| In recent years,AgNPs has been widely used in the field of production and life.AgNPs in the environment enter the sewage treatment plant through the sewage system and affect the microbial treatment process.At present,there are few and incomplete studies on AgNPs for biological phosphorus removal.Therefore,it is necessary to study the phosphorus removal performance of AgNPs for EBPR and the changes of microbial population.Therefore,in this experiment,the artificial construction of SBR reactor to simulate EBPR system,artificial water distribution,activated sludge as the research object,through the short and long-term exposure of different concentrations of AgNPs to explore its impact on the EBPR system,after the end of the long-term experiment,16 S rRNA high-throughput sequencing technology to explore the structural changes of the microbial community.Through the short-term exposure of different concentrations of AgNPs to EBPR system,it was found that the concentrations of AgNPs at 0.5 mg/L and 1 mg/L had no significant effect on the phosphorus removal performance.When AgNPs concentration was 8 mg/L,the system basically lost the ability of phosphorus removal.When AgNPs concentration reached 10 mg/L,the system completely lost the ability of phosphorus removal.The removal rate of COD and the degradation rate of COD in anaerobic segment decrease gradually with the increase of AgNPs concentration,but the degradation rate of COD in aerobic segment had no obvious rule.The Ag~+ content in the water was detected after the end of the cycle,and it was found that the Ag~+ content accounted for about 10% of the AgNPs concentration.According to the results of short-term experiment,0 mg/L,2 mg/L,4 mg/L,8 mg/L AgNPs and 0.8 mg/L Ag~+ were selected for long-term experiment for 200 days,and the groups were named A1,A2,A3,A4,A5.Long-term experiments showed that 0.8 mg/L Ag~+ had no significant effects on phosphorus removal performance,COD removal rate,microbial metabolites,biomass and ROS in the system.The removal rate of PO43--P,anaerobic phosphorus release,aerobic phosphorus uptake,COD removal rate and anaerobic COD degradation decreased gradually with the increase of AgNPs concentration.COD in all systems was mainly removed in the anaerobic section.Compared with PO43--P,AgNPs had less influence on COD.SEM observation showed that the higher the concentration of AgNPs,the more serious the degree of cell morphology change and the more cells with morphological change,while 0.8 mg/L Ag~+had no significant effect on cell morphology.After the long-term experiment,16 S rRNA high-throughput sequencing technology was used to analyze each system,and it was found that 0.8 mg/L Ag~+ could significantly improve species richness and diversity,high concentrations of AgNPs could significantly reduce species richness and diversity,while low concentrations of AgNPs might stimulate the growth of some microorganisms.The blank group,0.8 mg/L Ag~+ group,4 mg/L AgNPs group and 8 mg/L AgNPs group had high similarity in microbial community composition,while the other four groups of 2 mg/L AgNPs group had significant differences.At the taxonomical level,Proteobacteria,Bacteroidetes and Chloromycota were the top three dominant phyla.Proteobacteria and Firmicutes had a certain tolerance to AgNPs environment,and the sludge swelling phenomenon was more serious in the 4mg/L and 8 mg/L AgNPs groups.Genus level cluster heat maps show that Candidatus_Accumulibacter was the main bacteria in the blank group and 0.8 mg/L Ag~+groups for phosphorus removal,while 4 mg/L and 8 mg/L AgNPs groups mainly provided phosphorus removal performance for Dechloromonas.The results of species association network analysis showed that most species exist in the system as synergies,and typical phosphorus accumulating bacteria Tetrasphaera and Candidatus_Accumulibacter exist in the system as synergies with each other,guaranteeing a high phosphorus removal capacity of the system.The above results indicate that the influence of AgNPs on EBPR system mainly come from AgNPs itself,rather than Ag~+ released by AgNPs. |
