Acid-base dual closed-loop recovery system and recovery method for the resource utilization of weak organic acid salt wastewater

Abstract

This invention discloses a closed-loop acid-base recovery system and method for the resource recovery of weak organic acid salt wastewater. The front-end neutralization unit neutralizes fresh organic acid wastewater with alkali solution to generate a weak organic acid salt solution to be treated, which is then fed into a diffusion dialysis unit. The diffusion dialysis unit is divided into a diffusion liquid channel and a receiving liquid channel by a diffusion dialysis anion exchange membrane, achieving pre-enrichment of organic acid ions through concentration difference. The bipolar membrane electrodialysis unit, driven by a DC electric field, breaks down the weak organic acid salt into organic acid and alkali solution. The inlet of the acid chamber is connected to the diffusion liquid outlet of the diffusion dialysis unit, and all the produced dilute organic acid solution is transported to the diffusion dialysis unit as an acid receiving liquid for recycling. All the regenerated alkali solution produced in the alkali chamber is transported to the front-end neutralization unit for recycling. The receiving liquid outlet of the diffusion dialysis unit is connected to an acid product collection unit. This invention fundamentally inhibits the back diffusion of weak acid molecules, achieving efficient recovery of organic acids and recycling of alkali solution.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment and resource recovery technology, and in particular to an acid-base dual closed-loop recovery system and method for the resource recovery of weak organic acid salt wastewater. Background Technology

[0002] In the production processes of industries such as chemical, pharmaceutical, food, fermentation, and mineral processing, a large amount of wastewater containing organic acids is generated. The industry commonly uses alkali neutralization to convert free organic acids into weak organic acid salts (such as sodium acetate, sodium lactate, sodium citrate, and sodium mercaptoacetate), and then recovers the organic acids and recycles the alkali solution through resource recovery processes. Bipolar membrane electrodialysis (BMED) technology, under the action of a DC electric field, generates H⁺ and OH⁻ through bipolar membrane water dissociation, directly breaking down weak organic acid salts into organic acids and alkali solutions without the need for the addition of large amounts of chemicals. It is currently the core green process in the field of weak organic acid salt resource recovery.

[0003] However, traditional bipolar membrane electrodialysis technology for treating weak organic acid salts has consistently faced a core technical bottleneck that is widely recognized in the industry and has remained unresolved for a long time—the back diffusion (leakage) problem of weak organic acid molecules. Taking sodium acetate as an example, in the strongly acidic environment of the acid chamber, the generated acetic acid mainly exists in the form of uncharged neutral molecules. Conventional electrodialysis anion exchange membranes separating the acid and salt chambers have extremely poor barrier properties against neutral small organic molecules. Driven by the concentration gradient, acetic acid molecules diffuse back from the acid chamber to the salt chamber, directly leading to a series of problems such as decreased product yield, a sharp drop in current efficiency, soaring energy consumption, and poor system stability. Currently, there is no mature technology to solve this bottleneck.

[0004] The existing literature, "Research on the Regeneration of Thioglycolic Acid from Sodium Thioglycolic Acid Wastewater by Bipolar Membrane Electrodialysis," has clearly verified that when the traditional BMED process treats weak organic acid salts, the back diffusion of weak acid in the later stage of the reaction causes the current efficiency to drop from a peak of 83.82% to about 72%, resulting in a significant increase in energy consumption per unit product. The existing two-stage process has also failed to solve the above-mentioned core defects. The industry urgently needs a resource recovery solution for weak organic acid salts that can suppress the back diffusion of weak acid from the source, with low energy consumption and near-zero chemical consumption.

[0005] Therefore, for wastewater containing weak organic acid salts generated in industries such as chemical, pharmaceutical, food, fermentation, and mineral processing, how to couple diffusion dialysis with bipolar membrane electrodialysis to construct a closed-loop acid-alkali circulation system, thereby inhibiting the back diffusion of weak acid molecules from the source and achieving efficient recovery of organic acids and recycling of alkali solutions, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] In view of the above-mentioned deficiencies of the prior art, the present invention provides an acid-base dual closed-loop recovery system and method for the resource recovery of weak organic acid salt wastewater, the purpose of which is:

[0007] This fundamentally weakens the concentration gradient driving force of the back diffusion of weak acid molecules, completely breaking through the core bottleneck of weak acid leakage that has long existed in the traditional BMED process.

[0008] Constructing a dual closed-loop circulation system of acid and alkali achieves near-zero chemical consumption and eliminates secondary pollution and cost issues caused by external addition of acid and alkali.

[0009] Achieving deep synergy between DD and BMED units, completing organic acid pre-enrichment with zero power consumption, and significantly reducing overall system energy consumption and equipment investment;

[0010] It simplifies the process flow, improves the long-term operational stability of the system, broadens the process adaptability to different types of weak organic acid salts, and has value for large-scale engineering applications.

[0011] To achieve the above objectives, this invention discloses an acid-base dual closed-loop recovery system for the resource utilization of weak organic acid salt wastewater, comprising a front-end neutralization unit, a diffusion dialysis unit, a bipolar membrane electrodialysis unit, and an acid product collection unit connected in sequence.

[0012] The front-end neutralization unit obtains fresh organic acid wastewater from the organic wastewater inlet and uses it to neutralize the fresh organic acid wastewater with alkaline solution to generate a weak organic acid salt solution to be treated. Its outlet is connected to the diffusion liquid inlet of the diffusion dialysis unit.

[0013] The diffusion dialysis unit includes a diffusion dialysis anion exchange membrane, which is divided into a diffusion liquid channel and a receiving liquid channel, for pre-enrichment of organic acid anions by concentration difference under conditions without an external electric field.

[0014] The bipolar membrane electrodialysis unit is a three-compartment BMED configuration, comprising an anode plate, a cathode plate, and a membrane stack placed between the two.

[0015] The membrane stack includes a bipolar membrane, a cation exchange membrane, and an anion exchange membrane, which are separated to form a salt chamber, an acid chamber, and a base chamber.

[0016] The feed inlet of the acid chamber is connected to the diffusion liquid outlet of the diffusion dialysis unit. The outlet is directly connected to the receiving liquid inlet of the diffusion dialysis unit through an acid closed-loop circulation pipeline, forming an acid closed-loop circulation path, so that all the dilute organic acid solution produced by the acid chamber is 100% transported to the diffusion dialysis unit as acid receiving liquid for recycling.

[0017] The outlet of the alkali chamber is directly connected to the alkali inlet of the front-end neutralization unit through an alkali closed-loop circulation pipeline, forming an alkali closed-loop circulation flow path, so that all the regenerated alkali produced by the alkali chamber is 100% transported to the front-end neutralization unit for recycling.

[0018] The receiving liquid outlet of the diffusion dialysis unit is connected to the acid product collection unit, and the pre-enriched organic acid product is transported to the acid product collection unit.

[0019] The water desalinated by the bipolar membrane electrodialysis unit is discharged from the desalinated water outlet.

[0020] Preferably, the diffusion dialysis unit is a plate and frame countercurrent diffusion dialysis unit, which is internally separated by the diffusion dialysis anion exchange membrane into a countercurrent arrangement of the diffusion liquid channel and the receiving liquid channel.

[0021] Preferably, the acid closed-loop circulation pipeline is equipped with online monitoring instruments and flow regulating valves;

[0022] The closed-loop alkali circulation pipeline is equipped with a micro-alkali replenishment device to compensate for alkali loss in the system.

[0023] This invention also provides a recovery method using the above-mentioned acid-base dual closed-loop recovery system for the resource recovery of weak organic acid salt wastewater, comprising the following steps:

[0024] S1. Front-end neutralization pretreatment: The fresh organic acid wastewater is sent to the front-end neutralization unit, and the weak organic acid salt solution to be treated is generated by alkaline neutralization. After pretreatment to remove membrane fouling impurities, it is sent to the diffusion dialysis unit.

[0025] S2. Diffusion dialysis pre-desalination and pre-enrichment: The weak organic acid salt solution is used as a diffusion liquid and is introduced into the diffusion liquid channel of the diffusion dialysis unit. The acid receiving liquid is introduced into the receiving liquid channel, so that the weak organic acid salt solution and the acid receiving liquid come into countercurrent contact. Driven by the concentration difference, 40% to 60% of the organic acid anions in the diffusion liquid diffuse into the receiving liquid side to form a pre-enriched organic acid solution. A residual liquid with some organic acid anions removed is formed on the diffusion liquid side.

[0026] S3. Bipolar membrane electrodialysis deep treatment: The residual liquid is sent into the salt chamber of the bipolar membrane electrodialysis unit and a DC electric field is applied to disassemble the remaining weak organic acid salts in the residual liquid, generate a dilute organic acid solution in the acid chamber, and generate a regenerated alkali solution in the alkali chamber.

[0027] S4. Acid closed-loop circulation: 100% of the dilute organic acid solution produced in the acid chamber is transported to the diffusion dialysis unit and recycled as the acid receiving liquid in step S2, forming an acid closed-loop circulation path; at the same time, by pre-removing organic acid salts, the feed concentration of the bipolar membrane electrodialysis unit is reduced, weakening the concentration difference driving force of the back diffusion of weak acid molecules in the acid chamber.

[0028] S5. Alkali closed-loop circulation: 100% of the regenerated alkali solution produced by the alkali chamber is transported to the front-end neutralization unit and recycled as the alkali solution used for neutralization in step S1, forming an alkali closed-loop circulation flow path.

[0029] S6. Product collection: The pre-enriched organic acid solution is collected from the diffusion dialysis unit through the acid product collection unit as the final product.

[0030] Preferably, before executing step S1, the pipeline connection is completed, deionized water is introduced to flush the entire system, and it is checked that there are no leaks or blockages, and that the instruments and control system are operating normally.

[0031] Preferably, in step S2, the flow ratio of the diffusion liquid to the receiving liquid is controlled to be 1:0.8 to 1:1.2, and the operating temperature is 20°C to 45°C.

[0032] Preferably, the weak organic acid salt is one or more of sodium acetate, sodium propionate, sodium lactate, sodium citrate, sodium formate, and sodium mercaptoacetate, with a pKa value in the range of 3.0 to 6.0.

[0033] The beneficial effects of this invention are:

[0034] This invention addresses the core bottleneck of weak acid back diffusion at its source. Through the synergistic effect of a dual closed-loop cycle of acid and alkali, it achieves near-zero chemical consumption and eliminates secondary pollution. The diffusion dialysis unit and the bipolar membrane electrodialysis unit work together to significantly reduce system energy consumption and equipment investment, improve product purity and long-term system stability, enhance process adaptability, and have greater value for large-scale engineering applications.

[0035] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0036] Figure 1 A schematic diagram of an embodiment of the present invention is shown.

[0037] Figure 2 The diagram shows a schematic of the membrane stack arrangement of a bipolar membrane electrodialysis unit in one embodiment of the present invention.

[0038] The system comprises: 1. Front-end neutralization unit; 2. Diffusion dialysis unit; 3. Bipolar membrane electrodialysis unit; 3-1. Cathode plate; 3-2. Anode plate; 3-3. Cation exchange membrane; 3-4. Anion exchange membrane; 3-5. Bipolar membrane; 3-6. Salt chamber; 3-7. Acid chamber; 3-8. Alkali chamber; 4. Acid product collection unit; 5. Acid closed-loop circulation pipeline; 6. Alkali closed-loop circulation pipeline; 7. Organic wastewater inlet; 8. Desalinated water outlet. Detailed Implementation

[0039] Example: Figure 1 and Figure 2 As shown, the acid-base dual closed-loop recovery system for the resource utilization of weak organic acid salt wastewater includes a front-end neutralization unit 1, a diffusion dialysis unit 2, a bipolar membrane electrodialysis unit 3, and an acid product collection unit 4 connected in sequence.

[0040] The front-end neutralization unit 1 obtains fresh organic acid wastewater from the organic wastewater inlet 7 and uses it to neutralize the fresh organic acid wastewater with alkaline solution to generate a weak organic acid salt solution to be treated. Its outlet is connected to the diffusion liquid inlet of the diffusion dialysis unit 2.

[0041] The diffusion dialysis unit 2 includes a diffusion dialysis anion exchange membrane, which is divided into a diffusion liquid channel and a receiving liquid channel, and is used to achieve the pre-enrichment of organic acid anions by concentration difference under conditions without an external electric field.

[0042] The bipolar membrane electrodialysis unit 3 is a three-compartment BMED configuration, consisting of an anode plate 3-2, a cathode plate 3-1, and a membrane stack placed between them.

[0043] The membrane stack includes a bipolar membrane 3-5, a cation exchange membrane 3-3, and an anion exchange membrane 3-4, which are separated to form a salt chamber 3-6, an acid chamber 3-7, and a base chamber 3-8;

[0044] The feed inlet of acid chamber 3-7 is connected to the diffusion liquid outlet of diffusion dialysis unit 2. The outlet is directly connected to the receiving liquid inlet of diffusion dialysis unit 2 through acid closed-loop circulation pipeline 5, forming an acid closed-loop circulation flow path, so that all the dilute organic acid solution produced by acid chamber 3-7 is 100% transported to diffusion dialysis unit 2 as acid receiving liquid for recycling.

[0045] The outlet of alkali chamber 3-8 is directly connected to the alkali inlet of front-end neutralization unit 1 through alkali closed-loop circulation pipeline 6, forming an alkali closed-loop circulation flow path, so that all the regenerated alkali produced by alkali chamber 3-8 is 100% transported to front-end neutralization unit 1 for recycling.

[0046] The receiving liquid outlet of diffusion dialysis unit 2 is connected to acid product collection unit 4, and the pre-enriched organic acid product is transported to acid product collection unit 4.

[0047] The water desalinated by the bipolar membrane electrodialysis unit 3 is discharged from the desalinated water outlet 8.

[0048] In this invention, weak organic acid salts refer to salts formed by the neutralization of a mono- or poly-organic acid with a pKa value in the range of 3.0 to 6.0 with a base, including but not limited to one or more mixtures of sodium acetate, sodium propionate, sodium lactate, sodium citrate, sodium formate, and sodium thioacetate.

[0049] Diffusion dialysis unit 2, also known as DD unit, is a separation device that uses a diffusion dialysis anion exchange membrane as the core separation medium and relies on the concentration difference across the membrane as the driving force to achieve selective diffusion permeation of organic acid anions without the application of an external electric field.

[0050] The bipolar membrane electrodialysis unit 3, or BMED unit, adopts a standard three-compartment configuration, consisting of an anode plate 3-2, a cathode plate 3-1, and a membrane stack placed between them. Driven by a DC electric field, it is an electrodialysis device that decomposes weak organic acid salts into organic acids and alkaline solutions.

[0051] The membrane stack includes a bipolar membrane 3-5, a cation exchange membrane 3-3, and an anion exchange membrane 3-4, which are separated to form a salt chamber 3-6, an acid chamber 3-7, and a base chamber 3-8.

[0052] Acid closed-loop circulation: refers to the fact that all the dilute organic acid solutions produced by the acid chamber of the bipolar membrane electrodialysis unit 3, namely the BMED unit, are recycled as acid receiving liquid for diffusion dialysis unit 2, namely the DD unit, without the need for concentration or discharge, forming an internal closed-loop flow path of acid solution, without the need for external replenishment of acid solution.

[0053] Alkali closed-loop circulation: refers to the fact that all the regenerated alkali solution produced by the alkali chamber of the bipolar membrane electrodialysis unit 3, i.e. the BMED unit, is 100% returned to the front-end neutralization unit 1 without purification, and is used to neutralize the fresh organic acid wastewater to generate a weak organic acid salt solution to be treated, forming an alkali closed-loop flow path.

[0054] This invention utilizes a closed-loop acid cycle to deeply couple the diffusion dialysis unit 2 (DD unit) and the bipolar membrane electrodialysis unit 3 (BMED unit). By pre-removing 40% to 60% of the organic acid salts from the feed in the diffusion dialysis unit 2 (DD unit), the feed concentration in the bipolar membrane electrodialysis unit 3 (BMED unit) is significantly reduced. Simultaneously, the concentration of organic acids generated in acid chambers 3-7 is reduced, fundamentally weakening the concentration difference driving force of the back diffusion of weak acids between acid chambers 3-7 and salt chambers 3-6. This minimizes the back diffusion loss rate of weak acid molecules, completely overcoming a core pain point that traditional BMED processes have long struggled to address. Furthermore, this invention overcomes the technical bias in the field that "the higher the initial acid concentration of the diffusion dialysis receiving solution, the lower the mass transfer efficiency." Through a closed-loop BMED dilute acid cycle, it maintains the mass transfer efficiency of diffusion dialysis while achieving fundamental suppression of back diffusion—a synergistic effect unpredictable in existing technologies.

[0055] This invention constructs a dual closed-loop acid-alkali circulation system: the acid closed-loop circulation uses 100% of the dilute acid produced by the bipolar membrane electrodialysis unit 3 (BMED unit) as the acid receiving solution for diffusion dialysis, completely eliminating the need for external replenishment of dilute acid and thus eliminating secondary pollution and operating costs caused by external acid addition; the alkali closed-loop circulation reuses 100% of the regenerated alkali solution produced by the bipolar membrane electrodialysis unit 3 (BMED unit) in the front-end neutralization process 1, reducing the consumption of fresh alkali solution by more than 98%, requiring only a trace amount of alkali solution to compensate for system losses. Compared with existing two-stage processes, this completely eliminates the consumption of external chemicals, achieves closed-loop utilization of materials, and has significant green and environmentally friendly advantages.

[0056] This invention achieves deep synergy through deep coupling between diffusion dialysis unit 2, i.e., the DD unit, and bipolar membrane electrodialysis unit 3, i.e., the BMED unit:

[0057] Diffusion dialysis unit 2, namely the DD unit, relies on concentration gradient to achieve 40% to 60% organic acid recovery under zero power consumption conditions, which greatly reduces the processing load of bipolar membrane electrodialysis unit 3, namely the BMED unit.

[0058] Meanwhile, the closed-loop acid circulation eliminates the need for a separate acid storage tank and dosing system for diffusion dialysis unit 2 (DD unit), and also eliminates the need for a separate concentration device for the dilute acid in bipolar membrane electrodialysis unit 3 (BMED unit). This significantly simplifies the process flow, reduces equipment investment, and solves the problems of long and high-investment existing two-stage processes.

[0059] In this invention, after the back diffusion of weak acid is fundamentally suppressed, the cross-contamination between acid chamber 3-7 and salt chamber 3-6 and alkali chamber 3-8 is significantly reduced, the residual amount of metal cations in organic acid products is significantly reduced, and the product purity is greatly improved. At the same time, the low-concentration feed significantly alleviates the membrane fouling and concentration polarization problems of bipolar membrane electrodialysis unit 3, i.e., BMED unit, the membrane cleaning frequency is significantly reduced, the membrane service life is extended, and the system can operate stably for a long time.

[0060] This invention exhibits excellent treatment effects on various weak organic acid salts such as sodium acetate, sodium lactate, sodium citrate, and sodium mercaptoacetate. It is widely applicable to the resource utilization of organic acid wastewater in multiple industries, including chemical, pharmaceutical, food, fermentation, and mineral processing. The core process parameters are all within the reasonable range of industry norms, and those skilled in the art can flexibly adjust them according to the actual treatment scale and feed water quality without the need for non-standard equipment modifications. Compared with existing technologies, it has stronger engineering implementation capabilities.

[0061] In some embodiments, the diffusion dialysis unit 2 is a plate and frame countercurrent diffusion dialysis device, which is internally divided into a diffusion liquid channel and a receiving liquid channel arranged in countercurrent by a diffusion dialysis anion exchange membrane.

[0062] In some embodiments, the acid closed-loop circulation pipeline 5 is equipped with online monitoring instruments and flow regulating valves;

[0063] The closed-loop alkali circulation pipeline 6 is equipped with a micro-alkali replenishment device to compensate for alkali loss in the system.

[0064] This invention also provides a recovery method using the above-mentioned acid-base dual closed-loop recovery system for the resource recovery of weak organic acid salt wastewater, comprising the following steps:

[0065] S1. Front-end neutralization pretreatment: Fresh organic acid wastewater is sent to front-end neutralization unit 1, where it is neutralized with alkali to generate a weak organic acid salt solution to be treated. After pretreatment to remove membrane fouling impurities, it is sent to diffusion dialysis unit 2.

[0066] S2. Pre-desalination and pre-enrichment of diffusion dialysis: A weak organic acid salt solution is used as a diffusion liquid and is introduced into the diffusion liquid channel of diffusion dialysis unit 2. The acid receiving liquid is introduced into the receiving liquid channel, so that the weak organic acid salt solution and the acid receiving liquid come into countercurrent contact. Driven by the concentration difference, 40% to 60% of the organic acid anions in the diffusion liquid diffuse into the receiving liquid side to form a pre-enriched organic acid solution. A residual liquid with some organic acid anions removed is formed on the diffusion liquid side.

[0067] S3. Bipolar membrane electrodialysis deep treatment: The residual liquid is sent into the salt chamber 3-6 of the bipolar membrane electrodialysis unit 3 and a DC electric field is applied to disassemble the remaining weak organic acid salts in the residual liquid, generate a dilute organic acid solution in the acid chamber 3-7, and generate a regenerated alkali solution in the alkali chamber 3-8.

[0068] S4, Acid Closed-Loop Circulation: All the dilute organic acid solution produced in acid chamber 3-7 is 100% transported to diffusion dialysis unit 2 and recycled as the acid receiving liquid in step S2, forming an acid closed-loop circulation path; at the same time, by pre-removing organic acid salts, the feed concentration of bipolar membrane electrodialysis unit 3 is reduced, weakening the concentration difference driving force of the back diffusion of weak acid molecules in acid chamber 3-7.

[0069] S5, Alkali Closed-Loop Circulation: All the regenerated alkali solution produced by alkali chambers 3-8 is 100% transported to the front-end neutralization unit 1 and recycled as the alkali solution used for neutralization in step S1, forming an alkali closed-loop circulation path.

[0070] S6. Product collection: The pre-enriched organic acid solution is collected from the diffusion dialysis unit 2 through the acid product collection unit 4 as the final product.

[0071] In practical applications, the acid-base dual closed-loop cycle is used to achieve synergistic effect between the DD unit and the BMED unit, thereby suppressing the back diffusion of weak acids from the source.

[0072] In some embodiments, before performing step S1, the pipeline connection is completed, deionized water is introduced to flush the entire system, and it is checked that there are no leaks or blockages, and that the instruments and control system are operating normally.

[0073] In some embodiments, in step S2, the flow ratio of the diffusion liquid to the receiving liquid is controlled to be 1:0.8 to 1:1.2, and the operating temperature is 20°C to 45°C.

[0074] In some embodiments, the weak organic acid salt is one or more of sodium acetate, sodium propionate, sodium lactate, sodium citrate, sodium formate, and sodium mercaptoacetate, with a pKa value in the range of 3.0 to 6.0.

[0075] In practical applications, the membrane materials and equipment used in this invention are all commercially available, mature products with no non-standard customization requirements. The specific selection specifications are as follows:

[0076] Diffusion dialysis anion exchange membrane: Commercially available diffusion dialysis homogeneous / heterogeneous anion exchange membranes are selected;

[0077] Bipolar membrane electrodialysis supporting membranes: cation exchange membranes, anion exchange membranes, and bipolar membranes are all selected from industry-standard electrodialysis membrane products.

[0078] Core equipment: Front-end neutralization unit 1 is equipped with a conventional neutralization reaction vessel, online monitoring instruments and pretreatment filtration device; diffusion dialysis unit 2 uses an industry-standard plate and frame countercurrent diffusion dialysis unit; bipolar membrane electrodialysis unit 3 uses an industry-standard plate and frame three-compartment bipolar membrane electrodialysis unit, equipped with an adjustable DC power supply, corrosion-resistant circulating pump and online monitoring instruments.

[0079] The specific implementation and pipeline connection steps of the dual closed-loop coupling system of the present invention are as follows:

[0080] Connection of front-end neutralization unit 1: The organic acid wastewater inlet pipeline is connected to the inlet of the neutralization reaction tank, and the outlet of the neutralization reaction tank is connected to the inlet of the diffusion dialysis unit through the pretreatment filter device; the outlet of the alkali closed-loop circulation pipeline is connected to the alkali inlet of the neutralization reaction tank, and is equipped with a micro-alkali replenishment device.

[0081] Connections of diffusion dialysis unit 2: The inlet of the diffusion liquid channel is connected to the outlet of the front-end neutralization unit, and the outlet of the diffusion liquid channel is connected to the inlet of the salt chamber of the bipolar membrane electrodialysis unit; the inlet of the receiving liquid channel is connected to the outlet of the acid chamber of the bipolar membrane electrodialysis unit through the acid closed-loop circulation pipeline, and the outlet of the receiving liquid channel is connected to the acid product collection unit.

[0082] Connection of bipolar membrane electrodialysis unit 3: Assemble the membrane stack according to the membrane stack sequence specified in the instruction manual, control the membrane stack compression force to be uniform, and ensure no internal or external leakage of the feed solution; the inlet of salt chamber 3-6 is connected to the diffusion solution outlet of diffusion dialysis unit 2, and the outlet of salt chamber 3-6 is connected to the desalination water collection pipeline; the outlet of acid chamber 3-7 is divided into two paths, one path is connected to the receiving solution inlet of diffusion dialysis unit 2 through acid closed-loop circulation pipeline 5, and the other path is connected to acid product collection unit 4; the outlet of alkali chamber 3-8 is connected to the front-end neutralization unit 1 through alkali closed-loop circulation pipeline 6; the electrode chamber is equipped with an electrode water circulation pipeline and an electrode liquid tank;

[0083] Instrumentation and control system installation: Each pipeline is equipped with conventional flow, pressure and temperature monitoring instruments, and each liquid storage tank is equipped with pH and conductivity monitoring instruments. All instruments are linked with the control system to realize the automated control of process parameters.

[0084] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. An acid-base double closed loop recovery system for resource utilization of weak organic acid salt wastewater; characterized in that, It includes a front-end neutralization unit (1), a diffusion dialysis unit (2), a bipolar membrane electrodialysis unit (3), and an acid product collection unit (4) connected in sequence. The front-end neutralization unit (1) obtains fresh organic acid wastewater from the organic wastewater inlet (7) and uses it to neutralize the fresh organic acid wastewater with alkaline solution to generate a weak organic acid salt solution to be treated. Its outlet is connected to the diffusion liquid inlet of the diffusion dialysis unit (2). The diffusion dialysis unit (2) includes a diffusion dialysis anion exchange membrane, which is divided into a diffusion liquid channel and a receiving liquid channel, and is used to achieve the pre-enrichment of organic acid anions by concentration difference under the condition of no external electric field. The bipolar membrane electrodialysis unit (3) is a three-compartment BMED configuration, comprising an anode plate (3-2), a cathode plate (3-1), and a membrane stack placed between them; The membrane stack includes a bipolar membrane (3-5), a cation exchange membrane (3-3), and an anion exchange membrane (3-4) separated to form a salt chamber (3-6), an acid chamber (3-7), and a base chamber (3-8). The inlet of the acid chamber (3-7) is connected to the outlet of the diffusion liquid of the diffusion dialysis unit (2). The outlet is directly connected to the inlet of the receiving liquid of the diffusion dialysis unit (2) through the acid closed-loop circulation pipeline (5) to form an acid closed-loop circulation path, so that all the dilute organic acid solution produced by the acid chamber (3-7) is 100% transported to the diffusion dialysis unit (2) as acid receiving liquid for recycling. The outlet of the alkali chamber (3-8) is directly connected to the alkali inlet of the front-end neutralization unit (1) through the alkali closed-loop circulation pipeline (6) to form an alkali closed-loop circulation flow path, so that all the regenerated alkali produced by the alkali chamber (3-8) is 100% transported to the front-end neutralization unit (1) for recycling. The receiving liquid outlet of the diffusion dialysis unit (2) is connected to the acid product collection unit (4) to transport the pre-enriched organic acid product to the acid product collection unit (4). The water desalinated by the bipolar membrane electrodialysis unit (3) is discharged from the desalinated water outlet (8). 2.The acid-base double closed loop recovery system for resource utilization of weak organic acid salt wastewater according to claim 1, characterized in that, The diffusion dialysis unit (2) is a plate and frame countercurrent diffusion dialysis unit, which is internally separated into a diffusion liquid channel and a receiving liquid channel arranged in countercurrent by the diffusion dialysis anion exchange membrane. 3.The acid-base double closed loop recovery system for resource utilization of weak organic acid salt wastewater according to claim 1, characterized in that, The acid closed-loop circulation pipeline (5) is equipped with online monitoring instruments and flow regulating valves; The closed-loop alkali circulation pipeline (6) is equipped with a micro-alkali replenishment device for replenishing the alkali loss of the system.

4. The recovery method using the acid-base dual closed-loop recovery system for the resource recovery of weak organic acid salt wastewater according to claim 1, characterized in that, Includes the following steps: S1. Front-end neutralization pretreatment: The fresh organic acid wastewater is sent to the front-end neutralization unit (1) and neutralized by alkaline solution to generate the weak organic acid salt solution to be treated. After pretreatment to remove membrane fouling impurities, it is sent to the diffusion dialysis unit (2). S2, Pre-desalination and pre-enrichment of diffusion dialysis: The weak organic acid salt solution is used as a diffusion liquid and is introduced into the diffusion liquid channel of the diffusion dialysis unit (2). The acid receiving liquid is introduced into the receiving liquid channel, so that the weak organic acid salt solution and the acid receiving liquid come into countercurrent contact. Driven by the concentration difference, 40% to 60% of the organic acid anions in the diffusion liquid diffuse into the receiving liquid side to form a pre-enriched organic acid solution. The diffusion liquid side forms a residual liquid with some organic acid anions removed. S3. Deep treatment by bipolar membrane electrodialysis: The residual liquid is sent into the salt chamber (3-6) of the bipolar membrane electrodialysis unit (3) and a DC electric field is applied to disassemble the remaining weak organic acid salts in the residual liquid, generate a dilute organic acid solution in the acid chamber (3-7), and generate a regenerated alkali solution in the alkali chamber (3-8). S4, Acid Closed-Loop Circulation: All the dilute organic acid solution produced in the acid chamber (3-7) is 100% transported to the diffusion dialysis unit (2) and recycled as the acid receiving liquid in step S2, forming an acid closed-loop circulation path; at the same time, by pre-removing organic acid salts, the feed concentration of the bipolar membrane electrodialysis unit (3) is reduced, weakening the concentration difference driving force of the reverse diffusion of weak acid molecules in the acid chamber (3-7); S5, Alkali Closed-Loop Circulation: All the regenerated alkali solution produced by the alkali chamber (3-8) is 100% transported to the front-end neutralization unit (1) and recycled as the alkali solution used for neutralization in step S1, forming an alkali closed-loop circulation path; S6. Product collection: The pre-enriched organic acid solution is collected from the diffusion dialysis unit (2) through the acid product collection unit (4) as the final product.

5. The recycling method according to claim 4, characterized in that, Before performing step S1, complete the pipeline connection, flush the entire system with deionized water, check for leaks and blockages, and ensure that the instruments and control system are operating normally.

6. The recycling method according to claim 4, characterized in that, In step S2, the flow ratio of the diffusion liquid to the receiving liquid is controlled to be 1:0.8 to 1:1.2, and the operating temperature is 20℃ to 45℃.

7. The recycling method according to claim 4, characterized in that, The weak organic acid salt is one or more of sodium acetate, sodium propionate, sodium lactate, sodium citrate, sodium formate, and sodium mercaptoacetate, with a pKa value in the range of 3.0 to 6.0.

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