A water treatment system for removing PFOA in soil washing wastewater by electro-oxidation coupling hydrogen peroxide reduction and application

Abstract

The present application relates to a kind of water treatment systems and applications for removing PFOA in soil washing wastewater by electrooxidation coupling hydrogen peroxide reduction, by preparing CF / FeCo-N-C with high H2O2RR activity as cathode, replacing traditional HER cathode reaction, improving cathode potential, reducing cathode polarization, reducing the input voltage and energy consumption of system.In addition, the water treatment system is also used for electrooxidation degradation of actual PFOA-containing soil washing wastewater, compared with prior art, the theoretical value of cathode potential can be increased from 0V vs.RHE of HER to 1.78V vs.RHE, realizing 1.02V of ultra-low thermodynamic equilibrium potential, realizing the significant reduction of energy consumption for deep treatment of PFOA-containing soil washing wastewater, providing new theoretical insights and practical significance for sustainable treatment of PFOA-containing soil washing wastewater, and providing a new technical mode for post-processing 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 firefighting 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, facilitating subsequent treatment. It is simple to operate and suitable for large-scale application. However, this process produces high-concentration PFAS wastewater (tens to thousands of μg / L), which requires proper treatment before safe disposal or reuse.

[0003] Traditional chemical and biological methods are constrained by strong CF bonds (485kJ / mol) in the removal of PFAS, and the removal effect is limited. As shown in formula (1), electrochemical oxidation (EO) technology has become an effective means of removing difficult-to-degrade organic pollutants due to its high oxidation potential and ability to produce highly active oxygen species. In the EO system, BDD (boron-doped diamond) and Ti4O7 (titanium suboxide) anodes have been shown to significantly inhibit the competitive oxygen evolution side reaction 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 species 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 Equation (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 phenomenon in actual operation, the required operating 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 operating 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 this invention is to provide a low-energy, high-efficiency water treatment system and application for removing PFOA (perfluorooctanoic acid) from soil washing wastewater by electro-oxidation coupled with hydrogen peroxide reduction. This invention uses boron-doped diamond (BDD) as the anode and prepares CF / FeCo-NC with high H2O2RR activity as the cathode, replacing the traditional HER cathode reaction. This increases the cathode potential, reduces cathode polarization, and reduces the input voltage and energy consumption of the system. Furthermore, this water treatment system is also used for electro-oxidation degradation of actual 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 from 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 comprises an anode chamber and a cathode chamber, the BDD anode is disposed in the anode chamber, the cathode is disposed in the cathode chamber, and the ion exchange membrane is used to separate the anode chamber and the cathode chamber.

[0009] The cathode 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.

[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 foam 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 were mixed in a solvent, precipitated and dried to obtain a precursor, and the precursor was pyrolyzed under 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] Furthermore, the feed ratio of FeCo-NC and 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 feeding ratio of FeCo-NC and naphthol is 50 mg:100 μL.

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

[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 dual-chamber electrolytic cell is arranged above the magnetic stirrer, and a rotor is provided 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 compartment is 0.1 mol / L sodium sulfate, the pH value of the electrolyte in the anode compartment and the cathode compartment 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 for an EO-coupled hydrogen peroxide reduction reaction (H2O2RR). Using H2O2RR as the cathode reaction instead of the traditional HER, the cathode potential can be increased from 0V vs. RHE of HER to 1.78V vs. RHE (as shown in Equations (2) and (3)). The system's thermodynamic equilibrium potential can be further pushed to 1.02V, thereby resolving the problem of high energy consumption in the electro-oxidation system. The prepared high H2O2RR activated carbon felt loaded with iron, cobalt, nitrogen, and carbon (CF / FeCo-NC) is used as the cathode to reduce cathode polarization. The present invention applies the coupled water treatment system to the electro-oxidation degradation of actual soil washing wastewater containing PFOA. By optimizing the electrochemical conditions, the present invention achieves efficient degradation of soil washing wastewater containing PFOA in an actual wastewater environment where humus and inorganic ions coexist, while significantly reducing energy consumption.

[0044]

[0045] By coupling EO with H2O2RR, the present invention provides a highly efficient and low-energy technical solution 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 not only maintains a high PFOA degradation rate, but also reduces the thermodynamic potential of the EO system to 1.02V by replacing the traditional HER with H2O2RR, thereby reducing the external input voltage and lowering the system energy consumption. In practical applications, even under the competitive effects 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) This paper proposes an innovative electro-oxidation system for treating PFOA-containing soil washing wastewater by coupling a hydrogen peroxide reduction reaction. In this system, the hydrogen peroxide reduction reaction replaces the hydrogen evolution reaction in traditional electro-oxidation systems, successfully increasing the theoretical cathode potential from 0 V vs. RHE to 1.78 V vs. RHE, achieving an ultra-low thermodynamic equilibrium potential of 1.02 V, thereby effectively reducing the energy consumption of the electro-oxidation system.

[0048] 2) This invention provides a highly efficient PFOA-containing soil washing wastewater treatment system with strong anti-interference capabilities and excellent stability. Despite the competitive effects of coexisting substances such as humic acid and inorganic ions, the EO-H2O2RR system can still maintain a high PFOA removal rate while maintaining low energy consumption.

[0049] 3) The present application realizes efficient and deep treatment of PFOA-containing soil washing wastewater by optimizing the electro-oxidation treatment process, and significantly reduces energy consumption. The system design fully considers the simplicity and cost-effectiveness of operation, and has a wide application prospect, especially in the field of treatment of refractory wastewater.

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

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

[0052] Figure 2 Figure 3 is a thermodynamic and kinetic principle diagram for saving energy in the present application.

[0053] Figure 3 Figure 4 is a schematic diagram of the working state of two systems in Example 1, wherein A is an EO-HER system and B is an EO-H2O2 RR system.

[0054] Figure 1 is a schematic diagram of the water treatment system in the present application; DETAILED DESCRIPTION

[0055] The present application will be described in detail below in conjunction with the drawings and specific examples. The present embodiment is implemented on the basis of the technical solution of the present application, and gives a detailed implementation mode and specific operation process, but the protection scope of the present application is not limited to the following examples.

[0056] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

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

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

[0059] In the following examples, unless otherwise specified, the raw materials or processing techniques are all conventional commercially available raw material products or conventional processing techniques in the art. Unless otherwise specified, the functional components or structures are all conventional components or conventional structures adopted in the art to achieve the corresponding functions.

[0060] The following describes some embodiments of the present invention in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0061] Example 1

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

[0063] In this embodiment, the EO-H2O2RR system uses a dual-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 perpendicular to the bottom in the anode chamber and cathode chamber of a cylindrical double-chamber electrolytic cell 7, with the two electrodes placed parallel to each other and a distance of 4 cm between them.

[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, thereby achieving 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, thereby promoting 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. The preparation process of the CF / FeCo-NC cathode 3 is as follows:

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

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

[0070] Comparative Example 1

[0071] This comparative example provides a traditional electro-oxidation coupled hydrogen evolution reaction (EO-HER) water treatment system, which includes a dual-chamber electrolyzer 7, a BDD anode 2 arranged in the anode chamber, a cathode 3 arranged in the 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 PFOA pollutant was degraded using a dual-chamber electrolytic cell 7 in the EO-H2O2RR system. The specific degradation conditions were: anode chamber reaction solution volume: 10 mL, anode chamber to be treated pollutant: PFOA, PFOA concentration: 5 mg / L, anode chamber electrolyte: 5 mmol / L sulfuric acid, BDD anode 2 current density: 1-15 mA / cm 2 , initial pH of the PFOA solution to be treated: 3.0, cathode chamber reaction solution volume: 30 mL, cathode chamber electrolyte: 5 mmol / L sulfuric acid and 10 mmol / L H2O2, cathode chamber electrolyte initial pH: 3.0.

[0076] EO-HER system:

[0077] The EO-HER system used 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 dual-chamber electrolytic cell 7 to degrade PFOA. The cathode chamber electrolyte was 5 mmol / L sulfuric acid, and the other conditions were 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 specific results of the input voltage when the PFOA removal rate of the two systems reaches or approaches 99% are shown in Table 1; when the current density of the BDD anode 2 is 3mA / cm 2 Under the condition of 1.5h treatment time, the PFOA removal rates of the two systems reached or approached 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 1.78V vs. RHE, reducing the external input voltage of the system.

[0085] From the results in Table 1, we can see 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 the 0V vs. RHE of HER. From the results in Table 2, we can see that within the treatment time of 1.5h, the specific current density is 3mA / cm 2 Under the conditions of 3 mA / cm2, the traditional 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 was 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 has achieved 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 when achieving a PFOA degradation rate of 99%. 3 , compared to 1.57kWh / m 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. 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 were collected at a depth of 0 to 20 cm to remove soil animals, stones and plant litter. All soil samples were air-dried, ground and passed 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). 10 mL of the filtrate was added with 0.1 mol / L sodium sulfate as the electrolyte, and 1 mg / LPFOA was used as the target pollutant for 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 the cathode chamber reaction solution: 30 mL, cathode chamber electrolyte: 0.1 mol / L sodium sulfate and 10 mmol / L H2O2, initial pH of the 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 (1 cm × 2 cm) as the anode and a commercial platinum (Pt) sheet electrode (2 cm × 2 cm) 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. The other conditions remained the same as those of 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 2 h 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 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 by 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 achieving a PFOA removal rate of 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 in laboratory water. The electrodes and electrolytic cell 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 were collected at a depth of 0 to 20 cm to remove soil animals, stones and plant litter. All soil samples were air-dried, ground and passed 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). 10 mL of the filtrate was added with 0.1 mol / L sodium sulfate as the electrolyte, and 1 mg / LPFOA was used as the target pollutant for EO treatment in the electrolytic cell.

[0100] The EO-H2O2RR system constructed in Example 1 was used to treat actual PFOA-containing soil washing wastewater (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 the cathode chamber reaction solution: 30 mL, cathode chamber electrolyte: 0.1 mol / L sodium sulfate and 10 mmol / L H2O2, initial pH of the cathode chamber electrolyte: 6.2.

[0101] The above EO-H2O2RR system was used to treat PFOA in laboratory water (excluding soil dissolved organic matter). 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 the cathode chamber reaction solution: 30 mL, cathode chamber electrolyte: 0.1 mol / L sodium sulfate and 10 mmol / L H2O2, initial pH of the cathode chamber electrolyte: 6.2.

[0102] The EO-H2O2RR system was used to treat the above-mentioned actual soil washing wastewater and PFOA under laboratory water. 2 After 2 hours 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 EO-H2O2RR system was used to treat the actual PFOA-containing soil washing wastewater 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 anodic reaction solution pH before and after treatment of actual PFOA-containing soil washing wastewater using the EO-H2O2RR system

[0107]

[0108] The results, as shown in Table 4, show that the EO-H2O2RR system exhibits a high PFOA removal rate even in the presence of dissolved organic matter in actual soil washing wastewater. After 120 minutes of reaction, the PFOA degradation rate reached 95.3%, a mere 4.6% decrease compared to 99.9% under laboratory water conditions. This demonstrates the EO-H2O2RR system's ability to withstand interference from dissolved organic matter (such as coexisting humic acid) and its excellent PFOA removal rate in real-world wastewater applications. Table 5 shows that after treatment, the TOC content of the soil washing wastewater decreased from 120 mg / L to 2.46 mg / L, with a removal rate of 98.0%. The COD content decreased from 52 mg / L to 0.87 mg / L, with a removal rate of 98.3%. The PFOA concentration decreased from 1 mg / L to 0.047 mg / L, with a removal rate of 95.3%. The pH of the solution decreased from 6.2 to 5.9, with minimal changes. The treated soil washing wastewater meets the Class I discharge standard of the National Integrated 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 intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. 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; The cathode substrate is selected from any one of carbon felt, graphite felt or foam carbon; The catalytic layer is FeCo-NC; 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 were mixed in a solvent, precipitated and dried to obtain a precursor, which was then pyrolyzed under an argon atmosphere to obtain FeCo-NC. The electrolyte in the anode compartment is selected from 0.1 mol / L sodium sulfate or 5 mmol / L sulfuric acid. The electrolyte of the cathode chamber is selected from a mixed solution of 5 mmol / L sulfuric acid and 10 mmol / L H2O2 or a mixed solution of 0.1 mol / L sodium sulfate and 10 mmol / L hydrogen peroxide.

2. 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 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 h.

3. 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 preparation process of the cathode (3) is as follows: 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 (3).

4. The 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 feed ratio of FeCo-NC and 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).

5. 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.

6. Use 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 5, characterized in that: The water treatment system is used to degrade PFOA in soil washing wastewater.

7. 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 6, characterized in that: The degradation conditions include: the current density of the BDD anode (2) is 1-15 mA / cm 2 , 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 5 mmol / L sulfuric acid, the pH values ​​of the electrolytes in the anode chamber and the cathode chamber are controlled at 2.8 to 3.2.

Images