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.

Naphthenic acids quantification in organic solvents using fluorescence spectroscopy.

Quantification of naphthenic acids in water has been traditionally performed after extraction with organic solvents followed by analytic methods that are complex and costly for preliminary research or for continuous monitoring purposes. This study examines the application of fluorescence in organic solvents as an effective alternative, and the role of organic solvents on quantification results. Nine organic solvents were used: three polar protic alcohols (methanol, ethanol, and propanol), three polar aprotic (dichloromethane, acetone, and acetonitrile) and three non-polar (hexane, toluene, and diethyl ether). The calibration curves of the polar protic solvents performed the best; they had lower light scattering and higher method sensitivity than polar aprotic and non-polar. Methanol was selected for further experiments having a strong linearity for concentrations lower than 250 mg/L (R(2) > 0.99), and a low relative standard deviation (< 10%). The method sensitivity was improved by 70% using a methanol-deionized water mixture (50:50) as a solvent. The synchronous fluorescence mode with a reduced offset value of Δλ = 10 nm demonstrated potential for fingerprinting. The fluorescence technique for quantifying total naphthenic acids directly in organic solvents is a cost-effective analytical method compatible with the solid phase extraction of the sample.