| The contamination of marine environment with crude oil has become a serious worldwide marine pollution.It would go a long way to remove the crude oil pollution. Among the numerous techniques available for removing crude oil pollution, biodegradation and photodegradation have been shown to be two of the most significant degradation mechanisms. Although bioremediation has many advantages such as less secondary pollution and low-cost, it is vulnerable to environmental factors. Photocatalysis as an advanced oxidation processes can make some compounds fully degraded or increase the solubility of the compounds. But the operational costs are relatively high compared to those of bioremediation. So there are more potential advantages of the combined process than of the single process in the crude oil pollution treatment field.Crude oil from the Bohai Sea was selected. Firstly, the SARA fractions of the crude oil was measured.Secondly, comparison between photolytic and photocatalytic degradation of crude oil was conducted in mimic actual marine environment using seawater medium, UV-A radiation, focusing on the degradation rate of crude oil by nano-TiO2 with different quantity and coated with stearic acid or not. The changes of water soluble fraction and DOC concentration as well as the SARA fractions of crude oil and total number of bacterial colony in seawater were measured.Finally, the indigenous microbial population was cultivated to remove the crude oil pollution. Crude oil degradation rates were respectively compared under two strategies, that were photocatalytic oxidation after biodegradation, biodegradation after photocatalytic oxidation. Experimental results showed that:(1) The modified column chromatography method was accurate and reproducible. There was certain relation between the TGA and SARA data of the heavy crude oils.The thermaogravimetric curves exhibited two or three continuous weight loss regions, and the boundary of the low-temperature region and high-temperature region located at 400℃-500℃.For light crude oil,the sum of weight losses in low-temperature region were always more than the sum of saturates, aromatics fractions from SARA results, while the weight loss in high -temperature region was always less than the sum of resin and asphaltene fractions. For the heavy crude oil, the sum of weight losses in low-temperature region were roughly equal to the sum of saturates, aromatics fractions from SARA results.(2) Photocatalytic degradation worked better than photolytic degradation. It was the 12.5% quality fraction that exhibited the optimum catalytic activity. After 30d illumination, the crude oil lost 39.14% of its initial weight.While the photolytic degradation rate was 29.98%.The catalyst quantity had significant effects on photodegradation rate and the composition and concentration of WSF. while the catalyst whether coated had little influence.In addition, the estimated degradation rates of resins positively correlated with those of aromatics, and the n-alkanes increased in photocatalytic conditions. Photocatalytic degradation products had no significant effect on the growth of marine bacteria.(3) The combination of photocatalysis and biodegradation worked better than simple photocatalytic degradation or simple biodegradation. After 51 days reaction,The degradation rates of combination-1. combination-2. simple biodegradation and simple photolytic were 51.0%.56.60%,39.60%,41.52% respectively.Combination-2 worked better than combination-1, basically because the degradation effects of saturated fraction were different:combination-2 was as high as 82.35% and the combination-1 was only 44.27%.It was the result of the different order of photocatalysis and biodegradation combination. Saturated hydrocarbons which are susceptible to biodegradation were produced during photocatalytic degradation. Then biodegradation could remove not only the saturated hydrocarbons of the crude oil, but also the photocatalytic products. |
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