Mesocosm Study of Chemical Treatments on Methane Emissions in Oil Sands Tailings Ponds─Part I: Focusing on the Change of Microbial Communities and Tailings Dewaterability

In this study, we proposed mitigation strategies to reduce methane emissions from oil sands tailings ponds and determined the extent to which certain chemicals (Na₂MoO₄·2H₂O, Fe₂(SO₄)₃, Na₂SO₄, and Na₃C₆H₅O₇·2H₂O) could affect the methanogenesis process. Lab-scale mesocosms were used to compare the amount of fugitive emissions between paraffinic and naphthenic producer tailings. The inter-relationships among different parameters, such as methane, water chemistry, residual bitumen content in tailings, and microbial community, were investigated before and after the methane inhibition process. It was found that under different chemical treatment regimens, methanogenic populations were either suppressed or stimulated, demonstrating that functionally similar disturbances in natural systems may result in distinct responses of the microbial populations involved. The 16S RNA gene sequencing data revealed that both solvents and chemical treatments significantly impacted microbial diversity and communities in tailings, leading to notable shifts in dominant microbial families and a decrease in diversity in the treated samples. These treatments affected methanogenic families, reducing the abundance of archaeal methanogens (e.g., <i>Methanegulaceae</i>) while increasing the presence of microbial families involved in hydrocarbon degradation, such as <i>Spirochaetaceae</i> and <i>Thermovirgaceae</i>. This study lays the groundwork for potential economically viable approaches to reduce methane emissions from oil sands tailings ponds.