The Influence of Liquid Conductivity on Electrical Breakdown and Hydrogen Peroxide Formation in Non-Thermal Plasma Generated in a Water Film Plasma Reactor

Non-thermal plasma technology is under intensive investigation for the use in water treatment since the hydroxyl radical formed during the plasma discharge in contact with water is a strong oxidant and can degrade many organic pollutants 1. However, high liquid conductivity in some waste water can influence the electrical breakdown at a gas-liquid interface and thereby influence the formation of hydroxyl radicals causing reduced water treatment efficiency. In the current study, we used a nanosecond pulsed power supply with a water film plasma reactor to investigate the influence of liquid conductivity on the electrical breakdown, H2O2 formation, and plasma properties, including the electron density, gas temperature, and electron temperature. The liquid conductivity of water was adjusted by adding potassium chloride. Both argon and helium were used as the carrier gas, and the sensitivity of both argon and helium discharges to the liquid conductivity were compared. The results show that the H2O2 production rate drops 5% and 10% for argon and helium discharges, respectively. The electron density slightly increases while the electron temperature decreases as the liquid conductivity was increased from $5\mu \mathrm{S}/\text{cm}$ to 40mS/cm. This result is correlated with the increase of current dissipation in the water as the liquid conductivity was increased. However, the reactor/power supply system has a high tolerance to liquid conductivity and can generate a strong discharge when the liquid conductivity is as high as 40 mS/ cm, This result suggests that the system has potential for treating sea water. In comparison with our previous study2, it is shown here that a nanosecond pulsed plasma discharge has a much better liquid conductivity tolerance than the microsecond pulsed discharge.