Investigation of the loss mechanisms of hydroxyl radicals in the decomposition of organic compounds using plasma generated over water

Many types of plasma processes have been investigated as potential agents for decomposing persistent organic compounds in water using hydroxyl radicals ( OH), and a wide range of energy efficiency in the reduction of total organic carbon (TOC) has been observed. In this study, loss mechanisms of OH that limit the energy efficiency were investigated using a plasma generated over an acetic acid solution. Various experiments, including the analysis of the decomposition process, a parametric study, and a numerical simulation, revealed that there are two main loss mechanisms: (i) a self-quenching reaction that generates hydrogen peroxide (H 2 O 2 ) and (ii) a reaction of OH with H 2 O 2 and hydroperoxyl radicals (HO 2 ). In the solution, OH reacts with these scavengers rather than target compounds. A pulsed plasma with a low current density, low repetition rate, and short pulse duration can be utilized to achieve high efficiency.