Study On The Volatilization And Biodegradation Of Oil Contaminants In Soil-water System

The extensive use of petroleum and its products with the development of economy and advancement of technology had made tremendous good for the mankind. During the production, refinery, transport and use of petroleum, large quantity of it enter the environment and leading contaminant in both soil and water, which destroy the ecosystem and do harm to human being. So the treatment of the oil contaminants is staring us in the face. Oil contaminants undergo a series of complex physical, chemical and biological processes in soil, which has different influence on the ultimate fate of oil contaminants in environment. So the study of the transform and transport processes of oil contaminants in soil will provide insight into the eventual fate in environment, which can provide gist for the effective oil contamination remediation and control underground pollution.The volatilization and biodegradation of hydrocarbons in soil-water system is studied systemically in this research. First, the volatilization test of four oil products (diesel oil, kerosene, gasoline and aromatic mixture) and the diesel oil volatilized from four different soils are discussed, and the volatilization behaviors of hydrocarbons are concluded. Second, six high hydrocarbon bacteria strains are isolated from two different soils, and the utilization of different hydrocarbons for individual isolates and bacteria mixture are conducted at the same time. The biosurfactant rhamnolipid is distilled from isolate of Al and the influence of it on the hydrocarbon degradation is analyzed. The different soil enzymes and other biological activities are surveyed during the hydrocarbons degradation test. At last, the individual population of a mixed culture is monitored by the antibiotic selection means. On the basis of sites of investigation and tests, the major conclusions presented in this paper can be summarized as follows:1. The volatilization test shows that there different volatilization kinetic model for different oil products. Diesel oil and kerosene volatilize at a polynomial rate withrespect to time, gasoline volatilize at a rate which can be modeled as logarithmic with respect to time, and the aromatic mixture (contain four components: benzene, toluene, ethylbenzene, xylene) volatilize at linear with time. The volatilization of diesel oil leads to the changes of physical properties, especially for the increase of viscosity. And there is positive relativity between the viscosity and the remaining content of diesel oil after volatilization, and the correlation coefficient is 0.9933.2. The soil texture and thickness of soil are the main factors on the diesel oil volatilization in different air-dry soils. When in the thin layer soils, the area for oil volatilize dominate the oil volatilize rate; as in the thick layer soils, the air porosity degree dominate the oil volatilize rate of oil contaminants in soils.3. The isolates from different environment have different capabilities of utilizing hydrocarbons. The bacteria strains that isolates from crude oil contaminated soil exhibit a narrow range of metabolic activities of saturate compounds and limit the degradation of aromatics. Where the bacteria strains that enriched in the absence of oil contaminants but domesticated by the aromatics are able to degrade a wider range of oil components either saturates or aromatics.4. Usually, the critical micelle content (CMC) of surfactant is measured in water, but we try to measure the CMC both in water and in soil, the results show that the CMC of rhamnolipid in water is 65mg/L, and is 185mg/L as in soil. There different influences on the diesel degradation when add different content of rhamnolipid into the water and soil systems respectively. When 0.01% rhamnolipid is added to water, the hydrocarbon degradation is enhanced, but when the same concentration of rhamnolipid is added to the soil, the degradation of hydrocarbons is inhibited instead. So the results show that, the addition of rhamnolipid to the medium must higher than corresponding of CMC of that medium. The further research also indicates that the appropriate addition of rhamnolipid will enhance the degradation of hydrocarbons, and at the same time it will shorten the time need for oil remediation.5. During the degradation tests, the relationships of the activities of dehydrogenase, catalase, lipase, the hydrocarbon degraders and the oil degradation rate are analyzed. And the results show that soil lipase activity correlate positivelywith the hydrocarbon degradation rate, and the dehydrogenase has low correlate. So the lipase activity can be used to evaluate the degree of oil biodegradation.6. The dynamic succession of individual populations and its proportion in mixed microbial culture during the test period are successfully monitored by the antibiotic selection test. And the results indicate that the succession of individual bacteria in mixture is respond to the availability of hydrocarbons for growth for specific population. In the start period of test, the isolates of Al, A2 and A6 are the dominant bacteria strains in mixture culture; but with the test follow, the saturates are degraded and the aromatics concentration relative residual oil is increased, so the isolates of A2, B2 and Al become the main bacteria in mixture culture.