Water treatment system for removing PFOA (perfluorooctanoic acid) in soil washing wastewater through electrooxidation coupled hydrogen peroxide reduction and application of water treatment system

Abstract

The invention relates to a water treatment system for removing PFOA (perfluorooctanoic acid) in soil washing wastewater through electrooxidation coupled hydrogen peroxide reduction and application, CF / FeCo-N-C with high H2O2RR activity is prepared as a cathode to replace the traditional HER cathode reaction, the cathode potential is improved, the cathode polarization is reduced, and the input voltage and energy consumption of the system are reduced. Besides, the water treatment system is used for electrooxidative degradation of actual PFOA-containing soil washing wastewater, and compared with the prior art, the water treatment system has the advantages that the theoretical value of cathode potential can be increased from 0V vs.RHE of HER to 1.78 V vs.RHE, the ultra-low thermodynamic equilibrium potential of 1.02 V is achieved, deep treatment of the PFOA-containing soil washing wastewater is achieved, energy consumption is remarkably reduced, and the method is suitable for industrial production. New theoretical insight and practical significance are provided for sustainable treatment of PFOA-containing soil washing wastewater, and a new technical mode is provided for a post-treatment stage in soil remediation.

Description

Technical Field

[0001] The present invention relates to the technical field of sewage treatment, and in particular to a water treatment system and application thereof for removing PFOA in soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) are highly persistent, bioaccumulative and toxic, posing a serious threat to human health and ecosystems. As an important environmental reservoir, soil may be contaminated with PFAS through a variety of pathways, including the use of fire-fighting foam containing PFAS, sewage discharged from sewage treatment plants, leachate from landfills, and leakage of contaminated waste. Soil washing technology can transfer PFAS from soil to flushing water for subsequent treatment. It is simple to operate and suitable for large-scale application. However, this process will produce high-concentration PFAS wastewater (tens to thousands of μg / L), which needs to be properly treated before safe disposal or reuse.

[0003] Traditional chemical and biological methods are limited in the removal of PFAS due to the strong CF bond (485 kJ / mol). As shown in formula (1), electrochemical oxidation (EO) technology has become an effective means to remove difficult-to-degrade organic pollutants due to its high oxidation potential and ability to produce highly reactive oxygen species. In the EO system, BDD (boron-doped diamond) and Ti4O7 (titanium suboxide) anodes have been shown to significantly inhibit competitive oxygen evolution side reactions and generate active substances such as hydroxyl radicals (·OH) with high Faraday efficiency, thereby achieving the degradation and mineralization of PFAS. Despite this, EO technology still faces the problem of high energy consumption when treating PFAS wastewater. The energy consumption is usually several kWh / m 3 To several hundred kWh / m 3 The main reason for the high energy consumption is the high input voltage required for water ionization and reactive oxygen generation. In addition, the mass transfer polarization caused by the slow migration of reactants and the ohmic polarization of the electrolyte are also important reasons for the high energy consumption.

[0004]

[0005] At present, the cathode reaction of the traditional EO system is usually the hydrogen evolution reaction (HER) (as shown in formula (2)), and its thermodynamic equilibrium potential is 0V vs. RHE. Combined with the anode EO reaction, the required theoretical input voltage is 2.80V. However, due to the electrolyte partial pressure and electrode polarization phenomena in actual operation, the required working voltage of the system will be higher than 2.80V, resulting in increased energy consumption. To this end, researchers have tried to use active electrode materials to reduce the electrolysis overvoltage, thereby reducing the working voltage of the system. However, due to the competition of the oxygen evolution side reaction, the Faraday efficiency of the system is still low, and the PFAS mineralization effect is incomplete. Summary of the invention

[0006] The purpose of the present invention is to provide a water treatment system and application for removing PFOA (perfluorooctanoic acid) from soil washing wastewater by electro-oxidation coupling with hydrogen peroxide reduction with low energy consumption. The present invention uses boron-doped diamond (BDD) as the anode and prepares CF / FeCo-NC with high H2O2RR activity as the cathode to replace the traditional HER cathode reaction, increase the cathode potential, reduce the cathode polarization, and reduce the input voltage and energy consumption of the system. In addition, the water treatment system is also used for electro-oxidation degradation of soil washing wastewater containing PFOA.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A water treatment system for removing PFOA in soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction, the water treatment system comprising a dual-chamber electrolytic cell, a BDD anode, a cathode and an ion exchange membrane, the dual-chamber electrolytic cell comprising an anode chamber and a cathode chamber, the BDD anode being arranged in the anode chamber, the cathode being arranged in the cathode chamber, and the ion exchange membrane being used to separate the anode chamber and the cathode chamber;

[0009] The cathode comprises a cathode substrate and a catalyst layer, and the catalyst layer is selected from any one or more of transition metal-doped carbon nitride, carbon nanosheets or carbon nanotubes.

[0010] As a preferred technical solution, the cathode is a cathode with high hydrogen peroxide reduction catalytic activity.

[0011] Furthermore, the cathode substrate is selected from any one of carbon felt, graphite felt or foamed carbon.

[0012] As a preferred technical solution, the cathode substrate is carbon felt.

[0013] Furthermore, the catalytic layer is FeCo-NC.

[0014] Furthermore, the preparation process of the FeCo-NC is as follows:

[0015] Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Zn(NO3)2·6H2O and 2-methylimidazole are mixed in a solvent, precipitated and dried to obtain a precursor, and the precursor is pyrolyzed in an argon atmosphere to obtain FeCo-NC.

[0016] Furthermore, the mass ratio of Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Zn(NO3)2·6H2O and 2-methylimidazole is (28-32 mg):(20-24 mg):(2.4-2.6 g):(2.9-3.1 g),

[0017] The pyrolysis temperature is 800-900° C., and the pyrolysis time is 1-2 hours.

[0018] As a preferred technical solution, the mass ratio of Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Zn(NO3)2·6H2O and 2-methylimidazole is 30mg:22mg:2.5g:3.0g.

[0019] The pyrolysis temperature is 900° C. and the pyrolysis time is 1 hour.

[0020] Furthermore, the cathode is prepared as follows:

[0021] FeCo-NC was dispersed in a mixed solution of ethanol, water and naphthol and ultrasonicated, and then a cathode substrate was added and immersed in ultrasonication to obtain a cathode substrate / FeCo-NC as a cathode.

[0022] In the above, the feed ratio of FeCo-NC to naphthol is (45-55) mg: (98-110) μL.

[0023] The mass ratio of the cathode substrate to FeCo-NC is (220-230 mg):(50-55 mg).

[0024] As a preferred technical solution, the feed ratio of FeCo-NC and naphthol is 50 mg:100 μL.

[0025] The mass ratio of the cathode substrate to FeCo-NC is 230mg:50mg.

[0026] As a preferred technical solution, the naphthol is introduced into the reaction system in the form of a 50% (w / w) H2O solution.

[0027] As a preferred technical solution, the ultrasonic time is 30 minutes, the ultrasonic power is 600W, and the ultrasonic frequency is 25-28kHz.

[0028] Furthermore, the ion exchange membrane is a naphthol N117 proton exchange membrane.

[0029] As a preferred technical solution, the BDD anode and cathode are placed parallel to each other, and the distance between two adjacent electrodes is 3-4 cm, preferably 4 cm.

[0030] As a preferred technical solution, the BDD anode is a commercial plate electrode, and the BDD anode electrolyzes water to generate ·OH, thereby achieving efficient degradation of PFOA.

[0031] As a preferred technical solution, the size of the BDD anode is 1 cm×2 cm.

[0032] The size of the cathode is (1 to 3) cm×(1 to 3) cm, preferably 2 cm×2 cm.

[0033] As a preferred technical solution, the BDD anode and cathode are externally connected to a DC regulated power supply, the BDD anode is connected to the positive electrode of the DC regulated power supply, and the cathode is connected to the negative electrode of the DC regulated power supply.

[0034] As a preferred technical solution, the double-chamber electrolytic cell is arranged above the magnetic stirrer, and a rotor is arranged in the anode chamber.

[0035] As a preferred technical solution, the double-chamber electrolytic cell is in the shape of a cylindrical shell.

[0036] In addition, the present invention also provides an application of a water treatment system for removing PFOA in soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction, wherein the water treatment system is used for degrading PFOA in soil washing wastewater.

[0037] Furthermore, the degradation conditions include: the current density of the BDD anode is 1-15 mA / cm 2 , preferably 3 mA / cm 2 ;

[0038] The electrolyte in the anode chamber is selected from 0.1 mol / L sodium sulfate or 5 mmol / L sulfuric acid,

[0039] The electrolyte in the cathode chamber is selected from a mixed solution of 5mmol / L sulfuric acid and 10mmol / L H2O2 or a mixed solution of 0.1mol / L sodium sulfate and 10mmol / L hydrogen peroxide;

[0040] When the electrolyte in the anode chamber is 0.1 mol / L sodium sulfate, the pH value of the electrolyte in the anode chamber and the cathode chamber is controlled at 6.0 to 7.5, preferably 6.2.

[0041] When the electrolyte in the anode chamber is 5 mmol / L sulfuric acid, the pH value of the electrolyte in the anode chamber and the cathode chamber is controlled at 2.8 to 3.2, preferably 3.0.

[0042] The working principle of the present invention is as follows:

[0043] The present invention provides an EO-H2O2RR electrolysis system of EO coupled hydrogen peroxide reduction reaction (H2O2RR), which uses H2O2RR as a cathode reaction to replace the traditional HER, and can increase the cathode potential from 0V vs.RHE of HER to 1.78V vs.RHE (as shown in formula (2) and formula (3)), and can further push the thermodynamic equilibrium potential of the system to 1.02V, thereby solving the problem of high energy consumption of the electro-oxidation system. The prepared high H2O2RR activated carbon felt loaded with iron cobalt nitrogen carbon (CF / FeCo-NC) is used as the cathode to reduce cathode polarization. The present invention applies the coupled water treatment system to the process of electro-oxidation degradation of actual soil washing wastewater containing PFOA. By optimizing the electrochemical conditions, in an actual wastewater environment where humus and inorganic ions coexist, the present invention achieves efficient degradation of soil washing wastewater containing PFOA, while significantly reducing energy consumption.

[0044]

[0045] The present invention provides an efficient and low-energy technical solution by coupling EO with H2O2RR, which is suitable for the treatment of soil washing wastewater containing PFOA. EO technology can generate highly active and oxidizing ·OH radicals on the electrode surface, showing significant effects in removing PFOA. Combining EO with H2O2RR can not only maintain a high PFOA degradation rate, but also reduce the thermodynamic potential of the EO system to 1.02V by replacing the traditional HER with H2O2RR, thereby reducing the external input voltage and reducing the system energy consumption. In practical applications, even under the competitive action of coexisting substances such as humic acid and inorganic ions, the EO-H2O2RR system can still maintain a high PFOA removal rate while achieving low-energy operation.

[0046] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0047] 1) The present invention proposes an innovative electro-oxidation system to treat soil washing wastewater containing PFOA by coupling hydrogen peroxide reduction reaction. In this system, the hydrogen peroxide reduction reaction replaces the hydrogen evolution reaction in the traditional electro-oxidation system, successfully increasing the theoretical cathode potential from 0V vs.RHE to 1.78V vs.RHE, achieving an ultra-low thermodynamic equilibrium potential of 1.02V, thereby effectively reducing the energy consumption of the electro-oxidation system.

[0048] 2) The present invention provides an efficient PFOA-containing soil washing wastewater treatment system with strong anti-interference ability and good stability. Under the competitive action of coexisting substances such as humic acid and inorganic ions, the EO-H2O2RR system can still maintain a high PFOA removal rate and keep low energy consumption.

[0049] 3) The present invention not only achieves efficient and deep treatment of soil washing wastewater containing PFOA by optimizing the electro-oxidation treatment process, but also significantly reduces energy consumption. The system design fully considers the ease of operation and cost-effectiveness, and has broad application prospects, especially in the field of difficult-to-degrade wastewater treatment.

[0050] 4) The present invention provides a new theoretical basis and practical value for the sustainable treatment of PFOA-containing soil washing wastewater, and provides an innovative technical model for the post-treatment stage in soil remediation. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a structural schematic diagram of the water treatment system in the present invention;

[0052] Figure 2 Thermodynamic and kinetic principle diagram for energy saving of the present invention.

[0053] Figure 3 Schematic diagram of the working status of the two systems in Example 1, wherein A is the EO-HER system and B is the EO-H2O2RR system.

[0054] Explanation of the accompanying figures: 1. DC regulated power supply, 2. BDD anode, 3. cathode, 4. ion exchange membrane, 5. rotor, 6. magnetic stirrer, 7. double-chamber electrolytic cell. DETAILED DESCRIPTION

[0055] 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.

[0056] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0057] In the following embodiments, the sources of the equipment are as follows:

[0058] The BDD anode was purchased from Hunan Xinfeng Technology Co., Ltd., and the magnetic stirrer was purchased from Qun'an Scientific Instrument (Zhejiang) Co., Ltd.

[0059] In the following embodiments, if there is no special description of raw materials or processing technology, it means that they are all conventional commercially available raw materials or conventional processing technologies in the field. If there is no special description of functional components or structures, it means that they are all conventional components or conventional structures used in the field to achieve corresponding functions.

[0060] In conjunction with the accompanying drawings, some embodiments of the present invention are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0061] Example 1

[0062] The present embodiment provides a water treatment system (EO-H2O2RR system) for removing PFOA in soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction (EO-H2O2RR), wherein the water treatment system comprises a dual-chamber electrolytic cell 7, a BDD anode 2 arranged in an anode chamber, a cathode 3 arranged in a cathode chamber, and an ion exchange membrane 4, wherein the cathode 3 adopts H2O2RR.

[0063] In this embodiment, the EO-H2O2RR system uses a double-chamber electrolytic cell 7 to treat the pollutant PFOA, and its structure is as follows: Figure 1 As shown, it includes a DC regulated power supply 1, a BDD anode 2, a CF / FeCo-NC cathode 3, an ion exchange membrane 4, a rotor 5, a magnetic stirrer 6 and a double-chamber electrolytic cell 7;

[0064] The BDD anode 2 and the CF / FeCo-NC cathode 3 are respectively placed vertically to the bottom in the anode chamber and cathode chamber of the double-chamber electrolytic cell 7 of the cylindrical shell, and the two electrodes are placed parallel to each other, and the distance between the two electrodes is 4 cm;

[0065] The BDD anode 2 is connected to the positive electrode of the DC regulated power supply 1, and the CF / FeCo-NC cathode 3 is connected to the negative electrode of the DC regulated power supply 1. The BDD anode 2 electrolyzes water to generate ·OH to achieve efficient degradation of PFOA, and the CF / FeCo-NC cathode 3 generates H2O2RR.

[0066] In this embodiment, a rotor 5 is provided at the bottom of the anode chamber, and a magnetic stirrer 6 is provided below the anode chamber, with a rotation speed of 800 rpm, so as to promote the anode PFOA electro-oxidation process.

[0067] In this embodiment, the EO-H2O2RR system uses a BDD electrode (1 cm×2 cm) as the anode 2 and a CF / FeCo-NC electrode (2 cm×2 cm) as the cathode 3, wherein the preparation process of the CF / FeCo-NC cathode 3 is as follows:

[0068] 1) Preparation of FeCo-NC catalytic layer: A methanol solution containing 30 mg Fe(NO3)3·9H2O was mixed with a methanol solution containing 22 mg Co(NO3)2·6H2O, heated to 60°C and stirred for 2 h. A methanol solution containing 2.5 g Zn(NO3)2·6H2O and 3.0 g 2-methylimidazole was added, stirred and mixed, and the precipitate was dried to form a precursor, which was pyrolyzed at 900°C in an argon atmosphere for 1 h to obtain a FeCo-NC catalytic layer.

[0069] 2) Preparation of CF / FeCo-NC cathode: 50 mg FeCo-NC was dispersed in a mixed solution of 500 μL ethanol, 400 μL water and 100 μL naphthol (50% (w / w) H2O) and ultrasonicated for 30 min (600 W, 25-28 kHz). Then, carbon felt was added for immersion ultrasonication to obtain a carbon felt-loaded phosphorus-doped iron nitrogen carbon (CF / FeCo-NC) electrode.

[0070] Comparative Example 1

[0071] This comparative example provides a conventional electro-oxidation coupled hydrogen evolution reaction (EO-HER) water treatment system, the water treatment system comprising a dual-chamber electrolyzer 7, a BDD anode 2 disposed in an anode chamber, a cathode 3 disposed in a cathode chamber, and an ion exchange membrane 4, wherein the cathode 3 adopts HER.

[0072] Performance Test Example 1

[0073] Under the same conditions, the water treatment system constructed in Example 1 (EO-H2O2RR system) and the water treatment system constructed in Comparative Example 1 (traditional EO-HER system) were used to degrade PFOA in laboratory water, as follows:

[0074] EO-H2O2RR system:

[0075] The double-chamber electrolytic cell 7 in the EO-H2O2RR system was used to degrade the pollutant PFOA. The specific degradation conditions were: the volume of the reaction solution in the anode chamber: 10 mL, the pollutant to be treated in the anode chamber: PFOA, the PFOA concentration was 5 mg / L, the electrolyte in the anode chamber: 5 mmol / L sulfuric acid, and the current density of the BDD anode 2: 1-15 mA / cm 2 , initial pH of the PFOA solution to be treated: 3.0, volume of cathode chamber reaction solution: 30 mL, cathode chamber electrolyte: 5 mmol / L sulfuric acid and 10 mmol / L H2O2, initial pH of cathode chamber electrolyte: 3.0.

[0076] EO-HER system:

[0077] The EO-HER system uses a BDD electrode (1 cm×2 cm) as the anode 2, a commercial platinum (Pt) sheet electrode (2 cm×2 cm) as the cathode 3, and a double-chamber electrolytic cell 7 to degrade PFOA. The electrolyte in the cathode chamber is 5 mmol / L sulfuric acid, and the other conditions are maintained the same as the EO-H2O2RR system.

[0078] The above two systems are used to degrade PFOA. Figure 3 Schematic diagram of the working state of the EO-H2O2RR system constructed in Example 1 and the EO-HER system constructed in Comparative Example 1, at different BDD anode 2 current densities (1-15 mA / cm 2 ), the input voltage when the PFOA removal rate of the two systems reached or approached 99% is shown in Table 1; when the current density of the BDD anode 2 was 3 mA / cm 2 Under the condition that the treatment time is 1.5h, the PFOA removal rates of the two systems reach or approach 99%. At this time, the specific results of the comparison of the anode and cathode potentials, input voltages and energy consumption of the EO-H2O2RR system and the EO-HER system are shown in Table 2.

[0079] Table 1 Results of input voltage when PFOA removal rate of the two systems reached or approached 99% under different BDD anode 2 current densities

[0080]

[0081] Table 2 Comparison of cathode and anode potential, input voltage and energy consumption of EO-H2O2RR system and EO-HER system

[0082]

[0083]

[0084] The results show that the EO-H2O2RR dual cathode system increases the theoretical value of cathode potential from 0V of HER to 1.78Vvs.RHE, reducing the external input voltage of the system.

[0085] From the results in Table 1, it can be seen that at the same current density, the input voltage required by the EO-H2O2RR system is lower than that of the EO-HER system. This is because the theoretical electrode potential of H2O2RR is 1.78V vs.RHE, which is much higher than 0V vs.RHE of HER. From the results in Table 2, it can be seen that within the treatment time of 1.5h, the specific current density is 3mA / cm 2 Under the condition of 3 mA / cm2, the conventional EO-HER system and the EO-H2O2RR system of this embodiment showed almost the same performance in terms of PFOA removal rate. This result shows that the degradation of PFOA in the system mainly depends on the anodic electrooxidation process. 2Under the conditions of current density and reaction for 1.5h, the anode potential of the EO-HER system and the EO-H2O2RR system both rose to 2.90V, which is slightly higher than the standard electrode potential of OH, as shown in formula (1). From the cathode potential point of view, the CF / FeCo-NC cathode in the EO-H2O2RR system is polarized from the theoretical value of 1.78V to 0.90V, and the Pt cathode in the EO-HER system is polarized from the theoretical value of 0V to -0.38V. It has been determined that the actual input voltage required for the EO-H2O2RR system (CF / FeCo-NC cathode) is 2.12V, which is much lower than the 3.48V of the EO-HER system (Pt cathode). This proves that the EO-H2O2RR system constructed in Example 1 achieves a significant increase in the cathode potential by regulating the cathode reaction. Further energy consumption analysis shows that the energy consumption of the EO-H2O2RR system is 0.95kWh / m 3 , compared with 1.57kWh / m of EO-HER system 3 , achieving a significant energy saving effect of 39.5%, further verifying the EO-H2O2RR system's 99% PFOA degradation rate and energy-saving advantages.

[0086] Performance Test Example 2

[0087] In this test example, the water treatment system (EO-H2O2RR system) constructed in Example 1 and the water treatment system (traditional EO-HER system) constructed in Comparative Example 1 were used to treat actual soil washing wastewater containing PFOA, wherein the electrodes and electrolytic cells used in the EO-H2O2RR system and EO-HER system in this example are exactly the same as those in Example 1.

[0088] The soil in this test case was taken from the South Campus of Tongji University. The specific soil pretreatment method was as follows: soil samples at a depth of 0 to 20 cm were collected to remove soil animals, stones and plant litter. All soil samples were air-dried, ground and sieved through a 2 mm sieve. 30 g of soil was added to 400 ml of ultrapure water (300 rpm, 25 ° C) and shaken for 24 hours to extract soil solution organic matter. After centrifugation, the soil suspension was filtered through a glass fiber filter membrane (0.45 μm). Take 10 mL of the filtrate and add 0.1 mol / L sodium sulfate as the electrolyte, take 1 mg / LPFOA as the target pollutant, and carry out EO treatment in the electrolytic cell.

[0089] EO-H2O2RR system:

[0090] The above EO-H2O2RR system was used to treat actual soil washing wastewater containing PFOA. The specific reaction conditions were: anode chamber reaction solution volume: 10 mL, anode chamber pollutant to be treated: PFOA, PFOA concentration: 1 mg / L, anode chamber electrolyte: 0.1 mol / L sodium sulfate, BDD anode 2 current density: 3 mA / cm 2 , initial pH of the PFOA solution to be treated: 6.2, volume of cathode chamber reaction solution: 30 mL, cathode chamber electrolyte: 0.1 mol / L sodium sulfate and 10 mmol / L H2O2, initial pH of cathode chamber electrolyte: 6.2.

[0091] EO-HER system:

[0092] The above-mentioned EO-HER system was used to treat actual soil washing wastewater containing PFOA. The EO-HER system used a BDD electrode (1cm×2cm) as the anode and a commercial platinum (Pt) sheet electrode (2cm×2cm) as the cathode. A double-chamber electrolytic cell was used to degrade PFOA. The electrolyte in the cathode chamber was 0.1 mol / L sodium sulfate, and the other conditions were maintained the same as the EO-H2O2RR system.

[0093] The above two systems were used to degrade actual soil washing wastewater containing PFOA at 3mA / cm 2 At a fixed current density, the specific results of input voltage and energy consumption when the PFOA removal rate of the two systems reaches or approaches 95% after 2h of reaction are shown in Table 3.

[0094] Table 3 at 3 mA / cm 2 Input voltage and energy consumption results when the PFOA removal rate of EO-H2O2RR system and EO-HER system reaches or approaches 95% after 2h of reaction at a fixed current density

[0095]

[0096] The results show that: From the results in Table 3, it can be seen that the EO-H2O2RR system and the EO-HER system are at 3mA / cm 2 When treating actual soil washing wastewater containing 1mg / L PFOA, the removal rate of PFOA in both systems reached 95% after 2h of reaction, which shows that the BDD electro-oxidation water treatment system used in this embodiment has a good removal effect on PFOA. In addition, it can be seen from the overall external input voltage of the two systems that the voltage of EO-H2O2RR is only 2.60V when treating actual soil washing wastewater containing PFOA, which is significantly lower than the 4.20V of the EO-HER system. It is calculated that the energy consumption of the EO-H2O2RR system is only 1.56kWh / m when the PFOA removal rate reaches 95%. 3, saving 38.1% of energy consumption compared to the EO-HER system. This shows that the EO-H2O2RR system constructed in Example 1 still has significant economic value and environmental protection when treating actual PFOA-containing soil washing wastewater.

[0097] Performance Test Example 3

[0098] This test example uses the water treatment system (EO-H2O2RR system) constructed in Example 1 to treat actual soil washing wastewater and PFOA under laboratory water distribution, wherein the electrodes and electrolytic cells used in the EO-H2O2RR system in this test example are exactly the same as those used in the EO-H2O2RR system in Test Example 2.

[0099] The soil in this test case was taken from the South Campus of Tongji University. The specific soil pretreatment method was as follows: soil samples at a depth of 0 to 20 cm were collected to remove soil animals, stones and plant litter. All soil samples were air-dried, ground and sieved through a 2 mm sieve. 30 g of soil was added to 400 ml of ultrapure water (300 rpm, 25 ° C) and shaken for 24 hours to extract soil solution organic matter. After centrifugation, the soil suspension was filtered through a glass fiber filter membrane (0.45 μm). Take 10 mL of the filtrate and add 0.1 mol / L sodium sulfate as the electrolyte, take 1 mg / LPFOA as the target pollutant, and carry out EO treatment in the electrolytic cell.

[0100] The EO-H2O2RR system constructed in Example 1 was used to treat actual soil washing wastewater containing PFOA (containing soil soluble organic matter). The specific reaction conditions were: anode chamber reaction solution volume: 10 mL, anode chamber pollutant to be treated: PFOA, PFOA concentration of 1 mg / L, anode chamber electrolyte: 0.1 mol / L sodium sulfate, BDD anode 2 current density: 3 mA / cm 2 , initial pH of the PFOA solution to be treated: 6.2, volume of cathode chamber reaction solution: 30 mL, cathode chamber electrolyte: 0.1 mol / L sodium sulfate and 10 mmol / L H2O2, initial pH of cathode chamber electrolyte: 6.2.

[0101] The above EO-H2O2RR system was used to treat PFOA (excluding soil soluble organic matter) in laboratory water. The specific reaction conditions were: anode chamber reaction solution volume: 10 mL, anode chamber pollutant to be treated: PFOA, PFOA concentration: 1 mg / L, anode chamber electrolyte: 0.1 mol / L sodium sulfate, BDD anode 2 current density: 3 mA / cm 2 , initial pH of the PFOA solution to be treated: 6.2, volume of cathode chamber reaction solution: 30 mL, cathode chamber electrolyte: 0.1 mol / L sodium sulfate and 10 mmol / L H2O2, initial pH of cathode chamber electrolyte: 6.2.

[0102] The EO-H2O2RR system was used to treat the PFOA in the above-mentioned actual soil washing wastewater and laboratory water. 2 After 2 h of reaction at the current density, the degradation rate results of the two wastewaters are shown in Table 4. The total organic carbon (TOC), chemical oxygen demand (COD), PFOA concentration and pH of the anode reaction solution before and after the actual PFOA-containing soil washing wastewater was treated by the EO-H2O2RR system are shown in Table 5

[0103] Table 4 Degradation rate results of two wastewaters

[0104]

[0105]

[0106] Table 5 Total organic carbon, chemical oxygen demand, PFOA concentration and pH of anode reaction solution before and after the treatment of actual PFOA-containing soil washing wastewater using the EO-H2O2RR system

[0107]

[0108] The results show that, as shown in Table 4, the EO-H2O2RR system still has a high PFOA removal rate when the actual soil washing wastewater contains dissolved organic matter. After 120 minutes of reaction, the PFOA degradation rate is 95.3%, which is only 4.6% lower than 99.9% under laboratory water distribution conditions. This proves the EO-H2O2RR system's ability to resist the interference of dissolved organic matter (coexisting humic acid, etc.) and excellent PFOA removal rate in actual wastewater applications. As shown in Table 5, after treatment, the TOC of soil washing wastewater decreased from 120 mg / L to 2.46 mg / L, with a removal rate of 98.0%, COD decreased from 52 mg / L to 0.87 mg / L, with a removal rate of 98.3%, PFOA concentration decreased from 1 mg / L to 0.047 mg / L, with a removal rate of 95.3%, and the solution pH decreased from 6.2 to 5.9, with little change. The water quality of the treated soil washing wastewater can meet the first-level discharge standard of the National Comprehensive Wastewater Discharge Standard (GB8978-1996). The above results successfully demonstrate the significant advantages of the EO-H2O2RR coupling system in treating actual PFOA-containing soil washing wastewater.

[0109] 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 water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction, characterized in that: The water treatment system comprises a dual-chamber electrolytic cell (7), a BDD anode (2), a cathode (3) and an ion exchange membrane (4), wherein the dual-chamber electrolytic cell (7) comprises an anode chamber and a cathode chamber, the BDD anode (2) is arranged in the anode chamber, the cathode (3) is arranged in the cathode chamber, and the ion exchange membrane (4) is used to separate the anode chamber and the cathode chamber; The cathode (3) comprises a cathode substrate and a catalytic layer, wherein the catalytic layer is selected from any one or more of transition metal-doped carbon nitride, carbon nanosheets or carbon nanotubes.

2. A water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction according to claim 1, characterized in that: The cathode substrate is selected from any one of carbon felt, graphite felt or foamed carbon.

3. The water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction according to claim 1 is characterized in that: The catalytic layer is FeCo-NC.

4. A water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction according to claim 3, characterized in that: The preparation process of the FeCo-NC is as follows: Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Zn(NO3)2·6H2O and 2-methylimidazole are mixed in a solvent, precipitated and dried to obtain a precursor, and the precursor is pyrolyzed in an argon atmosphere to obtain FeCo-NC.

5. A water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction according to claim 4, characterized in that: The mass ratio of Fe(NO3)3·9H2O, Co(NO3)2·6H2O, Zn(NO3)2·6H2O and 2-methylimidazole is (28-32 mg):(20-24 mg):(2.4-2.6 g):(2.9-3.1 g), The pyrolysis temperature is 800-900° C., and the pyrolysis time is 1-2 hours.

6. The water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction according to claim 3 is characterized in that: The preparation process of the cathode (3) is as follows: FeCo-NC is dispersed in a mixed solution of ethanol, water and naphthol and ultrasonically treated, and then a cathode substrate is added and immersed in ultrasonic treatment to obtain a cathode substrate / FeCo-NC as a cathode (3).

7. A water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction according to claim 6, characterized in that: The feed ratio of FeCo-NC to naphthol is (45-55) mg: (98-110) μL. The mass ratio of the cathode substrate to FeCo-NC is (220-230 mg):(50-55 mg).

8. The water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction according to claim 1, characterized in that: The ion exchange membrane (4) is a naphthol N117 proton exchange membrane.

9. An application of a water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction as claimed in any one of claims 1 to 8, characterized in that: The water treatment system is used to degrade PFOA in soil washing wastewater.

10. The use of a water treatment system for removing PFOA from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction according to claim 9, characterized in that: The degradation conditions include: the current density of the BDD anode (2) is 1-15 mA / cm 2 , The electrolyte in the anode chamber is selected from 0.1 mol / L sodium sulfate or 5 mmol / L sulfuric acid, The electrolyte in the cathode chamber is selected from a mixed solution of 5mmol / L sulfuric acid and 10mmol / L H2O2 or a mixed solution of 0.1mol / L sodium sulfate and 10mmol / L hydrogen peroxide; When the electrolyte in the anode chamber is 0.1 mol / L sodium sulfate, the pH value of the electrolyte in the anode chamber and the cathode chamber is controlled at 6.0 to 7.

5. When the electrolyte in the anode chamber is 5mmol / L sulfuric acid, the pH value of the electrolyte in the anode chamber and the cathode chamber is controlled at 2.8 to 3.2.

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