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

Abstract

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.

Numerical simulations for sonochemistry

“…In sections 3–5, chemical reactions inside a bubble are numerically simulated, and chemical reactions in the liquid phase are not simulated. One of the unsolved problems in numerical simulations for sonochemistry is the chemical reactions in the liquid phase outside a bubble [80] , [81] , [82] , [83] , [84] . The important questions are as follows.…”

Synthesis of calcium oxalate crystals in culture medium irradiated with non-equilibrium atmospheric-pressure plasma

“…were decomposed into carbon dioxygen and water by the advanced oxidization mechanism of the plasma. 19,20) Thus, the plasma irradiations potentially provide a wider variety of chemical reactions than expected, even at low temperatures. NEAPP irradiation uniquely induces the synthesis of crystalline particulates via precipitation and particle coalescence.…”

A Novel Wastewater Treatment Method Using Electrical Pulsed Discharge Plasma over a Water Surface

“…The lifetime and diffusion constant of OH in the gas phase are on the order of 10 À5 s and 10 À10 m 2 /s, respectively, and the diffusion length is several tens of μm [51]. The lifetime of dissolved OH is on the order of 10 À6 $ 10 À7 s with penetration lengths on the order of 10 À5 $ 10 À6 m [52][53][54]. Figure 9 shows the hydrogen peroxide (H 2 O 2 ) concentration produced by the OH recombination reaction, as described later, as a function of treatment time by plasma generated inside Ar or O 2 bubbles.…”