PFAS wastewater treatment process and treatment equipment thereof

Abstract

The invention relates to the field of PFAS wastewater treatment, in particular to a PFAS wastewater treatment process which comprises the following steps: step 1, electrochemical enrichment and preliminary degradation; step 2, catalytic wet air oxidation deep degradation; the treatment equipment for the PFAS wastewater treatment process is an adsorption column, the adsorption column comprises an outer cylinder, a sleeve is fixedly connected in the outer cylinder, an inner cylinder is mounted in the sleeve, an aeration unit is arranged on the lower surface of the outer cylinder to perform aeration in the outer cylinder, a water absorption ring pipe is laid at the inner bottom of the sleeve, and the water absorption ring pipe is fixedly connected with the outer cylinder. The inner cylinder is sleeved with the water absorption ring pipe, and a water inlet ring pipe is arranged at the inner bottom of the inner cylinder. Through the three-stage combination of electrochemical activation, catalytic deep degradation and physical purification, complete mineralization of PFAS molecules is realized, and simple phase transfer is not needed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of PFAS wastewater treatment, in particular to a PFAS wastewater treatment process and a treatment device thereof. BACKGROUND

[0002] Perfluoroalkyl substances (PFAS) are a class of persistent organic pollutants with high chemical stability and bioaccumulation. Due to their hydrophobic and oleophobic properties, they are widely used in metal surface coatings and rubber products, and also produce a large amount of industrial wastewater. Due to the high energy of C-F bond in their molecules, traditional water treatment technologies are difficult to effectively degrade them, resulting in their long-term existence in the environment, which poses a serious threat to the ecosystem and human health. Currently, the main treatment methods for PFAS include adsorption, advanced oxidation technology and membrane separation technology, among which advanced oxidation is still in the laboratory stage and has high cost.

[0003] Chinese patent CN120229846A discloses a method and device for removing polyfluoroalkyl substances from water bodies. It uses a three-stage synergistic process of "electrochemical oxidation-adsorption enrichment-membrane separation". Long-chain PFAS is decomposed into short-chain products by electrochemical oxidation, and then removed by modified biochar adsorption and nanofiltration membrane interception. Although this method improves the removal efficiency of PFAS to some extent, it still has the following problems: electrochemical oxidation mainly converts long-chain PFAS into short-chain products, which cannot be completely mineralized, and the degradation process may release fluoride ions, which may pose a risk of fluorine pollution. At the same time, the nanofiltration membrane of the above treatment device is easy to be contaminated, and needs to be cleaned, which increases the cost.

[0004] Chinese patent CN118388086A discloses a system and method for treating PFAS in landfill leachate. The system sequentially includes a treatment unit, a foam fractionation unit and a UV destruction unit. PFAS is concentrated by membrane separation and foam fractionation, and then degraded by UV photolysis. The UV destruction unit has limited degradation effect on short-chain PFAS, and is affected by water transparency, light source life and other factors, making it difficult to achieve complete mineralization of PFAS. The treatment effect of PFAS wastewater with high concentration and complex components is unstable, and the device relies on membrane and foam fractionation for physical concentration, which has high treatment load and high energy consumption.

[0005] Therefore, there is a need to develop a PFAS wastewater treatment process and a treatment device thereof that can completely mineralize PFAS in wastewater, adsorb and degrade fluoride ions to avoid secondary pollution, and have strong adaptability. SUMMARY

[0006] To solve the above technical problems, the PFAS wastewater treatment process and treatment equipment provided by the application can completely mineralize PFAS in wastewater, adsorb and degrade fluorine ions, avoid secondary pollution, and have strong adaptability, so as to solve the problems that the existing PFAS wastewater treatment technology cannot completely mineralize PFAS, the mineralization is not complete, fluorine ions may cause secondary pollution, and the treatment effect on high-concentration and complex-component PFAS wastewater is unstable.

[0007] To solve the above technical problems, the PFAS wastewater treatment process and treatment equipment provided by the application can completely mineralize PFAS in wastewater, adsorb and degrade fluorine ions, avoid secondary pollution, and have strong adaptability, so as to solve the problems that the existing PFAS wastewater treatment technology cannot completely mineralize PFAS, the mineralization is not complete, fluorine ions may cause secondary pollution, and the treatment effect on high-concentration and complex-component PFAS wastewater is unstable.

[0008] Step one, electrochemical activation and preliminary degradation: introducing the PFAS-containing wastewater into an electrochemical reactor, which is equipped with an anode and a cathode; electrolysis is carried out under a preset current density, so that strong oxidative free radicals are generated on the surface of the anode to preliminarily oxidize PFAS, and the cathode degrades PFAS molecules through reduction or generates hydrated electrons;

[0009] Step two, catalytic wet air oxidation deep degradation: pumping the wastewater treated in step one into a high-temperature and high-pressure reaction kettle; introducing an oxygen-containing gas into the reaction kettle and adding a bimetallic composite catalyst; carrying out the reaction under preset temperature and pressure conditions, and using the synergistic effect of the catalyst and the oxidant to completely break the carbon-fluorine bond in the PFAS molecules, so as to mineralize them into fluorine ions, carbon dioxide and water;

[0010] Step three, fluorine ion capture and water quality purification: introducing the water body degraded in step two into an adsorption column containing a fluorine ion-specific adsorbent; through adsorption, the fluorine ions in the water are efficiently captured, so that the water quality of the final effluent meets the discharge standard.

[0011] Further, before step one, the pH value of the PFAS-containing wastewater is adjusted, and the initial pH value of the wastewater is adjusted to 3-9.

[0012] Further, the anode in step one is a boron-doped diamond electrode, and the cathode is a MOS structure electrode or a high-efficiency hydrogen evolution electrode; the current density ranges from 10 to 100 mA / cm2.

[0013] Further, the bimetallic composite catalyst in step two is one of iron-copper or iron-cerium composite oxides supported on mesoporous carbon material, the molar ratio of the metals is 1:1 to 5:1, and the specific surface area of the mesoporous carbon carrier is greater than 500 m2 / g; the temperature in step two is 150-250°C, the pressure range is 2-5 MPa, and the reaction time is 30-120 minutes.

[0014] Further, the adsorbent in step three is modified hydrotalcite or bone charcoal; the adsorbent can be regenerated by elution with acid-base solution after saturation, realizing recycling.

[0015] In order to solve the above technical problems, the application further provides a treatment device for the PFAS wastewater treatment process, which is the adsorption column in step three, the adsorption column comprises an outer cylinder, a sleeve is fixedly connected in the outer cylinder, an inner cylinder is installed in the sleeve, a water inlet hole is formed in the lower end of the outer cylinder and an aeration unit for aerating the outer cylinder is arranged, a water suction ring pipe is connected to the bottom of the sleeve, a water inlet ring pipe is arranged at the bottom of the inner cylinder, the water inlet ring pipe communicates with the water suction ring pipe, a water outlet pipe is installed at the upper end of the inner cylinder, a plurality of disc plates for placing adsorbents are fixedly and separately connected in the middle of the inner cylinder, and through holes are formed in the disc plates.

[0016] Further, the aeration unit comprises a circular ring-shaped aeration ring, a plurality of insertion pipes are fixedly connected to the upper surface of the aeration ring, the upper ends of the insertion pipes extend to the inside of the outer cylinder through the lower surface of the outer cylinder, an input pipe is connected to the aeration ring, and the end of the input pipe is connected to the output end of an aerator.

[0017] Further, the inner bottom of the sleeve is fixedly connected with a short column, the inner cylinder is arranged on the short column, the water suction ring pipe is connected with a horizontal pipe in the diameter direction, the horizontal pipe is connected with a vertical pipe through a tee joint at the center of the horizontal pipe, the vertical pipe penetrates the center of the inner cylinder and extends to the inside of the inner cylinder, a water pump is installed at the end of the vertical pipe, and the output end of the water pump is connected with the water inlet ring pipe through a water pipe.

[0018] Further, the bottom of the disc plate located at the lowermost position in the inner cylinder is provided with a plurality of feet, the height of the feet is greater than the installation height of the water pump and the water inlet ring pipe, the outer surface of the upper end of the inner cylinder is fixedly connected with an anti-overflow sleeve, the height of the outer edge of the anti-overflow sleeve is higher than the top end of the inner cylinder, and one side of the anti-overflow sleeve is fixedly connected with a flow guide groove plate.

[0019] Further, the height of the sleeve is less than the height of the outer cylinder, the height of the inner cylinder is greater than the height of the outer cylinder, and a plurality of notches are formed in the sleeve at the port along the circumference and are spaced apart.

[0020] Compared with the prior art, the application has the following advantages:

[0021] 1. This invention utilizes a two-stage wastewater treatment process combining electrochemical activation and catalytic deep degradation. Electrochemical enrichment and preliminary degradation, under the synergistic action of the anodic and cathodic electrodes, disrupt the PFAS structure. Then, catalytic wet air oxidation, under high temperature, high pressure, and the action of a bimetallic catalyst, thoroughly mineralizes PFAS into CO2, water, and fluoride ions. This achieves complete mineralization of PFAS molecules, rather than a simple phase transfer. Both long-chain and emerging short-chain PFAS can be effectively decomposed, fundamentally eliminating the accumulation of intermediate products and the risk of secondary pollution. The removal and mineralization rates are significantly improved. Finally, physical purification is achieved through a fluoride ion-specific adsorption column, efficiently capturing fluoride ions. Once captured, the fluoride ions can be recycled or stabilized, avoiding the generation of secondary pollutants such as waste adsorbents and membrane concentrates. This ensures that the effluent is free of secondary pollution, improves the system's environmental safety, and forms a complete "degradation-mineralization-defluorination" chain, making the PFAS degradation pathway more complete and thorough.

[0022] 2. This invention reduces the burden on subsequent catalytic oxidation stage units through electrochemical pretreatment. Preliminary degradation and molecular activation significantly lower the energy barrier for CF bond breaking, enabling the catalytic oxidation stage to operate efficiently under milder temperature and pressure conditions, thereby greatly reducing the overall system's equipment investment and operating energy consumption.

[0023] 3. The wastewater treatment process of this invention combines electrochemical free radical oxidation and catalytic wet air oxidation to break bonds, forming a dual degradation pathway. It exhibits excellent treatment effects on various PFAS substances with different structures and chain lengths, and is especially suitable for high-concentration, recalcitrant PFAS wastewater, with broader application prospects.

[0024] 4. The wastewater treatment equipment of the present invention generates bubbles and foam through aeration, which enriches hydrophobic PFAS and other pollutants at the gas-liquid interface to form a foam layer, thereby achieving preliminary concentration and separation of pollutants. This improves the feed concentration and treatment efficiency of subsequent adsorption units. The wastewater is then adsorbed by the inner cylinder packing, achieving dual treatment and improving the removal rate of PFAS. In particular, it has a good effect on difficult-to-treat short-chain PFAS. The concentric design of the outer cylinder, sleeve, and inner cylinder forms a complete circulating treatment system. Wastewater enters from the outer cylinder, the foam liquefies in the sleeve, and finally is purified through the inner cylinder packing layer, achieving continuous treatment without intermittent operation.

[0025] 5. The foam enrichment technology of the wastewater treatment equipment of the present invention increases the concentration of PFAS, reduces the amount of water to be treated, and also reduces the amount of adsorbent used, thus lowering operating costs. The design of the inner cylinder being taller than the outer cylinder and the outer cylinder being shorter than the inner cylinder optimizes foam collection and water flow path, improving the enrichment efficiency of PFAS. This design allows for direct placement in wastewater for treatment without the need for a dedicated treatment tank, reducing infrastructure investment and broadening its applicability. Attached Figure Description

[0026] Figure 1 The external structure of the wastewater treatment equipment in this invention Figure One .

[0027] Figure 2 The appearance structure of the wastewater treatment equipment in this invention Figure Two .

[0028] Figure 3 This is a cross-sectional view of the wastewater treatment equipment in this invention.

[0029] Figure 4 This is a cross-sectional view of the assembly of the outer cylinder and the sleeve in this invention.

[0030] Figure 5 This is a cross-sectional view of the assembly of the sleeve and inner cylinder in this invention.

[0031] Figure 6 This is a structural diagram of the connection between the water suction ring pipe and the water inlet ring pipe in this invention.

[0032] In the diagram: 101, outer cylinder; 1011, aeration ring; 1012, insertion pipe; 1013, input pipe; 102, sleeve; 1021, slot; 103, inner cylinder; 1031, gasket; 1032, anti-overflow sleeve; 1033, guide trough plate; 1034, outlet pipe; 104, suction ring pipe; 1041, water pump; 1042, connecting pipe; 1043, inlet ring pipe. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings.

[0034] Example 1:

[0035] A PFAS wastewater treatment process and equipment, comprising the following steps:

[0036] Step 1, Electrochemical Enrichment and Preliminary Degradation: PFAS-containing wastewater is introduced into an electrochemical reactor equipped with an anode and cathode. Electrolysis is performed under preset current density and voltage conditions, generating highly oxidizing free radicals on the anode surface to initially oxidize PFAS. Simultaneously, the cathode degrades PFAS molecules through reduction or the generation of hydrated electrons. This step is crucial for "activation." A boron-doped diamond electrode is chosen as the anode due to its extremely high oxygen evolution potential, which efficiently generates highly oxidizing hydroxyl radicals instead of producing byproducts like chlorine. These hydroxyl radicals can attack the hydrophilic ends (such as carboxyl groups) of PFAS molecules, achieving decarboxylation or opening the molecular chain, making them easier for subsequent treatment. The cathode is chosen to generate hydrated electrons to attack PFAS via the reduction pathway, forming a redox synergistic effect and improving preliminary degradation efficiency. Therefore, a MOS structure electrode is used. The current density is 45 mA / cm², and the initial pH of the wastewater is adjusted to 7.

[0037] Step 2, Catalytic Wet Air Oxidation Deep Degradation: The wastewater treated in Step 1 is pumped into a high-temperature, high-pressure reactor; oxygen-containing gas is introduced into the reactor, and a bimetallic composite catalyst is added; the reaction is carried out under preset temperature and pressure conditions, utilizing the synergistic effect of the catalyst and oxidant to completely break the carbon-fluorine bonds in the PFAS molecules, mineralizing them into fluoride ions, carbon dioxide, and water; the electrochemically "activated" wastewater enters the catalytic wet air oxidation deep degradation unit. The key here is the bimetallic catalyst, which is an iron-copper composite oxide supported on mesoporous carbon material, iron-based... The catalyst exhibits good activity in wet oxidation. The introduction of a second metal (copper) can significantly enhance the catalyst's redox ability and attack on CF bonds through electron transfer and the formation of lattice defects. The mesoporous carbon support provides a large reaction interface. Electrochemical pretreatment significantly reduces the temperature and pressure required for the catalytic oxidation stage, which is the core of the energy reduction achieved by this invention. The bimetallic composite catalyst has a metal molar ratio of 3:1, a support specific surface area of ​​580 m² / g, and a reaction temperature range of 250°C, a pressure range of 4 MPa, and a reaction residence time of 30 minutes.

[0038] Step 3, Fluoride Ion Capture and Water Purification: The water degraded in Step 2 is introduced into an adsorption column containing a fluoride ion-specific adsorbent; fluoride ions in the water are efficiently captured through adsorption, ensuring that the final effluent meets discharge standards; modified hydrotalcite with high selectivity for fluoride ions is selected as the adsorbent for capture, ensuring the environmental safety of the final effluent; the captured fluoride ions can be recycled or solidified in the form of stable calcium fluoride; after the fluoride ion adsorbent is saturated, it can be eluted and regenerated using acid and alkali solutions for recycling.

[0039] To address the aforementioned technical solutions, this application provides a treatment device for a PFAS wastewater treatment process. The treatment device is an adsorption column, such as... Figure 3 As shown, the adsorption column includes an outer cylinder 101. The lower end of the outer cylinder 101 has a circumferentially distributed water inlet. The outer cylinder 101 serves to support and accommodate the internal components. The circumferentially distributed water inlet allows raw water to enter the system uniformly. A sleeve 102 is fixedly connected inside the outer cylinder 101, and an inner cylinder 103 is installed inside the sleeve 102. The outer cylinder 101, sleeve 102, and inner cylinder 103 are concentric. An aeration unit is provided on the lower surface of the outer cylinder 101 to aerate the water inside. In this embodiment, the design of the sleeve 102 creates an annular channel between it and the outer cylinder 101, promoting uniform water distribution and sufficient aeration. The inner cylinder 103 is the main area for containing the adsorption medium. Water completes the main adsorption process when passing through the inner cylinder 103. Figure 2 In this embodiment, the aeration unit includes an aeration ring 1011, and multiple insertion tubes 1012 are circumferentially connected to the aeration ring 1011. The ends of the insertion tubes 1012 extend through the lower surface of the outer cylinder 101 into the interior of the outer cylinder 101. The insertion tubes 1012 are inserted around the sleeve 102. An input pipe 1013 is connected to the aeration ring 1011, and an aerator is externally connected to the end of the input pipe 1013. In this embodiment, the aerator supplies air to the aeration ring 1011 through the input pipe 1013, and the gas then enters the interior of the outer cylinder 101 through the insertion tubes 1012. In this embodiment, aeration is combined with chemical treatment. Aeration forms a gas-liquid mixture, which enhances water flow disturbance and promotes the interaction between the adsorbate and the absorbent. The adsorbent comes into contact with the water and forms bubbles, which float the pollutants. A water-absorbing ring pipe 104 is laid at the bottom of the inner sleeve 102 and is fitted over the inner cylinder 103. In this embodiment, the water-absorbing ring pipe 104 is used to collect and guide the foam water. The ring design ensures that the water flow is evenly distributed and avoids local short circuits. A water-inlet ring pipe 1043 is provided at the bottom of the inner cylinder 103 and is connected to the water-absorbing ring pipe 104. In this embodiment, the water-absorbing ring pipe 104 introduces the collected water into the inner cylinder 103 for deep treatment. The ring design also ensures that the water flow is evenly distributed. A water outlet pipe 1034 is installed at the top of the inner cylinder 103 for discharging the treated clean water.

[0040] It is worth noting that in this embodiment, the height of the sleeve 102 is less than the height of the outer cylinder 101, which facilitates the entry of foam. The height of the inner cylinder 103 is greater than the height of the outer cylinder 101 to avoid secondary pollution of the purified water. Furthermore, a groove is formed around the upper end of the sleeve 102. When the foam enters the sleeve 102 through the groove, it will break and become liquid again due to the narrowing path when passing through the groove, which is conducive to extraction.

[0041] exist Figure 5 and Figure 6In the sleeve 102, a short column is provided at the bottom of the inner cylinder, and the inner cylinder 103 is placed on the short column. The short column serves as a support structure for the inner cylinder 103, ensuring that the inner cylinder 103 and the bottom of the sleeve 102 maintain a certain distance, forming an installation cavity. This provides installation space for the horizontal pipe along the diameter direction of the suction ring pipe 104. The center of the water pipe is connected to the vertical pipe through a tee. The vertical pipe passes through the center of the inner cylinder 103 and extends into the inner cylinder 103. The tee connects the horizontal collection system formed by the horizontal pipe and the vertical conveying system formed by the vertical pipe, allowing the liquid to be transported from below to the upper part of the inner cylinder 103, forming a complete circulation path. A water pump 1041 is installed at the end of the vertical pipe. The output end of the water pump 1041 is connected to the inlet ring pipe 1043 through a water pipe. The water pump 1041 provides the circulation power for the system, pumping the liquid collected at the bottom to the inlet ring pipe 1043 at the upper part of the inner cylinder 103, where it is evenly sprayed out.

[0042] exist Figure 4 and Figure 5 In the inner cylinder 103, multiple gaskets 1031 are provided. These gaskets 1031 provide a support platform for the packing material within the inner cylinder 103 and can be used to separate different treatment stages. The lowest gasket 1031 in the inner cylinder 103 has multiple supports on its lower surface. The height of these supports is greater than the installation height of the water pump 1041 and the inlet ring pipe 1043. These supports lift the lowest gasket 1031, thus providing space for the installation of the water pump 1041. Figure 1 In order to prevent the water outlet pipe 1034 from not pumping water in time, an anti-overflow sleeve 1032 is fixedly connected to the upper outer surface of the inner cylinder 103 in this embodiment. The side height of the anti-overflow sleeve 1032 is higher than the port of the inner cylinder 103. The anti-overflow sleeve 1032 prevents liquid from overflowing from the inner cylinder 103 when the water level is high. A guide plate 1033 is provided on the side of the anti-overflow sleeve 1032, and the water entering the anti-overflow sleeve 1032 is discharged through the guide plate 1033.

[0043] In use, the outer cylinder 101 is placed in wastewater, with the wastewater level lower than the height of the sleeve 102. The wastewater flows through the inlet to level the levels inside and outside the outer cylinder 101. The aeration unit aerates the wastewater in the outer cylinder 101, generating foam. The foam accumulates on the wastewater surface and flows into the sleeve 102, where it liquefies. The foam-water in the sleeve 102 is pumped by the water pump 1041 from the suction ring pipe 104 into the inlet ring pipe 1043, and then sprayed from the inlet ring pipe 1043 into the inner cylinder 103. The foam-water flows upward through the packing material in the inner cylinder 103, is purified, and then discharged through the outlet pipe 1034. The final effluent PFAS concentration is <0.5 μg / L (ND*), and the total PFAS removal rate is >99.9%; the final effluent fluoride ion concentration is 2.1 μg / L.

[0044] Example 2:

[0045] The difference between this embodiment and Example 1 is as follows: In this embodiment, the initial pH of the wastewater is adjusted to 3 in step one, the current density is 10 mA / cm², and the bimetallic catalyst in step two is an iron-copper composite oxide supported on mesoporous carbon material with a metal molar ratio of 1:1, a carrier specific surface area of ​​600 m² / g, a reaction temperature range of 185°C, a pressure range of 5 MPa, and a reaction residence time of 120 minutes. The final effluent PFAS concentration is <0.5 μg / L (ND*), the total PFAS removal rate is >99.9%, and the final effluent fluoride ion concentration is 2.3 μg / L.

[0046] Example 3:

[0047] The difference between this embodiment and Embodiment 1 is as follows:

[0048] In this embodiment, the initial pH of the wastewater in step one was adjusted to 9, and the current density was 75 mA / cm². In step two, the bimetallic composite catalyst was an iron-cerium composite oxide supported on mesoporous carbon material with a metal molar ratio of 5:1 and a carrier specific surface area of ​​560 m² / g. The reaction temperature range was 150°C, and the reaction residence time was 60 minutes. The final effluent PFAS concentration was <0.5 μg / L (ND*), and the total PFAS removal rate was >99.9%; the final effluent fluoride ion concentration was 2.3 μg / L.

[0049] Example 4:

[0050] The difference between this embodiment and Embodiment 1 is as follows:

[0051] In this embodiment, the cathode in step one is a high-efficiency hydrogen evolution electrode with a current density of 100 mA / cm². In step two, the bimetallic catalyst is an iron-copper composite oxide supported on mesoporous carbon material with a metal molar ratio of 2:1, a carrier specific surface area of ​​600 m² / g, a reaction temperature range of 200°C, a pressure range of 2 MPa, and a reaction residence time of 85 minutes. In step three, the adsorbent is bone char. The final effluent PFAS concentration is <0.5 μg / L (ND*), and the total PFAS removal rate is >99.9%; the final effluent fluoride ion concentration is 2.5 μg / L.

[0052] Comparative Example 1:

[0053] The difference between this comparative example and Example 1 is as follows:

[0054] This comparative example only treated PFAS wastewater using steps one and three, omitting the catalytic wet air oxidation deep degradation step. The final effluent PFAS concentration was 75 μg / L, with a total PFAS removal rate of 85.2%; the final effluent fluoride ion concentration was 18 μg / L. This comparative example shows that the lack of the catalytic wet air oxidation deep degradation step two resulted in incomplete PFAS degradation. Although fluoride ion release was low, the TOC removal rate was only 38.6%, indicating a high TOC content and the presence of a large number of intermediate products. This demonstrates the incompleteness of single electrochemical treatment.

[0055] Comparative Example 2:

[0056] The difference between this comparative example and Example 1 is as follows:

[0057] This comparative example only treated PFAS wastewater using steps one and two, omitting fluoride ion capture and water purification steps. The final effluent PFAS concentration was <0.5 μg / L (ND*), and the total PFAS removal rate was >99.9%; the final effluent fluoride ion concentration was 184 μg / L. This comparative example clearly shows that after steps one and two, due to the lack of the synergistic degradation of "electrochemical activation + catalytic deep degradation" in step two, PFAS was essentially completely degraded. However, the absence of the fluoride ion capture and water purification step three resulted in a severe excess of fluoride ions, easily causing secondary pollution.

[0058] Comparative Example 3:

[0059] This comparative example uses a method and apparatus for removing polyfluorinated and perfluorinated compounds (PFAS) from water, as disclosed in document CN120229846A. This method employs a three-stage synergistic process of "electrochemical oxidation—adsorption enrichment—membrane separation" to treat PFAS wastewater. The final effluent PFAS concentration was 26 μg / L, with a total PFAS removal rate of 94.8%; the final effluent fluoride ion concentration was 38 μg / L. This comparative example shows that mineralization is incomplete, PFAS degradation is incomplete, unknown fluoride-containing intermediates are present, and the TOC removal rate only reaches 81.4%. Therefore, the treatment thoroughness is still inferior to the technical solution described in this application.

[0060] The specific experimental data of Examples 1-4 and Comparative Examples 1-3 are shown in Tables 1, 2 and 3 below.

[0061] Table 1 Key process parameters for each experimental group

[0062]

[0063] Table 2. PFAS concentration and removal rate in the effluent of each process stage

[0064]

[0065] In Table 2 above, ND indicates: below the detection limit (0.5 μg / L).

[0066] Table 3. Fluoride ion concentration and mineralization effect in the final effluent

[0067]

[0068] In Table 3 above, the theoretical maximum fluoride ion represents the total amount of fluoride ions released assuming all PFAS molecules in the raw water are completely mineralized.

[0069] The total PFAS removal rate of Examples 1-4 was all >99.9%, and the PFAS concentration in the effluent was below the detection limit, which was significantly better than Comparative Example 3 (81.4%). At the same time, it can be seen from Comparative Example 1 that the PFAS degradation was incomplete in Comparative Example 1 because the catalytic wet air oxidation deep degradation step was not performed, which proved the incompleteness of single electrochemical treatment. This shows that the "electrochemical activation + catalytic deep degradation" synergistic degradation pathway of the present invention is far superior to the "electrochemical oxidation - adsorption enrichment - membrane separation" pathway in the prior art in terms of completely destroying the PFAS molecular structure.

[0070] Examples 1-4, through the fluoride ion capture process in step three, utilize the final adsorption unit to reduce the fluoride ion concentration to 2.1-2.5 μg / L, which is far lower than the fluoride ion concentration of 185.5 mg / L in Comparative Example 2. This demonstrates the necessity and effectiveness of the fluoride ion capture process. Without this process, there may be serious secondary fluoride ion pollution problems during the treatment process.

Claims

1. A PFAS wastewater treatment process, characterized in that: Includes the following steps: Step 1, Electrochemical Activation and Preliminary Degradation: Wastewater containing PFAS is introduced into an electrochemical reactor equipped with an anode and a cathode; electrolysis is carried out under a preset current density condition, so that strong oxidizing free radicals are generated on the anode surface to preliminarily oxidize PFAS, while the cathode degrades PFAS molecules in a coordinated manner through reduction or the generation of hydrated electrons. Step 2, catalytic wet air oxidation deep degradation: The wastewater treated in Step 1 is pumped into a high-temperature and high-pressure reactor; oxygen-containing gas is introduced into the reactor and a bimetallic composite catalyst is added; the reaction is carried out under preset temperature and pressure conditions, and the carbon-fluorine bond in the PFAS molecule is completely broken by the synergistic effect of the catalyst and oxidant, so that it is mineralized into fluoride ions, carbon dioxide and water. Step 3, Fluoride Ion Capture and Water Purification: The water that has been degraded in Step 2 is introduced into an adsorption column containing a fluoride ion-specific adsorbent, where fluoride ions are efficiently captured through adsorption.

2. The PFAS wastewater treatment process according to claim 1, characterized in that: Before starting step one, the pH of the PFAS-containing wastewater is adjusted to 3-9.

3. The PFAS wastewater treatment process according to claim 1, characterized in that: In step one, the anode is a boron-doped diamond electrode, and the cathode is a MOS structure electrode or a high-efficiency hydrogen evolution electrode; the current density range is 10-100 mA / cm².

4. The PFAS wastewater treatment process according to claim 1, characterized in that: The bimetallic composite catalyst mentioned in step two is one of iron-copper or iron-cerium composite oxides supported on mesoporous carbon material, with a metal molar ratio of 1:1 to 5:1 and a specific surface area of ​​the mesoporous carbon support greater than 500 m² / g; the temperature mentioned in step two is 150-250°C, the pressure range is 2-5 MPa, and the reaction time is 30-120 minutes.

5. The PFAS wastewater treatment process according to claim 1, characterized in that: The adsorbent mentioned in step three is modified hydrotalcite or bone char; after the adsorbent is saturated, it can be eluted and regenerated by acid or alkali solution to achieve recycling.

6. A treatment device based on the PFAS wastewater treatment process according to any one of claims 1-5, characterized in that: The treatment device is the adsorption column in step three above. The adsorption column includes an outer cylinder (101), a sleeve (102) is fixedly connected inside the outer cylinder (101), and an inner cylinder (103) is installed inside the sleeve (102). The lower end of the outer cylinder (101) is provided with a water inlet hole and an aeration unit for aeration into the outer cylinder (101). The bottom of the sleeve (102) is connected with a water suction ring pipe (104), and the bottom of the inner cylinder (103) is provided with a water inlet ring pipe (1043). The water inlet ring pipe (1043) is connected to the water suction ring pipe (104). The upper end of the inner cylinder (103) is provided with a water outlet pipe (1034). Multiple pads (1031) for placing adsorbent are fixedly connected at intervals in the middle of the inner cylinder (103). The pads (1031) are provided with through holes.

7. The treatment equipment for the PFAS wastewater treatment process according to claim 6, characterized in that: The aeration unit includes an aeration ring (1011) with a circular structure. Multiple insertion tubes (1012) are fixedly connected to the upper surface of the aeration ring (1011). The upper end of the insertion tube (1012) extends through the lower surface of the outer cylinder (101) into its interior. An input tube (1013) is connected to the aeration ring (1011). The end of the input tube (1013) is connected to the output end of the aerator.

8. The treatment equipment for the PFAS wastewater treatment process according to claim 6, characterized in that: A short column is fixedly connected to the bottom of the sleeve (102), the inner cylinder (103) is placed on the short column, the water suction ring pipe (104) is connected to a horizontal pipe along the diameter direction, the center of the horizontal pipe is connected to a vertical pipe through a tee, the vertical pipe passes through the center of the inner cylinder (103) and extends into its interior, a water pump (1041) is installed at the end of the vertical pipe, and the output end of the water pump (1041) is connected to the water inlet ring pipe (1043) through a water pipe.

9. The treatment equipment for the PFAS wastewater treatment process according to claim 8, characterized in that: The bottom of the pad (1031) located at the bottom of the inner cylinder (103) is provided with multiple support feet. The height of the support feet is greater than the installation height of the water pump (1041) and the inlet ring pipe (1043). An overflow sleeve (1032) is fixedly connected to the upper outer surface of the inner cylinder (103). The outer edge of the overflow sleeve (1032) is higher than the top of the inner cylinder (103). A flow guide plate (1033) is fixedly connected to one side of the overflow sleeve (1032).

10. The treatment equipment for the PFAS wastewater treatment process according to claim 6, characterized in that: The height of the sleeve (102) is less than the height of the outer cylinder (101), the height of the inner cylinder (103) is greater than the height of the outer cylinder (101), and the sleeve (102) has a plurality of slots spaced circumferentially at the upper end.

Images