Influence of Rise Rate of Applied Voltage for Water Treatment by Pulsed Streamer Discharge in Air-Sprayed Droplets

This paper investigates a water treatment method of spraying droplets of wastewater into a pulse discharge space. Water treatment is performed by applying a pulsed voltage with different rise rates to investigate the influence of rise rate. The rise rates of the applied voltage are 1300, 830, and 240 V/ns, and the discharge current in the faster rise rates is higher. The plasma diameter of the streamer discharge is believed to increase with an increase in the rise rate. The treatment is applied to an aqueous solution of indigo carmine. Active species, e.g., ozone and OH radicals, generated by the discharge increase owing to the effect of a higher rise rate. Therefore, the chromogenic bond of the indigo carmine is decomposed more rapidly with a higher rise rate. The decomposition speed of the benzene ring of the indigo carmine is, however, similar because the more OH radicals there are, the shorter their lifetime is. The energy efficiency for the decomposition of the indigo carmine depends on the discharge power and the discharge duration, which varies owing to the difference of the rise rate.