A method for treating high-salinity wastewater by bipolar membrane electrodialysis based on in-situ photo-thermal interfacial evaporation of salt solution

Abstract

The application discloses a method for treating high-salinity wastewater by bipolar membrane electrodialysis based on in-situ photothermal interface evaporation of a salt solution chamber, and relates to a method for treating high-salinity wastewater by bipolar membrane electrodialysis. In order to solve the problem that the production rate of acid and alkali is reduced and energy consumption is increased due to the decrease of ion concentration in a salt solution chamber in the process of treating high-salinity wastewater by traditional bipolar membrane electrodialysis, the application sets a photothermal interface evaporator at the gas-liquid interface of the salt solution chamber of the bipolar membrane electrodialysis, so that the photothermal interface evaporator converts light energy into heat energy under illumination, and promotes water evaporation and temperature rise of the salt solution chamber synchronously during the operation of the electrodialysis, thereby improving the availability of ions in the salt solution chamber, reducing the solution resistance, relieving the adverse effects caused by ion depletion in the later operation stage, and realizing efficient preparation of acid and alkali products. The application belongs to the technical field of high-salinity wastewater treatment and ion resource utilization.

Description

Technical Field

[0001] This invention relates to a bipolar membrane electrodialysis method for treating high-salt wastewater, belonging to the field of high-salt wastewater treatment and ion resource utilization technology. Background Technology

[0002] High-salinity wastewater is widely generated in industrial processes such as seawater desalination, dyeing and printing, coal chemical industry, salt chemical industry, metallurgy, and pharmaceuticals, and typically contains high concentrations of inorganic salt ions. If high-salinity wastewater is discharged directly without effective treatment, the large amount of soluble salts it contains can lead to problems such as increased salinity in receiving water bodies, soil salinization, and ecosystem damage. Therefore, how to achieve efficient desalination, volume reduction, and resource utilization of high-salinity wastewater has become a crucial issue that urgently needs to be addressed in the field of industrial wastewater treatment.

[0003] Currently, high-salinity wastewater treatment mainly includes technologies such as pressure-driven membrane separation, electrodialysis, and evaporation crystallization. While pressure-driven membrane separation can achieve a certain degree of water-salt separation, it is easily limited by problems such as increased osmotic pressure, membrane fouling, and secondary treatment of concentrate when treating high-salinity, high-pollution-load wastewater. Evaporation crystallization can achieve salt concentration and solid salt recovery, but it typically requires a large amount of heat energy input, resulting in high operating energy consumption and significant equipment investment and maintenance costs. In contrast, electrodialysis membrane separation technology has advantages such as mild operating conditions, strong process controllability, and ease of coupling with resource recovery processes, and has attracted widespread attention in the field of high-salinity wastewater treatment.

[0004] Bipolar membrane electrodialysis is a typical electrodialysis resource recovery technology. It utilizes hydrogen and hydroxide ions generated by water dissociation in a bipolar membrane. Under the influence of an applied electric field, these ions drive the anions and cations in the brine solution to migrate to the acid and alkali chambers, respectively, thereby converting the salts in wastewater into the corresponding acids and bases. This technology not only desalinates high-salinity wastewater but also simultaneously yields valuable acid and alkali products, thus it is considered an important technological pathway for the ion resource recovery of high-salinity wastewater.

[0005] However, during the operation of traditional bipolar membrane electrodialysis, as ions migrate from the brine chamber to the acid and alkali chambers, the ion concentration in the brine chamber gradually decreases, leading to a decline in solution conductivity, an increase in membrane stack resistance, and further problems such as limited ion mass transfer and increased concentration polarization. Especially in the later stages of operation, insufficient mobile ions in the brine chamber make it difficult for ions to be replenished to the ion exchange membrane surface area in a timely manner, easily causing a decrease in effective ion migration flux and thus reducing the acid and alkali production rate. Simultaneously, as the concentrations in the acid and alkali chambers increase, the co-ion leakage problem of hydrogen and hydroxide ions also gradually worsens, resulting in a decrease in current efficiency and an increase in energy consumption per unit product. Therefore, traditional bipolar membrane electrodialysis still suffers from problems such as decreased operating efficiency, high energy consumption, and significant limited mass transfer in the later stages of high-salinity wastewater resource recovery.

[0006] To address the aforementioned issues, existing technologies have attempted to improve the operational efficiency of bipolar membrane electrodialysis through methods such as adding external ions, supplementing electrolytes, pre-concentration treatment, or coupling electrodialysis with bipolar membrane electrodialysis. While these methods can maintain ion availability in the brine chamber or enhance transmembrane mass transfer to some extent, they also suffer from drawbacks such as increased consumption of exogenous chemical reagents, complex system processes, increased additional energy input, and higher operating costs, hindering the low-carbon and green treatment of high-salinity wastewater.

[0007] Solar-driven interfacial evaporation is a technology that utilizes photothermal materials to absorb solar energy and convert it into interfacial heat energy, thereby promoting the evaporation of water at the gas-liquid interface. This technology has advantages such as clean energy sources, mild operating conditions, and simple structure, and is currently widely used in seawater desalination and freshwater acquisition. However, existing solar interfacial evaporation technologies typically focus on the evaporation and condensation process for water production, and are rarely used as an in-situ enhancement method in electrodialysis resource recovery processes. If the photothermal interfacial evaporation process can be used to in-situ concentrate and gently heat the brine chamber of bipolar membrane electrodialysis, it is expected to improve the ion availability of the brine chamber, reduce system resistance, and mitigate the effects of concentration polarization and co-ion leakage without adding additional chemical reagents or significantly increasing electrical energy input. This would improve the efficiency and green, low-carbon level of the ion resource recovery process for high-salinity wastewater.

[0008] Therefore, developing a novel high-salt wastewater resource treatment technology that can enhance the operation of bipolar membrane electrodialysis by utilizing natural photothermal conversion processes is of great significance for improving acid and alkali production efficiency and realizing the green resource utilization of salt in wastewater. Summary of the Invention

[0009] This invention addresses the problems of decreased acid and alkali production rates and increased energy consumption caused by the decline in ion concentration in the brine chamber during traditional bipolar membrane electrodialysis treatment of high-salt wastewater. It proposes a bipolar membrane electrodialysis method for treating high-salt wastewater based on in-situ photothermal interface evaporation in the brine chamber.

[0010] The technical solution adopted by the present invention to solve the above problems is as follows: The steps of the present invention include: Step 1: Pass the high-salt wastewater to be treated into the brine chamber of the bipolar membrane electrodialysis device, and pass the electrode solution, acid solution and alkali solution into the electrode solution chamber, acid solution chamber and alkali solution chamber of the bipolar membrane electrodialysis device respectively. Step 2: Place the interfacial evaporator for photothermal conversion at the gas-liquid interface of the brine chamber of the bipolar membrane electrodialysis device, so that it floats on the surface of the high-salt wastewater. Step 3: Under illumination, the interfacial evaporator absorbs sunlight and converts it into heat energy to promote the evaporation of water in the brine chamber at the gas-liquid interface. Step 4: Apply an external electric field to the bipolar membrane electrodialysis device, causing anions in the brine chamber to migrate through the anion exchange membrane to the acid chamber, and causing cations in the brine chamber to migrate through the cation exchange membrane to the alkali chamber; simultaneously, H+ generated by the hydrolysis of the bipolar membrane... + and OH - They enter the acid chamber and the alkali chamber respectively, and combine with the migrating anions and cations to generate the corresponding acids and bases; Step 5: When the conductivity of the salt solution chamber drops to the preset endpoint, stop the treatment process and collect the acid and alkali resource products in the acid and alkali solutions chambers respectively to realize the resource utilization of ions in high-salt wastewater.

[0011] Furthermore, the high-salt wastewater in step 1 is saline wastewater, including seawater reverse osmosis concentrate, dyeing and printing wastewater, and coal chemical reverse osmosis concentrate; The membrane stack of the bipolar membrane electrodialysis device is composed of bipolar membranes, anion exchange membranes and cation exchange membranes arranged in a stack, so that anions and cations in the brine chamber can migrate to the acid chamber and alkali chamber respectively under the action of an applied electric field.

[0012] Furthermore, in step 2, the interfacial evaporator is composed of a porous substrate and a photothermal conversion material loaded on the surface of the porous substrate.

[0013] Furthermore, in step 3, as molecules continue to detach from the salt chamber, the salt solution in the salt chamber is concentrated in situ, increasing the concentration of mobile ions per unit volume. At the same time, some of the heat generated by photothermal conversion is transferred to the salt chamber solution, causing the temperature of the salt chamber to rise gently.

[0014] Furthermore, the heat generated by photothermal conversion is transferred to the brine chamber solution through one or more of the following methods: heat conduction, convection, and radiation.

[0015] The beneficial effects of this invention are: 1. This invention places a photothermal interface evaporator at the gas-liquid interface of the brine chamber in a bipolar membrane electrodialysis device. This allows the photothermal interface evaporation process to directly act on the brine chamber containing high-salt wastewater, simultaneously achieving in-situ evaporation concentration and gentle temperature rise in the brine chamber during bipolar membrane electrodialysis operation. Compared to enhancement methods such as external electrolyte replenishment, ion implantation, pre-concentration treatment, or additional electrodialysis coupling, the enhancement effect of this invention occurs inside the brine chamber, eliminating the need for additional salts, electrolytes, or other chemical agents, and requiring no separate electrically driven concentration unit. The process coupling method is simple, and the enhancement location is clearly defined.

[0016] 2. By using in-situ evaporation and concentration in the brine chamber, this invention can increase the effective concentration of migratable ions in the brine chamber, thus mitigating the mass transfer limitation caused by ion depletion in the brine chamber during the later stages of traditional bipolar membrane electrodialysis. The gentle temperature increase caused by photothermal conversion reduces the solution resistance in the brine chamber and the operating resistance of the membrane stack, improving ion diffusion and mitigating the effects of concentration polarization. The synergistic effect of in-situ concentration and temperature increase improves ion transmembrane migration efficiency, thereby increasing acid and alkali production flux, reducing energy consumption per unit product, and improving current efficiency. Attached Figure Description

[0017] Figure 1 This is a process flow diagram of photothermal interface evaporation enhanced bipolar membrane electrodialysis; Figure 2 This is a schematic diagram illustrating the acid-base flux production process of the photothermal interface evaporation enhanced bipolar membrane electrodialysis process. Figure 3 This is a schematic diagram of the energy consumption of the photothermal interface evaporation enhanced bipolar membrane electrodialysis process; Figure 4 This is a schematic diagram of the current efficiency of bipolar membrane electrodialysis enhanced by photothermal interface evaporation. Detailed Implementation

[0018] Specific implementation method one: as follows Figures 1 to 4 As shown, the steps of the bipolar membrane electrodialysis method for treating high-salinity wastewater based on in-situ photothermal interface evaporation in a brine chamber, as described in this embodiment, include: Step 1: Pass the high-salt wastewater to be treated into the brine chamber of the bipolar membrane electrodialysis device, and pass the electrode solution, acid solution and alkali solution into the electrode solution chamber, acid solution chamber and alkali solution chamber of the bipolar membrane electrodialysis device respectively. Among them, high-salt wastewater can be seawater reverse osmosis concentrate, dyeing and printing wastewater, coal chemical reverse osmosis concentrate or other types of saline wastewater; The bipolar membrane electrodialysis membrane stack is composed of bipolar membrane, anion exchange membrane and cation exchange membrane stack, which enables anions and cations in the brine chamber to migrate to the acid chamber and alkali chamber respectively under the action of an applied electric field; Step 2: Place the interfacial evaporator for photothermal conversion at the gas-liquid interface of the brine chamber of the bipolar membrane electrodialysis device, allowing it to float or be fixed on the surface of the high-salt wastewater. The interfacial evaporator consists of a porous substrate and a photothermal conversion material loaded on the surface of the porous substrate; The preferred evaporator is one with high photothermal conversion efficiency, strong evaporation performance, and strong resistance to salt crystallization (such as a melamine foam evaporator supported on reduced graphene oxide with a Janus structure). This type of evaporator can exist stably on the surface of the salt solution chamber and provide reaction sites for photothermal conversion and interfacial evaporation. Step 3: Under illumination, allow the interfacial evaporator to absorb sunlight or simulate sunlight and convert it into heat energy to promote the evaporation of water in the brine chamber at the gas-liquid interface. As water continues to detach from the brine chamber, the salt solution in the chamber is concentrated in situ, increasing the concentration of mobile ions per unit volume. At the same time, some of the heat generated by photothermal conversion is transferred to the brine chamber solution through heat conduction, convection, or radiation, causing the temperature of the brine chamber to rise gently. Step 4: Apply an external electric field to the bipolar membrane electrodialysis device, causing anions in the brine chamber to migrate through the anion exchange membrane to the acid chamber, and causing cations in the brine chamber to migrate through the cation exchange membrane to the alkali chamber; simultaneously, H+ generated by the hydrolysis of the bipolar membrane... + and OH - They enter the acid chamber and the alkali chamber respectively, and combine with the migrating anions and cations to generate the corresponding acids and bases; By using the interface evaporator to concentrate and heat the brine chamber in situ, the solution resistance of the brine chamber and the operating resistance of the membrane stack can be reduced, thus alleviating the problems of mass transfer limitation and concentration polarization caused by ion depletion in the brine chamber during the later stages of bipolar membrane electrodialysis operation. Step 5: When the conductivity of the brine chamber decreases to the preset endpoint, or when the bipolar membrane electrodialysis device has run for a set time, stop the treatment process and collect the acid and alkali resource products in the acid and alkali chambers respectively to realize the resource utilization of ions in high-salt wastewater.

[0019] Example Example 1 The process flow diagram for in-situ photothermal interface evaporation-enhanced BMED treatment of sodium sulfate-type high-salt wastewater is shown in Figure 1. This embodiment uses sodium sulfate-type simulated high-salt wastewater as the treatment target and constructs a photothermal interface evaporation-enhanced bipolar membrane electrodialysis device. The bipolar membrane electrodialysis stack uses a combination of bipolar membranes, anion exchange membranes, and cation exchange membranes, with an effective membrane area of ​​9 cm². 2 The brine chamber, electrode solution chamber, acid chamber, and alkali chamber were respectively purged with 100 mL of 0.3 mol / L Na₂SO₄ solution, 100 mL of 5% Na₂SO₄ solution, 100 mL of 0.025 mol / L H₂SO₄ solution, and 100 mL of 0.05 mol / L NaOH solution. The bipolar membrane electrodialysis device operated under constant pressure, with an operating voltage of 8 V and a membrane surface flow rate of 2 cm / s.

[0020] The photothermal interface evaporator was prepared using melamine foam supported on reduced graphene oxide. Specifically, reduced graphene oxide was added to n-hexane and ultrasonically dispersed for 15 min; then hexadecyltrimethoxysilane and glacial acetic acid were added, and the mixture was stirred at 500 r / min for 3 h; finally, polydimethylsiloxane and a curing agent were added, and the mixture was ultrasonically treated for 15 min to obtain the photothermal coating liquid. The obtained photothermal coating liquid was sprayed onto one side of the melamine foam surface, with a loading of approximately 12 mg / cm³. 2 The evaporator was cured at 65°C for 6 hours to obtain a photothermal interface evaporator with a Janus structure.

[0021] The fabricated photothermal interface evaporator was placed at the gas-liquid interface of high-salt wastewater in the brine chamber, allowing it to float on the surface of the brine. A xenon lamp with an AM 1.5G filter was used as a simulated solar light source, with an irradiance of 1000 W / m². 2 During operation, the photothermal interface evaporator absorbs light energy and converts it into heat energy, causing the water in the brine chamber to evaporate at the gas-liquid interface, thereby achieving in-situ concentration of the brine chamber and gently raising the brine temperature. Simultaneously, under the influence of an external electric field, SO4 in the brine chamber... 2- Migrate to the acid chamber and react with H + Combine to form H2SO4, Na + Migrate to the alkali chamber and react with OH - NaOH is generated. When the conductivity of the salt solution chamber decreases to 10 mS / cm, operation is stopped and the acid and alkali products in the acid and alkali chambers are collected.

[0022] Example 2 To verify the impact of the photothermal interface evaporation-enhanced bipolar membrane electrodialysis (SDIE-BMED) process on acid and alkali production flux, high-salinity wastewater was treated according to the method in Example 1, with a conventional bipolar membrane electrodialysis (BMED) process without a photothermal interface evaporator used as a control. The acid and alkali production flux of the photothermal interface evaporation-enhanced bipolar membrane electrodialysis process is shown in [reference needed]. Figure 2 Experimental results show that the acid production flux and alkali production flux of the traditional bipolar membrane electrodialysis process are 0.37 kg / (m²). 2 ·h) and 0.40 kg / (m 2 The photothermal interface evaporation enhanced bipolar membrane electrodialysis process of the present invention increases the acid production flux and alkali production flux to 0.43 kg / (m³). 2 ·h) and 0.47 kg / (m 2(h). Compared with the conventional bipolar membrane electrodialysis process, the acid production flux and alkali production flux of the present invention are increased by approximately 14.0% and 14.9%, respectively. The above results indicate that after the photothermal interface evaporator is introduced into the brine chamber, it can improve the ion availability of the brine chamber through in-situ evaporation and concentration, and promote ion diffusion and transmembrane migration through gentle heating, thereby increasing the acid and alkali production flux of the bipolar membrane electrodialysis process.

[0023] Example 3 To verify the impact of photothermal interface evaporation-enhanced bipolar membrane electrodialysis on operating energy consumption and current efficiency, high-salinity wastewater was treated according to the method in Example 1, with a conventional bipolar membrane electrodialysis process used as a control. The energy consumption and current efficiency of the photothermal interface evaporation-enhanced bipolar membrane electrodialysis process are shown below. Figure 3 and Figure 4 Experimental results show that the unit product energy consumption of the traditional bipolar membrane electrodialysis process is 7.9 kWh / kg, while the unit product energy consumption of the photothermal interface evaporation enhanced bipolar membrane electrodialysis process described in this invention is reduced to 7.3 kWh / kg, a reduction of approximately 7.8%. The current efficiency of the traditional bipolar membrane electrodialysis process is 67.7%, while the current efficiency of the process described in this invention is increased to 73.4%. These results demonstrate that the photothermal interface evaporation enhanced bipolar membrane electrodialysis process can reduce unit product energy consumption and improve current efficiency. This is because in-situ evaporation and concentration in the brine chamber can increase the ion concentration per unit volume and reduce solution resistance; the gentle temperature rise caused by photothermal conversion can improve the thermal motion and diffusion capacity of ions, alleviating the mass transfer limitation and concentration polarization caused by ion depletion in the brine chamber in the later stages of operation. Simultaneously, the shortened processing time also helps to reduce current loss caused by co-ion leakage.

[0024] In summary, this invention introduces a photothermal interface evaporator into the brine chamber of a bipolar membrane electrodialysis system, allowing the photothermal interface evaporation process to occur simultaneously with the ion migration process within the electrodialysis membrane. This enables in-situ concentration and gentle temperature increase of the brine chamber, thereby increasing acid and alkali production flux, reducing operating energy consumption, and improving current efficiency. This invention provides a highly efficient and low-carbon ion resource recovery method for high-salinity wastewater, and has promising application prospects.

[0025] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent substitutions, and improvements made to the above embodiments without departing from the scope of the present invention, based on the technical essence of the present invention and within the spirit and principles of the present invention, shall still fall within the protection scope of the present invention.

Claims

1. A method for treating high-salinity wastewater using bipolar membrane electrodialysis based on in-situ photothermal interface evaporation in a brine chamber, characterized in that, The specific steps include: Step 1: Pass the high-salt wastewater to be treated into the brine chamber of the bipolar membrane electrodialysis device, and pass the electrode solution, acid solution and alkali solution into the electrode solution chamber, acid solution chamber and alkali solution chamber of the bipolar membrane electrodialysis device respectively. Step 2: Place the interfacial evaporator for photothermal conversion at the gas-liquid interface of the brine chamber of the bipolar membrane electrodialysis device, so that it floats on the surface of the high-salt wastewater. Step 3: Under illumination, the interfacial evaporator absorbs sunlight and converts it into heat energy to promote the evaporation of water in the brine chamber at the gas-liquid interface. Step 4: Apply an external electric field to the bipolar membrane electrodialysis device, causing anions in the brine chamber to migrate through the anion exchange membrane to the acid chamber, and causing cations in the brine chamber to migrate through the cation exchange membrane to the alkali chamber; simultaneously, H+ generated by the hydrolysis of the bipolar membrane... + and OH - They enter the acid chamber and the alkali chamber respectively, and combine with the migrating anions and cations to generate the corresponding acids and bases; Step 5: When the conductivity of the salt solution chamber drops to the preset endpoint, stop the treatment process and collect the acid and alkali resource products in the acid and alkali solutions chambers respectively to realize the resource utilization of ions in high-salt wastewater.

2. The method for treating high-salinity wastewater by bipolar membrane electrodialysis based on in-situ photothermal interface evaporation in a brine chamber, as described in claim 1, is characterized in that... In step 1, high-salt wastewater refers to saline wastewater, including seawater reverse osmosis concentrate, dyeing and printing wastewater, and coal chemical reverse osmosis concentrate. The membrane stack of the bipolar membrane electrodialysis device is composed of bipolar membranes, anion exchange membranes and cation exchange membranes arranged in a stack, so that anions and cations in the brine chamber can migrate to the acid chamber and alkali chamber respectively under the action of an applied electric field.

3. The method for treating high-salinity wastewater by bipolar membrane electrodialysis based on in-situ photothermal interface evaporation in a brine chamber, as described in claim 1, is characterized in that... In step 2, the interfacial evaporator consists of a porous substrate and a photothermal conversion material loaded on the surface of the porous substrate.

4. The method for treating high-salinity wastewater by bipolar membrane electrodialysis based on in-situ photothermal interface evaporation in a brine chamber, as described in claim 1, is characterized in that... In step 3, as molecules continue to detach from the salt chamber, the salt solution in the salt chamber is concentrated in situ, increasing the concentration of mobile ions per unit volume. At the same time, some of the heat generated by photothermal conversion is transferred to the salt solution, causing the temperature of the salt chamber to rise gently.

5. The method for treating high-salinity wastewater by bipolar membrane electrodialysis based on in-situ photothermal interface evaporation in a brine chamber, as described in claim 1, is characterized in that... The heat generated by photothermal conversion is transferred to the brine chamber solution through one or more of the following methods: heat conduction, convection, and radiation.

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