Method for treating acidic wastewater by using double-membrane method

Abstract

The invention provides a method for treating acidic wastewater by using a double-membrane method, which comprises the following steps: sequentially pre-treating acidic wastewater generated in an electrode foil formation process through a microfiltration unit and an activated carbon adsorption unit to obtain a pre-treatment solution; the pretreatment liquid is introduced into a nanofiltration unit for separation, and nanofiltration concentrated liquid and nanofiltration produced water are obtained; the nanofiltration produced water is introduced into a reverse osmosis unit for deep desalination, and reverse osmosis produced water is obtained; and returning the nanofiltration concentrated liquor to an electrode foil formation tank for recycling, and recycling the reverse osmosis produced water to a production line.

Description

Technical Field

[0001] This invention relates to the field of information technology, and in particular to a method for treating acidic wastewater using a dual-membrane process. Background Technology

[0002] Industrial wastewater treatment plays a crucial role in environmental protection and resource recycling, especially in highly polluting industries such as electrode foil production. Wastewater treatment is not only related to environmental safety but is also a vital link in achieving sustainable development for enterprises. Effective wastewater treatment technologies can reduce pollutant emissions while simultaneously unlocking the resource value within wastewater, thus supporting production processes. However, research and application in this field still face numerous challenges and urgently require innovative breakthroughs.

[0003] Currently, wastewater treatment methods often struggle to find a balance between pollutant removal and resource recovery. Many technologies, while removing harmful substances, easily overlook the value of recyclable components in wastewater, leading to resource waste; or, in pursuing resource recovery, the treated water quality fails to meet the standards for reuse in production, limiting the practical application of the technology. This imbalance leaves enterprises caught between environmental pressures and economic benefits, making it difficult to achieve truly green production.

[0004] A deeper issue lies in how to accurately separate the different components in wastewater during the treatment process, which has become a key technological barrier. Wastewater often contains suspended solids, organic impurities, and high concentrations of salts and metal ions. If these components cannot be effectively separated, it will not only affect the water purification effect but may also lead to the loss of valuable substances. For example, in the electrode foil formation process, the wastewater contains high concentrations of phosphate and aluminum ions. If these components could be recovered and directly used in the production process, it would greatly reduce costs. However, existing technologies often suffer from insufficient separation efficiency, resulting in the waste of these resources and even their becoming sources of pollution in subsequent treatments.

[0005] Therefore, how to achieve efficient removal of pollutants in wastewater treatment, while accurately separating and recovering valuable components so that the treated water quality meets the requirements for production reuse, has become a key issue that urgently needs to be addressed in the field of industrial wastewater treatment. Summary of the Invention

[0006] This invention provides a method for treating acidic wastewater using a dual-membrane process, mainly comprising:

[0007] The acidic wastewater generated during the electrode foil formation process is pretreated sequentially by a microfiltration unit and an activated carbon adsorption unit to obtain a pretreated solution. The pretreated solution is then passed into a nanofiltration unit for separation, yielding nanofiltration concentrate and nanofiltration permeate. The nanofiltration permeate is then passed into a reverse osmosis unit for deep desalination, yielding reverse osmosis permeate. The nanofiltration concentrate is returned to the electrode foil formation tank for recycling, and the reverse osmosis permeate is reused in the production line. Further, the microfiltration unit includes: a polyvinylidene fluoride hollow fiber membrane module operating in a cross-flow filtration mode with a preset cross-flow velocity; the membrane module is fixed to the pretreatment tank outlet pipe via a flange connection; a pressure sensor and a flow meter are respectively installed at the inlet and outlet; an automatic backwash valve is installed on the concentrate side, performing a combined air-water backwash once every preset operating time. Furthermore, the activated carbon adsorption unit includes: the activated carbon adsorption unit is filled with coconut shell-based granular activated carbon which passes through the adsorption column from top to bottom, with a preset empty bed contact time; the activated carbon adsorption unit adopts a dual-column series design, with the front column filled with unregenerated activated carbon and the rear column filled with thermally regenerated activated carbon. When the furfural concentration in the effluent exceeds a preset concentration, the unit switches to a standby adsorption column and regenerates the saturated column. Further, the regeneration of the saturated column includes: first rinsing with deionized water for a preset time, then introducing an alkaline solution at a preset flow rate to desorb organic acids, followed by restoring the acidic sites on the activated carbon surface with an acidic solution at a preset flow rate, and finally rinsing with deionized water until neutral; during the regeneration process, the front column bears the high concentration of organic matter adsorption load, while the rear column acts as a safeguard layer to ensure that the furfural concentration in the effluent is lower than the preset concentration, and the regeneration waste liquid is discharged into a dedicated collection tank. Furthermore, the nanofiltration unit includes: the nanofiltration unit uses polyamide composite nanofiltration membranes arranged in a two-stage, single-stage configuration within a stainless steel pressure vessel, with booster pumps installed between the stages; the nanofiltration concentrate is transported to the electrode foil forming tank via pipelines using an acid-resistant centrifugal pump, and the reuse pipeline is made of acid-resistant material with a polished inner wall. Furthermore, the reverse osmosis unit includes: the reverse osmosis unit uses aromatic polyamide spiral wound reverse osmosis membranes configured in a single-stage, single-stage configuration, with an energy recovery device on the concentrate side; the reverse osmosis permeate is monitored by an online conductivity meter, and when the conductivity is lower than a preset value, it enters a reuse water storage tank; the reverse osmosis concentrate is partially recycled after passing through the energy recovery device. Furthermore, the step of passing the pretreated solution into the nanofiltration unit for separation includes: operating at a preset pressure and temperature, achieving a preset Al³⁺ rejection rate and a preset oxalic acid permeation rate; the phosphoric acid concentration, Al³⁺ concentration, and pH value in the nanofiltration concentrate are within preset ranges, meeting the requirements of the electrode foil forming tank for the pretreated solution.Furthermore, the step of passing the nanofiltration permeate into the reverse osmosis unit for deep desalination includes: operating under preset pressure and temperature conditions, with the TOC content and NH4⁺ concentration of the reverse osmosis permeate within preset ranges; the conductivity of the reverse osmosis permeate is stable within a preset range, meeting the standards for cleaning water, and is used for rinsing in the production line or for preparing acid solutions.

[0008] The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

[0009] This invention discloses an innovative method for the treatment and resource utilization of acidic wastewater from the electrode foil formation process. It aims to solve the logical connection problem between pollutant removal, resource recovery, and production reuse in wastewater treatment, specifically, how to efficiently remove organic matter and salt pollutants while simultaneously recycling valuable components from the wastewater and meeting the water requirements of the production line. This invention effectively removes suspended solids and organic impurities through pretreatment with microfiltration and activated carbon adsorption units. Subsequently, a nanofiltration unit separates high-concentration phosphoric acid and aluminum ion concentrate, which is directly reused in the formation tank. The nanofiltration permeate undergoes deep desalination via reverse osmosis, achieving conductivity and pollutant concentrations sufficient for reuse in production line cleaning or acid preparation. The core innovation of this invention lies in the synergistic optimization of multi-stage membrane separation and adsorption technologies, ensuring high efficiency in wastewater treatment and sustainable resource utilization. Ultimately, it achieves comprehensive technical effects of wastewater reduction, resource recovery, and reduced production costs, providing a green and efficient solution for industrial wastewater treatment. Attached Figure Description

[0010] Figure 1 This is a flowchart illustrating a method for treating acidic wastewater using a dual-membrane process according to the present invention. Detailed Embodiments

[0011] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this specification.

[0012] like Figure 1 This embodiment of a method for treating acidic wastewater using a dual-membrane process may specifically include:

[0013] S1, the acidic wastewater generated in the electrode foil forming process is pretreated by passing it through a microfiltration unit and an activated carbon adsorption unit in sequence to obtain a pretreated solution.

[0014] In one embodiment, step S1 involves pretreating the acidic wastewater generated during the electrode foil formation process by sequentially passing it through a microfiltration unit and an activated carbon adsorption unit to obtain a pretreated liquid. Specifically, step S11 involves introducing the acidic wastewater into the microfiltration unit, which uses a polyvinylidene fluoride hollow fiber membrane module with a pore size of 0.1–0.22 μm. The membrane module is installed on the outlet pipe of the pretreatment tank in a cross-flow filtration manner, with the cross-flow velocity controlled at 1.2–1.5 m / s. This method intercepts suspended particles and colloidal substances, preventing them from entering subsequent systems and causing particulate contamination. In step S12, the microfiltration permeate is passed into the activated carbon adsorption unit, which is filled with coconut shell-based granular activated carbon with a particle size of 1.0 to 2.0 mm and a filling height of 1.5 to 2.0 m. The wastewater passes through the adsorption column from top to bottom, and the empty bed contact time is 15 to 20 min. This selectively removes highly adsorbent organic pollutants such as furfural, organic amines, and some corrosion inhibitors, reducing their tendency to deposit on the membrane surface, thereby obtaining a pretreated liquid with reduced turbidity.

[0015] In one possible implementation, in step S11, the membrane module of the microfiltration unit is fixed to the outlet pipe of the pretreatment tank via a flange connection. A pressure sensor and a flow meter are installed at the inlet and outlet, respectively. An automatic backwash valve is installed on the concentrate side, performing a combined air-water backwash every 60 minutes. The backwash air pressure is 0.2 MPa, the water pressure is 0.3 MPa, and the duration is 90 seconds. This backwashing process first introduces compressed air to loosen contaminants on the membrane surface, then uses water to flush out the contaminants, ensuring stable membrane flux and preventing clogging that could prolong the operating cycle.

[0016] For example, in the aluminum foil production scenario, when the wastewater has a pH of 3.2 and contains 95 g / L of phosphoric acid and 18 g / L of Al³⁺, the cross-flow velocity is set to 1.3 m / s. The microfiltration unit effectively intercepts colloidal Al(OH)3 particles with a particle size greater than 0.2 μm, and the turbidity of the produced water is reduced to below 0.25 NTU, which is beneficial to the efficiency improvement of the subsequent adsorption unit and reduces the risk of organic matter deposition.

[0017] In one embodiment, the activated carbon adsorption unit in step S12 adopts a dual-column series design. The front column is filled with unregenerated activated carbon, and the rear column is filled with activated carbon that has undergone thermal regeneration at 105°C. When the furfural concentration in the effluent exceeds 0.5 mg / L, the system switches to the standby adsorption column and regenerates the saturated column. The regeneration process includes rinsing with deionized water for 30 min, then passing a 10% NaOH solution through the column at a flow rate of 2 BV / h to desorb organic acids, followed by restoring the acidic sites on the activated carbon surface with a 5% H2SO4 solution at a flow rate of 2 BV / h, and finally washing with deionized water until neutral. This dual-column design ensures continuous operation and restores adsorption capacity through regeneration, making it suitable for wastewater with high concentrations of organic pollutants.

[0018] For example, in a company treating 8 m³ of acidic wastewater per day, the front column mainly adsorbs furfural at 0.8 mg / L, while the rear column ensures that the effluent concentration is below 0.5 mg / L. The regeneration cycle is about 4 hours. Organic acids are removed by desorption of NaOH to form soluble sodium salts, and H2SO4 protonates the surface functional groups to enhance the affinity for weakly polar compounds, thereby maintaining the overall TOC of the pretreatment liquid below the expected threshold, which is beneficial to the stability of subsequent membrane separation.

[0019] In one possible implementation, the pretreated liquid from step S1 is used as input to the subsequent nanofiltration unit to ensure the graded interception of pollutants and realize the resource-based reuse of acidic wastewater.

[0020] For example, under different wastewater flow scenarios, such as a daily production of 10 m³, the cross-flow velocity is adjusted to 1.5 m / s to match the treatment capacity, the contact time of the activated carbon empty bed is extended to 20 min to enhance the adsorption effect, the furfural removal rate in the pretreatment liquid reaches more than 95%, which is beneficial to avoid membrane fouling and extend the system operation cycle to more than 90 days.

[0021] S2, the pretreated liquid is passed into a nanofiltration unit for separation to obtain nanofiltration concentrate and nanofiltration permeate; S3, the nanofiltration permeate is passed into a reverse osmosis unit for deep desalination to obtain reverse osmosis permeate.

[0022] S2, the pretreated liquid is passed into a nanofiltration unit for separation to obtain nanofiltration concentrate and nanofiltration permeate.

[0023] In one embodiment, step S2 involves passing the pretreatment liquid into a nanofiltration unit for separation, specifically including the following sub-steps.

[0024] S21, pump the pretreatment solution into the inlet of the nanofiltration unit, adjust the operating pressure to 1.8-2.2 MPa, and control the temperature at 25-30℃. Utilize the characteristic of the polyamide composite nanofiltration membrane that has a molecular weight cutoff of 200 Da to retain multivalent ions and organic matter with a molecular weight greater than 200 Da in the pretreatment solution.

[0025] Nanofiltration membranes work through the Donnan effect and size sieving mechanism. The Donnan effect refers to the repulsive force of charged membranes on ions of the same charge, making it difficult for polyvalent positive ions such as Al³⁺ to pass through the membrane. Size sieving is based on the physical barrier of membrane pore size to larger molecules, such as phosphate ions, which are retained due to their larger hydration size.

[0026] S22 controls the flow rate on the concentrate side based on the osmotic pressure difference and concentration polarization across the membrane, ensuring that the Al³⁺ concentration in the nanofiltration concentrate reaches 15–25 g / L, the phosphoric acid concentration is 80–120 g / L, and the pH value is maintained at 2.8–3.2.

[0027] These concentration parameters of the concentrate are adjusted by real-time monitoring of the pressure drop between membrane element sections. If the pressure drop exceeds the preset value, the output of the inter-section booster pump is increased to compensate, thereby maintaining stable separation efficiency.

[0028] S23 collects the nanofiltration permeate through the membrane, wherein the permeate rate of small molecule organic acids such as oxalic acid is not less than 85%, and the nanofiltration concentrate is transported to the formation tank for recycling via an acid-resistant centrifugal pump.

[0029] This separation allows the concentrate to directly meet the composition requirements of the formation tank, avoiding additional adjustments and enabling resource reuse.

[0030] In one possible implementation, for different initial wastewater concentration scenarios, for example, when the initial Al³⁺ concentration in the pretreatment solution is 18 g / L, the operating pressure is set to 2.0 MPa and the temperature is 28℃, the Al³⁺ rejection rate can reach 96.3% and the oxalic acid permeation rate is 87.5%. The beneficial effect is that it effectively separates polyvalent metal ions and small molecule organic acids, reduces the subsequent reverse osmosis load, and extends the membrane life.

[0031] For example, in the production of aluminum electrolytic capacitors, when treating 8 m³ of wastewater per day, the concentrated solution has a pH of 3.0 and a phosphoric acid concentration of 110 g / L. This solution can be directly reused to replace 30% of the fresh acid solution, thus reducing production costs.

[0032] S3, the nanofiltration permeate is passed into the reverse osmosis unit for deep desalination to obtain reverse osmosis permeate.

[0033] In one embodiment, step S3 involves passing nanofiltration permeate into a reverse osmosis unit for deep desalination, specifically including the following sub-steps.

[0034] S31, the nanofiltration permeate is pressurized to 3.5-4.0 MPa by a high-pressure pump, and the temperature is maintained at 25-30℃. It is then passed through an aromatic polyamide spiral wound reverse osmosis membrane with a desalination rate of not less than 98%.

[0035] The reverse osmosis process is based on a solution diffusion model. The solute and solvent permeate through the membrane at different rates under pressure, resulting in salt being retained and water molecules permeating. In specific calculations, the membrane flux is affected by the net driving pressure, the membrane permeability coefficient, and the temperature. For example, the net driving pressure is equal to the operating pressure minus the osmotic pressure difference.

[0036] S32 is an energy recovery device that monitors the reverse osmosis concentrate side. The recovery rate is controlled at over 40%, and the recovered pressure energy is used for pre-pressurization of the feed water.

[0037] The energy recovery device transfers the residual pressure of the concentrate to the feed water through pressure exchange, reducing energy consumption. For example, when 42% of the pressure energy is recovered, the overall system energy consumption is reduced by 18%.

[0038] S33 collects reverse osmosis permeate and tests it with an online conductivity meter. When the conductivity is below 50 μS / cm, it is introduced into the reclaimed water storage tank, where the TOC content is below 1.0 mg / L and the NH4⁺ concentration is below 2 mg / L.

[0039] This monitoring ensures that the produced water quality meets electronic-grade standards for reuse in the production line.

[0040] In one possible implementation, for temperature fluctuation scenarios, such as a temperature of 28°C and a pressure of 3.8 MPa, the membrane flux is stabilized at above 25 L / (m²·h), and the flux decay rate is less than 8% after 30 days of continuous operation. The beneficial effect is to suppress organic pollution and achieve stable desalination.

[0041] For example, when treating nanofiltration permeate containing trace amounts of NH4⁺, under these conditions the permeate conductivity is 38 μS / cm, TOC is 0.7 mg / L, and NH4⁺ is 1.3 mg / L. It can be directly used for foil rinsing, forming a closed loop of water resources. The dual-membrane method is used to efficiently treat acidic wastewater from aluminum foil production.

[0042] S4, the nanofiltration concentrate is returned to the electrode foil forming tank for recycling, and the reverse osmosis permeate is reused in the production line.

[0043] S4, the nanofiltration concentrate is returned to the electrode foil forming tank for recycling, and the reverse osmosis permeate is reused in the production line.

[0044] In one embodiment, step S4 involves returning the nanofiltration concentrate to the electrode foil forming tank for recycling, specifically including the following sub-steps.

[0045] S41 uses an acid-resistant centrifugal pump to transport nanofiltration concentrate from the concentrate outlet of the nanofiltration unit to the formation tank. The transport pipeline is made of PVDF material, and the inner wall is mirror-polished to reduce scale adhesion. The inner diameter of the pipeline is 32 mm, and the roughness Ra≤0.8 μm ensures that the concentrate does not precipitate or corrode during the transport process.

[0046] S42 monitors the addition of nanofiltration concentrate and the mixing ratio of the original pretreatment solution in the formation tank, controlling the addition rate to 0.5-1.0 m³ / h. The recycling ratio is adjusted according to the real-time pH value and Al³⁺ concentration to maintain the pH of the mixed solution at 2.8-3.2, the phosphoric acid concentration at 80-120 g / L, and the Al³⁺ concentration at 15-25 g / L. This directly replaces part of the fresh acid solution without the need for additional acid replenishment or formula adjustment.

[0047] S43, during the recycling process, the nanofiltration concentrate and the original solution are evenly mixed by the stirring device in the formation tank to ensure the stability of the electrode foil formation process. The stirring speed is controlled at 200-300 rpm, and the cycle is replenished once a day to achieve an acid recycling rate of over 90%.

[0048] For example, in the production of electrode foil for aluminum electrolytic capacitors, nanofiltration concentrate enriches components such as Al³⁺ and phosphoric acid. After being pumped into the formation tank through the S41 delivery system, it is mixed with the original solution, and the pH value is adjusted from the initial 3.0 to 3.1. The Al³⁺ concentration is stabilized at 20 g / L. This reuse method reduces the amount of fresh acid solution used by 30% and maintains the uniformity of aluminum foil corrosion in the formation process. The beneficial effects are reduced production costs and avoidance of waste acid discharge.

[0049] In one embodiment, S42 can be expanded to monitor multiple parameters for different wastewater treatment scales. For example, in a factory with a daily wastewater production of 8 m³, the addition rate is 0.8 m³ / h, and the phosphoric acid concentration after mixing reaches 100 g / L, ensuring stable liquid level in the formation tank and avoiding electrode foil quality problems caused by overflow or concentration fluctuations.

[0050] For example, if furfural residue in wastewater has been removed through pretreatment, the organic load in the formation tank is reduced by 15% after the nanofiltration concentrate is reused, thereby extending the service life of the tank solution and improving overall production efficiency.

[0051] In one embodiment, step S4 involves recycling the reverse osmosis permeate into the production line, specifically including the following sub-steps.

[0052] S44 monitors the reverse osmosis permeate with an online conductivity meter. When the conductivity is below 50 μS / cm, it is transported to a recycled water storage tank through a PE pipeline. The storage tank has a volume of 5 m³ and is equipped with a level gauge to control the water level.

[0053] S45 extracts product water from the recycled water storage tank as process makeup water for foil rinsing or new acid preparation on the production line, achieving a water reuse rate of over 85%.

[0054] For example, in the same electrode foil manufacturing enterprise, the TOC content of the reverse osmosis permeate is 0.7 mg / L and the NH4⁺ content is 1.3 mg / L. After being transported to the storage tank, it is used in the rinsing section, with a daily reuse volume of 6 m³. This reduces the consumption of fresh water and has the beneficial effect of forming a closed-loop utilization of water resources and meeting electronic-grade cleaning standards.

[0055] S104. The microfiltration unit includes: S21, the microfiltration unit uses a polyvinylidene fluoride hollow fiber membrane module to operate in a cross-flow filtration mode, and the cross-flow velocity is a preset value; S22, the membrane module of the microfiltration unit is fixed to the outlet pipe of the pretreatment tank through a flange connection, and the inlet and outlet are respectively equipped with a pressure sensor and a flow meter, and an automatic backwash valve is installed on the concentrate side, which performs air-water combined backwashing once every preset operating time.

[0056] S21, the microfiltration unit uses a polyvinylidene fluoride hollow fiber membrane module to operate in a cross-flow filtration mode, and the cross-flow velocity is a preset value.

[0057] In one embodiment, cross-flow filtration is achieved by allowing wastewater to flow horizontally across the membrane surface. The preset cross-flow velocity is set to 1.2 to 1.5 m / s to generate sufficient shear force to remove deposits from the membrane surface. S211: Monitor the speed of the feed pump and the inner diameter of the pipe, calculate and adjust the flow velocity to the preset value to ensure that suspended particles do not accumulate in the acidic wastewater. S212: Adjust the valve opening according to the calculated flow velocity to create a stable laminar flow of wastewater within the membrane module, avoiding energy waste caused by turbulence. S213: Utilize the shear force generated by the flow velocity to discharge the trapped colloidal substances with the concentrate, obtaining a clarified pretreated solution as input for subsequent activated carbon adsorption.

[0058] S22, the membrane module of the microfiltration unit is fixed to the outlet pipe of the pretreatment tank via a flange connection. The inlet and outlet are respectively equipped with a pressure sensor and a flow meter. An automatic backwash valve is installed on the concentrate side, and air-water combined backwash is performed once every preset operating time.

[0059] In one embodiment, the flange connection uses acid-resistant bolts to secure the membrane assembly, ensuring a leak-free seal under high pressure. S221, a pressure sensor monitors changes in inlet water pressure in real time, and a flow meter records the product water volume; an alarm is triggered when the pressure exceeds a threshold. S222, an automatic backwash valve is controlled by a timer, starting every 60 minutes. The combined air-water backwash first introduces 0.2 MPa compressed air to purge the membrane surface for 30 seconds, followed by rinsing with 0.3 MPa deionized water for 60 seconds, for a total duration of 90 seconds, removing loose contaminants and restoring membrane flux.

[0060] For example, in the scenario of electrode foil forming wastewater treatment, when the cross-flow velocity is preset to 1.3 m / s, the microfiltration unit can reduce the turbidity from the initial 5 NTU to below 0.5 NTU when treating wastewater with pH 3.2 containing 18 g / L Al³⁺. The beneficial effect is to extend the membrane life to 90 days of continuous operation with a decay rate of less than 10%.

[0061] In one possible implementation, if the wastewater contains a high furfural content of 0.8 mg / L, adjusting the flow rate to 1.5 m / s can enhance shearing, reduce organic matter adhesion, and improve pretreatment efficiency by 15%.

[0062] It should be noted that the backwashing time is preset to 60 minutes, which can effectively remove colloidal Al(OH)3 particles, avoid clogging and resulting in a decrease in throughput, thus bringing the benefit of stable system operation.

[0063] For example, for the backwashing of S22, the air-water combined method first uses air to loosen the contaminants and then flushes them out with water. In a plant that treats 8 m³ of wastewater per day, this mechanism extends the membrane module maintenance cycle from weekly cleaning to monthly cleaning, reduces energy consumption by 18%, and has the benefit of reducing downtime and ensuring continuous production.

[0064] In one embodiment, by combining S21 and S22, after the clarified liquid is output from the cross-flow operation, backwashing is performed to maintain membrane cleanliness, forming a closed loop. This method is suitable for acidic wastewater with a phosphoric acid concentration of 95 g / L, achieving efficient pretreatment.

[0065] S105, the activated carbon adsorption unit includes: S21, the activated carbon adsorption unit is filled with coconut shell-based granular activated carbon which passes through the adsorption column from top to bottom, and the empty bed contact time is a preset time; S22, the activated carbon adsorption unit adopts a dual-column series design, the front column is filled with unregenerated activated carbon, and the rear column is filled with activated carbon that has undergone thermal regeneration treatment. When the furfural concentration in the effluent exceeds the preset concentration, the system switches to the standby adsorption column and regenerates the saturated column.

[0066] S21, the activated carbon adsorption unit is filled with coconut shell-based granular activated carbon which passes through the adsorption column from top to bottom, and the empty bed contact time is a preset time.

[0067] In one embodiment, the adsorption column of the activated carbon adsorption unit is filled with coconut shell-based granular activated carbon with a particle size of 1.0 to 2.0 mm, and the filling height is set to 1.5 to 2.0 m to ensure sufficient contact between the wastewater and the activated carbon during the top-down flow. The preset empty bed contact time is controlled at 15 to 20 minutes, which is achieved by adjusting the influent flow rate. For example, with a column inner diameter of 400 mm, the flow rate is set to the level corresponding to the volume to match the daily wastewater treatment capacity of 8 m³. This setting helps to selectively remove highly adsorbent organic pollutants such as furfural, reducing the fouling load on the subsequent membrane system.

[0068] S211, calculate the volume of the adsorption column and determine the empty bed contact time based on the wastewater flow rate.

[0069] Specifically, the volume of the adsorption column is calculated based on the filling height and inner diameter. For example, when the height is 1.8 m and the inner diameter is 400 mm, the volume is approximately 0.226 m³. Then, based on the wastewater flow rate, such as 0.33 m³ per hour, the empty bed contact time is approximately 18 minutes to ensure that the pollutants have sufficient time to be adsorbed.

[0070] S212 monitors the flow direction of wastewater and adjusts the flow rate to maintain the preset contact time.

[0071] For example, during operation, the flow rate of wastewater flowing from top to bottom is monitored in real time by an electromagnetic flow meter. If the flow rate fluctuation causes the contact time to deviate from the range of 15 to 20 minutes, the pump speed is automatically adjusted to restore it to the preset value, forming a continuous adsorption process.

[0072] S22, the activated carbon adsorption unit adopts a dual-column series design, with the front column filled with unregenerated activated carbon and the rear column filled with activated carbon that has undergone thermal regeneration. When the furfural concentration in the effluent exceeds the preset concentration, the system switches to the standby adsorption column and regenerates the saturated column.

[0073] In one possible implementation, a dual-column series design uses fresh or unregenerated coconut shell-based activated carbon in the front column to handle the initial adsorption load of high-concentration organic matter. The rear column is filled with activated carbon that has undergone thermal regeneration at 105℃, serving as a backup layer to capture residual pollutants. A preset concentration threshold is set at 0.5 mg / L. When the online detector detects that the furfural concentration in the effluent from the rear column exceeds this value, the system automatically switches to the standby adsorption column via a three-way valve controlled by a PLC, simultaneously initiating the regeneration sequence of the saturated column. This design ensures the continuity of the treatment process, avoiding interruptions in wastewater treatment due to the saturation of a single column.

[0074] S221, configured with two columns connected in series and distinguishing the filling materials of the front and rear columns.

[0075] For example, the front column is filled with unregenerated activated carbon, which has high surface activity and is suitable for rapid adsorption of pollutants such as furfural; the rear column is filled with thermally regenerated activated carbon, which has partially restored its microporous structure through drying at 105°C, thus improving the capture efficiency of low-concentration pollutants. When the two are connected in series, the wastewater first undergoes coarse adsorption in the front column and then fine adsorption in the rear column, forming a gradient purification effect.

[0076] S222, monitors the furfural concentration in the effluent in real time and determines whether it exceeds the preset threshold.

[0077] It should be noted that if the concentration of furfural exceeds 0.5 mg / L after continuous sampling of the column effluent using an online furfural detector, an alarm signal will be triggered. This monitoring is based on ultraviolet spectrophotometry, with a detection limit of 0.1 mg / L, to ensure accurate capture of the saturation point.

[0078] S223, execute the switch to the standby adsorption column and start the regeneration of the saturated column.

[0079] In one embodiment, the switching process is completed by closing the inlet and outlet valves of the current column and opening the valve of the standby column, taking no more than 1 minute. Subsequently, the saturated column is regenerated by first rinsing with deionized water at a flow rate of 2 BV / h for 30 minutes to remove inorganic salts, then passing 10% NaOH solution through it at the same flow rate to desorb organic acids for 60 minutes, followed by restoring the surface acidic sites with 5% H2SO4 solution for 45 minutes, and finally washing with water until neutral. This regeneration sequence restores more than 80% of the adsorption capacity of the activated carbon, which is beneficial for recycling and reducing operating costs.

[0080] Preferably, in the aluminum electrode foil production scenario, for the daily generation of 8 m³ of acidic wastewater with pH 3.2 and furfural 0.8 mg / L, the dual-column design can maintain continuous operation. The front column becomes saturated after adsorbing about 500 BV of wastewater, and the rear column extends the overall cycle to 1000 BV. Regeneration after switching ensures that the system has no downtime.

[0081] In one embodiment, for wastewater with large fluctuations in furfural concentration, the preset concentration is adjusted to 0.4 mg / L to enhance sensitivity; during regeneration, the NaOH desorption is extended to 75 min to improve the organic matter removal rate to 95%, thereby adapting to high pollution load scenarios.

[0082] For example, when treating wastewater containing 1.2 mg / L furfural, the dual-column series connection reduces the effluent concentration to below 0.3 mg / L. Compared with the single-column design, the operating cycle is extended by 2 times, which helps reduce membrane fouling and improve the overall water reuse rate.

[0083] Understandably, the configuration and operation logic of this activated carbon adsorption unit are tightly integrated into the overall method of treating acidic wastewater using a dual-membrane process. This pretreatment effectively removes organic pollutants, supports the stable operation of subsequent nanofiltration and reverse osmosis, and enables efficient resource utilization.

[0084] S106. The regeneration of the saturated column includes: S41, first rinsing with deionized water for a preset time, then introducing an alkaline solution at a preset flow rate to desorb organic acids, then using an acidic solution at a preset flow rate to restore the acidic sites on the activated carbon surface, and finally rinsing with deionized water until neutral; S42, during the regeneration process, the front column bears the adsorption load of high-concentration organic matter, the rear column acts as a protective layer to ensure that the furfural concentration in the effluent is lower than the preset concentration, and the regeneration waste liquid is discharged into a special collection tank.

[0085] In one embodiment, the regeneration of the saturated column includes the following steps.

[0086] S41, first rinse with deionized water for a preset time, then pass an alkaline solution through at a preset flow rate to desorb organic acids, then use an acid solution at a preset flow rate to restore the acidic sites on the activated carbon surface, and finally rinse with deionized water until neutral.

[0087] Specifically, in this embodiment, the preset time is set to 30 minutes to ensure the initial removal of residual inorganic salts and loose deposits within the column, avoiding interference with subsequent desorption steps. Next, a 10% NaOH alkaline solution is introduced at a flow rate controlled at 2 BV / h. This flow rate is calculated based on the activated carbon bed volume to ensure uniform solution penetration and the formation of soluble salts with adsorbed organic acids such as oxalic acid, thereby effectively desorbing them. Subsequently, a 5% H₂SO₄ acid solution is used at the same flow rate of 2 BV / h. The acid solution protonates the oxygen-containing functional groups, such as hydroxyl and carboxyl groups, on the surface of the activated carbon, restoring its acidic sites. These sites are crucial for the adsorption of weakly polar organic compounds such as furfural by activated carbon; after restoration, the adsorption capacity can be increased to over 95% of the initial level. Finally, the column is rinsed with deionized water until the effluent pH reaches neutral, i.e., 6.5-7.0, ensuring no residual chemicals remain, and ready for reuse.

[0088] S411: After determining the saturation level of the saturated column, regeneration is initiated. The saturation level is determined by monitoring the furfural concentration in the effluent to ensure it does not exceed 0.5 mg / L. This determination is based on data from the online monitoring instrument, forming a logical chain from monitoring to regeneration.

[0089] S412, during the rinsing step, monitor the rinsing water flow rate and adjust it to 2 BV / h to match the subsequent desorption flow rate and ensure process continuity.

[0090] S413. When desorbing organic acids, collect the eluent and analyze its organic content, such as the concentration of oxalic acid, to verify the desorption efficiency, which directly affects the effect of subsequent acid recovery steps.

[0091] After restoring the acidic sites, S414 was tested on a small sample to confirm that the adsorption rate of furfural by activated carbon had returned to normal, thus forming a closed loop for verifying the regeneration effect.

[0092] In one possible implementation, for the extension of S41, different wastewater load scenarios are considered. For example, in high-concentration furfural wastewater, the preset time can be adjusted to 45 min to enhance the initial rinsing, the alkaline solution concentration is increased to 12% to enhance desorption, while the acid solution is kept at 5% but the flow rate is reduced to 1.5 BV / h to prolong the contact time and ensure that the sites are fully restored. This adjustment can shorten the regeneration cycle by 10% and is suitable for electrode foil production lines with a large daily wastewater volume.

[0093] For example, when treating acidic wastewater with pH 3.2, the wastewater is first rinsed with deionized water for 35 min to remove salts, then 11% NaOH solution is introduced at 2 BV / h for 60 min for desorption. After desorption, the organic acid recovery rate reaches 85%. Subsequently, 5% H2SO4 at 2 BV / h is used to treat the activated carbon for 45 min to restore the activated carbon sites. Finally, the activated carbon is washed with water to pH 7.0. The entire process extends the activated carbon life by 2 times and helps reduce operating costs.

[0094] S42, during the regeneration process, the front column bears the adsorption load of high-concentration organic matter, and the rear column acts as a protective layer to ensure that the furfural concentration in the effluent is lower than the preset concentration, and the regenerated waste liquid is discharged into a special collection tank.

[0095] Specifically, the front column preferentially adsorbs high-concentration organic matter such as furfural and corrosion inhibitors from the influent, reaching up to 80% of the initial concentration. The rear column then treats the remaining low-concentration pollutants, ensuring that the overall effluent furfural concentration is below 0.5 mg / L. This dual-column design creates a load gradient distribution, extending the system's operating time. Regeneration wastewater, including rinsing water, desorption liquid, and acid treatment liquid, is uniformly discharged into a dedicated collection tank made of acid-resistant PE material with a capacity of 1 m³. Equipped with a level sensor to prevent overflow, this forms a complete chain from regeneration to wastewater management.

[0096] S421, when regeneration starts, switches the front column to regeneration mode, while the rear column continues to run as a temporary backup to maintain uninterrupted system operation.

[0097] S422, the collected recycled waste liquid is neutralized and then further treated, such as by adding calcium oxide to precipitate phosphate, and then connected to the overall wastewater treatment process.

[0098] In one embodiment, for S42, the preset concentration can be adjusted according to the wastewater type. For example, in a scenario with high furfural content, it can be set to 0.4 mg / L. The front column load is designed to adsorb 90% of pollutants, and the rear column ensures the remainder, ensuring stable effluent and benefiting the membrane protection of the downstream nanofiltration unit.

[0099] For example, in the treatment of wastewater from electrode foil formation, the front column adsorbs the initial furfural concentration from 0.8 mg / L to 0.1 mg / L, and the rear column further reduces it to below 0.05 mg / L. After the regenerated waste liquid is discharged into the collection tank, the pH is adjusted to 7.0 to facilitate subsequent biochemical treatment. This design increases the continuous operating time of the system by 30%.

[0100] It should be noted that by combining S41 and S42, the regeneration process not only restores the performance of activated carbon, but also ensures the reliability of the dual-column system, achieving efficient circulation in acidic wastewater treatment.

[0101] In one possible implementation, the desorption step principle of S41 is illustrated by example: when the alkaline solution is introduced, OH- ions react with the adsorbed organic acids to form salts. These salts have high solubility and are easy to wash out from the pores of the activated carbon, which helps to prevent membrane fouling from spreading downstream.

[0102] For example, when the furfural concentration in the wastewater is 1.0 mg / L, the surface cleanliness of the activated carbon improves after desorption, and the adsorption rate recovers to 98%.

[0103] For example, regarding the protective layer function of S42, the switching occurs after the front column is saturated, and the collection of regenerated waste liquid avoids secondary pollution.

[0104] Specifically, when treating 8 m3 / day of wastewater, the front column handles 6 m3 of the high-concentration portion, while the rear column ensures the remaining amount, ensuring that the effluent furfural concentration is 0.3 mg / L, and the overall resource recovery rate is over 85%.

[0105] In one embodiment, the acid recovery step of S41 is extended: the acid solution recovery site enhances the adsorption of organic matter by van der Waals forces and hydrogen bonds by increasing surface acidity.

[0106] For example, when using 4% H2SO4, the recovery time is shortened to 40 minutes, which is suitable for rapid regeneration scenarios and is beneficial to production continuity.

[0107] It should be noted that these steps are closely related to the method of using a dual-membrane process to efficiently treat acidic wastewater that has been converted into aluminum foil, ensuring the stable operation of the activated carbon unit in the pretreatment stage.

[0108] S107. The nanofiltration unit includes: S21. The nanofiltration unit uses a polyamide composite nanofiltration membrane arranged in a two-stage manner and installed in a stainless steel pressure vessel, with a booster pump installed between the stages; S22. The nanofiltration concentrate is transported to the electrode foil forming tank through a pipeline by an acid-resistant centrifugal pump, and the recycled pipeline is made of acid-resistant material with a polished inner wall.

[0109] S21, the nanofiltration unit uses a polyamide composite nanofiltration membrane and is installed in a stainless steel pressure vessel in a two-stage arrangement, with a booster pump installed between the stages.

[0110] In one embodiment, the polyamide composite nanofiltration membrane has a molecular weight cutoff of 200 Da to ensure effective retention of multivalent ions such as Al³⁺ while allowing small organic acid molecules to permeate. The membrane elements are arranged in a single-stage, two-section configuration within the stainless steel pressure vessel, with four membrane elements installed in the first section and two membrane elements installed in the second section. This arrangement helps to evenly distribute the wastewater flow and reduce concentration polarization.

[0111] S211, based on the initial pressure and flow rate of the pretreatment liquid, adjust the inlet pressure of the first membrane element to 1.8 MPa, and when the pressure at the end of the monitoring section drops below 1.5 MPa, start the inter-section booster pump to raise the pressure back to 2.0 MPa.

[0112] S212 utilizes a booster pump to compensate for the pressure loss in the second stage, maintaining a constant operating pressure of 2.0 MPa throughout the nanofiltration process, resulting in nanofiltration permeate turbidity below 0.25 NTU and Al³⁺ concentration of 15–25 g / L in the nanofiltration concentrate.

[0113] For example, in treating acidic wastewater with pH 3.2, the Al³⁺ rejection rate reached 90% after the first stage membrane element treatment, but the pressure drop caused the flux to decrease. After the booster pump intervened, the flux of the second stage recovered to 95% of the initial level, thereby improving the overall separation efficiency by 15% and avoiding rapid clogging under the single-stage configuration.

[0114] In one possible implementation, for scenarios with fluctuating wastewater temperature, the temperature is controlled at 25–30°C, and combined with the automatic adjustment of the booster pump, the shear force on the membrane surface is ensured to be uniform, reducing the risk of organic matter deposition.

[0115] Specifically, the stainless steel pressure vessel is made of 316L material, which is resistant to acid corrosion. The interior is polished to Ra≤0.4 μm to reduce contaminant adhesion. In conjunction with the membrane arrangement, it achieves a flux decline of less than 8% after 30 days of continuous operation.

[0116] S22, the nanofiltration concentrate is transported to the electrode foil forming tank via an acid-resistant centrifugal pump and pipeline. The recycled pipeline is made of acid-resistant material and its inner wall is polished.

[0117] Preferably, the acid-resistant centrifugal pump uses a PVDF pump head, and the flow rate is controlled at 5 m³ / h when pumping nanofiltration concentrate to ensure that the phosphoric acid concentration in the concentrate is stably delivered to the formation tank at 80-120 g / L.

[0118] S221, monitor the pH value of the concentrate (2.8–3.2), adjust the pump speed to match the replenishment needs of the formation tank, and avoid overflow due to excessively fast delivery.

[0119] S222 uses PVDF pipes with inner walls polished to Ra≤0.8 μm for transport, reducing scale formation and allowing the concentrate to be directly reused without additional formulation adjustments.

[0120] For example, in a production setting, after the concentrate is output from the nanofiltration unit, it is transported through pumps and pipelines, maintaining the Al³⁺ concentration at 20 g / L, achieving a reuse rate of 90%. Pipe polishing reduces maintenance frequency by 20%, ensuring the efficient resource recovery and reuse of acidic wastewater treatment methods.

[0121] S108. The reverse osmosis unit includes: S21. The reverse osmosis unit uses an aromatic polyamide spiral wound reverse osmosis membrane and operates in a one-stage configuration. An energy recovery device is installed on the concentrate side. S22. The reverse osmosis permeate is monitored by an online conductivity meter. When the conductivity is lower than a preset value, it enters the recycled water storage tank. The reverse osmosis concentrate is partially recycled after passing through the energy recovery device.

[0122] In one embodiment, the reverse osmosis unit in step S21 uses an aromatic polyamide spiral wound reverse osmosis membrane and operates in a one-stage configuration, with an energy recovery device installed on the concentrate side, specifically including the following sub-steps.

[0123] S211 uses an aromatic polyamide spiral wound reverse osmosis membrane. This membrane material has a high desalination rate and acid resistance. The membrane elements are installed in a fiberglass pressure vessel, forming a single-stage configuration. That is, all membrane elements are arranged in parallel in a single pressure vessel, eliminating the need for multi-stage grading, thus simplifying the structure and adapting to the treatment of high-salt loads of acidic wastewater.

[0124] S212, an energy recovery device is installed on the concentrate side. This device is a pressure exchange type energy recovery device. It realizes energy recovery by transferring the remaining high pressure energy of the reverse osmosis concentrate to the feed water. The recovery rate is not less than 40%, thereby reducing the energy consumption of the high pressure pump. For example, in the treatment of acidic wastewater for aluminum foil formation, the concentrate pressure is reduced from 3.8 MPa to recover part of the energy for pre-pressurization nanofiltration permeate, and the overall system energy consumption can be reduced by 18%.

[0125] S213 operates at a controlled pressure of 3.5–4.0 MPa and a temperature of 25–30°C to ensure that the membrane flux remains stable at over 25 L / (m²·h). The flux decay rate is less than 8% within 30 days of continuous operation. This is thanks to the fact that the pre-filter has removed most of the organic pollutants, thus avoiding fouling on the membrane surface.

[0126] In one possible implementation, for the energy recovery device of S21, considering different wastewater treatment scales, such as a scenario where 8 m³ of acidic wastewater is treated per day, the energy recovery unit is selected with a matching diameter, the concentrate flow rate is controlled at 30% of the total system flow rate, and the recovered pressure can be directly applied to the inlet of the water pump to improve water recovery efficiency and reduce power consumption, which is beneficial for long-term stable operation.

[0127] Specifically, in step S22, the reverse osmosis permeate is monitored by an online conductivity meter. When the conductivity is lower than a preset value, it enters the recycled water storage tank. The reverse osmosis concentrate is partially recycled after passing through an energy recovery device. This includes the following sub-steps.

[0128] The S221 online conductivity meter is installed at the product water outlet. The preset value is 50 μS / cm. It monitors the conductivity of the product water in real time. If it is lower than this value, the electric valve will open to introduce the product water into the recycled water storage tank for rinsing in the production line or acid preparation, so as to realize the closed-loop utilization of water resources.

[0129] S222: After the reverse osmosis concentrate is treated by the energy recovery device, part of it is returned to the nanofiltration permeate inlet. The return flow rate is adjusted according to the system recovery rate, for example, set to 20% of the total concentrate volume, in order to optimize the overall desalination efficiency and prevent the accumulation of pollutants.

[0130] For example, in the treatment of acidic wastewater containing phosphoric acid and Al³⁺, S22 monitoring ensures that the TOC of the produced water is below 1.0 mg / L and NH₄⁺ is below 2 mg / L. When the values ​​are below the preset values, the wastewater is directly reused. If the values ​​exceed the preset values, the wastewater is returned for retreatment. This helps maintain system stability and increases the acid reuse rate to over 90%.

[0131] In one embodiment, in the application scenarios of S21 and S22, the synergy of energy recovery and monitoring is achieved. For example, when operating at a temperature of 28°C and a pressure of 3.8 MPa, the energy recovery device first processes the concentrate, recovers energy, and then returns part of the concentrate. This forms a chain with the production water monitoring: energy recovery reduces energy consumption, and monitoring ensures water quality. Together, they support the resource-based treatment of acidic wastewater from aluminum foil formation using the dual-membrane method, achieving a water reuse rate of over 85%.

[0132] S109. The step of passing the pretreated liquid into the nanofiltration unit for separation includes: S21, operating under preset pressure and temperature conditions, with the Al³⁺ rejection rate and oxalic acid permeability reaching a preset rate; S22, the phosphoric acid concentration, Al³⁺ concentration, and pH value in the nanofiltration concentrate are within preset ranges, meeting the requirements of the electrode foil forming tank for the pretreated liquid.

[0133] S21 operates under preset pressure and temperature conditions, achieving preset Al³⁺ retention rate and preset oxalic acid permeability.

[0134] In one embodiment, step S21 involves passing the pretreatment liquid into a nanofiltration unit for separation. Specifically, step S211 involves setting the operating pressure to 2.0 MPa as the preset pressure and maintaining the temperature at 28°C as the preset temperature through a plate heat exchanger and a circulating cooling water system. Under these conditions, the nanofiltration membrane is started to operate. The polyamide composite nanofiltration membrane has a molecular weight cutoff of 200 Da and can selectively separate ions based on the Donnan effect and sieving mechanism.

[0135] In step S212, the Al³⁺ retention rate is monitored according to the operating conditions to ensure that it reaches a preset rate of over 95%, and the oxalic acid permeation rate is monitored to ensure that it reaches a preset rate of over 85%. This separation relies on the large hydration radius of Al³⁺ and its trivalent charge, which leads to its effective retention by the membrane. Oxalic acid, as a small molecule weak acid, exists in molecular form in an acidic environment and is easy to permeate through the membrane pores.

[0136] S22, the phosphoric acid concentration, Al³⁺ concentration, and pH value in the nanofiltration concentrate are within preset ranges to meet the requirements of the electrode foil forming tank for the pretreatment solution.

[0137] For example, the nanofiltration concentrate obtained in step S22 has a phosphoric acid concentration controlled within a preset range of 80 to 120 g / L, an Al³⁺ concentration within a preset range of 15 to 25 g / L, and a pH value within a preset range of 2.8 to 3.2. These parameters are naturally formed through the aforementioned separation process and do not require additional adjustment. They can be directly pumped into the formation tank for recycling.

[0138] In one possible implementation, if the operating pressure in step S21 is adjusted to 1.8 MPa and the temperature is maintained at 28°C, the Al³⁺ rejection rate can reach 94% and the oxalic acid permeability can reach 84%. Subsequently, in step S22, the concentrated phosphoric acid concentration is about 78 g / L, the Al³⁺ concentration is 14 g / L, and the pH value is 2.7. Although this is slightly lower than the standard range, it can be adjusted to meet the requirements of the formation tank by adding a small amount of phosphoric acid. This adjustment demonstrates the adaptability brought about by parameter flexibility, which is beneficial for treating scenarios with large fluctuations in wastewater composition.

[0139] Specifically, in another embodiment, when the operating pressure is set to 2.2 MPa and the temperature is 30°C, the Al³⁺ rejection rate increases to 97% and the oxalic acid permeation rate is 86%, resulting in a phosphoric acid concentration of 125 g / L, an Al³⁺ concentration of 26 g / L, and a pH value of 3.3 in the concentrate of step S22, which exceeds the preset upper limit. However, it can be diluted and reused to ensure that it still meets the composition requirements of the formation tank for the pretreatment solution. This improves the separation efficiency and reduces the risk of membrane fouling.

[0140] For example, considering a scenario where the initial Al³⁺ concentration in the wastewater is 18 g / L, after step S21 is run, the concentrated Al³⁺ concentration is enriched to 22 g / L, the phosphoric acid concentration to 110 g / L, and the pH to 3.0, which is exactly in the middle of the preset range. It can be directly reused to replace 30% of the fresh acid solution, demonstrating the effect of resource utilization.

[0141] In one embodiment, if the wastewater contains a high amount of furfural, it enters S21 after pretreatment. The separation process ensures efficient permeation of oxalic acid, preventing its accumulation in the concentrate and thus increasing its viscosity. This keeps the pH of the S22 concentrate stable at 2.8–3.2, which is beneficial for maintaining the consistency of the acidic environment in the formation tank.

[0142] Specifically, the control of these parameters enables the stable separation and reuse of acidic wastewater in the entire dual-membrane treatment process, significantly improving resource utilization.

[0143] S1010, The step of passing the nanofiltration permeate into the reverse osmosis unit for deep desalination includes: S21, operating under preset pressure and temperature conditions, with the TOC content and NH4⁺ concentration of the reverse osmosis permeate within preset ranges; S22, the conductivity of the reverse osmosis permeate is stable within a preset range, meeting the standards for cleaning water, and is used for rinsing in the production line or for preparing acid solutions.

[0144] Step S21: Operate the reverse osmosis unit under preset operating pressure and temperature conditions to ensure that the TOC content and NH4⁺ concentration of the reverse osmosis permeate are within preset ranges.

[0145] Step S211: Set the operating pressure and temperature parameters of the reverse osmosis unit to ensure the membrane element operates under suitable conditions for deep desalination. The reverse osmosis unit uses aromatic polyamide spiral wound membranes with a desalination rate of not less than 98%, and the membrane element is installed in a fiberglass pressure vessel. The operating pressure is set between 3.5 and 4.0 MPa, and the temperature is controlled within the range of 25 to 30°C. Constant conditions are achieved through a high-pressure pump and a plate heat exchanger in conjunction with a circulating cooling water system. Precise control of pressure and temperature aims to optimize membrane flux and retention efficiency, avoiding membrane structure damage due to excessive pressure or increased solute permeation due to temperature fluctuations, thereby ensuring stable product water quality.

[0146] Step S212: Monitor the TOC content and NH4⁺ concentration of the reverse osmosis permeate to ensure they reach preset ranges. The TOC content must be below 1.0 mg / L, and the NH4⁺ concentration must be below 2.0 mg / L. This data is obtained in real-time through online monitoring equipment. During operation, the reverse osmosis membrane deeply retains residual monovalent ions and small-molecule organic matter in the nanofiltration permeate. Especially after the nanofiltration unit has removed most of the polyvalent ions and large-molecule organic matter, the fouling load of the reverse osmosis unit is significantly reduced, and the risk of organic deposition on the membrane surface is decreased, thus ensuring long-term stability of the permeate quality. Monitoring data is recorded by the PLC system. If fluctuations in the indicators exceed the preset range, the operating pressure is automatically adjusted or a low-pressure flushing procedure is triggered to restore membrane performance.

[0147] Step S213: Optimize energy recovery and concentrate management of the reverse osmosis unit to improve system operating efficiency. A pressure exchange type energy recovery device is installed on the concentrate side of the reverse osmosis unit, with a recovery rate of no less than 40%, converting some of the pressure energy in the concentrate into pre-pressurization power for the feed water, reducing overall energy consumption. Simultaneously, the concentrate flow rate is controlled by a regulating valve to prevent excessive concentration ratios from causing membrane scaling, ensuring that the system can maintain the TOC and NH4⁺ concentrations of the permeate water within preset ranges even at high recovery rates.

[0148] In one embodiment, the operating parameters of the reverse osmosis unit in the treatment of acidic wastewater were optimized. The operating pressure was set to 3.8 MPa and the temperature was maintained at 28°C. This combination, after multiple experimental verifications, enabled the membrane flux to remain stable above 25 L / m²·h, with a flux decay rate of less than 8% over 30 days of continuous operation. The TOC content monitoring results were 0.7 mg / L and the NH₄⁺ concentration was 1.3 mg / L, both far below the preset standards, indicating that organic pollution and ion permeation were effectively suppressed under these conditions.

[0149] In another embodiment, for scenarios with large wastewater treatment volumes, the operating pressure is adjusted to 3.9 MPa and the temperature is controlled at 27°C to accommodate higher influent loads. At this point, the membrane flux is slightly increased to 27 L / m²·h, the TOC content in the permeate is 0.8 mg / L, and the NH₄⁺ concentration is 1.5 mg / L, still meeting the preset requirements. Furthermore, the energy recovery rate of the energy recovery device is increased to 43%, further reducing operating costs and demonstrating how parameter adjustments provide dual assurance for system efficiency and water quality control.

[0150] Step S22: The conductivity of the reverse osmosis permeate is stabilized within a preset range, meeting the standards for cleaning water, and is used for rinsing in the production line or for preparing acid solutions.

[0151] Step S221: Detect the conductivity of the reverse osmosis permeate to ensure it remains stable within a preset range. The permeate conductivity must be below 50 μS / cm. This is monitored in real-time using an online conductivity meter, and the data is input to the PLC system. If the conductivity meets the standard, an electric valve opens to direct the permeate into the recycled water storage tank; if it exceeds the standard, it automatically flows back to the nanofiltration inlet for reprocessing. This process ensures that the permeate quality meets the standards for electronic-grade cleaning water.

[0152] Step S222 involves using the compliant reverse osmosis permeate for rinsing or acid preparation in the production line. The permeate is transported from the recycled water storage tank to the rinsing section of the production line or the new acid preparation tank via pipeline, achieving closed-loop utilization of water resources and reducing the consumption of fresh water.

[0153] For example, in the electrode foil production scenario, the conductivity of reverse osmosis permeate is stable at 38 μS / cm, which is far below the preset standard. It can be directly used in the final rinsing process of the foil, which not only ensures the cleaning effect but also significantly reduces water consumption, demonstrating the practical benefits of efficient reuse.

[0154] Obviously, those skilled in the art can make various modifications and variations to the embodiments of this application without departing from the spirit and scope of the embodiments of this application. Therefore, if these modifications and variations to the embodiments of this application fall within the scope of the claims of this application and their equivalents, this application also intends to include these modifications and variations.

Claims

1. A method for treating acidic wastewater using a dual-membrane process, characterized in that, include: The acidic wastewater generated during the electrode foil forming process is pretreated by passing it through a microfiltration unit and an activated carbon adsorption unit to obtain a pretreated solution. The pretreated liquid is passed into a nanofiltration unit for separation to obtain nanofiltration concentrate and nanofiltration permeate. The nanofiltration permeate is passed into a reverse osmosis unit for deep desalination to obtain reverse osmosis permeate; the nanofiltration concentrate is returned to the electrode foil forming tank for recycling, and the reverse osmosis permeate is reused in the production line.

2. The method as described in claim 1, characterized in that, The microfiltration unit includes: the microfiltration unit uses a polyvinylidene fluoride hollow fiber membrane module to operate in a cross-flow filtration mode, and the cross-flow velocity is a preset value; the membrane module of the microfiltration unit is fixed to the outlet pipe of the pretreatment tank through a flange connection, and the inlet and outlet are respectively equipped with a pressure sensor and a flow meter, and an automatic backwash valve is set on the concentrate side, which performs air-water combined backwashing once every preset operating time.

3. The method as described in claim 1, characterized in that, The activated carbon adsorption unit includes: the activated carbon adsorption unit is filled with coconut shell-based granular activated carbon which passes through the adsorption column from top to bottom, and the empty bed contact time is a preset time; the activated carbon adsorption unit adopts a dual-column series design, with the front column filled with unregenerated activated carbon and the rear column filled with activated carbon that has undergone thermal regeneration treatment. When the furfural concentration in the effluent exceeds the preset concentration, the unit switches to the standby adsorption column and regenerates the saturated column.

4. The method as described in claim 3, characterized in that, The regeneration of the saturated column includes: first rinsing with deionized water for a preset time, then introducing an alkaline solution at a preset flow rate to desorb organic acids, followed by restoring the acidic sites on the activated carbon surface with an acidic solution at a preset flow rate, and finally rinsing with deionized water until neutral. During the regeneration process, the front column bears the adsorption load of high-concentration organic matter, and the rear column acts as a protective layer to ensure that the furfural concentration in the effluent is lower than the preset concentration. The regeneration waste liquid is discharged into a special collection tank.

5. The method as described in claim 1, characterized in that, The nanofiltration unit includes: the nanofiltration unit uses polyamide composite nanofiltration membranes arranged in a two-stage configuration and installed in a stainless steel pressure vessel, with booster pumps installed between the stages; the nanofiltration concentrate is transported to the electrode foil forming tank via an acid-resistant centrifugal pump and pipeline, and the reuse pipeline is made of acid-resistant material with its inner wall polished.

6. The method as described in claim 1, characterized in that, The reverse osmosis unit includes: the reverse osmosis unit adopts an aromatic polyamide spiral wound reverse osmosis membrane and operates in a one-stage configuration; an energy recovery device is installed on the concentrate side; the reverse osmosis permeate is monitored by an online conductivity meter, and when the conductivity is lower than a preset value, it enters the recycled water storage tank; the reverse osmosis concentrate is partially recycled after passing through the energy recovery device.

7. The method as described in claim 1, characterized in that, The step of passing the pretreated solution into the nanofiltration unit for separation includes: operating under preset pressure and temperature conditions, achieving a preset Al³⁺ rejection rate and a preset oxalic acid permeation rate; and ensuring that the phosphoric acid concentration, Al³⁺ concentration, and pH value in the nanofiltration concentrate are within preset ranges to meet the requirements of the electrode foil forming tank for the pretreated solution.

8. The method as described in claim 1, characterized in that, The process of passing the nanofiltration permeate into the reverse osmosis unit for deep desalination includes: operating under preset pressure and temperature conditions, with the TOC content and NH4⁺ concentration of the reverse osmosis permeate within preset ranges; the conductivity of the reverse osmosis permeate is stable within a preset range, meeting the standards for cleaning water, and is used for rinsing in the production line or for preparing acid solutions.

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