A method for degrading pfas in wastewater using alternating current technology

Abstract

The application discloses a PFAS wastewater degradation method based on alternating current technology, which adopts the same electrode material as the cathode and the anode, uses an Ag / AgCl electrode as a reference electrode to construct a three-electrode system, and degrades PFAS in wastewater by applying alternating current with different intensities. By adjusting the frequency of the alternating current, the periodic polarity reversal of the electrode is realized, so as to dynamically change the reaction environment on the surface of the electrode. The application effectively avoids the problems of electrode polarization and by-product accumulation in the traditional electrochemical method, and generates more active sites and oxidizing substances on the surface of the electrode, thereby significantly improving the degradation efficiency and defluorination rate of PFAS, and exhibiting excellent redox synergistic effect and environmental sustainability. Compared with the traditional direct current technology, the application utilizes the unique advantages of alternating current to improve the degradation efficiency, prolong the service life of the electrode and reduce the energy consumption, thereby providing an efficient, environmentally friendly and economical solution for PFAS wastewater treatment.

Description

Technical Field

[0001] This invention relates to the field of electrochemical degradation of organic pollutants, specifically to a method for efficiently degrading PFAS in wastewater by adjusting varying alternating current parameters. Background Technology

[0002] Per- and polyfluoroalkyl compounds (PFAS) are a class of synthetic organic compounds that have been widely used in various fields since the 1940s due to their unique physicochemical properties, including pharmaceuticals, industrial production, paint manufacturing, aqueous film-forming foams (AFFF), and food packaging. However, the strong CF bonds in PFAS endow them with extremely high chemical and thermal stability, making them difficult to degrade naturally. This leads to their long-term accumulation in the environment and organisms, making them one of the pollutants of global concern. The persistence of PFAS is not only reflected in their environmental persistence but also in their widespread distribution in ecosystems and the food chain, 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 have carcinogenic risks. More seriously, their half-life in water can be as long as decades, further exacerbating environmental pollution problems. Therefore, how to efficiently and safely remove PFAS has become a pressing technical challenge in the field of environmental pollution control.

[0003] Electrochemical oxidation (AC) technology has garnered significant attention in recent years due to its high efficiency and environmental friendliness in addressing the degradation of PFAS. Traditional direct current (DC) technology suffers from significant shortcomings in PFAS treatment, such as electrode polarization effects, byproduct accumulation, and electrode scaling and aging. These issues limit its long-term operational efficiency and economic viability. Therefore, new solutions are needed to achieve efficient PFAS treatment. AC technology, with its high efficiency and sustainability, has demonstrated enormous potential in PFAS wastewater treatment. This technology has not only shown excellent performance in laboratory research but also provides an important technological foundation for future large-scale practical applications, offering a feasible solution to the global challenge of PFAS pollution. Summary of the Invention

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

[0005] To address the aforementioned technical problems, this invention discloses a method for degrading PFAS in wastewater using alternating current technology, comprising the following steps:

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

[0007] (2) Select the same electrode material as the cathode and anode respectively. Preferably, select the same electrode material with the same reaction surface as the cathode and anode respectively. Use the Ag / AgCl electrode as the reference electrode to construct a three-electrode system and introduce oxygen.

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

[0009] 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 cm². 2 .

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

[0015] The AC frequency is 0.001-0.5Hz, preferably 0.01-0.5Hz.

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

[0018] Alternating current (AC) technology offers a novel solution for PFAS degradation due to its unique electrochemical reaction mechanism. Unlike traditional electrochemical methods, AC dynamically alters the reaction environment on the electrode surface by periodically reversing the electrode polarity. This characteristic not only effectively avoids electrode polarization but also continuously generates active sites on the electrode surface, significantly enhancing the synergistic performance of oxidation and reduction reactions, thereby greatly improving the degradation efficiency of PFAS. Furthermore, the dynamic characteristics of the AC electric field can suppress the formation of byproducts, reduce pollution in the reaction system, extend electrode lifespan, and reduce equipment maintenance costs. In practical applications, AC technology can achieve efficient degradation with low energy consumption, demonstrating excellent economic and sustainability advantages. These characteristics make AC technology a highly promising innovative method in the field of PFAS pollution control. By introducing a dynamic electric field, AC technology breaks through the limitations of traditional methods, opening up a new technological path for the efficient treatment of PFAS.

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

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

[0021] (2) In this invention, the role of the alternating current electrode is dynamically switched to promote the further degradation of short-chain by-products, effectively reduce their accumulation, and improve the wastewater treatment effect.

[0022] (3) In this invention, the alternating current balances the electrode load, reduces scaling and aging problems, greatly extends the electrode life, and reduces operating and maintenance costs. Attached Figure Description

[0023] Figure 1 These are X-ray powder diffraction (XRD) images of the hydrophobic carbon paper before and after the reaction in Specific Embodiment 1 of the present invention;

[0024] Figure 2 This is a graph showing the degradation efficiency of PFOA 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 This is a graph showing the efficiency of AC degradation of PFOA in Application Example 1;

[0028] Figure 6 This is a graph showing the efficiency of AC degradation of PFNA in Application Example 2;

[0029] Figure 7 This is a graph showing the efficiency of AC degradation of PFHpA in Application Example 3;

[0030] Figure 8 This is a graph showing the efficiency of DC electrodegradation of PFOA in Comparative Examples 1 and 2. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0032] Example 1

[0033] In this embodiment, 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. Two pieces with an area of ​​1 cm² were used... 2 Hydrophobic carbon paper was used as both the cathode and anode, and an Ag / AgCl electrode was used as the reference electrode to construct a three-electrode system. Oxygen was introduced at a flow rate controlled at 2 mL / min. -1 The AC power supply was provided by the multi-potential step mode of the electrochemical workstation, with a positive voltage of 2.5V and a negative voltage of -0.7V. Multiple parallel experiments were set up, using the AC frequency as the variable (i.e., all conditions were the same except for the AC frequency), at frequencies of 0.5Hz, 0.1Hz, 0.05Hz, 0.025Hz, 0.02Hz, 0.01Hz, 0.008Hz, and 0.006Hz. The experiment lasted for 3 hours. During the degradation process, reaction solution samples were collected at 0h, 0.5h, 1h, 2h, and 3h. After dilution, the degradation rate of PFOA was tested using 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. The highest degradation efficiency of 92% is achieved at 0.02 Hz. This result demonstrates that optimizing the AC frequency can significantly improve the degradation efficiency of PFOA. In particular, the electrolysis reaction exhibits the best synergistic degradation effect at 0.02 Hz, showcasing the unique advantage of this invention in achieving efficient degradation through AC frequency modulation.

[0034] Example 2

[0035] In this embodiment, 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. Two pieces with an area of ​​1 cm² were used... 2 Hydrophobic carbon paper was used as both the cathode and anode, with Ag / AgCl as the reference electrode, to construct a three-electrode system. Oxygen was introduced at a flow rate controlled at 2 mL / min. -1 The AC power supply was provided by an electrochemical workstation. Multiple parallel experiments were set up with the positive voltage as the variable. The positive voltages were set to 1.3V, 1.5V, 1.7V, 1.9V, and 2.3V, respectively, while the negative voltage was fixed at -0.02V. The AC frequency was 0.02Hz. The experiment lasted for 3 hours, and samples were collected at 0h, 0.5h, 1h, 2h, and 3h during the degradation process. After dilution, the residual concentration of PFOA in the collected samples was determined by HPLC-MS / MS to calculate the removal rate. The experimental results are as follows: Figure 3 As shown, the adjustment of the forward voltage has a significant impact on the degradation efficiency of PFOA, with the highest efficiency (90%) observed at a forward voltage of 2.3V. This result indicates that appropriately increasing the forward voltage can significantly enhance the degradation effect of the electrolytic reaction. This invention achieves highly efficient synergistic effects of the redox reaction by adjusting the voltage with alternating current, fully demonstrating the superiority of this method.

[0036] Example 3

[0037] In this embodiment, a 50 mL electrolytic cell was selected as the reaction apparatus. 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 plates have an area of ​​1 cm². 2 Carbon paper was used as both the cathode and anode, with Ag / AgCl as the reference electrode, to construct a standard three-electrode system. Oxygen was then introduced at a flow rate controlled at 2 mL / min. -1 The AC power supply for the electrolysis reaction was provided by the electrochemical workstation within the electrochemical workstation. The positive voltage was fixed at 2.3V, and the negative voltage was used as a variable to set up multiple parallel experiments with negative voltages of -0.02V, -0.08V, -0.1V, -0.3V, -0.5V, and -0.7V, and the AC frequency was 0.02Hz. The experiment ran for 3 hours, and samples were collected at 0h, 0.5h, 1h, 2h, and 3h during the degradation process. After dilution, the collected samples were tested for PFOA removal rate by HPLC-MS / MS. The experimental results are as follows: Figure 4As shown, adjusting the negative voltage significantly affects the degradation efficiency of PFOA. With a gradual increase in the negative voltage, the degradation efficiency increases significantly, reaching a maximum of 90% at -0.02V. This invention achieves highly efficient synergistic effects between oxidation and reduction reactions by adjusting the negative voltage with alternating current, verifying the unique advantages of this method in improving degradation efficiency. This method provides an efficient and flexible solution for treating recalcitrant organic pollutants.

[0038] Application Example 1

[0039] In an application example of this 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. Two pieces, each with an area of ​​1 cm², were used. 2 Hydrophobic carbon paper was used as both the cathode and anode, and an Ag / AgCl electrode was used as the reference electrode to construct a three-electrode system. Oxygen was introduced at a flow rate controlled at 2 mL / min. -1 In the experiment, an electrochemical workstation was used to provide AC power, with a positive voltage of 2.3V, a negative voltage of -0.5V, and an AC frequency of 0.02Hz. Dynamic regulation of electrode surface activity was achieved through periodic polarity reversal to improve degradation efficiency. The experiment lasted for 3 hours, with reaction solution samples collected at 0h, 0.5h, 1h, 2h, and 3h. After dilution, the collected samples were analyzed for PFOA removal rate using HPLC-MS / MS, and the concentration of generated fluoride ions was determined using IC40 to evaluate the defluorination rate. The experimental results are as follows: Figure 5 As shown, under the conditions described, the proposed method achieves a PFOA degradation efficiency of 91% and a defluorination rate of 82%, fully validating the significant effects of this technology in degrading PFOA and achieving complete mineralization. These results demonstrate that the AC degradation method proposed in this invention has excellent application value in treating PFAS-contaminated wastewater, providing an efficient and environmentally friendly solution for environmental pollution control.

[0040] Application Example 2

[0041] The method of this invention is also applicable to the treatment of other types of PFAS-contaminated wastewater, such as PFNA. In one specific application, a 50 mL electrolytic cell is selected as the reaction vessel, and 20 mL of 200 mg / L PFNA solution and 20 mL of 0.5 M H₂SO₄ electrolyte solution are added as the working solution for the degradation reaction. Two plates, each with an area of ​​1 cm², are selected. 2 Carbon paper was used as both the cathode and anode, with an Ag / AgCl electrode as the reference electrode, to construct a three-electrode system. Oxygen was then introduced at a flow rate controlled at 2 mL / min. -1The AC power supply was provided through the multi-potential step mode of the electrochemical workstation. The positive voltage was set to 2.3V, the negative voltage to -0.5V, and the AC frequency to 0.02Hz. The experiment ran for 3 hours, with samples collected for analysis at 0h, 0.5h, 1h, 2h, and 3h. After dilution, the PFNA removal rate was determined by HPLC-MS / MS, and the amount of fluoride ions generated in the solution was analyzed using IC40 to assess the defluorination rate. The experimental results are as follows: Figure 6 As shown, under the above conditions, the method of the present invention achieves a PFNA degradation rate of 70% and a defluorination rate of 46%. 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 a highly efficient defluorination reaction, providing an efficient and environmentally friendly solution for practical water treatment.

[0042] Application Example 3

[0043] The method of this invention is also applicable to treating other types of PFAS-contaminated wastewater, such as perfluoroheptanoic acid (PFHpA). In this embodiment, a 50 mL electrolytic cell is selected as the reaction vessel, and 20 mL of 200 mg / L PFHpA solution and 20 mL of 0.5 M H2SO4 electrolyte solution are added to it as the working solution for the degradation reaction. Two pieces with an area of ​​1 cm² are used... 2 Carbon paper was used as both the cathode and anode, and an Ag / AgCl electrode was used as the reference electrode to construct a standard three-electrode system. Oxygen was then introduced at a flow rate controlled at 2 mL / min. -1 In the experiment, AC power was provided through the multi-potential step mode of the electrochemical workstation, with a positive voltage of 2.3V, a negative voltage of -0.5V, and an AC frequency of 0.02Hz. The total experimental run time was 3 hours, and samples were collected for analysis at 0h, 0.5h, 1h, 2h, and 3h. After dilution, the collected samples were analyzed by HPLC-MS / MS to determine the removal rate of PFHpA, and the concentration of fluoride ions generated during the degradation process was determined using IC40 to assess the defluorination rate. The experimental results are as follows: Figure 7 As shown, under the conditions described, the method of the present invention achieves a degradation rate of 47% for PFHpA and a defluorination rate of 34%. This result indicates that the method of the present invention also exhibits superior degradation capabilities in treating wastewater contaminated with medium-chain PFAS (such as PFHpA).

[0044] Comparative Example 1

[0045] To verify the superiority of the AC degradation technology of this invention, a comparative experiment was conducted using DC technology. A 50 mL electrolytic cell was used as the reaction vessel, and 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. Two pieces with an area of ​​1 cm² were used... 2 Hydrophobic carbon paper was used as both the cathode and anode, and an Ag / AgCl electrode was used as the reference electrode to construct a three-electrode system. Oxygen was introduced at a flow rate controlled at 2 mL / min. -1 The DC power supply was provided by an electrochemical workstation, with the operating voltage set to 2.3V and the reaction time to 3 hours. During the degradation process, reaction solution samples were collected at 0 hours, 0.5 hours, 1 hour, 2 hours, and 3 hours. After dilution, the residual concentration of PFOA was determined by HPLC-MS / MS to calculate the removal rate, and the concentration of generated fluoride ions was determined using IC40 to assess the defluorination rate. Experimental results are as follows: Figure 8 As shown in (a), after 3 hours, the DC degradation method achieved a PFOA degradation rate of 44%, but a defluorination rate of only 13%. Compared with the AC technology of this invention, the AC technology exhibits significant disadvantages in both degradation efficiency and mineralization degree. This result further demonstrates the significant technical advantages of the AC degradation method proposed in this invention for treating PFAS-contaminated wastewater.

[0046] Comparative Example 2

[0047] To further verify the superiority of the AC degradation technology of this invention, a comparative experiment was conducted using DC technology. A 50 mL electrolytic cell was used as the reaction vessel, and 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. The experiment used two pieces with an area of ​​1 cm²... 2 Hydrophobic carbon paper was used as both the cathode and anode, and an Ag / AgCl electrode was used as the reference electrode to construct a three-electrode system. Oxygen was introduced at a flow rate controlled at 2 mL / min. -1 The DC power supply was provided by an electrochemical workstation, with the operating voltage set to -0.5V and the reaction time to 3 hours. Samples were collected at 0 hours, 0.5 hours, 1 hour, 2 hours, and 3 hours during the degradation process. After dilution, the residual concentration of PFOA in the collected samples was determined by HPLC-MS / MS to calculate the removal rate; simultaneously, the concentration of generated fluoride ions was analyzed using IC40 to assess the defluorination rate. Experimental results are as follows: Figure 8As shown in (b), under the aforementioned DC degradation conditions, the degradation rate of PFOA 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 advantages in treating PFAS-contaminated wastewater. This result further proves the superiority of AC technology in terms of efficiency, mineralization capacity, and practical applications.

[0048] This invention provides a method and approach for degrading PFAS in wastewater using alternating current technology. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for degrading PFAS in wastewater using alternating current technology, characterized in that, Includes the following steps: (1) Add PFAS aqueous solution and electrolyte aqueous solution to the electrolytic cell as working solution for degradation reaction, so that the concentration of PFAS in the working solution is 10~200 mg / L; (2) Select the same electrode materials as the cathode and anode respectively, and use the Ag / AgCl electrode as the reference electrode to construct a three-electrode system and introduce oxygen; (3) Use a multi-potential step mode to provide AC power, set positive and negative voltages, and achieve periodic polarity reversal of the electrodes at a certain AC frequency, and continue the reaction for 1-4 hours. The oxygen flow rate is 1-5 mL / min. -1 The AC frequency is 0.01-0.05 Hz; the positive voltage of the AC is 2.1-2.5V; the negative voltage of the AC is -0.02~-1V; the PFAS is any one or a mixture of perfluoroheptanoic acid, perfluorononanoic acid and perfluorooctanoic acid; the electrode material is any one of hydrophobic carbon paper, titanium sheet, graphite sheet, nickel foam, copper foam and platinum sheet.

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

3. The method according to claim 1, characterized in that, The concentration of the electrolyte in the working solution is 0.05-1M.

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

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