Biodegradation of Hydrocarbons in Bitumen: Exploring Plant-Assisted and Microbial Stimulation Techniques

Abstract

While bitumen is one of the oldest construction materials in the world and currently provides an important fuel needed to sustain our modern lifestyle, the disturbances caused by extracting and refining this material are considerable, with 895 km2 of land being disturbed in Alberta as of 2018 that needs reclamation. As part of reclaiming the mined landscape, landforms made of lean oil sands (low-grade bitumen containing < 7 % hydrocarbons by volume) are covered with a cap of suitable soil to provide a base for revegetation. However, the effects of hydrocarbons present in lean oil sand are concerning due to their adverse effects on ecological health and plant growth. Revegetating reclaimed areas with native plant species not only supports restoring locally common forests but may also enhance the degradation of hydrocarbons. The goal of my research is twofold: 1) to determine whether trembling aspen (Populus tremuloides) and jack pine (Pinus banksiana), tree species that are native to the region and commonly used in reclamation, are effective phytoremediation candidates, and 2) to determine the effects of lean oil sands on the soil microbial community and their potential for hydrocarbon degradation. I conducted a growth chamber experiment to assess hydrocarbon degradation over 30 weeks in two grades of LOS, 4.54 % hydrocarbons and 1.95 % hydrocarbons, in the presence and absence of each of the plant species. In addition to hydrocarbon degradation, I also measured biomass of plants in response to the two grades of LOS. Analysis of phospholipid fatty acids (PLFA) was used to determine how the soil microbial community was altered by plant species and LOS grade. While my study determined that the plants studied here did not enhance degradation of hydrocarbons, the addition of nutrients and water to the system may have acted as a biostimulant. This biostimulant effect may have enabled microbes to degrade groups of hydrocarbons generally considered to be recalcitrant. Furthermore, analysis of PLFAs showed that increased concentrations of hydrocarbons corresponded to increased microbial PLFA concentrations regardless of functional group, potentially indicating that the local microbial community can use hydrocarbons to produce additional biomass. At low concentrations, such as those used in my study, the native microbial community may be stimulated in the presence of hydrocarbons to degrade these compounds and immobilize them via incorporation into new biomass. Taken together, my research indicates that while the plant species used here are not suitable to enhance degradation under the tested conditions, nutrient and moisture amendments may enhance the degradation of hydrocarbons in LOS by stimulating the soil microbial community.