Mesocosm Study of Chemical Treatments on Methane Emissions in Oil Sands Tailings Ponds – Part II: Illustrating the Relationship of Naphthenic Acids with Methanogenesis

Naphthenic acid fraction compounds (NAFCs) are primary toxic components in oil sands process-affected water. Chemical treatments in tailings ponds can influence their concentration and composition, which may affect their toxicity. It is therefore crucial to measure the levels and distribution of NAFCs if there is any chemical treatment process being implemented in the tailings ponds. In the literature, some potential chemical treatment processes have shown promising results in terms of methane inhibition, thus reducing fugitive greenhouse gas (GHG) emissions from tailings ponds. However, little has been established to date on how the methanogenesis process along with chemicals used in the treatment affects the concentration and compositional characteristics of the NAFCs in the tailings ponds. In this study, laboratory scale bottle tests simulating oil sands tailings pond environments were used to investigate joint outcomes of chemical treatments on methanogenesis in relation to the concentrations and molecular level characteristics of NAFCs. Among the four chemicals (Na₂MoO₄·2H₂O, Fe₂(SO₄)₃, Na₂SO₄, and Na₃C₆H₅O₇·2H₂O) tested, Fe₂(SO₄)₃ reduced both methane production and the concentration of the NAFCs. There was also evidence for oxidative transformation of classical naphthenic acids (i.e., O₂-NAFCs) presented in the study. These findings suggest the potential of using Fe₂(SO₄)₃ as a chemical amendment for NAFC attenuation and methane reduction to assist with the cleanup effort for oil sands tailings ponds.