Microbubble Techniques for Enhanced Separation of Dispersed Pollutants in Slurry Flows
Creators: Zhou, Kaiyu
Publisher: name: University of Alberta Library
Year: 2024

<p>Wastewater slurries have a widespread over the world from industrial activities such as mining and oil extraction. In comparison to other aquatic environments, waste slurries consist of a large amount of coarse and fine solid particles and droplets. Among them, fine solids and droplets are well dispersed in the water as suspended colloids, causing a high viscosity and entrainment of various pollutants in the slurry. The accumulation of pollutants such as microplastics and oil in the slurry has become a significant threat to the ecosystem. However, it is challenging to remove those dispersed particulates from the viscous slurries of high solid contents with application of current technologies like membrane filtration and coagulation. In this work, we explored an innovative strategy by application of microbubbles for enhanced separation of dispersed pollutant from slurries. Microbubbles techniques have been well developed for wastewater treatment. However, how to apply microbubbles for pollutant separation efficiently from slurry flows is still unclear.</p>

<p>First, this thesis investigated how substances in water and gas type affect the size distribution and stability of microbubbles formed by a commercial nanobubble generator in Chapter 3. Air injection generated a higher number of microbubbles (&lt;10um) than CO2 injection. Increasing detergent concentration led to a rapid increase in the number of microbubbles generated by both air and CO2 injection which suggested that surface-active molecules may inhibit the growth and coalescence of bubbles. In contrast, the addition of salts (NaCl and Na2CO3) in water did not significantly affect the number or size distribution of bubbles.</p>

<p>Based on the understanding of microbubble generation and stability in contaminated water, we further explored the application of MBs for bitumen removal from highly concentrated  oilsands tailings. In Chapter 4, a modified venturi tube allowing gas suction was developed to generate MBs in the oilsands tailings for removal of residual bitumen in a laboratory-scale pipeline loop. It is revealed that microbubbles had a positive impact on bitumen recovery. Meanwhile, bitumen recovery efficiency increased significantly with temperature increasing up to 52  C. Additionally, CO2 bubbles were more effective in separating bitumen than air bubbles. An optimal recovery efficiency of 61 % bitumen was obtained from an extremely low initial fraction of 0.2 wt% bitumen at solid contents of 50 wt% with microbubbles. Our work demonstrated an effective combination of bubbles and operational conditions for separating bitumen effectively from highly concentrated tailings in a pipeline loop.</p>

<p>In chapter 5, based on the catalytic properties of mineral compounds in the oilsands tailings, we successfully produced microbubbles from in-situ catalytic decomposition of H2O2 at low concentrations in the oilsands tailings, bitumen aggregation is enhanced on the top part of the hydrotransport pipeline. Notably, more than 70 % bitumen was recovered from a lab-scale pipeline loop within 30 mins after H2O2 injection. The bitumen recovery efficiency from the collected froth was quantitatively compared under seven conditions with varied dosages, the concentration of H2O2. Our results confirmed  that the total dosage of H2O2 is the dominant factor in microbubble formation for enhanced bitumen aggregation in the tailings. The results from our study provide insights into microbubble formation by catalytic decomposition in minerals for bitumen recovery in tailings without the requirement for an additional device. </p>

<p>Taking advantage of the aforementioned work that recovered bitumen with H2O2, microbubbles by catalytic decomposition are used to remove aged microplastics (MPs) from slurries in Chapter 6. Significant experimental parameters including particle density, size, wettability and bubble volume fraction were systematically studied. A better performance in MP removal comes up with larger size, higher H2O2 volume and more hydrophobic surface, achieving the optimal removal efficiency of approximately 95 % of PS MPs. A higher H2O2 volume contributed to a larger number of MBs. Additionally, simulation results from computational fluid dynamics (CFD) illustrates the effect of microbubbles on the flow field of slurries and MPs accumulation in the pipe. This work presents an innovative and efficient method for MB generation, markedly improving MP removal.</p>

<p>This thesis demonstrates innovative microbubble techniques for pollutants removal from slurries, supported by both experimental findings and simulation results.</p>