Screening Of Biosurfactant Strains And Studying Biodegradation Effect Of Petroleum Hydrocarbon

Biosurfactants synthesized by microorganisms are natural surface-active compounds.Compared with chemical surfactant, biosurfactant has obtained international attention because of its environment friendly and potential application.The works of exploitation of biosurfactant microorganism resources,improving their yield in fermentation solution and studying biodegradation of petroleum hydrocarbon have extensive biological and economic significance.Therefore,it was developed independently and the breeding of high-yield biosurfactant strains was studied . The main research and experimental results are as follows:Breeding high-yield biosurfactant strains is the premise and foundation of biosurfactant production. After primarily screened by using oil agar plates and secondarily screened by oil displacement activity from oil slurry, strains capable of producing biosurfactant were obtained. The surface tension of their fermentation broth was measured. The strain was pseudomonas aeruginosa based on the results of morphological characteristics of colony, micrograph of gram staining, physiological biochemical characterization and PCR products electrophoresis of 16SrDNA.The high-yield biosurfactant strain BS-15 was measured with the surface tension of 36.82mN/m and the emulsifying ability of 92% after five days. The biosurfactant was rhamnolipid based on the results of column chromatography experiment,color column chromatography and IR spectrum of biosurfactants superstratum liquid. Response surface methodology was used to optimize fermentation medium for rhamnolipid biosurfactant production. Firstly, fractional factorial design was used to evaluate the influence of related factors.It showed that two factors playing the important roles in the medium,including NaNO3 and MgSO4·7H2O. Secondly,steepest ascent path was adopted to approach the optimal region. Then the central composite design and response surface analysis were used to determine the optimal levels of the mainfactors.They are5.0 g/L and 4.0 g/L .Under the optimal conditions,the yield of rhamnolipid was 2.45 times and the production.reached 25.5g/L. The study has been foundated optimal fermentation medium for the fermentation production of rhamnolipid .Microbial degradation of petroleum hydrocarbon was examined. After the strain was cultured for 120 hour on a rotary shaker (150rmp)at 32℃, the degradation rate of diesel oil by the strain reached 53% . The biodegradation of diesel oil was significantly enhanced by the amendment of rhamnolipid biosurfactant. It indicated that rhamnolipid increased microbial biodegradation and the biodegradation of diesel oil was 11%~20% higher than that without rhamnolipid. By designing orthogonal tests, the effects of three major factors, culture temperature, culture time and dosage of rhamnolipid on the degradation rate of hydrocarbons in water were studied. It showed that culture time was the most important factor.Biodegradation rate of petroleum hydrocarbon was increased from 82% to 97% by a hydrogen peroxide dosage of 200 mg/L.Synergistic effect of rhamnolip and deep oxidation would be helpful to increase the biodegradation rate of petroleum hydrocarbon contaminants.