Study On Occurrence And Biodegradation Mechanism Of PAHs In Closed Coal Mine

Due to the exhaustion of coal resources and the adjustment of national industrial policy,a large number of coal mines have been abandoned or closed,which has posed a serious threat to the environment and the safety of coal mining.After the closure of the coal mines,the goaf and roadway will be filled with water,and the hydrogeological conditions will be changed significantly.Moreover,the pollutants in the goaf will release and migrate to mine water,and contaminate other aquifers through mining-induced fractures,faults,and poorly sealed drilled holes.In this article,the distribution of polycyclic aromatic hydrocarbons?PAHs?in coal mining areas and the source and sink of PAHs in mine water are studied through field investigation,theoretical analysis and simulation experiment.Then,the release and degradation mechanism of PAHs under special conditions of closed coal mines were discussed.The main conclusions are as follows:?1?The result of the occurrence of PAHs in coal from different mining areas in China showed that the content of 16-PAHs in coal is 10.540±7.973?g/g,and low molecular weight PAHs is the main component,accounting for 44%.The content of 16-PAHs in bituminous coal is the highest,which is mainly affected by volatile matter and H/C mole ratio,and both of them contribution to the change of 16-PAHs is 61%.?2?The 16-PAHs in sludge and mine water of typical coal mining area,such as Xuzhou,Huainan,Zibo,Fengfeng and Yanzhou,are 0.64-24.02ug/g and 0.56-4.61ug/L,respectively,mainly 3-5 rings.Among them,naphthalene,acenaphthene,phenanthrene and other low molecular weight PAHs have a higher detection rate.The pollution assessment of PAHs in mine water showed that the benzo[a]pyrene generally exceeded III limits of the groundwater quality standard,and the ecological risk of PAHs in mine water was at medium and high risk level.?3?The static release experiments of PAHs in coal-gangue-mine water system,lasted 360 days,were carried out.The results showed that the release of 16-PAHs from coal-gangue was mainly low molecular weight PAHs at the initial stage of the experiment under the condition of anoxic and dark.The content of 16-PAHs in water could reach 20.83ug/L,and the residual emulsified oil can promote the release of PAHs.The release process of PAHs in coal-gangue of closed coal mine accorded with the first-order kinetic model?R²=0.901,P<0.05?.?4?The distribution of bacterial community in 600-700m deep coal mine were studied.The results show that the bacterial phyla were mainly Proteobacteria?36.9%?,Firmicutes?24.0%?and Actinobacteria?20.0%?.And the difference of bacterial community abundance was mainly affected by pH and C/N.The 135-days simulation experiment of bacterial community succession showed that some aerobic bacteria?such as Arthrobacter?will be replaced by anaerobia and facultative anaerobes?such as Geobacillus?after the closure of the coal mine,and the bacteria abundance increased first and then decreased.?5?Pseudomonas Sp.P-1,a PAHs degrading bacterium,was screened.The degradation experiments of phenanthrene with Pseudomonas Sp.P-1 showed that the degradation process under anoxic-dark conditions accorded with the first-order kinetic model,and the degradation rate constant was 0.0348h^-1?30??.The strain had strong environmental adaptability and could survive and degrade phenanthrene at 20-40?and pH 6-8.The strain had stronger degradation ability under 25-30 C and weak alkaline conditions,with the degradation rate of 96.0%-98.9%.Besides,Fe?III?and sulfate in mine water could promote the degradation.?6?A total of 5750 functional genes were obtained from the genome sequence of Pseudomonas Sp.P-1 strain by genome sequencing analysis,and about 80%were annotated.According to the results of NR and KEGG annotations,13 functional genes were identified to involve in the degradation of phenanthrene.Combined with the analysis of intermediate products,the degradation pathway of phenanthrene by Pseudomonas Sp.P-1 under anoxic-dark conditions was determined,mainly through the Phenanthrenequinone pathway.Sulfate in mine water have a great influence on the process.Besides being an electron acceptor for hypoxia degradation of phenanthrene,it also participated in the formation of phenanthrenequinone.