Enhancement and Stability of Reactive Oxygen and Nitrogen Species in Water Treatment Processes Using Cold Plasma

Abstract

Cold plasma technology has significant potential for application in water treatment due to its capacity to generate highly reactive oxygen and nitrogen species (RONS). This study compared the performance of dielectric barrier discharge (DBD) and corona discharge (CD) plasma reactors, both operated using ambient air, to evaluate the influence of reactor geometry on RONS generation under identical operating conditions. Comparative analysis showed that the CD method consistently produced higher concentrations of RONS, including H₂O₂, NO₂⁻, NO₃⁻, and O₃⁻, than the DBD system. Based on this superior performance, the CD method was selected for a detailed investigation into the effects of treatment time and water volume, and, crucially, the temporal stability of RONS. The long-term analysis revealed that hydrogen peroxide (H₂O₂) and nitrate (NO₃⁻) are relatively stable in plasma-activated water (PAW) over a week of storage, while ozone (O₃) and nitrite (NO₂⁻) were unstable, with O₃ rapidly decomposing and NO₂⁻ converting into the stable NO₃⁻. This PAW, rich in stable RONS, demonstrated strong microbicidal activity, achieving over 90% inactivation against single and mixed bacterial cultures (including E. coli, P. aeruginosa, and S. aureus). These findings not only identify the CD configuration as the more efficient plasma generation method but also provide critical insights into RONS transformation pathways and the storage potential of PAW, highlighting its viability as a sustainable approach for water quality enhancement.