Soil Vapor Extraction(SVE)has been widely used to remove volatile organic compounds(VOCs)from unsaturated soil.It is safe,economical,and highly efficient.In this paper,a total differential equation of the mass transfer in soil porous media under one-dimensional steady-state has been established,followed by the decontamination mechanism study of VOCs removal from red earth through SVE.Then analytic and numerical solutions were acquired for balanced and kinetic models,respectively.Results of the experiments and model simulations showed that the two in good agreement.For mass transfer of contaminant,the balanced and kinetic model were applied to different stages of soil column ventilation process.At the beginning of ventilation,a balanced model matched the experimental results well.However,as time went by,the balanced model prediction curve gradually deviated from data points.By the end of ventilation,only the kinetic model could describe and predict experimental results.

Soil vapor extraction (SVE) has been effectively used for removal of volatile organic compounds (VOCs) from unsaturated soil. It is safe, economical and highly efficient. Column-venting experiment was used to simulate the SVE in the typical red earth in south China. Benzene, one of the most common VOCs, was selected as the single compound. Fluvo-aquic soil of Beijing and black soil of Jilin were selected as the control samples to study the effect of soil types on the SVE remediation process. Different soil water content on the venting behavior of a binary mixture (benzene and ethylbenzene) from the red earth was also investigated. The results showed that the best soil water content was 16.8% at the 600 ml·min -1 vapor flow rate for the binary mixture. Control experiments indicated that soil type and soil organic matter were also key factors in SVE. © All Rights Reserved.

The concentrations of polycyclic aromatic hydrocarbons (PAHs) were determined in groundwater and soil profiles from upland field and paddy field in the Hunpu wastewater-irrigated area of northeast China. In the study area, the peak concentrations of total PAHs were within or just below the topsoil, and the contents decline with depth at various trend verified by the Spearman’s rank correlation test. The total PAH concentrations in upland soil layers ranged from 46.8 to 2,373.0 μg/kg (dry wt.), while the concentrations in paddy soil layers ranged from 23.1 to 1,179.1 μg/kg (dry wt.). The 16 priority PAHs were all detected in the analyzed soil samples, and naphthalene (Nap), phenanthrene (Phe), fluoranthene (Fla), chrysene (Chr), and benzo[a]pyrene (Bap) were selected for further study in terms of their vertical distributions. The concentrations of both total and individual PAHs in upland soil were generally higher than those in the corresponding layers of paddy soil. The concentrations of total and individual PAH were notably different between the corresponding horizons in upland and paddy soil were probably attribute to the different sources and properties of the PAHs and soil; different methods of soil tillage and plant growing. Special PAH compound ratios, such as phenanthrene/anthracene, fluoranthene/pyrene, LMW/HMW, and parent PAH ratios (Ant/178, Fla/202, BaA/228, and Ilp/276) were used to identify the source of soil PAHs. The data suggests that the possible sources of PAHs in the Hunpu wastewater-irrigation area are the incomplete combustion of coal, petroleum and crude oil, automobile exhausts. These sources lead to pollution of the soil and groundwater by wet/dry deposition and vertical downward migration.

Vertical distribution of polycyclic aromatic hydrocarbons(PAHs) in Hunpu and Shenfu wastewater irrigated soil and Qingyuan soil(control site) was discussed.The qualitative results demonstrated that 10 kinds of EPA priority PAHs were detected in Shenfu,while 12 kinds of the PAHs in Hunpu and 8 kinds of the compounds in Qingyuan are detected.The total concentration of PAHs was found to have peak at(2～5) and 5～10 cm layer and decline with depth.Four-ring and five-ring PAHs had a high proportion in each profile.The principal PAHs compounds were fluoranthene,benzo[a]anthracene and benzo[k]fluoranthene which was similar with surface soil.The highest concentration of low-ring compounds distributed at 0～2 cm,and the others at 5～10 cm.PAHs ratios inferring the sources of PAHs indicated that the main sources of PAHs in the soils were incomplete combustion of petrol,crude soil and coal as well as the contribution of wastewater irrigation.