Method and device for removing polyfluorinated perfluorides in water body

Abstract

The invention discloses a method and device for removing polyfluorinated perfluorides in a water body, and the method comprises the following steps: 1, pretreatment: removing large-particle impurities in the water body to be treated through a grid, then feeding the water body to be treated into a pH adjusting tank, and adding an acidic mixed solution to reduce the pH value to 4.0; 2, electrochemical oxidation: enabling the water body to flow into an electrochemical oxidation module, and reacting for 20-40 minutes under the voltage of 10V; when the method is implemented, long-chain PFAS is decomposed into short-chain products through three-stage cooperation of electrochemical oxidation, adsorption enrichment and membrane separation, so that subsequent removal of the short-chain PFAS is facilitated, the removal rate can be improved, the whole process is simpler compared with the prior art, and a large amount of cost is saved; the boron-doped diamond anode and the iron-cobalt bimetallic cathode are combined, and the modified biochar adsorbent is combined, so that the PFAS degradation rate is increased, and meanwhile, the electrode loss can be reduced.

Description

Technical Field

[0001] The present application relates to the technical field of water treatment, and specifically relates to a method and device for removing polyfluoro / perfluorinated compounds from water bodies. Background Art

[0002] As a class of persistent organic pollutants with high stability and recalcitrance to degradation, polyfluoro / perfluorinated compounds (PFAS) pose a significant threat to the environment and human health. These compounds are widely distributed in industrial wastewater discharges, surface water bodies, and groundwater resources. Due to the special nature of their chemical structures, once they enter the environment, they are difficult to be naturally eliminated. Long-term accumulation can cause irreversible damage to the ecosystem and affect human health through the food chain.

[0003] Currently, although there are many treatment technologies for PFAS, they all have limitations to varying degrees. Traditional adsorption methods, such as using activated carbon or resin for adsorption, can effectively enrich PFAS in the short term. However, the regeneration process of the adsorption materials is complex and costly. More importantly, this method cannot achieve the complete decomposition of pollutants, but only transfers the problem from one link to another. On the other hand, advanced oxidation technologies, such as ozone oxidation and photocatalytic oxidation, although they show good degradation effects on some short-chain PFAS, the degradation efficiency for long-chain PFAS is greatly reduced, and more toxic short-chain intermediate products may be generated during the degradation process, which instead exacerbates the environmental risks. Therefore, developing new treatment technologies that are efficient, environmentally friendly, and can completely decompose PFAS has become an urgent task in the current field of environmental science research. Summary of the Invention

[0004] To this end, the present application provides a method and device for removing polyfluoro / perfluorinated compounds from water bodies to solve the problems of complex process, high cost, and low degradation efficiency existing in the prior art.

[0005] To achieve the above object, the present application provides the following technical solutions:

[0006] In a first aspect, a method for removing polyfluoro / perfluorinated compounds from water bodies includes the following steps.

[0007] In the first step, pretreatment: the water body to be treated enters the pH adjustment tank after removing large particulate impurities through a grid, and an acidic mixture is added to lower the pH to 4.0.

[0008] In the second step, electrochemical oxidation: the water body flows into the electrochemical oxidation module and reacts at a voltage of 10V for 20 - 40 minutes. Hydroxyl radicals and sulfate radicals are generated at the anode to decompose long-chain PFAS into short-chain products.

[0009] Step 3: Adsorption and enrichment. The water body after electrochemical treatment passes through the adsorption module, and the modified biochar adsorbs the residual short-chain PFAS. After adsorption saturation, the regeneration program is triggered.

[0010] Step 4: Membrane separation. The water body after adsorption is intercepted by the nanofiltration membrane for PFAS that has not been degraded. The concentrated liquid is returned to the electrochemical module for cyclic treatment, and the produced water meets the standards for discharge.

[0011] Step 5: Adsorbent regeneration. The saturated biochar enters the pyrolysis furnace and is pyrolyzed for 2 hours in a nitrogen atmosphere at 500 °C to decompose the adsorbed PFAS. Fe3O4 is recovered by magnetic separation and resulfonated.

[0012] Step 6: Intelligent regulation. The PFAS concentration is monitored in real time by an on-line detector. If the concentration at the membrane outlet exceeds 10 ng / L, the current density is increased to 15 mA / cm2 and the membrane operating pressure is increased to 1.2 MPa.

[0013] Preferably, the specific parameters of the electrochemical oxidation in Step 2 are as follows:

[0014] The current density is 10 - 15 mA / cm2;

[0015] The electrolyte of the electrolytic solution is Na2SO4 with a concentration of 0.1 mol / L;

[0016] During the reaction process, the water temperature is controlled ≤ 35 °C.

[0017] A device for removing polyfluoro / perfluorinated compounds from water bodies includes a pretreatment unit, an electrochemical oxidation module, an adsorption module, a membrane separation component, an adsorbent regeneration device, and a monitoring and control system;

[0018] The pretreatment unit includes a grille and a pH adjustment tank. The grille is used to remove suspended solids, and the pH adjustment tank is used to adjust the pH of the water body to 3.0 - 5.0;

[0019] The electrochemical oxidation module is equipped with a boron-doped diamond anode and an iron-cobalt bimetallic cathode. The plate spacing in the electrochemical oxidation module is 5 - 10 mm, and the working voltage is 5 - 15 V;

[0020] The adsorption module is filled with a modified biochar adsorbent. The modified biochar adsorbent is prepared by loading Fe3O4 and sulfonation treatment on straw biochar, with a particle size of 0.5 - 2 mm and a packing density of 300 - 500 g / L;

[0021] The membrane separation component uses a polyvinylidene fluoride nanofiltration membrane resistant to organic pollution, with a membrane pore size of 1 - 2 nm and an operating pressure of 0.5 - 1.5 MPa;

[0022] The adsorbent regeneration device includes a pyrolysis furnace and a magnetic separator. The pyrolysis temperature of the pyrolysis furnace is 400 - 600 °C, and the magnetic separator is used to separate Fe3O4 from the regenerated biochar.

[0023] The monitoring and control system includes an on-line PFAS detector, a current regulator and a membrane pressure controller, and the on-line PFAS detector is interlocked with the membrane pressure controller through a PLC.

[0024] Preferably, the surface of the boron-doped diamond anode of the electro-chemical oxidation module has a microporous structure with a pore diameter of 10-50 μm, the mass ratio of iron to cobalt of the iron-cobalt bimetallic cathode is 3:1, and the surface of the iron-cobalt bimetallic cathode is coated with a carbon nanotube conductive layer.

[0025] Preferably, the Fe3O4 loading of the modified biochar adsorbent is 8%-12%, and the sulfonation treatment is carried out by reacting concentrated sulfuric acid with biochar at a mass ratio of 1:2 at 80 °C for 2 hours.

[0026] Preferably, the surface of the polyvinylidene fluoride nanofiltration membrane of the membrane separation module has a polyethyleneimine hydrophilic coating with a coating thickness of 50-100 nm.

[0027] Preferably, nitrogen is introduced into the pyrolysis furnace of the adsorbent regeneration device for protection. After the biochar after pyrolysis is separated from Fe3O4 by a magnetic separator, it is resulfonated and returned to the adsorption module.

[0028] Preferably, the on-line PFAS detector in the monitoring and control system adopts ultra-high performance liquid chromatography-mass spectrometry technology, and the detection limit is 0.1 ng / L.

[0029] Preferably, a mixed solution of sulfuric acid and citric acid is added to the pH adjustment tank of the pretreatment unit, the volume ratio of the two is 2:1, and the pH adjustment accuracy is ±0.2.

[0030] Compared with the prior art, the present application has at least the following beneficial effects:

[0031] 1. Through the three-stage coordination of "electrochemical oxidation-adsorption enrichment-membrane separation", long-chain PFAS is decomposed into short-chain products for subsequent removal of short-chain PFAS, which can improve the removal rate, and the whole process is simpler than the prior art, saving a large amount of costs;

[0032] 2. The combination of a boron-doped diamond anode and an iron-cobalt bimetallic cathode, combined with a modified biochar adsorbent, can improve the PFAS degradation rate while reducing electrode loss. Description of the Drawings

[0033] To more intuitively illustrate the prior art and this application, exemplary drawings are given below. It should be understood that the specific shapes and structures shown in the drawings generally should not be regarded as limiting conditions when implementing this application; for example, those skilled in the art are capable of making routine adjustments or further optimizations to the addition / deletion / attribution division of certain units (components), specific shapes, positional relationships, connection methods, dimensional proportional relationships, etc. based on the technical concept disclosed in this application and the exemplary drawings.

[0034] Figure 1 This is a flowchart of a method for removing polyfluoro and perfluoroalkyl substances from water provided by this application. Detailed implementation manners

[0035] The following further details this application through specific embodiments in conjunction with the drawings.

[0036] As Figure 1 shown, a method for removing polyfluoro and perfluoroalkyl substances from water includes the following steps.

[0037] First step, pretreatment: The water to be treated enters the pH adjustment tank after removing large particulate impurities through a grille, and an acidic mixed solution is added to lower the pH to 4.0. At this time, the generation rate of OH - radicals at the electrochemical anode is the highest.

[0038] Second step, electrochemical oxidation: The water flows into the electrochemical oxidation module and reacts for 20 - 40 minutes at a voltage of 10V. Hydroxyl radicals and sulfate radicals are generated at the anode, decomposing long-chain PFAS into short-chain products. At a voltage of 10V, the C-F bond of long-chain PFAS (such as PFOA) breaks, generating short-chain products.

[0039] Third step, adsorption and enrichment: The water after electrochemical treatment passes through the adsorption module. The modified biochar in the adsorption module adsorbs the residual short-chain PFAS. After adsorption saturation, the regeneration program is triggered. The modified biochar preferentially adsorbs short-chain PFAS to avoid membrane fouling.

[0040] Fourth step, membrane separation: The water after adsorption is intercepted by a nanofiltration membrane for the PFAS that has not been degraded. The concentrated solution returns to the electrochemical module for cyclic treatment, and the water that has not been intercepted meets the discharge standard. The concentrated solution is cyclically treated to ensure that the effluent meets the standard.

[0041] Fifth step, adsorbent regeneration: The saturated biochar in the adsorption module enters a pyrolysis furnace and is pyrolyzed for 2 hours in a nitrogen atmosphere at 500°C to decompose the adsorbed PFAS, and Fe3O4 is recovered by magnetic separation and re-sulfonated. The PFAS is decomposed through pyrolysis, and the pyrolysis products (such as calcium fluoride) can also be used as industrial raw materials.

[0042] Step 6: Intelligent regulation. The PFAS concentration is monitored in real time by an on-line detector. If the concentration at the membrane outlet exceeds 10 ng / L, the current density is increased to 15 mA / cm2 and the membrane operating pressure is increased to 1.2 MPa.

[0043] The specific parameters of the electrochemical oxidation in Step 2 are as follows:

[0044] The current density is 10 - 15 mA / cm2 to balance the degradation efficiency and energy consumption. Excessive current will also cause the oxygen evolution side reaction.

[0045] The electrolyte of the electrolytic solution is Na2SO4 with a concentration of 0.1 mol / L, which can provide high conductivity. At the same time, SO4 2- participates in the formation of SO4 2- radicals.

[0046] During the reaction process, the water temperature is controlled ≤ 35 °C to prevent the high-temperature volatilization of PFAS and the corrosion of the electrodes.

[0047] A device for removing polyfluoro / perfluoroalkyl substances in water bodies includes a pretreatment unit, an electrochemical oxidation module, an adsorption module, a membrane separation component, an adsorbent regeneration device, and a monitoring and control system.

[0048] The pretreatment unit includes a grille and a pH adjustment tank. The grille is used to remove suspended solids, and the pH adjustment tank is used to adjust the water body pH to 3.0 - 5.0. The grille is used to intercept large particle impurities to prevent blockage of subsequent modules. The pH adjustment tank reduces the water body pH to 3.0 - 5.0 by adding an acidic mixture to enhance the electrochemical oxidation efficiency.

[0049] The electrochemical oxidation module is equipped with a boron-doped diamond anode and an iron-cobalt bimetallic cathode. The plate spacing in the electrochemical oxidation module is 5 - 10 mm, and the working voltage is 5 - 15 V. The boron-doped diamond anode generates highly active hydroxyl radicals, and the iron-cobalt bimetallic cathode catalyzes the reduction reaction to synergistically decompose long-chain PFAS into short-chain products.

[0050] The adsorption module is filled with a modified biochar adsorbent. The modified biochar adsorbent is prepared by loading Fe3O4 and sulfonation treatment of straw biochar, with a particle size of 0.5 - 2 mm and a packing density of 300 - 500 g / L. The modified biochar selectively enriches short-chain PFAS through the magnetic adsorption of Fe3O4 and the ion exchange effect of sulfonic acid groups.

[0051] The membrane separation component uses an organic pollution-resistant polyvinylidene fluoride nanofiltration membrane with a membrane pore size of 1 - 2 nm and an operating pressure of 0.5 - 1.5 MPa. The PVDF nanofiltration membrane intercepts residual PFAS based on size exclusion and charge repulsion effects, and the concentrate is returned to the electrochemical module for secondary treatment.

[0052] The adsorbent regeneration device includes a pyrolysis furnace and a magnetic separator. The pyrolysis temperature of the pyrolysis furnace is 400 - 600 °C. The magnetic separator is used to separate Fe3O4 from the regenerated biochar. The pyrolysis furnace pyrolyzes PFAS on the adsorbent at high temperature, and the magnetic separator recovers Fe3O4 to realize the recycling of the adsorbent;

[0053] The monitoring and control system includes a PFAS on-line detector, a current regulator and a membrane pressure controller. The PFAS on-line detector and the membrane pressure controller are interlocked through a PLC to regulate parameters such as current and membrane pressure in real time to ensure the stable operation of the system.

[0054] The surface of the boron-doped diamond anode of the electro-chemical oxidation module has a microporous structure with a pore size of 10 - 50 μm. The mass ratio of iron to cobalt in the iron-cobalt bimetallic cathode is 3:1, and the surface of the iron-cobalt bimetallic cathode is coated with a carbon nanotube conductive layer to increase the electrode specific surface area and improve the generation efficiency of -OH radicals. The micropores (10 - 50 μm) can delay the electrode passivation caused by bubble accumulation. Iron provides high conductivity, cobalt enhances the catalytic activity, and the carbon nanotube coating further reduces the electron transfer impedance. The PFAS degradation rate is significantly increased under the same voltage, and the electrode life is extended.

[0055] The Fe3O4 loading of the modified biochar adsorbent is 8% - 12%. The sulfonation treatment is carried out by reacting concentrated sulfuric acid with biochar at a mass ratio of 1:2 at 80 °C for 2 hours. Magnetic nanoparticles are embedded in the biochar pores by the co-precipitation method to realize magnetic separation and recovery after adsorption. Concentrated sulfuric acid introduces sulfonic acid groups (-SO3H) at 80 °C to enhance the ion exchange ability for short-chain PFAS (such as PFBA), thereby improving the adsorption capacity.

[0056] The surface of the polyvinylidene fluoride nanofiltration membrane of the membrane separation module has a polyethyleneimine hydrophilic coating with a coating thickness of 50 - 100 nm. A positively charged layer is formed on the PVDF membrane surface by graft polymerization to reduce membrane fouling and enhance the rejection rate of negatively charged PFAS, thereby improving the membrane flux and increasing the PFAS rejection rate.

[0057] Nitrogen is introduced into the pyrolysis furnace of the adsorbent regeneration device for protection and heated to 500 °C under anoxic conditions to avoid the generation of toxic gases (such as HF) during the high-temperature pyrolysis of PFAS. At the same time, PFAS is decomposed into CO2, H2O and fluorides. After the pyrolyzed biochar is separated from Fe3O4 by a magnetic separator, it is re-sulfonated and returned to the adsorption module, and the recovered Fe3O4 can be re-loaded onto the biochar.

[0058] The PFAS on-line detector in the monitoring and control system uses ultra-high performance liquid chromatography-mass spectrometry technology, and the detection limit is 0.1 ng / L.

[0059] A sulfuric acid and citric acid mixture is added to the pH adjustment tank of the pretreatment unit, with a volume ratio of 2:1 between the two, and the pH adjustment accuracy is ±0.2. Sulfuric acid can quickly reduce the pH, and citric acid chelates metal ions (such as Fe 3+ ) to prevent fouling of the electrochemical module.

[0060] The technical features of the above embodiments can be combined arbitrarily (as long as there is no contradiction in the combination of these technical features). For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described; these embodiments not explicitly written out should also be considered to be within the scope described in this specification.

Claims

1. A method for removing polyfluorinated perfluorinated compounds from water, characterized in that: The following steps are included: The first step is pretreatment. The water to be treated passes through a screen to remove large particles of impurities and then enters a pH adjustment tank, where an acidic mixed solution is added to reduce the pH to 4.

0. The second step is electrochemical oxidation. The water flows into the electrochemical oxidation module and reacts at a voltage of 10V for 20-40 minutes. Hydroxyl radicals and sulfate radicals are generated at the anode, which decompose the long-chain PFAS into short-chain products. The third step is adsorption enrichment. The electrochemically treated water passes through the adsorption module. The modified biochar in the adsorption module adsorbs the residual short-chain PFAS. After adsorption saturation, the regeneration process is triggered. The fourth step is membrane separation. After adsorption, the water body is filtered through a nanofiltration membrane to intercept the undegraded PFAS. The intercepted concentrated liquid is returned to the electrochemical module for cyclic treatment, and the unretained produced water meets the discharge standards. The fifth step is adsorbent regeneration. The saturated biochar in the adsorption module enters the pyrolysis furnace and is pyrolyzed at 500°C in a nitrogen atmosphere for 2 hours to decompose the adsorbed PFAS, and the Fe3O4 is recovered by magnetic separation and re-sulfonated. The sixth step is intelligent regulation. The PFAS concentration is monitored in real time through an online detector. If the concentration at the membrane outlet exceeds 10 ng / L, the current density is increased to 15 mA / cm2 and the membrane operating pressure is increased to 1.2 MPa.

2. A method for removing polyfluorinated perfluorinated compounds from water according to claim 1, characterized in that: The specific parameters of the electrochemical oxidation in the second step are: The current density is 10-15mA / cm2; The electrolyte of the electrolyte is Na2SO4 with a concentration of 0.1 mol / L; During the reaction, the water temperature was controlled to be ≤35°C.

3. A device for removing polyfluorinated perfluorinated compounds from water, characterized in that: It includes a pretreatment unit, an electrochemical oxidation module, an adsorption module, a membrane separation component, an adsorbent regeneration device, and a monitoring and control system; The pretreatment unit includes a screen and a pH adjustment tank. The screen is used to remove suspended matter, and the pH adjustment tank is used to adjust the pH of the water to 3.0-5.

0. The electrochemical oxidation module is equipped with a boron-doped diamond anode and an iron-cobalt bimetallic cathode. The plate spacing in the electrochemical oxidation module is 5-10mm, and the operating voltage is 5-15V; The adsorption module is filled with modified biochar adsorbent, which is made from straw biochar through Fe3O4 loading and sulfonation treatment, with a particle size of 0.5-2 mm and a filling density of 300-500 g / L; The membrane separation component uses polyvinylidene fluoride nanofiltration membrane that is resistant to organic pollution, with a membrane pore size of 1-2nm and an operating pressure of 0.5-1.5MPa; The adsorbent regeneration device includes a pyrolysis furnace and a magnetic separator. The pyrolysis temperature of the pyrolysis furnace is 400-600°C, and the magnetic separator is used to separate Fe3O4 in the regenerated biochar; The monitoring and control system includes a PFAS online detector, a current regulator and a membrane pressure controller. The PFAS online detector and the membrane pressure controller are interlocked through a PLC.

4. The device for removing polyfluorinated and perfluorinated compounds from water according to claim 3, characterized in that: The boron-doped diamond anode surface of the electrochemical oxidation module has a microporous structure with a pore size of 10-50 μm, the iron-cobalt mass ratio of the iron-cobalt bimetallic cathode is 3:1, and the surface of the iron-cobalt bimetallic cathode is coated with a carbon nanotube conductive layer.

5. The device for removing polyfluorinated and perfluorinated compounds from water according to claim 3, characterized in that: The Fe3O4 loading of the modified biochar adsorbent is 8%-12%, and the sulfonation treatment is carried out by reacting concentrated sulfuric acid with biochar at a mass ratio of 1:2 at 80°C for 2 hours.

6. The device for removing polyfluorinated and perfluorinated compounds from water according to claim 3, characterized in that: The surface of the polyvinylidene fluoride nanofiltration membrane of the membrane separation component is provided with a polyethyleneimine hydrophilic coating with a coating thickness of 50-100 nm.

7. The device for removing polyfluorinated and perfluorinated compounds from water according to claim 3, characterized in that: Nitrogen is introduced into the pyrolysis furnace of the adsorbent regeneration device for protection, and the biochar after pyrolysis is separated from Fe3O4 by a magnetic separator, and then re-sulfonated and returned to the adsorption module.

8. The device for removing polyfluorinated and perfluorinated compounds from water according to claim 3, characterized in that: The PFAS online detector in the monitoring and control system adopts ultra-high performance liquid chromatography-mass spectrometry technology, and the detection limit is 0.1 ng / L.

9. The device for removing polyfluorinated and perfluorinated compounds from water according to claim 3, characterized in that: A mixed solution of sulfuric acid and citric acid is added to the pH adjustment tank of the pretreatment unit, the volume ratio of the two is 2:1, and the pH adjustment accuracy is ±0.2.

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