The Effect Of Rhamnolipid On Phytoremediation And Microbial Remediation Of Petroleum Contaminated Soil

The petroleum hydrocarbon pollution of the soil has imposed a serious threat to the safety of human being health and the ecosystem health. Bioremediation has been the technology of potential for its cost effectiveness. Low bioavailability is the main factor which limits its biodegradation, and could be improved by adding biosurfactants. Biosurfactants can enhance the solubility of petroleum hydrocarbons, improve the properties of the cell surface and therefore increase the mass transfer rate and its bioavailability.On the basis of determination of surface-active substances secreted strains which are selected from petroleum hydrocarbon contaminated soil, the structure, fermentation medium, optimization of culture conditions and physical and chemical properties of the product for the rhamnolipid biosurfactant are systematically studied. Then, the microbial degradation of polycyclic aromatic hydrocarbons and the mechanism of phytoremediation produced from rhamnolipid are demonstrated. Furthermore, the technology for rhamnolipid enhancing plant - microbial bioremediation of oil pollution is put forward. This study provides a technical reference for large-scale bioremediation of oil-contaminated soil and can be used to protect soil safe of farmland and water safety of river. The main results of the study are as follows:(1) Highly efficient bacteria from surface active agents are selected, and the chemical structure of each component for the rhamnolipid homologues is identified.The high bacteria surfactant of BD-5 in oily soil is determined using twice selection from some processes of enrichment culture, blood plate separation, emulsifying properties and surface tension test. This high bacterium can be termed as pseudomonas aeruginosa. As diesel is the sole carbon source, the high bacteria surfactant of BD-5 contains 8 rhamnolipid homologues, all of which are composed by 1-2 molecules of rhamnose and 1-2?-hydroxy-containing carbon chain length of 8-12.(2) The optimum conditions of pseudomonas aeruginosa produced from rhamnolipid are determined. It is showed that rhamnolipid is a bioactive substance with low surface tension, thermal stability, high tolerance, emulsifying properties and good solubilization.The production of pseudomonas aeruginosa rhamnolipid fermentation is mainly resulted from sources of carbon and nitrogen and their concentration, pH, temperature anddissolved oxygen. When the rhamnolipid concentration is greater than critical micelle concentration (CMC), the apparent solubility of long-chain alkanes and polycyclic aromatic hydrocarbons in the water phase is linear correlated to rhamnolipid concentration. The variation of the molar solubilization ratio is thexadecane> naphthalene> phenanthrene> pyrene, and performance of compound solubilization with non-ionic surfactants shows rhamnolipid of tween 80> rhamnolipid - lauryl ether.(3) The effect mechanism of rhamnolipid and the enhanced pseudomonas aeruginosa of BD-5 from compound rhamnolipid on PAHs are demonstrated.The impact mechanism of rhamnolipid on polycyclic aromatic hydrocarbons (PAHs) can be concluded as follows: When the rhamnolipid concentration is greater than critical micelle concentration (CMC), PAH molecules can be wrapped in internal micelle by solubilization, and then, the combined particles of surfactant PAHs are formed, which induces passive diffusion into the cells and further result in degradation of organic matter. Moreover, rhamnolipid can change the hydrophobicity of cell, which can enhance binding of cells and PAHs and promote the degradation of aromatics. The effect of surfactant on the biodegradation of PAHs mainly results from concentration and type of surfactant. Besides, in soil materials, adding surfactant can enhance the mass transfer rate for the philippines transferring into water phase from solid phase, and thus improve the biodegradability.(4) The effect of rhamnolipid enhanced alfalfa on the degradation of PAHs is explained. It is showed that low concentration of rhamnolipid enhances the absorption of the Philippines while high concentration iinhibits its absorption. The affect mechanism of rhamnolipid on enhancing phytoremediation is mainly reflected in soil treated by surfactant with different concentration. The accumulation amount of alfalfa Philippines is less than 15% of the total amount of Philippines degradation in soil. It is showed that the fact of surfactant enhanced the efficiency of phytoremediation didn't not mainly result from the accumulation of plant. The concentration of rhamnolipid plays a great role on the degradation of Philippines.(5) The plant-microbial remediation measures using rhamnolipid to enhance biodegradation of oil-contaminated soil are put forward.Adding rhamnolipid and inoculated degradation bacteria can promote the growth of alfalfa. The promoting inefficient on the stems and leaves is obviously less than that of root This causes a highest increase amount of microbial biomass and nearly one order of magnitude can be upgraded if compared to the soil planted with sole alfalfa. The trend of soil dehydrogenase activity is close related to microorganisms and degradation of petroleum hydrocarbons. It can be concluded from multi-factor orthogonal test that the significant impact factor on oil degradation is concentration of oil pollutants, followed by surfactant and input amount of bacteria, respectively. The degradation rate of petroleum hydrocarbon from the optimized plant - microbial bioremediation reaches up to 69%.This study is jointly supported by project of environmental remediation of oil pollution and water quality control in northwest loess region from National Nature Science Foundation of China (50378077), the biodegradable effect of rhamnolipid biosurfactant petroleum hydrocarbons in the loess plateau from the special fund of Shaanxi Provincial Department of Education (07JK388).