Solvent Extraction-microbial Degradation On The Remediation Of Petroleum Hydrocarbon Contaminated Soil

In this paper,the actual petroleum hydrocarbon contaminated sites are studied.The main experiment is two-step scheme,which uses the extraction of organic solvents under ultrasonic environment as the pretreatment and the microbial inoculation and remediation as the post-treatment.Firstly,most of the petroleum hydrocarbon contaminants in contaminated soil are removed by organic solvent extraction,so as to reduce the consumption cycle relative to the single microbial treatment.Then,the residual petroleum hydrocarbon contaminants are further treated by inoculating domesticated in situ microorganisms into the treated soil.At the same time,the physiological activities of microorganisms are utilized to accelerate nutrient cycling in the soil and restore soil quality and expands the application scope of microorganisms as a means of restoration.(1)Solvent Selection and Extraction SchemeThe combination of different extraction environments and different organic solvents was investigated by single factor experiment.The oil hydrocarbons in soil were extracted by petroleum ether ultrasound.The remediation scheme was obtained with ultrasonic power of 40 KHz,solid-liquid ratio of 1:5,extraction time of 20 minutes and extraction times of 2 times.The total oil hydrocarbon extraction rate in contaminated soil could reach 96.85%.It has high application value.(2)Isolation and domestication of petroleum hydrocarbon degrading bacteriaThe strain HJ-06 was isolated and domesticated from the sludge of petroleum hydrocarbon contaminated soil and identified as Enterobacter xiangfangensi of Enterobacteriaceae by sequencing.It belongs to fermentation-type bacteria and is facultative anaerobic.The optimum growth pH value is 6.5-7.0,and the optimum growth temperature is 36-39 C.It has the highest tolerance to NaCl of 9%.It has mobility.It is acid-producing,methyl red reaction is positive,and can not decompose starch and indole trans.It should be negative and has no oxidase activity.It can use citric acid to produce H2 S from physiological activities,reduce nitrate,and has hydrogen peroxide catalyst.The strain HJ-06 degraded in liquid medium containing mixed mechanical oil for 15 days,and the degradation rate of petroleum hydrocarbons reached 30.67%,and it had obvious degradation effect on long-chain petroleum hydrocarbons.The maximum strength of petroleum hydrocarbons decreased by 19.45% after 30 days of degradation in actual petroleum hydrocarbon-contaminated soil,suggesting that the strain had good degradation effect on actual contaminated soil.(3)Application and planting evaluation of microbial remediation of soilSolvent extraction method was used to treat petroleum hydrocarbon contaminated soil,which reduced soil aggregates and increased water holding capacity by 68.22%.However,the organic matter content in soil decreased significantly and became more compact.After 45 days of planting alfalfa in this soil,the chlorophyll content and nitrogen content of plant leaves increased to 3.11 times and 2.04 times of original soil,root activity increased 72.89%,total protein content increased by 1.7 ug/ml,soluble sugar decreased by 39.16%,and hydrogen peroxide content decreased by 10.04%.It shows that although solvent extraction causes a lot of loss of soil organic matter,the method still has a certain degree of remediation compared with the effect of petroleum hydrocarbons on soil quality and plant cultivation.After 30 days of inoculation with HJ-06 strain,soil particles became loose and rough,organic matter content increased by 35.00%,water holding capacity increased by 9.01%,and total water holding capacity increased by 83.35% compared with the original soil.The chlorophyll content and nitrogen content of alfalfa leaves increased by 9.52% and 7.55% respectively after 45 days of inoculation,which were 3.41 and 2.19 times higher than those of the original soil,and the root activity increased by 44.60%,which was 2.5 times higher than that of the original soil.The results showed that the soil quality affected by solvent extraction was effectively improved by inoculating microorganisms in the soil after solvent extraction,and microorganisms could promote the growth of plants to a certain extent.It is suggested that solvent extraction and microbial degradation have obvious remediation effect on petroleum hydrocarbon contaminated soil.