Isolation, Identification And Degradation Characteristics Of Naphthalene Degrading Bacteria And Its Application In EMBR

Polycyclic aromatic hydrocarbons(PAHs)are typical refractory persistent organic pollutants in the environment.Because of their high thermodynamic stability,PAHs can be bioaccumulated and persistent in the environment with carcinogenic effects.Therefore,it is urgent and important to find efficient ways to eliminate PAHs from the environment.Biodegradation is considered as the most important and efficient way of eliminating polycyclic aromatic hydrocarbons(PAHs),but there are still some limits.In this study,two strains of naphthalene-degrading bacteria named DGN4 and DGN9 were screened from the contaminated soils near the Dagang oilfield in Tianjin.The morphological and 16 S r DNA sequencing were studied,and the growth optimum conditions and the degradation characteristics of naphthalene were investigated.The results provide theoretical basis and practical conditions for further studies on naphthalene degrading bacteria.Finally,experiments on optimum operating conditions of the extraction membrane bioreactor were conducted,and the feasibility of the combination of DGN9 and EMBR was investigated.The results are as follows:1.Strain DGN9 and DGN4 were isolated from Da Gang oilfield in Tianjin.Through morphological characteristics and 16 S r DNA gene sequence analysis,strain DGN9 was affiliated to Achromobacter sp.,strain DGN4 was affiliated to Sphingobacterium.2.The optimum growth temperature conditions for strain DGN4 was 30 ?,and initial concentration of naphthalene was 700 mg/L,with p H around 9.0;The optimum growth temperature conditions for strain DGN9 was 30 ?,and initial concentration of naphthalene was 1000 mg /L,with p H between 7-9,and salinity between 1%-2%.3.When strain DGN4 was cultured under optimum condition utilizing naphthalene as the sole carbon source,the concentration of naphthalene could be 2.73mg/L after 5 days' degradation.When DGN9 was cultured under optimum condition utilizing naphthalene as the sole carbon source,the concentration of naphthalene could be 3.86mg/L after 5 days' degradation.In addition,DGN9,with broader auxanogram,could grow well using different aromatic compounds as carbon source.With the experiment of substrate specificity,the salicylic acid degradation route could be determined primarily.4.Naphthalene dioxygenase gene(nah AC)and salicylic acid synthase gene(nah G),the key enzyme genes in the process of naphthalene degradation,were found with the PCR method,which was further confirmed that salicylic acid degradation pathway existed in strain DGN9 degradation.At the same time,the existence of intermediates of the process is detected by GC-MS,a proposed pathway for the degradation of naphthalene by DGN9 was determined.5.In this experiment,the laboratory extractive membrane bioreactor was set up.Results showed that the optimum operating conditions were: initial concentration of naphthalene was 5 g/L and Rev was 10 r/min.Strain DGN9 was applied to EMBR,it turned out that EMBR device could effectively degrade the wastewater containing naphthalene,which is confirmed to be feasible in the laboratory.