Method for degrading PFAS in wastewater by using alternating current technology

Abstract

The invention discloses a PFAS wastewater degradation method based on an alternating current technology, which comprises the following steps: constructing a three-electrode system by using the same electrode material as a cathode and an anode and using an Ag / AgCl electrode as a reference electrode, and degrading PFAS in wastewater by applying alternating currents with different intensities. The periodic polarity inversion of the electrode is realized by adjusting the alternating current frequency, so that the surface reaction environment of the electrode is dynamically changed. The problems of electrode polarization and by-product accumulation in a traditional electrochemical method are effectively avoided, more active sites and oxidizing substances are generated on the surface of the electrode, so that the degradation efficiency and defluorination rate of PFAS are remarkably improved, and excellent redox synergistic effect and environmental sustainability are shown. Compared with the traditional direct current technology, the method has the advantages that the unique advantages of alternating current are utilized, the degradation efficiency is improved, the service life of the electrode is prolonged, the energy consumption is reduced, and an efficient, environment-friendly and economical solution is provided for PFAS wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of electrochemical degradation of organic pollutants, and particularly to a method for efficiently degrading PFAS in wastewater by adjusting variable alternating current parameters. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) are a class of synthetic organic compounds that have been widely used in various fields since the 1940s due to their unique physical and chemical properties, including medicine, industrial production, paint manufacturing, aqueous film-forming foams (AFFF), and food packaging. However, the presence of strong C-H bonds in PFAS gives them extremely high chemical and thermal stability, making them difficult to degrade naturally, resulting in their long-term accumulation in the environment and organisms, making them one of the pollutants of global concern. The recalcitrance of PFAS is reflected not only in their environmental persistence, but also in their widespread distribution in ecosystems and food chains, posing a potential threat to health. Studies have shown that PFAS compounds can cause serious damage to the liver, kidneys, endocrine system, and immune function, and even pose a carcinogenic risk. More seriously, their half-life in water can be as long as decades, further exacerbating the problem of environmental pollution. Therefore, how to efficiently and safely remove PFAS has become a technical challenge that needs to be urgently addressed in the field of environmental pollution control.

[0003] In response to the degradation of PFAS, electrochemical oxidation technology has received widespread attention in recent years due to its high efficiency and environmental friendliness. Traditional direct current (DC) technology has obvious shortcomings in treating PFAS, such as electrode polarization effects, by-product accumulation problems, and electrode scaling and aging. These problems limit its efficiency and economy in long-term operation. Therefore, new solutions are needed to achieve efficient treatment of PFAS. Therefore, AC technology, with its high efficiency and sustainability advantages, has demonstrated great potential in the field of PFAS wastewater treatment. This technology not only demonstrates excellent performance in laboratory studies, but also provides an important technical foundation for future large-scale practical applications, providing a practical solution to addressing the global PFAS pollution challenge. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and provide a method for degrading PFAS in wastewater using alternating current technology, so as to solve the shortcomings of the existing technology of PFAS wastewater degradation electrodes, such as easy scaling and aging, low degradation efficiency, high energy consumption and slow mass transfer rate of active substances.

[0005] In order to solve the above technical problems, the present invention discloses a method for degrading PFAS in wastewater using alternating current technology, comprising the following steps:

[0006] (1) adding a PFAS aqueous solution and an electrolyte aqueous solution into an electrolytic cell as a working solution for the degradation reaction, so that the PFAS concentration in the working solution is 10 to 200 mg / L;

[0007] (2) Selecting the same electrode material as the cathode and anode, preferably, selecting the same electrode material with the same reaction surface as the cathode and anode, using Ag / AgCl electrode as the reference electrode, constructing a three-electrode system, and passing oxygen;

[0008] (3) Use a multi-potential step mode to provide AC power, set the positive voltage and negative voltage, and achieve periodic polarity reversal of the electrode at a certain AC frequency, and continue the reaction for 1 to 4 hours.

[0009] Wherein, the PFAS is any one or more of perfluoroheptanoic acid (PFHpA), perfluorononanoic acid (PFNA), and perfluorooctanoic acid (PFOA).

[0010] The electrolyte solution is a solution containing any one of KOH, NaOH, Na2SO4, NaCl, and H2SO4.

[0011] Preferably, the concentration of the electrolyte in the working solution is 0.05-1M.

[0012] The electrode material is any one of hydrophobic carbon paper, titanium sheet, graphite sheet, nickel foam, copper foam and platinum sheet.

[0013] In some embodiments, the area of the electrode material is 1-3 cm 2 .

[0014] Preferably, the oxygen flow rate is 1-5 mL min -1 .

[0015] The frequency of the alternating current is 0.001-0.5 Hz. Preferably, the frequency of the alternating current is 0.01-0.5 Hz.

[0016] Preferably, the positive voltage of the alternating current is 1.5 to 2.5 V (vs. Ag / AgCl); and the negative voltage of the alternating current is -0.02 to -1 V (vs. Ag / AgCl).

[0017] In a preferred embodiment, the oxygen flow rate is 1-5 mL min -1 The frequency of the alternating current is 0.01 to 0.05 Hz, the forward voltage of the alternating current is 1.5 to 2.5 V (vs. Ag / AgCl), and the negative voltage of the alternating current is -0.02 to -1 V (vs. Ag / AgCl).

[0018] Alternating current (AC) technology, with its unique electrochemical reaction mechanism, provides a new solution for the degradation of PFAS. Unlike traditional electrochemical methods, AC dynamically changes the reaction environment on the electrode surface by periodically reversing the polarity of the electrode. This feature not only effectively avoids electrode polarization, but also continuously generates active sites on the electrode surface, significantly improving the synergistic performance of oxidation and reduction reactions, thereby greatly improving the degradation efficiency of PFAS. In addition, the dynamic characteristics of the AC electric field can inhibit the formation of by-products, reduce pollution in the reaction system, extend the service life of the electrode, and reduce equipment maintenance costs. In practical applications, AC technology can achieve efficient degradation with low energy consumption, showing good economic and sustainable advantages. These characteristics make AC technology a highly promising innovative method in the field of PFAS pollution control. AC technology breaks through the limitations of traditional methods by introducing dynamic electric fields, opening up a new technical path for the efficient treatment of PFAS.

[0019] Beneficial effects: Compared with the existing technology, it has the following advantages and beneficial effects:

[0020] (1) The present invention achieves periodic reversal of electrode polarity by adjusting the frequency of alternating current, effectively avoiding the polarization effect and significantly improving the activity of the electrochemical reaction interface, thereby enhancing the degradation efficiency of PFAS;

[0021] (2) The alternating current in the present invention dynamically switches the electrode roles, promoting the further degradation of short-chain byproducts, effectively reducing their accumulation, and improving the wastewater treatment effect;

[0022] (3) The alternating current in the present invention balances the electrode load, reduces scaling and aging problems, significantly extends the electrode life, and reduces operating and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 1 is an X-ray powder diffraction (XRD) pattern of the hydrophobic carbon paper before and after the reaction in Example 1 of the present invention;

[0024] Figure 2 This is a graph of PFOA degradation efficiency obtained by adjusting the frequency in Example 1;

[0025] Figure 3 This is a graph showing the degradation efficiency of PFOA obtained by adjusting the positive voltage in Example 2;

[0026] Figure 4 This is a graph showing the degradation efficiency of PFOA obtained by adjusting the negative voltage in Example 3;

[0027] Figure 5 is an efficiency diagram of PFOA degradation by AC power in Example 1;

[0028] Figure 6 is an efficiency diagram of PFNA degradation by AC power in Example 2;

[0029] Figure 7 is a graph showing the efficiency of PFHpA degradation by alternating current in Example 3;

[0030] Figure 8 This is a diagram showing the efficiency of PFOA degradation by direct current in Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0032] Example 1

[0033] In this example, a 50 mL electrolytic cell was used as the reaction vessel, and 20 mL of 200 mg / L PFOA solution and 20 mL of 0.5 M H2SO4 electrolyte solution were added as the working solution for the degradation reaction. 2 The hydrophobic carbon paper was used as cathode and anode, and the Ag / AgCl electrode was used as reference electrode to construct a three-electrode system. Oxygen was introduced at a flow rate of 2 mL min -1 . The AC power supply is provided by the multi-potential step mode provided by the electrochemical workstation. The forward voltage is set to 2.5V, the negative voltage is set to -0.7V, and the AC frequency is used as a variable. Multiple groups of parallel experiments are set up (that is, except for the frequency of the AC power, other conditions are the same between the experiments in each group). The frequencies are 0.5Hz, 0.1Hz, 0.05Hz, 0.025Hz, 0.02Hz, 0.01Hz, 0.008Hz, and 0.006Hz respectively. The experimental running time is 3h. During the degradation process, reaction liquid samples are collected at 0h, 0.5h, 1h, 2h and 3h respectively. After the collected samples are diluted, the degradation rate of PFOA is tested by HPLC-MS / MS. The experimental results are as follows. Figure 2 As shown in the figure, the degradation efficiency of PFOA varies under different frequency conditions. Among them, the degradation efficiency reaches a maximum of 92% at 0.02Hz. This result proves that the degradation efficiency of PFOA can be significantly improved by optimizing the AC frequency. In particular, under the condition of 0.02Hz, the electrolysis reaction shows the best synergistic degradation effect, demonstrating the unique advantage of the present invention in achieving efficient degradation through AC frequency regulation.

[0034] Example 2

[0035] In this example, a 50 mL electrolytic cell was used as the reaction vessel, and 20 mL of a 200 mg / L PFOA solution and 20 mL of a 0.5 M H2SO4 electrolyte solution were added as the working solution for the degradation reaction. 2 The hydrophobic carbon paper was used as cathode and anode respectively, and Ag / AgCl was used as reference electrode to construct a three-electrode system. Oxygen was introduced at a flow rate of 2 mL min -1 . The AC power supply was provided by an electrochemical workstation. With the forward voltage as a variable, multiple parallel experiments were set up. The positive voltages were set to 1.3V, 1.5V, 1.7V, 1.9V, and 2.3V, the negative voltage was fixed at -0.02V, and the AC frequency was 0.02Hz. The experimental running time was 3h. During the degradation process, samples were collected at 0h, 0.5h, 1h, 2h, and 3h. After dilution, the collected samples were used to determine the residual concentration of PFOA by HPLC-MS / MS to calculate the removal rate. The experimental results are shown in the figure. Figure 3 Adjusting the forward voltage significantly impacts the PFOA degradation efficiency, with the highest efficiency reaching 90% at a forward voltage of 2.3 V. This result demonstrates that appropriately increasing the forward voltage can significantly enhance the degradation effect of the electrolytic reaction. The present invention achieves efficient coordination of the redox reaction by regulating the voltage with alternating current, fully demonstrating the superiority of this method.

[0036] Example 3

[0037] In this example, a 50 mL electrolytic cell was used as the reaction device, and 20 mL of 200 mg / L PFOA solution and 20 mL of 0.5 M H2SO4 electrolyte solution were added as the working solution for the degradation reaction. Both pieces have an area of 1 cm 2 The carbon paper was used as cathode and anode respectively, and the reference electrode was Ag / AgCl. A standard three-electrode system was constructed and oxygen was introduced. The oxygen flow rate was controlled at 2 mL min -1 . The AC power supply for the electrolysis reaction is provided by the electrochemical workstation in the electrochemical workstation. The forward voltage of the experiment is fixed at 2.3V, and the negative voltage is used as a variable. Multiple sets of parallel experiments are set up, with negative voltages of -0.02V, -0.08V, -0.1V, -0.3V, -0.5V, and -0.7V, and the AC frequency is 0.02Hz. The experimental running time is 3h, and samples are collected at 0h, 0.5h, 1h, 2h and 3h respectively during the degradation process. After dilution, the collected samples are tested for the removal rate of PFOA by HPLC-MS / MS. The experimental results are as follows Figure 4As shown in the figure, adjusting the negative voltage has a significant impact on the degradation efficiency of PFOA. As the negative voltage gradually increases, the degradation efficiency significantly improves, reaching a maximum of 90% at -0.02V. This method achieves efficient synergy between oxidation and reduction reactions by adjusting the negative voltage with alternating current, demonstrating its unique advantage in improving degradation efficiency. This method provides an efficient and flexible solution for treating difficult-to-degrade organic pollutants.

[0038] Application Example 1

[0039] In the application example of the present invention, a 50 mL electrolytic cell was selected as the reaction vessel, and 20 mL of 200 mg / L PFOA solution and 20 mL of 0.5 M H2SO4 electrolyte solution were added as the working solution for the degradation reaction. 2 The hydrophobic carbon paper was used as cathode and anode, and the Ag / AgCl electrode was used as reference electrode to construct a three-electrode system. Oxygen was introduced at a flow rate of 2 mL min -1 . In the experiment, an electrochemical workstation was used to provide AC power, and the forward voltage was set to 2.3V, the negative voltage was -0.5V, and the AC frequency was 0.02Hz. The dynamic regulation of the electrode surface activity was achieved through periodic polarity reversal to improve the degradation efficiency. The experimental running time was 3h, during which reaction liquid samples were collected at 0h, 0.5h, 1h, 2h and 3h. After the collected samples were diluted, the removal rate of PFOA was tested by HPLC-MS / MS, and the concentration of fluoride ions generated was determined by IC to evaluate the defluorination rate. The experimental results are as follows Figure 5 As shown, under the described conditions, this method achieved a 91% PFOA degradation efficiency and an 82% defluorination rate, fully demonstrating the technology's remarkable effectiveness in degrading PFOA and achieving complete mineralization. These results demonstrate the exceptional application value of the AC degradation method proposed in this paper in treating PFAS-contaminated wastewater, providing an efficient and environmentally friendly solution for environmental pollution control.

[0040] Application Example 2

[0041] The method of the present invention is also applicable to the treatment of other types of PFAS-contaminated wastewater, such as PFNA. In a specific application, a 50 mL electrolytic cell was selected as the reaction vessel, and 20 mL of a 200 mg / L PFNA solution and 20 mL of a 0.5 M H2SO4 electrolyte solution were added as the working solution for the degradation reaction. Two plates with an area of 1 cm 2 Carbon paper was used as cathode and anode respectively, and Ag / AgCl electrode was used as reference electrode to construct a three-electrode system. Oxygen was introduced and the oxygen flow rate was controlled at 2 mL min -1. The AC power supply was provided by the multi-potential step mode in the electrochemical workstation. The forward voltage of the experiment was set to 2.3V, the negative voltage was -0.5V, and the AC frequency was 0.02Hz. The experimental running time was 3h, during which samples were collected for analysis at 0h, 0.5h, 1h, 2h and 3h. After dilution, the collected samples were used to determine the removal rate of PFNA by HPLC-MS / MS, and IC was used to analyze the amount of fluoride ions generated in the solution to evaluate the defluorination rate. The experimental results are shown in Figure 2. Figure 6 As shown, under the above conditions, the method of the present invention achieved a 70% degradation rate for PFNA and a 46% defluorination rate. This result demonstrates that the AC degradation technology of the present invention not only has a significant degradation effect on persistent organic pollutants such as PFNA, but also achieves efficient defluorination, providing a highly efficient and environmentally friendly solution for practical water treatment.

[0042] Application Example 3

[0043] The method of the present invention is also applicable to the treatment of other types of PFAS contaminated wastewater, such as perfluoroheptanoic acid (PFHpA). In this embodiment, a 50 mL electrolytic cell was selected as the reaction vessel, into which 20 mL of 200 mg / L PFHpA solution and 20 mL of 0.5 M H2SO4 electrolyte solution were added as the working solution for the degradation reaction. 2 Carbon paper was used as cathode and anode respectively, and Ag / AgCl electrode was used as reference electrode to construct a standard three-electrode system. Oxygen was introduced and the oxygen flow rate was controlled at 2 mL min -1 . In the experiment, AC power was provided by the multi-potential step mode in the electrochemical workstation, and the forward voltage was set to 2.3V, the negative voltage was set to -0.5V, and the AC frequency was set to 0.02Hz. The total running time of the experiment was 3h, and samples were collected for analysis at 0h, 0.5h, 1h, 2h and 3h. After dilution, the collected samples were tested for the removal rate of PFHpA by HPLC-MS / MS, and IC was used to determine the concentration of fluoride ions generated during the degradation process to evaluate the defluorination rate. The experimental results are as follows. Figure 7 As shown, under the conditions, the degradation rate of PFHpA by the method of the present invention reached 47%, and the defluorination rate was 34%. This result shows that the method of the present invention also exhibits excellent degradation ability in treating medium-chain PFAS (such as PFHpA) contaminated wastewater.

[0044] Comparative Example 1

[0045] In order to verify the superiority of the AC degradation technology of the present invention, a comparative experiment was conducted using DC technology. The experiment selected a 50 mL electrolytic cell as the reaction vessel, into which 20 mL of 200 mg / L PFHpA solution and 20 mL of 0.5 M H2SO4 electrolyte solution were added as the working solution for the degradation reaction. 2 The hydrophobic carbon paper was used as cathode and anode, and the Ag / AgCl electrode was used as reference electrode to construct a three-electrode system. Oxygen was introduced at a flow rate of 2 mL min -1 The DC power supply was provided by an electrochemical workstation, the working voltage was set to 2.3V, and the reaction time was 3h. During the degradation process, reaction liquid samples were collected at 0h, 0.5h, 1h, 2h and 3h respectively. After the collected samples were diluted, the residual concentration of PFOA was determined by HPLC-MS / MS to calculate the removal rate, and the concentration of fluoride ions generated was determined by IC to evaluate the defluorination rate. The experimental results are shown in Figure 2. Figure 8 As shown in (a), after 3 hours, the DC degradation method achieved a PFOA degradation rate of 44%, with a defluorination rate of only 13%. Compared with the AC method of the present invention, the AC method exhibited significant disadvantages in both degradation efficiency and mineralization. This result further demonstrates the significant technical advantages of the AC degradation method proposed in the present invention for treating PFAS-contaminated wastewater.

[0046] Comparative Example 2

[0047] To further verify the superiority of the AC degradation technology of the present invention, a comparative experiment was conducted using DC technology. A 50 mL electrolytic cell was used as the reaction vessel, into which 20 mL of 200 mg / L PFHpA solution and 20 mL of 0.5 M H2SO4 electrolyte solution were added as the working solution for the degradation reaction. 2 The hydrophobic carbon paper was used as cathode and anode, and the Ag / AgCl electrode was used as reference electrode to construct a three-electrode system. Oxygen was introduced at a flow rate of 2 mL min -1 The DC power supply was provided by an electrochemical workstation, the working voltage was set to -0.5V, and the reaction time was 3h. During the degradation process, samples were collected at 0h, 0.5h, 1h, 2h and 3h. After dilution, the collected samples were used to determine the residual concentration of PFOA by HPLC-MS / MS to calculate the removal rate; at the same time, the concentration of fluoride ions generated was analyzed by IC to evaluate the defluorination rate. The experimental results are shown in Figure 2. Figure 8As shown in Figure (b), under the aforementioned DC degradation conditions, the PFOA degradation rate was 37% after 3 hours, and the defluorination rate was only 28%. In contrast, the AC degradation method of the present invention significantly improved the degradation efficiency and defluorination rate within the same experimental time, demonstrating its significant technical advantage in treating PFAS-contaminated wastewater. This result further demonstrates the superiority of AC technology in terms of efficiency, mineralization capacity, and practical application.

[0048] The present invention provides a concept and method for degrading PFAS in wastewater using alternating current technology. There are numerous methods and approaches for implementing this technical solution. The foregoing description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for degrading PFAS in wastewater using alternating current technology, characterized in that: The following steps are involved: (1) Adding PFAS aqueous solution and electrolyte aqueous solution into the electrolytic cell as the working solution for the degradation reaction, so that the PFAS concentration in the working solution is 10~200 mg / L; (2) Select the same electrode material as the cathode and anode, use Ag / AgCl electrode as the reference electrode, construct a three-electrode system, and introduce oxygen; (3) Use a multi-potential step mode to provide AC power, set the positive voltage and negative voltage, and achieve periodic polarity reversal of the electrode at a certain AC frequency, and continue the reaction for 1-4 hours.

2. The method according to claim 1, characterized in that The PFAS is any one of perfluoroheptanoic acid, perfluorononanoic acid and perfluorooctanoic acid or a mixture of several thereof.

3. The method according to claim 1, characterized in that The electrolyte solution is a solution containing any one of KOH, NaOH, Na2SO4, NaCl, and H2SO4.

4. The method according to claim 1, wherein The concentration of the electrolyte in the working solution is 0.05-1M.

5. The method according to claim 1, wherein The electrode material is any one of hydrophobic carbon paper, titanium sheet, graphite sheet, nickel foam, copper foam and platinum sheet.

6. The method according to claim 1, characterized in that The area of the electrode material is 1-3 cm².

7. The method according to claim 1, characterized in that The oxygen flow rate is 1-5 mL min -1 .

8. The method according to claim 1, characterized in that The frequency of the alternating current is 0.001-0.5 Hz.

9. The method according to claim 1, characterized in that The positive voltage of the alternating current is 1.5~2.5V; the negative voltage of the alternating current is -0.02~-1V.

10. The method according to claim 1, characterized in that The oxygen flow rate is 1-5 mL min -1 , the frequency of the alternating current is 0.01-0.05 Hz, and the forward voltage of the alternating current is 1.5-2.5 V; The negative voltage of the alternating current is -0.02 ~ -1 V.

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