Study On In-situ Remediation Of Heavy Metal Contaminated Groundwater By Sulfur-based Mixotrophic Biological Permeable Reactive Barrier

Groundwater is an important source of water in agriculture,urban and industrial.However,with the rapid development of modern industry and economy,heavy metal pollution in groundwater is becoming more and more serious.In particular,the widely used metal vanadium in industry and the uranium required for the development of nuclear industry both cause serious pollution to the groundwater ecosystem.Mixotrophic remediation technology combines the advantages of autotrophic and heterotrophic microbial remediation technology,which can make autotrophic microorganisms and heterotrophic microorganisms synergy,significantly improving the efficiency of microbial remediation of heavy metal contaminated groundwater,and reducing the risk of secondary pollution of groundwater.Firstly,the advantages of mixotrophic repair technology compared with heterotrophic and autotrophic repair technology were explored.A column reactor was established with wood chips and sulfur particles(S(0))as electron donors and mixed shells as inorganic carbon sources.The removal efficiency of pentavalent vanadium(V(V))in the column reactor reached 97.4 ± 0.99%.The continuous flow column experiments demonstrated that the shorter hydraulic residence time and the higher initial V(V)concentration would reduce the removal efficiency of V(V)by the reactor.At the same time,in the presence of V(V)and nitrate,there was an electronic competition relationship between the two pollutants.The changes of microbial community under different conditions were explored.Microorganisms such as Geobacter,Sulfuricurvum and Thiobacillus play an important role in V(V)reductionSubsequently,the optimium organic electron donor for sulfur-based column reactor of hexavalent uranium(U(VI))contamination was explored.The experiment proved that wood chip had a higher efficiency to reduce U(VI)than sawdust and rice husk,reaching 90.2 ± 4.61%.After that,continuous flow column experiments were carried out with woodchips and sulfur particles as fillers.The experiment proved that the reduction of hydraulic residence time and the increase of initial U(VI)concentration could reduce the removal efficiency of U(VI)by the reactor.Comamonadaceae,Mycobacterium and Plantomytomycetaceae may play an important role in the reduction of U(VI).Finally,the woodchip sulfur column reactor was used to remove co-contamination of V(V)and U(VI).By changing the initial concentration of V(V)and U(VI),it was proved that there is an electronic competition relationship between V(V)and U(VI).At the same concentration,V(V)was more receptive to electrons transmitted by microorganisms.Microorganisms such as Planctomycetaceaer,Gaiellales and Actinobacteria may play an important role in the reduction of V(V)and U(VI).This study confirms the feasibility of microbial remediation of V(V)and U(VI)contaminated groundwater under mixotrophic culture conditions,and simulatee the process of in situ remediation by continuous flow column experiment.Experiment provides new ideas for in situ remediation of groundwater contaminated by V(V)and U(VI).