Biosurfactant enhanced treatment of petroleum oil contaminated soils

Abstract

This thesis reports the experimental measurements on the ability of biological origin surfactants (i.e. biosurfactants - aescin, lecithin, rhamnolipid, saponin and tannin) on removing crude oil and a heavy fuel oil blend from various soils, through soil washing process. The greatest advantage of soil washing is that it is a physical means of separating oil from soil using water or surfactants without chemically modifying either the soil or the oil. The oil removal performance of the biosurfactants was evaluated against that of a well studied synthetic surfactant (sodium dodecyl sulphate, SDS) using water as a base case. For this purpose, different washing settings (i.e. test tubes, stirred flasks, packed column, and air bubble assisted stirred tank) were used to treat contaminated soils with high oil toxicity. The effects of operational parameters such as washing temperature (5 to 500C), washing time (1 to 20 minutes), concentration of surfactant solutions (0.004 to 0.5%-mass), volume of surfactant solution (5 to 20 cm3), flow rate (2 to 16 cm3/minutes), pore volume (10 to 70) and contamination history was investigated. The interaction of the surfactant solutions with the oil and soils was also investigated, which was used to explain the dominant mechanisms behind soil washing. The contaminated soils were prepared in the laboratory by mixing the oil and soils. Two different contamination cases were considered: weathered contamination in which freshly contaminated soils were subjected to heat treatment in a fan assisted oven (simulating weathering effect in the natural hot environments), and non-weathered contamination in which contaminated soils were not subjected to any heat treatment. The different washing techniques employed in this study yielded a novel and informative description on the selection of biosurfactants in the remediation of crude oil contaminated soils. This is believed to have major academic and industrial values for the treatment of (1) soil contaminated with oil, (2) sand produced with oil, (3) drill cuttings, (4) enhanced oil recovery, and (5) waste drilling mud and sludge from oil storage tank. In addition, the characterization of the biosurfactants in oil-water, soilwater and oil-soil systems give a general knowledge of their behaviour, which is important in the application for effective removal of oil from soil. Soil washing was found to have a considerable potential in removing oil from the different contaminated soils and results were comparable with those reported in literature. Oil removal by rhamnolipid was more effective than the other biosurfactants and water was effective at higher parameter levels. Further, biosurfactants can preferentially remove certain aromatic groups, which may be desirable for more rapid soil remediation. The rhamnolipid can be equally as efficient at removing oil from soil as SDS at a repeatability range of ± 6%. However, rhamnolipid have advantages over SDS beacuase the use of rhamnolipid will eliminate the need for removing surfactants from effluents as their release will not damage the environment due to their safe natures. Other surfactants (bio and/or synthetic) can be blended with rhamnolipid to achieve greater performance characteristics. In general, the stirred tank and air bubble assisted stirred tank reactors settings were more effective in removing oil from the weathered and the non-weathered contaminated soil samples. The most influential parameter on the oil removal was washing solution temperature with more than 80% of crude oil removal at 500C.