Decoloration of Organic Dye in Water by Pulsed Discharge Plasma Generated Simultaneously in Gas and Liquid Media

A new process for decomposing organic contaminants in water was proposed. Pulsed discharge plasma was generated in the gas phase, and the produced plasma was permeated through a pinhole into the water phase. Water (upper) and gas (lower) were separated by an insulating plate, where a pinhole was perforated at the center of the plate. Gas was bubbled into the water phase through the pinhole. In the gas phase, the high voltage pulse was applied between the needle electrode and the ground electrode (immersed in the water phase). The high voltage pulsed discharge plasma was generated in the gas phase, simultaneously the plasma channel was permeated into the water phase accompanying by the gas bubbles. The water phase plasma produced a lot of active species, UV light, and high-energy electrons. Porous ceramic tube was tried to use for producing water phase plasma, instead of the insulating plate in a pinhole reactor. It was observed that the gas phase plasma also permeated through many small pores into the water and generated streamer discharge in water. Chicago sky blue aqueous solution was effectively decolored with oxygen gas bubbling than the cases of argon gas and air. With applying pulsed voltage of 20 kV and pulse frequency of 25 Hz with 500 mL/min oxygen bubbling, the dye aqueous solution with 10 ppm initial concentration was decolored about 95% in 10 min treatment. The decoloration rate increased with increasing electrical conductivity of the solution. This type of simultaneous discharge plasma reactor is expected to have high-energy efficiency degradation rate.