Inhibition of methanogenesis through redox processes in oil sands tailings

Bitumen extraction from oil sands ore in Alberta, Canada, has generated > 1.3 billion m 3 of tailings comprised of slurry of fine silt, clay, residual bitumen, and diluent hydrocarbons, deposited in ponds. Key environmental issues associated with oil sands tailings include biogenic greenhouse gas emissions (methane and carbon dioxide), water toxicity and its potential seepage, water reuse, and solids consolidation. Methane produced during anaerobic microbial metabolism of hydrocarbons is emitted from tailings ponds and end-pit lakes where tailings are reclaimed. This study tests one of the strategies to minimize methane emissions using iron minerals and other terminal electron acceptors for the biodegradation of residual hydrocarbons under alternative, non-methanogenic redox conditions. Preliminary data exhibited biodegradation of a higher number of hydrocarbons (heptane, octane and decane, and toluene) under sulfate-reducing conditions compared to toluene biodegradation only under nitrate- and iron-reducing conditions. Amorphous iron mineral suppressed methanogenesis, whereas iron crystalline mineral enhanced methane production. Our overall results reveal the potential of indigenous microbes to biodegrade hydrocarbons in the tailings under different redox conditions, and thereby channel carbon flow from hydrocarbons to carbon dioxide.