Isolation And Optimization Of Strain Producing Surfactants And The Study On Its Degradation Of N-hexane

With the development of the economy,the emission of atmospheric pollutants has caused serious environmental problems.Bioreactors have broad market prospects in the treatment of low concentration of volatile organic pollutants.However,when processing the refractory degradable and hydrophobic volatile organic compounds(VOCs),the removal is poor.The presence of surfactants in biofilters could enhance hydrophobic VOC removal,but it will increase the cost.The purpose of this study is to screen strains that could biodegrade n-hexane and produce biosurfactants simultaneously from oil-contaminated soils,to enhance the degradation performance and provide a theoretical basis for the further application of bioreactors.In this study,blood agar plate,methylene blue agar plate and a culture with n-hexane as the only carbon source were used to screen strains that could biodegrade n-hexane and produce biosurfactants simultaneously.The isolated strain was identified as Bacillus licheniformis by 16S rDNA sequencing.Studies on the biosurfactant production and n-hexane removal showed that the biosurfactant produced by the metabolism of the strain was related to the initial concentration of n-hexane(132-2640 mg/L),and the biosurfactant produced by the strain promoted n-hexane removal.At low,medium and high n-hexane concentrations,the strain growth,surface tension reduction,and removal of n-hexane have different trends,respectively.It was found that the strain grew fastest under the condition of medium and low concentration(2.64-264 mg/L)of n-hexane.Under the condition of high concentration of n-hexane(2640 mg/L),the surface tension of the culture medium decreased most obviously.The 5-day removal rate of n-hexane in the 50 ?L(132 mg/L)and 200 ?L(528 mg/L)group was significantly higher than that in the other groups.When the concentration of n-hexane was 132 mg/L,the removal rate of n-hexane in two days reached 60%.Compared with other n-hexane-degrading strains,B.licheniformis NEE1 could tolerate high concentrations of n-hexane.The effects of pH,temperature and nitrogen on the degradation of n-hexane by B.licheniformis NEE1 were investigated by single factor experiments.The studies showed that the strain was suitable for growth under conditions of neutral alkaline,ammonium sulfate as nitrogen source and temperature of 25-30 ?.The study on the substrate utilization showed that the strain could utilize hydrophobic VOCs,non-volatile alkanes and hydrophilic VOC-acetone,but could not utilize polycyclic aromatic hydrocarbons-phenanthrene/anthracene.