The main concerns of air travel are the operating costs of general aviation aircraft. Hybrid-electric system design provides a great opportunity for future aircraft models to be environmentally friendly. The Hybrid-electric power propulsion system experienced a growing interest driven by determined targets. Electric technologies have proven promising success to achieve a successful result in the near- and long-term. Combining fuel cells and batteries, this technology can enable a significant reduction in fuel consumption, noise, and emissions. Different types of fuel cells and batteries are proposed and discussed during this work. The Cessna C-172 is a candidate to test the combination of the most promising fuel cells and batteries for a hybridization or complete electrification strategy.

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Acid mine drainage (AMD) is a major issue for the mining industry and a global environmental concern. It is facilitated heavily by microbially catalyzed sulfur oxidation/ disproportionation reactions involving reduced sulfide components in mine wastes that result in the release of harmful acidity and metals. The microbial processes catalyzing sulfide mineral leaching of mine waste rock resulting in AMD have been previously studied. However, the initiation of AMD processes in mining wastewaters has not been well studied. Post extraction, highly contaminated, mining wastewater is stored in retention (tailings) impoundments on site and treated to prevent impacts such as toxicity, contamination, and acidity prior to discharge to the receiving environment. Tailings, the waste stream generated through extraction of sulfide ores contains a variety of aqueous sulfur oxidation intermediate compounds (SOIs), such as polysulfides, elemental sulfur, and sulfur oxyanions, of the form SxOy2- termed “thiosalts” by the industry, which can also generate AMD. These wastewaters typically initially start off with circumneutral pH, but if thiosalts are present in high enough concentrations, microbial processes can cause net-acid generation leading to AMD. The microbial ecology and functionality of endemic tailings impoundment microbial assemblages in the “pre-net acid generating phase” (PNAG) of circumneutral mine wastewaters, as well as the associated sulfur species and reactions are not well understood. Thus, early-stage indicators that would offer mines proactive monitoring tools for improved tailings impoundment management are currently lacking. In collaboration with our mining industry partners, who provided tailings impoundment water samples, this dissertation tackles these limitations. This dissertation aimed to identify important microbes and the SOI important to the initiation of AMD in PNAG tailings impoundment wastewaters and to determine potential markers (microbial and/or geochemical) associated with these initiating AMD processes that would inform the development of monitoring tools in mine water management. The objectives of this doctoral research were to constrain the S biogeochemistry of the PNAG phase by characterizing both expression levels of sulfur oxidation genes and sulfur speciation under experimental conditions designed to assess the roles of microbial community, SOI geochemistry and pH. Specifically three well constrained laboratory experiments determined: (1) gene expression by a pure culture of Acidithiobacillus thiooxidans and sulfur speciation with either thiosulfate or elemental sulfur added as the starting SOI substrate (Chapter 3); (2) parent mining wastewater communities and associated sulfur oxidizing bacteria (SoxB) enrichments collected seasonally at two mines and grown at either pH 7-5 or pH 5-3 genetically (16S amplicon) (Chapter 4); and (3) geochemical sulfur pathways of three unique mine wastewater SoxB enrichment communities for six distinct simulated mine wastewater thiosulfate and/or tetrathionate treatments (Chapter 5). Results presented in Chapter 3 expand the understanding of the reactions and enzymes involved in S0 and S2O32- metabolism by a pure strain sulfur oxidizing bacteria A. thiooxidans ATCC 19377 by developing the first models integrating gene expression, solution sulfur speciation, electron microscopy and spectroscopy. These novel results reveal that A. thiooxidans S2O32- metabolism involves the conversion of S2O32- to SO42-, S0 and S4O62-, mediated by the sulfur oxidase complex (Sox), tetrathionate hydrolase (TetH), sulfide quinone reductase (Sqr) and heterodisulfate reductase (Hdr) proteins. These same proteins, with the addition of rhodanese (Rhd), were identified to convert S0 to SO32-, S2O32- and polythionates in the A. thiooxidans S0 metabolism model. The results of this chapter advance understanding by revealing (1) the important role specifically of TetH in S2O32- metabolism; (2) Hdr proteins, rather than Sdo proteins, are likely associated with S0 oxidation; (3) that formation of intracellular S2O32- is a critical step in S0 metabolism, and (4) that recycling of internally generated SO32- occurs, through comproportionating reactions that result in S2O32-. Results summarized in Chapter 4, identify that pH is the most important factor influencing which sulfur oxidizing bacteria (SoxB) occur irrespective of total S concentration of SOI substrate provided in enrichment experiments for two mines of different parent wastewater geochemistry. Mine 1 exhibited a lower total S and reactive soluble sulfur compounds (oxidation state < +VI) concentrations, and greater parent wastewater microbial community diversity with more unique sequences relative to Mine 2. All experimental SoxB enrichment experiment microbial communities evidenced a shift in dominance from primarily Alphaproteobacteria (28% - 77%) at circumneutral pH to Gammaproteobacteria (>80%) under moderately acidic pH values. A further pH dependent shift was observed at the genus level, from Halothiobacillus spp. dominating the circumneutral pH SoxB enrichments to Thiomonas spp. dominating the mildly acidic SoxB enrichments. These results provide some of the first putative biological indicators to improve prediction and management of sulfur processes and AMD onset within mining wastewaters. Chapter 5 results importantly assess the influences of SOI chemistry and SoxB consortia identity on SOI cycling. Results identify that SOI substrate, whether S2O32- , S4O62-, or S2O32- + S4O62-, was a more important determinant of microbial sulfur outcomes than the relative abundances of Halothiobacillus spp. and Thiomonas spp.. Further, three pH dependent phases of microbial sulfur processing were identified: Phase 1, pH > 5, dis/comproportionation reactions and acid consuming reactions were prevalent alongside oxidation, with S2O32- identified as an important indicator; Phase 2, pH 5 – 3, further dis/comproportionation occurred, with S0 emerging as an important indicator signalling the progression of the system towards net acid generation with S4O62- or S2O32- as the major S species present and; Phase 3, pH < 3, i.e. full AMD conditions, with dominant oxidation reactions resulting in SO42- and acid generation. Collectively, these results identify specific SOI species important at different pH stages in AMD initiation and development across different microbial SoxB, providing new indicators that may serve as signals associated with predictive tool development. The integration of the novel results of this thesis revealed some of the first biologically informed possible indicators (bacterial and geochemical) that will enable improved management through proactive monitoring tools for AMD initiation in mining wastewaters. / Dissertation / Doctor of Science (PhD)

As oil production increases in Alberta’s Athabasca Oil Sands Region (AOSR), optimization of tailings management processes will be integral to the successful reclamation of tailings-based environments. Syncrude Canada Ltd. has established an innovative dry-storage method for their wastes known as composite tailings (CT) that supports mine closure objectives by providing a base for terrestrial reclamation landscapes. Syncrude’s Sandhill Reclamation Fen is the first instrumented research wetland of its kind to be developed in the AOSR and it overlays a sand-capped composite tailings deposit in a retired open-pit mine site. This stratified sulfur-rich environment is highly anthropogenically altered and consists of three distinct zones: a constructed wetland, a 10m layer of sand, and 40m of CT. As oil sands tailings systems are becoming globally significant sulfur reservoirs due to their size, sulfur content, and diverse microbial communities, understanding the mechanisms behind H2S generation in novel tailings structures will help inform our understanding of sulfur-rich environments. This study is the first to characterize the sulfur biogeochemistry in each zone of the Sandhill Reclamation Fen deposit in an effort to establish the potential for microbial sulfur cycling and explore the mechanisms controlling H2S generation. Porewater ΣH2S(aq) was detected at all depths, increasing with depth from the surface of the wetland (<1.1 μM) and peaking in the sand cap (549 μM). Across all sampling trips, ΣH2S(aq) concentrations were consistently highest in the sand cap, with sampling-associated H2S gas concentrations in the wells reaching 104-180 ppm. Abundance of dissolved sulfate (0.14-6.97 mM) did not correlate to the distribution of ΣH2S, and dissolved organic carbon (21.47-127.72 mg/L) only positively correlated with the observed maxima of ΣH2S in the sand-cap. Identical sodium and chloride distributions in the sand and CT supported the model of upward migration of CT-derived porewater and fines into the sand cap. Functional metabolic enrichments established the ability of endemic microbial communities from all depths of the deposit to oxidize and reduce sulfur. Experimental microcosms demonstrated 1) the dependence of ΣH2S generation on the presence of fine particles; 2) stimulation of endemic microbial sulfur reduction through amendment with labile carbon and 3) increased generation of ΣH2S in the presence of thiosulfate over sulfate. Field and experimental results indicated that the bioaccessibility of recalcitrant organic carbon in the deposit likely controls rates of ΣH2S generation at depth. While the mechanisms relating CT-derived fines to ΣH2S in the sand cap are still unconstrained, the sand layer is clearly a bioreactive mixing-zone supporting optimal conditions for ΣH2S accumulation. These findings inform our understanding of biogeochemical sulfur cycling in novel oil sands reclamation deposits and will advise on-going optimization of tailings-based landscape management practices. / Thesis / Master of Science (MSc)

This study seeks to determine the value of sulfur dioxide as a method for the dehydration of sweet potatoes for use in cow feed.

<p> The mass spectra of disubstituted 1,4-dithiane, 1,4-oxathiane, and 1,4-oxaselenane, as well as the mass spectra of some disubstituted bicyclic and tricyclic sulfur and selenium compounds, were studied. The exact composition of the major ions of many of these compounds was determined. Fragmentation mechanisms are proposed to account for the major peaks in their spectra.</p> / Thesis / Master of Science (MSc)

Cerium and zirconium oxides are materials that have unique catalytic properties and are finding many applications in industrial catalysis. Particularly, the great advances attained in the past 30 years in curbing the amount of gaseous pollutants released can be attributed to the development of catalysts employing such materials. However, oxides of sulfur are known poisons of many catalytic systems and are encountered in many commercial applications. In this investigation, polycrystalline ceria-zirconia solid solutions of various molar ratios were synthesized. High resolution x-ray photoemission spectra were obtained and examined to reveal the surface species that form on these metal oxides after exposure to sulfur dioxide under various conditions. The model catalysts are exposed to sulfur dioxide using an in-situ high-pressure reaction cell. A reliable sample platen heater was designed to allow the observation of any temperature dependency up to 673 K. The results of this study demonstrate the formation of sulfate and sulfite adsorbed sulfur species. Temperature and compositional dependencies are also displayed, with higher temperatures and ceria mole fractions displaying a larger propensity for the formation of surface sulfur species.