Glow Discharge Formation over Water Surface at Saturated Water Vapor Pressure and Its Application to Wastewater Treatment

Abstract

With the aim of wastewater treatment using the active reaction of OH radicals generated in gas discharges, DC, low frequency (LF, 100 kHz) and RF (13.56 MHz) glow discharges were generated over the water surface at saturated water vapor pressure. Low-pressure glow discharge over the water surface has an advantage of uniform OH radical production near the water surface. A very stable and uniform glow discharge was obtained with an RF power source, whereas the discharges obtained with the DC and LF power sources were sometimes localized. The effective OH radical production was confirmed from the strong optical emission of OH(A2Σ+–X2Π) near the water surface. The OH(A2Σ+–X2Π) emission intensity near the water surface increased almost linearly with an increase in discharge power. N,N-Dimethyl- p-nitrosoaniline (RNO) solution as a persistent test pollutant was treated by RF glow discharge over the water surface. We confirmed that the RNO solution was certainly decolorized by OH radicals generated in the RF glow discharge. It was found that the degradation of target compounds by OH radicals was concentrated near the water surface in the solution because very slow diffusion of target compounds limited the reaction rate.