Fate of Polymer-Based Coagulants/Flocculants in Oil and Gas Wastewater Treatment
Creators: Li, Jia
Publisher: name: University of Alberta Library
Year: 2023

<p>Bitumen is extracted either using surface mining or in situ processes, such as Steam Assisted Gravity Drainage (SAGD), that could produce large quantities of oil sands process water (OSPW) and SAGD produced water. SAGD produced water is generally characterized by a slightly basic pH (7-8), high temperature (80-90 °C), and high levels of colloidal impurities, total dissolved solids (TDS) and total organic carbon (TOC). OSPW is also a highly complex mixture containing sands, silts, heavy metals, and recalcitrant organics such as naphthenic acids (NAs). Currently, OSPW is retained on site in tailings ponds without active return to the regional watershed. In order to treat, recover and recycle these two types of wastewaters, polymer-based coagulants and flocculants are widely applied. However, limited knowledge about the fate of these polymers in wastewater from oil and gas industry is known. Therefore, in this thesis, the interactions and degradations of different polymer-based coagulants/flocculants in oil and gas wastewater were investigated.<br><br>
Firstly, response surface methodology (RSM) was employed to optimize the thermal softening-coagulation-flocculation-sedimentation process with softeners, poly-DADMAC as the coagulant, and cationic polyacrylamide (PAM) as the flocculant, and assess the interaction effects of operational variables for sludge volume index (SVI) and the removal efficiency of turbidity, total suspended solids (TSS), particulate hardness, silica, total organic carbon (TOC) and total inorganic carbon (TIC) in synthetic SAGD produced water. Poly-DADMAC dose and mixing time with softeners only were demonstrated to be the most influential factors for the treatment process. Temperature was found to facilitate the removal of colloidal impurities by forming larger and denser flocs and changing their surface composition. More importantly, adsorption and subsequent bridging are the main interaction mechanisms between the polymers and particles in the coagulation-flocculation process.<br>
The long-term fate of dissolved organics in OSPW under various controlled conditions was examined to enhance the understanding of the physiochemical characteristics of OSPW during long-term storage. The highest removal of dissolved organics was observed in ozonated OSPW stored at 20 °C with the highest reduction of COD, DOC, and total NAs. Biodegradation was believed to be the main reason for dissolved organics removal. Additionally, temperature has been demonstrated to be the most important impact factor for the characteristics of OSPW. The limited changes of various parameters in OSPW samples stored at 4 °C supported the common practice of storing OSPW in the cold room as an effective way to preserving the water quality in the laboratory. The microorganism analysis indicated that Bacillus and Fontimonas might be the key microorganisms for degrading dissolved organics like NAs in OSPW.<br>
Under oxic conditions, the degradation of anionic polyacrylamide (A-PAM) in different temperatures and microorganism conditions in oil sands tailings was studied. The maximum removal efficiency of A-PAM without releasing acrylamide (AMD) monomer was observed in tailings water with augmented microorganisms at 20 °C. No substantial effect on acute toxicity and no genotoxicity were found from aerobic degradation of A-PAM in tailings. It was revealed that in the oil sands tailings oxic zone, macromolecular A-PAM could partially degrade into ammonia and smaller molecules, like organic acids, with help of extracellular amidases.<br>
Finally, anaerobic A-PAM degradation in tailings was studied at various A-PAM dosages. Higher methane yield was observed in the tailings samples with lower concentrations of A-PAM (10 and 100 mg/kg TS) than in higher concentrations of A-PAM (250 to 2000 mg/kg). A-PAM molecules could be partially degraded into smaller molecules, such as AMD and polyacrylic acid, which could be utilized as both carbon and nitrogen source to microbes. No contribution to the acute toxicity and genotoxicity was found from anaerobic degradation of A-PAM. The A-PAM concentration could affect the degradation via affecting the flocs structure and composition, which subsequently affected the microbial colonization and metabolic activity. The analysis of microbial community suggested that Smithella, Candidatus_Cloacimonas, W5, XBB1006, and DMER64 were critical microorganisms involved in anaerobic degradation of A-PAM. The potential metabolic pathways for producing different volatile fatty acids (VFAs) from the intermediates of A-PAM degradation were proposed. </p>