Mitigating GHG emissions from oil sands tailings through redox processes

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Surface mining of oil sands has a significant environmental footprint. Currently tailings ponds contain more than 1 billion m3 of fluid fine tailings (FFT) that need to be reclaimed. Expression of porewater from settling FFT contributes oil sands process-affected water to the water cap volume and chemistry. Tailings ponds are anaerobic and harbor microbial communities that degrade residual hydrocarbons in FFT producing greenhouse gases (GHG), primarily methane. Similarly, methanogenesis can continue in end-pit lakes where FFT is reclaimed under water and the conditions are aerobic near the surface. The overarching objective of this current project is to reduce net GHG emissions. A two-pronged strategy will be employed: 1) to understand the role of iron minerals and other redox compounds (nitrate and sulfate) in the inhibition of methanogenesis and 2) to understand the roles of these alternative electron acceptors, along with molecular oxygen (O2), in the oxidation of produced methane. Exploring the metabolic potential of indigenous microorganisms and investigating linkages between methanogenesis and iron, nitrogen, and sulfur cycling in the FFT will help develop strategies that will include in situ amendments of redox compounds and ex-situ application of redox processes to inhibit methanogenesis and stimulate methane oxidation. The approach will mitigate GHG emissions from tailings ponds and future end-pit lakes in the Athabasca Oil Sands region in Alberta, Canada.