|CSLM image (63x) of 3-day-old aerobically grown bioﬁlm on CBD pegs. Autoflouresence of hydrocarbons from the tailings can be seen in the background and small clusters of cells are indicated with a white arrow. Source: Golby et al. Click to enlarge.|
Researchers at the Universities of Calgary and Alberta are collaborating on a project for the microbial remediation of oil sands tailings—the waste byproducts of oil sands surface mining that are collected in large manufactured settling basins called tailing ponds. Tailings contain water, sand, clay, residual bitumen, heavy metals, naphtha diluent, and naphthenic acids (NAs); the latter contribute to the toxicity of the tailings ponds, which are managed under a zero discharge policy.
The research project, funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), is focused on biofilms—consortia of microorganisms of one or more species that adhere to a surface and are enveloped in an extra polymeric substance. A paper into the first round of research will be published in the January edition of FEMS Microbial Ecology.
Biofilms have been applied in biotreatment efforts, particularly in wastewater treatment facilities, for decades. Biofilms exhibit an altered physiological state from their planktonic counterparts, which likely contribute to their robustness in natural environments. It is now widely believed that compared to planktonic cultures, biofilms have a decreased susceptibility to environmental stressors such as heavy metals or hydrocarbons , which exist in many contaminated sites including oil sands tailings ponds.
...The aim of this study was to cultivate microorganisms from oil sands tailings ponds by selecting them to grow as a mixed species biofilm directly from their environment in an in vitro model. The hypothesis was that this approach would provide for a different view of the microbes in this tailings pond environment in comparison with previously published studies.
The Calgary Biofilm Device (CBD) has been used to establish mixed species biofilms from colonoscopy sections that closely reflect the diversity of microbial populations seen in individual patients. We therefore investigated whether the CBD can be similarly used to obtain representative mixed species biofilms from tailings ponds environments. Biofilm formation was tested under different laboratory culture conditions and the resulting communities were compared using molecular tools. Our study demonstrates that a good representation of the tailings pond microorganisms can be cultured if grown directly as a biofilm. As expected, media augmentation and different growth conditions altered the community recovered.—Golby et al.
The researchers took a sediment sample (sludge) from a tailings pond in the Athabasca oil sands region of northern Alberta in July 2009 from a depth of 0.45 m below the surface. The average temperature of the tailings pond is c. 18 °C (64.4 °F), regardless of season. The sample was approximately 80–85% solid, and the sample jar was filled completely to limit oxygen exposure.
A single tailings sample was used for all inoculants to help maintain reproducibility as the tailings are very heterogeneous and different physical samplings can be quite unique to each other and can vary with depth, aeration, and company/mine type, the team noted.
The Calgary Biofilm Device (now called the MBEC Assay) has grown many bacteria and fungi as microbial biofilms. Scientists have used a variety of woods, plastics, paints and even hydroxyapatite (chemically similar to tooth enamel) in place of the standard 96 polystyrene pins on the lid of the assay, to mimic the natural environment of biofilms, to encourage growth.
Experimental media sometimes require modification to resemble the natural setting of the bacterial biofilm organism; scientists at Innovotech, which is commercializing the MBEC Assay, have grown biofilms in artificial urine, plasma, serum and many other media that reflect that natural environment of the organism.
Because of the nature of the tailings sludge, the team coated the CBD pegs with oil organics that adhered to the peg surface during inoculation. These oil organics were able to serve as carbon sources and/or electron donors in addition to the supplemented growth media.
Using the CBD, the team successfully cultivated mixed species biofilms under aerobic, microaerobic, and anaerobic growth conditions. The study recovered more than 10 different genera of microbes from the sample per biofilm; changes to the culture conditions such as growth media and oxygen tension selected for or against certain species resulting in slightly different communities.
We’ve isolated biofilms that are indigenous to the oilsands environment and are highly tolerant to the stress associated with toxins and metals found in tailings water. Those consortia of biofilms are able to, slowly, detoxify the water.—Raymond Turner, U. of Calgary and co-leader of the project
Turner and his team are actively growing biofilms on the support material to test in bioreactors, which are being developed by professors and their graduate students in the civil and environmental engineering department at University of Alberta.
The ultimate goal, says Turner, is to develop tailings water treatment plants for all the oilsands operations.
The plant would take all tailings water, completely clean it, and return it to the river system. Just like wastewater in Calgary is cleaned and returned to the Bow River.—Raymond Turner
Susanne Golby, Howard Ceri, Lisa M. Gieg, Indranil Chatterjee, Lyriam L.R. Marques, Raymond J. Turner (2012) Evaluation of microbial biofilm communities from an Alberta oil sands tailings pond. FEMS Microbiology Ecology doi: 10.1111/j.1574-6941.2011.01212.x