Exploring the capacity for anaerobic biodegradation of polycyclic aromatic hydrocarbons and naphthenic acids by microbes from oil-sands-process-affected waters. (March 2016) - Folwell, Benjamin D.
Abstract: Both polycyclic aromatic hydrocarbons (PAHs) and naphthenic acids (NAs) are natural components of fossil fuels, but they are also widespread toxic and environmentally persistent pollutants. They are the major cause of environmental toxicity in oil-sands-process waters (OSPW). This study aimed to investigate the anaerobic biodegradation of the PAHs pyrene and 2-methylnaphthalene, and the NAs adamantane-1-carboxylic acid and a "natural" NA mixture (i.e., acid-extractable NAs from OSPW) under sulfate-reducing and methanogenic conditions by a microbial community derived from an oil sands tailings pond. Using gas-chromatography mass spectrometry (GC–MS), the rate of biodegradation was measured in relation to changes in bacterial community composition. Only 2-methylnaphthalene was significantly degraded after 260 days, with significantly more degradation under sulfate-reducing (40%) than methanogenic conditions (25%). During 2-methylnaphthalene biodegradation, a major metabolite was produced and tentatively identified as 2-naphthoic acid. Denaturing gradient gel electrophoresis (DGGE) demonstrated an increase in intensity of bands during the anaerobic biodegradation of 2-methylnaphalene, which derived from species of the genera Fusibacter, Alkaliphilus, Desulfobacterium, Variovorax, Thaurea, and Hydrogenophaga . Despite the biodegradation of 2-methylnaphthalene, this study demonstrates that, under anaerobic conditions, NAs and high-molecular-weight PAHs are the predominant molecules likely to persist in OSPW. Therefore alternative remediation strategies are required. Highlights: 2-Methylnaphthalene was degraded anaerobically by up to 40% by day 260. Significantly more 2-methylnaphthalene was degraded under sulfate-reducing conditions than under methanogenic conditions. 2-Naphthoic acid was produced during 2-methylnaphthalene degradation. Pyrene or naphthenic acids were not significantly degraded anaerobically during 260 days. Firmicutes, Beta- and Deltaproteobacteria were identified during 2-methylnaphthalene degradation.