Application of cold plasma for inactivation of waterborne pathogens

Abstract

The inactivation of harmful pathogenic microorganisms during water treatment is essential for ensuring safe and clean water for human consumption. Current treatment technologies exhibit limitations in effectively eliminating pathogenic contaminants, necessitating the exploration of advanced disinfection technologies. This study investigates the application of atmospheric cold plasma (ACP) as a novel disinfection method for water contaminated with various pathogens, optimising key treatment parameters such as electrode distance and gas type (oxygen, argon and air) at voltages of 9.56 kV- 13.53 kV over treatment durations of 0.5-2.5 minutes. The study assessed ACP’s efficacy against chlorine-resistant and non-chlorineresistant bacteria, examining direct ACP treatment and effects after 24 h storage post-treatment. Bacterial suspensions at initial concentrations of 1 x 107 CFU/mL were exposed to varying treatment conditions, with bacterial inactivation analysed via colony counts and statistical analyses (two-way ANOVA with Tukey’s post-hoc). The results indicated significant log reductions in bacterial populations, with ACP achieving up to 4-log reductions, particularly against chlorine-resistant, Gram-negative bacteria. Among the gases tested, argon plasma had the highest bacterial inactivation rates, outperforming oxygen and air plasma, particularly against chlorine–resistant bacteria. Environmental water samples treated with ACP showed 90-100% bacterial inactivation, corresponding to log reductions of 3-5 logs, consistent across both direct and 24 h storage post-treatment samples. Argon and oxygen plasma showed high efficacy, with oxygen plasma having the highest inactivation in the uMhlanga Lagoon sample. The sustained antibacterial effect of ACP after 24 h storage post-treatment was attributed to its disruption of bacterial cellular functions, effectively inhibiting regrowth and ensuring long-term water safety. These findings confirm the potential of ACP as a highly effective and adaptable disinfection technology for water purification, particularly in targeting bacteria with carrying resistance profiles. While this study highlights the efficacy of ACP in inactivating pathogenic bacteria, further research is needed to ensure the safety of treated water for human consumption and to evaluate its effectiveness in removing chemical contaminants. This study demonstrates that ACP is a highly effective disinfection technology for water treatment, with consistent success in inactivating a wide range of pathogenic bacteria.