A multi-process phytoremediation system for decontamination of persistent total petroleum hydrocarbons (TPHs) from soils

Multiple techniques that affect different aspects of contaminant removal can improve remediation of persistent hydrocarbons from soils. We have developed a multi-process phytoremediation system (MPPS) that is composed of land-farming (aeration and light exposure), contaminant degrading bacteria, plant-growth-promoting rhizobacteria (PGPR), and growth of the contaminant-tolerant plant, Tall Fescue (Festuca arundinacea). In this study, the MPPS was applied to a contaminated soil acquired from the Imperial Oil land farm site in Sarnia, Ontario, Canada. This soil was contaminated with oil refinery sludge to a level of approximately 5% (w/w) total petroleum hydrocarbons (TPHs). Over an initial 4-month period, the average efficiency of removal of persistent TPHs by the MPPS was twice that of land-farming alone, 50% more than bioremediation alone, and 45% more than phytoremediation alone. Importantly, the MPPS removed oil fractions 2, 3 and 4 with equal efficiency. Therefore, the highly hydrophobic, recalcitrant TPH fractions were remediated from the soil with the MPPS. After a second 4-month period, the MPPS removed 90% of all fractions of TPHs from the soil. Phytoremediation alone was able to remove only about 50% of TPHs in the same time period. The key elements for successful phytoremediation were the use of a plant species that can proliferate in the presence of high levels of contaminants, and strains of PGPR that increase plant tolerance and accelerate plant growth in heavily contaminated soils.