Decomposition of persistent materials using atmospheric pressure plasmas operated in processing water

Summary form only given. Water treatment by atmospheric oxygen plasma was examined for decomposing persistent materials such as dioxin. In the previous experiments the acetic acid (CH₃COOH) as an alternative to the dioxin was successfully decomposed by the combination of fast oxygen flow and a DC driven micro hollow cathode discharge (MHCD). Meanwhile no decomposition was observed with ozone injection. The plasma was generated just under the processing water, because the surface tension was big enough to separate the discharge space from the water due to the small hole-diameter. The life time of the electrodes, however, is considerably short because of the high current density within the hole. In this report, two types of plasmas with fast oxygen flow were examined for the water treatments. One of them is a DC driven micro plasma generated between the processing water and a plane electrode. The plasma reacts with the water through a small hole that separates plasma and water as like in the MHCD reactor. The plasma voltage rapidly decreased when the plasma was generated and the voltage and current characteristics is similar to arc discharge. The plasma showed the generation and extinction repetitively. The concentration of acetic acid decreased from 10 ppm to almost its half value after plasma treatment. Another type of the reactor consists of coaxial glass tubes that act as barrier electrodes driven by AC voltage source which creates a sinusoidal, triangle or rectangular waveform with a frequency up to 10 kHz. The material of the inner glass tube has porous structure so the oxygen is fed from the inside of the inner tube to the plasma area. The processing water filled between the two glass tubes is bubbled by oxygen flow. The micro discharges are generated between the tube and reacts with the processing water. The reduction rate of the acetic acid was evaluated on the point of decomposition efficiency