Study On The Stimulation Effect Of Low-dose Nano-ZnO Exposure On Microbial Anaerobic Remediation Performance

With the rapid growth of production and utilization,nanomaterials have been increasingly released into the environment with potentially adverse ecological impacts.However,the current actual environmental concentrations of nanomaterials are relatively low and not yet sufficient to cause serious consequences to ecological safety.Therefore,the non-toxic environmental effects of nanomaterials have gradually attracted attention in recent years.But few studies have been conducted on the effect of nanomaterials on the anaerobic remediation efficacy of environmental microorganisms.Therefore,this thesis employed nano-Zn O(nZnO)as the research object to explore the effects of nZnO exposure on the anaerobic degradation of azo dyes and biological denitrification using pure bacterium Shewanella oneidensis MR-1 and mixed microflora activated sludge,respectively,and elucidated the mechanism of low-dose stimulation effect of nZnO on microbially anaerobic remediation process.Several preliminary conclusions were obtained from this study as follows:(1)Low-dose nZnO enhanced anaerobic degradation efficiency of methyl orange by S.oneidensis MR-1.It was found that nZnO concentration of 0.075 mg/L,particle size of 30 nm and ambient p H of 7 promoted the decolorization rate of methyl orange with the best efficiency.When the nZnO concentration exceeded 0.5 mg/L,the degradation rate of methyl orange was gradually inhibited,and the inhibitory effect became more obvious as the nZnO concentration increased.(2)Low-dose nZnO enhanced the anaerobic metabolic efficacy of S.oneidensis MR-1.0.075 mg/L nZnO moderately enhanced the expression of genes of outer membrane permeability and transmembrane transport channels of S.oneidensis MR-1,accelerated the efficiency of transmembrane electron transfer and transmembrane transport of substances,enhanced lactate dehydrogenase activity,lactate consumption and ATP production by increasing the expression of genes involved in carbon source utilization to promote bacterial metabolism,thus enhancing the anaerobic metabolism of S.oneidensis MR-1 to promote the anaerobic degradation efficiency of methyl orange.(3)Low-dose nZnO enhanced the anaerobic denitrification efficiency of activated sludge.When the concentration of nZnO reached 0.75 mg/L,it could drastically facilitate the improvement of sludge denitrification efficiency.With the increase of nZnO concentrations,the denitrification efficiency was gradually suppressed.Addition of exogenous NH₄⁺significantly promoted the removal of NO₂^-and accelerated the process of denitrification.(4)Low-dose nZnO improved the performance of activated sludge and influence species abundance.nZnO(0.075 mg/L)could improved the flocculation of activated sludge,promoted the secretion of protein and polysaccharides in extracellular polymeric substances,and increased the abundance of denitrifying bacteria,thereby promoting the denitrification process.