A treatment method and device for gradient electro-catalytic reinforced degradation of organic wastewater

Abstract

The application relates to a treatment method and device for gradient electro-catalytic reinforced degradation of organic wastewater, which comprises the following steps: taking a membrane electrode and a metal electrode as double cathodes and taking a counter electrode as an anode; the membrane electrode and the counter electrode form a first electric circuit; the metal electrode and the counter electrode form a second electric circuit; the voltage of the first electric circuit is lower than that of the second electric circuit, the membrane electrode mainly reduces O2 to generate H2O2 and ·O2 ‑ ; the metal electrode mainly reduces H2O2 to generate ·OH and recombines free radicals to form singlet oxygen O2 1 . The application applies gradient voltage according to the different reduction potentials of H2O2 and active oxygen species, avoids the reduction of part of O2 to H2O through a four-electron path, guarantees the efficient conversion and utilization of H2O2 and active oxygen species, realizes the reinforced degradation of organic pollutants, and saves energy and reduces consumption.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment and resource utilization, and particularly relates to a treatment method and device for gradient electrocatalysis reinforced degradation of organic wastewater. BACKGROUND

[0002] Water pollution has been one of the major environmental pollution problems in the world. Industrial wastewater, livestock breeding wastewater, pharmaceutical wastewater, and landfill leachate all contain a large amount of refractory organic matter. Various newly emerging trace organic pollutants and secondary derived pollutants pose a serious threat to public health and ecosystems. At present, water pollution caused by the discharge of wastewater containing refractory organic pollutants is an important problem that needs to be solved in sustainable development.

[0003] Under the background of global energy saving and low carbon sustainable development, high-efficiency and low-energy wastewater treatment has become the top priority in this field. In order to solve the pollution problem of refractory organic wastewater and realize the recycling of water resources, advanced oxidation processes (AOPs) represented by Fenton process have been continuously developed. In the field of environmental remediation, the active oxygen species (ROS) generated by AOPs is a powerful tool for degrading persistent and stubborn refractory organic pollutants into harmless small molecules. The existing treatment method is to mix the aqueous solution of Fe 2+ and H2O2 to efficiently remove organic pollutants, which has the advantages of high efficiency, simple operation, high overall mineralization possibility, and easy automation, and therefore is a very promising environmental remediation strategy. However, in practical application, AOPs still has limitations, such as the difficulty of long-distance transportation and storage of high-concentration H2O2, and a large amount of iron sludge generated during reaction operation, which hinders its wide application. Therefore, some researchers have proposed an electrochemical Fenton process for in-situ generation of H2O2 by electrolysis of O2, which has solved the problem of H2O2 to some extent, but still has problems such as cost increase caused by catalyst loss and iron sludge accumulation, and low catalytic efficiency and low electron utilization efficiency.

[0004] In order to solve the above problems, the present application provides a treatment method and device for gradient electrocatalysis reinforced degradation of organic wastewater. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a treatment method and device for gradient electrocatalysis reinforced degradation of organic wastewater. The purpose is to provide a green, energy-saving and efficient refractory organic wastewater treatment process.

[0006] The technical solution of the present application to solve the above technical problems is as follows:

[0007] The first aspect is a treatment method for gradient electro-catalytic reinforced degradation of organic wastewater, comprising the following steps: taking a membrane electrode and a metal electrode as double cathodes and taking a counter electrode as an anode; the membrane electrode and the counter electrode form a first electric circuit; the metal electrode and the counter electrode form a second electric circuit; the voltage of the first electric circuit is lower than the voltage of the second electric circuit, and the membrane electrode mainly reduces O2 to generate H2O2 and ·O2 - , and the metal electrode mainly reduces H2O2 to generate ·OH and recombines ·OH and ·O2 - to form singlet oxygen 1 O2.

[0008] In addition, it should be noted that the counter electrode can also directly oxidize organic pollutants.

[0009] On the basis of the above technical solution, the application can be further improved as follows.

[0010] Further, the voltage of the first electric circuit is less than or equal to 1V, and the voltage of the second electric circuit is 1V-2V.

[0011] Further, the voltage of the first electric circuit is 1V, and the voltage of the second electric circuit is 2V.

[0012] Further, the membrane electrode is carbon cloth fiber, the metal electrode is stainless steel mesh, and the counter electrode is a graphite plate.

[0013] Further, the membrane electrode is made by wrapping carbon cloth fiber on an organic glass tube with a perforated structure.

[0014] Further, the following specific steps are included:

[0015] (1) taking a membrane electrode and a metal electrode as double cathodes and taking a counter electrode as an anode; the membrane electrode and the counter electrode form a first electric circuit; the metal electrode and the counter electrode form a second electric circuit; and adding the refractory organic wastewater to be treated into the first electric circuit and the second electric circuit, so that the membrane electrode, the metal electrode and the counter electrode are immersed;

[0016] (2) turning on the power supply, so that the voltage of the first electric circuit is lower than the voltage of the second electric circuit, aerating to complete the supply of O2, the membrane electrode mainly reduces O2 to generate H2O2 and ·O2 - , and the metal electrode mainly reduces H2O2 to generate ·OH and recombines ·OH and ·O2 - to form singlet oxygen 1 O2; and the generated singlet oxygen 1 O2, ·O2 - and ·OH degrade the refractory organic wastewater to be treated.

[0017] In a second aspect, a treatment device for gradient electro-catalytic enhanced degradation of organic wastewater comprises a reaction container, a counter electrode, a membrane electrode, a metal electrode, an aeration device and a direct current power source, the counter electrode, the membrane electrode, the metal electrode and the aeration device are located in the reaction container, the membrane electrode and the metal electrode are electrically connected to the negative pole of the direct current power source, and the counter electrode is electrically connected to the positive pole of the direct current power source. The membrane electrode, the counter electrode and the metal electrode are connected to a constant potential instrument by titanium wires, the reactor is continuously aerated to ensure sufficient dissolved oxygen in the wastewater to generate hydrogen peroxide and to enhance liquid disturbance, thereby achieving sufficient conversion of substances in the solution and rapid transfer of electrons.

[0018] Further, the membrane electrode is arranged at the center of the reaction container, the counter electrode is arranged in a counter electrode slot, the metal electrode is arranged in a single slot, and the aeration device is arranged between the counter electrode and the membrane electrode.

[0019] Further, the counter electrode slot comprises two counter electrode slots, and the two counter electrode slots are respectively located on opposite sides of the reaction container; and the single slot is located on the side of the reaction container between the two counter electrode slots.

[0020] Further, the distance between the counter electrode and the membrane electrode is 2-3 cm, and the distance between the counter electrode and the metal electrode is 2-3 cm.

[0021] The present application combines electro-Fenton with a membrane electrode, applies a gradient voltage according to the different reduction potentials of O2 and H2O2, applies a gradient voltage on the double negative electrodes of the membrane electrode and the metal electrode respectively, the voltage of the membrane electrode is lower than that of the metal electrode, O2 is reduced to H2O2 on the membrane electrode (reaction formula 1), and the generated H2O2 can be immediately reduced to ·OH and ·O2 - active oxygen species (reaction formula 3, 8), and the generated free radicals are recombined on the metal electrode to generate more singlet 1 O2 (reaction formula 7), and degrade organic pollutants.

[0022] The above-mentioned membrane electrode is carbon cloth fiber, and the carbon cloth fiber is wrapped on a multi-cavity cylindrical acrylic tube, and the solution continuously flows in the tube under aeration condition, thereby strengthening the contact between the pollutants and the membrane electrode and enhancing the mass transfer.

[0023] Since O2 is reduced to H2O2 and ·O2 - The required reduction potential is lower than 1V, so when a voltage of 1V is applied on the carbon cloth, ·O2 -Compared with the double cathode electrodes applying a voltage higher than 1V (e.g. 2V) at the same time, more 1 O2、O2 - and ·OH reactive oxygen species; in addition, ·OH generated on the metal electrode can also be generated by self-disproportionation (reaction formula 6) 1 O2, or a small amount of O2 on the anode - Reoxidized to 1 O2 (Reaction 4). Under gradient electrocatalysis, there are also a series of other material conversion processes, such as Haber-Weiss (Reaction 5) and other similar redox reactions between free radicals.

[0024] Therefore, the present invention uses free radicals (including ·OH, ·O2 - reactive oxygen species) and non-free pathways (including direct electrochemical oxidation and 1 The synergistic effect of the electrochemical oxidation process (with the action of oxygen) degrades organic pollutants or completely mineralizes them into small-molecule inorganic compounds such as carbon dioxide and water. This avoids the anode loss of traditional electro-Fenton, improves electron utilization efficiency, reduces catalyst loss, enhances the degradation of difficult-to-degrade organic matter, and reduces energy consumption. Direct electrochemical oxidation, as described above, occurs when the potential of the graphite plate counter electrode reaches the oxidation potential for organic pollutant degradation, resulting in direct electron transfer at the anode, degrading difficult-to-degrade organic pollutants. 1 The role of O2 refers to the H2O2 and ·OH, ·O2 produced by free radical pathways - Reactive oxygen species such as 1 O2 directly attacks difficult-to-degrade organic pollutants.

[0025] Double cathode reaction:

[0026] O2+2H + +2e - →H2O2 E 0 =0.69V (1)

[0027] O2+e - → O2 - E 0 =0.56V (2)

[0028] H2O2+e - → OH+OH - E 0 =1.78V (3)

[0029] Anodic reaction:

[0030] O2 - -e - → 1O2 (4)

[0031] Other chemical reactions:

[0032] ·O2 - +2H + +H2O2→·OH+H2O+ 1 O2 (5)

[0033] 4·OH→ 1 O2+2H2O (6)

[0034] ·O2 - +·OH→H2O+ 1 O2 (7)

[0035] Fe 3+ +H2O2→Fe 2+ +·O2 - +H + (8)

[0036] Advantages of the present application:

[0037] (1) The present application generates H2O2 by electrolyzing O2 on the membrane electrode through cathodic reduction reaction under two different voltages, and the generated H2O2 is immediately converted into active oxygen species such as ·OH, ·O2 - on the metal electrode, and a large amount of 1 O2 is produced by free radical recombination, avoiding the cost increase problem caused by adding H2O2, Fe 2+ in the conventional electro-Fenton reaction.

[0038] (2) A large amount of singlet oxygen is produced in the reaction process of the present application, realizing the synergistic degradation of organic pollutants by free radicals and non-free radicals.

[0039] (3) The present application selects different cathode materials to apply gradient voltage according to the different reduction potentials of H2O2 and active oxygen species in the reaction process, the voltage of the membrane electrode is slightly lower than that of the metal electrode, avoiding the reduction of part of O2 to H2O through four-electron path, ensuring the efficient conversion and utilization of H2O2 and active oxygen species, realizing the enhanced degradation of organic pollutants, and saving energy and reducing consumption. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a schematic diagram of the gradient electro-catalytic enhanced degradation of organic wastewater treatment device of the present application.

[0041] Figure 2 is a schematic diagram of the double cathode reaction of the present application.

[0042] Figure 3 is a schematic diagram of the steady-state concentration of free radicals and non-free radicals in Example 1 of the present application.

[0043] In the figure: 1 - counter electrode; 2 - membrane electrode; 3 - metal electrode; 4 - direct current power supply, 5 - aeration device, 6 - reaction vessel. DETAILED DESCRIPTION

[0044] The principles and features of the present application are described below, and the examples are only used to explain the present application, and are not intended to limit the scope of the present application. If the specific technology or condition is not specified in the examples, it is performed according to the technology or condition described in the literature in the art, or according to the product manual. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be purchased through a regular channel.

[0045] Source description of materials and reagents:

[0046] In the following examples, the potentiostat is CHI1030C multi-channel potentiostat, which is commercially available from Shanghai Chenhua Instrument Co., Ltd.; the carbon cloth fiber in the examples is commercially available from Shanghai Hesen Electrical Co., Ltd.; the stainless steel mesh, graphite plate, titanium wire, acrylic plate, aeration device, sodium sulfate, and norfloxacin (NOR) used are commercially available products.

[0047] Example 1:

[0048] This example relates to a treatment method for gradient electrocatalytic enhanced degradation of organic wastewater, comprising the following steps: Figure 2 , Figure 2 GP is a graphite plate, CC is a carbon cloth fiber, and SSM is a stainless steel mesh):

[0049] (1) The membrane electrode (2) and the metal electrode (3) are used as double cathodes, and the counter electrode (1) is used as an anode; the membrane electrode (2) and the counter electrode (1) form a first electric circuit; the metal electrode (3) and the counter electrode (1) form a second electric circuit; the refractory organic wastewater to be treated is added to the first electric circuit and the second electric circuit, so that the membrane electrode (2), the metal electrode (3), and the counter electrode (1) are immersed;

[0050] (2) Turn on the power supply, so that the voltage of the first electric circuit is lower than that of the second electric circuit, perform aeration to complete the supply of O2, and the membrane electrode (2) mainly reduces O2 to generate H2O2 and ·O2 - , the metal electrode (3) mainly reduces H2O2 to generate ·OH, and ·OH and ·O2 - are recombined to form singlet oxygen 1 O2; the generated 1 O2, ·O2 - and ·OH degrade the refractory organic wastewater to be treated.

[0051] This embodiment also relates to a treatment device for gradient electrocatalytic enhanced degradation of organic wastewater ( Figure 1 ), the treatment device used in the treatment method comprises a reaction container (6), a counter electrode (1), a membrane electrode (2), a metal electrode (3), an aeration device (5) and a DC power supply (4), wherein the counter electrode (1), the membrane electrode (2), the metal electrode (3) and the aeration device (5) are located in the reaction container (6), the membrane electrode (2) and the metal electrode (3) are electrically connected to the negative electrode of the DC power supply (4), respectively, and the counter electrode (1) is electrically connected to the positive electrode of the DC power supply (4).

[0052] In this embodiment, preferably, the membrane electrode (2), the counter electrode (1), and the metal electrode (3) are all made of titanium wire as conductors, connected to a constant potential meter, and the reactor is continuously aerated to ensure that there is sufficient dissolved oxygen in the wastewater to produce hydrogen peroxide, enhance liquid disturbance, and achieve full conversion of various substances in the solution and rapid transfer of electrons. The membrane electrode (2) is arranged at the center of the reaction container (6), the counter electrode (1) is arranged in the counter electrode (1) slot, the metal electrode (3) is arranged in a single slot, and the aeration device (5) is arranged between the counter electrode (1) and the membrane electrode (2). The counter electrode (1) slot includes two counter electrode (1) slots, and the two counter electrode (1) slots are respectively located on the opposite sides of the reaction container (6); the single slot is located on the side of the reaction container (6) between the two counter electrode (1) slots. The spacing between the counter electrode (1) and the membrane electrode (2) is 2 cm to 3 cm; the spacing between the counter electrode (1) and the metal electrode (3) is 2 cm to 3 cm.

[0053] The present embodiment provides a method for treating organic wastewater by gradient electrocatalytic enhanced degradation, which is specifically as follows: adding the refractory organic wastewater to be treated into a reactor to completely cover the three electrodes, wherein the reaction liquid of the refractory organic wastewater to be treated is about 1L; after the hydrophobic carbon cloth fiber membrane electrode (2) is completely wetted, the counter electrode (1) and the metal electrode (3) are completely immersed and in a stable state; turning on the power supply, applying a voltage of 1V to the carbon cloth membrane electrode (2), a voltage of 2V to the stainless steel mesh metal electrode (3), and connecting the two positive electrode interfaces to the two counter electrodes (1) at the same time to realize the parallel connection of the three electrodes; turning on the aeration device (5) to allow the entire solution to fully contact with the air and continuously replenish the dissolved oxygen in the water body; wherein, a mixed solution of 15mg / L norfloxacin and 10mmol / L sodium sulfate is used to simulate the refractory organic wastewater.

[0054] The water sample treated by the reactor of the example for 3h is taken to detect the treatment effect of the refractory organic matter, and the removal rate of norfloxacin in the three-electrode system reactor is 72% under the condition that the stainless steel mesh metal electrode (3) is applied with a stable voltage of 2V, the carbon cloth membrane electrode (2) is applied with a stable voltage of 1V, and the aeration device (5) is turned on.

[0055] The detection method of the removal rate of norfloxacin: the concentration of norfloxacin is detected by ultraviolet-visible spectrophotometry, UV-vis full-wave NOR solution is used, and the characteristic wavelength is detected. The results show that the NOR solution shows a maximum absorption peak at 277nm, indicating that the characteristic wavelength λ is 277nm. The concentration of norfloxacin under each reaction condition is measured at the wavelength, and the removal efficiency of the pollutant is calculated.

[0056] In the gradient voltage of 1V-2V in example 1 of the application, the steady-state concentrations of free radicals and non-free radicals are as follows Figure 3 ; it can be known from Figure 3 that under the gradient voltage of 1V-2V, the active oxygen species mainly generated by singlet oxygen degrade organic pollutants.

[0057] Comparative example 1

[0058] The comparative example is different from example 1 in that the voltage applied to the carbon cloth fiber membrane electrode (2) is increased to 2V, the water sample treated by the three-electrode reactor for 3h is taken, and the removal rate of norfloxacin in the reactor is 54% (the detection method is the same as that in example 1). The rest is the same as that in example 1.

[0059] Comparative example 2

[0060] The comparative example is different from example 1 in that the aeration device (5) is not turned on, the water sample treated by the reactor for 3h is taken, and the removal rate of norfloxacin in the reactor is 6% (the detection method is the same as that in example 1). The rest is the same as that in example 1.

[0061] Comparative example 3

[0062] The comparative example is different from example 1 in that the voltage applied to the stainless steel mesh metal electrode (3) is reduced to 1V, the water sample treated by the membrane reactor for 3h is taken, and the removal rate of the organic matter in the membrane reactor is 36% (the detection method is the same as that in example 1).

[0063] As can be known from the above, the cathode reduction reaction under two different voltages is used in the application to electrolyze O2 to generate H2O2 on the membrane electrode (2), the generated H2O2 is immediately converted into ·OH, ·O2 - and 1 O2 and other active oxygen species on the metal electrode (3), which avoids the addition of H2O2, Fe2+ The reaction process of the present application is also accompanied by the generation of a large amount of singlet oxygen, realizing the synergistic enhanced degradation of organic pollutants by free radicals and non-free radicals. In view of the different reduction potentials of H2O2 and active oxygen species in the reaction process, different cathode materials are selected to apply a gradient voltage. The voltage of the membrane electrode (2) is slightly lower than that of the metal electrode (3), avoiding the reduction of part of O2 to H2O through a four-electron path, ensuring the efficient conversion and utilization of H2O2 and active oxygen species, realizing the enhanced degradation of organic pollutants, and saving energy and reducing consumption.

[0064] Although the embodiments of the present application have been shown and described above, it should be understood that the above-described embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method for treating organic wastewater by gradient electrocatalytic enhanced degradation, characterized in that: The specific steps include: (1) The membrane electrode and the metal electrode are used as double cathode electrodes, and the counter electrode is used as the anode; the membrane electrode and the counter electrode form a first electrical circuit; the metal electrode and the counter electrode form a second electrical circuit; the refractory organic wastewater to be treated is added into the first electrical circuit and the second electrical circuit until the membrane electrode, the metal electrode and the counter electrode are immersed; (2) Turn on the power supply to make the voltage of the first circuit lower than that of the second circuit, and perform aeration to complete the supply of O2. The membrane electrode mainly reduces O2 to generate H2O2 and O2 - The metal electrode mainly reduces H2O2 to generate ·OH, and converts ·OH and ·O2 - Recombination to form singlet oxygen 1 O2; the singlet oxygen generated 1 O2、O2 - and ·OH to degrade the refractory organic wastewater to be treated; The voltage of the first electrical circuit is 1V, and the voltage of the second electrical circuit is 2V; The membrane electrode is made of carbon fiber; the metal electrode is made of stainless steel mesh; and the counter electrode is made of graphite plate.

2. The method for treating organic wastewater by gradient electrocatalytic enhanced degradation according to claim 1, characterized in that: The membrane electrode is made by wrapping carbon cloth fibers on an organic glass tube with a perforated structure.

3. A gradient electrocatalytic enhanced degradation of organic wastewater treatment device, characterized in that: The treatment device used in the treatment method according to any one of claims 1 to 2 comprises a reaction vessel, a counter electrode, a membrane electrode, a metal electrode, an aeration device, and a DC power supply, wherein the counter electrode, the membrane electrode, the metal electrode, and the aeration device are located in the reaction vessel, the membrane electrode and the metal electrode are electrically connected to the negative electrode of the DC power supply, respectively, and the counter electrode is electrically connected to the positive electrode of the DC power supply; The membrane electrode and the counter electrode form a first electrical circuit; the metal electrode and the counter electrode form a second electrical circuit; The membrane electrode mainly reduces O2 to generate H2O2 and O2 - The metal electrode mainly reduces H2O2 to generate ·OH, and converts ·OH and ·O2 - Recombination to form singlet oxygen 1 O 2； The voltage of the first electrical circuit is 1V, and the voltage of the second electrical circuit is 2V.

4. A device for treating organic wastewater by gradient electrocatalytic enhanced degradation according to claim 3, characterized in that: The membrane electrode is arranged at the center of the reaction container, the counter electrode is arranged in the counter electrode slot, the metal electrode is arranged in the single slot, and the aeration device is arranged between the counter electrode and the membrane electrode.

5. The device for treating organic wastewater by gradient electrocatalytic enhanced degradation according to claim 4, characterized in that: The pair of electrode slots includes two pair of electrode slots, and the two pair of electrode slots are respectively located on two opposite sides of the reaction container; the single slot is located on the side of the reaction container between the two pair of electrode slots.

6. The device for treating organic wastewater by gradient electrocatalytic enhanced degradation according to claim 5, characterized in that: The distance between the counter electrode and the membrane electrode is 2 cm to 3 cm; the distance between the counter electrode and the metal electrode is 2 cm to 3 cm.

Images