Indirect Non-thermal Plasma Treatment in Public Health, Agricultural and Food Safety Applications
Authors:   , He Jinjie , Sales Christopher 
Published: December 2023

The pursuit of innovative technologies to ensure microbial control and decontamination has gained paramount importance in safeguarding public health, fortifying food safety, and upholding environmental sustainability. Among these technologies, non-thermal plasma (NTP) has emerged as a compelling and multifaceted solution, poised to redefine conventional disinfection methodologies. This study investigated the antimicrobial efficacy and efficiency of NTP, with a focus on plasma-activated water (PAW) and plasma-activated mist (PAM). In essence, this paper brings forth a constellation of exemplars, each attesting to NTP's transformative potentials. First, the comprehensive exploration encompasses the submerged spark plasma technology to combat challenges pertinent to aquaculture. This approach seeks to eliminate antibiotics, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs) from aquatic environments. Noteworthy findings include the efficient removal of rifampicin antibiotics, achieving a remarkable 99.43% removal rate in distilled water within 8 minutes using single spark plasma. Moreover, multiple sparks plasma achieved a 78.46% removal rate in 10 minutes. The substantial reduction of E. coli O157:H7 by 5 logs within 10 minutes using single spark plasma demonstrates NTP's significant inactivation potential. These results underscore NTP's effectiveness in combatting antibiotic contamination and its associated risks. Further investigations delve into the domain of food safety, particularly the post-harvest washing of fresh produce using gliding arc-generated PAW. This research highlights the impressive decontamination capabilities of PAW, showcasing reductions in E. coli O157:H7 counts ranging from 0.7-log to 2.7-log across spinach, kale, and lettuce. Notably, the combination of PAW and a low concentration of chlorine (10 ppm) resulted in a synergistic enhancement of decontamination, achieving a 1.6-log reduction in E. coli. These findings emphasize PAW's potential to revolutionize industrial produce washing processes by mitigating pathogenic risks and reducing cross-contamination. Expanding further, certain types of fresh produce necessitate a "dry" approach due to their susceptibility to water-induced damage. The pursuit of an alternative, "dry" method for disinfection led to the investigation of PAM's efficacy on fresh produce. Notably, the research revealed that PAM is a promising solution, achieving over 1-log reduction of E. coli O157:H7 on various produce types included spinach, kale, lettuce, and strawberry. Additionally, a mathematical diffusion model was developed to predict PAM's transport and efficacy on multi-layered produce, offering insights into scaling up NTP technologies for industrial applications. Beyond the investigation into the application of PAM for fresh produce treatment, this study also introduces a solution for disinfecting N95 respirators, an urgent need in the face of persistent viral challenges. Through the utilization of PAM, respirators laden with viral agents undergo a disinfection process, resulting in substantial reduction of contamination. The atmospheric pressure pulsed dielectric barrier discharge (DBD) combined with 7.8% hydrogen peroxide mist successfully attains at least a 3-log reduction of MS2 and T4 bacteriophages on N95 respirators. The enduring filtration efficiency of treated N95 respirators after 20 cycles, coupled with elastic strap durability considerations, illuminates the potential of plasma for PPE reusability during critical times, such as the recent COVID-19 pandemic. The synthesis of this research underscores the transformative potential of non-thermal plasma across a spectrum of applications, from aquaculture water treatment to fresh produce decontamination and PPE sterilization, fostering new frontiers in public health, safety, and sustainable practices.