Microbubble-enhanced cold plasma activation in water treatment
Creators: Gao, Yawen
Publisher: name: University of Alberta Library
Year: 2023

<p>The limitation of global water resources requires a sustainable and advanced technology to acquire clean water. Cold plasma emerges as a green and sustainable technology in wastewater treatment, food processing and agricultural field. Synergy of a myriad of reactive oxygen and nitrogen species (RNOS) contributes to desirable properties of plasma activated water (PAW). However, during the formation of plasma activated water the transfer of gaseous plasma into water is challenging. Meanwhile, it is quite necessary to make a good design for water activation by cold plasma with a simple configuration, portable design, low energy consumption and high activation efficiency. Moreover, the adaptability and scalability of cold plasma reactor are necessary to be demonstrated in the lab scale before the practical applications of the technology.  This Ph.D. thesis first focuses on understanding the formation and stability of microbubbles generated in a venturi tube through cavitation and air suction effects. Chapter 3 compares the effects of temperature and air suction on formation and stability of microbubbles formed in tap water and process water collected from oilsands industry. Microbubbles with a diameter of 1-50 µm are generated by using a venturi tube and characterized by focused beam reflectance measurement. Based on the air suction of a venturi tube and microbubbles, a reactor called microbubble-enhanced cold plasma activation (MB-CPA) is developed in Chapter 4. Gaseous plasma is supplied through self-suction to water flowing in a venturi tube. A large amount of microbubbles transfer reactive species in the gas phase into the water flow. The degradation of methyl orange shows that with the same energy input, MB-CPA reactor can achieve more than 5 times higher degradation efficiency, compared to the configuration in absence of microbubbles. Meanwhile, the physicochemical properties of PAW are examined, including the concentration of ozone, nitrite, nitrate, temperature, pH, conductivity and dissolved oxygen. To the best of our knowledge, this is the first-time integrating bubbles in plasma activation to transfer active species from the gas phase into the flow of water.Later, the optimization of MB-CPA design is investigated in Chapter 5. The degradation rate of a model antibiotic compound, sulfathiazole, in water is compared under activation conditions by varying the dimensions of the cavitation tube, the flow rate of water and the distance between the discharge and the flow surface. Machine learning, including multiple linear regression (MLR) and artificial neural network (ANN), can predict degradation efficiency in good agreement with the experimental data. The width of the air inlet of a venturi tube is found to be the most important parameter for water activation.In demonstration of PAW, we focus on the development of MB-CPA to produce PAW for enhancing plant growth in hydroponics in Chapter 6. A solar-driven MB-CPA system is developed, utilizing externally linked solar panels, enabling portable water activation with zero-energy consumption. Three vegetables, including peanut, garlic, soybean sprouts are fed with PAW. The results show a significant enhancement on the sprout length as 1.66 times for peanuts, 1.5 times for garlic, and 1.8 times longer for soybean, fed with PAW compared to untreated water. Moreover, MB-CPA integrated with a commercial hydroponic system achieves the growth enhancement lasted for 32 days (3 growing cycles) with recycled water. The portable MB-CPA system developed in this work represents a sustainable and environmentally friendly technology for vegetable cultivation and water treatment.In Chapter 7, we focus on the influence of plasma activation on chemical properties of nanoparticles and carbon dots. The investigation delves into the surface properties of the nanoparticles, including zeta-potential, surface morphology and chemical bonding through comprehensive analysis. Although the study shows the preliminary results, it promises to continue offering deeper insights into the material treatment in the future.This thesis firstly comes up with MB-CPA system to active water, supported by both experimental findings and machine learning results. The study also encompasses an investigation into how parameters during activation process affect the efficiency. The design can effectively reach to the satisfied performance in enhancing the degradation efficiency of organic contaminants in water. Furthermore, the applications in the plant growth and particle modification show great potential as a sustainable technology to be used in large scale.</p>