Effect Of Microbes On Sequestration Of Hydrocarbons In Aquifers

Sequestration is the main reason which leading to the long persistence oforganic compounds in soil. It is happened when the organic chemicals enter into thesoil. At the same time, microbes also can affect the sequestration of organiccontaminants. In this study, batch-type experiment is employed and benzene,1,3,5-trimethylbenzene and naphthalene is selected as the representative oilpollutants, and uncontaminated soil form vadose zone in an oilfield is used toinvestigated the effect of microorganisms on the sequestration of characteristiccontaminants in this media. Moreover, oil soil that has the long contaminationhistory from same area is also used to test and verify the results.From the results, it is found that the adsorption quantity of single benzene,1,3,5-trimethylbenzene and naphthalene is29%,103%and136%higher than theyare mixed. And the desorption of single benzene,1,3,5-trimethylbenzene andnaphthalene from the adsorbed soil without microbes presence is0, but it goes up to1.5%,2.1%and0.1%when they are mixed. The extractable quantity of singlebenzene,1,3,5-trimethylbenzene and naphthalene is132%,126%and327%lowerthan they are mixed, this means that the increased adsorption quantity of mixedbenzene,1,3,5-trimethylbenzene and naphthalene can be totally extracted and alsopromote the desorption of sequestrated contaminants. Moreover, the proportion ofsequestration quantity in the adsorption quantity of single or mixed benzene,1,3,5-trimethylbenzene and naphthalene is75%,21%,84%and55%,12%,71%,respectively.In the uncontaminated soil/250g-water/1L system, where the originalconcentration of single and mixture benzene,1,3,5-trimethylbenzene andnaphthalene in the liquid phase is3.2,1.5,1.3mg/L and33.2、2.5、2.2mg/L,respectively. Microorganisms were added after the adsorption equilibrium ofpollutants with uncontaminated soil, and the concentration of benzene,1,3,5-trimethylbenzene and naphthalene in the liquid is increased after microbesadded. It increased11.6,1.5,6.6mg/L for single contaminants, and14.1,2.0,4.7 mg/L for mixed chemicals. This means that microorganisms can accelerate theorganic chemicals desorption. The increasing amount of single benzene,1,3,5-trimethylbenzene and naphthalene in the liquid phase is19.0,6.1,4.2mg, butthe decreasing quantity in the soil is only3.4,0.3,2.0mg. Therefore, microbes canlead to the desorbing of sequestrated organics.In the oil soil with long contamination history/250g-water/1L system, theexisting of microbes can lead to the7,2,4times and4,3,5times quantityincreasing of benzene,1,3,5-trimethylbenzene and naphthalene in liquid and soilphase (36,19,2704μg VS5,8,662μg in liquid and84,1030,40052μg VS23,399,8514μg in soil). This means that microorganisms can not only accelerate thedesorbing of organics, but also lead to the desorbing of sequestrated chemicals fromsoil.These results make some helpful ideas on the biological remediation technologyin groundwater, where the pollutants degrading is unobservable even the microbialactivity is very strong.