Study On The Biodegradation Characteristics Of Hydrocarbon Compounds In Crude Oil And Their Environmental And Geochemical Significance

In order to investigate the effects of microbial degradation on the geochemical parameters of some typical saturated and aromatic hydrocarbons in the crude oil and PAHs source apportionment parameters,simulated experiments of crude oil are carried out using Pseudomonas,Mycobacterium,Sphingomonas and Bacillus to determine evaluation parameters with higher stability.The results show that the highest biodegradation level of crude oil reaches about 5 after degradation of 200 days,reaching a moderate degree of biodegradation.(1)In the parameters that characterize the maturity of crude oil:As the degree of biodegradation increases,the values of Ts/(Ts+Tm)and C₂₉Steranes 20S/(20S+20R)rise up,while C₃₁Hopanes 22S/(22S+22R),C₂₉ Steranes??/(??+aa)and C₂₉Ts/C₂₉H are less affected which can be applied normally.(2)In the parameters that determine the deposition environment:With the enhancement of biodegradation,the ratio of Pr/Ph decreases evidently which is no longer suitable for crude oil;The values of 22R C₃₁homohopane/hopane,gammacerane/hopane and moretane/hopane have unobvious increasements,while the ascending hopane index decreases slightly;The above 4 parameters are still effective in the crude oil with medium biodegradation level;Moretane and gammacerane are more stable than hopane under the effect of microbial degradation.(3)In exploring the parameters of crude oil organic matter input types:???20R Steranes C₂₇/C₂₉and???20R Steranes C₂₈/C₂₉decrease with the extension of the degradation time,and the latter has a much larger decrease,which could not indicate the real result.(4)The order of sensitivity of monomethyl phenanthrene series to microbial degradation is 1-MP>2-MP>3-MP>9-MP;The methyl phenanthrene index continues to increase which may interfere with the evaluation results during prolonged degradation time.(5)The order of anti-microbial degradation of three fluorene is SF>F>OF.The ratio of SF/OF has a significant increasing trend,which is no longer suitable for crude oil with moderate biodegradation degree;(6)While ANT/(ANT+PHE),FLT/(FLT+PYR),Ba A/(Ba A+CHR)and IPY/(IPY+BPE)have varing degrees of change,the source analysis results of these parameters are unchanged under the 5 biodegradation degree;The ratio of 4-6 ring PAHs/TPAHs increases and the source analysis result of this parameter is no longer valid.