The Biosurfactant-producing Microorganisms Isolated From Coking Wastewater And Its Effect On The Degradation Of Polycyclic Aromatic Hydrocarbons

Polycyclic aromatic hydrocarbons?PAHs?as one of the typical organic pollutants of coking wastewater are largely adsorbed in the sludge during the treatment process,which greatly limit their biodegradability.Surfactants enhanced remediation?SER?is considered as a viable method for increasing the degradation of PAHs,because surfactants can improve the biodegradability of PAHs by increasing the dissolution rate of PAHs which adsorbed in the sludge and enhancing the mass transfer efficiency between PAHs and PAH-degrading microorganisms.However,the use of a large amount of synthesized surfactants will cause secondary pollution to environment and is being replaced by biosurfactants which are low toxicity,eco-friendly and easily degraded.Due to the complex and expensive extraction processofbiosurfactant,therefore,itisnecessarytostudytheeffectof biosurfactant-producing microorganisms on degradation of PAHs and hope it is possible to produce biosurfactants in the polluted environment and promote the degradation of PAHs by regulating certain growth conditions.The main research contents and results are as follows:?1?The sludge-water mixture of first aerobic tank of A/O/H/O process of coking wastewater treatment system in Songshan Iron and Steel Corporation was used as microorganisms'source.After enrichment,acclimation,screening and purification,7microorganisms which can produce biosurfactant were isolated by determining diameter of oil displacement,surface tension and emulsification activity.Among them,strain S5 was selected for futher study due to the biosurfactant produced by strain S5 have the largest diameter of oil displacement?88.3 mm?,thee lowest surface tension(28.4 mN·m^-1)and the highest emulsification activity(E_Hexane=48.9%,E_{Paraffin oil}=44.2%).Strain S5 was identified as Pseudomonas aeruginosa using 16s rRNA sequencing analysis and physiological-biochemical tests.?2?The performance of the surfactant will directly affect its function in application.Therefore,it is necessary to study the series of physiological and biochemical indicators of S5biosurfactant such as critical micelle concentration?CMC?,acid-tolerance,alkali-tolerance,salt-tolerance,and solubilization ability of PAHs.The yield of the biosurfactant produced by strain S5 which extracted by acid-base precipitation method and purified with organic solvents was 1.8±0.4 g·L^-1?The results of chemical analysis and Fourier transform infrared spectroscopy?FTIR?demonstrated that the biosurfactant produced by strain S5 belong to glycolipid biosurfactant.In addition,the biosurfactant produced by strain S5 also has good environmental adaptability,which was stable at a wide range of pH?3.5-9.5?and salinities?0%-15%?with 96.5 mg·L^-1critical micelle concentration.The solubilization results of three different rings PAHs showed that the the biosurfactant produced by strain S5 can enhance the solubility of phenanthrene,fluoranthene and benzo[a]pyrene evidently in the aqueous phase,moreover,these PAHs exhibit synergistic solubilization when they co-solubilised.?3?In order to investigate the effect of strain S5 on the degradation of PAHs,firstly,PAHs were added as the sole carbon source in mineral salt medium to determine whether S5bacteria had the ability to directly degrade PAHs.Secondly,strain S5 was cultured with glucose and PAHs degrading bacteria to determine whether S5 bacteria can promote the degradation of PAHs by the biosurfactant produed by strain S5.The results showed that strain S5 could not degrade PAHs,mainly because strain S5 did not possess enzymes which required for the degradation of PAHs.When glucose was added as a biosurfactant-producing inducer,strain S5 can improve the degradation efficiency of PAHs by Stenotrophomonas sp.N5,which is one of the PAH-degrading microorganisms,indicating that strain S5 can produce surfactant during the degradation process,increasing the bioavailability of PAHs,and thus promote the degradation of PAHs.When strain S5 was added to a culture system containing actual wastewater and sludge with flowing glucose,strain S5 also can improve the degradation efficiency of PAHs,indicating that strain S5 can survive in this complex environment and play a role in the degradation of PAHs.Consequently,when carbon source are controlled,it is feasible to increase the degradation efficiency of PAHs by directly adding surfactant-producing microorganism in coking wastewater.