| The chemical oxidation is an important technique for the remediation of soil organic contamination,which has been widely used in the field.The type of oxidant and its appropriate dosage are key factors to realize the maximum benefit of the chemical oxidation,which influences the goal of“green remediation”.In our study,the soil samples with polycyclic aromatic hydrocarbons?PAHs?were collected form a coking plant,and the batch experiment were conducted to explore the technical parameters of chemical oxidation with two typical oxidants?activated sodium sulfate and potassium permanganate?,to compare their removal of PAHs,and to comprehensively evaluate their potential in the utilization for the remediation of soil PAHs pollution.The removal of PAHs in the soil were ranged 61.25%-78.33%in the treatmentswith different dosage of activated sodium sulfate.The treatments with low dosage of potassium permanganate(0.05-0.10 mmol·g-1)had low degradation ratios of PAHs,which were only 32.30%-68.84%.However,the removal were significantly increased in the treatments with higher dosage of potassium permanganate(>0.20 mmol·g-1),which were higher than 85.0%.There were significant differences among the removal of 16 US EPA priority PAHs?16 US EPA PAHs?by two chemical oxidants.The removal effeciencies of phenanthrene,fluoranthene,pyrene,benzo?a?anthracene,benzo?b?fluoranthene,dibenzo?a,h?anthracene Indeno?1,2,3-cd?pyrene and benzo?g,h,i?perylene were over 85%in the treatments with optimal dosage of either oxidant.Moreover,the removal of Acenaphthylene,acenaphthene,chrysene,benzo?k?fluoranthene and benzo?a?pyrene were ranged from 48.89%to 74.31%.In contrast,the removal of naphthalene and fluorene were both lower than 30%.Overall,the removal effciencies of PAHs in the soil in the tests performed with potassium permanganate was greater compared with activated sodium sulfate.The physical-chemical properties of the soil after chemical oxidation for 7 days were analyzed.The results showed that the effect of chemical oxidation on the soil pH,organic matter content,particle size distribution,carbonate content and dissolved organic carbon were varied depending on the type and dosage of oxidant.In the activated sodium persulfate oxidation treatments,the soil pH and carbonate content were significantly decreased,while the specific surface area,the content of dissolve organic carbon and the free iron oxide were remarkably increased.In contrast,the pH and carbonate content of soils with potassium permanganate oxidation were increased,and the contents of total organic carbon and free iron oxide were decreased.In general,activated sodium persulfate oxidation led to greater change in The physical-chemical properties of the soil than potassium permanganate oxidation.The chemical speciations of heavy metals in soils with chemical oxidation for 7days were also analyzed.The results indicated that both two chemical oxidations significantly influenced the speciation of Co,Ni,Cu,As and Cr in the soils,which were correlated with the oxidant dosage.Compared to the control,the contents of bioavailabile Co,Ni,Cu,As and Cr were increased by 81.56,28.31,9.93,6.10 and26.78 times in the soils oxidized with 1.60 mmol·g-11 of activated sodium persulfate,respectively.For the speciations,the more stable phases?Fe-Mn oxide bound-and residual fractions?of Cu,Ni,Co and As in the soil samples were transformed to the labile phases?exchangeable and carbonate bound fractions?.However,In the treatments with permanganate of dosage of 0.05-0.40 mmol·g-1,the contents of available Cu,Ni,Co and As in soil were dramatically decreased.However,the content of available Cr was increased with the increase of oxidant dosage.Moreover,the contents of Cu,Ni,Co and As as the labile fractions?exchangeable-and carbonate bound fractions?were decreased for the benefit of the more stable fractions?Fe-Mn oxide bound and residual fraction?in the soil samples.The result of soil ecotoxicity showed that,compared to the treatment without chemical oxidation,in the treatments with activation sodium persulfate oxidation,the inhibition of water extracts of the soils to luminescent of Vibrio fischeri were increased at the rate of 19.66%-37.98%.Meanwhile the inhibition of water extract of soils to seedling growth of Chinese cabbage were increased,and the root length and fresh weight were significantly decreased at the treatments with activatedsodium persulfate over 0.80 mmol·g-1.It suggested the activated sodium persulfate oxidation led to the increase of soil ecotoxicity.However,the inhibition of water extracts of the soil to luminescent of Vibrio fischeri after potassium permanganate oxidation were significantly decreased,ranging from 26.42%to 34.77%.Moreover,the inhibition of soil methanol extract to seedling growth of Chinese cabbage were significantly reduced,the root length and fresh weight of Chinese cabbage were significantly increased.So potassium permanganate oxidation significantly reduced the soil ecotoxicity. |
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