Date of Award
Master of Science (MS)
Environmental Engineering and Earth Sciences
Dr. James W. Castle, Committee Chair
Dr. John H. Rodgers, Jr.
Dr. Monique Simair
Extensive volumes of oil sands process-affected waters (OSPWs) are produced at surface mines in the Athabasca Oil Sands. OSPW contains constituents, including a complex mixture of refractory organics known as naphthenic acid fraction compounds (NAFCs), that require treatment prior to government-mandated reclamation of mining leases. Hybrid constructed wetland treatment systems (CWTSs) implementing film-based TiO2 photocatalysis were investigated as a passive, low-energy method for treatment of constituents of concern (COCs) in OSPW.
Bench-scale settled TiO2 batch reactors were assembled and degradation of NAFCs in a specific OSPW was measured as a function of cumulative solar ultraviolet radiation (UV insolation) and by high performance liquid chromatography (HPLC) of naphthenic acids (NA) derivatives. Settled layers of TiO2 were photoactivated by solar UV-A radiation transmitted through OSPW, which decreased naphthenic acid (NA) mass by 86% at an exponential rate with a mean UV insolation half-life of 1.1±0.2 MJ·m-2. Evapotranspiration increased half-lives for NA concentration removal by approximately 90%, highlighting the need for further experimentation with flow-through fixed-film reactors to evaluate if this approach can increase removal rates and efficiencies of NA concentration in OSPW. Following this proof of concept experiment, solar TiO2 fixed-film photocatalytic reactors and wetland cells were implemented into a hybrid pilot-scale CWTS. Performance of the hybrid CWTS was measured in terms of changes in toxicity and constituent concentration and composition over three sampling periods. NAFC concentrations decreased by 75.9% from inflow (43.1±5.9 mg/L) to outflow (10.4±6.0 mg/L) of the hybrid pilot-scale CWTS, and class distribution shifted from regimes dominated by acutely toxic classical NAs (i.e. O2 NAs; O2=40.3%, ∑O3–9=45.0%) to sparingly toxic poly-oxygenated classes (O3–9; O2=13.6%, ∑O3–9=77.0%). The influence of weather conditions on performance was demonstrated by increases in Cl- concentrations due to evapotranspiration during the first sampling period and inhibition of NAFC aerobic degradation by near freezing temperatures in the third sampling period. In sampling periods 2 and 3, toxicity to C. dubia was eliminated in all samples collected from the hybrid CWTS. Reproduction of C. dubia was impaired in 4 of 8 samples collected during sampling period 1, likely due to increased Cl- concentrations. Changes in toxicity and distribution of NAFC classes reported with biogeochemical conditions in the hybrid pilot-scale CWTS will inform further development of this technology.
In this study of a specific OSPW, solar photocatalysis over settled TiO2 significantly decreased NA concentration and mass, aerobic degradation in wetland cells paired with fixed-film photocatalysis altered composition and decreased concentration of NAFCs, and in both experiments toxicity associated with NAFCs in OSPW decreased. Results from these bench- and pilot-scale experiments provide proof of concept data supporting further development of fixed-film photocatalytic reactors and testing of CWTSs in the Athabasca Oil Sands for treatment of NAFCs in OSPW.
Gaspari, Daniel Peter, "A Hybrid Approach for Treatment of Naphthenic Acid Fraction Compounds in Oil Sands Process-Affected Water" (2017). All Theses. 2806.