Lime-Based Stabilization of Residual Petroleum Hydrocarbons in Contaminated Soils after Biodegradation

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Petroleum hydrocarbons are one of the most frequently identified compounds in contaminated sites in Canada. In general, indigenous hydrocarbon-degrading bacteria are often present in hydrocarbon-contaminated soils and groundwater, and active bioremediation and natural attenuation (intrinsic biodegradation) are therefore frequently considered cost-effective, minimally destructive site remediation strategies. However, the origin of the major limitation of bioremediation and natural attenuation is that hydrocarbon-degrading microorganisms must be able to access hydrocarbons in soil microenvironments. After bioremediation or natural attenuation, hydrocarbon concentrations often rebound and exceed environmental criteria in the soil due to the reduced bioaccessibility of hydrocarbons in the soil matrix, which minimizes microbial activity. Residual hydrocarbons can be gradually mobilized and leached out by climatic events such as seasonal soil freeze-thaw cycles and precipitation. The risk of hydrocarbon exposure for humans and wildlife is elevated during this slow process and cannot be predicted precisely. This represents a significant environmental concern for a large number of hydrocarbon-contaminated sites and lean oil sands tailings dump sites, most of which are passively remediated by intrinsic microbial activity. In collaboration with Graymont Western Canada Inc., Dr. Won Jae Chang's research group at the University of Saskatchewan is developing a stabilization post-treatment technology for residual hydrocarbons in soils that have undergone bioremediation or natural attenuation. In the proposed research, quicklime and hydrated lime will be tested as the key remedial agents for the stabilization technique. The lime products will be employed to enhance the volatilization of light hydrocarbons during exothermic pozzolanic reactions, immobilize heavy hydrocarbon fractions during lime cementation, and promote cation exchanges to remove adsorbed salts (mainly sodium chloride, a common co-contaminant) within biologically weathered, field-aged, petroleum hydrocarbon-contaminated soils.