| With the development of society, the adjustment of the industrial structure and the transformation of economic development, many industrial enterprises shut down or moved out the city for off-site relocation, resulting in many contaminated sites which desiderate to be remediated. Polycyclic aromatic hydrocarbons (PAHs), a common type of soil organic pollutants, endanger the human health and ecological environment severely. Physical remediation technology as an important site remediation technology has been widely used. But the conventional physical remediation technologies such as thermal remediation and replacement method have big shortcoming with large energy consumption, low processing efficiency and major damage to soil structure. However, the microwave technology has the advantages of non-selective treatment, small energy consumption and removable equipment.In recent years, researches on contaminated site remediation using microwave technology have been paid pay great attention to gradually.Polycyclic aromatic hydrocarbons (PAHs) which are common organic pollutants were set as research objects in this paper. An experiment for simulated PAHs contaminated soil treatment by microwave was carried out. The study explored the influence factors and the dynamic mechanism of PAHs digestion by microwave, and investigated the effects of absorbing materials on PAHs digestion. On the basis, actual PAHs contaminated soils were treated by microwave to validate the remediation performance. Results obtained are shown as follows:(1) Effects of the factors such as microwave power, microwave time, soil moisture content and initial concentration of pollutant on PAHs digestion efficiency by microwave were investigated. The results indicated that under the conditions of microwave power of 800 W, microwave time of 10 minutes, soil moisture content of 10% and initial concentration of 7.2 mg/kg, the digestion efficiency of benz[a]nthracene reached the maximum of 68.92%, and the residual concentration was 2.24 mg/kg. Higher or lower soil moisture content inhibited the PAHs digestion. And the digestion dynamics obeyed the second order kinetic model,With the increase of initial concentration, the digestion rate constant decreased, but the requisite time for microwave treatment goals also decreased. In addition, the digestion efficiencies of phenanthrene, pyrene and dibenz[a,h]anthracene under the optimal microwave conditions were 100.00%,86.06% and 70.50%, respectively.(2) The enhanced roles of different absorbing materials for digesting PAHs in contaminated soils by microwave were investigated. The results indicated that all additives could improve the digestion efficiencies of PAHs, and the order of enhanced role was as follows:manganese dioxide> aluminum powder> pencil core> hydrogen peroxide> silicon carbide. At microwave time of 10 minutes and in their optimal addition amount, the microwave digestion efficiencies of benz[a]anthracene were 88.21%,83.06%,80.39%,83.06%,79.74% and 66.60%, respectively. Thereinto, for the treatment of adding manganese dioxide, the residual concentration of benz[a]anthracene in the treated soil was only 0.85 mg/kg, which reached "A" level of the soil environmental quality evaluation standards for land use in the exhibition (provisional) (HJ350-2007). Moreover, when manganese dioxide was added into soils as absorbing material, the microwave digestion efficiency of phenanthrene, pyrene and dibenz[a,h]anthracene were 100.00%,96.79% and 81.09%, respectively.(3) Actual PAHs contaminated soils were treated by microwave under the optimal conditions, and the treatment efficiencies of naphthalene, fluorine, acenaphthylene, acenaphthene, phenanthrene, anthracene, fluoranthene, chrysene, pyrene, benz[a]anthracene, benzo[b]fluoranthene and benzo[g,h,i]pyrene in soils were determined. When manganese dioxide was added into soils as absorbing material and the contaminated soils were treated by microwave under the optimal conditions for 10 minutes, the residual concentration of total PAHs both in seriously contaminated and slightly contaminated soils trended to balance and the digestion efficiencies of total PAHs were 96.70% and 95.54%, respectively. Nevertheless, the balance times of different kinds of PAHs were different and increased with an increase of the number of benzene ring in PAHs molecule. Besides, the digestion dynamics of total PAHs in seriously contaminated soil was analyzed, and the result showed that the digestion dynamics of total PAHs obeyed the first order kinetic model. |
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