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

拟议的研究计划旨在调查控制尾矿库和尾矿湖温室气体(GHG)排放的碳动态和生物地球化学过程。产甲烷是尾矿库的主导过程，是由携带有机物的微生物代谢驱动的。完全了解基本的厌氧生物降解过程不仅有助于预测温室气体排放，还有助于设计更好的生物医学方法来管理加拿大受污染的地下环境，如尾矿库、沉水土壤和沉积物、湿地和含水层。艾伯塔省在提炼沥青的过程中产生了大量的油砂尾矿。与油砂尾矿有关的环境问题包括碳氢化合物等有机污染物的存在；温室气体的排放；尾矿的缓慢固结；尾矿池的孔水回收不足，以便在沥青提取过程中重新利用。我研究的长期目标是发现为这些问题提供解决方案所需的基本科学知识。我们的长期(1-7年)实验表明，逃逸萃取剂中的某些碳氢化合物被本土尾矿微生物依次生物降解，从尾矿库中产生甲烷(CH4)和其他温室气体。甲烷条件下生物可降解碳氢化合物范围的扩大使我能够改进我们的数学模型，该模型将夹带的溶剂型碳氢化合物作为主要来源，对尾矿库的温室气体排放总量做出贡献(~50%-95%)。这些观察结果促使我提议对油砂尾矿中难降解碳氢化合物(环烷烃)、多环芳烃(PAH)和聚丙烯酰胺(PAM)在产甲烷条件下的生物降解及其代谢途径进行研究，以便可以利用碳质量平衡来确定碳流，以便更好地进行模型预测。尾矿中未回收的沥青是PAH的来源之一，PAM作为絮凝剂添加到尾矿中。我还建议全面研究铁的循环及其与甲烷生成的关系，因为我们在铁还原条件下通过生物降解烃来缓解温室气体的初步研究表明，铁(FeIII)矿物促进了油砂尾矿中CH4的产生。因此，了解铁矿物在甲烷产生或抑制中的作用是很重要的。拟议研究的结果将(1)提高我们对碳氢化合物在缺氧环境中的生物降解性的认识；(2)为准确的模型预测尾矿库中的温室气体排放和甲烷生成的支持提供数据，特别是在尾矿池中，在这些尾矿池中，甲烷生成可诱导影响末端坑湖泊可持续性和健康的化学通量；以及(3)深入了解可导致制定温室气体缓解战略的氧化还原过程。

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.