| Crude oil can enter the soil and groundwater system through a variety of pathways, such as leakage of underground storage tanks and accidental spill during the exploration, production, and transportation process. Due to the carcinogenicity, teratogenicity and mutagenicity of petroleum hydrocarbons, crude oil contamination can result in serious ecological and human health problems. Therefore, the effective remediation of crude oil contaminated soil and groundwater is of critical importance. Bioremediation has been proved to be an effective and low-cost treatment option for the cleanup of organic pollution. However, the low bioavailability of petroleum hydrocarbons in crude oil and the environmental complexity can lead to slow biodegradation rate. Various measures can be taken to enhance the bioremediation of crude oil contaminated soil and groundwater. This study was aimed to investigate the surfactant enhanced bioremediation of crude oil contaminated soil and groundwater system. The influence of environmental factors on the surface property of bio-surfactant rhamnolipid and its sorption onto different soils, such as clay, loam and sand, were examined. The impacts of bio-surfactant on the solubility of saturated and polycylic aromatic fractions in crude oil, and on the desorption of these fractions from soil, were investigated. The effects of surfactant and various environmental factors on the bioremediation of petroleum hydrocarbons in crude oil were analyzed. The impact of salinity on the bioremediation of crude oil contaminated soil was also examined in order to provide theoretical basis and data support for the remediation of soil contaminated with both salt and crude oil, which is a common problem in the oil and gas industry. A simulation model was lastly developed to investigate the bioremediation of crude oil contaminated groundwater based on the experimental data obtained from a sand box model. The main results of this thesis were summarized as follows:(1) Impact of environmental factors on the surface property of biosurfactant:a series of experiments were conducted to test the effect of pH, salinity and soil adsorption on the surface property of rhamnolipid. The results indicated that pH showed no obvious effect on the surface tension change of rhmnolipid, but salinity had a positive effect on changing the surface tension of rhamnolipid. The pH and salinity didn't affect the critical micelle concentration (CMC) of bio-surfactant solution. The sorption loss of rhamnolipid was calculated as75.0%,66.7%, and50.0%for loam, sandy loam, and sand, respectively, indicating that soil properties such as particle size and organic matter had significant impact on bio-surfactant sorption which may generate negative effect on remediating oil contaminated soil.(2) Impact of biosurfactant on the solubility enhancement of saturated aromatic fractions (SAT) and polycyclic aromatic fractions (PAH) in crude oil:It was found that the bio-surfactant can remarkably enhace the solubility of SAT and PAH in crude oil. However, when the biosurfactant concentration approached a certain level (i.e. mass-0.04%), the solubilization effect of these crude oil components was weakened. The solubility of PAH was much lower than that of SAT because of its strong hydrophobic feature. Based on the Taguchi experimental design method, a series of laboratory experiments were conducted to examine the impact of rhamonipid concentration, pH, and salinity on the solubility of SAT and PAH fractions. The results showed that the rhamnolipid concentration was the most important factor influencing SAT and PAH solubility. The results also showed that these three factors and their interactions had obvious effect on solubility of SAT and PAH In this study, the SAT solubility decreased with increasing salinity, while the variation of salinity had little influence on PAH solubility. And the increasing pH in the alkaline range had a positive impact on solubility of SAT as weli as PAH.(3) Impact of biosurfactant on the desorption of saturated aromatic fraction (SAT) and polycyclic aromatic fraction (PAH) from crude oil contaminated soil: adding rhamnolipid to the crude oil-water-soil system at concentration above its critical micelle concentration (CMC) value, can benefit the desorption of SAT and PAH fractions from soil. The sandy soil was associated with less amount of rhamnolipid adsorption. The desorption of these two fractions were much lower when rhamnolipid solution concentrations were mass-0.02and0.04%. The desorption of both fractions were most significant when rhamnolipid concentration increased to mass-0.08～0.1%. The change of pH can have distinct effect on rhamnolipid performance concerning its own micelle structure and soil properties. With the increase of salinity, the solubilization and desorption of petroleum hydrocarbon fractions were more significant due to the difference of soil physical and chemical properties.(4) Impact of environmental factors on the bioremediation of crude oil contaminated soil:based on the Taguchi experimental design method, a series of laboratory experiments were conducted to investigate the impacts of five environmnetal factors on the remediation efficiency of crude oil contaminated soil. They include the soil type, the type of surfactant, the surfactant concentration, the initial petroleum hydrocarbon concentration in soil, and the soil salinity. It was found that there was a distinct decline of soil total petroleum hydrocarbons (TPH) concentration when using surfactant during the bioremediation period of30days. TPH degradation efficiencies of Taguchi experiment were66.21-94.00%which was much higher than the control of28.44-56.23%. The analysis of variance (ANOVA) indicated that the five study factors had little effect on the soil TPH biodegradation except for soil type on day20and day30. The interaction effect between the five factors was not significant. The soil type was observed to be the most important factor affecting the bioremediation efficiency, but the impacts of other four factors were enhanced in the later stage of bioremediation.(5) Impact of biosurfactant concentration and soil salinity on the bioremediation of crude oil contaminated soil:a series of laboratory experiments were conducted to further examine the impact of biosurfactant concentration and salinity on TPH removal from crude oil contaminated soil. Rhmnolipid was selected as the study biosurfactant. It was found that the remediation was more effective with the concentration of bio-surfactant just slightly above or below its CMC (i.e.,0.5,1,2CMC). The most effective remediation that occurred was with rhamnolipid concentration in soil solution of2CMC, and the TPH biodegradation rate constant was0.0866d-1. Salts had a negative impact on soil TPH degradation. Consequently, the rhamnolipid can significantly increase bioavailability of TPH to soil microorganisms, and salts should be removed first before applying bio-surfactant for the remediation of soils contaminated with both crude oil and salts.(6). Experiments and simulation of bioremediation for diesel contaminated groundwater:a sand tank box model was established to conduct experiments on the bioremediation of diesel contaminated groundwater so that a numerical model can be developed to simulate the remediation process. The Visual MODFLOW was applied to simulate and calculate the diesel concentration distribution in the saturated zone. It was found that the experimental data obtained from the sand box modeling matched very well with the prediction values obtained form the Visual MODFLOW model. The results proved that bio-biosurfactant enhanced bioremediation system can quickly and effectively remove the organic pollution from the groundwater zone.
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