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Fractionation of oil sands process water and fractions influence and degradation by advanced oxidation processes
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- Author / Creator
- Rui Qin
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One of the most serious issues associated with the oil sands production is the generation of large volumes of oil sands process water (OSPW). OSPW is a highly complex mixture of sands, silts, salts, heavy metals, and refractory organic compounds. Currently, OSPW is retained on site in large tailings ponds and there is no active return to the regional watershed. Therefore, there is an urgent need to develop water treatment processes for the safe release of treated OSPW into the environment. In this thesis, novel separation methods were developed to isolate and fractionate OSPW inorganics and organics that allowed more accurate and comprehensive study on the characterization, influence and degradation of each OSPW fraction by ozonation or photo-oxidation.
OSPW organic fraction (OSPW-OF) was extracted by solid phase extraction (SPE) and OSPW containing only inorganic fraction (OSPW-IF) was obtained after the organic compounds were adsorbed by granular activated carbon (GAC). SPE using hydrophilic lipophilic balanced (HLB) cartridge combined with methanol elution achieved the highest dissolved organic carbon (DOC) (95.4%) and NA (90.0%) recovery as compared with other tested cartridges and liquid-liquid extraction (LLE) with dichloromethane. A recovery higher than 80.0% for each NA species was achieved using HLB cartridge with methanol elution. After passing through GAC cartridge, 96.1% of DOC in OSPW was adsorbed. The difference of pH, alkalinity, conductivity, and the concentrations of detected ions in OSPW and GAC cartridge effluent were negligible. Thus, GAC adsorption was found to be a promising method to obtain OSPW-IF representable of real OSPW.
A silver-ion SPE approach was utilized to separate OSPW NAs into 20 fractions with aliphatic O2-NAs, aromatic O2-NAs, O3-NAs, and O4-NAs dominated in different fractions. Ozonation of these fractions was conducted to study the ozonation reactivity of isolated aromatic and oxidized NA species. The removals of aliphatic O2−NAs fraction, aromatic O2−NAs fraction, O3−NAs fraction, and O4−NAs fraction with an applied ozone dosage of 16.8 mg/L were 97.2%, 94.7%, 59.4%, and 44.7%, respectively. Aromatic and oxidized NAs (O3−NAs and O4−NAs) with larger carbon number were favorably removed during ozonation treatment. A comparison of the ozone utilization efficiency for different NA species indicated that the degradation of oxidized NAs consumed more ozone in molar ratio than the degradation of aliphatic and aromatic O2-NAs, which resulted in the lower reactivity of oxidized NAs than that of O2-NAs.
OSPW-IF adversely affected the ozonation of a model compound cyclohexanecarboxylic acid (CHA) by competitively consuming ozone. Main inorganic ions present in OSPW were separately added into CHA in buffer solution to investigate their individual influence on the ozonation of CHA. NH4+, Mn2+, HCO3- and Cl- showed slight reduction on CHA degradation. In addition, higher NA degradation was observed after the ozonation of extracted organics dissolved in buffer than the ozonation of OSPW, which demonstrated that the inorganics in OSPW inhibited the degradation of NAs during OSPW ozonation process. Moreover, ozonation of non-filtered and filtered OSPW showed that there was a negligible influence of particles on the ozonation of NAs. The results from this research suggested that ozonation would be better utilized as an intermediate or post treatment process in a treatment train for OSPW remediation and intermittent ozonation might achieve higher ozone utilization than the continuous ozonation process.
Direct photolysis of OSPW was conducted to investigate the photodegradation of NAs in OSPW without adding external catalysts. It was observed that 60 min of direct UV exposure of OSPW with the irradiance intensity of 2.92 mW/cm2 achieved the removal of O2-, O3-, and O4-NAs to be 46.4%, 11.2%, and 9.9%, respectively, which were higher than the degradation of extracted organics dissolved in buffer. This indicated that the presence of inorganics in OSPW enhanced the photodegradation of NAs. Meanwhile, the effect of OSPW-IF on the photodegradation of model NA, 1-adamantanecarboxylic acid (ACA,) was studied. A 34% of ACA was removed in the presence of OSPW-IF, while no ACA degradation was observed in buffer solution after 60 min of UV exposure. The results indicated that OSPW-IF induced the photodegradation of ACA. Individual ions present in OSPW were added into ACA in buffer solution to clarify whether the inorganic species in OSPW could act as photosensitizers. Nitrate had demonstrated to be an active ion present in OSPW that induced the photodegradation of ACA. In the presence of nitrate, both hydroxyl radicals (•OH) and reactive nitrogen species (•NO, •NO2) were generated, where •OH was the dominant reactive species that contributed to the degradation of ACA. Ten by-products including single and multiple hydroxyl, nitro, nitroso and carbonyl substituted by-products were proposed to be produced from the nitrate induced photodegradation process through three different pathways. -
- Subjects / Keywords
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- Graduation date
- Fall 2019
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.