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碳动力学和生物地球化学过程，这些过程控制着尾矿池和尾坑湖的温室气体排放。产甲烷是主导过程，由尾矿库中夹带有机物的微生物代谢驱动。全面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，而且有助于设计更好的生物补救方法来管理加拿大受污染的地下环境，如尾矿池、淹没土壤和沉积物、湿地和含水层。在阿尔伯塔省的沥青开采过程中产生了大量的油砂尾矿。与油砂尾矿相关的环境问题包括碳氢化合物等有机污染物的存在；温室气体排放；尾矿缓慢固结；尾矿库孔隙水在沥青提取过程中的回用回收率较差。我研究的长期目标是发现解决这些问题所需的基本科学知识。长期（1 ~ 7年）的实验表明，尾矿库的微生物对挥发性萃取溶剂中的某些碳氢化合物进行了生物降解，产生甲烷（CH4）和其他温室气体。在产甲烷条件下，生物可降解碳氢化合物的范围扩大了，这使我能够改进我们的数学模型，该模型将携带的溶剂碳氢化合物视为尾矿池温室气体排放总量的主要来源（~50-95%）。这些观察结果促使我提出对产甲烷条件下油砂尾矿中顽固性碳氢化合物（环烷烃）、多环芳烃（PAH）和聚丙烯酰胺（PAM）的生物降解及其代谢途径进行研究，以便利用碳质量平衡来确定碳流量，从而更好地进行模型预测。尾矿中未回收的沥青是多环芳烃的来源，PAM作为絮凝剂加入尾矿中。我还建议全面研究铁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碳氢化合物来减轻温室气体的初步研究表明，铁（FeIII）矿物增加了油砂尾矿中CH4的产生。因此，了解铁矿物在CH4生成或抑制中的作用是很重要的。本研究的结果将：(1)提高我们对碳氢化合物在缺氧环境下生物降解性的认识；(2)为精确的模型预测尾矿库，特别是尾坑湖的温室气体排放和甲烷生成维持量提供数据，其中甲烷生成可诱导影响尾坑湖可持续性和健康的化学通量；(3)深入了解可导致制定温室气体减缓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.