Researches On The Stability Of Polycyclic Aromatic Hydrocarbons And The Mechanism Of Degradation In The Processes Of Biodegradation

Researches on the stability of polycyclic aromatic hydrocarbons(PAHs)most focused on the thermal stability under surface environment and biodegradation degrees of some compounds in underground oil under anaerobic biodegradation by some unknown flora.In this paper,the biostability of PAHs in oil under aerobic and anaerobic biodegradation by mixed and pure strains have been researched.Through biodegradation by oil-driving microorganisms under natural situation and240 d simulated anaerobic biodegradation under sulfate reducing and methanogenic conditions at moderate(35℃)and high temperature(65℃)in the laboratory,four results concluded:(1)naphthalene,phenanthrene and the series compounds with biostability from high to low is: trimethylphenanthrene > dimethylphenanthrene >monoethylphenanthrene > phenanthrene ≈ pentamethylnaphthalene >tetramethylnaphthalene > trimethylnaphthalene > dimethylnaphthalene,the biostability grows along with the increasing of substituents.The biostability of isomers also vary.Under natural situation,the isomers with stability from high to low are: isomers withαα-methyl substituents at different sides of benzene ring > adjacency αβ-methyl substituents > adjacency ββ-methyl substituents > interpositive substituent,the moreα-methyl substituent,the higher the stability.The sequence of biostability is contray to that of thermal stability.In the laboratory,the biostability of isomers with adjacencyββ-methyl substituents increase,which is not only relating to the position of methyl substituent,but also to the structural symmetry of the isomers.(2)For fluorine,dibenzofuran,dibenzothiophene and substituted series compounds,under natural situation,as the number of substituents increases,the biostability increases.But in the laboratory,the biostability of parent compounds is higher than that of alkyl substituted derivatives.(3)For aromatic hydrocarbons with four to six rings,under natural situation,the biostability of aromatic hydrocarbons with five to six rings is higher than those with four rings.And four-ring aromatic hydrocarbons with biostability from high to low is:fluoranthene > pyrene > benzofluorene > chrysene.In the laboratory,at high temperature,the stability of aromatic hydrocarbons with five to six rings is higher than those with four rings,which is contray to that at low temperature.For four-ring aromatic hydrocarbon,at high temperature,with stability from high to low is:chrysene > benzofluorene > pyrene > fluoranthene,and at moderate temperature,no difference of the stability exists.The number of aromatic ring,the kinds of microorganisms and the temperature are all related to the biostability of the compounds.The biostability of PAHs under simulated condition is not the same with that under natural condition.(4)The biostability of pyrene under sulfate reducing condition at moderate temperature is higher than that at high temperature,but it is lowest under methanogenic condition at high temperature.Through in-situ and simulated remediation of refining-oil contaminated soil by Bacillus tequilensis(B.tequilensis),it is concluded that: for PAHs(except phenanthrene,fluorine,dibenzofuran and dibenzothiophene)with less than four rings,the biostability decrease along with the increasing of the substituents,and for those with four to six rings,the more aromatic rings,the higher the biostability.The stability of the isomers also vary.Research on the biostability of PAHs in the larboratory can be used in the field research.The biostability of PAHs under biodegradation by different microorganisms are much different.Under biodegradation of Stenotrophomonas rhizophila(S.rhizophila),along with the increasing of substitutents,the biostability of PAHs with less than four rings increase,and PAHs with four rings are more stable than those with five to six rings.The biostability of the isomers also vary.The biostability of PAHs in oil under biodegradation of B.tequilensis are the same with that in in-situ remediation of refinging-oil contaminated soil.But the difference of biostability of PAHs under biodegradation of Cupixiaolia alcoholanaerobia are not obvious.The biostability of pyrene is lower under the biodegradation of Acinetobacter lwoffii than S.rhizophila,and it is relatively high of S.maltophilia and S.acidaminiphila.Under the biodegradation of Dictyoglomus thermophilum,the biostability of pyrene is the highest.In addition,the interaction relationship between microorganisms and crude oil may exist,and some biomarkers may instruct this relationship which need to be furtherly studied.