JP-2026075218-A - Method for treating organofluorine compounds contained in a liquid.

Abstract

[Problem] In a method for treating organofluorine compounds in a liquid by bubbling a gas into the liquid and applying a pulse voltage between electrodes to generate plasma in the bubbles, the present invention provides a method that can use air as the bubbling gas, can effectively treat organofluorine compounds that are difficult to decompose, and does not use tungsten electrodes. [Solution] Aluminum or an aluminum alloy is used as the material for the electrodes that generate plasma, and plasma is generated with the aluminum electrodes 2a and 2b inserted into the treated water 6 in which bubbles 7 are being generated. [Selection Diagram] Figure 1

Inventors

• 渡部 宏典
• 杉原 雅彦

Assignees

• 京都府
• 株式会社栗田製作所

Dates

Publication Date

20260508

Application Date

20241022

Claims (3)

1. In a method for treating organofluorine compounds in a liquid by bubbling a gas into the liquid containing the organofluorine compound and applying a pulsed voltage between electrodes to generate plasma within the bubbles, A method for treating organofluorine compounds contained in a liquid, characterized in that at least one of the electrodes is made of aluminum or an aluminum alloy, and the aluminum electrode is inserted into the liquid in which bubbles are generated while plasma is generated.
2. A method for treating organofluorine compounds contained in a liquid, according to claim 1, wherein air is used as the gas bubbling into the liquid.
3. A method for treating organofluorine compounds contained in a liquid, according to claim 1, wherein nitrogen gas is used as the gas bubbling into the liquid.

Description

This invention relates to a method for treating water-soluble organofluorine compounds (PFAS) such as perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and perfluorohexanesulfonic acid (PFHxS) contained in a liquid, and more particularly to a method for treating organofluorine compounds in a liquid using a plasma treatment method. Organofluorine compounds (OCFs) are widely used as water repellents and surfactants, but because they have a stable structure, they are known to be less reactive and difficult to decompose even with ozone treatment or accelerated oxidation treatment using OH radicals. Water-soluble OFCs are toxic to humans and animals, and therefore need to be treated effectively. Methods for treating OFCs in liquids can be broadly classified into two categories: methods for recovering and removing OFCs from the liquid, and methods for decomposing and mineralizing OFCs in the liquid. Methods for recovering OFCs include adsorption using activated carbon and membrane separation. Methods for decomposing OFCs include incineration, photodegradation, photochemical decomposition using chemicals, and hydrothermal decomposition using metals as reducing agents. However, recovery methods have problems such as the recovered material becoming industrial waste and leaking into the environment due to desorption. Furthermore, activated carbon treatment has the problem that if the concentration of coexisting organic matter is high, it is simultaneously adsorbed onto the activated carbon, causing a rapid decrease in the removal rate of perfluorinated compounds. Membrane separation treatment presents challenges in the secondary treatment of highly concentrated separated water. On the other hand, decomposition by incineration requires high energy due to the high temperature of around 1000°C, and the hydrogen fluoride gas generated during treatment can damage the incinerator material. Additionally, photodecomposition, photochemical decomposition, and hydrothermal decomposition treatments generate secondary treatment materials during the process, requiring the addition of chemicals. Under the circumstances described above, a treatment method has been proposed for rapidly decomposing organic fluorine compounds in liquids using a liquid-phase plasma method without using chemicals or generating secondary waste. This treatment method involves bubbling oxygen gas into a liquid containing organic fluorine compounds contained in a container, applying a high voltage (such as a pulsed voltage) from a high-voltage power supply between a first metal electrode and a second metal electrode positioned inside and outside the container, generating a discharge plasma within the bubbling gas (bubbles), and decomposing the organic fluorine compounds in the liquid using the discharge plasma (see, for example, Patent Document 1). Japanese Patent Publication No. 2011-56451 (pages 4-6, Figures 1 and 2) This is a schematic diagram showing the general configuration of the apparatus used in an experiment to confirm that the processing method according to this invention can efficiently remove organofluorine compounds contained in a liquid.This graph shows the change over time in the PFOS removal rate when treating organofluorine compounds using the experimental apparatus shown in Figure 1, by changing the type of electrode used to generate plasma, and also compares it with the results of treatment using the conventional activated carbon adsorption method.Similarly, this graph shows the time course of fluoride ion ( F- ) concentration when organofluorine compounds are treated with different types of electrodes used to generate plasma.Similarly, this graph shows the change over time in the PFOS removal rate when treating organofluorine compounds using electrodes made of pure aluminum and electrodes made of aluminum alloy, respectively, as aluminum electrodes for generating plasma.Similarly, to investigate the effect of coexisting substance concentrations, this graph shows the change over time in the PFOS removal rate when treating organofluorine compounds with varying concentrations of sodium chloride (NaCl) in the liquid, compared to the change over time in the PFOS removal rate when NaCl is not present.Similarly, this graph shows the change over time in the PFOS removal rate when treating organofluorine compounds with different types of coexisting substances.Similarly, this graph shows the change over time in the PFOS removal rate when using an aluminum (Al) electrode, with and without the presence of coexisting substances (NaCl) in the liquid.Similarly, this graph shows the change over time in the PFOS removal rate when using a SUS (Fe) electrode, with and without the presence of coexisting substances (NaCl) in the liquid.Similarly, this graph shows the change over time in the PFOS removal rate when using a copper (Cu) electrode, with and without the presence of coexisting substances (NaCl) in the liquid.Similarly, this graph