Solar-Activated Photocatalytic Treatment of Oil Sands Process Water by using Zinc Oxide-Based Photocatalysts
Creators: Suara, Monsuru A
Publisher: name: University of Alberta Library
Year: 2024

<p>Oil sands process water (OSPW), generated from the extraction of bitumen from oil sands, is an industrial process effluent with a significant presence of petroleum-derived organic compounds, including naphthenic acids (NAs), which requires effective treatment for successful reclamation and water reuse. While different biological, physical, and chemical processes have been applied to treat its organic constituents of interest, advanced oxidation processes (AOPs) have attracted research interests as potential treatment technologies for the remediation of OSPW. Semiconductor-based photocatalysis is a form of AOP that holds potential as a method for treatment of OSPW. However, studies on the application of this technology in the field of OSPW remediation are limited. Therefore, in this thesis, the application of solar-based semiconductor photocatalysis of OSPW and its implications on treated water was investigated. The studies focused on the application of ZnO-based semiconductors as photocatalysts.<br>
First, the applicability and impact of solar-activated ZnO photocatalysis on the degradation of NAs and the aromatic compounds in real OSPW and the elimination of its acute toxicity were investigated. With the photocatalyst applied at 1 g/L under simulated solar radiation of steady irradiance of ~278 W/m2, more than 99% conversion of NAs was achieved after 4 hours of treatment, while nearly all aromatics were simultaneously attenuated. The photocatalysis was observed to be preferentially reactive towards categories of NAs of environmental interest regarding their potential toxic effects. Assessment of the toxicity levels in raw and treated OSPW samples indicated that the photocatalytic treatment resulted in a considerable reduction in acute toxicity and reduced immunotoxicity.<br>
The next part of the thesis investigated material synthesis to raise the efficiency of the photocatalytic treatment in harnessing solar radiation energy. ZnO nanoparticles were synthesized and applied to treat OSPW. Also, BaO was incorporated into ZnO in a measured proportion to enhance its photocatalytic activity in degrading the organic constituents of OSPW. The incorporation of BaO into the ZnO matrix facilitated a considerable reduction in the recombination of photo-excited electrons and holes during the photocatalytic reaction, which tends to reduce the photocatalytic activity of catalysts. As a result, the optimized BaO-coupled ZnO gave a rate constant 50% higher than that of pristine ZnO for the degradation of classical NAs.<br>
In another study, the effects of relevant water parameters in OSPW including pH, chlorides, and carbonates on the photocatalytic degradation of NAs in OSPW were examined. For this study, commercial NAs were used as surrogates to assess the effects of the various factors. Furthermore, the structure-related reactivity of NAs to heterogeneous photocatalysis was investigated and the possible reaction mechanisms for NAs were probed. It was determined that the isoelectric points (IEPs) of photocatalysts could markedly influence their photocatalytic activities in the water and that the presence of anions such as sulfate, carbonate, and chloride ions could noticeably alter the rates of photocatalytic degradation of NAs.<br>
In the final study, a pumice-ZnO composite catalyst was fabricated through a facile, easily reproducible, and less chemical-intensive suspension-calcination technique. The as-prepared composite material was applied under both simulated solar and real sun radiation to assess the practicability of using the catalyst as a floatable material for the passive renewable energy-drive treatment of OSPW. 91.5% degradation of classical NAs was achieved in 6 h of simulated solar irradiation while the corresponding degradation in real sun radiation was ~72% on average. The toxicity and bioavailability assessment of the treated and untreated water samples indicated significant reductions in the acute toxic effect of OSPW and the bioavailable dissolved organics. The prepared composite photocatalyst exhibited high stability, excellent recoverability, and consistent photoactivity over repeated use in OSPW.<br>
As a whole, the findings of these studies further the knowledge of the application of photocatalysis in attenuating the organics in OSPW and provide fundamental insights into the mechanisms and factors affecting the photocatalytic degradation of organic compounds in OSPW.  They also provide further insights on the challenges and potential scale-up application of solar-based photocatalysis as an environmentally friendly treatment process for the remediation of OSPW.</p>