| PAHs (Polycyclic Aromatic Hydrocarbons, PAHs) the general term of hydrocarbons arrange by more than 2 or 2 benzene rings in linear, angular, or cluster-like. PAHs are products of incomplete combustion such as coal, oil, garbage and so on, because of its three-induced effects-carcinogenic, teratogenic and mutagenic, it can be great harm to the ecological environment and human health through the food chain. In recent years, PAHs is widespread concerned as a group highly representative organic pollutants, the PAHs has been included in the environmental pollution blacklist in China.it has been seen as an important chemical pollutants widely present in the environment, and also an important chemical contaminants in groundwater.The clay layer in groundwater system has been seen as impermeable layer, saturated clay under natural state, there are three pore structuresrset intergranular pore,set of particles within the pore,set intergranular pore contacts. Three kinds of pores haye good connectivity, The main presence of water is bound water. Clay layer is not absolute impermeable,under certain osmotic pressure, it may be permeable. The presence of pores provide a more stream-channel for the pore water pressure streaming and groundwater more streaming, meanwhile the pollutant in water may also penetrate the clay layer, over-exploitation of deep water can cause poor water quality of shallow groundwater flow through the permeable layer to deep water, led to the deterioration of deep confined water quality. In recent years there has been a lot of research reports about how water and contaminant flow through aquitard pollute deep groundwater. But how organic pollutants migrate and transfort through aquitard should be further research.In PAHs,the phenanthrene is relatively simple and low molecular weight PAHs, formed by three benzene rings has similar regional structure of carcinogenic polycyclic aromatic hydrocarbons, so phenanthrene as a typical model compound of the toxicity of polycyclic aromatic hydrocarbons is often used to research degradation pathways, migration and transformation mechanisms. This paper designed a high-osmotic flow device, simulated the permeable process of polycyclic aromatic hydrocarbons-the phenanthrene through infiltration saturated cohesive soil in underground environment. The following rules were obtained by experiments:1,The natural attenuation regular of phenanthrene in the aquitard.(1)The natural attenuation of phenanthrene in the aquitard was divided into three stages: physical adsorption; Strong microbial degradation period; stable microbial degradation period. The degradation rate of phenanthrene was 99.42%.(2)The migration form of Phenanthrene through the aquitard was based in 4-ethoxy benzoic acid ethyl ester and 3,5-di-tert-butyl -4-hydroxybenzaldehyde, and also a lot of straight-chain alkanes.2,The affection regular of pH, salinity, ligands to the migration flow behavior of phenanthrene in the aquitard.(1) The increase of salinity made phenanthrene migrate become weak in the aquitard. Under high salinity, in participate of HCO3-, phenanthrene and Ca2+, Mg2+ occurred complex-precipitation., the residual concentration Ct of Phenanthrene decreased with salinity increased, the remaining concentration and salinity showed logarithmic variation, fitting equation:Ct=-0.13751n(TDS)+0.6688; The fitting curve of decay rate and salinity showed logarithmic variation, with the increase of salinity, this trend became weak, that decay slowly, migrate weakly, fitting equation:Decay rate(%)=0.12591n(TDS)+2.3281.(2)Different pH,the concentration decay curve of phenanthrene through the aquitard was divided into rapid decay section, slow recovery section, smooth tend section. The rejection of phenanthrene in the aquitard was in amount to 82%-96%. Downward migration was only 1.1%-1.3%.The most favorable pH was 8 for soil to adsorpt phenanthrene, the downward migration concentration of Phenanthrene was the minimum. Under high osmotic pressure, the moving speed of pollution migration front was 0.714cm/d. Retardation factor R=8.053, Under different pH, sulfate participated the migrate flow of phenanthrene in the aquitard in the form of complex through the formation of redox reactions with phenanthrene, a small amount of Mg2+,Ca2+, CF formed complexes with phenanthrene.The remaining concentration Ct of phenanthrene decreased with the pH increased, pH and the remaining concentration of phenanthrene after transforming showed linear variation, fitting equation: Ct=-1.499(pH)+47.215;pH and the decay rate of phenanthrene fitted with linear variation, fitting equation:Decay rate(%)=0.042(pH)+0.515.(3)When bicarbonate was the major ligand. mainly occurred Ca2+HCO3-→CaHCO3+ Mg2+HCO3-→MgHC03+, then formed complexes with phenanthrene; When sulfate wse the major ligand, SO42-and phenanthrene occured the complexation reaction; When EDTA was the main ligand, enhanced the interaction degree of HCO3- and phenanthrene, and also the relevance of content. Indirectly promoted Mg2++HCO3-→MgHCO3+ formed complexes with phenanthrene. Under different ligand, the attenuation of the phenanthrene was in line with second-order reaction kinetics equation.Under the conditions of the three ligands, Half-life of Phenanthrene was 32-61h. the decay rate constant of phenanthrene had no significant difference, very small (0.0002-0.0003).The order of rate constant was sulfate> EDTA> bicarbonate.These conclusions provided theoretical basis and parameters basis for evaluating migration intensity,transformation mechanism,control measures of organic pollutants through the aquitard.
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