Biological Removal Characteristics And Mechanism Of Petroleum Hydrocarbons In Loess Soil By Applying Organic Fertilizer

In the process of oil exploitation,transportation,refining and application,the oil leakage caused by operation error or maintenance is not timely and so on will cause serious harm to soil ecological environment.When the content of petroleum pollutants in the soil is low,most of the petroleum hydrocarbons can be removed by photodegradation,volatilization,biodegradation,weathering,etc.In the polluted areas with high petroleum content,it may take months or years to remove them,and even cause the permanent residue of petroleum hydrocarbons in the soil.When the content of petroleum hydrocarbons in the soil exceeds the safety threshold,it is necessary to carry out remediation treatment to achieve the harmlessness of petroleum hydrocarbons in the soil.Paper using organic fertilizer,potassium nitrate,and the desulfurization gypsum to stimulate oil contaminated time different soil restoration,by measuring the total petroleum hydrocarbon content in the repair process,p H,microbial quantity changes,the microbial metabolic activity,research suitable for yellow spongy soils of removing oil hydrocarbon from the optimal biological stimulants and removal mechanisms of petroleum hydrocarbons in the soil.The results show that compared with potassium nitrate and desulfurization gypsum,adding organic fertilizer has better degradation effect on petroleum hydrocarbon in soil.After 210 days of remediation,the total petroleum hydrocarbons in freshly contaminated and aged contaminated soil decreased from 16846 mg·kg^-1 and 17746 mg·kg^-1 to 5588 and 10331 mg·kg^-1,respectively,and the corresponding petroleum hydrocarbon removal rates were 66.83%and 41.78%.The removal rates of alkanes and PAHs in freshly contaminated soil by organic fertilizer application were 68.88%and 50.00%,respectively,which were 44.19%and 18.33%higher than those of the control treatment.The removal rates of alkanes and polycyclic aromatic hydrocarbons were 44.47%and 30.81%,respectively.The degradation rates of alkanes and PAHs were 21.32%and 15.88%,respectively,in CK soil without biological stimulants.In the process of bioremediation with organic fertilizer,the p H value of soil,the number of soil microorganisms and the metabolic activity of degrading bacteria changed.For the freshly contaminated soil,the soil p H decreased from the initial 8.50 to the minimum 7.37 after 60 days with the addition of organic fertilizer as a biological stimulator,and then gradually increased to 7.76.The number of microorganisms in newly contaminated soil increased from 1.1×10⁴ cfu·g^-1 to 8.6×10⁶ cfu·g^-1.When organic fertilizer was added to the aged contaminated soil for 60 days,the soil p H decreased to 7.53,and then increased slightly.After 210 days of remediation,the soil p H decreased from the initial 8.61 to 7.74.The number of microorganisms in the old contaminated soil increased from 3.3×10⁴ cfu·g^-1 to 7.8×10⁶ cfu·g^-1.The number and activity of microorganisms in the two soils with different contaminated time reached the maximum at 15～30 days after remediation.The removal rate of total petroleum hydrocarbons in the soil treated with organic fertilizer accorded with the pseudo first order kinetic equation.For freshly contaminated soil,the pseudo-first-order kinetic constant is 0.0691d^-1,and the correlation coefficient（R²）is 0.9675.For the aged contaminated soil,the pseudo-first-order kinetic constant is0.0258 d^-1,and the correlation coefficient（R²）is 0.9786.The degradation of alkanes in freshly contaminated soil conforms to the second-order kinetic equation（R²is 0.9173）,while the degradation of alkanes in aged contaminated soil conforms to the pseudo-first-order kinetic equation.The degradation of PAHs in soils with different pollution duration conforms to the pseudo first order kinetic equation.By applying intact organic fertilizer and sterilized organic fertilizer to the contaminated soil for remediation,the interaction between the dominant bacteria abundant in organic fertilizer and soil indigenous bacteria was investigated.After 60days of remediation with intact organic fertilizer and sterilized organic fertilizer,the removal rates of total petroleum hydrocarbons in freshly contaminated soil were 56.25%and 51.68%,respectively.The total petroleum hydrocarbon removal rates were 53.34%and 40.61%when integrated organic fertilizer and sterilized organic fertilizer were applied to the aged contaminated soil,while the total petroleum hydrocarbon removal rates were 9.25%and 5.46%in the freshly contaminated and aged contaminated soil without fertilization treatment.The results indicated that both sterilized organic fertilizer and intact organic fertilizer had good effects on the removal of petroleum hydrocarbons in the soil,and the microbial flora in organic fertilizer had no antagonistic effect on the indigenous flora in the soil.In addition,the removal effect of the whole organic fertilizer applied to the aged contaminated soil was significantly better than that of the sterilized organic fertilizer,indicating that there may be a synergistic mechanism between the indigenous flora in the aged contaminated soil and the microorganisms in the organic fertilizer.Compared with the control treatment,theα-subunit dioxygenase gene controlling the degradation of PAHs and the monooxygenase gene controlling the degradation of paraffin were increased by 25 times and 25～625 times in the freshly contaminated soil treated with organic fertilizer for biological stimulation remediation.In the aged contaminated soil,theα-subunit dioxygenase gene and the monooxygenase gene controlling the degradation of PAHs were increased by 5～25 times by applying organic fertilizer,indicating that the enrichment of functional genes controlling the degradation of petroleum hydrocarbons in contaminated soil could be increased through fertilization.