Description of Two Treatment Methods for Detoxifying Oil Sands Tailings Pond Water

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Abstract
Large quantities of toxic wastewater are produced in the processing of oil sands. The toxicity appears to be due primarily to polar organic carboxylic acids (naphthenic acids). These surfactants occur naturally in oil sands and are released during the caustic hot-water extraction process. Relatively high concentrations of suspended particulate matter, bitumen, and dissolved solids, as well as low dissolved oxygen levels, may also contribute to the toxicity of the water. Tailings pond water can be detoxified by rapid chemical treatments which involve coagulation at a pH between 4.5 - 5.0, followed by flocculation with an anionic polyelectrolyte. This method has been successfully scaled up to large batch and flowthrough systems under field conditions. A second treatment method involves the storage of tailings pond water in shallow, well aerated pits for 1 - 2 years, during which period natural processes result in a significant improvement in water quality. Bioassays with bacteria (Beckman Microtox), trout and Daphnia indicate that both treatment met hods result in removal of acute toxicity ( EC50 and LC50 greater than 100%). Ten-week tests with multi-species, simulated pond “ecosystems” in 10 m3 outdoor pooIs indicate some chronic effects remain after treatment. However, these effects are not considered to be limiting to the environmental acceptability of the treated waters.

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