Decomposition of Dye in Water Solution by Pulsed Power Discharge in a Water Droplet Spray

A method for decomposing dye by spraying water solution of dye into nonequilibrium plasma in gas phase was investigated using a pulsed-corona discharge reactor. The corona reactor consists of a discharge wire and a cylindrical electrode. The water solution of indigo carmine with a concentration of 20 mg/L was sprayed into the reactor from a showerhead. The sprayed water solution was circulated into the reactor. The dependence of the discharging power injected into the reactor on the decomposition rates of chromogenic and unsaturated bonds in indigo carmine was investigated. Indigo blue was decolored by 1-min circulation with the discharging power of 8.6 W. The nuclear magnetic resonance spectrometry showed that indigo carmine was decomposed completely by 60-min treatment. The chromogenic and unsaturated bonds were almost decomposed at 9 and 360 J/mg, respectively. As the discharging power increased, the decomposition rates of both bonds in indigo carmine increased. The decomposition rates of the chromogenic bond showed equal values in equal discharging power regardless of the difference of discharge repetition rate and charging voltage of the capacitor. In contrast, the higher repetitive pulses were more effective for the decomposition of the unsaturated bond rather than the magnitude of charging voltage in equal discharging power.