A new method for a water treatment utilizing radicals produced by a discharge inside bubbles in water is proposed. Radicals with short lifetime (atomic oxygen and OH radical) are used effectively for the water purification because those are generated by discharge inside bubbles in water. OH radical production was confirmed by ;a light emission of the discharge using the spectroscopic technique. Dissolved ozone concentration of about 0.3 mg/l was obtained when oxygen was used as a bubbling gas. Decolorization process of' indigo solution by a discharge inside bubbles in water was investigated.

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Carbon dioxide (CO2) and water vapors effects on NO x removal efficiency was studied in the wire-cylinder discharge reactor utilizing a DC power supply. The content of CO2 in both wet and dry aired initial gases was 0%, 5%, 10%, 15% and 20%, respectively. NO x treatment efficiency strongly depended on a DC positive corona discharge mode, which changed with CO2 concentration regardless the water content. A glow mode of corona discharge, established when the concentration of CO2 in the initial gas was 0% and 5%, exhibited very low removal efficiency (removal rate under 10% and energy yield about 1.1 NO g/kWh). In the cases of 10%-, 15%- and 20%-content-of-CO2 input gas, the glow corona mode was transferred into a streamer for both wet and dry initial gases. Therefore, the removal efficiency dramatically enhanced–the most efficient treatment was achieved when 15% of CO2 was included in the initial gas (5.1 NO g/kWh for wet gas and 4.8 NO g/kWh for dry gas). Water vapors played an important role in NO2 removal via the mutual reaction forming HNO3. Therefore, in the wet-air supplied reactor the highest removal rates of NO x were as high as 48%, while in dry-air supplied reactor only 15%.

The final goal of this research is to realize the efficient utilization of radicals such as atomic oxygen, OH radical, and ozone for water purification. The radicals were generated by a discharge occurring inside the bubbles produced by a bubbling tube immersed in water. The Blumlein line, a repetitive pulsed power generator, was used as the power source. In the experiments, a maximum ozone concentration of approximately 300 ppm was obtained when the repetition rate of pulsed power generator, the peak value of applied voltage and the gap length were 15 pps, approximately 30 kV, and 7.5 mm, respectively. Oxygen was used as the bubbling gas. The time duration of voltage pulse was approximately 200 ns.