Printing and dyeing wastewater desizing water alkali recovery method

Abstract

The invention relates to the technical field of industrial wastewater treatment and resource recovery, discloses a printing and dyeing wastewater desizing water alkali recovery method, and solves the problem of low recovery treatment efficiency caused by serious membrane pollution when printing and dyeing desizing wastewater is treated by an existing membrane separation technology. The method comprises the following steps: carrying out homogenization and dissolved air flotation pretreatment on high-temperature desizing water to remove most of grease and suspended solids; then, clear liquid is filtered through an ultrafiltration membrane, a negative pressure environment is constructed on the membrane shell side to extract penetrating fluid in real time, meanwhile, fine bubbles are injected into feeding liquid to form gas-liquid two-phase flow, and the net pushing force of the membrane surface is controlled to be maintained in a 0.02-0.04 MPa micro-positive pressure interval so as to reduce membrane pollution; and carrying out nanofiltration purification on the primarily filtered water to finally obtain high-purity recovered alkali liquor. According to the invention, the problems of serious membrane pollution and fast flux attenuation in the traditional membrane treatment process are effectively solved, and efficient recovery of alkali and long-term stable operation of the system are realized.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment and resource recovery technology, and in particular to a method for recovering alkali from desizing wastewater in dyeing and printing. Background Technology

[0002] Wastewater generated during the dyeing and printing process, especially desizing wastewater, has long posed a significant challenge to environmental management and resource recycling due to its unique physicochemical properties. Desizing wastewater typically exhibits high alkalinity, high temperature, high viscosity, and high solids content. Its core pollutants include not only large amounts of polyvinyl alcohol (PVA) sizing agents but also a wide variety of oils, waxes, and various auxiliaries. These complex components make the treatment of desizing wastewater far more difficult than that of general industrial wastewater. Traditional water treatment methods often struggle to achieve efficient and economical deep purification and recovery of useful substances, particularly in the recycling of alkaline substances, where significant bottlenecks exist.

[0003] Among various treatment technologies, membrane separation technology has been gradually introduced into the treatment of dyeing and printing wastewater due to its advantages of high efficiency, energy saving and environmental protection, especially showing great potential in the field of alkali recovery.

[0004] However, due to the various pollutants in the desizing wastewater, severe membrane fouling (concentration polarization and gel layer formation) is easily caused in traditional membrane filtration processes, leading to a sharp decline in membrane permeate flux, frequent cleaning, and unstable system operation. This results in low alkali recovery efficiency and high costs. Furthermore, calcium and magnesium ions in the wastewater easily combine with carbonate ions to form scale, exacerbating membrane fouling. Existing membrane separation technologies struggle to maintain high recovery rates while ensuring long-term stable operation.

[0005] Therefore, it is necessary to provide a method for recovering alkali from desizing wastewater in dyeing and printing to solve the above-mentioned technical problems. Summary of the Invention

[0006] This invention overcomes the shortcomings of the prior art and provides a method for recovering alkali from desizing wastewater in dyeing and printing.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for recovering alkali from desizing wastewater in dyeing and printing, comprising the following steps: S1. After homogenization of the high-temperature desizing water, most of the oil, wax and suspended solids in the desizing water are removed by dissolved air flotation to obtain a clear liquid. S2. The treated clear liquid is filtered through an ultrafiltration membrane. At the same time, a negative pressure environment is created on the membrane shell side of the ultrafiltration membrane to extract the permeate that has passed through the ultrafiltration membrane in real time, thus obtaining the initial filtered water. S3. The primary filtered water is purified by nanofiltration membrane. Under pressure, the nanofiltration membrane selectively retains polyvalent ions and trace organic matter in the primary filtered water, while allowing water and caustic soda to pass through. S4. The nanofiltration permeate obtained in S3 is used as a high-purity recycled alkali solution and directly reused in the printing and dyeing production process.

[0008] In a preferred embodiment of the present invention, in step S2, during the ultrafiltration process, an inert gas is injected into the feed liquid to form a gas-liquid two-phase flow, wherein the ratio of the injected amount of the inert gas to the volumetric flow rate of the feed liquid is 0.05-0.5:1.

[0009] In a preferred embodiment of the present invention, the inert gas is nitrogen, which is injected in the form of microbubbles with a diameter of 20μm-100μm.

[0010] In a preferred embodiment of the present invention, in step S2, the net driving force on the surface of the ultrafiltration membrane is maintained in a slightly positive pressure range of 0.02 MPa to 0.04 MPa by real-time adjustment of the pressure on the feed side and the pressure on the membrane shell side.

[0011] A device for recovering alkali from desizing wastewater in dyeing and printing includes: a homogenization and conditioning mechanism, a dissolved air flotation mechanism, an ultrafiltration membrane separation mechanism, and a nanofiltration mechanism connected in sequence; The ultrafiltration membrane separation mechanism includes an ultrafiltration membrane module, an ultrafiltration feed pump, an ultrafiltration circulation pump, a gas injection module, and a permeate booster pump. The ultrafiltration feed pump is used to feed the clarified liquid into the ultrafiltration membrane separation mechanism. The ultrafiltration circulation pump is used to drive the clarified liquid to circulate at high speed within the ultrafiltration membrane module. The gas injection module is used to inject inert gas into the circulating clarified liquid to form a gas-liquid two-phase flow. The permeate booster pump is connected to the membrane housing side of the ultrafiltration membrane module to create a negative pressure environment on the membrane housing side and extract the permeate while simultaneously pressurizing the permeate. The inlet of the nanofiltration unit is connected to the outlet of the permeate booster pump to receive the pressurized pre-filtered water. The system is electrically connected to the homogenization adjustment mechanism, dissolved air flotation mechanism, ultrafiltration membrane separation mechanism and nanofiltration mechanism, and is used to monitor and regulate the operating parameters of each mechanism.

[0012] In a preferred embodiment of the present invention, the gas injection module includes a gas source, a flow controller, and a mixer, wherein the mixer is a high-pressure jet pump or a static mixer.

[0013] In a preferred embodiment of the present invention, the control system is configured to collect the inlet pressure, outlet pressure and membrane housing side pressure of the ultrafiltration membrane module in real time, and dynamically adjust the operating status of the ultrafiltration feed pump and the permeate booster pump so that the net driving force on the surface of the ultrafiltration membrane is maintained within the range of 0.02MPa-0.04MPa.

[0014] In a preferred embodiment of the present invention, the ultrafiltration membrane module is a tubular membrane module, and the membrane material is polyvinylidene fluoride or polyethersulfone.

[0015] In a preferred embodiment of the present invention, the mixer outlet is located at the inlet of the ultrafiltration membrane module, near the edge of the membrane, and is arranged in a ring shape, so that the generated bubble clusters are close to the inner wall of the membrane.

[0016] In a preferred embodiment of the present invention, the dissolved air flotation mechanism includes a high-pressure dissolved air tank, a release device and an air flotation tank, and a sludge scraping mechanism is provided above the air flotation tank.

[0017] This invention addresses the shortcomings of the prior art and has the following beneficial effects: (1) This invention provides a method for recovering alkali from desizing wastewater in dyeing and printing. By injecting a specific proportion of inert gas into the feed liquid during the ultrafiltration process to form a gas-liquid two-phase flow, the local turbulence and shearing effect generated by microbubbles on the membrane surface effectively washes and peels off macromolecular pollutants such as polyvinyl alcohol (PVA) and gel layers attached to the membrane surface. This process significantly reduces concentration polarization and inhibits the deposition of pollutants on the membrane surface, thereby directly increasing the permeate flux of the ultrafiltration membrane and delaying flux decay. Compared with the prior art, which relies solely on high-speed circulation or simple cross-flow filtration, this invention maintains the high-efficiency operation of the membrane without the need for frequent chemical cleaning through the synergistic effect of gas-liquid two-phase flow.

[0018] (2) This invention collects the pressure parameters of the ultrafiltration membrane feed side and membrane shell side in real time, and dynamically estimates the membrane surface boundary layer pressure drop based on the built-in fluid dynamics model, thereby accurately controlling the operation of the ultrafiltration feed pump and the permeate booster pump, so that the net driving force of the membrane surface is stably maintained in the micro-positive pressure range of 0.02MPa–0.04MPa; effectively overcomes the reverse adsorption force on macromolecular pollutants when simply applying negative pressure on the shell side, and avoids rapid blockage of membrane pores while making full use of negative pressure to improve mass transfer efficiency, thus achieving a balance between high flux and low pollution.

[0019] (3) This invention integrates a multi-stage treatment process of dissolved air flotation pretreatment, gas-liquid two-phase flow ultrafiltration and nanofiltration deep purification, and uses a permeate booster pump to pressurize the ultrafiltration permeate and send it directly into the nanofiltration unit; this device realizes the compactness of the process flow and the cascade utilization of energy, avoiding secondary boosting and energy loss in intermediate links; compared with traditional separate treatment units, this invention, through system optimization and control integration, not only reduces equipment investment and floor space, but also improves the overall efficiency of alkali recovery and energy utilization rate. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is an overall structural diagram of the recycling device of the present invention; Figure 2 This is a flowchart of the recycling method of the present invention.

[0021] In the diagram: 1. Homogenization adjustment mechanism; 2. Dissolved air flotation mechanism; 21. High-pressure dissolved air tank; 22. Release device; 23. Air flotation tank; 3. Ultrafiltration membrane separation mechanism; 31. Ultrafiltration membrane module; 32. Ultrafiltration circulation pump; 33. Ultrafiltration feed pump; 34. Gas injection module; 35. Permeate booster pump; 4. Nanofiltration mechanism. Detailed Implementation

[0022] Existing membrane filtration systems, whether employing cross-flow filtration to mitigate membrane fouling or specifically designing pretreatment units to reduce the fouling load entering the membrane system, still generally face a series of inherent challenges when treating complex systems such as dyeing and printing desizing wastewater. Specifically, in traditional pressure-driven membrane filtration processes, high molecular weight polymers such as PVA, oils, waxes, and suspended solids in the desizing wastewater readily form a dense gel layer on the membrane surface, triggering severe concentration polarization. Concentration polarization refers to the phenomenon where the concentration of solute retained near the membrane surface is much higher than the concentration of the bulk solution. It significantly increases the resistance to mass transfer of solute to the membrane surface, leading to a sharp decline in membrane permeate flux and low system efficiency. To maintain the necessary flux, frequent chemical cleaning is often required, which not only increases operating costs and shortens membrane lifespan but also makes it difficult for the entire system to achieve long-term stable operation. In addition, the calcium and magnesium hardness ions commonly found in desizing wastewater readily combine with carbonate ions in alkaline environments to form insoluble salts such as calcium carbonate and magnesium hydroxide. These substances easily form scale inside or on the surface of the membrane pores, further exacerbating membrane clogging. This makes it difficult to balance high recovery rates with long-term stable operation in practical applications of membrane separation technology.

[0023] With increasingly stringent requirements for membrane separation efficiency and stable operation, the applicant, while exploring more efficient membrane separation strategies, has gradually focused on a new approach aimed at optimizing membrane flux and mitigating concentration polarization: applying low-pressure suction on the permeate side to remove permeate in real time. The theoretical basis for this approach lies in creating a localized low-pressure environment on the permeate side of the membrane, allowing the pure water or small-molecule solutes that have just passed through the membrane to be rapidly "pulled away," thereby effectively preventing the accumulation of these substances on the membrane surface. This, in turn, eliminates or significantly reduces concentration polarization and maintains a stable mass transfer driving force across the membrane. This "push-pull" synergistic effect is highly anticipated, as it is believed to significantly increase membrane permeate flux, inhibit gel layer formation, and even alleviate inorganic salt fouling to some extent.

[0024] However, when the applicant applied this "low-pressure suction on the permeate side" technology to complex systems containing large amounts of high-molecular-weight pollutants, such as dyeing and printing desizing wastewater, a non-obvious inherent contradiction gradually emerged, becoming a key bottleneck limiting its effectiveness. The reason lies in the fact that when a suction negative pressure is applied to the permeate side (i.e., the membrane shell side) of the ultrafiltration membrane, this negative pressure does not only act on the supernatant that has already permeated the membrane, causing it to be rapidly extracted; its physical effect is also transmitted back to the membrane surface on the feed side through the membrane pore structure. For high-concentration, high-viscosity macromolecular pollutants such as polyvinyl alcohol (PVA) in dyeing and printing desizing wastewater, these substances are retained because their molecular size is much larger than the pore size of the ultrafiltration membrane. At this time, the reverse negative pressure transmitted from the permeate side will generate a strong "adsorption" or "suction" force towards the membrane surface within the membrane feed boundary layer for these impermeable pollutants. Although these large molecules are ultimately blocked by the ultrafiltration membrane and cannot truly penetrate it, the continuous reverse pull causes them to adhere to the ultrafiltration membrane surface with a stronger tendency, thus being forced into or firmly adsorbed at the inlet of the membrane pores. This "adsorption clogging" phenomenon differs from the traditional concentration polarization and gel layer formation mechanisms; it is a physical adsorption enhancement effect driven by negative pressure. The consequence is severe clogging of the ultrafiltration membrane pores, leading to a significant reduction in the effective filtration area and a decrease in permeability. This fouling may even be more rapid and severe than in traditional pressure-driven modes.

[0025] Therefore, the applicant further proposed a method for alkali recovery from desizing water in dyeing and printing wastewater, which can effectively utilize the positive mass transfer gain brought about by low-pressure suction on the permeate side, while avoiding or significantly reducing the reverse adsorption force on macromolecular pollutants, thereby achieving efficient and long-term stable membrane separation and alkali recovery of highly polluted and high-viscosity wastewater.

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0028] Figure 1 The diagram shows the overall structure of a dyeing and printing wastewater desizing water alkali recovery device according to the present invention. The device includes: a homogenization and conditioning mechanism 1, a dissolved air flotation mechanism 2, an ultrafiltration membrane separation mechanism 3, a nanofiltration mechanism 4, and a control system, all interconnected in a specific manner.

[0029] In this embodiment, the homogenization conditioning mechanism 1 receives desizing wastewater from the dyeing and printing production line and controls its water quality characteristics and temperature fluctuations within a stable range acceptable to subsequent treatment units. Specifically, the homogenization conditioning mechanism 1 includes at least two homogenization conditioning tanks, each tank body is made of corrosion-resistant 304L stainless steel, and the internal volume is designed to be 20-30m³. 3 It is sufficient to cope with the impact of water volume and quality caused by intermittent wastewater discharge during the production process. The homogenization tank is equipped with a liquid outlet at the bottom, which is connected to the dissolved air flotation mechanism 2 through a high-temperature and corrosion-resistant UPVC pipe.

[0030] The homogenizing tank is equipped with an internal stirring mechanism, which includes a planetary gear reducer motor installed on the top of the homogenizing tank and a three-bladed propeller agitator located at the output end of the reducer motor. The diameter of the three-bladed propeller agitator blades is 1 to 1.5 m, and the rotation speed can be continuously adjusted within the range of 30-80 rpm / min by a frequency converter to ensure that the wastewater in the tank can be fully mixed, effectively avoiding the sedimentation of solid matter and local uneven concentration.

[0031] Furthermore, the homogenizing tank is surrounded by a jacketed temperature control mechanism. By circulating industrial waste heat steam or hot water, the temperature of the wastewater inside the tank is maintained within a preset range of 70℃-90℃. A temperature sensor (such as a PT100 type resistance thermometer) monitors the temperature inside the tank in real time and transmits the data to the control system, which then precisely adjusts the flow rate of steam or hot water in the jacket according to the preset value.

[0032] The dissolved air flotation (DAF) unit 2 receives the effluent from the homogenization conditioning unit 1. This DAF unit 2 removes a large amount of oil, wax, and suspended solids from the homogenized deslurry, reducing the pressure of subsequent ultrafiltration processes. The DAF unit 2 includes a high-pressure dissolved air tank 21, a release device 22, and a flotation tank 23. The high-pressure dissolved air tank 21 is made of Q235-B carbon steel with an anti-corrosion coating on the inner wall. Its design pressure is 1.0 MPa, and the working pressure is typically set between 0.4 MPa and 0.6 MPa. The high-pressure dissolved air tank 21 uses a vortex pump to forcibly mix a portion of the treated water with compressed air, causing the air to dissolve into the water under high pressure. The dissolved gas-water mixture enters the release device 22 through a pipe. The release device 22 is precision-machined from stainless steel and has a special internal flow channel structure that can instantly reduce the pressure of the high-pressure dissolved gas-water mixture to atmospheric pressure, thereby generating microbubbles with a diameter of approximately 20 μm to 50 μm at the bottom of the flotation tank 23. As these microbubbles rise, they combine with oils, waxes, and suspended solid particles in the wastewater through adsorption and bridging, forming scum with a density less than water that floats to the surface of the flotation tank 23.

[0033] Furthermore, the dissolved air flotation (DAF) tank 23 is constructed with reinforced concrete. The tank body is built according to requirements and actual space. In one specific embodiment, the tank dimensions are 8m long, 3m wide, and 3.5m deep, and it is designed with an inlet water distribution area, a scum separation area, and an outlet water collection area. A reciprocating scum scraping mechanism is installed above the DAF tank 23. This mechanism includes: a geared motor for driving, a sprocket and chain or gear and rack transmission system driven by the geared motor and spanning the DAF tank 23, a scraper plate rigidly connected to the transmission system, and limit switches located at both ends of the tank body to control the stroke range of the scraper plate. Driven by the transmission system, the scraper plate reciprocates linearly along a track at the top of the tank, periodically scraping the floating scum into a scum collection trough at the side of the tank, which is then pumped to the sludge treatment system by a screw pump. The air-to-water ratio in the dissolved air flotation process is precisely controlled by the control system and maintained at 1:5-1:10 (volume ratio) to ensure optimal pollutant removal.

[0034] After treatment by the dissolved air flotation unit 2, most of the oil, wax, and suspended solids in the deslurry are effectively removed. The turbidity of the effluent is significantly reduced, thereby greatly reducing the pollution load on the subsequent ultrafiltration membrane separation unit 3. The treated clarified liquid is collected in the effluent collection area of ​​the flotation tank 23, and its water quality meets the feed requirements of the ultrafiltration system. It is then smoothly sent to the subsequent ultrafiltration membrane separation unit 3 by a transfer pump.

[0035] The treated clarified liquid is transported to the ultrafiltration membrane separation unit 3, which is used for solid-liquid separation of the clarified liquid, efficiently retaining large molecules such as polyvinyl alcohol (PVA), while allowing small molecules such as water and alkali to permeate. The ultrafiltration membrane separation unit 3 includes: at least six tubular ultrafiltration membrane modules 31 operating in parallel, an ultrafiltration circulation pump 32, an ultrafiltration feed pump 33, a gas injection module 34, and a permeate booster pump 35.

[0036] The tubular ultrafiltration membrane module 31 uses a hydrophilic modified porous tubular membrane made of polyvinylidene fluoride (PVDF) or polyethersulfone (PES) to enhance its antifouling performance. Specifically, the membrane module uses a PVDF tubular membrane with an outer diameter of 25 mm and an inner diameter of 16 mm, with an average pore size of 20 nm and a rejection rate of over 99% for polyvinyl alcohol (PVA). Each membrane tube is arranged inside a membrane shell made of UPVC material, forming an open cross-flow filtration channel. It should be noted that each membrane module contains 20 membrane tubes, with an effective membrane area of ​​5 m². 2 .

[0037] The ultrafiltration circulation pump 32 is a variable frequency controlled centrifugal pump with a rated flow rate of 50 m³ / h. 3 The ultrafiltration circulation pump 32 has a head of 20m and a flow rate of 30m / h. It forms a circulation loop with the feed side of the tubular ultrafiltration membrane module 31. The ultrafiltration feed pump 33 is a frequency-controlled screw pump used to stably send the pretreated clarified liquid into the circulation loop. The ultrafiltration circulation pump 32 is used to drive the clarified liquid to circulate at high speed in the membrane tube of the tubular ultrafiltration membrane module 31. The linear velocity is adjustable in the range of 3 to 6 m / s, generating strong shear force, thereby effectively suppressing concentration polarization and membrane fouling.

[0038] A gas injection module 34 is positioned between the outlet pipe of the ultrafiltration circulation pump and the inlet of the tubular ultrafiltration membrane module. It is used to uniformly inject inert gas into the clarified liquid in the circulation loop, forming a stable gas-liquid two-phase flow. This gas injection module 34 includes a gas source, a flow controller, and a high-pressure jet pump or static mixer. The gas source is an industrial-grade liquid nitrogen storage tank or an on-site nitrogen generator, providing nitrogen with a purity of not less than 99.9%. The flow controller uses a Coriolis mass flow meter for precise measurement and control, achieving a control accuracy of ±0.5%FS and a response time of less than 1 second, ensuring that the ratio of the injected gas volume to the volumetric flow rate of the feed clarified liquid (gas-liquid ratio) is controlled within the volume ratio range of 0.05-0.5:1. The high-pressure jet pump or static mixer is used to achieve uniform dispersion of micron-sized bubbles in the clarified liquid.

[0039] The gas injection module 34 utilizes the Venturi effect or a special internal turbulent structure design to efficiently and uniformly disperse and mix a measured amount of nitrogen gas into the feed liquid in the form of microbubbles with a diameter of 20μm-100μm, forming a stable gas-liquid two-phase flow. These microbubbles, in the high-speed flowing liquid phase, continuously "scrub" the membrane surface through their own upward buoyancy and convective shear force, effectively stripping away macromolecular pollutants and inhibiting the formation of concentration polarization layers.

[0040] The permeate booster pump 35 is a variable frequency controlled centrifugal pump with dual functions: Function 1: The permeate booster pump 35 connects to the permeate side (i.e., the membrane housing side) of the tubular ultrafiltration membrane module 31, maintaining a preset negative pressure environment (-0.01MPa to -0.08MPa) on the membrane housing side, and extracting the permeate that has permeated through the membrane in real time to ensure the continuous operation of the permeate process; Function 2: The permeate booster pump 35 pressurizes the extracted permeate, increasing its pressure to the range of 0.8MPa-1.5MPa, thereby increasing the pressure of the pre-filtered water (water and small molecules such as caustic soda) after filtration by the tubular ultrafiltration membrane module 31. The high-pressure pre-filtered water has higher purification efficiency in the subsequent nanofiltration unit 4, achieving optimization of system integration and energy efficiency.

[0041] In this embodiment, the nanofiltration unit 4 is connected to the outlet of the permeate booster pump 35 and is used to further purify the primary filtered water. This is because the primary filtered water after ultrafiltration membrane filtration still contains polyvalent ions (such as calcium and magnesium ions) and trace organic matter in addition to water and caustic soda. Therefore, the nanofiltration unit 4 is used to purify the primary filtered water, selectively retaining polyvalent ions (such as calcium and magnesium ions) and trace organic matter in order to recover high-purity alkali solution.

[0042] Specifically, the nanofiltration mechanism 4 includes: at least three spirally wound nanofiltration membrane modules, and a nanofiltration circulation pump and a nanofiltration feed pump connected to the nanofiltration membrane modules. The nanofiltration membrane modules, the nanofiltration circulation pump, and the nanofiltration feed pump together constitute a nanofiltration membrane separation circuit, with a feed pressure of 0.8 MPa-1.5 MPa. Each nanofiltration membrane module has an effective membrane area of ​​40 m². 2 The membrane is selected from NF270 or similar composite polyamide nanofiltration membranes, with a molecular weight cutoff (MWCO) ranging from 150 Da to 300 Da. This membrane has a rejection rate of over 95% for divalent ions (such as calcium and magnesium ions) and a permeability of over 70% for monovalent ions (such as sodium ions), ensuring the purity of the recovered alkali solution.

[0043] Importantly, the control system is linked to the operation of the entire dyeing and printing wastewater desizing alkali recovery device. This control system coordinates the operation of each processing unit to achieve automated operation and parameter optimization of the homogenization adjustment mechanism 1, dissolved air flotation mechanism 2, ultrafiltration membrane separation mechanism 3, and nanofiltration mechanism 4, thereby ensuring the high efficiency and stability of the alkali recovery process.

[0044] The control system is based on a programmable logic controller (PLC), equipped with distributed I / O modules and a Supervisory Control and Data Acquisition (SCADA) human-machine interface to achieve real-time monitoring and visual control of process parameters such as temperature, pressure, flow rate, and liquid level. The system is equipped with various sensors, including pressure sensors located at the inlet, outlet, and membrane housing of the ultrafiltration membrane module 31; electromagnetic flow meters and mass flow meters for liquid and gas flow monitoring; a PT100 temperature sensor; and a liquid level sensor. Actuators include frequency converters (for adjusting the speed of the pump and agitator), electric regulating valves (for flow and pressure control), and pneumatic valves.

[0045] Specifically, the control system also integrates an intelligent control method for suppressing ultrafiltration membrane fouling, which includes the following steps: Step A1: Real-time monitoring of the inlet pressure of the ultrafiltration membrane module 31 is performed using pressure sensors installed at the inlet, outlet, and membrane housing sides of the ultrafiltration membrane module 31. Export pressure Pressure on the membrane shell side The data is transmitted to the PLC controller; simultaneously, the conductivity and turbidity parameters provided by the online water quality analyzer are acquired.

[0046] Step A2: Based on the pressure data collected in step A1, calculate the average transmembrane pressure difference: The average transmembrane pressure difference reflects the overall pressure dynamics driving liquid permeation across the entire membrane module.

[0047] The control system uses a built-in preset fluid dynamics model to dynamically estimate the local pressure drop within the boundary layer at the membrane surface. The pressure drop is mainly caused by the fluid resistance encountered when flowing through the boundary layer on the membrane surface, and is a key factor leading to the difference between the actual pressure acting on the membrane surface and the bulk flow pressure. The fluid dynamics model is a pressure drop calculation model constructed based on the Darcy-Weisbach equation and the flow regime (laminar or turbulent) criterion within the membrane channel. To ensure the accuracy of the estimation, the model incorporates online water quality parameters for real-time calibration and correction: specifically, the system uses measurements from an online conductivity sensor to indirectly characterize changes in solute concentration in the feed solution, and uses measurements from an online turbidity meter to reflect the content of colloidal substances. These real-time water quality parameters serve as input variables to the model, dynamically adjusting the frictional resistance coefficient and boundary layer thickness parameters to achieve the desired effect. The estimated values ​​can more accurately reflect the actual hydrodynamic state of the membrane surface under current water quality conditions.

[0048] Based on the above calculations and estimations, the net driving force on the membrane surface is further calculated: This net driving force represents the effective pressure that actually acts on the membrane surface and can be used to drive permeation after overcoming the boundary layer pressure drop on the feed side. Maintaining this value as slightly positive is the core of this control method to prevent contaminants from adsorbing and clogging the membrane surface.

[0049] Step A3: Using a composite algorithm of PID and fuzzy logic, output control commands to the frequency converter and electric regulating valve: adjust the speed of the ultrafiltration feed pump 33 to control the feed flow rate, and adjust the speed of the permeate booster pump 35 to control the negative pressure on the membrane housing side, so that... It is stably maintained in the micro-positive pressure range of 0.02MPa-0.04MPa, thereby effectively inhibiting the reverse adsorption of macromolecular pollutants on the membrane surface and ensuring the continuous and stable operation of the ultrafiltration process.

[0050] With the above-mentioned intelligent control method for ultrafiltration membrane fouling suppression, even when there is negative pressure suction on the membrane shell side, the local effective driving force on the membrane feed side is sufficient to overcome any reverse force that may cause macromolecular pollutants (especially PVA) to be reversely adsorbed. Thus, while effectively promoting permeation, it prevents macromolecular pollutants from being excessively adsorbed on the membrane surface under negative pressure.

[0051] In addition, the control system also performs closed-loop regulation of the nitrogen flow rate of the gas injection module 34 according to the preset gas-liquid ratio to maintain the stable state of the gas-liquid two-phase flow, and has the functions of fault self-diagnosis, alarm prompt and remote monitoring, thereby comprehensively improving the reliability and long-term operation capability of the device.

[0052] Figure 2 A flowchart of a method for recovering alkali from desizing wastewater in dyeing and printing industries, provided by this invention, is shown. Based on the aforementioned apparatus, the recovery method includes the following steps: Step S1: After homogenization of the high-temperature desizing water, most of the oils, waxes, and suspended solids in the desizing water are removed by dissolved air flotation to obtain a clear liquid; Step S2: The treated clear liquid is filtered through an ultrafiltration membrane, while a negative pressure environment is constructed on the membrane shell side of the ultrafiltration membrane to extract the permeate through the ultrafiltration membrane in real time, obtaining primary filtrate; Step S3: The primary filtrate is purified through a nanofiltration membrane. Under pressure, the nanofiltration membrane selectively retains multivalent ions and trace organic matter in the primary filtrate, allowing water and caustic soda to permeate; Step S4: The nanofiltration permeate obtained in S3 is used as a high-purity recovered alkali solution and directly reused in the dyeing and printing production process.

[0053] By employing integrated membrane separation technology, the efficient recovery and reuse of caustic soda from dyeing and printing desizing wastewater is achieved, while effectively solving the membrane fouling problem. The various components and operating mechanisms of the method will be described in detail below to ensure that those skilled in the art can fully understand and implement this invention.

[0054] In step S1, after homogenization of the high-temperature desizing water, most of the oil, wax and suspended solids in the desizing water are removed by dissolved air flotation to obtain a clear liquid.

[0055] First, the desizing process itself needs to be carried out in a hot alkaline solution. High temperature can accelerate the swelling and dissolution of the sizing agent (such as polyvinyl alcohol (PVA), starch, etc.), thereby improving the desizing efficiency. Therefore, the temperature of the desizing solution is relatively high, between 70℃ and 95℃.

[0056] In other words, the desizing water itself is at a high temperature. After desizing, the wastewater is directly collected and pumped to the homogenization and conditioning unit 1. In this unit, the desizing water is thoroughly mixed by the stirring unit 12 to eliminate instantaneous fluctuations in water quality, concentration, and temperature. Simultaneously, the temperature control unit maintains the desizing water temperature within the range of 70℃-90℃, optimizing the efficiency of subsequent dissolved air flotation and ultrafiltration membrane separation. After approximately 2 hours of homogenization and temperature maintenance, the homogenized desizing water is discharged at a constant flow rate (e.g., 10 m³ / h). 3 The water (water / h) is transported to the dissolved air flotation unit 2. In the dissolved air flotation unit 2, the water is mixed with air under high pressure in the high-pressure dissolved air tank 21 until saturation. The high-pressure dissolved air water is then depressurized instantaneously through the release device 22, generating a large number of microbubbles. These bubbles combine with oil, wax, and suspended solid particles in the desizing water in the flotation tank 23 and float to the surface, forming a scum layer. The scum scraping mechanism 24, located above the flotation tank 23, periodically scrapes away the scum.

[0057] In step S1, the dissolved air pressure is between 0.4 MPa and 0.6 MPa, and the air-to-water ratio is 1:5 to 1:10 (volume ratio). After this step, the main oils and suspended solids in the deslurry are effectively removed, and the turbidity of the effluent is significantly reduced, thereby greatly reducing the fouling load of ultrafiltration membrane separation in subsequent steps.

[0058] In step S2, the treated clear liquid is filtered through an ultrafiltration membrane. At the same time, a negative pressure environment is created on the membrane shell side of the ultrafiltration membrane to extract the permeate that has passed through the ultrafiltration membrane in real time, thus obtaining the initial filtered water.

[0059] The filtration principle of ultrafiltration membranes is based on sieving and pressure difference across the membrane. Specifically, the clarified liquid after step S1 flows through the surface of the ultrafiltration membrane under the pressure on the feed side. The ultrafiltration membrane has a specific pore size distribution (preferably nanoscale). Due to its physical sieving effect, it allows small molecules such as water molecules and dissolved alkali (NaOH) to pass through the membrane pores and become permeate, while pollutants with molecular weights much larger than the membrane pore size, such as high molecular polymers like polyvinyl alcohol (PVA), as well as colloids and residual oils, are selectively retained on the feed side.

[0060] In other words, the clarified liquid after step S1 is fed into the tubular ultrafiltration membrane module 31 at a constant pressure of 0.3MPa-0.8MPa by the ultrafiltration feed pump 33. Before entering the tubular ultrafiltration membrane module 31, the gas injection module 34 starts working: high-purity nitrogen (purity not less than 99.9%) is precisely metered by the flow controller and uniformly injected into the clarified liquid in the form of micron-sized bubbles with a diameter of 20μm-100μm via a high-pressure jet pump or static mixer. The resulting stable gas-liquid two-phase flow circulates inside the tubular ultrafiltration membrane at a linear velocity of 3-6m / s under the drive of the ultrafiltration circulation pump 32.

[0061] In this gas-liquid two-phase flow ultrafiltration process, a preset negative pressure environment (-0.01 MPa to -0.08 MPa) is applied to the membrane shell side, forming a component of the transmembrane pressure difference (TMP). This negative pressure not only enhances the permeate extraction efficiency and increases membrane flux but also helps mitigate concentration polarization. However, for large molecular pollutants that are trapped, this negative pressure generates a reverse force pointing towards the membrane surface through the membrane pores, posing a risk of exacerbating membrane surface adsorption and fouling. Therefore, this invention dynamically adjusts the feed-side pressure and the membrane shell-side negative pressure through a control system to achieve a net driving force on the membrane surface. The pressure is consistently maintained within a slightly positive range of 0.02MPa-0.04MPa, thereby effectively suppressing the reverse adsorption and deposition of large molecular pollutants on the membrane surface while utilizing negative pressure to improve mass transfer efficiency, ensuring the stable and efficient operation of the ultrafiltration process. Simultaneously, the local turbulence and vortex effects generated by the high-speed flow of bubbles within the membrane tube significantly enhance the shear force on the membrane surface, creating a continuous "scrubbing" and peeling effect on large molecular pollutants such as polyvinyl alcohol (PVA) that are being applied to or have already been adsorbed onto the membrane surface. This effectively inhibits the formation of concentration polarization layers and gel layers, ensuring high permeate flux. The initial filtered water (permeate) is extracted and pressurized by the permeate booster pump 35 and enters the subsequent nanofiltration unit 4.

[0062] In step S3, the pre-filtered water is purified by nanofiltration membrane. Under pressure, the nanofiltration membrane selectively retains polyvalent ions and trace organic matter in the pre-filtered water, allowing water and caustic soda to pass through.

[0063] In other words, the pressure of the pre-filtered water obtained in step S2 has been increased to 0.8MPa-1.5MPa by the permeate booster pump 35, and then sent to the nanofiltration unit 4 for further purification. The nanofiltration unit 4 operates at a constant operating pressure of 0.8MPa-1.5MPa provided by the nanofiltration feed pump. Its nanofiltration membrane selectively retains polyvalent ions (such as calcium and magnesium ions) and trace organic matter in the pre-filtered water, while allowing monovalent ions (such as sodium ions) in water and high-purity alkaline solution to pass through efficiently, thereby ensuring the acquisition of high-purity alkaline solution.

[0064] In step S4, the nanofiltration permeate obtained in S3 is used as a high-purity recycled alkali solution and directly reused in the printing and dyeing production process.

[0065] In other words, the nanofiltration permeate obtained in step S3, i.e., the high-purity recovered alkali solution, has a conductivity of less than 2000 μS / cm and a stable pH of around 12.5. It can be directly reused in the desizing or scouring stages of the dyeing and printing production process, significantly reducing the company's consumption of fresh caustic soda. The nanofiltration concentrate, which is enriched with multivalent ions and a small amount of difficult-to-remove organic matter, undergoes further treatment (e.g., evaporation crystallization or biochemical treatment) or is discharged in compliance with standards, depending on its water quality characteristics. This recycling and reuse process not only reduces production costs but also significantly reduces the total discharge and pollutant load of dyeing and printing wastewater, demonstrating significant economic and environmental benefits.

[0066] To further clarify the technical solution and beneficial effects of the present invention, a detailed comparative analysis will be conducted below through specific embodiments and comparative examples. All embodiments and comparative examples used desizing wastewater from the same source and with the same initial composition. The key water quality indicators are as follows: pH value 12.8, chemical oxygen demand (COD) 8500 mg / L, polyvinyl alcohol (PVA) concentration 1250 mg / L, suspended solids (SS) concentration 850 mg / L, oil content 320 mg / L, and calcium ion (Ca) concentration... 2+ The concentration was 95 mg / L, and the magnesium ion concentration was Mg2+. 2+ The concentration was 35 mg / L, and the temperature was 85 ± 5℃.

[0067] Example 1:

[0068] This embodiment uses the dyeing and printing wastewater desizing water alkali recovery device and method described in this invention to treat desizing wastewater.

[0069] The specific configuration of the ultrafiltration membrane separation mechanism in the device is as follows: a PVDF tubular ultrafiltration membrane with a membrane area of ​​30 m² is used. 2The average pore size is 20 nm. The operating parameters are as follows: ultrafiltration feed pressure 0.35 MPa, ultrafiltration circulation linear velocity 5 m / s, membrane housing side permeate pressure -0.03 MPa, transmembrane pressure difference 0.22 MPa, membrane surface net driving force 0.025 MPa (maintained by the control system), gas injection rate (nitrogen) 10% of feed liquid volume flow rate, and operating temperature 80℃.

[0070] The device operated continuously for 120 hours (5 days), during which membrane flux was recorded every 24 hours, and samples of the recovered alkali solution were taken for analysis at the end of the operation. The results showed that the initial membrane flux was 85 L / (m²). 2 After 120 hours of operation, the membrane flux stabilized at 78 L / (m²). 2 The flux decay rate was only 8.2% (·h). The recovered alkali solution was clear and transparent, with key indicators as follows: PVA not detected (<5mg / L), COD 185mg / L, conductivity 1850μS / cm, and pH 12.6. This indicates that the method of the present invention can maintain high throughput and recover extremely high purity alkali solution during long-term operation, meeting the requirements for reuse.

[0071] Example 2:

[0072] This embodiment uses the same desizing water and core device configuration as Embodiment 1. The difference lies in adjusting some parameters in the gas-liquid two-phase flow ultrafiltration process to verify the effectiveness of the parameter range of the present invention. The operating parameters are adjusted as follows: ultrafiltration feed pressure 0.45 MPa, ultrafiltration circulation linear velocity 4 m / s, membrane housing side permeate pressure -0.05 MPa, transmembrane pressure difference 0.28 MPa, membrane surface net driving force 0.038 MPa (maintained by the control system), and gas injection rate (nitrogen) 20% of the feed liquid volume flow rate.

[0073] During 120 hours of continuous operation, the initial membrane flux was 88 L / (m²). 2 (·h), with the final membrane flux maintained at 75 L / (m²). 2 The flux decline rate was 14.8% (·h). The recovered alkali solution parameters were: PVA 8 mg / L, COD 225 mg / L, and conductivity 1950 μS / cm. Although the flux decline after parameter adjustment was slightly higher than in Example 1, it was still within the excellent range, and the alkali solution quality also met the standards, fully demonstrating the validity of the parameter range described in this invention (e.g., h). The effectiveness and operability of maintaining a pressure range of 0.02MPa-0.04MPa.

[0074] Comparative Example 1: This comparative example uses desizing water with the same composition as in Example 1, but the ultrafiltration membrane separation mechanism of the device lacks a gas injection module and a permeate booster pump. It employs a traditional unidirectional pressure-driven ultrafiltration mode, without shell-side negative pressure suction and gas-phase washing. The operating parameters are: feed pressure 0.35 MPa, no shell-side negative pressure, therefore the transmembrane pressure difference is 0.35 MPa, and there is no gas injection.

[0075] The results showed that the initial membrane flux was high, at 92 L / (m²). 2 However, membrane fouling occurs extremely rapidly. After 24 hours of operation, the membrane flux drops sharply to 45 L / (m²). 2 After 120 hours, the membrane flux had decreased to 22 L / (m³), with a flux decay rate of 51.1%. 2 (·h), the system could not operate stably and required chemical cleaning. The quality of the recovered alkali solution was also poor, with a PVA concentration of 65 mg / L and a COD of 680 mg / L. This indicates that although the traditional mode has a high initial flux, it suffers from severe membrane fouling, cannot operate stably for a long time, and has poor recovery quality.

[0076] Comparative Example 2: This comparative example uses desizing water with the same composition as in Example 1. The only difference in the device configuration is the lack of a gas injection module, but the permeate booster pump is retained to create a shell-side negative pressure of -0.03 MPa. Operating parameters: feed pressure is 0.35 MPa, transmembrane pressure differential is 0.22 MPa, net driving force on the membrane surface is maintained at 0.025 MPa by the control system, and there is no gas injection.

[0077] The operational results show that the shell-side negative pressure has a certain effect on maintaining the flux. The initial membrane flux was 83 L / (m²). 2 After 120 hours, the flux decreased to 58 L / (m³). 2 The flux decline rate was 30.1% (·h). However, compared with Example 1, the decline was significantly aggravated, and the PVA concentration (28 mg / L) and COD (320 mg / L) in the recovered alkali solution were both higher than those in Example 1. This proves that relying solely on shell-side negative pressure without gas-phase elution is still insufficient to effectively suppress membrane surface fouling and contaminant adsorption.

[0078] Comparative Example 3: This comparative example uses deslurry with the same composition as in Example 1, and the apparatus is fully configured (including gas injection and booster pump), but the control system does not implement the intelligent control method for ultrafiltration membrane fouling suppression. The feed pressure is fixed at 0.35 MPa, the membrane housing side pressure is fixed at -0.03 MPa, the transmembrane pressure difference is fixed at 0.22 MPa, and the gas injection rate is fixed at 10%. The system does not dynamically calculate or adjust the net driving force on the membrane surface.

[0079] After 120 hours of operation, the membrane flux increased from the initial 85 L / (m²) 2The volume of water in the h-meter range decreased to 65 L / (m³). 2 The flux decline rate was 23.5% (·h). The recovered alkali indicators were PVA: 20 mg / L, COD: 280 mg / L. The results indicate that even with the same hardware, the lack of intelligent regulation to maintain a constant net driving force on the membrane surface leads to a higher fouling rate and worse permeate quality.

[0080] Comparative Example 4: This comparative example, based on the same principles as Comparative Example 3 (without intelligent control), further sets the operating parameters outside the scope required by this invention: fixing the feed pressure at 0.5 MPa, fixing the membrane shell side pressure at -0.08 MPa, and achieving a transmembrane pressure difference as high as 0.54 MPa), attempting to obtain high throughput by increasing the driving force. The gas injection rate is fixed at 10%.

[0081] Serious operational problems have occurred. The initial membrane flux was indeed very high (10⁵ L / (m²)). 2 Due to excessively high negative pressure and transmembrane pressure difference, large molecular pollutants such as PVA were rapidly and strongly adsorbed and blocked the membrane pores. After only 12 hours of operation, the membrane flux plummeted to 30 L / (m²). 2 After 48 hours of operation, the membrane flux had fallen below 15 L / (m²). 2 (h) The system becomes completely clogged, requiring shutdown and chemical cleaning. This comparative example demonstrates that blindly setting high negative pressure and high TMP is not only unhelpful, but can also exacerbate the "adsorption clogging" effect, leading to catastrophic membrane fouling and system failure.

[0082] The experimental data of the above embodiments and comparative examples are summarized in Table 1.

[0083] Table 1. Summary of Experimental Data

[0084] By comparing and analyzing the experimental data of the above embodiments and comparative examples, the following conclusions can be drawn: Experimental data show that the method and apparatus for recovering alkali from desizing wastewater in dyeing and printing industries provided by this invention have significant advantages over traditional processes. By synergistically utilizing negative pressure suction on the membrane shell side, gas-liquid two-phase flow elution, and an intelligent control strategy based on the net driving force of the membrane surface, long-term stable operation and efficient pollutant separation of the ultrafiltration process have been successfully achieved. During 120 hours of continuous operation, the membrane flux decay rate of this embodiment can be as low as 8.2%, significantly better than the comparative example without gas injection and intelligent control (the decay rate is as high as 76.1% or more), and the PVA concentration in the recovered alkali solution is less than 5 mg / L, the COD value is less than 185 mg / L, and the purity is significantly improved. In particular, by precisely maintaining the net driving force of the membrane surface in the micro-positive pressure range of 0.02 MPa-0.04 MPa, the technical problem of large molecular pollutants being easily reverse-adsorbed into the membrane pores under high negative pressure suction environment is effectively overcome, avoiding rapid pore blockage. Comparative experiments confirm that the lack of any of the above technical elements, or improper control of key parameters, will lead to increased membrane fouling, a sharp decline in flux, and deterioration of the quality of the recovered alkali solution. In summary, this invention effectively resolves the contradiction between maintaining high flux and controlling membrane fouling, achieving efficient recovery of high-purity alkali solution and long-term stable system operation, and has outstanding industrial application value.

[0085] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for recovering alkali from desizing wastewater in dyeing and printing, characterized in that, Includes the following steps: S1. After homogenization of the high-temperature desizing water, most of the oil, wax and suspended solids in the desizing water are removed by dissolved air flotation to obtain a clear liquid. S2. The treated clear liquid is filtered through an ultrafiltration membrane. At the same time, a negative pressure environment is created on the membrane shell side of the ultrafiltration membrane to extract the permeate that has passed through the ultrafiltration membrane in real time, thus obtaining the initial filtered water. S3. The primary filtered water is purified by nanofiltration membrane. Under pressure, the nanofiltration membrane selectively retains polyvalent ions and trace organic matter in the primary filtered water, while allowing water and caustic soda to pass through. S4. The nanofiltration permeate obtained in S3 is used as a high-purity recycled alkali solution and directly reused in the printing and dyeing production process.

2. The method for recovering alkali from desizing wastewater in dyeing and printing wastewater according to claim 1, characterized in that: In S2, during the ultrafiltration process, an inert gas is injected into the feed liquid to form a gas-liquid two-phase flow, and the ratio of the injected inert gas to the volumetric flow rate of the feed liquid is 0.05-0.5:

1.

3. The method for recovering alkali from desizing wastewater in dyeing and printing wastewater according to claim 2, characterized in that: The inert gas is nitrogen, which is injected in the form of microbubbles with a diameter of 20μm-100μm.

4. The method for recovering alkali from desizing wastewater in dyeing and printing wastewater according to claim 1, characterized in that: In S2, by adjusting the pressure on the feed side of the ultrafiltration membrane and the pressure on the membrane housing side in real time, the net driving force on the surface of the ultrafiltration membrane is maintained in a slightly positive pressure range of 0.02MPa-0.04MPa.

5. A device for recovering alkali from desizing wastewater in dyeing and printing, characterized in that, include: The homogenization conditioning mechanism, dissolved air flotation mechanism, ultrafiltration membrane separation mechanism, and nanofiltration mechanism are connected in sequence. The ultrafiltration membrane separation mechanism includes an ultrafiltration membrane module, an ultrafiltration feed pump, an ultrafiltration circulation pump, a gas injection module, and a permeate booster pump. The ultrafiltration feed pump is used to feed the clarified liquid into the ultrafiltration membrane separation mechanism. The ultrafiltration circulation pump is used to drive the clarified liquid to circulate at high speed within the ultrafiltration membrane module. The gas injection module is used to inject inert gas into the circulating clarified liquid to form a gas-liquid two-phase flow. The permeate booster pump is connected to the membrane housing side of the ultrafiltration membrane module to create a negative pressure environment on the membrane housing side and extract the permeate while simultaneously pressurizing the permeate. The inlet of the nanofiltration unit is connected to the outlet of the permeate booster pump to receive the pressurized pre-filtered water. The system is electrically connected to the homogenization adjustment mechanism, dissolved air flotation mechanism, ultrafiltration membrane separation mechanism and nanofiltration mechanism, and is used to monitor and regulate the operating parameters of each mechanism.

6. The dyeing and printing wastewater desizing water alkali recovery device according to claim 5, characterized in that: The gas injection module includes a gas source, a flow controller, and a mixer, wherein the mixer is a high-pressure jet pump or a static mixer.

7. The dyeing and printing wastewater desizing water alkali recovery device according to claim 5, characterized in that: The control system is configured to collect the inlet pressure, outlet pressure and membrane housing side pressure of the ultrafiltration membrane module in real time, and dynamically adjust the operating status of the ultrafiltration feed pump and the permeate booster pump to maintain the net driving force on the surface of the ultrafiltration membrane within the range of 0.02MPa-0.04MPa.

8. The dyeing and printing wastewater desizing water alkali recovery device according to claim 5, characterized in that: The ultrafiltration membrane module is a tubular membrane module, and the membrane material is polyvinylidene fluoride or polyethersulfone.

9. The dyeing and printing wastewater desizing water alkali recovery device according to claim 6, characterized in that: The mixer outlet is located at the inlet of the ultrafiltration membrane module, near the edge of the membrane, and is arranged in a ring.

10. The dyeing and printing wastewater desizing water alkali recovery device according to claim 5, characterized in that: The dissolved air flotation mechanism includes a high-pressure dissolved air tank, a release device, and an air flotation tank, with a sludge scraping mechanism installed above the air flotation tank.

Images