Plasma treatment of contaminated liquid water: A comparison between steam bubble and gas bubble discharge

The treatment of contaminated water with atmospheric pressure, nonequilibrium plasma in recent years has been the subject of much research. The ability of such plasmas to treat water stem from the production of radicals that are capable of rapidly oxidizing organic contaminants. A common method of producing such radicals is by producing plasma within a gas bubble (typically air) in the liquid.However, while efficiently destroying contaminants, this practice of igniting the plasma in air bubbles has the unwanted side effect of creating acidic solutions (pH of 2.0 and lower). This acidity is believed to stem from NOx radicals produced in the plasma that diffuse into the water. To circumvent this issue, a steam discharge is investigated. Presented here is a study of the effect of a steam plasma on both tap water and tap water contaminated with organic dye, quantifying changes in acidity and nitrate/nitrite concentrations in the liquid water with treatment time.