Henian Guo | ALES Graduate Seminar

Event details: A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Henian Guo. This seminar is open to the general public to attend.

MSc with Dr. Tariq Siddique.

Thesis Topic: 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.