Abstract
Oil sands process-affected water (OSPW), generated from bitumen extraction in the Canadian oil sands, may require treatment to enable safe discharge to receiving watersheds, as dissolved naphthenic acids (NAs) and other acid extractable organics (AEO), identified as the primary toxic components of OSPW, are environmentally persistent and poorly biodegradable. However, conventional advanced oxidation processes (AOPs) are impractically expensive to treat the volumes of OSPW stockpiled in the Athabasca region. Here we prepared floating photocatalysts (FPCs) by immobilizing TiO2 on glass microbubbles, such that the composite particles float at the air-water interface for passive solar photocatalysis. The FPCs were demonstrated to outperform P25 TiO2 nanoparticles in degrading AEO in raw OSPW under natural sunlight and gentle mixing conditions. The FPCs were also found to be recyclable for multiple uses through simple flotation and skimming. This paper thus demonstrates the concept of a fully passive AOP that may be scalable to oil sands water treatment challenges, achieving efficient NA reduction solely through the energy provided by sunlight and natural mixing processes (wind and waves).
Highlights
Bitumen extraction in Canada’s oil sands uses large volumes of water, which is contaminated in the process by compounds leached from the oil sands ore, and referred to as oil sands process-affected water (OSPW)
Release of OSPW to the environment is hindered by the toxicity of the water, due primarily to dissolved naphthenic acids (NAs) and other acid extractable organics (AEO) [1,2], and an estimated 1 billion m3 of OSPW to date has been retained in tailings ponds on site
In contrast to other advanced oxidation processes (AOPs) that have been tested for OSPW treatment [10,11], solar photocatalysis enables complete degradation of even recalcitrant NAs, without the need for chemical amendment of the water or electrical power consumption
Summary
Bitumen extraction in Canada’s oil sands uses large volumes of water, which is contaminated in the process by compounds leached from the oil sands ore, and referred to as oil sands process-affected water (OSPW). The oil sands industry has sought passive, or low energy, water treatment technologies capable of addressing large volumes of OSPW [6]. Considering the large sunlight-exposed surface area of oil sands tailings ponds, solar photocatalysis is a promising advanced oxidation process (AOP) with demonstrated capability to fully degrade OSPW AEO through hydroxyl and superoxide radical-mediated oxidative mineralization [7,8,9]. It was hypothesized that immobilizing a photocatalyst onto a buoyant support could address the above challenges, while adapting this promising treatment technology into a passive platform enabling large-scale deployment. In this work we sought to demonstrate treatment of AEO in raw OSPW by use of floating photocatalysts under natural sunlight. While buoyant photocatalysts have been synthesized previously [12,13,14], this report represents the first demonstration of such materials as a passive treatment for OSPW remediation
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