Treating Waste with Waste – Calcined Bauxite Residue (CBR) as a Potential Wastewater Treatment Option for Oil Sands Process-affected Water (OSPW) and Municipal Wastewater
Creators: Cheng, Fei
Publisher: name: University of Alberta Library
Year: 2023

<p>Bauxite residue is a byproduct generated during the extraction of alumina from bauxite ore. It is highly alkaline and has the potential to release toxic substances (metals) into the surrounding environment during storage. Hence, there is a growing interest in exploring the potential for metal recovery and/or repurposing of bauxite residue to reduce the substantial accumulation of tailings, subsequently contributing to more sustainable waste management practices. This study examined the efficacy of calcined bauxite residue (CBR) as a sorbent material during wastewater treatment. Four types of wastewaters were examined, but this thesis ultimately focused on oil sands process-affected water (OSPW) and municipal wastewater treatment plant (WWTP) effluents. The applicability of CBR in the treatment of industrial wastewater polluted with organic dye (e.g., textile wastewater) and natural waters that receive treated effluents was also evaluated. The treatment performance of CBR was evaluated using a combination of analyses including (1) physical via characterization of CBR via imaging, elemental and crystallographic composition, and surface area/pore size distribution ; (2) chemical via measurement of specific pollutant removal including methylene blue, acid-extractable organics (AEOs), metals, and other general water quality parameters; (3) biological via evaluation of toxicity (cytotoxicity, estrogenicity, and mutagenicity) via in vitro bioassays and measurement of total coliform bacteria. Post-treatment neutralization with acetic acid was further implemented as the pH and the concentration of dissolved metals in water, especially aluminum (Al), increased significantly after CBR treatment. For oil sands process-affected water (OSPW), CBR effectively removed AEOs, a surrogate measurement for naphthenic acids, with an equilibrium adsorption capacity of 0.244 mg/g (pseudo-second-order adsorption kinetic model, R2=0.99). After applying post-treatment neutralization, the CBR-treated OSPW showed lower estrogenicity (EC10 reduced from 0.14 REF to 1.0–56.5 REF) and mutagenicity (ECIR1.5 reduced from 6.7 REF to &gt;12.5 REF) but exhibited higher cytotoxicity (IC1015min increased from 0.52 REF to 0.15-0.28 REF) compared to the raw OSPW. The application of CBR for OSPW treatment was deemed effective but can be further optimized given the acceptable removals of AEOs (45%), estrogenicity, and mutagenicity achieved at 100 g/L CBR dosage. CBR treatment coupled with post-treatment neutralization considerably reduced cytotoxicity, estrogenicity, mutagenicity, coliforms, and nutrients from primary (post-biological nutrient removal [BNR]), secondary (post-secondary clarifier), and tertiary (post-UV) effluents from an operational WWTP. Furthermore, it was shown that the treatment of primary effluent with 50 g/L CBR resulted in a smaller amount of Al leached (1.5 mg/L) from CBR but still maintained good removals in comparison to 100g/L (3.2 mg/L Al was released). Although the need for further optimization of the treatment process is apparent, overall, the results showed that CBR was effective for the treatment of municipal WWTP effluents. CBR was also found to be effective for the removal of methylene blue with an equilibrium adsorption capacity ranging from 0.39 to 1.11 mg/g (pseudo-second-order adsorption kinetic model, R2 = 0.98 - 1.00). Finally, the application of CBR for the improvement of natural river bodies with sewage pollution was examined using diluted municipal WWTP tertiary effluent (5% tertiary effluent + 95% river water) (without post-treatment neutralization). In this case, the use of CBR was considered less attractive because it did not result in substantial removal of cytotoxicity, estrogenicity, mutagenicity, dissolved organic carbon, metals, and nutrients. Though post-treatment neutralization might be able to mitigate the toxicity and metal leaching from CBR, considering the insufficient removals of pollutants observed, the cost associated with implementing CBR will likely surpass the advantages of treating polluted water bodies at the current stage.</p>