Studies On The Oil-degradation Effect And Influencing Factors Of Surfactant Producing Salt Microorganisms

Liaohe wetland is an important oil industry base of China. However, there is a large number of oil into the surrounding environment during the extraction and refining of oil, which seriously pollute the environment of marine and soil.That cause serious harm to the local ecological environment, health of the resident and local economic development. Bioremediation has been an important treatment option of hydrocarbon contamination because of it’s effectiveness, low-cost and simple operation. However, the hydrophobicity of hydrocarbon leads to their slow biodegradation.. Adding biosurfactants is an option to enhance the bioavailability and biodegradation of hydrocarbon. Biosurfactants have the advantages of non-toxic, stable performance and being readily biodegradable which makes them more valuable in hydrocarbon biodegradation.In this paper, how to use biosurfactants and its producing strain to enhance the biodegradation of diesel oil is studied. A oil-degrading strain named LH-10that is capable of high-producing biosurfactant was finally isolated from crude oil-contaminated soil in the vicinity of Liaohe wetland oil-field by hydrocarbon enrichment culture, separation and testing its ability to degrade diesel and the oil spreading diameter and surface tension of fermentation broth. The optimal growth conditions of biosurfactants production by the strain LH-10were studied using "one-variable-at-a-time" method. The biosurfactant produced by strain LH-10is identified as glycolipid. The surface tension of the medium was reduced to45.3mN/m from82.9mN/m by LH-10cultured for4days, and the diesel degradation rate is58.9%cultured for7days. The results showed that the optimal medium for biosurfactant production by this strain was40.0g/L peanut and2.5g/L NaNO3. Under such conditions, the surface tension of the medium was36.5mN/m and the yield of crude extracts of biosurfactant is1306.8mg/L within4days cultivation.The effect of strain LH-10, rhamnolipid and rhamnolipid concentration to the degradation of diesel oil in seawater were studied by determining the number of bacteria, the degradation rate n-alkanes component changes of diesel useing shake flask experiments in laboratory. The diesel degradation rate is30%with LH-10in seawater medium and it is higher with the increases of rhamnolipid concentration added in medium. The degradation rate of diesel increased to70%by adding200mg/L rhamnolipid and reached to72%with500mg/L rhamnolipid. At the same time, with adding200mg/L rhamnolipid in the culture medium the number of bacteria is increased three orders of magnitude, the removal rate of n-alkanes in diesel increased to98%from75%and greatly enhanced the degradation capacity of the strain to the refractory part of diesel. The results show that the strains LH-10and rhamnolipid both have good salt tolerance and can be applied to the marine environment.A bioremediation simulation test indoor for60days to petroleum contaminated soil form Liaohe wetlands with strains LH-10and rhamnolipid is done. The number of colonies of all heterotrophic bacteria, petroleum-degrader count, activity of dehydrogenase, oil-degradation rate and the rhamnolipid content in the experimental soil is determined regularly. The results showed that adding high levels of rhamnolipid can significantly enhance the diesel degradation ability of indigenous microbial. The diesel degradation rate added to88%from70%and the decontamination time reduced about30days with adding5000mg/kg rhamnolipid to the experimental soil, during which the microbial biomass and the of activity dehydrogenase also increased significantly. Adding strain LH-10to petroleum contaminated soil can not enhance the degradation rate of diesel, but adding rhamnolipid at the same time can also improve diesel-degradation rate to85%. The rhamnolipid added to the soil can be degraded by microbial, so will be left in the soil and contaminate the soil again. Therefore, adding biosurfactants directly to the soil is the best way to control the petroleum-contamination. This way not only enhances the pollutant removal efficiency of oil form soil, but also shorten the removal time, and will not cause secondary pollution.