An Experimental Investigation About Vertical Transport Of PHEs In Clay Column

Polycyclic aromatic hydrocarbons (PAHs) with high lipid solubility and relatively low water solubility is persistent organic pollutant, receiving much concern in the field of environment protection for their high toxicity, low fluidity and hard to biodegradability. Human activities such as petroleum fuel burning, motor vehicles, waste combustion, production of cokes or asphalt and production of aluminium can yield a great deal of PAHs, which are wildly distributed in the environment. With the rapid development of society and economy, the urban population has being expanded rapidly, which produces more and more municipal solid waste. The growth rate is faster than10%, above the average of worldwide. Proceeding from our national conditions, sanitation landfill is mainly urban waste disposal method in a very long time. PAHs are surly can be found in landfill leachate while the landfill is the final place for soil wastes. PAHs from leachate will enter environment media such as soil and water with many ways if isolation control is not effective.As a category of Polycyclic aromatic hydrocarbons, Phenanthrene (PHEs) is on the list of 16 PAHs listed as priority pollutants by US EPA (Environmental Protection Agency). Its concentration in landfill leachete is relatively high. Phenanthrene has poisoning effect on respiratory tract and skin of human, and also it is the smallest carcinogenic polycyclic aromatic hydrocarbons feature unit. This study selects the Phenanthrene as the sample to explore its vertical transport mechanism in silty clay, which is widely distributed in North China Plain, get filtration capability of silty clay to cut off Phenanthrene. The result are obtained by adsorption tests, leaching test and numerical simulation of BTCs by CXTFIT2.0, then can be used to optimize the design of impermeable barrier lining. Main conclusions and productions from this research are as follows:1. The main adsorption mechanism of clay to the Phenanthrene is surface adsorption. The organic content of soil samples is less, though its distribution function did not keep the dominant position, and it played play a supplementary role. The adsorption is with staggered variation, and equilibrium time is 9 hours. The adsorption isotherm of silty clay to the Phenanthrene coordinated with Freundlich model, the soil—water partition coefficient of Philippine(Kd) is 0.01, and the organic carbon and water partition coefficient (Koc)is 14.29.2. The adsorption capacity of silty clay to Phenanthrene reach the best state when the ratio of humic acid reach 5%, the adsorption ratio of Phenanthrene would reach 98.5%. The max adsorption is in the inverse ratio of soil particle size, in direct proportion to the content of the soil clay and specific surface area. Adsorption effects both of clay and silty clay are good, without big difference. When the pH was 7.42, the adsorption capacity of clay to Phenanthrene would increased if the pH became larger or smaller, and such tend was more obvious in the alkaline environment. When pH>7.42, the adsorption capacity of soil samples increased rapidly with the pH value became larger.3. The water velocity is very slow in soil column leaching test, and immobile water in silty clay is relatively much. There is physical nonequilibrium process in transport of conservative solute Cl-, and effect of molecular diffusion can not be neglected. As a result, properties porous media and floe field will not be characterized accurately by dispersion coefficient got by BTC of Cl". 4. Only 0.048%o Phenanthrene drenches out silty soil column, filtration capability is bigger than 1.46g/kg.Retardation factor in leaching test is smaller than precomputed by absorption test. There is chemical nonequilibrium process in transport of reactive solute Phenanthrene, and simulation result of its BTC with two-site model by using CXTFIT2.0 is good. Because of properties porous media and floe field can not be characterized well by dispersion coefficient of Cl- and data of concentration changes of Phenanthrene in leachate are limited, the correlation coefficient is not very good.