Circulating water treatment system and method for preventing regenerated leather production spunlace needle from being blocked

Abstract

The invention discloses a circulating water treatment system and method for preventing blockage of a spunlace needle head in regenerated leather production. Wastewater generated in the spunlace reinforcement process is sequentially subjected to water collection sedimentation, screen filtration, air floatation treatment and refined filtration treatment and then enters a clarification tank, reuse water is obtained and subjected to terminal purification and then enters the spunlace reinforcement process again, and a saponification-sedimentation-neutralization integrated treatment process is further included between the air floatation treatment and the refined filtration treatment. The process is realized through a saponification-precipitation-neutralization integrated facility, the integrated facility comprises a first group of integrated treatment units and a second group of integrated treatment units which are arranged in parallel and are switched and controlled through valves, and the two groups of integrated treatment units alternately perform the processes of water feeding, saponification, precipitation, sludge discharge, neutralization, water drainage and standing so as to realize continuous operation. A simple and feasible saponification technical route is provided on the basis of the inherent reason of frequent blockage of a spunlace device for production of regenerated leather, and the problem that a spunlace needle head is blocked due to long-term reuse of circulating water is solved.

Description

Technical Field

[0001] This invention belongs to the field of industrial wastewater treatment technology, specifically relating to a circulating water treatment system and method for preventing clogging of hydroentangled needles in recycled leather production. Background Technology

[0002] Recycling technology for leather scraps is a green process that "turns waste into treasure." By transforming solid leather waste into high-value recycled substrates, it fundamentally reduces environmental pollution and resource waste. This not only significantly lowers raw material costs and waste disposal fees, creating considerable economic benefits, but also produces products with uniform performance and customizability, achieving a win-win situation for both environmental and economic benefits. Currently, the process of manufacturing recycled leather from leather scraps mainly involves a series of steps, including fiber debonding, pulping, web laying, hydroentangling reinforcement, drying, and shaping.

[0003] Hydroentanglement technology, in particular, uses high-speed micro-flows of water to pierce the fiber web with an instantaneous impact force of 10-30 MPa. This allows the leather fibers to fully entangle and form a fabric through purely physical action, achieving one-step molding without the need for chemical adhesives. This completely avoids the problem of organic solvent residues and maximizes the preservation of the natural strength and feel of the collagen fibers. Hydroentanglement is the core leap for regenerated leather, transforming it from "fiber felt" into high-quality rolls that can be cut, sewn, and embossed. However, this process uses a huge amount of water. Treating and recycling the wastewater is not only an inherent requirement for controlling process costs and improving operational efficiency, but also the cornerstone for achieving sustainable operation that meets clean production standards. Because hydroentanglement requires strong impact force, the needles inside the device have a small inner diameter, mostly between 100 and 120 μm, making them prone to clogging. Therefore, the interception and treatment of suspended particulate matter in the circulating water is crucial to ensuring the continuous and stable operation of the process.

[0004] The current circulating water treatment process flow diagram widely used by some recycled leather enterprises is as follows: Figure 1 As shown, the wastewater from the hydroentangling process first enters a sedimentation tank, where larger solid particles (such as large-diameter fibers and proteins) settle naturally, achieving initial solid-liquid separation. Subsequently, the wastewater is filtered through a screen to further remove residual suspended solids and fibers. Next, PAC (polyaluminum chloride) and PAM (polyacrylamide) are added to the wastewater before it enters the first air flotation stage, causing fine suspended solids and fibers to flocculate into larger flocs, which are then removed by air flotation. The wastewater then enters a second air flotation stage for further removal of remaining suspended solids. After two stages of air flotation treatment, the wastewater enters a filtration system for physical fine filtration and then flows into a clarified reclaimed water tank for reuse. To ensure water quality, the circulating water returning from the clarification tank undergoes mechanical filtration and sand filtration for final purification before re-entering the hydroentangling process.

[0005] This circulating water treatment system removes most of the micron-sized solid organic and inorganic impurities such as leather fibers, proteins, tanning agents, and dyes from the circulating water through processes such as coagulation and flotation. In the initial stage of operation of the entire unit (when producing recycled leather of different colors, especially light colors, fresh water needs to be changed), the circulating water system can operate normally. After the circulating water has been circulating for a certain period of time (generally 0.5 to 1 month), the hydroentangling needles begin to become clogged, resulting in unstable hydroentangling pressure. This not only affects the quality of recycled leather products (such as surface defects), but also requires frequent shutdowns for replacement and cleaning (replacement is required every 10-20 minutes of operation), seriously affecting production continuity and restricting production efficiency.

[0006] Therefore, identifying the root cause of hydroentanglement needle clogging and proposing a thorough solution to achieve long-term stable operation of the hydroentanglement system has become an urgent technical problem to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to provide a circulating water treatment system and method for preventing clogging of hydroentangled needles in the production of recycled leather, so as to prevent clogging of hydroentangled needles from the source and thus ensure the long-term stable operation of the hydroentangled system.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a circulating water treatment method to prevent clogging of hydroentangled needles in the production of recycled leather, comprising the following steps: wastewater generated in the hydroentanglement process is sequentially subjected to water collection and sedimentation, screen filtration, air flotation, and fine filtration (sequentially including mechanical filtration, sand filtration, and fiber bag filtration) before entering a clarification tank to obtain recycled water. The recycled water in the clarification tank is then subjected to final purification through mechanical filtration and sand filtration before being reintroduced into the hydroentanglement process. Between the air flotation and fine filtration processes, an integrated saponification-sedimentation-neutralization treatment process is included. This process is implemented using an integrated saponification-sedimentation-neutralization facility. The integrated facility includes a first set of integrated treatment units and a second set of integrated treatment units arranged in parallel and controlled by valve switching. The two sets of integrated treatment units alternately perform water intake, saponification, sedimentation, sludge discharge, neutralization, drainage, and settling processes to achieve continuous operation.

[0010] Furthermore, the saponification process involves pumping the alkali solution into an integrated treatment unit filled with wastewater. During pumping, the solution is stirred and the pH is monitored. When the wastewater pH exceeds 12, the pumping of the alkali solution is stopped and the stirring is stopped. The reaction time is 30 ± 3 minutes.

[0011] Furthermore, the precipitation process involves reacting lipids such as fatliquoring agents in the wastewater with an alkaline solution to produce substances such as sodium fatty acids and glycerol, both with densities greater than 1 g / cm³.3 A precipitate will form, and the precipitation time shall not be less than 30 minutes.

[0012] Furthermore, the sludge discharge process involves installing a sludge hopper, a sludge discharge pipe, and a sludge pipe valve at the bottom of the integrated facility. The sludge in the sludge hopper is discharged by opening the sludge pipe valve, and the sludge discharge time is 15±1 minutes. After the sludge discharge is completed, the sludge pipe valve is closed.

[0013] Furthermore, the neutralization process involves gradually pumping the acid solution into the integrated treatment unit while stirring and monitoring the pH. When the wastewater pH is below 8, the pumping of the acid solution and stirring are stopped, and the reaction time is 15±1 min.

[0014] Furthermore, the drainage process involves installing a decanter within the integrated facility to discharge wastewater from the system to subsequent processes, with a drainage time of 15±1 minutes.

[0015] Furthermore, the settling process refers to the facility being left to stand still, awaiting the next water intake, for a settling time of 15 ± 1 min.

[0016] This invention also provides a circulating water treatment system for preventing clogging of hydroentangled needles in the production of recycled leather. The system includes, in sequence, a hydroentangled reinforcement process outlet, a sedimentation tank, a screen filter, an air flotation device, a filtration unit, a clarification tank, and a terminal purification unit. The circulating water treatment system further includes an integrated saponification-sedimentation-neutralization facility located between the air flotation device and the filtration unit. This integrated facility comprises a first set of integrated treatment units and a second set of integrated treatment units arranged in parallel and controlled by valve switching. The two sets of integrated treatment units alternately perform water intake, saponification, sedimentation, sludge discharge, neutralization, drainage, and settling processes to achieve continuous operation.

[0017] The water collection and sedimentation tank is used to perform preliminary solid-liquid separation on the wastewater generated in the hydroentanglement process and to settle large-diameter solid particles.

[0018] The aforementioned screen filtration device is used to trap suspended solids and fibers;

[0019] The aforementioned air flotation device is equipped with PAC and PAM dosing units, which are used to remove fine suspended matter and fiber flocculation by air flotation.

[0020] The filtration unit includes a mechanical filtration device, a sand filtration device, and a fiber bag filtration device connected in sequence, used for physical fine filtration of wastewater after flotation treatment;

[0021] The clarification tank is used to collect water treated by the filtration unit for reuse.

[0022] The terminal purification unit includes a mechanical filtration device and a sand filtration device arranged in sequence, which are used to purify the effluent from the clarification tank and then return it to the hydroentanglement reinforcement process for reuse.

[0023] Furthermore, the integrated saponification-precipitation-neutralization facility is equipped with a stirring device and a pH meter electrode to monitor the pH of the wastewater in real time.

[0024] Furthermore, the saponification-precipitation-neutralization integrated facility is equipped with a plate and frame filter press for sludge dewatering, and the filtrate is recycled to the alkali tank for dissolving alkali solution.

[0025] This invention provides a circulating water treatment method to prevent clogging of hydroentangled needles in the production of recycled leather. It is based on a mature and stable process, and is precisely optimized and enhanced. The equipment and devices added to the solution can be added to the original process in a relatively simple way, which minimizes the technical risks brought about by the introduction of new variables and solves the problem of clogging of hydroentangled needles by long-term reuse of circulating water.

[0026] The beneficial effects of this invention are as follows:

[0027] (1) Through scientific analysis, this invention reveals the underlying cause of frequent clogging of hydroentanglement devices in the production of recycled leather. Based on this, a simple and feasible saponification technology route is proposed, which solves the problem of clogging hydroentanglement needles by long-term reuse of circulating water.

[0028] (2) The saponification-precipitation-neutralization integrated facility and its supporting acid and alkali storage tanks and control system of the present invention have a simple structure and clearly defined unit functions. By precisely introducing the key step of saponification reaction, this solution fundamentally eliminates the micron-sized "oil separation" particles that cause blockages, while having almost no disturbance to other stages of the original mature process. This engineering design, which solves the core contradiction with minimal technical variables, ensures the high reliability of the system and lays a solid foundation for large-scale, low-risk promotion and application in the recycled leather and even the entire spunlace nonwoven fabric industry.

[0029] (3) This invention reduces downtime caused by equipment failure, thereby significantly improving the production efficiency of recycled leather. Simultaneously, it enables more efficient and stable recycling of water resources during the recycled leather production process. This not only reduces reliance on fresh water resources and lowers the company's water costs, but also reduces wastewater discharge, which is of positive significance for environmental protection.

[0030] (4) The core of this invention lies in identifying and solving the common technical bottleneck of micron-sized particle blockage caused by the "oil separation" phenomenon in the spunlace process. Its technical principle of completely eliminating soluble oils in water through saponification is also universally applicable to fields such as nonwoven fabrics and medical hygiene materials that widely adopt spunlace reinforcement processes. The production wastewater in these industries generally contains various spinning oils, surfactants, and similar organic substances, and also faces the risk of needle blockage. Therefore, the technical route provided by this invention offers an efficient, reliable, and universally applicable solution to the common problems of the entire spunlace nonwoven industry. Attached Figure Description

[0031] Figure 1 This is a common treatment process for circulating water.

[0032] Figure 2 This describes the generation of particulate matter in the effluent from the circulating water flotation section and after settling.

[0033] Figure 3 Particle size analysis of naturally precipitated particulate matter.

[0034] Figure 4 SEM and EDS analysis of naturally precipitated particulate matter.

[0035] Figure 5 EA analysis of naturally precipitated particulate matter.

[0036] Figure 6 LC-MS analysis of naturally precipitated particulate matter.

[0037] Figure 7 This is a process flow diagram of a circulating water saponification treatment system.

[0038] Figure 8 Schematic diagram of the small-scale experimental setup.

[0039] Figure 9 This represents the water flow rate over 8 months of continuous operation of the hydroentangled needle after saponification (without pH reversion for neutralization).

[0040] Figure 10 The water flow rate of the hydroentangled needle after saponification (pH neutralization) for 8 consecutive months. Detailed Implementation

[0041] Example 1: Investigating the root cause of hydroentanglement needle clogging

[0042] 1) Research on the Causes of Blockage: Circulating water from a recycled leather production plant was tested at different circulation stages. After two stages of air flotation, the suspended solids (SS) concentration was approximately 7 mg / L. After passing through a 0.45 μm filter membrane (transparent), particulate matter was visibly precipitated after 30 days of settling. The SS concentration was then retested and found to be 33.9 mg / L (30-day increase in particulate matter). Detailed water sample test data are shown in Table 1. Experimental verification revealed that the main cause of blockage was the precipitation of a large amount of particulate matter even after the circulating water had circulated or settled for a period of time without entering the hydroentangling process. The particulate matter precipitation status of the effluent from the air flotation section after a certain period of settling is shown in Table 1. Figure 2 .

[0043] Table 1. Overview of Water Quality Parameters

[0044] Note: 1. Data in parentheses represent the re-precipitation of particulate matter after 30 days and 60 days, respectively; 2. Maximum values ​​indicate that no particulate matter was detected in 3 out of 4 water samples.

[0045] 2) Analysis of the composition of naturally precipitated particles: The main components of naturally precipitated particles were identified as synthetic fatliquoring agents added during the leather production process (accompanied by adsorbed organic components such as dyes and proteins, as well as inorganic salts). These compounds are oily compounds with a certain solubility in water. However, with changes in external conditions, oil precipitation will occur (the oily components that were originally uniformly dispersed in the liquid system can no longer be stably dispersed due to the disruption of the system's stable state, thus causing them to aggregate, separate, and precipitate).

[0046] a) Particle size analysis: Naturally precipitated particles were dispersed in pure water, and their size was analyzed using a laser particle size analyzer. The particle size was mainly concentrated between 50 μm and 300 μm, with particles larger than 100 μm accounting for over 70% of the bulk density. The inner diameter of the hydroentangling needle was between 100 and 120 μm. Over time, the continuous accumulation of naturally precipitated particles eventually led to clogging of the hydroentangling needle. The particle size analysis of naturally precipitated particles is as follows: Figure 3 .

[0047] b) SEM and EDS combined analysis: Morphological observation of the naturally precipitated particles from the sedimentation section effluent (after passing through a 0.45 μm filter membrane) and the coagulation and flotation effluent (after passing through a 0.45 μm filter membrane) was performed using SEM. The particles exhibited both crystalline and flocculent structures, and their sizes also varied. The specific elemental composition of the naturally precipitated particles from the two sections is shown in Table 2. Based on the above morphological and surface elemental composition analysis, the composition of the naturally precipitated particles from the different sections was not significantly different, consisting mainly of organic components such as C, O, and S, and inorganic salts such as Na, Mg, Ca, and Cl. SEM and EDS images of the naturally precipitated particles are shown below. Figure 4 The EDS analysis results of the element content of the effluent naturally precipitated after settling in different treatment sections are shown in Table 2.

[0048] Table 2. EDS elemental analysis of naturally precipitated effluent from different treatment stages.

[0049]

[0050] c) Organic Element Analysis: Based on the raw materials and production process of recycled leather, as well as the circulating water treatment process, the possible organic components in the circulating water were analyzed and determined to include dyes, proteins, oils, and polyacrylamide (PAM, flocculant). EA (elemental organic analysis) was performed on the organic components of the naturally precipitated particles. The results showed that the mass ratio of C:N:H:S was approximately 24:4:14:1. Combined with the above wastewater component analysis, the C / N mass ratio of proteins is generally between 2.9 and 3.6, and the C / N mass ratio of PAM is approximately 2.6, with both showing high nitrogen content. The C / N mass ratio of the naturally precipitated particles was close to 6, indicating that the components of the naturally precipitated particles should be mainly oils, dyes, or a combination of both (mass percentage exceeding 50%), with a small amount of sulfur possibly originating from sulfonated dye components. The EA analysis results of the naturally precipitated particles are as follows: Figure 5 .

[0051] d) LC-MS Results Analysis: Content of each substance in positive and negative modes as follows Figure 6 .

[0052] Acid washing of naturally precipitated particles: The pH of the water sample containing naturally precipitated particles was adjusted to 2 and then stirred and washed. It was found that the naturally precipitated particles partially dissolved, and the particle content decreased from 55.3 mg / L before acid washing to 22.0 mg / L, a decrease of about 60%.

[0053] In summary, the main component of naturally precipitated particulate matter is synthetic fatliquoring agents, accounting for about one-third. These are not animal or vegetable oils or petroleum-based substances, and are difficult to biodegrade. They have relatively higher water solubility than ordinary oily substances, resulting in oil precipitation. After oil precipitation, the fatliquoring agents are insoluble in acid. During oil precipitation, acidic dyes, proteins, inorganic salts, and other compounds are adsorbed onto the particle surface; these adsorbed substances can be dissolved by acid washing.

[0054] Example 2: A circulating water treatment method to prevent clogging of hydroentangled needles in recycled leather production.

[0055] By using the original processing system process ( Figure 1 An integrated saponification-sedimentation-neutralization facility and its supporting equipment are added between the air flotation and mechanical filtration sections. This section can be designed as intermittent. Two sets of integrated facilities are installed after the air flotation section, each operating intermittently, with continuous operation of the entire process achieved through automatic valve control. The improved system process flow diagram is shown below. Figure 7 After the entire process starts, valve #1 is opened first, and valve #2 is closed, allowing wastewater to enter facility #1 and gradually fill it (inlet time 2 hours); after 2 hours, valve #1 is closed, and valve #2 is opened, allowing wastewater to enter facility #2 and gradually fill it (inlet time 2 hours). During this period, facility #1 completes saponification, sedimentation, sludge removal, neutralization, drainage, and settling processes (running time 2 hours); after another 2 hours, valve #1 is opened, and valve #2 is closed, allowing water to enter facility #1, while facility #2 continues saponification, sedimentation, sludge removal, neutralization, drainage, and settling processes. This cycle repeats continuously.

[0056] Strong alkali dilute solution: Set up an alkali tank (approximately 1m). 3 Strong alkalis such as sodium hydroxide (NaOH) are dissolved in an alkali tank to a concentration of 1 mol / L. The filtrate and effluent from the clarifier can then be reused for dissolution.

[0057] Acid solution: Set up an acid tank (approximately 1m). 3 Dissolve acids such as hydrochloric acid (HCl) in an acid tank to a concentration of 1 mol / L, and then return the effluent from the clarifier to the tank for further dissolution.

[0058] Integrated facility mixing and pH monitoring system: The integrated facility is equipped with mixing equipment and pH meter electrodes to monitor the pH of wastewater in real time.

[0059] Saponification: A strong alkali solution is gradually pumped into an integrated facility filled with water. The pumping is carried out while stirring and the pH is monitored. When the pH of the wastewater exceeds 12, the pumping of the alkali solution is stopped and stirring is stopped. The reaction time is about 30 minutes.

[0060] Precipitation: Fat additives and other lipids in wastewater react with strong alkalis to produce substances such as sodium fatty acids and glycerol, both with densities greater than 1 g / cm³. 3 A precipitate will form, and the precipitation time shall not be less than 30 minutes.

[0061] Sludge removal: The integrated facility is equipped with a sludge hopper, sludge removal pipe and sludge pipe valve at the bottom. Open the sludge pipe valve to discharge the sludge in the sludge hopper. The sludge removal time is about 15 minutes. After the sludge removal is completed, close the sludge pipe valve.

[0062] Neutralization: The acid solution is gradually pumped into the integrated facility. While pumping, the solution is stirred and the pH is monitored. When the pH of the wastewater is lower than 8, the pumping of the acid solution is stopped and the stirring is stopped. The reaction time is about 15 minutes.

[0063] Drainage: The integrated facility is equipped with a decanter to discharge wastewater from the system to subsequent filtration and other processes. The drainage time is approximately 15 minutes.

[0064] Settling: The facility is left to settle, awaiting the next well water supply. The settling time is approximately 15 minutes.

[0065] Supporting equipment - Plate and frame filter press: used for sludge dewatering, and the filtrate is recycled to the alkali tank to dissolve strong alkali.

[0066] Example 3: Laboratory-scale test (dynamic simulation experiment)

[0067] To verify the feasibility of the saponification treatment scheme of this invention, a simulation device for the treatment process was built in the laboratory for dynamic simulation experiments. The experimental device is as follows: Figure 8 In a laboratory setting, a small-scale test of the above-mentioned invention was conducted. Water samples treated with the above method were subjected to a simulated hydroentanglement dynamic experiment. The electronic constant flow pump used was a Jiapeng DHL-A model, the simulated hydroentanglement needle had an orifice diameter of 100 μm, the pump speed was 10 r / min, the water flow rate was approximately 67 mL / h, and the maximum pressure was 3 kg / cm². 2 .

[0068] On August 20, 2024, a laboratory simulation experiment was conducted. The amount of naturally precipitated particulate matter generated in the effluent after saponification treatment was 0 under all conditions (as of April 25, 2025, no naturally precipitated particulate matter was generated, which has exceeded 8 months).

[0069] 1. After saponification to pH=12, the effluent was filtered through a membrane and allowed to stand until April 25, 2025, with zero naturally precipitated particulate matter. The supernatant from the saponification system was subjected to a simulated hydroentanglement experiment. As of April 25, 2025, it had been running continuously for 8 months without needle clogging, and the flow rate was as follows... Figure 9 .

[0070] 2. After saponification to pH 12, the effluent was filtered through a membrane and then adjusted back to pH 7. After standing until April 25, 2025, the naturally precipitated particulate matter was zero. The supernatant from the saponification system was adjusted back to pH 7 for a simulated hydroentanglement experiment. As of April 25, 2025, it had been running continuously for 8 months without needle clogging, and the flow rate was as follows... Figure 10 .

Claims

1. A circulating water treatment method for preventing clogging of hydroentangled needles in the production of recycled leather, comprising sequentially subjecting wastewater generated in the hydroentanglement and strengthening process to water collection and sedimentation, screen filtration, air flotation, and fine filtration before entering a clarification tank to obtain recycled water, and then subjecting the recycled water in the clarification tank to final purification before re-entering the hydroentanglement and strengthening process, characterized in that... Between the air flotation treatment and the fine filtration treatment, there is also an integrated saponification-sedimentation-neutralization treatment process. This process is achieved through an integrated saponification-sedimentation-neutralization facility. The integrated facility includes a first set of integrated treatment units and a second set of integrated treatment units arranged in parallel and controlled by valve switching. The two sets of integrated treatment units alternately perform water intake, saponification, sedimentation, sludge discharge, neutralization, drainage and settling processes to achieve continuous operation.

2. The circulating water treatment method for preventing clogging of hydroentangled needles in recycled leather production according to claim 1, characterized in that, The saponification process involves pumping the alkali solution into an integrated treatment unit filled with wastewater. While pumping, the solution is stirred and the pH is monitored. When the wastewater pH exceeds 12, the pumping of the alkali solution is stopped and the stirring is stopped. The reaction time is 30 ± 3 minutes.

3. The circulating water treatment method for preventing clogging of hydroentangled needles in recycled leather production according to claim 1, characterized in that, Furthermore, the precipitation process involves reacting lipids in the wastewater with an alkaline solution to form a precipitate, with a precipitation time of no less than 30 minutes.

4. The circulating water treatment method for preventing clogging of hydroentangled needles in recycled leather production according to claim 1, characterized in that, The sludge discharge process involves installing a sludge hopper, sludge discharge pipe, and sludge pipe valve at the bottom of the integrated facility. The sludge in the sludge hopper is discharged by opening the sludge pipe valve. The sludge discharge time is 15±1 minutes. After the sludge discharge is completed, the sludge pipe valve is closed.

5. A circulating water treatment method for preventing clogging of hydroentangled needles in recycled leather production according to claim 1, characterized in that, The neutralization process involves pumping the acid solution into the integrated treatment unit while stirring and monitoring the pH. When the wastewater pH is below 8, the pumping of the acid solution and stirring are stopped. The reaction time is 15 ± 1 min.

6. A circulating water treatment method for preventing clogging of hydroentangled needles in recycled leather production according to claim 1, characterized in that, The drainage process involves installing a decanter within the integrated facility to discharge wastewater from the system to subsequent processes. The drainage time is 15 ± 1 min.

7. A circulating water treatment method for preventing clogging of hydroentangled needles in recycled leather production according to claim 1, characterized in that, The settling process refers to the facility being left to stand still, awaiting the next water intake, for a settling time of 15 ± 1 min.

8. A circulating water treatment method for preventing clogging of hydroentangled needles in recycled leather production according to claim 1, characterized in that, The fine filtration process includes mechanical filtration, sand filtration, and fiber bag filtration in sequence, and the terminal purification process includes mechanical filtration and sand filtration in sequence.

9. A circulating water treatment system for preventing clogging of hydroentangled needles in recycled leather production, comprising, in sequence, a hydroentangled reinforcement process outlet, a sedimentation tank, a screen filter, an air flotation device, a filtration unit, a clarification tank, and a terminal purification unit, characterized in that, The circulating water treatment system further includes an integrated saponification-sedimentation-neutralization facility located between the flotation device and the filtration unit. The integrated saponification-sedimentation-neutralization facility includes a first set of integrated treatment units and a second set of integrated treatment units arranged in parallel and controlled by valve switching. The two sets of integrated treatment units alternately perform water intake, saponification, sedimentation, sludge discharge, neutralization, drainage and settling processes to achieve continuous operation.

10. A circulating water treatment system for preventing clogging of hydroentangled needles in recycled leather production according to claim 9, characterized in that, The aforementioned water collection and sedimentation tank is used for preliminary solid-liquid separation of wastewater generated during the hydroentanglement process, and for settling large-diameter solid particles. The aforementioned screen filtration device is used to trap suspended solids and fibers; The aforementioned air flotation device is equipped with PAC and PAM dosing units, which are used to remove fine suspended matter and fiber flocculation by air flotation. The filtration unit includes a mechanical filtration device, a sand filtration device, and a fiber bag filtration device connected in sequence, used for physical fine filtration of wastewater after flotation treatment; The clarification tank is used to collect water treated by the filtration unit for reuse. The terminal purification unit includes a mechanical filtration device and a sand filtration device arranged in sequence, which are used to purify the effluent from the clarification tank and then return it to the hydroentanglement reinforcement process for reuse.

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