Using fluorescence spectroscopy to measure the biodegradation of naphtha in Athabasca oil sands tailings ponds
This study used fluorescence spectroscopy and solid phase microextraction (SPME) to develop a time-efficient and cost-effective method to measure naphtha biodegradation in Athabasca Oil Sands Region mature fine tailings (MFT) samples. Diverse microbial communities in tailings ponds can readily utilize certain fractions of the available naphtha and support methanogenesis (Holowenko et al. 2000). This has negative implications for the environment as it results in the release of methane, a potent greenhouse gas (Holowenko et al. 2000). As such, there is a need to better track this biodegradation to determine the amount of naphtha within the ponds and the rate at which methane is released. Direct fluorescence analysis by extracting all hydrocarbons could not track changes in naphtha concentrations (ranging from 0-1%) because of high background from bitumen hydrocarbons. When using SPME, with the addition of a silicone polymer to the MFT suspension, there was a multiphase equilibrium of the naphtha hydrocarbons, and less extraction of the bitumen background hydrocarbons. After equilibration in the MFT sample, the polymer was transferred to ethanol, and the hydrocarbons were extracted into the pure solvent phase to be analyzed. Results indicated that while SPME does help reduce the background bitumen signal, samples must still be diluted. This makes it more difficult to track small changes in naphtha over time. However, results do support the use of the polymer providing linear results, good repeatability, and high desorption in the 270-290 nm naphtha region. Thus, SPME can be used to detect naphtha degradation when it ranges from >25-100%. The values generated from the SPME fluorescence calibration were used in a multiphase equilibrium model to estimate the volume of bitumen in a sample as well as the amount of naphtha in the water and bitumen phases. Results indicated that the %volume bitumen for MFT was 1.01±0.26% which is within the literature range for the % bitumen in MFT by volume, and that the % naphtha in the water phase was ~10%. These estimates can be used in future remediation studies that require an understanding of bitumen-diluent volumes in MFT such as those looking to track biodegradation over time.