate and aerobic phosphorus absorption rate of the EBPR system,and has little effect on the aerobic COD degradation rate.When the concentration of Ag NPs is higher than 8 mg/L,the degree of inhibition of aerobic phosphorus absorption is higher than that of anaerobic phosphorus release,and the degree of inhibition of anaerobic COD degradation by Ag NPs is always higher than that of aerobic COD degradation.The phosphorus removal rate of the system without Ag NPs is 91%,and the phosphorus removal rate of the system with 10 mg/L Ag NPs is-10%.The higher the Ag NPs concentration,the stronger the inhibition effect on phosphorus removal efficiency.In the non-substrate inhibition kinetic model,the Vadivelu model can better reflect the inhibition law of Ag NPs on anaerobic phosphorus release and aerobic phosphorus uptake,and is the optimal model for the inhibition kinetics of Ag NPs short-term exposure.Based on the experiment of long-term exposure of Ag NPs on the phosphorus removal efficiency of EBPR system,this study found that:in the long-term operation process,the phosphorus removal rate of the EBPR system without Ag NPs and the addition of Ag NPs was higher,and the biological activity of activated sludge was higher,biomass and dehydration performance are relatively stable;the EBPR system with Ag NPs can not maintain a high phosphorus removal rate,the biological activity,biomass and dehydration performance of activated sludge are constantly deteriorating,and the higher the Ag NPs concentration,the worsening the higher the degree.Based on 16S r RNA high-throughput sequencing technology to analyze the population structure of microorganisms,this study found that:The higher the concentration of Ag NPs added,the lower the species richness,diversity and uniformity of the EBPR system.Different concentrations of Ag NPs can cultivate and domesticate their own unique microbial flora.The higher the concentration of Ag NPs,the more similar the microbial population structure of the sample.Proteobacteria was the most dominant phylum,and its relative abundance increased with the increase of Ag NPs concentration.The relative abundance of the main functional bacteria of the EBPR system,Ca.Accumulibacter and Ca.Competibacter decreased as the Ag NPs increased.Bacteroidetes,β-Proteobacteria,Thiotrichaceae,andγ-Proteobacteria are the significant marker species under the Ag NPs concentrations of 0 mg/L,2 mg/L,4 mg/L and 8 mg/L,respectively.The surface of microbial cells in the system without Ag NPs and the addition of Ag~+was complete and smooth,while the EBPR system with high concentration of Ag NPs had more depressions and wrinkles on the surface of microbial cells.In this study,the influence of Ag NPs on EBPR system was comprehensively explored,and the process of Ag NPs influence on EBPR system was clarified,which provided a reference and reference for the comprehensive evaluation of the influence of Ag NPs on wastewater biological treatment system.