Enhanced Biodegradation of Petroleum Hydrocarbons in Contaminated Soil

Soil samples taken from a contaminated site in Northern Quebec, Canada, exhibited a low capacity for biodegradation of total petroleum hydrocarbons (TPH), despite a high capacity for the mineralization of aromatic hydrocarbons and a low toxicity of soil leachates as measured by Microtox assay. Toxicity assays directly performed on surface soil, including earthworm mortality and barley seedling emergence, indicated moderate to high levels of toxicity. Soil biostimulation did not improve the removal of petroleum hydrocarbons, while bioaugmentation of soil with a developed enrichment culture increased the efficiency of hydrocarbon removal from 20.4% to 49.2%. A considerable increase in the removal of TPH was obtained in a bioslurry process, enhancing the mass transfer of hydrocarbons from soil to the aqueous phase and increasing the efficiency of hydrocarbon removal to over 70% after 45 days of incubation. The addition of ionic or nonionic surfactants did not have a significant impact on biodegradation of hydrocarbons. The extent of hydrocarbon mineralization during the bioslurry process after 45 days of incubation ranged from 41.3% to 58.9%, indicating that 62.7% to 83.1% of the eliminated TPH were transformed into CO₂ and water.