Study On The Performance And Mechanism Of Cyclodextrins Enhanced Nitrate Reduction And Azo Dyes Decolorization

In microbial environmental governance,pollutant properties and microbial activity are the key factors affecting the biological transformation of pollutants.Cyclodextrins(CDs)was widely used in solubilization of insoluble organic compounds due to its special outer hydrophilic and inner hydrophobic structure.However,the effect of interaction between CDs and bioactive substances on microbial activity is not clear.Therefore,water-soluble nitrate and azo dyes were selected as model pollutants to explore the effect and mechanism of CDs on microbial activity and pollutant biotransformation performance in this paper.(1)CDs enhanced the bio-reduction of nitrate.α-CD,β-CD and γ-CD could enhance the biological reduction of nitrate,and β-CD has the best enhancement effect.When the concentration of β-CD was 0.5 m M,the nitrate reduction rate increased 1.35 times.In the mechanism study,β-CD increased cell membrane permeability and biomass of microorganisms during nitrate reduction,which made microorganisms absorb nutrients more effectively and promote their growth and reproduction.At the same time,β-CD increased the secretion of extracellular polymer(EPS)from 150.79 mg/g VSS to 197.63 mg/g VSS,and EPS contained more electron transfer substances.β-CD increased the electron transport system activity and current exchange density(Tafel)by 99.5 % and 11.4 %,respectively,which effectively promoted the electron transport activity and electron exchange rate.β-CD enhanced the key nitrate reductase activity during denitrification,thereby increasing microbial metabolic activity.In summary,CDs can effectively improve the metabolic activity of microorganisms,thereby strengthening the biological reduction of nitrate.(2)CDs enhanced the bio-decolorization of azo dyes.β-CD can effectively improve the biological decolorization efficiency of different azo dyes by 1.2～1.4times.In the mechanism study,β-CD increased the permeability of microbial membrane and absorbed more nutrients into electron donor(NADH).At the same time,β-CD improved electrochemical activity,reduced electron transfer resistance,and accelerated electron transfer and consumption.β-CD not only improved enzyme activity to better regulate microbial metabolism,but also increased ATP content from 3.59 mg/L to 4.13 mg/L,providing more energy for microbial metabolism.In addition,β-CD had protective effect on microorganisms and reduced the toxicity of intermediates to microorganisms.The experimental results showed that CDs had beneficial effect on microorganisms in the process of enhancing the pollutants transformation.In this paper,the performance and mechanism of CDs in enhancing microbial activity and promoting pollutant transformation were studied for the first time.The beneficial effects of CDs on microorganisms were explored,which provided theoretical basis for broadening the application of CDs in the field of environmental microorganisms.