Method for treating salt-containing organic wastewater by stepwise electrodialysis-electro-Fenton-like synergistic treatment

Abstract

The application discloses a kind of step-by-step electrodialysis-Fenton-like synergistic treatment of salt-containing organic wastewater method, it is related to water pollution control field, wastewater is filtered by filter membrane, and humification index HIX is scanned and calculated by three-dimensional fluorescence spectrometer;According to the HIX index measured, using pre-catalytic electrodialysis unit, the Cl ‑ Concentration in wastewater is regulated, and pH value is adjusted simultaneously, to obtain product one;Fe 3+ Catalyst precursor is added in product one, Fe 2+ / HClO Fenton-like catalytic reaction is started, and deep desalination is carried out by post-catalytic electrodialysis unit, finally realizing the synergistic catalytic removal of salt and organic matter.The advantage of this method is: using HIX index as the basis for judgment, dynamically adjusting Cl ‑ Removal to achieve efficient and safe operation of Fenton-like process, both can realize the synergistic efficient removal of organic pollutants and salt, and can achieve the goal of "Cl ‑ First use and then remove", it is an ideal method for treatment of salt-containing organic wastewater.

Description

Technical Field

[0001] This invention relates to the field of water pollution control, and in particular to a method for the synergistic treatment of saline organic wastewater by stepwise electrodialysis and electro-Fenton-like methods. Background Technology

[0002] Catalytic oxidation technology is one of the core technologies for treating saline organic wastewater such as pharmaceutical wastewater, saline-alkali land improvement wastewater, and landfill leachate. It can degrade recalcitrant organic matter in wastewater into small molecule intermediates or directly mineralize it by generating highly oxidizing active ingredients. It has the advantages of short reaction time, thorough oxidation, and easy automation, and has good application prospects in the treatment of wastewater containing high concentrations of salt (such as Cl⁻, SO4²⁻, Ca²⁺, Na⁺) and high concentrations of organic pollutants.

[0003] In catalytic oxidation technology systems, Fe²⁺ / HClO-based electro-Fenton catalytic systems have gradually gained attention due to their adaptability to saline water conditions. Traditional electro-Fenton systems require continuous aeration to generate H₂O₂ (reaction formula: Fe²⁺ + H₂O₂ → Fe³⁺ + OH⁻), resulting in high operating costs. In contrast, Fe²⁺ / HClO-based electro-Fenton systems can utilize Cl⁻ in saline wastewater, generating HClO through anodic oxidation (reaction formula: 2Cl⁻ - 2e⁻ → Cl₂↑; Cl₂ + H₂O ⇌ HClO + H⁺ + Cl⁻). HClO then reacts with Fe²⁺ to generate strong oxides such as FeIVO²⁺ (reaction formula: Fe²⁺ + HClO + H⁺ → Fe). IV The process involves the addition of O²⁺, Cl⁻, and H₂O, which degrades organic matter. This process requires no additional aeration and utilizes Cl⁻ in the wastewater to reduce operating costs, making it an important technological approach for the catalytic treatment of saline organic wastewater.

[0004] It should be noted that Cl⁻ is the core substrate of Fe²⁺ / HClO type electro-Fenton catalytic systems. Its concentration is directly related to the generation efficiency of HClO, the activity of oxide species in the system, and the generation of byproducts. Therefore, the reasonable control of Cl⁻ concentration is a key prerequisite for the efficient and safe operation of this type of catalytic system.

[0005] While existing technologies explore treatment processes, there are still significant shortcomings in the attention and control of Cl⁻. For example, patent CN107540135B discloses a "Safe and Efficient Combined Process for Treating Landfill Leachate Nanofiltration Concentrate," which removes organic pollutants and toxic byproducts through three processes: iron-based flocculation and sedimentation, electro-Fenton-like advanced oxidation, and activated carbon adsorption. However, it does not address the impact of Cl⁻ on the operation of the electro-Fenton-like system. Similarly, patent CN115745097A discloses a "Dual-Electro-Fenton Treatment Device for High-Salinity Organic Wastewater," which integrates a water quality and quantity adjustment system, a pH adjustment system, a dual-electro-Fenton reaction system, and a mixing system. Although it utilizes active chlorine by operating a Fe²⁺ / HClO electro-Fenton system, it does not address the concentration of Cl⁻. Collaborative and precise control; Patent CN112679559A discloses "A method for separating and purifying xylose using electrodialysis combined with flocculation technology", which uses bipolar membrane electrodialysis to recover high-purity inorganic acids, while raising the pH to near the isoelectric point of the xylose hydrolysate colloidal system, and adding flocculants to enhance the destabilization and precipitation of colloidal macromolecules, with the goal of xylose purification, but does not involve a catalytic treatment system for saline organic wastewater; Patent CN117185436A discloses "An electrodialysis-three-dimensional electrode reaction method for simultaneous desalination and pollution reduction of high-salt landfill leachate", which uses magnetic nitrogen-doped biochar particle electrode material, which is placed in the concentration chamber of the electrodialysis reaction tank to construct a three-dimensional electrode reaction system, and the particle electrode is suspended by aeration, but does not focus on the role and control method of Cl⁻ in the catalytic reaction.

[0006] Therefore, current catalytic oxidation technologies for treating saline organic wastewater generally lack in-depth analysis of the impact of Cl⁻ on the operation mechanism of Fe²⁺ / HClO electro-Fenton catalytic systems, and there are no precise methods for controlling Cl⁻ under different water quality conditions. Most technical solutions either passively rely on the background Cl⁻ concentration of the wastewater to carry out catalytic reactions, or treat Cl⁻ only as an impurity to be removed, resulting in insufficient operating efficiency and stability of Fe²⁺ / HClO electro-Fenton catalytic systems, which cannot fully meet the actual needs for efficient and safe treatment of saline organic wastewater. Summary of the Invention

[0007] The purpose of this invention is to provide a stepwise electrodialysis-electro-Fenton synergistic treatment method for saline organic wastewater, in order to overcome the above-mentioned shortcomings of the prior art.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for stepwise electrodialysis-Fenton-like synergistic treatment of saline organic wastewater, comprising the following steps:

[0009] S1. Pretreatment: The wastewater to be treated is stirred and filtered using a basket filter and a bag filter to obtain pretreated wastewater;

[0010] S2. Catalytic fluorescence analysis: The pretreated wastewater was heated to 25-35℃, and the pH was adjusted to 6.0-7.5 using a pH adjuster. After filtration through a 0.45μm filter membrane, it was scanned using a three-dimensional fluorescence spectrometer. The humification index HIX was accurately calculated based on the fluorescence intensity.

[0011] S3. Pre-catalytic electrodialysis control: The catalytic reaction system is controlled according to the HIX value: when HIX ≤ 4, the Cl⁻ concentration is controlled to 1000-8000 mg / L through the pre-catalytic electrodialysis unit; when HIX > 4, it is controlled to 600-5000 mg / L; after control, acid or alkali is added to adjust the pH to 2.0-4.0 to obtain product one;

[0012] S4, Electro-Fenton-like catalytic reaction: Add catalyst precursor Fe to product 1. 3+ Construct Fe 2+ / HClO-type electro-Fenton catalytic reaction system; the anode is a ruthenium-iridium coated titanium electrode, and the cathode is a 316L stainless steel electrode. The reaction time is 1-8 h to obtain product 2.

[0013] S5. Post-catalytic electrodialysis desalination: Product 2 is subjected to deep desalination through a post-catalytic electrodialysis unit to achieve a Cl⁻ concentration ≤200mg / L, thereby completing the reaction process.

[0014] Furthermore, the three-dimensional fluorescence spectrometer described in S2 has an excitation wavelength of 254 nm and an emission wavelength of 300–480 nm.

[0015] Furthermore, the formula for calculating the humification index HIX, as described in S2, is:

[0016] .

[0017] Furthermore, the voltage gradient of the pre-catalytic electrodialysis unit described in S3 is 8–15 V / cm, the flow rate is 3–8 cm / s, and the current density is 25–35 mA / cm². 2 .

[0018] Furthermore, as described in S4, Fe is added to product one. 3+ As a catalyst precursor, Fe in product one 3+ The concentration ranges from 0.5 to 2.0 mmol / L.

[0019] Furthermore, the voltage gradient of the post-catalytic electrodialysis desalination unit described in S5 is 10–20 V / cm, the flow rate is 3–8 cm / s, and the current density is 15–25 mA / cm². 2 .

[0020] Furthermore, both S3 and S5 electrodialysis units include cation exchange membranes and anion exchange membranes.

[0021] Compared with existing technologies, the present invention provides a stepwise electrodialysis-electro-Fenton-like synergistic treatment method for saline organic wastewater. The pre-removed Cl⁻ is transferred to the concentrate chamber for subsequent resource recovery. Cl⁻ in the wastewater is anolyzed to generate HClO, reducing reagent dosage and achieving Cl⁻ recycling. The degree of humification is accurately determined using the HIX index, and the degree of humification guides Cl⁻ regulation, dynamically adjusting the Cl⁻ removal target and preventing the formation of toxic catalytic oxidation byproducts in high-humic acid wastewater under excessive Cl⁻ conditions. Furthermore, the electro-Fenton-like method eliminates the need for aeration, resulting in energy savings compared to traditional electro-Fenton methods. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0023] Figure 1 This is a schematic diagram of the overall process of the stepwise electrodialysis synergistic electro-Fenton method provided in an embodiment of the present invention.

[0024] Figure 2 The experimental flowchart is shown for the stepwise electrodialysis synergistic electro-Fenton method provided in the embodiments of the present invention.

[0025] Figure 3 This is a schematic diagram of a fluorescence spectrum provided in an embodiment of the present invention. Detailed Implementation

[0026] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0027] Example 1:

[0028] Please see Figure 1 , Figure 2 A stepwise electrodialysis-Fenton-like synergistic treatment method for saline organic wastewater includes the following steps:

[0029] S1. Pretreatment: First, the saline organic wastewater to be treated is stirred to prevent sedimentation and homogenize the water quality. Then, it is filtered through a basket filter and a bag filter to remove impurities and protect the membrane and electrodes, resulting in pretreated wastewater.

[0030] S2. Catalytic fluorescence analysis: The temperature of the pretreated wastewater was adjusted to 25-35℃, and the pH was adjusted to 6.0-7.5 using a pH adjuster. After filtration through a 0.45μm filter membrane, the wastewater was scanned using a three-dimensional fluorescence spectrometer with an excitation wavelength of 254 nm and an emission wavelength of 300-480 nm. The humification index HIX was then calculated based on the obtained fluorescence intensity.

[0031] The specific implementation method is as follows: 30 ml of pretreated wastewater is collected. After adjusting the temperature, the pH value of the wastewater is adjusted using a 1 mol / L H2SO4 or NaOH solution to avoid excessive addition. While adjusting the pH value, continuous stirring is carried out to prevent local over-acidity / alkalinity of the wastewater. An online pH meter (accuracy ±0.1) is used in conjunction with a metering pump for automatic adjustment. After adjustment, stirring is performed for 1–10 min (100 rpm) to ensure homogenization, thereby obtaining the wastewater sample to be tested.

[0032] The wastewater sample to be tested was filtered through a 0.45 μm filter membrane and then scanned using a three-dimensional fluorescence spectrometer. The excitation wavelength (Ex) was 254 nm; the emission wavelength (Em) was 300–480 nm, the step size was 2 nm, the scan speed was 2000 nm / min, and the integration time was 0.5 s. Raman scattering was subtracted using ultrapure water (Millipore), and fluorescence intensity was corrected using quinine sulfate (1 μg / L). See reference. Figure 3 A schematic diagram of the fluorescence spectrum, where the horizontal axis represents the emission wavelength (nm) and the vertical axis represents the fluorescence intensity, according to the formula...

[0033] ,

[0034] The HIX is obtained by calculating the ratio of fluorescence intensity in the ranges of 435–480 nm and 300–345 nm, which reflects the degree of humification of organic matter.

[0035] S3. Pre-catalytic electrodialysis control: The catalytic reaction system is controlled according to the HIX value: when HIX ≤ 4, the Cl⁻ concentration is controlled to 1000–8000 mg / L through the pre-catalytic electrodialysis unit; when HIX > 4, the Cl⁻ concentration is controlled to 600–5000 mg / L; the voltage gradient of the pre-catalytic electrodialysis unit is 8–15 V / cm, the flow rate is 3–8 cm / s, and the current density is 25–35 mA / cm². 2 After the regulation is completed, 1 mol / L H2SO4 or NaOH solution is added to the regulated wastewater to adjust the pH to 2.0–4.0, yielding product one. The pre-catalytic electrodialysis unit includes a cation exchange membrane and an anion exchange membrane, with a membrane area of ​​0.1–0.5 m². 2 / For example, the number of membrane pairs n is calculated using the following formula:

[0036] ;

[0037] Where Q is the flow rate; v is the flow velocity; and A is the membrane area.

[0038] Electrodialysis reduces salt concentration by driving the directional migration of Cl⁻ through an electric field. While ensuring the Cl⁻ requirement for electro-Fenton-like reactions, it reduces side reactions such as the quenching of free radicals by Cl⁻ and the generation of oxidation byproducts in subsequent electrochemical catalytic oxidation, thereby improving reaction efficiency and product safety.

[0039] S4, Electro-Fenton-like catalytic reaction: Fe is added to product 1. 3+ As a catalyst precursor, Fe was constructed 2+ / HClO-type electro-Fenton catalytic reaction system, making Fe 3+ The final concentration of product one was 0.5–2.0 mmol / L. Then, a ruthenium-iridium coated titanium electrode was used as the anode and a 316L stainless steel electrode was used as the cathode. The temperature was 25–40℃ and the reaction time was 1–8 h. The reaction time was dynamically adjusted according to the COD removal rate to obtain product two.

[0040] In this reaction step, chlorine is produced at the anode to form the catalytic substrate: 2Cl⁻ → Cl₂ + 2e⁻ - Cl2 + H2O → HClO + H+ + +Cl⁻;Cathode regeneration catalyst Fe 2+ Fe 3+ +e - →Fe 2+ (Cathode reduction); Fe in the system 2+ Catalytic Fenton reaction: Fe²⁺ + HClO + H⁺ → Fe IV O²⁺ + Cl⁻ + H₂O (Fenton-like reaction). During this process, large organic molecules are mineralized into CO₂, H₂O, or converted into biodegradable small molecules.

[0041] S5. Post-catalytic electrodialysis desalination: Product 2 is subjected to deep desalination through a post-catalytic electrodialysis unit. The voltage gradient of the post-catalytic electrodialysis unit is 10–20 V / cm, the flow rate is 3–8 cm / s, and the current density is 15–25 mA / cm. 2 This ensures that the Cl⁻ concentration is ≤200mg / L, thus completing the treatment of saline organic wastewater. The post-catalytic electrodialysis unit includes cation exchange membranes and anion exchange membranes.

[0042] The specific implementation method is as follows: First, all of product two is transferred into an electrodialysis circulation tank with a heat-insulating jacket, so that product two is always maintained at 25℃±2℃; then, it is processed at a rate of 0.2 m... 2 Feed is supplied to the electrodialysis membrane stack at a flow rate equivalent to 3 L / min. The membrane stack consists of 5–10 pairs of alternating cation exchange membranes and anion exchange membranes, with a total effective membrane area of ​​1–2 m². 2After powering on, the initial measurements were performed at a voltage gradient of 10 V / cm, a membrane surface flow rate of 3 cm / s, and a membrane flow rate of 15 mA / cm. 2 The system was run for 15 minutes at a low current density to initially remove easily migrating small molecular ions, avoiding polarization and scaling caused by instantaneous high current. Subsequently, the voltage gradient was gradually increased to 20 V / cm at a rate of 1 V / cm per minute, while the flow rate was linearly increased to 8 cm / s and the current density was adjusted to 25 mA / cm. 2 During operation, the water quality at the desalination chamber outlet is continuously monitored using an online conductivity meter and a chloride ion selective electrode. When the Cl⁻ concentration drops to 200 mg / L, the voltage gradient is immediately reduced to 5 V / cm and the machine is shut down to prevent excessive desalination from increasing energy consumption, thus completing the treatment of saline organic wastewater.

[0043] Example 2:

[0044] This embodiment provides a technical solution based on Embodiment 1: verification of the correlation between HIX and Cl⁻ regulation.

[0045] Two sets of simulated saline organic wastewater with consistent background salinity were prepared using deionized water. Both sets had a fixed COD of 1500 mg / L and a NaCl matrix of 15 g / L. Humic acid and fulvic acid mixtures were then precisely added to each wastewater, stabilizing the HIX values ​​calculated by three-dimensional fluorescence spectroscopy at 2.0 ± 0.1 and 5.0 ± 0.1, respectively. Subsequently, following step S3, the wastewater was processed through a pre-catalytic electrodialysis unit at 30 mA / cm². 2 Cl⁻ was precisely adjusted to 5000 mg / L and 3000 mg / L under conditions of 12 V / cm, respectively. Then, the pH of the pre-catalytic electrodialysis treated (ED, HIX 2.0-ED, HIX 5.0-ED) and untreated (HIX 2.0, HIX 5.0) water samples was adjusted to 3.0±0.1 using 1 mol / L H₂SO₄. 200 mL of each of the four water samples was placed in a cylindrical electrochemical reactor with a constant temperature water bath, using a ruthenium-iridium coated titanium mesh as the anode and a 316L stainless steel cylinder as the cathode, and an electrochemical flow rate of 30 mA / cm. 2 Electrolysis was performed continuously at a constant current density for 6 h. During the reaction, magnetic stirring was used to maintain uniformity. After electrolysis, the COD of the solution was measured to compare the COD removal rate and the proportion of chlorinated organic molecules in the pre-catalytic electrodialysis treatment group (HIX 2.0-ED, HIX 5.0-ED) and the untreated group (HIX 2.0, HIX 5.0) under different "HIX-Cl⁻" gradients. The results showed (Table 1) that pre-catalytic electrodialysis treatment could improve the degradation effect of organic matter and reduce the generation of toxic oxidation byproduct "chlorinated organic matter" molecules under different "HIX-Cl⁻" gradients, which illustrates the scientific validity of the synergistic optimization of the degree of humification and the chloride ion level.

[0046] Table 1: Comparison of the effects of pre-catalytic electrodialysis treatment and untreated groups under electro-Fenton catalytic treatment.

[0047] HIX Cl⁻ concentration (mg / L) COD removal rate (%) Percentage of chlorinated organic molecules after the reaction (%) HIX 2.0-ED 5000 83±5 23 HIX 5.0-ED 3000 75±3 45 HIX 2.0 15000 66±3 34 HIX 5.0 15000 48±2 62

[0048] Example 3:

[0049] This embodiment, based on Example 1, uses actual wastewater to verify the scientific validity of the synergistic optimization of humification degree and chloride ion level in electro-Fenton-like catalysis.

[0050] Using nanofiltration concentrate from an aging landfill as the treatment sample (sample number LLNC, COD=3000 mg / L, Cl⁻=6000 mg / L, HIX=8.3), pre-treatment with electrodialysis was first performed to reduce Cl⁻ to a concentration of 2000 mg / L (sample number LLNC-ED). The solution was then passed through a pre-catalytic electrodialysis unit at 30 mA / cm². 2 Under conditions of 12 V / cm, Cl⁻ was adjusted to 2000 mg / L. Then, the pH of both the pre-catalytic electrodialysis treated (LLNC-ED) and untreated (LLNC) water samples was adjusted to 3.0 ± 0.1 using 1 mol / L H₂SO₄. 200 mL of each of the two water samples were placed in an electrochemical reactor with a constant temperature water bath and reacted for 8 h. Finally, post-catalytic electrodialysis was used to remove Cl⁻ from the LLNC-ED samples to a concentration of 200 mg / L. The results (Table 2) show that the stepwise electrodialysis synergistic electro-Fenton method can effectively improve the organic matter removal rate while reducing the formation of toxic oxidation byproducts "chlorinated organic matter" molecules and effluent salinity, indicating that the stepwise electrodialysis synergistic electro-Fenton method has significant advantages in the treatment of saline organic wastewater.

[0051] Table 2: Comparison of treatment effects between the experimental group and the control group

[0052] HIX Cl⁻ concentration (mg / L) COD removal rate (%) Percentage of chlorinated organic molecules after the reaction (%) Cl⁻ concentration after the reaction (mg / L) LLNC-ED 2000 73±4 32 200 LLNC 6000 55±3 53 5896

[0053] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for the stepwise electrodialysis-Fenton-like synergistic treatment of saline organic wastewater, characterized in that, Includes the following steps: S1. Pretreatment: The wastewater is filtered using a basket filter and a bag filter to obtain pretreated wastewater. S2. Catalytic fluorescence analysis: The pretreated wastewater was adjusted to 25-35℃, and the pH was adjusted to 6.0-7.5 using a pH adjuster. After filtration through a 0.45μm filter membrane, it was scanned using a three-dimensional fluorescence spectrometer. The humification index HIX was accurately calculated based on the fluorescence intensity. S3. Pre-catalytic electrodialysis control: The catalytic reaction system is controlled according to the HIX value: when HIX ≤ 4, the Cl⁻ concentration is controlled to 1000-8000 mg / L through the pre-catalytic electrodialysis unit; when HIX > 4, it is controlled to 600-5000 mg / L; after control, acid or alkali is added to adjust the pH to 2.0-4.0 to obtain product one; S4, Electro-Fenton-like catalytic reaction: Add catalyst precursor Fe to product 1. 3+ Fe 3+ Reduced to Fe at the cathode 2+ Construct Fe 2+ / HClO-type electro-Fenton catalytic reaction system; the anode is a ruthenium-iridium coated titanium electrode, and the cathode is a 316L stainless steel electrode. The reaction time is 1-8 h to obtain product 2. S5. Post-catalytic electrodialysis desalination: Product 2 is subjected to deep desalination through a post-catalytic electrodialysis unit to achieve a Cl⁻ concentration ≤200mg / L, thereby realizing the synergistic catalytic removal of salt and organic matter in the wastewater and completing the reaction process.

2. The method for stepwise electrodialysis-Fenton-like synergistic treatment of saline organic wastewater according to claim 1, characterized in that, The three-dimensional fluorescence spectrometer described in S2 has an excitation wavelength of 254 nm and an emission wavelength range of 300–480 nm.

3. The method for stepwise electrodialysis-Fenton-like synergistic treatment of saline organic wastewater according to claim 1, characterized in that, The voltage gradient of the pre-catalytic electrodialysis unit described in S3 is 8–15 V / cm, the flow rate is 3–8 cm / s, and the current density is 25–35 mA / cm². 2 .

4. The method for stepwise electrodialysis-Fenton-like synergistic treatment of saline organic wastewater according to claim 1, characterized in that, S4 describes the addition of catalyst precursor Fe to product one. 3+ Subsequently, Fe in product one 3+ The concentration ranges from 0.5 to 2.0 mmol / L.

5. The method for stepwise electrodialysis-Fenton-like synergistic treatment of saline organic wastewater according to claim 1, characterized in that, The voltage gradient of the post-catalytic electrodialysis unit described in S5 is 10–20 V / cm, the flow rate is 3–8 cm / s, and the current density is 15–25 mA / cm². 2 .

6. The method for stepwise electrodialysis-Fenton-like synergistic treatment of saline organic wastewater according to claim 1, characterized in that, The electrodialysis units described in S3 and S5 both include cation exchange membranes and anion exchange membranes.

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