Waste Vegetable Oil Increases the Bioaccessibility of Tar Oil Contaminants in Soil

In practice, besides the lack of suitable environmental conditions, the diffusion and strong sorption of PAH to the soil matrix is often found to inhibit pollutant degradation. Strongly sequestered contaminants are inaccessible for microbial degradation processes. While nutrients and electron acceptors can be administered in engineered processes or 'bioremediation' in- and ex-situ to support microbial contaminant degradation in contaminated soils, few practical methods exist to increase the contaminant fraction accessible to degradative processes. The contributions of accessible and inaccessible pollutant fractions in soils will, however, eventually determine the potential success of bioremediation measures for historically contaminated matrices. The use of plant lipids, specifically vegetable oils, as mild biocompatible extractants for bioaccessibility-limited soils was investigated in several studies. The results indicate that PAH ac-cessibility and degradation in industrial soils can be increased by up to 40 % by adding 1 % (w/w) of vegetable triglycerides. In order to cope with economic and ethic issues, the use of thermally stressed plant lipids, as present in waste cooking oil, for PAH extraction was also in-vestigated. Using artificially stressed oils and representative samples collected from a waste cooking oil collection centre, the influence of changed viscosity, saturation and lipid acidity on the heated oils' extraction properties were tested. Thermally stressed oils had slightly reduced extraction efficiency for PAH, most likely due to their increased viscosity. For an engineered application, e.g. as amendments in ex-situ soil bioremediation, these differences are, however, most likely negligible. The present study indicates that thermally stressed plant lipids, such as waste cooking oils, can efficiently be used to increase the efficacy of ex-situ bioremediation efforts to detoxify PAH-contaminated soils.