System and method for degrading pfas in concentrated water after reverse osmosis membrane for printing and dyeing by sequential cascade electrooxidation-photoreduction coupling

Abstract

The present application belongs to the technical field of electrochemical oxidation, and particularly relates to a system and method for sequentially cascading electro-oxidation and photo-reduction coupled degradation of PFAS in dyeing reverse osmosis membrane post-concentrated water. Through the synergistic cooperation of the sequentially cascading electro-oxidation unit and the photo-reduction unit, the whole system can realize efficient and stable treatment of the whole process from the overall concentration reduction to the deep defluorination of PFAS pollutants when facing the extremely complex composition of dyeing reverse osmosis concentrated water, and effectively avoids the problems of energy consumption increase, intermediate product accumulation and treatment effect fluctuation caused by improper process sequence. The present application constructs a flow-through membrane electrode cascade system based on the PDMS functionalized membrane anode / membrane cathode, and realizes the coupling of interface enrichment, mass transfer regulation and reaction cooperation in the PFAS removal process.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical oxidation technology, specifically relating to a system and method for sequential cascade electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane. Background Technology

[0002] With increasingly stringent industrial wastewater discharge standards, reverse osmosis (RO) technology, due to its highly efficient separation capabilities, has become a core process for the deep treatment and reuse of many high-concentration, recalcitrant wastewaters from industries such as dyeing, electroplating, and landfill leachate. However, while producing high-quality reclaimed water, RO also generates approximately 15-25% of the influent, resulting in ROC (reverse osmosis concentrate). ROC concentrates almost all the salts and unbiodegradable organic pollutants from the raw water, exhibiting complex composition, high salinity, and extremely poor biodegradability, becoming a key bottleneck hindering the achievement of "zero discharge" goals. Among the many pollutants, perfluorinated and polyfluoroalkyl substances (PFAS) have attracted significant attention due to their widespread use and extremely high environmental persistence; their concentration in ROC can be significantly enriched, posing potential environmental and health risks.

[0003] Currently, various technical approaches have been explored in the industry for treating PFAS-containing wastewater, but they all have significant limitations when applied to special matrices such as ROCs. Physical separation methods, such as activated carbon adsorption and ion exchange, can effectively transfer PFAS from the aqueous phase, but this is essentially a phase transfer of pollutants and does not achieve complete decomposition. Furthermore, they face problems such as easy saturation of adsorption materials, difficult regeneration, severe interference from high salinity, and high costs for subsequent hazardous waste disposal. Advanced oxidation technologies, such as ozone, Fenton, and persulfate activation, rely on the strong oxidizing free radicals (such as ·OH, SO4·) generated during the reaction. - PFAS molecules are used to attack organic pollutants. However, the CF bond energy in PFAS molecules is extremely high (about 116 kcal / mol), and their special "fluorine atom sheath" structure makes conventional hydroxyl radicals very inefficient at oxidizing them. This often requires extremely high reagent dosages or energy inputs, making it uneconomical and prone to generating a large number of fluorine-containing intermediates, thus failing to achieve efficient defluorination and mineralization.

[0004] In recent years, some more targeted technologies have been developed. For example, electrochemical oxidation, which utilizes direct electron transfer or the generation of strong oxide species on the anode surface, can effectively degrade some PFAS and is considered a promising technology. However, in practical applications, especially when treating ROCs with high salt and high organic content, this method faces challenges: First, high concentrations of competing substances in the wastewater (such as chloride ions and humic acid) severely deplete the active species generated by the electrode, resulting in poor selectivity and low current efficiency in PFAS treatment; second, simple oxidation processes often fail to completely mineralize long-chain PFAS, making it easier to convert them into a wide variety of short-chain fluorinated intermediates with unknown toxicity and migration, potentially posing new environmental risks. On the other hand, emerging treatment methods, such as UV-excited reduction technologies (e.g., UV / sulfite systems), attack the head groups of PFAS molecules with strong reducing agents like hydrated electrons, initiating the defluorination process. These methods have shown good defluorination capabilities for specific PFAS in laboratory pure water systems. However, when this technology is directly applied to real ROC treatment, its efficiency is greatly reduced due to the complex composition of the water (such as high concentrations of dissolved organic matter, nitrates and other hydrated electron quenchers), and the reduction of long-chain PFAS molecules is often slow and requires a long reaction time.

[0005] Designing an integrated process that is highly efficient, synergistic, and capable of achieving deep PFAS removal and efficient defluorination for real wastewater such as ROC, which has extremely complex composition and numerous interfering factors, remains a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention aims to overcome the shortcomings of existing technologies in the degradation and removal of PFAS in the concentrate after reverse osmosis membranes, such as poor selectivity in treating PFAS, difficulty in completely mineralizing long-chain PFAS, conversion into short-chain fluorinated intermediates with significant toxic side effects, poor defluorination effect, low efficiency, and long processing time. It provides a system and method for the sequential cascade electro-oxidation-photoreduction coupling degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membranes.

[0007] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution: A system for sequentially cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane treatment includes: A sequential cascaded electro-oxidation unit is used for electrochemical oxidation treatment of wastewater containing PFAS. The photo-reduction unit is used to perform ultraviolet light-excited reduction treatment on the effluent after being treated by the sequential cascaded electro-oxidation unit. A connecting pipeline is used to transport the effluent from the sequential cascaded electro-oxidation unit to the photo-reduction unit.

[0008] Because reverse osmosis concentrate has high conductivity, placing the sequential cascade electro-oxidation unit at the front end of the process allows it to start and operate with relatively low energy consumption. Simultaneously, the electrochemical process, particularly through mechanisms such as direct electron transfer at the anode, effectively attacks long-chain PFAS molecules, causing initial decomposition and shortening of their chains. This invention uses a sequential cascade electro-oxidation unit to electrochemically oxidize PFAS-containing wastewater, transforming the initially high-concentration, complex-structured mixture of PFAS into a series of relatively simple, short-chain fluorinated intermediates. Furthermore, the electrochemical oxidation process can also, to some extent, remove some oxidizable background organic matter in the concentrate, thereby reducing the interference load on subsequent steps. After electrochemical oxidation pretreatment, the PFAS composition of the effluent changes from being predominantly long-chain to being predominantly short-chain intermediates, simplifying the complexity of the water quality.

[0009] Short-chain intermediates typically have higher water solubility, and their molecular structure may be more sensitive to reducing attacks. More importantly, since the pre-oxidation process has already consumed some easily oxidizable background impurities, the risk of ineffective quenching of key reducing agents such as hydrated electrons is significantly reduced. This allows the reduction energy and reagents to act more concentratedly on the target fluorine-containing substance, thereby greatly improving the targeting and defluorination efficiency of the photoreduction step. This invention, through a cascade of "oxidation followed by reduction," essentially constructs a progressive processing pipeline of "decomposition-conversion-defluorination." Specifically, this invention utilizes the high salinity of the concentrated water itself to efficiently complete the initial decomposition and interference removal tasks through sequentially cascaded electrooxidation units, creating favorable conditions for the subsequent photoreduction unit, which has more stringent reaction conditions. The photoreduction unit, based on the preceding processes, focuses on the efficient defluorination and mineralization of short-chain fluorine-containing intermediates, overcoming the difficulty of deep defluorination in simple oxidation processes.

[0010] Preferably, the sequential cascaded electro-oxidation unit includes at least one flow-through electrochemical filtration reactor, which is provided with an anode and a cathode, and the wastewater to be treated passes through the anode and / or cathode under the drive of an applied current to react.

[0011] Preferably, the surfaces of the anode and / or cathode are hydrophobically modified to enhance the interfacial enrichment of PFAS.

[0012] Preferably, the hydrophobic modification treatment is achieved by introducing polydimethylsiloxane (PDMS) onto the surface of the anode and / or cathode.

[0013] Preferably, the anode is an electrode based on Magnéli phase titanium oxide, and the cathode is an electrode based on iron-based compounds.

[0014] Preferably, the anode is a Ti4O7 electrode and the cathode is a FeOCl electrode.

[0015] Preferably, the photoreduction unit is an ultraviolet / sulfite (UV / S) reaction system, which includes a reactor that provides an ultraviolet light source and a sulfite dosing device.

[0016] A method for sequentially cascaded electro-oxidation-photoreduction coupled degradation of PFAS in concentrate after dyeing and printing reverse osmosis membranes includes the following steps: S1. Based on the system described above, wastewater containing PFAS is passed into a sequential cascade electro-oxidation unit for electrochemical oxidation treatment. S2. The effluent after step S1 is passed into the photoreduction unit for ultraviolet light excitation reduction treatment.

[0017] Preferably, in step S1, the wastewater passes through the hydrophobically modified anode and / or cathode in a flow-through electrochemical filtration reactor.

[0018] Preferably, the electrochemical oxidation treatment in step S1 is operated in a constant current mode with a current density ranging from 0.5 to 5 mA / cm². 2 .

[0019] As a further preferred embodiment, the electrochemical oxidation treatment in step S1 is operated in a constant current mode with a current density range of 1.6 mA / cm². 2 .

[0020] Preferably, in step S2, the pH value of the photoreduction unit is controlled to be 9-13.

[0021] As a further preferred embodiment, in step S2, the pH value of the photoreduction unit is controlled to be 12.

[0022] Preferably, in step S2, the reduction treatment excited by ultraviolet light is carried out in the presence of sulfite.

[0023] Preferably, the PFAS includes perfluorooctanoic acid and / or perfluorooctane sulfonic acid.

[0024] Therefore, the present invention has the following beneficial effects: (1) Through the synergistic cooperation of sequential cascaded electro-oxidation units and photo-reduction units, the whole system can achieve efficient and stable treatment of PFAS pollutants from overall concentration reduction to deep defluorination when facing dyeing reverse osmosis concentrate with extremely complex composition. At the same time, it effectively avoids problems such as increased energy consumption, accumulation of intermediate products and fluctuation of treatment effect caused by improper process sequence. (2) The present invention constructs a flow-through membrane electrode cascade system based on PDMS functionalized membrane anode / membrane cathode, realizing the coupling of interface enrichment, mass transfer regulation and reaction synergy in the PFAS removal process. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the fabrication of a membrane electrode.

[0026] Figure 2 This is a photograph of the assembly of the membrane electrode and a flow-through electrochemical filtration reactor.

[0027] Figure 3 This is a schematic diagram of a flow-through electrochemical filtration and electrolysis device.

[0028] Figure 4 SEM images of PDMS-FeOCl / CNTs and PDMS-Ti4O7 / CNTs.

[0029] Figure 5 The image shows the EDS energy distribution and elemental distribution of PDMS-FeOCl / CNTs. Figure 5 In the diagram, A represents the EDS energy spectrum and elemental distribution of PDMS-Ti4O7 / CNTs; Figure 5 B in the diagram represents the EDS energy spectrum and elemental distribution of PDMS-FeOCl / CNTs.

[0030] Figure 6 XRD patterns of PDMS-Ti4O7 / CNTs and PDMS-FeOCl / CNTs.

[0031] Figure 7 This figure shows the effect of PDMS dosage on the wettability of the membrane electrode surface. Among them, Figure 7 In the figure, A represents the change in contact angle as a function of PDMS dose; Figure 7 B in the figure is a comparison of the permeation behavior of water droplets on the surfaces of the two membrane electrodes when there is no PDMS modification.

[0032] Figure 8 This figure shows the effect of DMS dosage on the electrochemical characteristics of the membrane anolyte. Among them, Figure 8 In the figure, A represents the LSV curve and oxygen evolution potential (OEP) graph of PDMS-Ti4O7 / CNTs; Figure 8 B in the figure represents the comparison of electrochemical impedance (EIS) Nyquist plots and the fitted interfacial charge transfer resistance (Rct) at different PDMS doses. Figure 8 In the figure, C represents the voltage change over time in the operating cell of a flow-through electrochemical filtration reactor equipped with different PDMS-Ti4O7 / CNTs anodes.

[0033] Figure 9The graph shows a comparison of the electrochemical impedance (EIS) and the fitted charge transfer resistance (Rct) of Ti4O7.

[0034] Figure 10 The figure shows the cyclic voltammetry (CV) curves (ORR verification) of the PDMS-FeOCl / CNTs membrane cathode in N2 and O2 saturated electrolyte.

[0035] Figure 11 This figure shows the effect of PDMS dosage on the ORR selectivity and active species generation of the membrane cathode. Figure 11 In the figure, A represents the relationship between H2O2 selectivity and electron transfer number n under different PDMS doses as a function of applied potential (calculated by the rotating disk electrode RRDE method); Figure 11 B in the figure represents the linear sweep curve of the RRDE ring current versus the disk current. Figure 11 C in the graph represents the cumulative concentration change of ·OH under different PDMS doses; Figure 11 In the figure, D represents the voltage change over time in the operating tank of a flow-through electrochemical filtration reactor equipped with different PDMS-FeOCl / CNTs cathodes.

[0036] Figure 12 The graph shows the removal of PFOA (attributed to adsorption) and the release of background inorganic fluorine under open-circuit (no power) cycling conditions. Figure 12 In the graph, A represents the change of PFOA concentration over time. Figure 12 B in the text represents fluoride ions (F). - Release over time graph.

[0037] Figure 13 Comparison of PFOA degradation and defluorination kinetics of membrane electrode pairs with different PDMS functionalization levels (in kJ / kJ) obs With k deF (Characteristics) diagram.

[0038] Figure 14 This is a comparison of PFOA removal and defluorination processes under different PDMS functionalization methods. Figure 14 Figures A and B in the diagram are comparisons of PFOA removal and defluorination processes under anodic PDMS modification only. Figure 14 C and D in the figure are comparison diagrams of PFOA removal and defluorination processes under cathode PDMS modification only; Figure 14 E and F in the figure are comparison diagrams of PFOA removal and defluorination processes under the anodic-cathode matched PDMS modification combination (solid line is pseudo-first-order fit). Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0040] Example 1: This embodiment provides a system for sequentially cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane, comprising: A sequential cascaded electro-oxidation unit is used for electrochemical oxidation treatment of wastewater containing PFAS. The photo-reduction unit is used to perform ultraviolet light-excited reduction treatment on the effluent after being treated by the sequential cascaded electro-oxidation unit. A connecting pipeline is used to transport the effluent from the sequential cascaded electro-oxidation unit to the photo-reduction unit.

[0041] This embodiment also provides a method for sequentially cascaded electro-oxidation-photoreduction coupling degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane.

[0042] A method for sequentially cascaded electro-oxidation-photoreduction coupled degradation of PFAS in concentrate after dyeing and printing reverse osmosis membranes includes the following steps: S1. Based on the system described above, wastewater containing PFAS is passed into a sequential cascade electro-oxidation unit for electrochemical oxidation treatment. S2. The effluent after step S1 is passed into the photoreduction unit for ultraviolet light excitation reduction treatment.

[0043] I. Water Samples and Testing Methods Simulated water preparation: This invention uses two types of water samples for comparative research: laboratory-prepared simulated water and actual reverse osmosis concentrate (ROC). The simulated water is Milli-Q ultrapure water (18.2 MΩ·cm). -1 The solution was prepared using Na₂SO₄ as the supporting electrolyte at a concentration of 100 mM. Based on this, the target PFAS standard was added to prepare the influent, simulating a total PFAS concentration of 5.0 mg·L⁻¹ in the water. -1(Including perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorohexanoic acid (PFHxA), hexafluoropropylene epoxy propylene dimer acid (HFPO-DA), perfluorohexane sulfonic acid (PFHxS), perfluorobutyric acid (PFBA), perfluorobutane sulfonic acid (PFBS), etc.). Simulated water circulates through the reaction apparatus at a set flow rate (5.0 mL / min) during the experiment. -1 This was used to evaluate the removal and defluorination performance of the process under controlled matrix conditions. To reflect the influence of actual high-salt / organic matrices, a spiked experiment was also conducted under ROC conditions: PFOA (100 μg·L⁻¹) was spiked into the ROC background. -1 This was used to investigate matrix effects and process stability. Liquid samples (250 μL each time) were collected at various time points during the experiment and filtered through a 0.22 μm polypropylene (PP) membrane before being analyzed by LC-MS / MS and ion chromatography (IC).

[0044] 2. Post-membrane concentrate water quality indicators: The actual water sample was taken from reverse osmosis concentrate (ROC) from a textile industrial park in Shaoxing. After collection, the ROC water sample was placed in a 20 L high-density polyethylene (HDPE) container and stored at 4℃. Its typical water quality characteristics are shown in Table 1 below: .

[0045] To ensure comparability, the laboratory-simulated water was matched to the ROC level at pH (approximately 7.3) and conductivity (simulated water conductivity approximately 5 mS·cm). -1 ).

[0046] II. Preparation of Membrane Electrode Pairs 1. Fabrication of Membrane Anode and Cathode: This invention employs a vacuum filtration method to load powder electrode materials onto a supporting membrane to prepare membrane electrodes, and surface functionalization is achieved by adding different dosages of polydimethylsiloxane (PDMS). The membrane anode is selected as PDMS-Ti4O7 / CNTs, and the membrane cathode is selected as PDMS-FeOCl / CNTs. A schematic diagram of the membrane electrode fabrication is shown below. Figure 1 As shown.

[0047] (1) Preparation of PDMS-Ti4O7 / CNTs membrane anode: 200 mg of Ti4O7 and 100 mg of carbon nanotubes (CNTs) were weighed and added to 100 mL of DMF, along with 10–1200 μL of PDMS. The mixture was then sonicated with a probe for 2 h to form a homogeneous dispersion. The resulting dispersion was then loaded onto a 47 mm diameter polytetrafluoroethylene (PTFE) support membrane using vacuum filtration to obtain a PDMS-Ti4O7 / CNTs membrane anode.

[0048] (2) Preparation of FeOCl / CNTs nanocomposites: FeOCl / CNTs were synthesized using an impregnation-calcination method: 2 g of CNTs were dispersed in a FeCl3 ethanol solution (0.71 g FeCl3 dissolved in 20 mL ethanol), and sonicated for 1 h using a probe; the resulting FeCl3-CNTs were dried and transferred to a sealed crucible, and then heated in a muffle furnace at 10 °C·min. -1 Heat to 220℃ and hold for 2 hours; after cooling, wash repeatedly with water and ethanol to remove impurities, and dry in a vacuum oven for later use.

[0049] (3) Preparation of PDMS-FeOCl / CNTs film cathode: Weigh 100 mg of FeOCl / CNTs and add it to 100 mL of DMF containing 10~600 μL of PDMS. Sonicate the mixture with the anode probe for 2 h to obtain a uniform dispersion. Then, vacuum filter the mixture to form a film and prepare a PDMS-FeOCl / CNTs membrane cathode.

[0050] 2. Assembly of membrane electrodes: The membrane electrode pair is assembled in a modified polycarbonate filter housing (Whatman) to form a flow-through electrochemical filter. During assembly, a 40 mm diameter titanium mesh is used as a current collector and tightly bonded to both the membrane anode (PDMS-Ti4O7 / CNTs) and membrane cathode (PDMS-FeOCl / CNTs), with the mesh leads directly connected to a DC power supply. The PTFE support membrane used for the membrane anode, besides supporting the electrode layer formed by filtration, also serves as insulation, separating the anode and cathode to prevent short circuits. The effective filtration area of ​​this filter is 12.56 cm². 2 During operation, the feed water flows sequentially through the membrane anode and membrane cathode in a set direction, realizing a series cascade reaction process. The assembly of the membrane electrode and a physical diagram of the flow-through electrochemical filtration reactor are shown below. Figure 2 As shown.

[0051] III. Apparatus and Test Methods 1. Flow-through electrochemical filtration reactor device: This invention utilizes a modified polycarbonate filter housing to construct a flow-through electrochemical filtration reactor. Influent flows through the membrane electrode pair in a "anode → cathode" direction, and the electrochemical reaction is driven by an applied current. In a simulated water system, influent (containing 100 mM Na₂SO₄ and the target PFAS) circulates through the electrochemical filtration reactor at a flow rate of approximately 5.0 mL / min. -1 Unless otherwise specified, the device operates in constant current mode with a total current of 20 mA (corresponding to a current density of approximately 1.6 mA·cm).-2 The reactor voltage was recorded over time. For complex matrices such as concentrated brine / ROC, multi-stage series operation can be used to improve residence time and mass transfer, with samples taken at set time points for subsequent quantitative analysis. A schematic diagram of a flow-through electrochemical filtration and electrolysis device is shown below. Figure 3 As shown.

[0052] 2. Adsorption test: To differentiate the contributions of physical adsorption and electrochemical degradation, a dark-state adsorption control experiment was conducted under open-circuit conditions: a solution containing the target PFAS was passed through the device or contacted with the membrane electrode in the same manner as in the reaction experiment, and the change in PFAS concentration was measured after equilibrium was reached. The removal rate of PFAS under open-circuit conditions was low (<10%), indicating that the removal by this device under the conditions of this invention mainly comes from electrochemical reactions rather than simple adsorption. Furthermore, to avoid background interference, a blank experiment was conducted under PFAS-free conditions to eliminate the influence of fluoride ion release and other effects caused by device background.

[0053] 3. Multi-stage tandem long-term degradation experiment: To evaluate the sustained removal and defluorination capabilities of a flow-through electrochemical filtration system for target pollutants (PFAS) under long operating times and extended cumulative residence times, a multi-stage series long-term degradation experiment was conducted. The multi-stage experiment used a flow-through electrochemical filtration reactor as the basic unit, with influent flowing through the membrane electrode pair in an "anodine → cathode" direction. The membrane electrodes were tightly attached to a titanium mesh current collector and connected to a DC power supply to provide constant current drive. The multi-stage operation employed a circulating flow method: a certain volume of the solution to be treated was placed in a storage bottle and pumped into the flow-through electrochemical filtration reactor at a constant flow rate using a peristaltic pump. This allowed the system to pass through the membrane electrode pair multiple times within a set time period, increasing the cumulative residence time and examining the stability during long-term operation. Under simulated water conditions, 100 mM Na₂SO₄ was used as the supporting electrolyte, and the typical operating flow rate was approximately 5.0 mL / min. -1 The constant current mode was used (total current 20 mA, corresponding to a current density of approximately 1.6 mA·cm). -2 The reactor was driven by a reaction, and the voltage change over time was recorded to characterize its operating status and stability. Liquid samples were collected at specified time points (parallel samples were set up at each time point). After filtration through a 0.22 μm polypropylene (PP) filter membrane, the samples were used for LC-MS / MS quantitative determination of target pollutant concentration and ion chromatography (IC) determination of F. - Release was performed to characterize the removal kinetics and defluorination process; all experiments were conducted at least three times in parallel to ensure repeatability. Furthermore, under complex matrix conditions such as actual concentrated brine / ROC, a single-pass operation mode with multiple stages connected in series can be adopted according to engineering adaptation requirements to improve treatment efficiency and enhance adaptability to complex water quality fluctuations.

[0054] 4. UV / EO cascade test: The UV / EO cascade experiment was used to compare the synergistic effects and sequence differences of different unit combinations. The UV / S (ultraviolet / sulfite) unit used a 750 mL photochemical reactor equipped with a quartz sleeve and a 16 W low-pressure mercury lamp. In the ROC water sample experiment, 200 mL of ROC wastewater was added to the reactor, and Na2SO3 (10 mM) was added before the start of the UV / S experiment. After thorough mixing, the UV irradiation reaction was started; 0.1 mol·L -1 The pH was adjusted to 12 with NaOH; the reactor was kept sealed during the reaction to avoid the influence of air exchange. Two different cascade sequences were formed: (1) UV→EO: First, react under UV / S conditions for a set time, and then introduce the effluent into a flow-through electrochemical filtration reactor for subsequent EO.

[0055] (2) EO→UV: First, perform EO treatment reaction for a set time, and then send the effluent into the UV / S unit.

[0056] In the cascade experiments, samples were taken every 6 hours, and quantitative evaluation was performed using LC-MS / MS. To ensure comparability, the two sequences maintained the same total processing time and system volume.

[0057] IV. PFAS Quantitative and Intermediate Product Testing Methods 1. PFAS Quantitative PFAS in laboratory simulated water was quantified using UPLC-MS / MS: a Waters Acquity UPLC / Xevo TQ-S BEH-C18 column (2.1 mm × 150 mm, 1.7 μm) was used at a flow rate of 0.3 mL·h. -1 The injection volume was 5 μL; mobile phase A was methanol and mobile phase B was 0.1 wt% ammonium acetate aqueous solution, with gradient elution as shown in Table 2; ESI negative ion mode detection was used, with a desolvation temperature of 350℃ and nitrogen atmosphere of 800 L·h. -1 The capillary voltage was 2.05 kV and the cone voltage was 28 V, and quantification was performed in MRM mode (see Table 3 for MRM transitions).

[0058] Table 2: Acquity UPLC Gradient Elution Procedure Time (minutes) Phase A (%) Phase B (%) 0 10 90 0.1 50 50 2.5 95 5 4.5 95 5 4.6 100 0 5.6 100 0 5.8 10 90 7.5 10 90

[0059] Table 3: MRM conversion parameters, collision energy, and method detection limit of PFAS .

[0060] Solid-phase extraction enrichment was performed on the ROC water sample before PFAS quantification: 50 mL of water sample after membrane filtration was taken and spiked with 4 μg·L⁻¹. -1 A mixed isotope internal standard (containing 9 compounds) was prepared using Oasis WAX (6 cc 150 mg). -1 SPE extraction and concentration to 1 mL; then quantification was performed using an Agilent 1290 Infinity UPLC / 6470B triple quadrupole, with a Poroshell HPH-C18 column (3.0 mm × 100 mm, 2.7 μm) and a guard column (4.6 mm × 50 mm, 2.7 μm), at a flow rate of 0.4 mL·min. -1 Injection volume: 10 μL; Mobile phase A: 5 mM ammonium acetate aqueous solution, Mobile phase B: 5 mM ammonium acetate methanol solution; ESI negative ion mode; Capillary voltage: 2500 V; Sheath gas: 375℃ / 12 L·min -1 Drying gas 230℃ / 6 L·min -1 Quantification was performed using the MRM mode. A calibration curve was established for ROC water sample quantification using a mixture of 38 PFAS standards, and correction was performed using isotope internal standards; information on the mixture components and 9 isotope internal standards is shown in Table 4.

[0061] Table 4: Information on PFAS Mixed Standards and Isotope Internal Standards .

[0062] 2. Intermediate product screening (Q-TOF) Screening of PFOA (or target PFAS) conversion products was performed using UPLC-Q-TOF-HRMS: an Agilent 1290 Infinity UPLC / Agilent 6545 Q-TOF was used, equipped with an Agilent Jet Stream ESI ion source, with scanning in both positive and negative ion modes; resolution 25,000-43,000 (m / z 100-1500), mass accuracy <5 ppm; full scan mode mass range 50-600 m / z, and automatic MS / MS with collision energies of 10, 20, and 40 eV to acquire fragment information (MS / MS range 50-1000 m / z). Specific gradient elution and acquisition parameters are shown in Tables 5 and 6. Common short-chain PFCAs and other products obtained from screening were further quantitatively confirmed using an Agilent 6470B triple quadrupole (ESI).

[0063] Table 5: UPLC-QTOF gradient elution procedure Time (minutes) Mobile phase A (%) Mobile phase B (%) initial 2 98 1 2 98 15 100 0 20 100 0 20.5 2 98 22 2 98

[0064] Table 6: UPLC-QTOF Operating Parameters .

[0065] V. Data Processing and Evaluation Indicators 1. Dynamic fitting (k obs k deF ) To quantitatively compare the removal and defluorination rates of target pollutants under different operating conditions, the change in target PFAS (or total PFAS) concentration over time was fitted using a pseudo-first-order kinetic model, with the apparent rate constant k. obs Calculate according to formula (1): (1); In the formula, C0 and C t These represent the initial and time t values ​​for the target PFAS concentration (or total concentration), respectively, where t is the reaction time. For Ln(C t,PFAS / C 0,PFAS When performing a linear regression on t, the negative of the slope is k. obs .

[0066] The defluorination process uses the defluorination kinetic parameter k. deF Characterization. When using fluoride ion release as an indicator of the degree of defluorination, the proportion of released inorganic fluorine to the initial theoretical total fluorine can be expressed as F = F0 t - / F theo F t - Let F be the concentration of fluoride ions measured in the solution at time t. theo The theoretical maximum releasable fluorine concentration is calculated from the initial PFAS concentration and its molecular fluorine number. Defluorination fitting is performed according to equation (2): (2); When the proportion of inorganic fluorine calculated using the total organic fluorine (such as TOF) or "real-time fluorine mass balance" is used instead of F=F t - / F theo In such cases, the apparent fit can still be performed using the form of equation (2) to maintain comparability between different experiments. Each experiment should be performed in at least three parallel runs, and the results are expressed as mean ± standard deviation.

[0067] 2. Energy consumption index (EE / O) To compare the energy consumption levels of different treatment processes, this invention uses the electrical energy per order (EE / O) index to characterize the electrical energy required to reduce the concentration of the target pollutant in a unit volume of water sample by one order of magnitude. The calculation of EE / O is shown in equation (3): (3); In the formula, Ucell is the average voltage of the electrolyzer during the reaction (V), I is the operating current (A), t is the reaction time (h), and V is the volume of water treated (m³). 3 ), C 0,PFOA With C t,PFOA These represent the initial concentration of PFOA and the concentration at time t, respectively. The units of all parameters in the calculation must be consistent with the units of EE / O.

[0068] 3. Fluoride ion and fluorine mass balance Fluoride ions (F) - Ion chromatography was used for determination: a Dionex ICS-2000 IonPac AS19 column (4 mm × 250 mm, 5.0 μm) with a conductivity detector was used, the eluent was 30 mM KOH, the column temperature was 30℃ (flow rate was 0.9 mL / min as originally recorded). -1 To track the fate of fluorine during the reaction and assess the completeness of defluorination, the "real-time fluorine mass balance" method is used. Taking PFOA as an example, the fluorine balance at time t can be expressed as: (4); Where Product is the conversion product and n is the corresponding number of fluorine atoms.

[0069] VI. Construction and Basic Characterization of Membrane Electrodes 1. Morphological characteristics and elemental distribution (SEM / EDS) Both the PDMS-functionalized anodic and cathode film electrodes maintained their porous composite structure and continuous conductive network. Scanning electron microscopy (SEM) images of the PDMS-FeOCl / CNTs and PDMS-Ti4O7 / CNTs film electrode surfaces are shown below. Figure 4 As shown. The EDS energy spectrum and elemental distribution of PDMS-FeOCl / CNTs are shown in the figure. Figure 5 As shown. The EDS energy spectrum and elemental distribution of PDMS-Ti4O7 / CNTs are shown in the figure. Figure 5 As shown in Figure A, the presence of Si (from PDMS), Ti, O (from Ti4O7), and C (from CNTs) was confirmed. The EDS energy distribution and elemental distribution of PDMS-FeOCl / CNTs are shown below. Figure 5 As shown in B, the presence of Si (from PDMS), Fe, Cl (from FeOCl), and C (from CNTs) was confirmed.

[0070] like Figure 4As shown in the SEM image of the anode (PDMS-Ti4O7 / CNTs), Ti4O7 is mainly distributed in the form of irregular particles, and CNTs are interwoven and bridging between the particles, giving the film good pore connectivity and structural stability. In the high magnification image, Ti4O7 particles and CNTs network are in close contact, which is conducive to the formation of continuous electron transport channels.

[0071] Figure 5 The EDS / mapping results showed that the Fe, O, and Cl signals corresponded well with the FeOCl enrichment regions, and the C signal also spanned the entire field of view. The Si signal was continuously distributed and showed a similar trend to the C signal, but it did not completely overlap with the Fe signal. This indicates that PDMS is more likely to selectively adhere to and partially cover the cathode surface, forming a hydrophobic control layer while retaining some FeOCl active sites exposed.

[0072] In summary, the results of SEM and EDS together show that the introduction of PDMS did not destroy the original porous conductive network of the cathode and anode films, but mainly adhered to the carbon framework and pore interface, while retaining the local exposure of the active phase, providing a structural basis for subsequent electron transport, mass transfer and interface microenvironment regulation.

[0073] 2. Crystal phase and material composition To confirm that the crystal structure of the membrane electrode remained stable during PDMS functionalization without the introduction of new crystal phases or disruption of the main framework, X-ray diffraction (XRD) characterization was performed on both membrane electrodes. The XRD patterns of PDMS-Ti4O7 / CNTs and PDMS-FeOCl / CNTs are shown below. Figure 6 As shown.

[0074] like Figure 6 As shown, the diffraction peaks of PDMS-Ti4O7 / CNTs agree well with the Ti4O7 standard card (PDF#50-0787), with no additional impurity peaks, indicating that the Ti4O7 main crystalline phase remains stable after film formation and PDMS coating. Meanwhile, the characteristic diffraction peaks of PDMS-FeOCl / CNTs are consistent with the FeOCl standard card (PDF#24-1005), indicating that the FeOCl active phase maintains its crystalline integrity after functionalization.

[0075] VII. Correlation and Optimization of PDMS Dosage-Surface Properties-Electrochemical Behavior 1. Contact angle changes with PDMS dose like Figure 7As shown in Figure A, compared with the unfunctionalized membrane electrode, the water contact angles of both types of membrane electrodes (anodide: 0-300 μL, anion: 0-100 μL) significantly increased after PDMS functionalization, indicating that the introduction of low surface energy groups in PDMS can effectively improve the apparent hydrophobicity of the electrode. This trend is consistent with... Figure 7 Consistent with B (water droplet penetration control) in the previous analysis: the unfunctionalized electrode exhibits rapid wetting and penetration of water droplets, which can enter the pores within seconds; however, the addition of PDMS significantly inhibits the spreading and penetration of water droplets on the surface, indicating a substantial change in surface wetting behavior. It is noteworthy that the contact angle does not change monotonically with PDMS dosage: when the PDMS dosage is excessive (e.g., ≥600 μL), the apparent hydrophobic enhancement effect may weaken, or even exhibit a more hydrophilic wetting behavior. This suggests that surface wettability is not only controlled by surface chemical composition but also closely related to the evolution of microstructure. The effect of PDMS dosage on the surface wettability of the membrane electrode is as follows: Figure 7 As shown. Among them, Figure 7 In the figure, A represents the change in contact angle as a function of PDMS dose; Figure 7 B in the figure is a comparison of the permeation behavior of water droplets on the surfaces of the two membrane electrodes when there is no PDMS modification.

[0076] 2. Anodic electrochemical properties as a function of PDMS dosage Anodic polarization behavior and oxygen evolution potential (OEP) were investigated using linear sweep voltammetry (LSV) (see...). Figure 8 (A) The results showed that OEP initially increased and then stabilized with increasing PDMS dosage, indicating that PDMS has a certain inhibitory effect on the oxygen evolution reaction (OER) in the low-dose range (approximately 50-100 μL). Since higher OEP usually corresponds to lower OER activity, this result suggests that appropriate PDMS functionalization is beneficial for reducing side reaction competition, thereby improving the relative efficiency of the anodic electro-oxidation process within the effective potential window. The effect of PDMS dosage on the electrochemical characteristics of the membrane anolyte is as follows: Figure 8 As shown. Among them, Figure 8 In the figure, A represents the LSV curve and oxygen evolution potential (OEP) graph of PDMS-Ti4O7 / CNTs; Figure 8 B in the figure represents the electrochemical impedance (EIS) Nyquist plot and the comparison of the interfacial charge transfer resistance (Rct) obtained by fitting at different PDMS doses; Figure 8 Figure C shows the voltage variation over time in a flow-through electrochemical filtration reactor equipped with different PDMS-Ti4O7 / CNTs anodes. For comparison, the electrochemical impedance spectroscopy (EIS) and fitted charge transfer resistance (Rct) of Ti4O7 are shown below. Figure 9 As shown, significantly higher than Figure 8 The resistance values ​​of each sample in B.

[0077] Electrochemical impedance spectroscopy (EIS) was used to characterize the charge transfer resistance Rct of the anolyte at the electrode / electrolyte interface (see [reference]). Figure 8 (B) in the example. Figure 9 As shown, considering the weak interfacial electron transfer capability of pure Ti4O7, the introduction of CNTs into Ti4O7 can significantly improve the interfacial conductive network, thereby increasing R... ct The Ω decreased from 207.2 Ω to 66.4 Ω, indicating that the incorporation of CNTs effectively improved the charge transfer capability at the anodic interface. Furthermore, Rct showed a significant positive correlation with increasing PDMS dosage (see...). Figure 8 (B in the text) indicates that the introduction of PDMS continuously increases the interfacial charge transfer resistance, which is detrimental to the anodic interfacial charge transfer process. This phenomenon can be attributed to the insulating and covering effects of PDMS: as the dosage increases, the polymer is more likely to form a continuous cover or occupy the pore throat structure on the particle / CNT surface, thereby weakening the effective conductive contact and the exposure of active sites.

[0078] The aforementioned interfacial impedance changes are further reflected in the device-scale operating voltage response. A comparison is made between flow-through electrochemical filtration reactors equipped with different PDMS-Ti4O7 / CNT anodes (see...). Figure 8 As shown in C), when the PDMS dosage is low (≤300 μL), the increase in internal resistance of the system is limited, and the operating voltage changes relatively slowly over time. However, when the PDMS dosage is too high (≥600 μL), the cell voltage rises rapidly, resulting in no voltage deactivation of the system under constant current conditions. This result indicates that excessive PDMS consumes more energy to overcome interfacial impedance and internal resistance, rather than converting it into effective electro-oxidation capacity.

[0079] In summary, the effect of PDMS on the electrochemical properties of membrane anodes exhibits a clear trade-off: low-dose PDMS can suppress OER and improve the relative effectiveness of the electro-oxidation process to some extent, but as the dose increases further, the interfacial charge transfer is hindered and the operating voltage penalty is rapidly enhanced, leading to rapid deactivation at the device level.

[0080] 3. Cathode ORR variation with PDMS dose The key role of cathode-side PDMS is to regulate 2e - ORR process. Cyclic voltammetry (CV) curves of the PDMS-FeOCl / CNTs membrane cathode in N2 and O2 saturated electrolytes (ORR verification) are shown below. Figure 10 As shown. The effect of PDMS dosage on the ORR selectivity and active species generation of the membrane cathode is as follows. Figure 11 As shown. Among them, Figure 11 In the figure, A represents the relationship between H2O2 selectivity and electron transfer number n under different PDMS doses as a function of applied potential (calculated by the rotating disk electrode RRDE method); Figure 11 B in the figure represents the linear sweep curve of the RRDE ring current versus the disk current. Figure 11 C in the graph represents the cumulative concentration change of ·OH under different PDMS doses; Figure 11 In the figure, D represents the voltage change over time in the operating tank of a flow-through electrochemical filtration reactor equipped with different PDMS-FeOCl / CNTs cathodes.

[0081] First, the occurrence of cathode ORR is verified by CV: such as Figure 10 As shown, a significant reduction peak appears at approximately 0.18 VRHE in the O2-saturated electrolyte, indicating that the cathode possesses clear ORR activity. Further RRDE was used to quantitatively evaluate the electron transfer number n and H2O2 selectivity. Figure 11 As shown in Figure A, when the PDMS dose increased from 0 to 300 μL, the ability of the cathode to generate H2O2 was generally enhanced in the range of 0–0.4 VRHE, indicating that an appropriate amount of PDMS helps to guide the ORR reaction to a 2e phase, which is more conducive to H2O2 generation. - The pathway; however, when PDMS was in excess (≥600 μL), the ORR was almost completely suppressed (see...). Figure 11 (B in the original text) is inferred to be due to polymer coverage causing the active sites to be shielded.

[0082] The goal of considering AO-EF synergy is not only the production of H2O2, but also the further generation of ·OH at the cathode. Considering both ORR current and n value, the 100 μL PDMS cathode exhibits more favorable overall characteristics (n≈3.1, see...). Figure 11 (A) is close to the dominant range required for the electric Fenton test. Using benzoic acid as a probe, at the same current density of 1.6 mA·cm⁻¹, -1 The cumulative amount of ·OH is measured below, such as Figure 11 As shown in Figure C, the ·OH concentration initially increases and then decreases with PDMS dosage, reaching its maximum value at 100 μL, again indicating an optimal dosage window at the cathode. On a device scale, Figure 11 The D-value in the data shows that the operating voltage remains relatively stable within a reasonable dosage range of 0–300 μL, indicating that an appropriate amount of PDMS on the cathode side does not cause a significant voltage penalty, but excessive amounts lead to ORR inactivation. In summary, there is a clear "dose window effect" for cathode-side PDMS: low to medium doses can improve H2O2 selectivity and increase ·OH output while maintaining ORR activity, while excessive amounts (≥600 μL) can lead to ORR suppression or even inactivation. This, combined with n, H2O2 selectivity, and... · Based on the overall OH output, the optimal dosage of cathode PDMS is 100 μL.

[0083] VIII. PFAS Degradation and Defluorination Performance 1. Evaluation of PFAS removal and defluorination performance To evaluate the destructive ability of the constructed flow-through membrane electrode to PFAS, this invention uses PFOA as a model pollutant and compares its removal from the parent compound and its defluorination. The system's removal of PFOA (attributed to adsorption) and release of background inorganic fluorine under open-circuit (no-electrode) cycling conditions are as follows: Figure 12 As shown. Among them, Figure 12 In the graph, A represents the change of PFOA concentration over time. Figure 12 B in the text represents fluoride ions (F). - Release variation over time. Comparison of PFOA degradation and defluorination kinetics of membrane electrode pairs with different PDMS functionalization levels (in kJ / kWh). obs With k deF (Characteristics) such as Figure 13 As shown. Comparison of PFOA removal and defluorination processes under different PDMS functionalization methods. Figure 14 As shown. Among them, Figure 14 Figures A and B in the diagram are comparisons of PFOA removal and defluorination processes under anodic PDMS modification only. Figure 14 C and D in the figure are comparison diagrams of PFOA removal and defluorination processes under cathode PDMS modification only; Figure 14 E and F in the figure are comparison diagrams of PFOA removal and defluorination processes under the anodic-cathode matched PDMS modification combination (solid line is pseudo-first-order fit).

[0084] Depend on Figure 12 As shown in A, under open-circuit cycling conditions, the PFOA removal rate remained below 10%, indicating that the material adsorption contribution in the system of this invention was relatively small, and the subsequent reduction of PFOA mainly came from electrochemical reaction-driven processes; simultaneously, from Figure 12 As can be seen from B in the figure, the background fluoride ion release of the system is negligible.

[0085] Based on this, the performance of membrane electrode pairs with different PDMS functionalization methods was compared. Figure 13 It can be seen that when PDMS functionalization is performed on only one side (either anode or cathode only), the degradation and defluorination rates of PFOA generally decrease with increasing PDMS dosage, with 50 μL being the optimal doping amount. Excessive PDMS coverage limits interfacial reactions. However, when the anode and cathode are synergistically functionalized with appropriate amounts of PDMS, the system exhibits significant synergistic enhancement. Specifically, the combination of 50 μL PDMS-Ti4O7 / CNTs anode and 100 μL PDMS-FeOCl / CNTs cathode results in the highest degradation and defluorination kinetic constants (k0). obs =0.82 h -1 k deF =0.44 h -1The results showed that the combined effect was 1.9 times and 1.6 times that of the unfunctionalized membrane electrode pair, respectively, indicating that the combination achieved a better balance between "interface enrichment / electron transport obstruction" and "accumulation of active species / site masking".

[0086] Figure 14 The optimal membrane electrode pair is visually demonstrated, and its concentration decay is compared with F. - Release varies over time. Within the same operating time, the optimal combination (50 / 100 μL) increased the PFOA removal rate from 82.3% under unfunctionalized conditions to 98.2%, and the defluorination degree from 80.9% to 93.8%, indicating that the system can not only achieve rapid removal of the parent pollutant, but also significantly enhance the deep destruction process corresponding to CF bond breakage.

[0087] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A system for sequential cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane, characterized in that, include: A sequential cascaded electro-oxidation unit is used for electrochemical oxidation treatment of wastewater containing PFAS. The photo-reduction unit is used to perform ultraviolet light-excited reduction treatment on the effluent after being treated by the sequential cascaded electro-oxidation unit. A connecting pipeline is used to transport the effluent from the sequential cascaded electro-oxidation unit to the photo-reduction unit.

2. The system for sequential cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane as described in claim 1, characterized in that, The electro-oxidation unit includes at least one flow-through electrochemical filtration reactor, which is equipped with an anode and a cathode. The wastewater to be treated passes through the anode and / or cathode under the drive of an applied current to undergo a reaction.

3. The system for sequential cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane according to claim 2, characterized in that, The surfaces of the anode and / or cathode are hydrophobically modified to enhance the interfacial enrichment of PFAS.

4. The system for sequential cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane according to claim 3, characterized in that, The hydrophobic modification treatment is achieved by introducing polydimethylsiloxane onto the surface of the anode and / or cathode.

5. The system for sequential cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane according to claim 2, characterized in that, The anode is a Ti4O7 electrode, and the cathode is a FeOCl electrode.

6. The system for sequential cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane according to claim 1, characterized in that, The photoreduction unit is an ultraviolet / sulfite reaction system, which includes a reactor that provides an ultraviolet light source and a sulfite dosing device.

7. A method for sequentially cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane, characterized in that, Includes the following steps: S1. Based on the system of any one of claims 1 to 6, wastewater containing PFAS is passed into a sequential cascade electro-oxidation unit for electrochemical oxidation treatment; S2. The effluent after step S1 is passed into the photoreduction unit for ultraviolet light excitation reduction treatment.

8. The method for sequential cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane according to claim 7, characterized in that, The electrochemical oxidation process in step S1 is operated in constant current mode with a current density ranging from 0.5 to 5 mA / cm². 2 .

9. The method for sequential cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane according to claim 7, characterized in that, In step S2, the pH value of the photoreduction unit is controlled to be 9~13.

10. The method for sequential cascaded electro-oxidation-photoreduction coupled degradation of PFAS in the concentrate after dyeing and printing reverse osmosis membrane according to claim 7, characterized in that, The PFAS includes perfluorooctanoic acid and / or perfluorooctane sulfonic acid.

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