Method for removing halogenated pollutants in water by alternating current pulse electrochemistry

Abstract

The invention relates to a method for removing halogenated pollutants in water through alternating current pulse electrochemistry. The method comprises the following steps: applying a periodic alternating current pulse, so that the halogenated pollutants in the water are alternately subjected to electrochemical oxidation and electrochemical reduction, and the process is repeated. In the electrochemical oxidation stage, the halogenated pollutants can be oxidized through intermediate species such as direct electron transfer or indirectly generated hydroxyl free radicals or the combination of the two; in the electrochemical reduction stage, the halogenated pollutants can be reduced through direct electron transfer or hydrogen free radicals and other reducing intermediates, or through the combination of the direct electron transfer and the hydrogen free radicals, redox degradation of the halogenated pollutants is achieved. Compared with the prior art, the alternating-current pulse electrochemical method combines the advantages of an oxidation method and a reduction method, and has the characteristics of high reaction rate, more thorough degradation, high dehalogenation rate, no need of additional chemical reagents, high stability and lower electric energy consumption.

Description

Technical Field

[0001] The invention relates to a method for removing halogenated pollutants in water by alternating current pulse electrochemistry, and belongs to the technical field of environmental science and electrochemistry. Background Art

[0002] Halogenated organic pollutants (HOPs) are mostly characterized by ecotoxicity, bioaccumulation, environmental persistence, and long-distance migration. HOPs are often used as raw materials, intermediates, solvents, etc. in organic synthesis and are widely used in human production and life. However, the large-scale use and discharge of HOPs have made halogenated pollution in water bodies increasingly serious, which not only endangers the environment and ecological security, but also threatens human health through the food chain.

[0003] It is difficult to achieve complete detoxification of HOPs through physical pathways such as adsorption. However, the degradation of HOPs by oxidation or reduction can convert HOPs molecules into other low-toxic or non-toxic products. According to the reaction type, it can be divided into reduction method and oxidation method. However, each single oxidation / reduction method has its own advantages and disadvantages. The degradation efficiency of HOPs by oxidation method alone is high and the oxidation mineralization is more thorough, but there may be problems such as low dehalogenation efficiency and accumulation of halogen-containing byproducts; although the dehalogenation efficiency of reduction method alone is high, its mineralization efficiency is often low, and some highly toxic intermediates may accumulate. At the same time, the number of halogen atom substitutions in HOPs affects the redox characteristics of HOPs parent pollutants and their dehalogenation degradation products, showing an overall trend of "all / multi-halogenated pollutants are easy to reduce, and low-halogenated pollutants are easy to oxidize". It is difficult to achieve deep dehalogenation and complete mineralization of HOPs by using a single oxidation or reduction method. In comparison, the establishment of a method for coupled redox degradation of HOPs is expected to increase the degradation rate of HOPs and enhance the dehalogenation and mineralization efficiency. Summary of the invention

[0004] Purpose of the invention: In view of the above background technology and the disadvantages of the existing technology, the present invention integrates the advantages of oxidation and reduction methods to provide an AC pulse electrochemical method, using positive and negative dual pulse coupled oxidation and reduction technology, organically combining and forming complementary advantages to achieve efficient degradation of HOPs.

[0005] Implementation of the invention: The present invention is an electrochemical method for HOPs coupled redox by direct electron transfer or indirect generation of free radical intermediate species, or a combination of the two, through AC pulse activation. The method is: applying periodic AC pulses to cause HOPs in water to undergo alternating electrochemical oxidation and electrochemical reduction, and the cycle repeats to achieve coupled redox degradation or even complete mineralization of HOPs.

[0006] The present invention rationally designs and constructs an AC pulse electrochemical system. In the electrochemical oxidation stage, HOPs can be oxidized by direct electron transfer, or intermediate species such as hydroxyl radicals indirectly generated by electrochemistry can be oxidized, or a combination of the two; in the electrochemical reduction stage, HOPs can be reduced by direct electron transfer, or by reducing intermediates such as hydrogen radicals, or a combination of the two. By alternating AC pulses and repeating cycles, thorough and efficient coupled redox degradation of HOPs can be achieved.

[0007] The system constituted by the electrochemical method of the present invention is characterized in that the electrode potential, pulse frequency and duty cycle of the electrochemical operation process are controllable, and the specific controllable range is: the applied electrode potential is -20 ~ 20 V, wherein the positive pulse potential is 0 ~ 20 V, the negative pulse potential is -20 ~ 0 V, the duty cycle is 1:100 ~ 100:1; the pulse width is 0.01 ~ 10 s.

[0008] The application of the electrochemical method of the present invention in coupled redox degradation of HOPs is characterized in that the pulse electrode potential in the electrochemical oxidation stage is greater than the direct oxidation potential of HOPs, or the indirect oxidation potential of oxidizing intermediate species such as hydroxyl radicals; the pulse electrode potential in the electrochemical reduction stage is less than the direct reduction potential of HOPs, or the indirect reduction potential of reducing intermediate species such as hydrogen radicals.

[0009] Compared with the prior art, the present invention realizes the redox coupling removal of HOPs through an AC pulse electrochemical method, combining the advantages of both oxidation and reduction methods; no external redox reagent is required; compared with the DC method, the AC method does not require rectification, is easy to control and realize automation; and reduces power consumption while ensuring the dehalogenation and degradation rate of HOPs.

[0010] The AC pulse electrochemical method of this method combines the advantages of oxidation method and reduction method, and has the characteristics of fast reaction rate, more thorough degradation, high dehalogenation rate, no need for external chemical reagents, strong stability and low power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 A schematic diagram of applying a pulse potential by the AC pulse electrochemical method adopted in the present invention; Figure 2 This is the degradation curve of chloramphenicol degradation by the AC pulse electrochemical method of the present invention; Figure 3 is the degradation curve of perfluorooctanoic acid by the AC pulse electrochemical method of the present invention; Figure 4 The defluorination rate and energy consumption of perfluorooctanoic acid degradation by the AC pulse electrochemical method of the present invention. DETAILED DESCRIPTION

[0012] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0013] Embodiment 1: An electrochemical system for coupled redox removal of pollutants by direct electron transfer or indirect generation of free radical intermediates, the principle of which is as follows Figure 1 As shown, its construction includes the following steps: (1) The electrochemical system uses an adjustable AC pulse power supply as the input voltage, and includes a three-electrode electrolytic cell with circulating cooling water. The anode material can be a coated titanium electrode, lead oxide, boron-doped diamond or any suitable electrode material, and a conductive carbon material or a metal material is used as the cathode material. A suitable reference electrode is selected according to the electrolyte. The pollutant solution to be degraded is added to the electrolytic cell and connected to the power supply.

[0014] (2) The operating conditions of the electrochemical system are: the positive pulse potential range is 0 to 20 V, the negative pulse potential range is -20 to 0 V, and it meets the characteristics of claims 3 and 4; the duty cycle is 1:100 to 100:1; and the pulse width is 0.01 to 10 s.

[0015] (3) Using a multi-function oscilloscope for detection, a regular AC pulse waveform can be observed.

[0016] Embodiment 2: In the electrochemical system shown in Example 1, the electrochemical method is applied to couple the oxidation and reduction of chloramphenicol pollutants. As the electrochemical system operates, the removal rate of chloramphenicol in the electrolyte gradually increases. Figure 2 As shown in the figure, after 60 minutes, the removal rate of chloramphenicol in the AC pulse electrochemical mode reached 92.2%, which was 14.3% higher than that in the traditional DC electrochemical mode. It can be seen that this method is highly efficient and thorough in degrading chloramphenicol.

[0017] Embodiment 3: In the electrochemical system shown in Example 1, the electrochemical method is applied to couple the oxidation and reduction of perfluorooctanoic acid pollutants. As the electrochemical system operates, the removal rate of perfluorooctanoic acid in the electrolyte gradually increases. Figure 3 As shown in the figure, after 90 minutes, the removal rate of PFOA in the AC pulse electrochemical mode reached 91.6%, which was 14.2% higher than that in the traditional electrochemical mode. It can be seen that compared with the traditional DC electrochemical method, this method is more efficient and thorough in degrading PFOA.

[0018] Embodiment 4: In the electrochemical system shown in Example 1, the electrochemical method is applied to couple the oxidation and reduction of perfluorooctanoic acid pollutants. Figure 4 As shown in the figure, the defluorination rate of the electrochemical method AC pulse method can reach 72.5%, however, the defluorination rate of the traditional electrochemical method DC electrolysis method is only 56.7%, and the energy consumption is 0.386 kWh more than that of the AC pulse method. It can be seen that compared with the traditional DC electrochemical method, this method has the characteristics of high defluorination rate and low energy consumption in the degradation of perfluorooctanoic acid.

[0019] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for removing halogenated pollutants from water by AC pulse electrochemistry, characterized in that: By using AC pulses and applying periodically changing positive and negative potentials, halogenated pollutants in water are alternately electrochemically oxidized and electrochemically reduced. The electrochemical oxidation stage and the electrochemical reduction stage occur alternately and repeatedly.

2. The method for removing halogenated pollutants from water by AC pulse electrochemistry according to claim 1, characterized in that: In the electrochemical oxidation stage, halogenated pollutants are oxidized by direct electron transfer, or hydroxyl radical species generated indirectly by electrochemistry are oxidized, or a combination of the two; in the electrochemical reduction stage, halogenated pollutants are reduced by direct electron transfer, or reduced through hydrogen radical reducing intermediates, or a combination of the two.

3. The method for removing halogenated pollutants from water by AC pulse electrochemistry according to claim 2, characterized in that: The pulse electrode potential in the electrochemical oxidation stage is greater than the direct oxidation potential of the halogenated pollutants or the indirect oxidation potential of the intermediate species that produce hydroxyl radicals.

4. The method for removing halogenated pollutants from water by AC pulse electrochemistry according to claim 2, characterized in that: The pulse electrode potential in the electrochemical reduction stage is less than the direct reduction potential of the halogenated pollutants or the indirect reduction potential of the intermediate species that produce hydrogen free radicals.

5. The method for removing halogenated pollutants from water by AC pulse electrochemistry according to claim 2, characterized in that: The electrode potential, pulse frequency and duty cycle of the electrochemical operation process are controllable; the specific controllable range is: the applied electrode potential is -20 ~ 20 V, where the positive potential is 0 ~ 20 V and the negative potential is -20 ~ 0 V; the duty cycle is 1:100 ~ 100:1; The pulse width is 0.01 ~ 10 s.

6. The method for removing halogenated pollutants from water by AC pulse electrochemistry according to claim 2, characterized in that: The electrochemical system operating time ranges from 10 minutes to 72 hours.

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