Migration And Transformation Of Petroleum Hydrocarbons In Soil And Response Characteristics Of Soil Flora

Petroleum is a complex mixture of alkanes,aromatics and a small amount of non hydrocarbons.In the process of oil exploitation,transportation and storage,it will inevitably bring oil pollution.When petroleum hydrocarbon pollutants enter the soil,they not only have a serious impact on the structure and permeability of the soil,but also change the physical and chemical properties of the soil,the structure and diversity of the soil flora.Based on the review of the changes of soil physical and chemical properties,the response of soil bacteria and the bioremediation technology of polluted soil under the condition of oil pollution,this paper studies the migration,transformation and natural removal characteristics of different components of petroleum hydrocarbons in the soil,and defines the natural degradation process of petroleum hydrocarbons in the soil.The structure and diversity of indigenous microbial community under oil stress were analyzed.The conclusion is as follows:(1)When the initial concentration of petroleum hydrocarbon in soil is lower than 2000mg/kg,after 90 days natural attenuation,the content of petroleum hydrocarbon is reduced to 500mg/kg,which is lower than the risk threshold of petroleum hydrocarbon in soil(500mg/kg).When the initial concentration of petroleum hydrocarbon in the soil is 2000mg/kg,after 90 days of natural attenuation,the content of petroleum hydrocarbon in the soil is basically stable and maintained at about 1000mg/kg,which is higher than the risk threshold of petroleum hydrocarbon in the soil.With the increase of the initial content of petroleum hydrocarbon in the soil,the residual amount of petroleum hydrocarbon in the soil increases after natural attenuation.After 90 days natural attenuation,the residual amount of petroleum hydrocarbon in soil with initial concentration of 5000mg/kg reached 2500mg/kg.(2)Under natural conditions,the natural purification of petroleum hydrocarbons in soil mainly includes volatilization,photodegradation and degradation of indigenous microorganisms.It is found that the degradation of indigenous microorganisms plays a major role in the natural removal of petroleum hydrocarbons,followed by photodegradation and volatilization.The degradation of indigenous microorganisms contributes the most to the natural removal of petroleum hydrocarbons.(3)Polycyclic aromatic hydrocarbons(PAHs)are not only the components of petroleum hydrocarbons,but also the highly toxic pollutants with "three effects".When the crude oil content of soil is 1000,1500,2000,3000,4000 and 5000mg/kg respectively,the 16 PAHs in soil are 0.3314,0.4970,0.6628,0.9940,1.320 and 1.650mg/kg.Under natural conditions,the 16 PAHs hardly degrade.(4)Four kinds of oil contaminated soil(a),oil contaminated soil + humic acid(b),oil contaminated soil + fine sand(c)and oil contaminated fine sand(d)were prepared and bioremediation was carried out to study the effect of soil organic matter adsorption locking on the removal of petroleum hydrocarbons.After 165 days of remediation,the removal rates of petroleum hydrocarbons in soil samples A,B,C and D were 5.9%,5.6%,3.5% and 13.5%,respectively.The results showed that the adsorption of petroleum hydrocarbons by soil organic matter blocked the biodegradation of petroleum hydrocarbons.(5)The dominant microflora in petroleum contaminated soil include Proteobacteria(29.11%),Firmicutes(2.07%),Actinobacteria(37.3%)and Bacteroides(4.48%);Nocardioides(3.14%),Protomonas(9.83%),Sphingomonas(5.45%),Gemmatimonas(3.24%),Arthrobacter(1.62%)are the main dominant bacteria.The main dominant fungi are Ascomycota(47.35%),Basidiomycota(7.07%);Aspergillus(30.12%),Sitotrema(6.15%),Penicillium(1.83%),Acrosporum(1.12%)are the main dominant genera.The main components of petroleum hydrocarbon degrading bacteria enriched from polluted soil are Proteobacteria(96.27%),Firmicutes(3.71%),Actinobacteria(0.01%)and Bacteroides(0.01%);the dominant bacteria are Pseudomonas(87.22%),Achromobacter(6.12%).The main components of degrading fungi are Ascomycota(68.45%),Basidiomycota(24.14%)and Zygomycota(7.24%);the dominant genera are Aspergillus(21.46%),Aureobasidium(14.76%),and Acrosporium(11.24%).There are significant differences in composition between the petroleum hydrocarbon degrading bacteria and the total soil microbial community.It shows that only a few microorganisms in the soil can metabolize petroleum hydrocarbon under the guidance of petroleum hydrocarbon.Petroleum hydrocarbon is not the only carbon source and energy source for the growth and metabolism of dominant bacteria and fungi in soil.It is necessary to inoculate degradation bacteria into soil to strengthen soil remediation.