System and process for advanced treatment and resource recycling of printing and dyeing wastewater

Abstract

The application discloses a kind of printing and dyeing wastewater advanced treatment and resource recycling system and process, it is related to printing and dyeing wastewater treatment technical field.System includes quality pretreatment unit, enhanced biochemical treatment unit, membrane concentration unit, membrane concentrated water purification salt separation unit and MVR evaporation crystallization unit.Silky wastewater is recovered concentrated alkali by MVR evaporation;Desizing wastewater is sequentially carried out hydrolysis acidification, AO biochemical, two sedimentation and coagulation precipitation treatment after air floatation and anaerobic pretreatment with comprehensive wastewater, again by ultrafiltration, ion exchange softening and multistage membrane concentration;Membrane concentrated water is obtained by ozone oxidation-carbon filter, nanofiltration, two-stage RO, STRO, integrated hardness removal and MVR evaporation crystallization, and crystallization salt and reclaimed water are obtained.Ion exchange wastewater is directly introduced into tail water regulating tank.The application can reduce the risk of membrane and evaporation system scale formation, realize concentrated alkali recovery, reclaimed water reuse, membrane concentrated water reduction and crystallization salt resource utilization.

Description

Technical Field

[0001] This invention relates to the field of dyeing and printing wastewater treatment technology, and in particular to a system and process for deep treatment and resource recycling of dyeing and printing wastewater. Background Technology

[0002] As a high-water-consuming and high-emission industry, the dyeing and printing industry generates 15%-20% of total industrial wastewater discharge. Dyeing and printing wastewater typically contains dyes, sizing agents, auxiliaries, surfactants, alkalis, inorganic salts, and recalcitrant organic matter. It is characterized by large volume, high color, high chemical oxygen demand (COD), high salinity, and poor biodegradability, making it challenging to treat. With increasingly stringent requirements for industrial water conservation and pollutant discharge control, dyeing and printing enterprises not only need to meet conventional pollutant discharge standards but also need to improve their internal wastewater recycling levels and reduce fresh water intake and external discharge.

[0003] Currently, dyeing and printing enterprises typically reuse non-process wastewater such as condensate directly, reuse some low-concentration wastewater or wastewater with good treated quality in the production system, and use the rest for processes with lower water quality requirements, such as plant landscaping and workshop washing. To further improve the reuse rate, dyeing and printing wastewater usually needs to undergo further advanced treatment after comprehensive treatment to meet the process water requirements of dyeing and finishing production. In existing technologies, advanced treatment of dyeing and printing wastewater often adopts a dual-membrane process combining ultrafiltration (UF) and reverse osmosis (RO). This process can obtain recycled water with good water quality and can improve the reuse rate of reclaimed water to a certain extent. However, while producing high-quality recycled water, the ultrafiltration-reverse osmosis dual-membrane process also generates a certain amount of membrane concentrate. Membrane concentrate has a high total salt content and is enriched with residual dyes, auxiliaries, recalcitrant organic matter, and easily scale-forming ions, making subsequent treatment more difficult. Because GB4287-2012 "Water Pollutant Discharge Standard for Textile Dyeing and Finishing Industry" has not set a unified mandatory discharge limit for total salinity, some enterprises typically only treat conventional pollutants such as chemical oxygen demand in the membrane concentrate to meet standards before discharging them, without effectively controlling the total salinity. With increasingly stringent environmental policies, some regions and river basins have begun to control the total salinity of wastewater, and the traditional dual-membrane method is no longer sufficient to solve the problems of high total salinity in membrane concentrate and the significant risk of excessive salinity in discharged wastewater.

[0004] In the prior art, CN107445406A discloses a method and system for the resource-based treatment of textile dyeing and printing wastewater, which utilizes an equalization tank-hydrolysis acidification tank-aerobic tank-secondary sedimentation tank-MBR reactor-RO system-DTRO system-MVR evaporator to achieve wastewater reduction and partial water resource recovery. However, the concentrate produced after membrane treatment of dyeing and printing wastewater usually contains organic pollutants, inorganic salts, hardness ions, and other impurities. If the membrane concentrate is not purified for organic matter, desalinated, and dehardened before evaporation and crystallization, and is directly sent to the MVR evaporator for evaporation and crystallization, the pollutants and impurities in the membrane concentrate may be further enriched during the evaporation and concentration process and may be carried or mixed into the crystallized salt. This results in a complex composition and low purity of the crystallized salt, making it difficult to achieve resource utilization. Furthermore, the high content of harmful substances may lead to its identification as hazardous waste, thereby increasing the difficulty and cost of subsequent treatment of the crystallized salt.

[0005] Therefore, it is necessary to develop a system and process for the deep treatment and resource reuse of dyeing and printing wastewater, which can reduce the risk of excessive total salt content in the effluent, while obtaining reclaimed water that can be reused in dyeing and printing production and crystalline salt that can be utilized for resource recovery, thereby realizing the reuse of water in dyeing and printing wastewater, reduction of membrane concentrate, and resource recovery of water and salt co-production. Summary of the Invention

[0006] The purpose of this invention, in view of the aforementioned existing technologies, is to provide a system and process for the deep treatment and resource recycling of dyeing and printing wastewater. The system includes a pretreatment unit, an enhanced biochemical treatment unit, a membrane concentration unit, a membrane concentrate purification and salt separation unit, and an MVR evaporation and crystallization unit. Mercerizing wastewater undergoes MVR evaporation to recover concentrated alkali; desizing wastewater, after air flotation and anaerobic pretreatment, is sequentially treated with combined wastewater through hydrolysis acidification, AO biochemical treatment, secondary sedimentation, and coagulation sedimentation, followed by ultrafiltration, ion exchange softening, and multi-stage membrane concentration; the membrane concentrate undergoes ozone oxidation-carbon filtration, nanofiltration, two-stage RO, STRO, integrated hardening removal, and MVR evaporation and crystallization to obtain reclaimed water and crystalline salts. Ion exchange wastewater from production is directly discharged into the tailwater equalization tank. This invention reduces the risk of scaling in the membrane and evaporation system, achieving concentrated alkali recovery, reclaimed water reuse, membrane concentrate reduction, and resource utilization of crystalline salts.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a system for the advanced treatment and resource recycling of dyeing and printing wastewater, comprising a pretreatment unit, an enhanced biochemical treatment unit, a membrane concentration unit, a membrane concentrate purification and desalination unit, and an MVR evaporation and crystallization unit; wherein, The separate pretreatment unit includes an alkali recovery branch for treating mercerizing wastewater, a desizing pretreatment branch for treating desizing wastewater, and a comprehensive wastewater pretreatment branch. The alkali recovery branch includes a mercerizing wastewater collection tank, an MVR evaporation alkali recovery device, and a concentrated alkali recovery tank connected in sequence; the desizing pretreatment branch includes a desizing wastewater collection tank, a desizing wastewater flotation device, and an anaerobic reaction device connected in sequence; the integrated wastewater pretreatment branch includes a total water collection tank and an integrated wastewater flotation device connected in sequence. The enhanced biochemical treatment unit includes an equalization tank and a hydrolysis acidification tank, an AO biochemical tank, a secondary sedimentation tank, and a mixed sedimentation tank arranged along the water flow direction; the equalization tank is connected to a comprehensive wastewater collection tank and an anaerobic reactor, respectively, and is used to receive comprehensive wastewater and pretreated desizing wastewater. The membrane concentration unit includes an intermediate water tank, an ultrafiltration tank, an ion exchange resin softening device, a first-stage RO tank, and an RO concentrate tank connected in sequence; the intermediate water tank is connected to the outlet of the sedimentation tank. The membrane concentrate purification and desalination unit includes an ozone oxidation-carbon filtration device, a nanofiltration device, a two-stage RO tank, a STRO membrane concentration device, and a STRO concentrate tank connected in sequence; the ozone oxidation-carbon filtration device is connected to the outlet of the RO concentrate tank. The MVR evaporation and crystallization unit includes an integrated hardening removal device and an MVR evaporation and crystallization device. The integrated hardening removal device is located between the STRO concentrate tank and the MVR evaporation and crystallization device and is used to remove hardness from the STRO concentrate before it enters the MVR evaporation and crystallization device.

[0008] Preferably, the system for deep treatment and resource reuse of dyeing and printing wastewater further includes a production ion exchange wastewater tank, a greywater reuse tank, and a tailwater equalization tank; wherein... The outlets of the first-stage RO tank, nanofiltration device, second-stage RO tank, STRO membrane concentration device, and MVR evaporation crystallization device are all connected to the greywater reuse tank. The outlet of the production ion exchange wastewater tank is connected to the tailwater equalization tank. The production ion exchange wastewater has low COD and ammonia nitrogen pollutant content and high hardness. This part of the wastewater is directly discharged into the tailwater equalization tank, which greatly reduces the risk of scale formation in the membrane system and enhances its operational stability. The greywater reuse tank is connected to the tailwater regulating tank via a pipeline. When the total salinity of the effluent is too high, the low-salt recycled water in the greywater reuse tank is introduced into the tailwater regulating tank for adjustment, so as to reduce the risk of the total salinity of the effluent exceeding the standard.

[0009] Preferably, the MVR evaporation crystallization apparatus is further provided with a crystallization salt outlet, which is connected to a crystallization salt collection device for collecting the crystallization salt obtained from evaporation crystallization.

[0010] Preferably, the anaerobic reactor is a UASB anaerobic reactor; through anaerobic metabolism, organic matter is decomposed into methane and carbon dioxide, significantly reducing its COD and improving its biodegradability.

[0011] Preferably, both the desizing wastewater flotation device and the integrated wastewater collection tank are equipped with a screen at the inlet to remove larger foreign objects such as waste cloth scraps and wool fibers from the wastewater; the screen includes a coarse screen and a fine screen, with the spacing between the fine screen bars not exceeding 2mm.

[0012] Preferably, the integrated wastewater flotation device is a dissolved air flotation device, which includes a PAC dosing device, a PAM dosing device, and a ferrous sulfate dosing device connected in sequence. These devices are used to add coagulants, coagulant aids, and flocculation regulators to the integrated wastewater to promote the flocculation, aggregation, and flotation removal of suspended solids, colloidal substances, fiber debris, and some organic pollutants in the desizing wastewater.

[0013] Preferably, a cooling tower and a cross-line pipeline are provided between the regulating tank and the hydrolysis acidification tank. The outlet of the regulating tank is connected to both the cooling tower and the cross-line pipeline, and the outlets of both the cooling tower and the cross-line pipeline are connected to the hydrolysis acidification tank. A water temperature detection device is installed at the outlet of the regulating tank. When the wastewater temperature is higher than 36°C, the effluent from the regulating tank is cooled by the cooling tower before entering the hydrolysis acidification tank. When the wastewater temperature is not higher than 36°C, the effluent from the regulating tank directly enters the hydrolysis acidification tank through the cross-line pipeline.

[0014] Preferably, the hydrolysis acidification tank is equipped with a reflux water collection system and a reflux water inlet tank. The outlet of the hydrolysis acidification tank is connected to the AO biochemical tank and the reflux water collection system respectively. The reflux water collection system is connected to the inlet of the hydrolysis acidification tank via the reflux water inlet tank, so that a portion of the effluent from the hydrolysis acidification tank is collected by the reflux water collection system and returned to the reflux water inlet tank, where it is mixed with the inlet water of the hydrolysis acidification tank and then enters the hydrolysis acidification tank.

[0015] Preferably, the sedimentation tank is connected to a PAC dosing device and a PAM dosing device for coagulation and sedimentation treatment of the effluent from the secondary sedimentation tank; the hydrolysis acidification tank, AO biological treatment tank, secondary sedimentation tank and sedimentation tank are all configured as two sets of parallel structures to improve the system's operational reliability, operational flexibility and shock resistance.

[0016] Preferably, the ultrafiltration tank is equipped with a curtain-type ultrafiltration membrane, which is made of modified polyvinylidene fluoride (PVDF) and has a filtration accuracy of 0.3 μm.

[0017] A second aspect of the present invention provides a process for deep treatment and resource recycling of dyeing and printing wastewater, comprising the following steps: (1) The dyeing and printing wastewater is pretreated separately. The mercerizing wastewater is treated by MVR evaporation and alkali recovery to collect concentrated alkali. The desizing wastewater is treated by air flotation and anaerobic treatment in sequence to obtain pretreated desizing wastewater. (2) After mixing the comprehensive wastewater and the pretreated desizing wastewater, homogenization treatment is carried out, followed by hydrolysis acidification treatment, AO biochemical treatment, secondary sedimentation treatment and coagulation sedimentation treatment to obtain effluent. (3) The effluent from the sedimentation process is successively treated by ultrafiltration, softened by ion exchange resin, and treated by a first-stage reverse osmosis to obtain a first-stage reverse osmosis permeate and a first-stage reverse osmosis concentrate. (4) The first stage of reverse osmosis concentrate is treated by ozone oxidation-carbon filtration, nanofiltration, second stage reverse osmosis and STRO membrane concentration to obtain STRO concentrate and STRO permeate; at the same time, nanofiltration permeate and second stage reverse osmosis permeate are also generated during the nanofiltration and second stage reverse osmosis processes. (5) The STRO concentrate is subjected to integrated hardness removal treatment and MVR evaporation and crystallization treatment to obtain MVR permeate and crystalline salt; (6) The permeate from the first stage of reverse osmosis, nanofiltration, second stage of reverse osmosis, STRO, and MVR is collected in the wastewater reuse tank and reused in dyeing and finishing production. When the wastewater in the wastewater reuse tank does not meet the requirements for reuse in dyeing and finishing production, it is transported to the tailwater equalization tank. At the same time, the production ion exchange wastewater is directly transported to the tailwater equalization tank, and after being mixed and tested, it is discharged.

[0018] The beneficial effects of this invention are: 1. This invention constructs a system that integrates pretreatment with different grades, enhanced biochemical treatment, antifouling membrane concentration, and MVR evaporation and crystallization to achieve water reuse, concentrated alkali recovery, resource utilization of crystalline salts, and control of total salt content in wastewater from dyeing and printing. The pretreatment with different grades includes air flotation pretreatment of desizing wastewater, MVR alkali concentration and recovery of mercerizing wastewater, and cross-discharge of ion exchange wastewater to the end of the system. The enhanced biochemical treatment includes hydrolysis acidification, AO biochemical treatment, and coagulation sedimentation to reduce COD and BOD in the wastewater, remove color, and achieve nitrogen and phosphorus removal. The antifouling membrane concentration treatment includes ultrafiltration, reverse osmosis, nanofiltration, STRO membrane concentration, and ozone oxidation-carbon filtration devices to produce reusable water for dyeing and finishing processes and to remove COD and harmful substances from the membrane concentrate. The MVR evaporation and crystallization includes an integrated hardening removal device and an MVR evaporation and crystallization device to produce crystalline salts for resource reuse as dyeing promoters.

[0019] 2. This invention classifies and treats mercerizing wastewater, desizing wastewater, production ion exchange wastewater, and general wastewater according to their sources and water quality characteristics. Specifically, mercerizing wastewater is concentrated into concentrated alkali using an MVR evaporation alkali recovery device, which can be reused in the mercerizing process, achieving alkali resource recovery. Desizing wastewater undergoes flotation and anaerobic reaction treatment, effectively reducing high COD load and improving wastewater biodegradability. Production ion exchange wastewater, characterized by high total salt content and hardness, is directly discharged into the tailwater equalization tank, bypassing the general wastewater treatment and membrane concentration systems, thus reducing the scaling impact of high-hardness water on the membrane and evaporation systems. This differentiated treatment approach reduces the processing pressure on subsequent biological treatment, membrane treatment, and evaporation crystallization systems, improving system operational stability.

[0020] 3. This invention incorporates a reflux water collection system and a reflux inlet tank within the hydrolysis acidification tank. A portion of the effluent from the hydrolysis acidification tank is collected by the reflux water collection system and then returned to the reflux inlet tank, where it mixes with the influent before re-entering the hydrolysis acidification tank. This structure effectively dilutes and homogenizes high-concentration influent, reducing the instantaneous concentration of pollutants entering the hydrolysis acidification system and mitigating the impact of water quality fluctuations on the hydrolysis acidification microbial system. This, in turn, improves the hydrolysis acidification tank's resistance to shock loads and its operational stability.

[0021] 4. This invention improves the removal efficiency of organic matter, color, nitrogen, phosphorus, and suspended pollutants in wastewater through a combination of hydrolysis acidification, AO biochemical treatment, secondary sedimentation, coagulation sedimentation, and enhanced biochemical-physicochemical treatment. Specifically, hydrolysis acidification converts large, recalcitrant organic molecules into smaller ones, improving the wastewater's biodegradability; AO biochemical treatment further removes COD and BOD and achieves nitrogen and phosphorus removal; the secondary sedimentation tank separates sludge from water; and the coagulation sedimentation tank further removes residual colloids, suspended solids, and some dissolved pollutants using PAC, PAM, and other agents. This combined treatment improves the water quality entering the subsequent membrane system, reduces the risk of membrane fouling, and ensures the stable operation of the subsequent membrane concentration system.

[0022] 5. This invention incorporates an ion exchange resin softening device before the first-stage RO tank to remove scale-forming ions such as calcium and magnesium from wastewater, reducing the scaling risk of membrane systems such as RO, nanofiltration, second-stage RO, and STRO. Simultaneously, an integrated hardness removal device is installed before the MVR evaporation and crystallization unit to further remove calcium and magnesium ions and other easily scale-forming components from the STRO concentrate, further reducing the scaling risk of the MVR evaporator. Furthermore, the production ion exchange wastewater does not enter the membrane concentration system, reducing the impact of high-hardness wastewater on the membrane and evaporation systems. This extends the operating cycle of the membrane modules and evaporators, reducing cleaning frequency and maintenance costs. Therefore, this invention, through its multi-node hardness removal design, reduces the scaling risk of membrane systems and MVR evaporation and crystallization systems.

[0023] 6. This invention utilizes a four-stage membrane concentration system consisting of a first-stage RO, nanofiltration, a second-stage RO, and a STRO to progressively concentrate and reduce the volume of membrane concentrate, thereby decreasing the amount of water entering the MVR evaporation and crystallization system, thus lowering the evaporation load and operating costs. Simultaneously, placing the ozone advanced oxidation-carbon filtration system after the first-stage RO concentrate and before the nanofiltration unit reduces the COD, TOC, and harmful organic matter content in the concentrate, improves the influent conditions for nanofiltration desalination, second-stage RO, STRO, and MVR evaporation and crystallization, and increases the likelihood of non-hazardous waste disposal and resource recovery of the final crystallized salt. Furthermore, an overflow drain pipe in the intermediate water tank allows for flexible adjustment of the external drainage and reclaimed water ratio according to total salt discharge requirements and reclaimed water needs, and allows for selective operation of some membrane treatment units, thereby improving system operational flexibility and reducing operating costs. Attached Figure Description

[0024] Figure 1 Schematic diagram of a system for advanced treatment and resource recycling of dyeing and printing wastewater. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0026] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0027] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0028] Example 1: This embodiment provides a system for the advanced treatment and resource recycling of dyeing and printing wastewater, such as... Figure 1 As shown.

[0029] The system for advanced treatment and resource recovery of dyeing and printing wastewater includes a pretreatment unit, an enhanced biochemical treatment unit, a membrane concentration unit, a membrane concentrate purification and desalination unit, and an MVR evaporation and crystallization unit; wherein... The separate pretreatment unit includes an alkali recovery branch for treating mercerizing wastewater and a desizing pretreatment branch for treating desizing wastewater. The alkali recovery branch includes a mercerizing wastewater collection tank, an MVR evaporation alkali recovery device, and a concentrated alkali recovery tank connected in sequence; the desizing pretreatment branch includes a desizing wastewater collection tank, a desizing wastewater flotation device, and an anaerobic reactor connected in sequence; the anaerobic reactor is a UASB anaerobic reactor, which decomposes organic matter into methane and carbon dioxide through anaerobic metabolism, significantly reducing its COD and improving its biodegradability; a screen is installed before the inlet of the desizing wastewater flotation device to remove large-sized foreign objects such as waste fabric scraps and wool fibers from the wastewater; the screen includes a coarse screen and a fine screen, with the spacing between the fine screen bars not exceeding 2mm; The enhanced biological treatment unit includes an equalization tank and, sequentially arranged along the water flow direction, a hydrolysis acidification tank, an AO biological treatment tank, a secondary sedimentation tank, and a mixed sedimentation tank. The AO biological treatment tank is used to perform anoxic-aerobic biological treatment on the hydrolyzed and acidified wastewater to remove COD and BOD and achieve nitrogen and phosphorus removal. The secondary sedimentation tank is used to separate mud and water in the effluent from the AO biological treatment tank. The mixed sedimentation tank is connected to a PAC dosing device and a PAM dosing device for coagulation and sedimentation treatment of the effluent from the secondary sedimentation tank, further removing colloidal substances, suspended solids, and some dissolved pollutants. The hydrolysis acidification tank, AO biological treatment tank, secondary sedimentation tank, and mixed sedimentation tank are all configured in two parallel structures to improve the system's operational reliability, operational flexibility, and shock resistance. The equalization tank is connected to both the integrated wastewater collection tank and the anaerobic reactor. It receives integrated wastewater and desizing wastewater treated by the desizing pretreatment branch, and adjusts the water quality and quantity. A screen is installed before the inlet of the integrated wastewater collection tank to remove large-sized foreign objects. A dissolved air flotation (DAF) device is also installed between the equalization tank and the integrated wastewater collection tank. This DAF device includes PAC, PAM, and ferrous sulfate dosing devices connected in sequence. These devices are used to add coagulants, coagulant aids, and flocculants to the integrated wastewater to promote the flocculation and flotation removal of suspended solids, colloidal substances, fiber fragments, and some organic pollutants in the desizing wastewater. A cooling tower and cross-line pipeline are connected between the equalization tank and the hydrolysis acidification tank. The outlet of the equalization tank is connected to the cooling tower. The cooling tower and the outlet of the cross-line pipeline are both connected to the hydrolysis acidification tank. A water temperature detection device is installed at the outlet of the regulating tank. When the wastewater temperature is higher than 36℃, the effluent from the regulating tank is cooled by the cooling tower before entering the hydrolysis acidification tank. When the wastewater temperature is not higher than 36℃, the effluent from the regulating tank directly enters the hydrolysis acidification tank via the cross-line pipeline. Furthermore, the hydrolysis acidification tank is equipped with a reflux collection system and a reflux inlet pool. The outlet of the hydrolysis acidification tank is connected to both the AO biological treatment tank and the reflux collection system. The reflux collection system is connected to the inlet of the hydrolysis acidification tank via the reflux inlet pool, allowing a portion of the effluent from the hydrolysis acidification tank to be collected by the reflux collection system and returned to the reflux inlet pool, where it mixes with the inlet water before entering the hydrolysis acidification tank. This reduces the concentration of pollutants entering the hydrolysis acidification tank and the instantaneous impact load, thereby improving the shock resistance of the hydrolysis acidification tank. The membrane concentration unit includes, in sequence, an intermediate water tank, an ultrafiltration tank, an ion exchange resin softening device, a first-stage RO tank, and an RO concentrate tank. The intermediate water tank is connected to the outlet of the sedimentation tank and is used to receive the effluent from the sedimentation tank. An overflow drain pipe is provided on the intermediate water tank, and when the total salinity of the wastewater meets the discharge requirements, part of the effluent from the intermediate water tank can be directly discharged to the municipal sewage system through the overflow drain pipe. The ultrafiltration tank is equipped with a curtain-type ultrafiltration membrane, which is made of modified polyvinylidene fluoride (PVDF) material and has a filtration accuracy of 0.3 μm. The ultrafiltration tank is used to remove fine suspended solids, colloidal substances, and macromolecular pollutants from the sedimentation effluent. The filtered water enters the ion exchange resin softening device, which is used to remove scale-forming ions such as calcium and magnesium from the wastewater, reducing the risk of scaling in the subsequent membrane system. The softened wastewater enters the first-stage RO tank, the product water end of which is connected to the reclaimed water tank, and the concentrate end of the first-stage RO tank is connected to the RO concentrate tank. The membrane concentrate purification and desalination unit includes an ozone oxidation-carbon filtration device, a nanofiltration device, a two-stage RO tank, a STRO membrane concentration device, and a STRO concentrate tank connected in sequence. The ozone oxidation-carbon filtration device is connected to the outlet of the RO concentrate tank and is used to reduce organic matter and perform adsorption filtration on the first-stage RO concentrate. The ozone oxidation-carbon filtration device includes an ozone generator, an ozone reaction tower, an ozone exhaust gas destroyer, a carbon filtration system, and a carbon filtration product water tank. The carbon filtration system uses activated carbon as the filter media, and the carbon filtration product water tank is connected to the nanofiltration device. The nanofiltration device is used to process the ozone oxidation-carbon filtration treated water. The concentrate is then subjected to salt separation treatment. The product water end of the nanofiltration unit is connected to the reclaimed water tank, and the concentrate end of the nanofiltration unit is connected to the second-stage RO tank via the nanofiltration concentrate tank. The second-stage RO tank is used to further concentrate the nanofiltration concentrate. The product water end of the second-stage RO tank is connected to the reclaimed water tank, and the concentrate end of the second-stage RO tank is connected to the STRO membrane concentration unit via the second-stage RO concentrate tank. The STRO membrane concentration unit is used to highly concentrate the second-stage RO concentrate. The product water end of the STRO membrane concentration unit is connected to the reclaimed water tank, and the concentrate end of the STRO membrane concentration unit is connected to the STRO concentrate tank. The MVR evaporation crystallization unit includes an integrated hardness removal device and an MVR evaporation crystallization device. The integrated hardness removal device is located between the STRO concentrate tank and the MVR evaporation crystallization device, and is used to remove hardness from the STRO concentrate before it enters the MVR evaporation crystallization device. The integrated hardness removal device is connected to a sodium hydroxide dosing device, a sodium carbonate dosing device, a PAC dosing device, and a PAM dosing device to remove calcium and magnesium hardness ions and suspended particles from the STRO concentrate. The integrated hardness removal device is also connected to a silica removal agent dosing device, which can remove silica-based scaling components according to the quality of the STRO concentrate, thereby reducing the risk of scaling inside the MVR evaporator. The hardness-removed STRO concentrate enters the MVR evaporator for evaporation and concentration. The evaporated concentrate enters a thickener for thickening and then enters a centrifuge for solid-liquid separation to obtain MVR permeate and crystallized salt. The MVR evaporation crystallization device has a crystallized salt outlet, which is connected to a crystallized salt collection device to collect the crystallized salt obtained from evaporation and crystallization. The system for deep treatment and resource reuse of dyeing and printing wastewater also includes a production ion exchange wastewater tank, a greywater reuse tank, and a tailwater equalization tank. The effluent outlets of the first-stage RO tank, nanofiltration device, second-stage RO tank, STRO membrane concentration device, and MVR evaporation crystallization device are all connected to the greywater reuse tank. The effluent outlet of the production ion exchange wastewater tank is connected to the tailwater equalization tank. The production ion exchange wastewater has low levels of pollutants such as COD and ammonia nitrogen, but mainly exhibits high total salinity and hardness. Therefore, this part of the wastewater does not enter the integrated wastewater treatment system but is directly mixed in the tailwater equalization tank before being discharged, in order to reduce the scaling load on the integrated treatment system and the membrane concentration system. The greywater reuse tank is connected to the tailwater equalization tank through a pipeline. When the total salinity of the discharged water is too high, the low-salt recycled water in the greywater reuse tank is introduced into the tailwater equalization tank for mixing, thereby reducing the risk of excessive total salinity in the discharged water.

[0030] Example 2: This embodiment, based on the system in Embodiment 1, provides a process for deep treatment and resource recycling of dyeing and printing wastewater, including the following steps: (1) Perform separate pretreatment on the dyeing and printing wastewater; Mercerizing wastewater is transported to a mercerizing wastewater collection tank for storage and subsequent evaporation to recover alkali. The mercerizing wastewater is then subjected to MVR evaporation alkali recovery device for evaporation and concentration treatment to obtain recovered concentrated alkali. The recovered concentrated alkali is collected in a concentrated alkali recovery tank and reused in the mercerizing process. The desizing wastewater is transported to a desizing wastewater collection tank and then sequentially passed through a desizing wastewater flotation device and an anaerobic reactor for flotation and anaerobic treatment. The flotation device removes suspended solids, colloidal substances, fiber debris, and some organic pollutants from the desizing wastewater, while the anaerobic reaction reduces the COD load and improves its biodegradability, resulting in pretreated desizing wastewater. (2) The combined wastewater is transported to the combined wastewater collection tank, and after being treated by the combined wastewater flotation device, it is transported to the equalization tank; the pretreated desizing wastewater and the combined wastewater after flotation are mixed in the equalization tank and homogenized; the effluent from the equalization tank is passed through the hydrolysis acidification tank, AO tank, secondary sedimentation tank and coagulation sedimentation tank in sequence for hydrolysis acidification treatment, AO biochemical treatment, secondary sedimentation treatment and coagulation sedimentation treatment to obtain coagulated effluent; During the hydrolysis acidification process, part of the effluent from the hydrolysis acidification tank is returned to the return inlet tank via the return water collection system, and mixed with the inlet water of the hydrolysis acidification tank before re-entering the hydrolysis acidification tank, in order to reduce the concentration of pollutants entering the hydrolysis acidification system and improve the shock load resistance of the hydrolysis acidification tank. (3) The effluent from the sedimentation is transported to the intermediate water tank. The effluent from the intermediate water tank flows sequentially through the ultrafiltration tank, the ion exchange resin softening device, the first-stage RO tank for ultrafiltration treatment, the ion exchange resin softening treatment, and the first-stage reverse osmosis treatment to obtain the first-stage reverse osmosis permeate and the first-stage reverse osmosis concentrate. The first-stage reverse osmosis concentrate enters the RO concentrate tank for further treatment, and the first-stage reverse osmosis permeate directly enters the greywater reuse tank. The ultrafiltration tank is used to remove fine suspended solids, colloidal substances and macromolecular pollutants from the effluent. The filtered water enters the ion exchange resin softening device, which is used to remove scale-forming ions such as calcium and magnesium from the wastewater, reducing the risk of scaling in the subsequent membrane system. (4) The first-stage reverse osmosis concentrate enters the ozone oxidation-carbon filtration unit for ozone oxidation-carbon filtration treatment to reduce the COD, TOC, color and content of recalcitrant organic pollutants in the first-stage reverse osmosis concentrate. Then it enters the nanofiltration unit for nanofiltration desalination treatment to obtain nanofiltration permeate and nanofiltration concentrate. The nanofiltration concentrate enters the second-stage RO tank for second-stage reverse osmosis treatment to obtain second-stage reverse osmosis permeate and second-stage reverse osmosis concentrate. The second-stage reverse osmosis concentrate is concentrated by the STRO membrane to obtain STRO concentrate and STRO permeate. (5) The STRO concentrate is sent to an integrated hardness removal device for integrated hardness removal treatment to remove calcium and magnesium ions and easily scale-forming components in the STRO concentrate, thereby reducing the risk of scaling during the MVR evaporation and crystallization process; then the hardness-removed STRO concentrate is sent to an MVR evaporation and crystallization device for evaporation, concentration and crystallization treatment to obtain MVR permeate and crystallized salt. (6) The permeate from the first stage of reverse osmosis, nanofiltration, second stage reverse osmosis, STRO, and MVR is collected and reused in the greywater reuse tank. When the total salinity of the greywater is too high and does not meet the requirements for reuse in production, it is transported to the tailwater equalization tank. The production ion exchange wastewater has low COD and ammonia nitrogen content, but mainly has high total salinity and hardness. It is directly sent to the tailwater equalization tank and does not enter the integrated wastewater treatment and membrane concentration system. It is directly transported to the tailwater equalization tank, which avoids the impact of hardness on the membrane, greatly reduces the risk of scaling, and improves the operational stability of the membrane system. The reclaimed water from the wastewater reuse tank is mixed with the production ion exchange wastewater in the tailwater equalization tank to reduce the total salt content, thereby avoiding the risk of excessive total salt content in the discharged water.

[0031] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A system for deep treatment and resource recycling of dyeing and printing wastewater, characterized in that, It includes a pretreatment unit, an enhanced biochemical treatment unit, a membrane concentration unit, a membrane concentrate purification and desalination unit, and an MVR evaporation and crystallization unit; among which, The separate pretreatment unit includes an alkali recovery branch for treating mercerizing wastewater, a desizing pretreatment branch for treating desizing wastewater, and a comprehensive wastewater pretreatment branch. The alkali recovery branch includes a mercerizing wastewater collection tank, an MVR evaporation alkali recovery device, and a concentrated alkali recovery tank connected in sequence; the desizing pretreatment branch includes a desizing wastewater collection tank, a desizing wastewater flotation device, and an anaerobic reaction device connected in sequence; the integrated wastewater pretreatment branch includes a total water collection tank and an integrated wastewater flotation device connected in sequence. The enhanced biochemical treatment unit includes an equalization tank and a hydrolysis acidification tank, an AO biochemical tank, a secondary sedimentation tank, and a mixed sedimentation tank arranged along the water flow direction; the equalization tank is connected to a comprehensive wastewater collection tank and an anaerobic reactor, respectively, and is used to receive comprehensive wastewater and pretreated desizing wastewater. The membrane concentration unit includes an intermediate water tank, an ultrafiltration tank, an ion exchange resin softening device, a first-stage RO tank, and an RO concentrate tank connected in sequence; the intermediate water tank is connected to the outlet of the sedimentation tank. The membrane concentrate purification and desalination unit includes an ozone oxidation-carbon filtration device, a nanofiltration device, a two-stage RO tank, a STRO membrane concentration device, and a STRO concentrate tank connected in sequence; the ozone oxidation-carbon filtration device is connected to the outlet of the RO concentrate tank. The MVR evaporation and crystallization unit includes an integrated hardening removal device and an MVR evaporation and crystallization device. The integrated hardening removal device is located between the STRO concentrate tank and the MVR evaporation and crystallization device and is used to remove hardness from the STRO concentrate before it enters the MVR evaporation and crystallization device.

2. The system for deep treatment and resource recovery of dyeing and printing wastewater as described in claim 1, characterized in that, The system for deep treatment and resource reuse of dyeing and printing wastewater also includes a production ion exchange wastewater tank, a reclaimed water tank, and a tailwater regulating tank. The outlets of the first-stage RO tank, nanofiltration device, second-stage RO tank, STRO membrane concentration device, and MVR evaporation crystallization device are all connected to the greywater reuse tank; the outlet of the production ion exchange wastewater tank is connected to the tailwater regulating tank; and the greywater reuse tank is connected to the tailwater regulating tank via a pipeline.

3. The system for deep treatment and resource recovery of dyeing and printing wastewater as described in claim 1, characterized in that, The MVR evaporation crystallization apparatus is also equipped with a crystallized salt outlet, which is connected to a crystallized salt collection device for collecting the crystallized salt obtained from evaporation crystallization.

4. The system for deep treatment and resource recovery of dyeing and printing wastewater as described in claim 1, characterized in that, Both the desizing wastewater flotation device and the integrated wastewater collection tank are equipped with screens at their inlets; the screens include coarse screens and fine screens, with the spacing between the fine screen bars not exceeding 2mm.

5. The system for deep treatment and resource recovery of dyeing and printing wastewater as described in claim 1, characterized in that, The integrated wastewater flotation device is a dissolved air flotation device.

6. The system for deep treatment and resource recovery of dyeing and printing wastewater as described in claim 1, characterized in that, A cooling tower and a cross-line pipeline are provided between the regulating tank and the hydrolysis acidification tank. The water outlet of the regulating tank is connected to the cooling tower and the cross-line pipeline respectively. The water outlets of the cooling tower and the cross-line pipeline are both connected to the hydrolysis acidification tank.

7. The system for deep treatment and resource recovery of dyeing and printing wastewater as described in claim 1, characterized in that, The hydrolysis acidification tank is equipped with a reflux water collection system and a reflux inlet tank. The outlet of the hydrolysis acidification tank is connected to the AO biochemical tank and the reflux water collection system respectively. The reflux water collection system is connected to the inlet of the hydrolysis acidification tank through the reflux inlet tank, so that a part of the effluent from the hydrolysis acidification tank is collected by the reflux water collection system and returned to the reflux inlet tank, and mixed with the inlet of the hydrolysis acidification tank before entering the hydrolysis acidification tank.

8. The system for deep treatment and resource recovery of dyeing and printing wastewater as described in claim 1, characterized in that, The sedimentation tank is connected to a PAC dosing device and a PAM dosing device; the hydrolysis acidification tank, AO biochemical tank, secondary sedimentation tank and sedimentation tank are all configured as two sets of parallel structures.

9. A process for deep treatment and resource recycling of dyeing and printing wastewater using the system described in any one of claims 1-8, characterized in that, Includes the following steps: (1) The dyeing and printing wastewater is pretreated separately. The mercerizing wastewater is treated by MVR evaporation and alkali recovery to collect concentrated alkali. The desizing wastewater is treated by air flotation and anaerobic treatment in sequence to obtain pretreated desizing wastewater. (2) After mixing the comprehensive wastewater and the pretreated desizing wastewater, homogenization treatment is carried out, followed by hydrolysis acidification treatment, AO biochemical treatment, secondary sedimentation treatment and coagulation sedimentation treatment to obtain effluent. (3) The effluent from the sedimentation process is successively treated by ultrafiltration, softened by ion exchange resin, and treated by a first-stage reverse osmosis to obtain a first-stage reverse osmosis permeate and a first-stage reverse osmosis concentrate. (4) The first stage of reverse osmosis concentrate is treated by ozone oxidation-carbon filtration, nanofiltration, second stage reverse osmosis and STRO membrane concentration to obtain STRO concentrate and STRO permeate; at the same time, nanofiltration permeate and second stage reverse osmosis permeate are also generated during the nanofiltration and second stage reverse osmosis processes. (5) The STRO concentrate is subjected to integrated hardness removal treatment and MVR evaporation and crystallization treatment to obtain MVR permeate and crystalline salt; (6) The permeate from the first stage of reverse osmosis, nanofiltration, second stage of reverse osmosis, STRO, and MVR is collected in the wastewater reuse tank and reused in dyeing and finishing production. When the wastewater in the wastewater reuse tank does not meet the requirements for reuse in dyeing and finishing production, it is transported to the tailwater equalization tank. At the same time, the production ion exchange wastewater is directly transported to the tailwater equalization tank, and after being mixed and tested, it is discharged.

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