著者

Naoyuki Kishimoto Atsuya Kitamura

出版者

Japan Society on Water Environment

雑誌

Journal of Water and Environment Technology (ISSN:13482165)

巻号頁・発行日

vol.20, no.5, pp.128-136, 2022 (Released:2022-10-10)

参考文献数

19

被引用文献数

1

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In an electrolytic water treatment, electrode reactions for pollutant removal can be easily controlled by changing an electrode potential. Thereby, it has a potential to realize an efficient water treatment process. However, its coulombic efficiency, η, strongly depends on reactant concentrations near electrodes. In a continuous electrolysis, the reactant concentrations near an electrode is lower than that in the bulk due to electrolytic consumption of reactant, which gives a negative impact on the η. Therefore, an introduction of intermittent electrolysis instead of the conventional continuous one was discussed in this research, where the reactant concentration near the electrode is recovered during the electrolysis-off stage. The intermittent electrolysis of 1 mM formic acid solution revealed that the η of formic acid removal under electrolysis-on/off time cycle of 1/10 s was 3.3 times higher than that under the continuous electrolysis. A popular technique to keep the reactant concentration near the electrode is an increase in the linear velocity of solution on the electrode. However, the η at a linear velocity of 20 cm/s was only ≤ 25% higher than that at 10 cm/s. Thus, the intermittent electrolysis was very effective in enhancing the energy-efficiency of electrolytic water treatment.

著者

Naoyuki Kishimoto Koki Hara

出版者

Japan Society on Water Environment

雑誌

Journal of Water and Environment Technology (ISSN:13482165)

巻号頁・発行日

vol.19, no.6, pp.283-293, 2021 (Released:2021-12-10)

参考文献数

29

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This study reports the availability of seawater as an economical chloride (Cl−) source for the UV/electro-chlorine process from the viewpoints of advanced oxidation performance and unwanted byproduct formation of chlorate ion (ClO3−) and bromate ion (BrO3−). In the electrochemical oxidant production stage, the oxidant production rate in diluted seawater containing 30 mM Cl− was 21% lower than that in the NaCl solution due to coexisting electrolytes in the seawater. The ClO3− formation during electrolysis was successfully inhibited under acidic conditions and BrO3− formation was not detected in the diluted seawater. However, ClO3− and BrO3− were steadily formed in the undiluted seawater electrolysis, even when the initial pH value was set to 3. The oxidant utilization efficiency for 1,4-dioxane removal during UV irradiation was not deteriorated in the diluted seawater but decreased under basic conditions due to the radical scavenging effect of electrochemically produced free bromine and free chlorine. As a result, the formation of BrO3− and ClO3− was enhanced under basic conditions, whereas BrO3− formation was completely inhibited at an initial pH ≤ 5. Consequently, the diluted seawater was thought to be available as a Cl− source for the UV/electro-chlorine process if an acidic condition was maintained throughout the operation.