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This Master’s degree study examined concentration and isotopic trends of dissolved methane, isotopic trends of phospholipid fatty acids (PLFA), and generated 1st order flux calculations to identify and assess biogeochemical cycling of dissolved methane in the first full-scale demonstration of EPL technology in the Alberta Oil Sands Region (AOSR). Base Mine Lake (BML) was commissioned by Syncrude Canada Ltd. in 2012 to facilitate the long-term storage and remediation of Fluid Fine Tailings (FFT) that are generated as a result of bitumen extraction via the Clark Hot Water Extraction (CHWE) processes. The results of this project provide evidence of methane oxidation by type I methanotrophs in BML, reducing dissolved oxygen concentrations in the hypolimnion layer. The FFT layer is identified as a source zone of fermentative methanogenesis, creating saturated conditions of dissolved gases. Dissolved methane is transferred to the water column primarily by advective processes related to FFT consolidation, while diffusion is a significant secondary transfer mechanism. Dissolved methane concentrations decrease significantly across the FFT-water interface where diffusive flux rates decrease by several orders of magnitude. Concentrations decreased linearly through the hypolimnion to trace concentrations by the metalimnion, resulting in a minor enrichment of δ13C of the residual dissolved methane pool. A minor enrichment of δ13C in C14:0, C16:0, and C16:1 PLFA coincided across the same interval, indicating utilization of a less depleted carbon source further away from the FFT-water interface where dissolved methane concentrations were lower. PLFA δ13C signatures were depleted relative to expected values of typical DOC substrates, further supporting the incorporation of a depleted signature by transfer of depleted carbon from dissolved methane. / Thesis / Master of Science (MSc)

The Mildred Lake Settling Basin (MLSB) is the largest disposal site for mature fine tailings (MFT) at the Syncrude Canada Ltd oil sands plant. Since 1996, MFT densification in the MLSB has significantly accelerated due to microbial activity. Methane-producing microorganisms, known as methanogens, have become very active. A field and laboratory research program has been performed to study the mechanisms leading to the rapid densification. This research program consisted of historical monitoring data analyses, field investigations, small-scale column tests, and gas MFT densification tests. The field investigations have shown that the rapid densification of the MFT has occurred in the southern part of the pond ranging from 8 m to 15 m below the water surface. A connection existed between the rapid densification zone and the zone with intense microbial activity at the pond. The small-scale column tests demonstrated that, with increases of biogas generation, water drainage from the MFT was enhanced. Gas MFT densification tests showed that, stress histories and total pressure affected MFT densification property during microbial activity. Under high total pressure (6-7 m below pond surface) gas bubbles had difficulty to release. For MFT without pre-consolidation or under a preloading, during rapid gas generation, water was rapidly drained out. For over-consolidated MFT, water flowed back into MFT quickly during intense biogas generation. The concept of operative stress, the difference between the total stress and pore water pressure for the soil with large gas bubbles, was introduced to analyze the densification behavior of gassy MFT. Under high total pressure and under a preloading (1 kPa), excess pore pressure increased and operative stress decreased during rapid gas generation while water drainage from the MFT was accelerated. Total pressure and stress history also affected the structure and permeability of the MFT during microbial activity. Under low total pressure (1 m below pond surface) and without pre-consolidation, the MFT permeability increased after intense microbial activity. / Geotechnical Engineering

Poor settling of solids increases land requirement for tailings containment and imposes severe constraints on the water balance. Consequent to these considerations, the alternating current electrocoagulation (AC/EC) technique emerged as a candidate for enhancing the settling behaviour of suspensions in the mineral, coal and oil sands industries. Hence, a fundamental study of AC/EC was undertaken with aluminum electrodes. Ground silica (d50 = 20 m), which formed a stable suspension, served as the model tailings solid at 5.0 wt % in water. The AC/EC process consisted of two developmental stages: coagulation, marked by pH decrease in the silica suspension; and floc growth, characterized by pH increase from the minimum (i.e., the end of coagulation). AC/EC enhanced the initial settling rate of silica by over three orders of magnitude, and exhibited remarkable flexibility by virtue of the wide range of process parameters that could be optimized. For example, AC/EC can be operated in either the indirect or direct mode. The settling behaviour of bentonite (estimated d50 < 1 m) was more enhanced by indirect AC/EC, while that of silica benefited more from direct AC/EC. Any condition that increased aluminum dosage (e.g., current, retention time), increased the initial settling rate of silica. Over the feed water pH range of 3.0 to 9.1, AC/EC was effective in enhancing the settling behaviour of silica. AC/EC was also effective over a wide range of temperatures (23 to 85C). High electrical energy demand by AC/EC was observed throughout this study. Its optimization was beyond the scope of this work. Dilution of a sample of Syncrude mature fine tailings (MFT) to 4.6 wt % solids sustained a stable suspension. Settling occurred after AC/EC treatment, a crystal-clear supernatant resulted and bitumen was recovered as froth. Entrained solids were easily spray-washed from the froth with water. The settling behaviour of a Luscar Sterco fine coal tailings sample was not augmented by AC/EC, possibly due to contamination by the companys own electrocoagulation operation. After having been stored dry for more than a year, electrocoagulated silica was an effective coagulant for as-received silica and Syncrude MFT. / Chemical Engineering

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A study was conducted to evaluate the properties and processes influencing the rate and magnitude of volume decrease and strength gain for oil sand fine tailings resulting from a change in bitumen extraction process (caustic versus non-caustic) and the effect of adding a coagulant to caustic fine tailings. Laboratory flume deposition tests were carried out with the objective to hydraulically deposit oil sand tailings and compare the effects of extraction processes on the nature of beach deposits in terms of geometry, particle size distribution, and density. A good correlation exists between flume deposition tests results using oil sand tailings and the various other tailings materials. These comparisons show the reliability and effectiveness of flume deposition tests in terms of establishing general relationships and can serve as a guide to predict beach slopes. Fine tailings were collected from the various flume tests and a comprehensive description of physical and chemical characteristics of the different fine tailings was carried out. The characteristics of the fine tailings is presented in terms of index properties, mineralogy, specific surface area, water chemistry, liquid limits, particle size distribution and structure. The influence of these fundamental properties on the compressibility, hydraulic conductivity and shear strength properties of the fine tailings was assessed. Fourteen two meter and one meter high standpipe tests were instrumented to monitor the rate and magnitude of self-weight consolidation of the different fine tailings materials. Consolidation tests using slurry consolidometers were carried out to determine consolidation properties, namely compressibility and hydraulic conductivity, as well as the effect of adding a coagulant (calcium sulphate [CaSO4]) to caustic fine tailings. The thixotropic strength of the fine tailings was examined by measuring shear strength over time using a vane shear apparatus. A difference in water chemistry during bitumen extraction was concluded to be the cause of substantial differences in particle size distributions and degree of dispersion of the comparable caustic and non-caustic fine tailings. The degree of dispersion was consistent with predictions for dispersed clays established by the sodium adsorption ratio (SAR) values for these materials. The biggest advantage of non-caustic fine tailings and treating caustic fine tailings with coagulant is an increased initial settlement rate and slightly increased hydraulic conductivity at higher void ratios. Thereafter, compressibility and hydraulic conductivity are governed by effective stress. The chemical characteristics of fine tailings (water chemistry, degree of dispersion) do not have a significant impact on their compressibility behaviour and have only a small influence at high void ratio (low effective stress). Fine tailings from a caustic based extraction process had relatively higher shear strengths than comparable non-caustic fine tailings at equivalent void ratios. However, shear strength differences were small and the overall impact on consolidation behaviour, which also depends on compressibility and hydraulic conductivity, is not expected to be significant.

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