Contribution of Dissolved Oxygen to Methyl Orange Decomposition by Liquid Phase Plasma Processes System

Degradation of methyl orange (MO) in liquid phase plasma (LPP) was investigated. A bipolar pulsed power supply was used to generate discharges in the aqueous solution. Properties of generated plasma were investigated by electrical and optical emission spectroscopy methods. The MO decomposition rate increased with increasing levels of applied voltage, pulse width and frequency. The concentrations of activated species, including OH center dot radicals, were increased by the supply of DO. The concentration of OH center dot increased with increasing DO concentration up to 50 ppm. Further increase in the DO concentration, however, reduced the OH center dot concentration because of recombination of OH center dot radicals. The trend of MO decomposition rate with varying DO concentration was the same as that observed for the OH center dot concentration, suggesting that OH center dot radicals play a critical role in the decomposition of MO. Therefore, the LPP process for MO decomposition should be operated with an optimum DO concentration where the OH center dot radical concentration becomes highest.