Plasma-activated water generated by bubble spark and dielectric barrier discharges differ in antimicrobial and dye-decolourization efficacy.

AIMS: The requirement for alternative wastewater treatment methods continues to increase as current systems are overwhelmed, leading to accumulation of both microbial and chemical pollutants. The purpose of this study was to evaluate and compare the potential of two distinct PAWs, The bubble spark discharge (BSD) and dielectric barrier discharge diffuser (DBDD), for both microbial inactivation and decolourization of model organic contaminants in wastewater. The potential mechanisms associated with each PAW was explored using ROS and RNS quantification and chemical scavenger assays.

METHODS AND RESULTS: Two direct plasma-in-liquid systems generating PAW in situ via microbubble discharge were evaluated: BSD and DBDD, tested for antimicrobial activity against relevant potential wastewater pathogens including Escherichia coli and Salmonella enterica. Their ability to degrade several water-soluble dyes (crystal violet, methylene blue, and Congo red) as relevant surrogates for environmental contaminants of industrial origin, was also assessed. The DBDD achieved the most rapid inactivation of all tested planktonic bacteria within 90 s, while the BSD took up to 5 min. The bactericidal activity of the DBDD was likely due to a greater production of short-lived species, such as O₂⁻ and ¹O₂, which specific scavenger assays (l-histidine and Tiron) confirmed were essential for the antimicrobial activity, while the longer-lived H2O2 contributed significantly to the antibacterial activity of the BSD system.

CONCLUSIONS: These findings suggest that PAW could be used as a rapid, on-demand advanced oxidation process for the tertiary stage of wastewater treatment, with potential to reduce reliance on conventional UV or chlorine disinfection while targeting both chemical contaminants and microbial bioburdens.