| Polycyclic aromatic hydrocarbons (PAHs) are a group of organic contaminants composed of fused benzene rings which has high toxicity, carcinogenic effects and environmental persistence. PAHs are usually produced from the incomplete combustion of fossil fuel, oil spill and industry release. PAHs pollution is quite serious in China, especially in the soils around coking plant, steel mills, oil exploitation, power plants areas.About 1.4% soil testing points of PAHs are above the Soil Environmental Quality Standard Two, and the average concentration in soil is 580 ?g/kg. The remediation techniques for PAHs removal from contaminated soils are needed to be applied urgently. In this study, we chose the hydrogen peroxide (H2O2), modified Fenton's reagent (H2O2 catalysed by ferrous ions and citric acid as chelating agent), potassium permanganate (KMnO4) and activated persulfate (Na2S2O8 catalysed by ferrous ions and citric acid) as the oxidant agents to degrade the high concentration PAHs polluted soils in steel mill.We measured the soil TOC, the FDA hydrolase and pH changes which was treated as the risk factors before and after the treatment. In order to find the best oxidant. we investigated the effectiveness of chemical oxidation, assessed the soil ecological risk. In order to find the optimum reaction parameters with this advantage oxidant, we changed its reaction conditions, such as increasing the concentration, extending soil water ratio, and prolonging the reaction time. The results obtained are as follows:(1) With the comparing of the four oxidants to the polycyclic aromatic hydrocarbons from contaminated soil, we found that the LMW were easier to be degraded than HMW. Some of the PAHs were hard to be degraded because of sorbed firmly which need more doses. It turned out that the total PAHs removal efficiency was 72.91%,81.15%,82.79% and 94.06% by hydrogen peroxide, modified Fenton's reagent, activated persulfate and potassium permanganate respectively. On the whole, potassium permanganate resulted in the best PAHs removal efficiencies when the added concentration was 2.0 mmol/g.(2) In the soil ecological risk analysis of chemical oxidation technology,we evaluated the index of assessment change such as of TOC. pH. FDA hydrolysis activity and other indicators before and after the treatments. It was relly had much influence on the soil properties even though under the condition of best oxidation efficiency respectively. After using the hydrogen peroxide, TOC decreased 6.39 g/kg, and soil microbial activity was reduced by 33.84%, and soil pH value increased by 1.68. After using the modified Fenton's reagent. TOC decreased 6.40 g/kg, and soil microbial activity was reduced by 18.35% which was relatively smaller, and soil pH value decreased by 1.08. After using the activated persulfate, TOC decreased 5.17 g/kg, and soil microbial activity was reduced by 41.18%. and soil pH value decreased by 1.80. After using the potassium permanganate, TOC decreased 4.81 g/kg, and soil microbial activity was reduced by 29.18%, and soil pH value increased by 1.48. In all these cases, potassium permanganate showed the least effects on soil followed by modified Fenton's reagent, and furthermore, for the hydrogen peroxide and activated persulfate.(3) The potassium permanganate had been chosen as the objective restoration agent, and experiments were conducted to get the best oxidation conditions of potassium permanganate. Based on the results of this study, it showed the best oxidation efficiency when the added concentration was 2.5 mmol/g and soil water ratio was 1:7.5 and the reaction time for 48 h.From what has been discussed above, the PAHs oxidation effect of permanganate oxidation seemed to be the best after adding into the contaminated soils. Polycyclic aromatic hydrocarbon residues concentration meeted the standards of "Zhejiang Province Brownfield Risk Assessment Technology Guideline (33 DB/T 892-2013)" which specified in the part of commercial and industrial land filter value. |
PDF Full Text Request