Full-quantitative removal method for PFAs in environmental water body

Abstract

The invention discloses a full-quantitative treatment method for PFAs in environmental water, which comprises the following steps: passing wastewater containing PFAs through a filter, then adsorbing the wastewater through an adsorption tank A or an adsorption tank B containing an active adsorbent to obtain treated water reaching the standard, directly discharging the treated water, introducing a NaOH solution for desorption after the adsorption tank A or the adsorption tank B is saturated, and discharging the treated water after the adsorption tank A or the adsorption tank B is saturated. An obtained desorption solution is introduced into a BDD reaction tank for electrochemical oxidative degradation and then returns to the adsorption tank A or the adsorption tank B for desorption, then the obtained desorption solution enters the BDD reaction tank for electrochemical oxidative degradation, after desorption-degradation circular treatment is carried out, desorption is completed, and an acid solution is introduced into the adsorption tank A or the adsorption tank B after desorption is completed so that the active adsorbent can be regenerated; and after the desorption is completed, the obtained desorbed liquid is firstly discharged to the storage tank, and after the adsorption tank A or the adsorption tank B is saturated by adsorption, the desorbed liquid is returned and introduced into the adsorption tank A or the adsorption tank B to enter the next cycle of desorption.

Description

Technical Field

[0001] The present invention relates to a method for completely quantifying and removing PFAs in environmental water bodies, belonging to the technical field of wastewater treatment. Background Art

[0002] Perfluorinated compounds (PFAs) are a class of organic compounds in which all hydrogen atoms in hydrocarbons are substituted by fluorine atoms. The high bond energy of the C-F bond (484 kJ / mol) makes PFAs have good hydrophobic and oleophobic properties and extremely high chemical stability, so that they are not easily degraded under the action of high temperature, strong light, biodegradation, etc. Therefore, they are widely used in the fields of textiles, leather, coatings, chemical engineering, food packaging, etc. There are up to 2,060 types of commercially available perfluorinated compounds circulating globally. Among them, perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) and their salts are the final products of the transformation of various PFAs and are the most common in the environment, so they have received extensive attention from research scholars. The characteristics of stable structure and poor biodegradability of PFAs result in their persistent presence in the global environment, causing large-scale environmental pollution. PFAs enter organisms along with drinking water, surface water and other media, and accumulate to relatively high concentrations in organisms through the transfer of the food chain, posing a serious threat to the health of the human reproductive, immune and other systems.

[0003] For the treatment of perfluorinated compounds, there are currently physical adsorption, ion exchange, nanofiltration, reverse osmosis, ozone oxidation, photocatalytic oxidation, electrocatalytic oxidation, etc. For physical treatment methods, complete final disposal has not been achieved yet. For chemical oxidation treatment, such as ozone oxidation, the treatment efficiency is low and the reaction time is long. Summary of the Invention

[0004] In order to solve the technical problems existing in the removal of perfluorinated compounds in environmental water bodies at present, the purpose of the present invention is to provide a method for completely quantifying and removing PFAs in environmental water bodies. By using modified activated carbon for adsorption and enrichment and combining with BDD electrochemically oxidative method to jointly treat the adsorption eluate, the method of the present invention can greatly improve the degradation efficiency.

[0005] The present invention is realized by the following technical solutions:

[0006] The present invention provides a full-quantification treatment method for PFAs in environmental water bodies. The wastewater containing PFAs is first passed through a filter, and then adsorbed by adsorption tank A or adsorption tank B containing an active adsorbent to obtain qualified treated water for direct external discharge. When adsorption tank A or adsorption tank B is saturated with adsorption, a NaOH solution is introduced for desorption. The obtained desorption liquid is introduced into a BDD reaction tank for electrochemical oxidation degradation, and then returned to adsorption tank A or adsorption tank B for desorption. The obtained desorption liquid then enters the BDD reaction tank for electrochemical oxidation degradation again. After cyclic treatment of desorption-degradation, the desorption is completed. After the desorption is completed, adsorption tank A or adsorption tank B is further introduced with an acid solution to regenerate the active adsorbent, which is then continuously used for wastewater adsorption in the next cycle. The desorption liquid obtained after the desorption is completed is the regenerated NaOH solution, which is first discharged to a storage tank and then returned to adsorption tank A or adsorption tank B for desorption in the next cycle when adsorption tank A or adsorption tank B is saturated with adsorption.

[0007] In the full-quantification treatment method provided by the present invention, the PFAs in the wastewater are completely adsorbed and removed by using an active adsorbent, and the PFAs are concentrated and enriched in the active adsorbent. Then, the PFAs enriched in the active adsorbent are desorbed by a NaOH solution, and then electrochemically oxidized and degraded by using a BDD reaction tank. Moreover, the desorption efficiency is improved through the cycle of desorption-degradation, and the regeneration adsorption activity of the active adsorbent is enhanced. After the desorption is completed, the active adsorbent is regenerated by an acid solution and continuously used for wastewater adsorption in the next cycle.

[0008] The inventor found that the oxygen evolution potential of BDD is high, reaching 2.5 - 2.8 V. The degradation and removal rate of refractory PFAc is higher than that of other advanced oxidations and can reach 100%. Moreover, during the BDD degradation process, due to factors such as mass transfer efficiency, the degradation efficiency of low-concentration organic matter is lower than that of high-concentration organic matter. For example, when the COD is 100 - 500 mg / l, the degradation efficiency of BDD is several times to dozens of times that of 0 - 100 mg / L. Therefore, the present invention uses BDD to treat the concentrated waste liquid desorbed by activated carbon, which greatly improves the efficiency and is more economical.

[0009] In addition, in the present invention, one is used while the other is reserved. When adsorption tank A is saturated with adsorption, the adsorption is switched to adsorption tank B. Adsorption tank A and adsorption tank B are alternately used for the processes of adsorption, desorption, and degradation in different cycles, that is, the two adsorption tanks are respectively used for different stages in the cycle processes of adsorption, desorption, and degradation, so that the wastewater containing PFAs can be continuously treated.

[0010] In a preferred embodiment, the porosity of the active adsorbent is 40 - 75%, and the specific surface area is 1000 - 2000 m² / g.

[0011] In a preferred embodiment, the active adsorbent is selected from at least one of biochar, activated carbon, and activated carbon fiber.

[0012] Preferably, the activated adsorbent is first subjected to a modification treatment. The process of the modification treatment is as follows: The activated adsorbent is added to a sulfuric acid solution for the first reaction, followed by solid-liquid separation. After the obtained solid phase is washed until the pH > 1, it is added to hydrogen peroxide for the second reaction to obtain the product. In the actual operation process, after the second reaction is completed, solid-liquid separation is carried out, and the solid phase is washed to neutrality and then dried for standby.

[0013] Further preferably, the concentration of the sulfuric acid solution is 1 - 2 mol / L.

[0014] Further preferably, the volume ratio of the activated adsorbent to the sulfuric acid solution is 1:1 - 2.

[0015] Further preferably, the temperature of the first reaction is 80 - 100 °C, and the time of the first reaction is 1 - 2 h.

[0016] Further preferably, the mass concentration of the hydrogen peroxide is 5 - 10%.

[0017] Further preferably, the volume ratio of the washed solid phase to the hydrogen peroxide is 1:1 - 2.

[0018] Further preferably, the time of the second reaction is 12 - 24 h.

[0019] The inventor found that in the water environment, there are a large number of competing compounds and colloids, which will compete with anionic PFAs for adsorption sites during the adsorption process, thereby reducing the adsorption capacity of the adsorption material. For perfluorinated compounds, mesoporous adsorption has a higher adsorption rate than microporous adsorption. The acid activation modification of the present invention can expand the pore size of the activated carbon, increase the number of mesopores, thereby improving the adsorption efficiency of the activated carbon and at the same time improving the adsorption selectivity, ensuring that after the wastewater containing PFAs passes through the adsorption tank A or adsorption tank B containing the activated adsorbent, PFAs can be completely adsorbed to obtain qualified treated water.

[0020] The mesopore ratio of the activated adsorbent modified by the method of the present invention is more than 50 - 70%, and the micropores are less than 15%.

[0021] Preferably, in the NaOH solution, the mass fraction of NaOH is 1 - 2%.

[0022] Preferably, during the process of passing the NaOH solution for desorption into the adsorption tank A or adsorption tank B, ozone is introduced into the activated carbon tank of the adsorption tank A or adsorption tank B, and the concentration of the introduced ozone is 1 - 3 mg / L.

[0023] The inventors found that ozone can cooperate with BDD to degrade PFAc, which can improve the degradation efficiency of the system. In particular, for the intermediate products formed after the chain breaking of BDD, the efficiency can be significantly improved by the synergistic treatment of ozone, and the degradation load of BDD can be reduced.

[0024] In a preferred embodiment, during the electrochemical oxidation degradation in the BDD reaction tank, the BDD electrode is used as the anode, the Ti electrode is used as the cathode, the current density is 50 - 100 mA / cm2, the reaction temperature is 30 - 60 °C, and the single degradation time is 0.5 - 2.5 h.

[0025] Further preferably, the BDD electrode is composed of a silicon carbide substrate, a gradient boron-doped SiC semiconductor transition layer disposed on the surface of the silicon carbide substrate, and a gradient boron-doped diamond semiconductor layer disposed on the surface of the gradient boron-doped SiC semiconductor transition layer. In the gradient boron-doped SiC semiconductor transition layer, the boron content gradient decreases from top to bottom; in the gradient boron-doped diamond semiconductor layer, the boron content gradient decreases from bottom to top.

[0026] In the present invention, since the organic fluorine in the wastewater containing PFAs is degraded and converted into inorganic fluorine after degradation, and the inorganic fluorine has strong corrosiveness, the electrode with the above-mentioned silicon carbide substrate can effectively improve the service life of the electrode. Moreover, the B doping treatment of the SiC semiconductor in the present invention can obtain a p-type semiconductor, which helps to improve the conductivity of the substrate, thereby improving the current efficiency during the electrochemical oxidation process; at the same time, it further improves the chemical bonding force between the SiC substrate and the BDD coating, and improves the service stability of the BDD composite coating material. The lower boron content at the bottom layer of the transition layer helps to retain the good chemical stability and heat conduction efficiency of the silicon carbide substrate; the higher boron content at the top layer enhances the chemical bonding force between the transition layer and the BDD coating and improves the conductivity of the substrate; the middle part adopts a way of decreasing boron content gradient, which helps to relieve the hardness gradient between the substrate and the transition layer and ensure the good combination of the transition layer and the substrate.

[0027] Even more preferably, the surface of the gradient boron-doped SiC semiconductor transition layer contains a number of grooves, and the depth of the grooves is 0.5 - 3 μm. The grooves are obtained by plasma etching of the gradient boron-doped SiC semiconductor transition layer.

[0028] The inventors found that etching the surface of the substrate with a gradient boron-doped SiC semiconductor transition layer helps to increase the specific surface area and further improve the current density at the film-substrate bonding interface; at the same time, increasing the surface roughness of the substrate helps to increase the diamond nucleation rate, further improve the film-substrate bonding force, and enhance the service performance of the material. However, the inventors found that plasma etching is required and the depth of the grooves needs to be controlled so that the final performance is optimal only on the surface of the gradient boron-doped SiC semiconductor transition layer.

[0029] More preferably, in the top of the gradient boron-doped SiC semiconductor transition layer, the total amount of B atoms is 10 16 ~10 19 cm -3 , wherein the ratio of B atoms directly doped into the SiC lattice is 20-30%, and the ratio of B atoms in B4C is 70%-80%.

[0030] The inventors found that when the total amount of B atoms is controlled within the scope of the present invention, the performance of the final semiconductor composite coating material is optimal. If the amount of B doping is high, a higher thermal diffusion temperature is required, which will cause SiC to oxidize to form SiO2 residues and the conductivity of SiO2 is poor, ultimately affecting the electrical properties of the substrate; if the amount of B doping is too low, the conductivity of the substrate and the film-substrate bonding performance cannot be effectively improved. In addition, when the ratio of B atoms directly doped into SiC is controlled within the scope of the present invention, the comprehensive performance of the obtained silicon carbide / boron-doped diamond semiconductor composite coating material is also better.

[0031] More preferably, the gradient boron-doped diamond layer, from bottom to top, sequentially includes a boron-doped diamond bottom layer, a boron-doped diamond intermediate layer, and a boron-doped diamond top layer. In the boron-doped diamond bottom layer, a uniform boron content is adopted. By atomic ratio, B / C is 46666-60000 ppm. In the boron-doped diamond top layer, a uniform boron content is adopted. By atomic ratio, B / C is 26666-40000 ppm. And the boron content in the boron-doped diamond intermediate layer decreases linearly from bottom to top, with the boron content of the boron-doped diamond bottom layer as the maximum value and decreasing linearly to the boron content of the boron-doped diamond top layer.

[0032] In the present invention, the boron-doped diamond bottom layer adopts a uniform boron content to ensure the conductivity of the coating to the greatest extent, enhance the chemical bonding force between the BDD coating and the gradient boron-doped SiC transition layer, and further improve the film-substrate bonding performance; in the boron-doped diamond top layer, a uniform boron content is also adopted to ensure the corrosion resistance of the top layer to the greatest extent, effectively reduce the coating peeling rate, and improve the service life of the composite coating material; for the boron-doped diamond intermediate layer, a linear decrease in boron gradient is adopted, which can make the transition between the coatings natural, not easily separated and broken, and improve the bonding force.

[0033] More preferably, the preparation method of the BDD electrode is: impregnate the silicon carbide substrate in a solution containing boron oxide powder, dry it to obtain a silicon carbide substrate wrapped with boron oxide powder, then perform thermal diffusion treatment on the silicon carbide substrate to obtain a gradient boron-doped SiC semiconductor transition layer, and then grow a gradient boron-doped diamond semiconductor layer on the silicon carbide substrate containing the gradient boron-doped SiC semiconductor transition layer by chemical vapor deposition to obtain the BDD electrode.

[0034] More preferably, the process of the thermal diffusion treatment is as follows: first, heat up to 200 - 650 °C, keep warm for 20 - 50 min, then heat up to 1250 - 1400 °C, keep warm for 45 - 90 min, and finally heat up to 1450 - 1650 °C, keep warm for 30 - 60 min; the atmosphere for the thermal diffusion treatment is air, oxygen or nitrogen.

[0035] More preferably, after the thermal diffusion treatment, the silicon carbide substrate subjected to the thermal diffusion treatment is sequentially subjected to chemical cleaning treatment and mechanical polishing treatment.

[0036] More preferably, the process of the chemical cleaning treatment is: cleaning the surface of the silicon carbide substrate subjected to the thermal diffusion treatment with BOE solution or HF solution.

[0037] More preferably, the process of the mechanical polishing treatment is as follows: heat the silicon carbide substrate subjected to the chemical cleaning treatment to 50 - 80 °C, then coat it with paraffin. Place the silicon carbide substrate coated with paraffin symmetrically on the surface of the sample carrier block in sequence to ensure the uniformity of the polishing thickness in different surface areas, and then carry out mechanical polishing treatment; take it off and cool it, remove the paraffin and take out the sample for cleaning; the composition of the polishing liquid is water:aluminum oxide = (8 - 10):1; the rotation speed of the polishing liquid is 80 - 100 r / min; the mechanical polishing time is 60 - 120 min.

[0038] Through the secondary cleaning treatment of chemical cleaning treatment and mechanical polishing treatment, the vitrified boron oxide remaining on the surface of the transition layer can be removed, so as to deposit the BDD semiconductor coating subsequently.

[0039] More preferably, the silicon carbide substrate with a gradient boron-doped SiC semiconductor transition layer is first subjected to plasma etching, and then a gradient boron-doped diamond semiconductor layer is grown by chemical vapor deposition; the plasma etching atmosphere includes etching gas, auxiliary gas and dilution gas. The etching gas is selected from one of SF6, CF4, CHF3, NF3, Cl2, preferably SF6. The auxiliary gas is selected from one of HBr, O2, Ar, preferably O2. The dilution gas is selected from one of He, Ne, N2; the auxiliary gas accounts for 1 - 20% of the total gas flow rate, preferably 1 - 8.3%, and the dilution gas accounts for 15% - 30% of the total gas flow rate, preferably 20% - 30%; during the etching process, the chamber pressure is 4 - 10 Pa, the radio frequency power adjustment range is 200 - 400 W, and the process time is 50 - 600 s.

[0040] Further preferably, the process of growing a gradient boron-doped diamond semiconductor layer on a silicon carbide substrate with a gradient boron-doped SiC semiconductor transition layer by chemical vapor deposition is as follows: First, place the silicon carbide substrate with a gradient boron-doped SiC semiconductor transition layer in a suspension containing nanocrystalline and / or microcrystalline diamond mixed particles; perform ultrasonic treatment and then dry it; obtain a silicon carbide substrate with nanocrystalline and / or microcrystalline diamond adsorbed on its surface. Then, place the silicon carbide substrate with nanocrystalline and / or microcrystalline diamond adsorbed on its surface in a chemical vapor deposition furnace, and introduce hydrogen, boron-containing gas, and carbon-containing gas to grow a gradient boron-doped diamond semiconductor layer by chemical vapor deposition. The temperature of the chemical vapor deposition is 600 - 1000 °C, the pressure is 10 3 -10 4 Pa, and the time is 3 - 20 h.

[0041] Further preferably, in the suspension containing nanocrystalline and / or microcrystalline diamond mixed particles, the mass fraction of the diamond mixed particles is 0.01% - 0.05%; the particle size of the diamond mixed particles is 5 - 30 nm, and the purity is ≥97%; the ultrasonic treatment time is 5 - 30 min.

[0042] Further preferably, during the chemical vapor deposition, the percentage of the carbon-containing gas in the total gas mass flow rate in the furnace is 0.5 - 10.0%, preferably 2 - 5%.

[0043] Further preferably, during the chemical vapor deposition, first control the percentage of the boron-containing gas in the total gas mass flow rate in the furnace to be 0.069% - 0.0884% to obtain a boron-doped diamond bottom layer, and then reduce the boron doping concentration in a linearly decreasing manner; until the percentage of the boron-containing gas in the total gas mass flow rate in the furnace is 0.03968% - 0.0593% to obtain a boron-doped diamond transition layer, and then control the percentage of the boron-containing gas in the total gas mass flow rate in the furnace to be 0.03968% - 0.0593% again to deposit a boron-doped diamond outer layer; thus obtaining a gradient boron-doped diamond semiconductor layer.

[0044] In a preferred embodiment, the acid solution is a sulfuric acid solution, and in the sulfuric acid solution, the mass fraction of sulfuric acid is 1 - 5%.

[0045] The process system used in the method for total quantification treatment of PFAs in environmental water bodies of the present invention includes an adsorption tank, a BDD reaction tank, a circulation pump, an intermediate water tank, a filter, an ozone microporous aeration facility, an ozone generator for the circulation treatment process, and also includes an automatic control device composed of a pressure, pH, fluoride on-line detector, and an electric valve.

[0046] Principle and advantages

[0047] The present invention provides a method for fully quantifying the removal of PFAs in environmental water bodies. The method comprises the following steps: firstly, the PFAs in wastewater are completely adsorbed and removed by using activated carbon adsorption, and the PFAs are concentrated and enriched in the activated carbon. Then, the PFAs enriched in the activated carbon are analyzed out by using a NaOH solution, and then electrochemical oxidation and degradation are performed in a BDD reaction tank. The analysis efficiency is improved through a cycle of analysis-degradation, and the regeneration adsorption activity of the activated carbon is improved. After the analysis is completed, the active adsorbent is regenerated by using an acid solution; and the PFAs are continuously used for wastewater adsorption in the next cycle.

[0048] Since BDD has a high oxygen evolution potential of 2.5-2.8V, its degradation and removal rate for difficult-to-degrade PFAc is higher than that of other advanced oxidation methods, which can reach 100%. In addition, during the BDD degradation process, due to factors such as mass transfer efficiency, the degradation efficiency of low-concentration organic matter is lower than that of low-concentration organic matter. For example, when COD is 100-500mg / l, the degradation efficiency of BDD is several times or even dozens of times that of 0-100mg / L. Therefore, the present invention adopts BDD to treat the concentrated waste liquid analyzed by activated carbon, which greatly improves the efficiency and is more economical.

[0049] Through the combination of the processes of the present invention, the full quantitative treatment of trace perfluorinated compounds in wastewater can be achieved. Compared with the degradation of BDD alone, the degradation efficiency can be increased by 8-12 times, and the investment and operation costs can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Process flow chart of the present invention. DETAILED DESCRIPTION

[0051] Example 1

[0052] The BDD electrode disposed in the BDD reaction tank of this embodiment is a gradient boron-doped silicon-based electrode produced by Xinfeng Technology.

[0053] The wastewater containing PFAs (PFOS concentration was 15.3 μg / L, PFOA concentration was 19.6 μg / L, flow rate was 10 m 3 / h) first passes through the filter, and then passes through the activated carbon (specific surface area of ​​1862m 2 / g, with a porosity of 57.6%, of which the mesopores are 21.9%, the adsorption tank A obtains up-to-standard treated water and discharges it directly. When it is detected that the active agent in the adsorption tank A is adsorbed to saturation, the pipeline is switched so that the wastewater filtered by the filter passes through the adsorption tank B, while the adsorption tank A is fed with a NaOH solution with a mass fraction of 2% for desorption. The obtained desorption liquid is fed into the BDD reaction tank for electrochemical oxidation degradation, and then returns to the adsorption tank A for desorption. The obtained desorption liquid then enters the BDD reaction tank for electrochemical oxidation degradation, and a cycle of desorption-degradation is carried out; during the desorption process, ozone is introduced into the adsorption tank A, and the concentration of ozone introduced into the desorption liquid is controlled at 2 mg / L. During the degradation process, the BDD electrode is used as the anode, the Ti electrode is used as the cathode, the current density is 60 mA / cm2, the reaction temperature is 40 - 50 °C, the single degradation time is 1.0 h. After repeating the desorption-degradation about 8 times, through on-line detection, when the desorption is completed, the obtained desorbed liquid is the regenerated NaOH solution, which is first discharged to the storage tank. After the adsorption tank B is adsorbed to saturation, it is returned and fed into the adsorption tank B to enter the desorption of the next cycle, while a sulfuric acid solution with a mass fraction of 4% is introduced into the adsorption tank A to regenerate the active adsorbent in the adsorption tank A for standby.

[0054] After adsorption by activated carbon, the PFOS concentration in the effluent is 33.6 ng / L, the PFOA is 29.1 ng / L, and the activated carbon adsorption capacity is 48.4 mg / g. The initial PFOS concentration in the regenerated alkali solution after washing the activated carbon is 66.5 mg / L, the PFOA is 61.9 mg / L. After BDD degradation, the PFOS concentration in the regenerated alkali solution is 1.17 μg / L, the PFOA is 1.02 μg / L, and the average energy consumption for BDD degradation of fluoride is 12.1 kw·h / g fluoride.

[0055] Example 2

[0056] The BDD used in this Example 2 is the same as that in Example 1.

[0057] In this Example 2, the granular activated carbon is first mixed with the active adsorbent in a solid-liquid volume ratio of 1:2 with a 2 mol / L sulfuric acid solution and reacted at 45 °C for 2 h. The sulfuric acid is poured out, and the adsorbent is washed until the pH of the washing liquid is > 1. Then, 10% hydrogen peroxide is added with a solid-liquid ratio of 1:2 and reacted for 24 h. After washing and drying, it is reserved for use. After the above modification of the active adsorbent, the mesopores are increased from 21.9% to 66.5%, and the total porosity is 73.4%.

[0058] The wastewater containing PFAs (PFOS concentration is 15.3 μg / L, PFOA is 19.6 μg / L, flow rate 10 m 3 / h) first passes through the filter, and then passes through the above-mentioned modified granular activated carbon (specific surface area is 2689 m 2The adsorption tank A (with an activated agent content of 25 g / g and a porosity of 73.4%, of which mesopores account for 66.5%) is used to obtain qualified treated water for direct discharge. When it is detected that the activated agent in the adsorption tank A is saturated with adsorption, the pipeline is switched so that the wastewater filtered by the filter passes through the adsorption tank B, while the adsorption tank A is fed with a 2% NaOH solution by mass for desorption. The obtained desorption liquid is fed into the BDD reaction tank for electrochemical oxidation degradation, and then returns to the adsorption tank A for desorption. The obtained desorption liquid then enters the BDD reaction tank for electrochemical oxidation degradation again, and a cycle of desorption-degradation is carried out. During the desorption process, ozone is introduced into the adsorption tank A, and the concentration of ozone introduced into the desorption liquid is controlled at 2 mg / L. During the degradation process, the BDD electrode is used as the anode, the Ti electrode is used as the cathode, the current density is 60 mA / cm2, the reaction temperature is 40 - 50 °C, the single degradation time is 2.5 h. After repeating the desorption-degradation 20 times and through on-line detection, the desorbed liquid obtained after desorption is the regenerated NaOH solution, which is first discharged to the storage tank. After the adsorption tank B is saturated with adsorption, it is returned and fed into the adsorption tank B for the desorption of the next cycle. And a 4% sulfuric acid solution by mass is introduced into the adsorption tank A to regenerate the active adsorbent in the adsorption tank A for standby.

[0059] After adsorption by activated carbon, the PFOS concentration in the effluent is 16.9 ng / L, the PFOA is 15.2 ng / L, and the activated carbon adsorption capacity is 95.8 mg / g. The initial PFOS concentration in the activated carbon washing and regenerating alkali solution is 139.8 mg / L, the PFOA is 140.7 mg / L. After BDD degradation, the PFOS concentration in the regenerated alkali solution is 0.54 μg / L, the PFOA is 0.51 μg / L, and the average energy consumption for BDD degradation of fluoride is 7.62 kw·h / g fluoride.

[0060] Example 3

[0061] The preparation process of the BDD electrode used in this Example 3 is as follows:

[0062] Boron oxide powder with a purity of 99.99% is dissolved in absolute ethanol, and the silicon carbide substrate is put in and heated and dried until the solvent is dried. The sample is put into a tubular annealing furnace for step heat treatment; the heat treatment atmosphere is nitrogen; then it is first heated to 200 °C and kept warm for 30 min, then heated to 1250 °C and kept warm for 60 min, and finally heated to 1450 °C and kept warm for 30 min.

[0063] After thermal diffusion, the surface of the transition layer is subjected to secondary cleaning treatment, and the secondary cleaning treatment process includes chemical cleaning and mechanical polishing; the chemical cleaning process is: using BOE solution to perform primary cleaning treatment on the surface of the sample; the mechanical polishing process is: placing the sample carrier block on a hot platform and heating it to 60 °C, uniformly coating paraffin wax, and placing the samples symmetrically on the surface of the sample carrier block in turn to ensure the uniformity of the polishing thickness in different regions of the surface, and performing mechanical polishing treatment; then removing the sample carrier block and cooling it, removing the paraffin wax, taking the slices and cleaning them; the composition of the polishing liquid is water: alumina = 10:1; the rotation speed of the polishing liquid is 100 r / min; the mechanical polishing time is 60 min.

[0064] The thickness of the gradient boron-doped SiC semiconductor transition layer is 2.98 μm. At the top of the transition layer, the total amount of B atoms is 2×10 18 cm -3 , where the ratio of B atoms directly doped into SiC is 23.1%, and the ratio of B atoms in B4C is 76.9%.

[0065] Then, the silicon carbide substrate with a gradient boron-doped SiC semiconductor transition layer on the surface is placed in a suspension containing nanocrystalline and / or microcrystalline diamond mixed particles; ultrasonic treatment is carried out and then dried; a substrate material with nanocrystalline and / or microcrystalline diamond adsorbed on the surface is obtained; in the suspension containing nanocrystalline and / or microcrystalline diamond mixed particles, the mass fraction of the diamond mixed particles is 0.02%; the particle size of the diamond mixed particles is 5 - 10 nm, and the purity is ≥97%; the ultrasonic treatment time is 30 min.

[0066] The silicon carbide matrix with nanocrystalline and / or microcrystalline diamond adsorbed on the surface is placed in a chemical vapor deposition furnace, and hydrogen, boron-containing gas, and carbon-containing gas are introduced. First, control the percentage of the boron-containing gas in the total gas mass flow rate in the furnace to be 0.0884% to obtain a boron-doped diamond bottom layer, and then reduce the boron doping concentration in a linearly decreasing manner; until the percentage of the boron-containing gas in the total gas mass flow rate in the furnace is 0.0593% to obtain a boron-doped diamond intermediate layer, and then control the percentage of the boron-containing gas in the total gas mass flow rate in the furnace to be 0.03968% to deposit again to obtain a boron-doped diamond top layer; thus, a gradient boron-doped diamond semiconductor layer is obtained;

[0067] The percentage of the carbon-containing gas in the total gas mass flow rate in the furnace is 3.0% in all cases. The deposition temperature of the boron-doped diamond is 800 °C, the air pressure is 10 3 Pa, and the deposition time is 10 h. The thickness of the gradient boron-doped diamond semiconductor layer is 10.24 μm.

[0068] In Example 3, granular activated carbon was first mixed with an activated adsorbent in a solid-liquid volume ratio of 1:2 using a 2 mol / L sulfuric acid solution and reacted at 45 °C for 2 h. The sulfuric acid was then poured out, and the adsorbent was washed until the pH of the washing liquid was >1. Then, 10% hydrogen peroxide was added with a solid-liquid ratio of 1:2, and the reaction was carried out for 24 h. After washing and drying, it was reserved for use. After the above modification, the mesopores of the activated adsorbent increased from 21.9% to 66.5%.

[0069] The wastewater containing PFAs (PFOS concentration of 15.3 μg / L, PFOA of 19.6 μg / L, flow rate of 10 m 3 / h) was first passed through a filter and then through adsorption tank A filled with the above-mentioned modified granular activated carbon (specific surface area of 2689 m2 / g, porosity of 73.4%, and mesopores of 66.5%) to obtain up-to-standard treated water for direct external discharge. When it was detected that the active agent in adsorption tank A was saturated with adsorption, the pipeline was switched so that the wastewater filtered by the filter passed through adsorption tank B, while adsorption tank A was passed through a 2% NaOH solution by mass for desorption. The obtained desorption solution was introduced into a BDD reaction tank for electrochemical oxidation degradation, and then returned to adsorption tank A for desorption. The obtained desorption solution was then introduced into the BDD reaction tank for electrochemical oxidation degradation again, and a cycle of desorption-degradation treatment was carried out; during the desorption process, ozone was introduced into adsorption tank A, and the concentration of ozone introduced into the desorption solution was controlled at 2 mg / L. During the degradation process, the BDD electrode was used as the anode, the Ti electrode was used as the cathode, the current density was 60 mA / cm2, the reaction temperature was 40 - 50 °C, the single degradation time was 2 h, and after repeating the desorption-degradation 16 times, through on-line detection, the desorption solution obtained after desorption was the regenerated NaOH solution, which was first discharged to a storage tank. After adsorption tank B was saturated with adsorption, it was returned and introduced into adsorption tank B for the desorption of the next cycle, while a 4% sulfuric acid solution by mass was introduced into adsorption tank A to regenerate the active adsorbent in adsorption tank A for standby use.

[0070] After adsorption by activated carbon, the effluent PFOS concentration was 25.3 ng / L, the PFOA was 18.4 ng / L, and the adsorption capacity was 96.1 mg / g. The initial PFOS concentration in the regenerated alkali solution for washing the activated carbon was 140.1 mg / L, the PFOA was 142.8 mg / L, the PFOS concentration in the regenerated alkali solution after BDD degradation was 0.42 μg / L, the PFOA was 0.37 μg / L, and the average energy consumption for BDD degradation of fluoride was 6.3 kw·h / g fluoride.

[0071] Example 4

[0072] All other conditions in this Example 4 are the same as those in Example 3, except that in the preparation process of the BDD electrode, after the plasma etching of the gradient boron-doped SiC semiconductor transition layer, chemical vapor deposition furnace is carried out. The etching gas is SF6, the auxiliary gas is O2, the dilution gas is N2, the auxiliary gas accounts for 5% of the total gas flow rate, and the dilution gas accounts for 15% of the total gas flow rate. During the etching process, the chamber pressure is 5 Pa, the radio frequency power is 300 W, and the process time is 300 s. A groove structure with a gradually decreasing depth from the bottom center to the edge is prepared, and the etching depth is 2 μm.

[0073] The wastewater containing PFAs (PFOS concentration is 15.3 μg / L, PFOA is 19.6 μg / L, flow rate 10 m 3 / h) first passes through a filter, and then passes through an adsorption tank A filled with the above-mentioned modified granular activated carbon (specific surface area is 2689 m 2 / g, porosity is 73.4%, of which mesopores are 66.5%) to obtain qualified treated water for direct external discharge. When it is detected that the active agent in the adsorption tank A is saturated with adsorption, the pipeline is switched to make the wastewater filtered by the filter pass through the adsorption tank B, while the adsorption tank A is passed through a NaOH solution with a mass fraction of 2% for desorption. The obtained desorption solution is introduced into the BDD reaction tank for electrochemical oxidation degradation, and then returned to the adsorption tank A for desorption. The obtained desorption solution then enters the BDD reaction tank for electrochemical oxidation degradation, and a cycle treatment of desorption-degradation is carried out. During the desorption process, ozone is introduced into the adsorption tank A, and the concentration of ozone introduced into the desorption solution is controlled to be 2 mg / L. During the degradation process, the BDD electrode is used as the anode, the Ti electrode is used as the cathode, the current density is 60 mA / cm2, the reaction temperature is 40 - 60 °C, the single degradation time is 1.75 h. After repeating the desorption-degradation 14 times, through on-line detection, the desorbed solution obtained after desorption is the regenerated NaOH solution, which is first discharged to the storage tank. After the adsorption tank B is saturated with adsorption, it is returned and introduced into the adsorption tank B for the desorption of the next cycle, and a sulfuric acid solution with a mass fraction of 4% is introduced into the adsorption tank A to regenerate the active adsorbent in the adsorption tank A for standby.

[0074] After adsorption by activated carbon, the PFOS concentration in the effluent is 16.3 ng / L, the PFOA is 14.9 ng / L, and the adsorption capacity is 98.2 mg / g. The initial PFOS concentration in the activated carbon washing and regenerating alkali solution is 139.2 m g / L, the PFOA is 142.3 mg / L, the PFOS concentration in the regenerated alkali solution after BDD degradation is 0.91 μg / L, the PFOA is 0.84 μg / L, and the average energy consumption for BDD degradation of fluoride is 5.56 kw·h / g fluoride.

[0075] Comparative Example 1

[0076] Other conditions were the same as those in Example 1, except that the wastewater containing PFAs was directly degraded in a BDD reaction tank until the qualified water was obtained after passing through a filter. After testing, the PFOS concentration in the effluent of the BDD reactor was 0.28 ng / L, and the PFOA was 0.33 ng / L. The average energy consumption for the BDD to degrade fluoride was 71 kw·h / g fluoride.

Claims

1. A full quantification method for PFAs in environmental water bodies, characterized in that: The wastewater containing PFAs is first passed through a filter and then adsorbed by adsorption tank A or adsorption tank B containing an active adsorbent to obtain qualified treated water for direct external discharge. When adsorption tank A or adsorption tank B is saturated with adsorption, a NaOH solution is introduced for desorption. The obtained desorbed solution is introduced into a BDD reaction tank for electrochemical oxidation degradation, and then returned to adsorption tank A or adsorption tank B for desorption. The obtained desorbed solution then enters the BDD reaction tank again for electrochemical oxidation degradation. After cyclic treatment of desorption-degradation, the desorption is completed. After the desorption is completed, adsorption tank A or adsorption tank B is introduced with an acid solution to regenerate the active adsorbent; It is continued to be used for the adsorption of wastewater in the next cycle, and the desorbed solution obtained after the desorption is completed is a regenerated NaOH solution. It is first discharged to a storage tank and then returned to adsorption tank A or adsorption tank B for desorption in the next cycle when adsorption tank A or adsorption tank B is saturated with adsorption.

2. The full quantification treatment method of PFAs in environmental water bodies according to claim 1, characterized in that: The porosity of the active adsorbent is 40 - 75%, and the specific surface area is 1000 - 2000 m² / g; The active adsorbent is selected from at least one of biochar, activated carbon, and activated carbon fiber.

3. The full quantification method for PFAs in environmental water bodies according to claim 2, characterized in that: The active adsorbent is first subjected to a modification treatment. The process of the modification treatment is as follows: the active adsorbent is added to a sulfuric acid solution for the first reaction, followed by solid-liquid separation. After the obtained solid phase is washed until the pH > 1, it is added to hydrogen peroxide for the second reaction to obtain the product; The concentration of the sulfuric acid solution is 1 - 2 mol / L; The volume ratio of the active adsorbent to the sulfuric acid solution is 1:1 - 2; The temperature of the first reaction is 80 - 100 °C, and the time of the first reaction is 1 - 2 h; The mass concentration of the hydrogen peroxide is 5 - 10%; The volume ratio of the washed solid phase to the hydrogen peroxide is 1:1 - 2; The time of the second reaction is 12 - 24 h.

4. The total quantification treatment method of PFAs in environmental water bodies according to claim 1, characterized in that: In the NaOH solution, the mass fraction of NaOH is 1 - 2%.

5. The total quantification treatment method for PFAs in environmental water bodies according to claim 1 or 4, characterized in that: During the process of introducing the NaOH solution into adsorption tank A or adsorption tank B for desorption, ozone is introduced into adsorption tank A or adsorption tank B, and the concentration of the introduced ozone is 1 - 3 mg / L.

6. The full quantification method for PFAs in environmental water bodies according to claim 1 or 4, characterized in that: During the process of electrochemical oxidation degradation in the BDD reaction tank, the BDD electrode is used as the anode, the Ti electrode is used as the cathode, the current density is 50 - 100 mA / cm², the reaction temperature is 30 - 60 °C, and the time of single degradation is 0.5 - 2.5 h.

7. A full quantification method for PFAs in environmental water bodies according to claim 6, characterized in that: The BDD electrode is composed of a silicon carbide substrate, a gradient boron-doped SiC semiconductor transition layer provided on the surface of the silicon carbide substrate, and a gradient boron-doped diamond semiconductor layer provided on the surface of the gradient boron-doped SiC semiconductor transition layer. In the gradient boron-doped SiC semiconductor transition layer, the boron content gradient decreases from top to bottom; in the gradient boron-doped diamond semiconductor layer, the boron content gradient decreases from bottom to top.

8. The full quantification method for PFAs in environmental water bodies according to claim 7, characterized in that: The surface of the gradient boron-doped SiC semiconductor transition layer contains a number of grooves, and the depth of the grooves is 0.5 - 3 μm; In the top of the gradient boron-doped SiC semiconductor transition layer, the total amount of B atoms is 10 16 ~10 19 cm -3 , where the ratio of B atoms directly doped between the SiC lattices is 20% - 30%, and the ratio of B atoms in B4C is 70% - 80%; The gradient boron-doped diamond layer, from bottom to top, successively includes a boron-doped diamond bottom layer, a boron-doped diamond intermediate layer, and a boron-doped diamond top layer. In the boron-doped diamond bottom layer, a uniform boron content is adopted, and in terms of atomic ratio, B / C is 46666 - 60000 ppm. In the boron-doped diamond top layer, a uniform boron content is adopted, and in terms of atomic ratio, B / C is 26666 - 40000 ppm. The boron content in the boron-doped diamond intermediate layer linearly decreases from bottom to top, linearly decreasing from the boron content of the boron-doped diamond bottom layer as the maximum value to the boron content of the boron-doped diamond top layer.

9. The full quantification method for PFAs in environmental water bodies according to claim 7 or 8, characterized in that: The preparation method of the BDD electrode is as follows: Immerse the silicon carbide substrate in a solution containing boron oxide powder, dry it to obtain a silicon carbide substrate wrapped with boron oxide powder, then perform thermal diffusion treatment on the silicon carbide substrate wrapped with boron oxide powder to obtain a gradient boron-doped SiC semiconductor transition layer, and then grow a gradient boron-doped diamond semiconductor layer on the silicon carbide substrate containing the gradient boron-doped SiC semiconductor transition layer by chemical vapor deposition; The process of the thermal diffusion treatment is as follows: First, heat up to 200 - 650 °C, keep the temperature for 20 - 50 min, then heat up to 1250 - 1400 °C, keep the temperature for 45 - 90 min, and finally heat up to 1450 - 1650 °C, keep the temperature for 30 - 60 min; The atmosphere for the thermal diffusion treatment is at least one of air, oxygen, and nitrogen; After the thermal diffusion treatment, the silicon carbide substrate subjected to the thermal diffusion treatment is successively subjected to chemical cleaning treatment and mechanical polishing treatment; The process of the chemical cleaning treatment is as follows: Use a BOE solution or an HF solution to clean the surface of the silicon carbide substrate subjected to the thermal diffusion treatment; The process of the mechanical polishing treatment is as follows: Heat the silicon carbide substrate subjected to the chemical cleaning treatment to 50 - 80 °C, then coat it with paraffin. Place the silicon carbide substrate coated with paraffin symmetrically on the surface of the sample carrier block in turn for mechanical polishing treatment; Take it off and cool it, remove the paraffin and take the wafer for cleaning; The composition of the polishing liquid is water:aluminum oxide = 8 - 10:1; The rotation speed of the polishing liquid is 80 - 100 r / min; The mechanical polishing time is 60 - 120 min; The silicon carbide substrate containing the gradient boron-doped SiC semiconductor transition layer is first subjected to plasma etching, and then a gradient boron-doped diamond semiconductor layer is grown by chemical vapor deposition; The plasma etching atmosphere includes an etching gas, an auxiliary gas, and a dilution gas. The etching gas is selected from one of SF6, CF4, CHF3, NF3, and Cl2, the auxiliary gas is selected from one of HBr, O2, and Ar, and the dilution gas is selected from one of He, Ne, and N2; The auxiliary gas accounts for 1 - 20% of the total gas flow rate, and the dilution gas accounts for 15% - 30% of the total gas flow rate. During the etching process, the chamber pressure is 4 - 10 Pa, the radio frequency power adjustment range is 200 - 400 W, and the process time is 50 - 600 s; The process of growing a gradient boron-doped diamond semiconductor layer on a silicon carbide substrate with a gradient boron-doped SiC semiconductor transition layer by chemical vapor deposition is as follows: First, place the silicon carbide substrate with a gradient boron-doped SiC semiconductor transition layer in a suspension containing a mixture of nanocrystalline and / or microcrystalline diamond particles; perform ultrasonic treatment and then dry it; obtain a silicon carbide substrate with nanocrystalline and / or microcrystalline diamond particles adsorbed on its surface. Then, place the silicon carbide substrate with nanocrystalline and / or microcrystalline diamond particles adsorbed on its surface in a chemical vapor deposition furnace, and introduce hydrogen, boron-containing gas, and carbon-containing gas to grow a gradient boron-doped diamond semiconductor layer by chemical vapor deposition. The temperature of the chemical vapor deposition is 600 - 1000 °C, the pressure is 10 3 -10 4 Pa, and the time is 3 - 20 h; In the suspension containing nanocrystalline and / or microcrystalline diamond hybrid particles, the mass fraction of the diamond hybrid particles is 0.01%-0.05%; the particle size of the diamond hybrid particles is 5-30 nm, and the purity is ≥97%; the ultrasonic treatment time is 5-30 min. During the chemical vapor deposition, the percentage of the carbon-containing gas in the total gas mass flow rate in the furnace is 0.5-10.0%. During the chemical vapor deposition, first control the percentage of the boron-containing gas in the total gas mass flow rate in the furnace to be 0.069%-0.0884% to obtain a boron-doped diamond bottom layer, and then reduce the boron doping concentration in a linearly decreasing manner; until the percentage of the boron-containing gas in the total gas mass flow rate in the furnace is 0.03968%-0.0593% to obtain a boron-doped diamond transition layer, and then control the percentage of the boron-containing gas in the total gas mass flow rate in the furnace to be 0.03968%-0.0593% to deposit again to obtain a boron-doped diamond outer layer; thus, a gradient boron-doped diamond semiconductor layer is obtained.

10. A full quantification method for PFAs in environmental water bodies according to claim 1, characterized in that: The acid solution is a sulfuric acid solution, and in the sulfuric acid solution, the mass fraction of sulfuric acid is 1-5%.

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