Influence of Pin-to-Plane Discharge Modes on the Physicochemical Properties of Single-Pass Flow-Through Plasma-Activated Water and Its Efficacy in Agricultural Applications

Abstract

This study investigates the effects of pin-to-plane discharge modes on the physicochemical properties and biological efficacy of plasma-activated water (PAW) generated using a single-pass flow-through system under atmospheric pressure. A custom-designed pin-to-plane plasma reactor with a fixed 1 cm electrode gap was developed to operate under three distinct discharge modes: diffuse streamer, spark, and glow. Among these, glow discharge yielded the most chemically reactive PAW, with concentrations of hydrogen peroxide (9.47 ± 0.28 mg/L), nitrate (96.77 ± 0.78 mg/L), and nitrite (18.95 ± 0.40 mg/L). Microbial inactivation tests demonstrated over 94% reduction in Escherichia coli, Salmonella spp., and Staphylococcus aureus within 30 min using PAW from glow and spark modes. Plant bioassays on Helianthus annuus, Raphanus sativus, and Catharanthus roseus showed enhanced germination and seedling growth under glow-mode PAW, particularly with the three-pin configuration. Preliminary evaluation in Wolffia globosa cultivation revealed transient phytotoxic effects due to residual hydrogen peroxide, although recovery and sustained nitrate availability were observed by Day 12. Electrical analysis confirmed that glow discharge required significantly higher input power (256.5 ± 5.5 W), while spark (38.3 ± 1.9 W) and diffuse (31.9 ± 2.1 W) modes offered lower energy alternatives. These findings highlight the critical role of discharge mode in tailoring PAW chemistry and demonstrate the broad applicability of flow-through PAW systems in sustainable agricultural practices.