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 (H2O2) and (ii) a reaction of ∙OH with H2O2 and hydroperoxyl radicals (HO2∙). 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.

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