Second-generation stoichiometric mathematical model to predict methane emissions from oil sands tailings

Microbial metabolism of fugitive hydrocarbons produces greenhouse gas (GHG) emissions from oil sands tailings ponds (OSTP) and end pit lakes (EPL) that retain fluid tailings from surface mining of oil sands ores. Predicting GHG production, particularly methane (CH4), would help oil sands operators mitigate tailings emissions and may assist regulators evaluating the trajectory of reclamation scenarios. Using empirical datasets from laboratory incubation of OSTP sediments with pertinent hydrocarbons, we developed a stoichiometric model for CH4 generation by indigenous microbes. This model improved on previous first-approximation models by considering long-term biodegradation kinetics for 18 relevant hydrocarbons from three different oil sands operations, lag times, nutrient limitations, and microbial growth and death rates. Laboratory measurements were used to estimate model parameter values and to validate the new model. Goodness of fit analysis showed that the stoichiometric model predicted CH4 production well; normalized mean square error analysis revealed that it surpassed previous models. Comparison of model predictions with field measurements of CH4 emissions further validated the new model. Importantly, the model also identified in-situ parameters that are currently lacking but are needed to enable future robust modeling of CH4 production from OSTP and EPL in-situ. [Display omitted] •Native microbes anaerobically biodegrade diluent hydrocarbons in tailings ponds.•Fugitive diluent in tailings is a significant biogenic methane (CH4) source.•About 40% mass of naphtha and 60% mass of paraffinic diluent are biodegradable.•Mathematical model is developed for CH4 biogenesis from hydrocarbon biodegradation.•About 50–75% of CH4 emissions in-situ are due to diluent biodegradation.