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• radicals, were increased by the supply of DO. The concentration of OH• increased with increasing DO concentration up to 50 ppm. Further increase in the DO concentration, however, reduced the OH• concentration because of recombination of OH• radicals. The trend of MO decomposition rate with varying DO concentration was the same as that observed for the OH• concentration, suggesting that OH• 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• radical concentration becomes highest. © 2014