What Are the Effective Reactants in the Plasma-Induced Wastewater Treatment?

We perform a series of experiments in a plasma-liquid system, aiming to explore in real time the change of a synthetic wastewater (methyl orange, MO) under an atmospheric pressure DC plasma exposure. The results indicate that the short-lived hydroxyl radicals generated from the plasma-liquid interactions are the predominant reactants in the MO molecules decomposition, while the long-lived species such as the plasma-induced hydrogen peroxide (H2O2) are ineffective. Nevertheless, the plasma-generated H2O2 can contribute to the MO decomposition by producing hydroxyl radicals from reacting with Fe2+ (Fenton's reaction) or by producing peroxynitrite from reacting with NO2-. Moreover, the MO decomposition rate in the case of liquid cathode is found to be significantly faster than that in the case of liquid anode. (C) 2018 The Electrochemical Society.