Article
Carbon and Sulfur Cycling by Microbial Communities in a Gypsum-Treated Oil Sands Tailings Pond
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n†, Sylvain Bordenave†, Shiping Lin†, Iyswarya Mani Bhaskar†, Xiaoli Dong‡, Christoph W. Sensen‡, Joseph Fournier§, Gerrit Voordouw†, and Lisa M. Gieg*†
n†, Sylvain Bordenave†, Shiping Lin†, Iyswarya Mani Bhaskar†, Xiaoli Dong‡, Christoph W. Sensen‡, Joseph Fournier§, Gerrit Voordouw†, and Lisa M. Gieg*†Petroleum Microbiology Research Group, Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4, Sun Center of Excellence for Visual Genomics, Faculty of Medicine, 3330 Hospital Drive NW, Calgary, Alberta, Canada, T2N 4N1, and Suncor Energy Inc., Ft. McMurray, Alberta, Canada
Environ. Sci. Technol., Article ASAP
Publication Date (Web): December 3, 2010
Copyright © 2010 American Chemical Society
* Corresponding author e-mail: lmgieg@ucalgary.ca., †
University of Calgary.
, ‡ Sun Center of Excellence for Visual Genomics, Faculty of Medicine.
, § Suncor Energy Inc.
Abstract
Oil sands tailings ponds receive and store the solid and liquid waste from bitumen extraction and are managed to promote solids densification and water recycling. The ponds are highly stratified due to increasing solids content as a function of depth but can be impacted by tailings addition and removal and by convection due to microbial gas production. We characterized the microbial communities in relation to microbial activities as a function of depth in an active tailings pond routinely treated with gypsum (CaSO4·2H2O) to accelerate densification. Pyrosequencing of 16S rDNA gene sequences indicated that the aerobic surface layer, where the highest level of sulfate (6 mM) but no sulfide was detected, had a very different community profile than the rest of the pond. Deeper anaerobic layers were dominated by syntrophs (Pelotomaculum, Syntrophus, and Smithella spp.), sulfate- and sulfur-reducing bacteria (SRB, Desulfocapsa and Desulfurivibrio spp.), acetate- and H2-using methanogens, and a variety of other anaerobes that have been implicated in hydrocarbon utilization or iron and sulfur cycling. The SRB were most abundant from 10 to 14 mbs, bracketing the zone where the sulfate reduction rate was highest. Similarly, the most abundant methanogens and syntrophs identified as a function of depth closely mirrored the fluctuating methanogenesis rates. Methanogenesis was inhibited in laboratory incubations by nearly 50% when sulfate was supplied at pond-level concentrations suggesting that in situsulfate reduction can substantially minimize methane emissions. Based on our data, we hypothesize that the emission of sulfide due to SRB activity in the gypsum treated pond is also limited due to its high solubility and oxidation in surface waters.
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