Isolation Of Diesel Oil Degradation Bacteria, Optimize Of Degradation Condition And The Research On Its Degradable Mechanism

There are many oil degrading strains in the nature. The degradation of the petroleum hydrocarbons is influenced by many factors, such as the sort and composition of petroleum hydrocarbons, the physical state, the concentration, temperature, pH, oxygen supply, nutrients, et al. The degrade speed of petroleum hydrocarbons and the final effect is the interactional result of all the factors.Because the natural degradation ratio of petroleum hydrocarbons is slow, adding some materials to the polluted environment, and optimizing the degradation condition can often accelerate the biodegradation of the petroleum pollutant. Some researches have indicated that surface-active compounds can promote the emulsification of the petroleum hydrocarbons, increase the solubility and the bioavailability of the petroleum hydrocarbons in the water. Compared with the chemical surfactants, biosurfactants are attentioned by more and more people because of their nontoxic, biodegradability, mildness to the environment, high bioactivity and so on. At present, it is becoming the hot of water pollution control. Our research was focus on the following aspects and received several results:Firstly, nine diesel oil degradable strains were obtained from oil-contaminated soil by using screening cultural medium method which using 0# diesel oil as the sole carbon source. The degradation ratio of diesel oil by the strains was tested by using ultraviolet spectrometry method. One of the strains showed potential for further utilization with a degradation ratio of diesel oil by 71.7% incubating for 3 days. Based on the morphological, physiological and biochemical test results, the strain was identified as Pseudomonas sp..Secondly, six factors that affect the strain growth and the degradation ratio to diesel oil, such as pH value of the culture medium, temperature, inoculation amount, N source, initial diesel oil concentration and incubation time, were also studied in the proposed paper. The result showed that the optimum culture condition for Pseudomonas sp. strain was pH5.0, inoculation by 5%, (NH4)2SO4 as the N source in the culture medium and incubation under 30℃. When the proposed strain grows under this condition, 80% of the diesel oil could be degraded with an initial concentration of 1000mg/L and incubating for 6d.Furthermore, this paper also studied the extract of biosurfactant from broth. The Pseudomonas was capable of producing glycolipids biosurfactant by a series of tests including surface tension determination, thin-layer chromatography assay etc, and could reduce the surface tension of fermentation solution. The analysis of different culture conditions indicated that the biosurfactant produced by Pseudomonas was able to reduce the surface tension of fermentation solution from 69mN/m to 31.4mN/m when incubating for two days in conditions that the temperature was 30℃, the initial pH was 8.0～9.0, the shaking speed was 200r/min, the nitrogen source was NH4NO3. At the same time, the output of biosurfactant was 1.62g/L. Employing the biosurfactant to degrade diesel oil, 85.7% of the diesel oil was removed after 72h,it had good effect. Using the techniques of GC-MS, the effect of biosurfactant on degrading the composition of diesel oil was analyzed. The results showed it could degrade C17-C29 straight chain alkanes and some branched ones into C14-C18 short chain alkanes. This paper will provide strong basis for the strain and its biosurfactants applied in oil-contaminated soil and water.