Effect of operating conditions on physicochemical properties of plasma activated water prepared from a low-cost gliding arc discharge system

In this work, plasma generated from a custom-made gliding arc discharge (GAD) system was used to produce plasma-activated water (PAW), which was characterized electrically and optically. The effects of applied voltage (16–24 V), treatment time (5–30 min), water volume (25–400 mL), and air flow rate (6–14 LPM) on PAW’s physical (pH, electrical conductivity (EC), total dissolved solids (TDS), oxidation–reduction potential (ORP), temperature) and chemical (nitrate and nitrite concentrations) properties were studied. Applied voltage, treatment time, and flow rate positively influenced EC, TDS, ORP, and nitrate/nitrite concentrations while reducing pH. Nitrate concentration increased from approximately 67 to 195 mg/L with voltage and from 184 to 490 mg/L with treatment time, whereas nitrite increased more moderately. Increasing water volume caused dilution, lowering nitrate concentration from 375 to 23 mg/L. Higher air flow enhanced nitrate and nitrite concentrations. Energy analysis indicated a maximum nitrate energy yield of 2447 mg/kWh at a treated water volume of 100 mL. These results suggest that moderate voltage and treatment time, combined with optimized water volume and higher air flow, enable energy-efficient PAW production with enhanced reactive nitrogen species.