Spectroscopic investigation of nanosecond pulsed discharges in underwater plasma for flowing water treatment applications

Ensuring access to clean water, particularly in industrial settings, remains a significant challenge in the 21st century. Conventional wastewater treatment methods often suffer from inefficiencies, high operational costs, and limited scalability, necessitating the development of advanced, cost-effective, and sustainable alternatives. This study investigates the potential of underwater plasma discharge for flowing wastewater treatment under high fluid flow rates, focusing on the impact of discharge parameters—particularly applied voltage and frequency—on plasma dynamics. Optical emission spectroscopy was used to characterize key plasma parameters, including electron temperature ( Te), gas temperature (Tg), and electron number density (ne). Degradation experiments were conducted in both oxygen-enriched and ambient air conditions at a fixed flow rate of 0.3 l min−1, achieving a degradation efficiency of 63.57% for methylene blue (MB) and 65.24% for rhodamine B (Rh-B) in the presence of 400 SCCM  oxygen flow rate. In contrast, degradation efficiencies in air were 52.47% for MB and 55.50% for Rh-B. Compared to conventional dye degradation techniques, this method offers rapid and efficient pollutant breakdown in continuously flowing samples, demonstrating its potential as a scalable and energy-efficient plasma-based water treatment technology.