MSc graduate defense seminar for LRIGS member, Henian Guo, Monday March 4 at 2:00 pm, 150 South Academic Building (SAB). “Methanogenic biodegradation of polycyclic aromatic hydrocarbons in oil sands tailings.”
Abstract:
Current hot water extraction method to recover bitumen from excavated oil sands ores after surface mining generates large volumes of fluid fine tailings (FFT) that are temporarily deposited in oil sands tailings ponds. Promising techniques for tailings ponds reclamation such as end-pit lakes are facing potential challenges including the aquatic toxicity and methane emissions caused by tailing-derived hydrocarbons such as polycyclic aromatic hydrocarbons (PAHs). However, little information is available about efficient PAHs determination in tailings as well as the behavior of PAHs under methanogenic conditions in tailings. Therefore, the method development for determination of PAHs and the investigation of PAHs potential biodegradation under methanogenic conditions in FFT are the aims of this study. Conventional methods for PAHs determination in solid samples such as soils and sediments yielded poor recovery of PAHs from oil sands tailings due to the potential adsorption of PAHs onto the fine particles and organic compounds of tailings. Thus, an optimized method for PAHs determination in tailings was developed, which achieved ~94% pooled mean recovery of PAHs. The optimized method includes: (1) pre-treatment of FFT sample with dichloromethane (DCM) for 24 hours before extraction; (2) extraction of PAHs from the pre-treated FFT with DCM in a Soxhlet extractor for 24 hours; (3) purification of the extract with a silica gel chromatography column using DCM as eluent; (4) measurement on Gas Chromatography-Mass Spectrometry (GC-MS). This method has high sensitivity and reproducibility and was used for the detection of PAHs in the bench-scale biodegradation experiments in this study. Sealed anaerobic microcosms containing tailing samples from 3 tailings ponds operated by Syncrude Canada Limited (Syncrude),Canadian Natural Resources Limited (CNRL), and Albian Sands Energy Incorporated (Albian), were set up to simulate methanogenic conditions below mudline of tailings ponds and to test if indigenous microbial community is capable to degrade PAHs. After ~700 days incubation under methanogenic conditions, no degradation of 6 abundant PAHs (naphthalene, phenanthrene, pyrene, dibenzofuran, fluorene, and dibenzothiophene) in tailings occurred, although toluene (added as a solvent of PAHs) was degraded within ~300 days in Syncrude and Albian microcosms. However, future degradation of PAHs can be expected since the potential PAHs degraders such as Clostridia have high relative abundance in the indigenous microbial communities of oil sands tailings.