Reinforcement And Mechanism Of Iron-based Materials And Shewanella For The Trichloroethene Reduction By Dehalococcoides

Trichloroethene(TCE)is extensively used as extractant,metal degreaser and so on.Due to improper disposal,it has contaminated soil and groundwater.TCE can be biologically removed by indigenous anaerobes.For example,Dehalococcoides could completely dechlorinate TCE to non-toxic ethene as final product.The TCE reduction rate by Dehalococcoides depended on the electron transfer efficiency through electron transfer chain,which composed of hydrogenase,iron-sulfur cluster binding enzyme and dehalogenase.They were corresponding the starting process of electron,the intermediate transfer of electron and the end utilization process of electron,respectively.To improve electron transfer efficiency,this article studied the mechanism of iron-based materials mediated TCE reduction by Dehalococcoides.The innovative results were summarized below:(1)In the starting process of electron,the free electrons and hydrogen provided by nano-zero-valent iron(nZVI)as electron donor were used for the TCE reduction by Dehalococcoides.The free electrons were transferred via iron-sulfur cluster binding enzyme and dehalogenase.Compared with hydrogen as the only electron donor,the reduction rate of TCE and its product by nZVI/Dehalococcoides was enhanced from 3.1?mol Cl^-/d to 4.7?mol Cl^-/d.Moreover,the addition of electron trapping agent and competitive electron acceptor significantly inhibited the reduction rate of TCE by nZVI/Dehalococcoides.The addition of formic acid(FA)enhanced the corrosion of nZVI which increased the transcripts of the dehalogenase gene tce A for 4.5 times.Compared with no FA,the reduction times of TCE further increased about 54.9%.(2)In the intermediate transfer of electron,we illustrated the mechanism that iron sulfide enhanced the electron transfer of Dehalococcoides,following the TCE reduction rate enhanced from 2.8?mol Cl^-/d to 4.5?mol Cl^-/d.With the addition of Fe S,transcriptome analysis proved that the expression of molybdenum transportion(DET1161,mod A),vitamin B₁₂(VB₁₂)absorption(DET0685,DET1139,cob A)and iron-sulfur clusters assembly genes(DET 1632)were up-regulated 2 times higher,which enhancedelectron transfer efficiency.Calculated from the TCE dechlorination to ETH,the cell yield with produced Cl^-1 increased from(3.71±0.5)×10⁷ to(2.37±0.4)×10⁸ cells mol^-1 Cl^-1on Day 12.(3)In the end utilization process of electron,Shewanella Oneidensis MR-1 enhanced the activity of dehalogenase of Dehalococcoides.With the addition of Shewanella Oneidensis MR-1,the period of reducing TCE to ethene by Dehalococcoides was shortened one third.Shewanella Oneidensis MR-1 promoted the secretion of VB₁₂ by methanogens following the concentration increased from 3.08?g/L to 6.01?g/L and reduced the high-valence state of VB₁₂.As the activity center of dehalogenase,the changed concentration and valence of VB₁₂ increased the transcripts of the dehalogenase gene vcr A for 10 times which alleviated the accumulation of intermediate products VC.