| Petroleum hydrocarbons and heavy metals contained in petroleum are persistent pollutants,both of which have strong toxicity characteristics,can cause teratogenicity,carcinogenicity,mutagenicity,and pose a great potential threat to human health and ecological safety.How to safely and effectively remedy oil-contaminated soil has become one of the urgent problems in the environmental field.Researchers at home and abroad have conducted many experiments on oil-contaminated soil management.Bioremediation technology has attracted more and more attention because of its low cost,no damage to the soil environment required for plant growth,no secondary pollution,and simple operation.However,studies have found that the petroleum chain hydrocarbons in the oily soil have s trong hydrophobicity and are easily adsorbed in the soil.The low water solubility and bioavailability of these substances make them difficult to be bio-degraded in the soil.In the process of repairing petroleum-contaminated soil by microbial remediation technology,heavy metals coexisting with petroleum hydrocarbons will affect the growth and metabolism of petroleum hydrocarbon degrading bacteria,thereby affecting their repair efficiency.In addition,petroleum hydrocarbons are often wrapped in the outer layer of the bacteria group due to their hydrophobic characteristics,and inhibit the respiratory growth and block the effect of microorganisms on the heavy metals in the water,which seriously inhibit the growth of microorganisms,thus making the heavy m etals in the soil more difficult to be removed,and increasing the difficulty of treatment of oil-contaminated soil.In recent years,cyclodextrin has received extensive attention in the field of petroleum contaminated soil treatment due to its special str ucture.Cyclodextrins(CDs)are a class of cyclic oligosaccharides formed by the action of cyclodextrin glucosyltransferase on starch.Cyclodextrin compounds are characterized by the presence of a hydrophilic outer edge and a hydrophobic cavity in the mole cular structure.Its hydrophobic cavity can combine with many organic substances to form host and guest inclusions,and the water solubility of the inclusion compound is greater than the water solubility of the organic matter itself due to the hydrophilici ty of the outer side of the CD,which can increase the solubility of the organic substance in water,and also have a certain coordination effect with heavy metals.The cyclodextrin itself is non-toxic and biodegradable,it is an environmentally friendly material.However,cyclodextrin only has a solubilizing effect on some hydrophobic organic pollutants,and its solubility in water is low,which limits the wide application of cyclodextrin to some extent.Based on the above reasons,we chemically modified cyclodextrin,selected cyclodextrin derivatives with stronger water solubility and coordination ability to heavy metals,studied the effects of initial concentration and soil acidity on their solubility and absorption,and optimized its application condition s.Glycine-?-cyclodextrin(G-?-CD)was prepared through multiple experiments.The infrared spectroscopy and XPS analysis showed that G-?-CD retained the original structure,at the same time,amino groups and carboxyl groups were added.Hydrophilic groups such as amino groups and carboxyl groups increased the solubility of ?-cyclodextrin in water and could form complex with heavy metals.The study found that in the treatment of petroleum-contaminated soil with G-?-CD,when the concentration of G-?-CD in the solubilizer was 70 g/L,the p H of the soil was 6.0 ?7.0,the reaction temperature was 30?40°C,and the ion concentration of the soil was 0.25mol/L,the organic matter content was 1%,the desorption effect of petroleum hydrocarbons and heavy metals achieved better results.Based on the previous research,we also analyzed the microbial degradation behavior of petroleum hydrocarbons in petroleum-contaminated soil under G-?-CD solubilization,and the changes of soil heavy metal species and bioavailability to ga in insight into the biological fate of petroleum hydrocarbons,and heavy metals in the soil environment and their ecological effects.It was found that after treatment of contaminated soil with G-?-CD,the form of heavy metals in the soil also changed greatly.The exchangeable fraction,carbonate bound fraction and organic binding fraction of Pb and Cu all decreased by more than 50%.The content of oxidizable and residual state of the matter decreased by about 60%,indicating that G-?-CD formed a stable soluble complex with heavy metals,which greatly reduced the adsorption of heavy metals in the soil,thereby reducing the toxicity and bioavailability of heavy metals in the soil.Moreover,the activities of polyphenol oxidase,catalase,dehydrogenase and lipase in petroleum-contaminated soil treated by G-?-CD were significantly improved.The results suggested that glycine-?-cyclodextrin could effectively amend petroleum hydrocarbon-heavy metal complex contaminated soil,which enhanced the activity of biologic al enzymes.It was found that the bio-remediation of petroleum-contaminated soils pretreated with G-?-CD combined with the soil itself was improved,but it was far from reaching normal soil.Therefore,this paper also strengthened petroleum hydrocarbon deg rading bacteria domestication,screening and identification of a highly efficient petroleum hydrocarbon degrading bacteria,and systematically studied the degradation ability and influencing factors of the degrading bacteria,and optimized the fermentation conditions of petroleum hydrocarbon degrading bacteria.The research not only considered the optimal conditions of the selected factors for the growth and reproduction of petroleum hydrocarbon degrading bacteria,but also the practical and economic problems such as low cost,practicality,and simple operation steps.The results showed that the bacteria cultured by adding soybean meal and corn starch into the inorganic salt medium had the same effect as the beef extract peptone liquid medium,and was more economical and suitable for the application of biological treatment on site.At the end of the experiment,the ecological toxicity test was used to comprehensively evaluate the repair effect of the chemical-microbial combined method.The effect of chemical-microbial combined remediation on soil microbial diversity was analyzed by denaturing gradient gel electrophoresis(PCR-DGGE).The results showed that the similarity of soil microbial population structure of oil-contaminated soil and clean soil was only 37.7%.After chemical-microbial combined remediation,the similarity increased to 76.2%,indicating that soil microbial diversity was well restored after chemical-microbial repair.The germination rate of seeds was observed by higher plant germination toxico logy experiment and crop absorption toxicology experiment,and the physiological and biochemical indexes of seedling leaves were measured to evaluate the ecotoxicity of soil after chemical-microorganism combined repair.The results showed that the seed germination rate,photosynthetic pigment content,superoxide dismutase(SOD)activity and malondialdehyde(MDA)content increased with the prolongation of chemical-microbial combined repair time,indicating that soil ecotoxicity was weakened.But there was some ecotoxicity in the soil during the whole period of restoration.The above results provided theoretical basis and technical support for the feasibility of the G-?-CD-microbial combined repair method. |
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