Decomposition process of volatile organic compounds dissolved into water by pulsed discharge inside bubble

Abstract

Decomposition process of volatile organic compound dissolved into water by discharge plasma inside bubble is investigated. The experiment is conducted on decomposition of dichloromethane (DCM). Argon or oxygen gas is injected into the water through a vertically positioned glass tube, in which high-voltage wire electrode is placed to generate plasmas at low applied voltage. The nanosecond pulsed high voltage generated by an inductive energy storage system pulsed power generator is applied to the tungsten wire to generate streamer discharge. Total organic carbon decreases and chloride ion concentration increases by the discharge treatment. To clarify the decomposition process, DCM and indigo carmine (IC) mixed solution is employed as specimen. The amount of IC decomposition decreases with increasing the DCM concentration. On the other hands, the amount of DCM decomposition is almost independent of IC concentration. These results show that DCM is quickly volatilized into the bubble, which is decomposed by hydroxyl radical produced by the discharge in gas phase inside bubble.

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“…The TOC decreases without discharges because of volatilization by bubbling gas. DCM can be successfully decomposed by discharges generated inside Ar bubbles [91]. The energy efficiency for DCM decomposition is approximately 60 mmol/kWh and is much higher than that for decolorization of dye solutions and 1,4-dioxane decomposition, as mentioned above, although the rate constant for DCM reacting with OH is low.…”

“…In this section, the decomposition of various kinds of organic compounds in water is systematically described. The decomposition characteristics of indigo carmine, a common blue dye, 1,4-dioxane [73] which has a high solubility in water, and formic acid, [90] which is an intermediate product of various organic compounds, such as dichloromethane (DCM), [91] which is a volatile organic compound, are introduced as an example.…”

“…The gas flow rate is 30 mL/min. Pulse voltages with an amplitude of 16 kV, a pulse width of 160 ns, and a pulse repetition rate of 250 Hz are applied to the wire electrode placed in the gas phase to generate plasma [91]. The amount of decomposed DCM is calculated from the Cl À concentration detached from DCM during the decomposition process.…”