Study On Mechanism Of Remediation Of Perchloroethylene Contaminated Groundwater By Emulsified Zero-valent Iron In Situ Reaction Zone

Perchloroethylene（PCE）is listed as a priority control pollutant and is mainly used in domestic and foreign dry cleaning and metal degreasing industries.It will cause harm to human health and the environment.Therefore,it is of great significance to restore PCE-contaminated groundwater.The traditional groundwater remediation technology will generate more toxic intermediate products when remediating PCE pollution,while the emulsified zero-valent iron（EZVI）in-situ reaction zone combines chemical reduction and biological reduction,which has the advantages of fast degradation rate,less accumulation of intermediate products,and promotion of due to the advantages of indigenous microorganism growth and low cost,the establishment of EZVI in situ reaction zone to remediate PCE contaminated groundwater has good application prospects.In this study,EZVI prepared by emulsified oil（EVO）-coated nano-zero valent iron（nZVI）was used as the remediation reagent,in which nZVI was used as a chemical reducing agent,EVO was added organic matter,and river sand was used as the source of indigenous microorganisms to construct EZVI remediation reaction system for PCE,analyzed the kinetics of EZVI reduction of PCE and the process and degradation performance of PCE;established an EZVI in-situ reaction zone in the simulation column,and clarified the degradation mechanism of PCE in the in-situ reaction zone according to the formation and evolution of the EZVI in-situ reaction zone.and related substances changes;investigated the changes in the microbial community structure in the EZVI reaction zone;and carried out an environmental,ecological and economic analysis of the EZVI in situ reaction zone.The comprehensive evaluation of the efficacy of EZVI in situ reaction zone technology to remediate PCE contaminated sites has laid a theoretical foundation for the application of EZVI in situ reaction zone technology in PCE-contaminated groundwater.（1）EZVI slurry coated with EVO（1%）nZVI（0.95 g/L）was prepared,and the kinetics and repair process of EZVI reduction to PCE were studied.The results of static batch experiments show that the reduction of PCE by EZVI conforms to first-order kinetics;in the PCE repair system with the same volume of EZVI（1%EVO and 0.95g/L nZVI）and EVO（1%）repair reagent,EZVI repairs PCE The accumulation of intermediate product DCE can be reduced,and the degradation efficiency is 68.9%higher than that of adding EVO alone to repair PCE.The process of EZVI reduction of PCE is to dechlorinate through Fe0 first chemical reduction.At the same time,EVO provides a good reducing environment for PCE anaerobic microbial dechlorination,which can promote the anaerobic biological dechlorination reaction.（2）The effects of the concentrations of Ca²⁺and SO₄^2-in groundwater on the reduction of PCE by EZVI were investigated.The results show that Ca²⁺can inhibit the reduction effect of EZVI on PCE.When the concentration of Ca²⁺is 10～100 mg/L,the reduction rate constant of PCE decreases by 4.8%～33.9%;SO₄^2-can promote the reduction rate of EZVI to PCE,and the reduction rate of PCE is reduced at 10～100mg/L.Within the range of 100 mg/L SO₄^2-,with the increase of SO₄^2-concentration,the effect on promoting the reduction of PCE by EZVI was more obvious.When the SO₄^2-concentration was 100 mg/L,the PCE reduction rate constant increased from0.184 d^-1 to 0.211d^-1.（3）A simulated column experiment of EZVI in situ reaction band repairing PCE was constructed,and the material changes and repair mechanism of EZVI reduction and repairing PCE were explored.In the simulation column of EZVI repairing PCE,the injection of EZVI can rapidly reduce the pollutant concentration at the pollution source,the abiotic dechlorination in the middle of the reaction is dominant,and no accumulation of intermediates is produced,and the biological reductive dechlorination is dominant in the late reaction.The Fe（II）and S（-II）formed in the reaction zone have electron transfer function,which is beneficial to the reduction and dechlorination of PCE;the iron and sulfur minerals formed on the surface of the medium are beneficial to the biogeochemical reduction;the in-situ reaction zone of EZVI is more efficient than adding EVO alone The degradation rate of reduced PCE was increased by 3.16times.（4）The changes in the microbial community structure in the EZVI in situ reaction zone were analyzed.The diversity index near the initial pollutant was low.After 100days of domestication,the microbial diversity was enhanced.The initial aerobic dominant bacteria were Pseudomonas,Pseudomonas,Acinetobacter has gradually evolved into Clostridium,OPB41 Dechloromonas,Dechlorobacter,Desulfomonas,Desulfite and Methanobacter,with anaerobic fermentation electron donors and dissimilatory iron the effect of reduction,strengthens the anaerobic biological dechlorination reaction.（5）The environmental,ecological and economic analysis of the EZVI in-situ reaction zone is carried out.EZVI preparation cost of repairing groundwater polluted by PCE per cubic meter is 610 yuan.The EZVI in-situ reaction zone has a lower economic cost and no pollution to the environment.