| In view of high remove efficiency and short processing cycle, the in situ chemical oxidation technology(ISCO) has attracted lots of attention in the area of soil remediation. However, in the process of contaminants removal, the side effect generated by the ISCO should be taken into account, in order to further utilize the restored sites. In the present study, two kinds of chemical oxidation methods were investigated to clean up the soil contaminated by pyrene, including persulphate oxidation and Fenton oxidation. Based on the condition optimization for the two oxidation methods, the influence of oxidation on the physic-chemical properties, soil enzymatic activities and the morphology of pyrene were determined. In addition, the impact of chemical oxidation on the soil quality was quantified by using soil evaluation index(SEI). Finally, choosing the ryegrass as the post treatment, the remove rate of pyrene was further increased.The main results were as follows:(1) To catalyze the oxidation of hydrogen peroxide for the dissipation of pyrene, four chelating reagents were selected to complex the Ferric ions. Apart from the determination of the chelating effect the four chelating reagents for pyrene degradation, the effect of the different chelating reagents on the decomposition of hydrogen peroxide was monitored by measuring the concentration of the hydrogen peroxide in the soil slurry. It was found that the sodium pyrophosphate could slow down the decomposition of hydrogen peroxide, whilst the other three could not. And it turned out that the highest remove rate of pyrene could be achieved by using oxalic sodium as the chelating reagent, followed by EDTA, SP and NTA. Taking the concentration of chelating reagent, Ferric ions and hydrogen peroxide into account, the optimal combination of these factors was screened by the method of Response surface methodology(RSM).(2) The oxidation efficiency appeared to be closely associated with the dosage of persulphate concentration. Analysis from RSM indicated that the interactions among temperature, dosage of hydrogen peroxide, and concentration of Fe2+ had marked influence on the oxidation efficiency. For the five grams of soil spiked with 500 mg/kg pyrene, the degradation rate of pyrene could be as high as 94% by using 2.62 m L 0.375 mol/L Fe2+ and 0.58 ml 30% H2O2 under the temperature of 50 °C.(3) The physic-chemical properties of soil was largely influenced by the persulphate oxidation and Fenton oxidation. The activities of invertase and urease were rapidly decreased by 80% and 95%, respectively, when subject to the chemical oxidation. Similarly, the content of total nitrogen and total organic matters decreased to a certain degree. Majority of the bioavailable fraction of pyrene was removed by the chemical oxidation, and the residual pyrene was not detected in the study. However, the absorbed fraction of pyrene remained relatively constant. Through the determination multiple factors involving the soil properties, enzymatic activities and fractions of pyrene, the soil quality was assessed by employing the soil evaluation index, which suggested that the soil quality was improved by the chemical oxidation process.(4) For the need of large scale experiment, an apparatus was designed which was equipped with temperature controlling functions. The oxidation treatment gave rise to significant decrease in the activity of polyphenol oxidase and dehydrogenase. On the other hand, the activity of catalase was markedly increased. It was noted that after sixty days planting, the activity of polyphenol oxidase and dehydrogenase were recovered to the original level. Ultimately, the concentration of pyrene declined to 130 mg/kg, and the total remove rate increased from 50% to 73%. |
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