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Photodegradation of bitumen-derived organics in oil sands process-affected water

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Abstract

The chemical composition of water-soluble organics in oil sands process-affected water (OSPW) is primarily composed of natural constituents of bitumen that are solubilized and concentrated during aqueous extraction of oil sands. OSPW organics are persistent and acutely toxic, and a leading remediation strategy is long-term ageing in end-pit lakes, despite limited data available on its photochemical fate. Here, direct photolysis of whole OSPW, or of its constituent fractions, was examined at environmentally relevant wavelengths (>290 nm) in bench-top studies. Changes in the chemical profiles of whole OSPW, acid- (AEO), and base-extractable organics (BEO) were characterized by liquid chromatography with ultra-high resolution mass spectrometry in negative (−) and positive (+) ionization modes. Following 18 d of irradiation, photolysis reduced the total ion intensity in all samples in both modes. The most photo-labile species included the O2, O3, O4, O2S, and O4S chemical classes, which were depleted in whole OSPW by 93–100% after only 5 d. In positive mode, detected species were more recalcitrant than those detected in negative mode, with an average reduction across all heteroatomic classes of 75 ± 11.0% after 18 d. Estimated environmental half-lives for heteroatomic classes ranged from 57 d (O4S) to 545 d (O3N+), with a greater recalcitrance for classes detected in positive mode compared to negative mode. Under field conditions in end-pit lakes, natural photolysis may be an important mechanism for effective OSPW remediation, and we suggest that future end-pit lakes be shallow to maximize light penetration and natural photolysis in ageing OSPW.

Graphical abstract: Photodegradation of bitumen-derived organics in oil sands process-affected water

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Supplementary files

Article information


Submitted
03 Jan 2020
Accepted
13 Mar 2020
First published
24 Mar 2020

Environ. Sci.: Processes Impacts, 2020, Advance Article
Article type
Paper

Photodegradation of bitumen-derived organics in oil sands process-affected water

J. K. Challis, A. Parajas, J. C. Anderson, E. Asiedu, J. W. Martin, C. S. Wong and M. S. Ross, Environ. Sci.: Processes Impacts, 2020, Advance Article , DOI: 10.1039/D0EM00005A

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