Study On The Performance And Mechanism Of Enhancing Denitrification By Clay Minerals

Electron transfer and energy flow between minerals and microorganism are important for environmental protection and bioearth circulation.Clay minerals are the most common and abundant minerals in the earth.The interaction between clay minerals and microorganism has been widely studied in the field of microorganism.However,the interface mechanism between clay minerals and microorganism in the process of biotransformation needs to be further studied,which limits the application of clay minerals in environmental biotransformation.In this study,nitrate was selected as pollutant to explore the characteristics of clay minerals affecting the dynamic process of denitrification,to clarify the internal law of interaction between clay minerals and microorganism,and to propose the interface interaction regulation mechanism between clay minerals and microorganism.The main conclusions are as follows:(1)The effects of three clay minerals,montmorillonite,illite and kaolinite,on denitrification characteristics were investigated through batch experiments.The results showed that montmorillonite,illite and kaolinite increased the denitrification rate by5.0,4.8 and 4.9-fold,respectively,and the reduction of nitrate nitrogen and nitrite nitrogen was accelerated in the denitrification process.Cyclic batch experiments demonstrated that the efficiency of clay mineral enhanced biological denitrification was repeatable.The electron supply capacity of clay mineral structure was analyzed by molecular orbital energy level calculation,and then it was theoretically analyzed that clay mineral could be used as redox medium to promote the electron transfer process of denitrification.(2)Based on the experimental system of montmorillonite enhanced denitrification,the macro-regulation mechanism of the interface between clay minerals and microorganisms was clarified from the aspects of morphology,electron transfer and microbial metabolic activity.The morphology and structure of clay mineral surface biofilm were analyzed by scanning electron microscope,and the interface interaction between clay mineral and microorganism was interpreted.The results showed that montmorillonite was beneficial to extracellular polymeric substances secretion and the content of electroactive substances,increased the capacitance of the system by 102.9μF and decreased the resistance by 26.9 Ω,and improved the electrochemical activity and electron transfer efficiency of the system.Enzymatic analysis showed that montmorillonite promoted the activities of NADH,nitrate reductase and nitrite reductase,and increased the metabolic activity of denitrifying microorganisms.Therefore,the mechanism of interaction between clay minerals and microorganisms interface,electron transfer,microbial metabolic activity and other aspects of collaborative macro-regulation was proposed.(3)Silica nanoparticles(Si NPs)was selected as the basic structural unit model of clay minerals to explore the micro-driving mechanism of the interface between clay minerals and microorganism on denitrification.Batch experiments showed that0.05～5g/L Si NPs enhanced denitrification.In the time current response,it is proved that Si NPs has the ability of electron supply/receiving.Fourier infrared spectroscopy showed that Si NPs could bond with extracellular polymers.Electrochemical properties showed that Si NPs improved the electron exchange capacity of the system,which proved that Si NPs promoted electron transfer in denitrification.Si NPs increased cytochrome c redox enzyme activity and microbial electron transport activity by 116.5%and 145.3%,and ATP content by 115.0%,indicating that Si NPs promoted microbial metabolic activity.Analysis of microbial community structure showed that Si NPs increased the abundance of denitrifying functional bacteria and positively regulated the structure of denitrifying bacteria community.In conclusion,the micro-driving mechanism of siloxide-tetrahedral structure of clay minerals on denitrification was proposed.In this study,the effect and associated mechanism of clay minerals and Si NPs on denitrification were systematically explored for the first time,providing theoretical basis for the application of clay minerals in strengthening the anaerobic biological treatment process of sewage and a new idea for anaerobic biological treatment of difficult degradation of pollutants.