Study Of Migration Laws Of PAHs In Porosity Medias Under Municipal Solid Waste Dump Site

Polycyclic Aromatic Hydrocarbons (PAHs) are one type of persistent organic pollutants. They exist widely in landfill leachate and pollute groundwater, hence endangering people’s health and environmental safety. Although the clayed soil beneath the municipal solid waste dump site is the natural parclose protecting the underground space, it cannot block the pollutants totally, and some of the pollutants still can leachate downward, moving with groundwater. Some researchers have already investigated the concentrations of PAHs in landfill leachate, soils and groundwater; some have conducted statistic adsorbtion experiments and soil column experiments; some have done numerical modeling studies about hydrophobic organic pollutants leachating from contaminated water. However, there are still lots of work to be done about PAHs in landfill leachate migrating in clayed soil and in aquifer.Naphthalene and Benzoperylene are the lowest and highest PAHs in molecular weight, respectively, thus they were taken as objects of this study. By conducting adsorption experiments of Naphthalene and Benzoperylene on the clayed soil taken from a waste dump site in Beijing, adsorption parameters were obtained and used in the numerical modeling procedure, thus the migration depth of PAHs was forecasted by Hydrus. Also, in the saturated zone, the migration length with groundwater was calculated by GMS.The adsorption equilibrium times of Naphthalene and Benzoperylene on clayed soil are12h and0.5h, respectively, while the adsorption capacities are5.51μg/g and1.05μg/g, respectively. The leachate can put off the adsorption equilibrium times, enhance the capacity of Naphthalene and reduce the capacity of Benzoperylene. Benzoperylene shows a poor capacity leaching in the soil column, while Naphthalene breaks through the column much more easily and quickly:The blocking efficiencies of20cm and30cm high soil columns are97.5%and70.5%, respectively. However, the leachate can reduce that results, making the20cm high column’s blocking efficiency only50%. One of the reasons may be that the dissolved organic materials in the leachate promote Naphthalene’s migration.By the numerical prediction of Hydrus, after8.5d’s leachting, the concentration of Naphthalene in the groundwater will be over the limit value of Ⅲ class, if it’s initial concentration was260μg/L; if Benzoperylene in the leachate moves as an initial concentration of1μg/L, it will break through the70cm deep’s vadose zone at1.16a. By the numerical prediction of GMS, while neglecting the adsorption, degradation, molecular diffusive and other physical-chemical reactions, Naphthalene and Benzopcrylene’s pollution plumes have the same shape, and they can move to94.5m with the groundwater within one year.The innovation points of this paper lie in that the adsorption and barrier effects of clayed soil to PAHs in different background solutions were compared and discussed for the first time. Also, the migration laws of the lowest and highest PAHs in clayed soil were compared, and the spatial and temporal distribution laws of PAHs in leachate in unsaturated and saturated zones were predicted, respectively.