Chemical Efficiency of $\hbox{H}_{2}\hbox{O}_{2}$ Production and Decomposition of Organic Compounds Under Action of DC Underwater Discharge in Gas Bubbles

A dc underwater discharge generated in gas bubbles (air, Ar, He, and N₂) in a NaH₂PO₄ · 2H₂O solution is studied. It is shown that the maximal concentration of hydrogen peroxide produced in the discharge does not depend on gas composition. The energy efficiency of H₂O₂ production is, however, gas dependent, and the highest value of 2.95 g/kWh is obtained for air. The decomposition efficiency of the Direct Blue 106 dye, which is used as a model organic pollutant at an initial concentration of 20 mg/L, increases linearly with current in the investigated range (10-30 mA). A maximal dye decoloration of 65% is observed in a N₂ discharge after 20 min of treatment at a current of 30 mA. Different mechanisms of dye decoloration by plasma are proposed and discussed.