Study On Cometabolic Biodegradation Of Chloroethenes In Landfill Cover

Chloroethenes was widely used in the key industries related to national national economy,such as paper and medical.Extensive use and inadequate disposal of chloroethenes have led to prevalent groundwater and soil contamination worldwide.It is a common human health and environment concern in urban areas.Landfill cover soil riched a variety of functional microorganisms during the long-term domestication of landfill gas.It oxidize a considerable fraction of the methane and chloroethenes.So landfillcover was considered to be a good greenhouse gas reduction biocatalytic material.In this paper typical landfill cover soil was used to a series study.The results are as follows.（1）Adsorption characteristics and kinetic of 8 VCHs in landfill cover soil was completely investigated by static adsorption experiments,respectively.The results demonstrated that adsorption isotherm of chlorinated alkanes and chlorinated aromatic hydrocarbons in the landfill cover soil were both consistent with the Freundlich model（R²=0.81-0.87）,and the adsorption isotherm of chloroalkene in the soil was consistent with the Langmuir model（R²=0.87-0.96）.Moreover,in this study,the 8 VCHs adsorption equilibrium time were all about 20 h,but the result of adsorption rate in the range of 26-250μg/(g_soil·h)was much higher than those reported by references.（2）Microbial community structure characteristics of landfil covered soil in the prensence of typical chlorinated hydrocarbon and landfill gas was investigated by static experiments.The result showed that degradation rate of chlorinated hydrocarbons in the cometabolic condition was in accordance with the first-order reaction kinetics,and the degradation activity of low-chlorine substituted VCHs was higher.The bacterial community composition was investigated by Illumina MiSeq sequencing targeting V3^V4 region of 16S rDNA gene.There is a significant difference that Thiobacillus,unclassified_Rhizobiales,Methlcocystis,Intrasporangium,Luteimonas,Lysobacter and uncultured_Gemmatimonadaceae after a perid acclimation.Those microorganisms may highly correlated to anaerobic metabolism of chlorinated hydrocarbons.（3）A simulated landfill cover system was constructed,which has a good degradation capacity of methane（CH₄）and chloroalkene.The degradation efficiency of PCE in the landfill cover soil increased maximum and then decreased with increasing biogas flux.The result showed that in the presence of trichloroethylene（TCE）can promotes the oxidation of methane.The TCE degradation rate was 0.66-2.45 g·m^-2·d^-1 The degradation rate of TCE increased maximum and then decreased with increasing methane flux and TCE flux.The maximum degradation efficiency is 72%.（4）Based on the distribution of chloroalkene,the co-metabolism degradation mechanism of chloroalkene in the landfill cover was fully explored.TCE was first dechlorinated to dichloroethylene（t-1,2-DCE and c-1,2-DCE）at the anaerobic zone.The result showed that the concentration of dichloroethylene reached a maximum at depth30-15 cm from the top.The remaining TCE and generated dichloroethylene were cometabolic oxidation at aerobic zone and facultative anaerobic zone;PCE was alao firstly dechlorinated to TCE and dichloroethylene at the anaerobic zone.Dechlorination product TCE can be further dechlorinated to dichloroethylene with the action of dechlorinating microorganisms（such as Dehalobacter）.The dechlorination and oxidation reaction are both occured at the facultative anaerobic zone.