Decolorization of indigo carmine solution using nanosecond pulsed power

Industrial application of pulsed power for water treatment has several advantages. Electrical discharges produced in atmosphere involve a variety of high energy phenomena which might be effective for water treatment. A water treatment system consisting of a coaxial cylinder reactor was constructed. The reactor consisted of a wire inner electrode and an outer cylinder electrode. A water layer was formed on the inner surface of the cylinder by water injection. By applying nanosecond pulse to the wire electrode, streamer discharges were developed from the wire to the water layer. Decolorization of indigo carmine solution was carried out by using the system. The indigo carmine solution was decolorized after treatment for 8 minutes with 50 pulses per second (pps) and then the decolorization efficiency at 80%-decolorization was determined to be about 5 mg/kJ. Increasing the pulse repetition rate shortened the treatment time but decreased the efficiency. The charging voltage of the storage capacitor of the pulse power generator influenced not only the decolorization time but also the efficiency of decolorization. When the charging voltage was 3.13 kV, the efficiency was 126.5 mg/kJ. Since ozone has a beneficial effect on decolorization, a sealed reactor confining the ozone enhances the effect of decolorization. The ozone produced by the same nanosecond pulsed power generator was injected into the Indigo carmine solution for comparison with the discharge reactor with water. The efficiency of decolorization using the discharge reactor was higher than that using ozone produced by the pulsed power.