Investigating carbon dynamics and process fundamentals to predict greenhouse gas emissions from tailings ponds

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The proposed research program is designed to investigate carbon dynamics and biogeochemical processes that govern greenhouse gas (GHG) emissions from tailings ponds and end-pit lakes. Methanogenesis is the dominant process and is driven by microbial metabolism of entrained organic substances in tailings ponds. Complete understanding of the fundamental anaerobic biodegradation processes will not only help predict GHG emissions but also aid in devising better bioremedial approaches to manage contaminated subsurface environments in Canada such as tailings ponds, submerged soils and sediments, wetlands, and aquifers. Enormous oil sands tailings are produced in Alberta during bitumen extraction. Environmental issues associated with oil sands tailings include presence of organic contaminants such as hydrocarbons; emission of GHG; slow consolidation of tailings; and poor recovery of porewater from tailings ponds for re-use in the bitumen extraction process. The long term goal of my research is to discover the basic scientific knowledge necessary to provide solutions to these issues. Our long-term (1-7 years) experiments revealed that certain hydrocarbons in fugitive extraction solvents were sequentially biodegraded by the indigenous tailings microbes to produce methane (CH4) and other GHG from tailings ponds. This expanded range of biodegradable hydrocarbons under methanogenic conditions allowed me to improve our mathematical model that attributed entrained solvent hydrocarbons as primary source contributing (~50-95%) to total GHG emissions from tailings ponds. These observations have led me to propose an investigation into the biodegradation of recalcitrant hydrocarbons (cycloalkanes), polycyclic aromatic hydrocarbons (PAH) and polyacrylamide (PAM) and their metabolic pathways in oil sands tailings under methanogenic conditions so that carbon mass balance could be used to determine carbon flow for better model prediction. Unrecovered bitumen in tailings is a source of PAH and PAM is added to tailings as a flocculant. I also propose to investigate comprehensively iron cycling and its connection with methanogenesis, because our preliminary study conducted to mitigate GHG by biodegrading hydrocarbons under iron-reducing conditions showed that iron (FeIII) minerals enhanced CH4 production in oil sands tailings. Therefore it is important to understand the role of iron minerals in the production or inhibition of CH4. The results from the proposed research will (1) advance our knowledge about the biodegradability of hydrocarbons in anoxic environments; (2) generate data for accurate model prediction of GHG emissions and sustenance of methanogenesis in tailings ponds and particularly in end-pit lakes where methanogenesis can induce chemical flux affecting sustainability and health of end-pit lakes; and (3) give insight into the redox process that can lead to development of GHG mitigation strategy.