Development and Optimization of a Microwave and Plasma Treatment System

Abstract

This dissertation details the development and optimization of a microwave and plasma disinfection system aimed at enhancing microbial inactivation for applications in healthcare, food safety, and environmental sanitation. The system integrates microwave and plasma technologies to leverage their synergistic effects. Microwave radiation provides rapid volumetric heating, disrupting microbial cells through thermal mechanisms, while plasma technology introduces reactive species that inactivate microorganisms via non-thermal pathways. This combination seeks comprehensive disinfection by utilizing microwaves' deep penetration and plasma's potent surface sterilization. A primary challenge addressed is precise temperature control to prevent overheating and ensure consistent disinfection efficacy. The system employs a solid-state microwave generator operating at 2.45 GHz with adjustable power from 140 W to 1400 W. Microwave energy is directed through a WR340 waveguide into a modified cavity with metal plates to prevent leakage and ventilation holes for airflow management. A WR340 horn antenna delivers microwaves directly to samples placed on a stationary glass plate within the cavity. For accurate temperature monitoring and control, the system uses both infrared (IR) and fiber optic (FO) temperature sensors. The FO sensor, immune to electromagnetic interference, provides real-time temperature data inside the microwave cavity. This data is processed by a Python-based control program that dynamically adjusts microwave power to maintain the sample temperature within a desired range, preventing overheating and material degradation. An atmospheric-pressure plasma jet is integrated into the cavity, introducing plasma above the sample. The plasma operates alongside the microwave system, either sequentially or simultaneously, enhancing disinfection through reactive species like radicals and ions. The synergy between microwave heating and plasma-induced chemical reactions results in more effective microbial inactivation. Experimental evaluations were conducted on various microorganisms, including Escherichia coli, yeast, and influenza A virus. The study explored different treatment parameters, such as microwave power levels (200 W, 400 W, 600 W), exposure times, and the effects of predefined microwave on/off cycles versus real-time temperature feedback control. Incorporating the FO sensor improved temperature regulation, leading to more consistent microbial inactivation compared to systems relying solely on IR sensors. Results demonstrated that the optimized system effectively inactivated a broad spectrum of microorganisms while preventing overheating and preserving material integrity. Predefined microwave cycles standardized pathogen exposure durations, enhancing the reproducibility and reliability of the disinfection process. Combining microwave and plasma treatments achieved higher disinfection efficacy than either method alone, confirming the benefits of their synergistic application. This research advances microwave and plasma disinfection technologies by providing practical solutions for system optimization and temperature control. The developed system addresses key challenges in the field, offering an efficient alternative to conventional sterilization methods. The findings have significant implications for applications requiring rapid and reliable disinfection, aligning with the growing demands of the global sterilization and disinfection market. Future work should explore scaling the system for industrial applications, investigate the long-term effects of microwave and plasma exposure on various materials, and further examine the mechanisms behind enhanced microbial inactivation. Addressing these areas will refine the technology for broader use, contributing to improved public health and safety.