Near-zero discharge treatment method for cotton textile dyeing and printing wastewater

Abstract

This invention provides a near-zero discharge treatment method for cotton textile dyeing and printing wastewater, comprising: (1) subjecting the cotton textile dyeing and printing wastewater to be treated to two-stage sand filtration and adjusting the pH to 6.4~6.6; (2) subjecting the wastewater treated in step (1) to nanofiltration in a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization and simultaneous inflow and outflow mode to obtain nanofiltration concentrate and nanofiltration permeate; (3) subjecting the nanofiltration permeate to ultra-high pressure reverse osmosis treatment to obtain RO concentrate and RO permeate; (4) subjecting the nanofiltration concentrate and RO concentrate to KMPR hardening purification, ultrafiltration decolorization, and ozone deep decolorization treatment respectively, and then subjecting them to multi-stage evaporation and crystallization to obtain salt; (5) reusing the RO permeate to cotton dyeing and printing production, and incorporating the evaporated condensate into the reuse system. This method achieves near-zero discharge of cotton textile dyeing and printing wastewater and resource-based reuse of water and salt.

Description

Technical Field

[0001] This invention belongs to the field of dyeing and printing wastewater treatment technology, and particularly relates to a method for treating near-zero discharge of cotton textile dyeing and printing wastewater. Background Technology

[0002] Dyeing and printing wastewater is the wastewater discharged by dyeing and printing plants that mainly process cotton, linen, chemical fibers, and their blended products. Dyeing and printing wastewater is characterized by large volume, high content of organic pollutants, high alkalinity, and large fluctuations in water quality. It is one of the most difficult industrial wastewaters to treat and contains dyes, sizing agents, auxiliaries, acids, alkalis, and inorganic salts.

[0003] Currently, the main treatment processes for dyeing and printing wastewater include physicochemical, biochemical, photocatalytic, micro-electrolysis, microwave catalysis, and advanced oxidation, covering almost every technical field of advanced wastewater treatment. These technologies primarily aim to further reduce the concentration of organic pollutants beyond meeting emission standards, but they still cannot achieve zero discharge. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a method for treating near-zero discharge of cotton textile dyeing wastewater, which realizes the resource-based reuse of water and salt in cotton textile dyeing wastewater and its industrial application with near-zero discharge.

[0005] This invention provides a method for treating near-zero discharge of cotton textile dyeing wastewater, comprising the following steps:

[0006] (1) The cotton textile dyeing wastewater to be treated is subjected to primary sand filtration and secondary sand filtration, and the pH value is adjusted to 6.4~6.6;

[0007] (2) The wastewater after step (1) is treated by nanofiltration in a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization and simultaneous inflow and outflow mode to obtain nanofiltration concentrate and nanofiltration permeate.

[0008] (3) The nanofiltration permeate obtained in step (2) is subjected to ultra-high pressure reverse osmosis treatment to obtain RO concentrate and RO permeate;

[0009] (4) The nanofiltration concentrate and RO concentrate are subjected to KMPR hardening purification, ultrafiltration decolorization and ozone deep decolorization treatment respectively, and then subjected to multi-stage evaporation and crystallization to obtain salt;

[0010] (5) The RO permeate is reused in cotton printing and dyeing production, and the evaporated condensate is incorporated into the reuse system.

[0011] In a specific embodiment of the present invention, both the primary sand filter and the secondary sand filter are equipped with 7 sand filter tanks, adopting a 6-in-1 standby mode;

[0012] The sand filter tank uses a dual logic backwashing system based on differential pressure and fixed time.

[0013] The secondary sand filtration permeate main pipe is equipped with an online pH meter, conductivity meter, and turbidity analyzer.

[0014] In a specific embodiment of the present invention, the nanofiltration process employs eight sets of three-stage continuous concentration membrane skid-mounted devices, using a 7-use-1-clean mode.

[0015] Each three-stage continuous concentration membrane skid-mounted unit adopts a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow mode.

[0016] In a specific embodiment of the present invention, the concentration factor is ≥20 times;

[0017] Nanofiltration membranes have a divalent ion rejection rate of ≥90%;

[0018] The mass ratio of monovalent salts to polyvalent salts in nanofiltration permeate is higher than that in nanofiltration concentrate.

[0019] The pressure of the first stage of the step-by-step pressurization is 1.2 MPa, the pressure of the second stage is 1.5 MPa, and the pressure of the third stage is 2.0 MPa.

[0020] In a specific embodiment of the present invention, the ultra-high pressure reverse osmosis treatment uses 4 sets of RO skid-mounted units, adopting a 3-use-1-wash mode;

[0021] Each RO skid-mounted unit adopts a four-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow mode.

[0022] In a specific embodiment of the present invention, the concentration factor is ≥20 times;

[0023] After 3 years, the water quality and quantity fluctuations of the RO membrane are less than 3%.

[0024] The water quality of RO permeate should meet the following requirements: COD≤50mg / L, TDS≤500mg / L, total hardness≤20mg / L, color 2~3 times, and pH 7~8.

[0025] In a specific embodiment of the present invention, the KMPR hardness removal purification includes a nanofiltration concentrate KMPR system and an RO concentrate KMPR system;

[0026] The nanofiltration concentrate KMPR system is equipped with 3 membrane tanks, and the RO concentrate KMPR system is equipped with 2 membrane tanks.

[0027] It adopts an automatic online backwashing system with an operating pressure of -0.02 to -0.05 MPa and a tolerance for influent suspended solids of 1000 to 10000 mg / L.

[0028] In a specific embodiment of the present invention, KMPR is a softening system. After the pH of the influent is stabilized by chemical dosing, it is pumped into the KMPR membrane tank by the KMPR feed pump. The KMPR product water pump draws negative pressure, and calcium carbonate, magnesium hydroxide, particulate matter, etc. are trapped outside the membrane fibers through the sieving principle. Meanwhile, the bottom aeration device continuously washes and shakes the membrane fibers with air to prevent pollutant deposition and better ensure the stable operation of the KMPR device. The filtrate after KMPR filtration enters the subsequent units, thus optimizing the stable and efficient operation of the subsequent membrane modules and evaporation system.

[0029] In a specific embodiment of the present invention, ultrafiltration decolorization adopts a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow mode, with a total concentration factor ≥10.

[0030] In a specific embodiment of the present invention, the pressure of the first stage of the ultrafiltration decolorization stepwise pressurization is 1.0 MPa, the pressure of the second stage is 1.2 MPa, and the pressure of the third stage is 1.5 MPa.

[0031] In a specific embodiment of the present invention, the reaction residence time of ozone deep decolorization treatment is 55~65min, the decolorization rate of dyeing and printing wastewater is ≥93%, and the effluent color is <50 times.

[0032] This invention provides a method for treating near-zero discharge of cotton textile dyeing wastewater, comprising the following steps:

[0033] (1) The cotton textile dyeing wastewater to be treated is subjected to primary sand filtration and secondary sand filtration, and the pH value is adjusted to 6.4~6.6; (2) The wastewater after step (1) is treated by nanofiltration in the mode of three-stage continuous concentration, step-by-step circulation, step-by-step pressurization and simultaneous inflow and outflow to obtain nanofiltration concentrate and nanofiltration permeate; (3) The nanofiltration permeate obtained in step (2) is treated by ultra-high pressure reverse osmosis to obtain RO concentrate and RO permeate; (4) The nanofiltration concentrate and RO concentrate are subjected to KMPR hardening purification, ultrafiltration decolorization and ozone deep decolorization treatment respectively, and then subjected to multi-stage evaporation crystallization to obtain salt; (5) The RO permeate is reused in cotton textile dyeing production, and the evaporation condensate is incorporated into the reuse system. This method adjusts the pH value to 6.4~6.6 before entering the membrane, and combined with the mode of "three-stage continuous concentration, step-by-step circulation, step-by-step pressurization and simultaneous inflow and outflow", it realizes near-zero discharge of cotton textile dyeing wastewater and resource reuse of water and salt. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the zero-discharge method for dyeing and printing wastewater in this invention. Detailed Implementation

[0035] This invention provides a method for treating near-zero discharge of cotton textile dyeing wastewater, comprising the following steps:

[0036] (1) The cotton textile dyeing wastewater to be treated is subjected to primary sand filtration and secondary sand filtration, and the pH value is adjusted to 6.4~6.6;

[0037] (2) The wastewater after step (1) is treated by nanofiltration in a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization and simultaneous inflow and outflow mode to obtain nanofiltration concentrate and nanofiltration permeate.

[0038] (3) The nanofiltration permeate obtained in step (2) is subjected to ultra-high pressure reverse osmosis treatment to obtain RO concentrate and RO permeate;

[0039] (4) The nanofiltration concentrate and RO concentrate are subjected to KMPR hardening purification, ultrafiltration decolorization and ozone deep decolorization treatment respectively, and then subjected to multi-stage evaporation and crystallization to obtain salt;

[0040] (5) The RO permeate is reused in cotton printing and dyeing production, and the evaporated condensate is incorporated into the reuse system.

[0041] This invention involves subjecting the cotton textile dyeing wastewater to primary and secondary sand filtration to adjust the pH value to 6.4-6.6. The wastewater is MBR permeate from cotton textile dyeing wastewater that has undergone MBR treatment. The wastewater described in this invention has a COD of 200-300 mg / L, a pH of 7-8, inorganic salts of 5000-6000 mg / L, and turbidity within 1 NTU.

[0042] In this invention, both the primary and secondary sand filters are equipped with seven sand filter tanks each, employing a six-in-use, one-out-of-service configuration. The primary and secondary sand filters are connected in series for pretreatment. The backwashing system is automatically controlled by both differential pressure and fixed-time signals, and the backwash water is reused in the MBR permeate tank or equalization tank. The average daily backwash water volume is approximately 500 m³ / s. 3 The secondary sand filtration permeate main pipe is equipped with an online pH meter, conductivity meter, and turbidity analyzer to monitor water quality parameters in real time, providing data support for precise pH control and stable operation of the subsequent membrane system. After primary and secondary sand filtration, the pH value is adjusted to 6.4-6.6, more preferably 6.5; this invention preferably uses hydrochloric acid to adjust the pH value. Using the above-mentioned pH value, this invention can effectively prevent scaling by hardness substances such as silicates, calcium, and magnesium, avoid irreversible damage to the subsequent membrane system caused by MBE membrane leakage, and provide stable feed water conditions for high-concentration downstream nanofiltration systems.

[0043] The present invention uses a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization and simultaneous inflow and outflow mode to treat the wastewater after step (1) by nanofiltration to obtain nanofiltration concentrate and nanofiltration permeate.

[0044] This invention employs a nanofiltration system with eight sets of three-stage continuous concentration membrane skid-mounted units, using a "7-in-1-clean" configuration and an automatic online cleaning system. Each skid-mounted unit utilizes a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow mode for nanofiltration treatment, yielding nanofiltration concentrate and nanofiltration permeate. This method ensures continuous and stable effluent quality while significantly reducing operating costs. The total concentration ratio across the three stages is ≥20 times, with monovalent salts entering the nanofiltration permeate and polyvalent salts entering the nanofiltration concentrate, achieving preliminary separation of monovalent and polyvalent salts and retaining the majority of COD. The first-stage pressure of the nanofiltration process is 1.2 MPa, the second-stage pressure is 1.5 MPa, and the third-stage pressure is 2.0 MPa. This invention achieves salt separation through the nanofiltration system, which operates at a pressure of 1.2~2.8 MPa. Monovalent anions mainly refer to sodium chloride, potassium chloride, etc.; polyvalent anions mainly refer to sodium sulfate, magnesium sulfate, etc.

[0045] This invention treats the nanofiltration permeate obtained in step (2) with ultra-high pressure reverse osmosis to obtain RO concentrate and RO permeate. The ultra-high pressure reverse osmosis treatment in this invention uses four RO skid-mounted units in a 3-use-1-wash mode, equipped with an automatic online cleaning system; it adopts a four-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow operation mode, with a total concentration ratio ≥ 20 times. The pressure of the first three stages of each RO skid-mounted unit used in the ultra-high pressure reverse osmosis treatment is 4~9 MPa, and the maximum pressure of the fourth stage of RO concentration reaches 12 MPa; the RO membrane in the RO skid-mounted unit has a 5-year warranty, and the water quality and quantity fluctuation of the RO membrane after 3 years is <3%; the RO membrane retains more than 98% of dissolved salts, heavy metals, bacteria, and viruses, and the RO permeate water quality meets the following requirements: COD ≤ 50 mg / L, TDS ≤ 500 mg / L, total hardness ≤ 20 mg / L, color 2~3 times, pH 7~8, ensuring stable reuse while extending membrane lifespan.

[0046] In this invention, the nanofiltration concentrate and RO concentrate are sequentially subjected to KMPR hardening purification, ultrafiltration decolorization, and ozone deep decolorization treatment, and then subjected to multi-stage evaporation and crystallization to obtain salt.

[0047] The KMPR hardness removal purification described in this invention includes an NF concentrate KMPR system and an RO concentrate KMPR system; the nanofiltration concentrate KMPR system is equipped with 3 membrane tanks, 2 in use and 1 on standby; the RO concentrate KMPR system is equipped with 2 membrane tanks, 1 in use and 1 on standby; both adopt an automatic online backwashing system with an operating pressure of -0.02~-0.05MPa and a tolerance of 1000~10000mg / L of suspended solids in the feed water, providing a guarantee for the stable operation of the subsequent ultrafiltration system.

[0048] In this invention, the KMPR hardening and purification system is a softening system. After the influent is treated with chemicals to stabilize its pH, it is pumped into the KMPR membrane tank by the KMPR feed pump. The KMPR product water pump draws negative pressure, and calcium carbonate, magnesium hydroxide, particulate matter, etc. are trapped outside the membrane fibers through a sieving principle. Meanwhile, the bottom aeration device continuously washes and shakes the membrane fibers with air to prevent pollutant deposition and better ensure the stable operation of the KMPR device. The filtrate after KMPR filtration enters the subsequent units, thus optimizing the stable and efficient operation of the subsequent membrane modules and evaporation system.

[0049] The ultrafiltration decolorization system of this invention includes NF concentrate ultrafiltration and RO concentrate ultrafiltration. The NF concentrate ultrafiltration system consists of two sets of devices, one for use and one for cleaning; the RO concentrate ultrafiltration system also consists of two sets of devices, one for use and one for standby. The ultrafiltration decolorization system of this invention adopts a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow mode, with a total concentration factor ≥10. In the step-by-step pressurization of ultrafiltration decolorization, the pressure of the first stage is 1.0 MPa, the pressure of the second stage is 1.2 MPa, and the pressure of the third stage is 1.5 MPa.

[0050] In this invention, the ultrafiltration permeate from NF concentrate and the ultrafiltration permeate from RO concentrate are separately introduced into an ozone contact tank; in a specific embodiment, the volume of the ozone contact tank is 20 m³. 3 The reaction residence time for ozone deep decolorization treatment is 55~65min, the decolorization rate of dyeing and printing wastewater is ≥93%, and the effluent color is <50 times, which ensures the purity of salt crystals after subsequent MVR evaporation.

[0051] This invention ensures the purity of salt crystals by subjecting membrane concentrate to KMPR softening, ultrafiltration decolorization, ozone deep decolorization, and multi-stage evaporation crystallization. The multi-stage evaporation crystallization produces polyvalent and monovalent salts, which are recycled for dyeing and color-fixing processes in production. Ultimately, the RO permeate reuse rate is ≥96%. Salt resources are classified and utilized, reducing wastewater operating costs by more than 30%. This invention solves the technical problems of substandard influent water quality, short membrane washing cycles, rapid membrane life decay, low salt purity, and high operating costs in traditional treatment processes, realizing the industrial application of near-zero discharge and resource-based reuse of water and salt in cotton textile dyeing wastewater.

[0052] This invention reuses the RO permeate in cotton printing and dyeing production, and the evaporated condensate is incorporated into the reuse system (see...). Figure 1The recycling system includes alkaline desizing, mercerizing, dyeing, and printing. High-chroma wastewater generated after washing in these processes undergoes complexation coagulation, primary sedimentation in a primary sedimentation tank, hydrolysis acidification, and bio-enhancing before entering a non-aerated MBR to obtain MBR permeate. The MBR permeate is then filtered through sand to obtain NF concentrate and NF permeate. The NF permeate undergoes high-pressure RO treatment to obtain RO concentrate and RO permeate. The NF concentrate and RO concentrate are then sequentially treated by KMPR, ultrafiltration (UF), and ozone deep decolorization, and then subjected to multi-stage evaporation crystallization (MVR) to obtain monovalent salts, such as sodium chloride, and divalent salts, respectively. The monovalent salts are recycled in a chemical plant, while the divalent salts are recycled in a dye plant. The concentrate obtained from ultrafiltration (UF) treatment undergoes MVR treatment (No. 3), drying, and solidification, and is used as fuel for a power plant.

[0053] Among them, the RO concentrate is subjected to ozone deep decolorization treatment, and the resulting monovalent anion concentrated brine is treated by MVR No. 1. The feed concentration is above 6%, and a step-by-step evaporation and concentration process of 2-stage falling film + 2-stage forced circulation is adopted. The temperature rise of the compressor is controlled at 22℃.

[0054] After the NF concentrate is subjected to deep ozone decolorization treatment, the resulting divalent anion concentrated brine is treated with MVR No. 2. The concentration of the brine is 1-3%. A one-step salt discharge process of falling film + forced circulation is adopted, and the temperature rise of the compressor is controlled at 15℃.

[0055] The RO permeate is used as reclaimed water and is then fed to the desizing, scouring, mercerizing, dyeing-printing, and washing processes. The permeate from the monovalent salt concentration system is reused in production.

[0056] To further illustrate the present invention, the following detailed description of a near-zero discharge treatment method for cotton textile dyeing wastewater provided by the present invention is provided in conjunction with embodiments, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0057] Example 1

[0058] A near-zero discharge treatment method for cotton textile dyeing wastewater, with a daily wastewater treatment capacity of 12,000 m³. 3 / d, the biochemical effluent parameters of the cotton textile dyeing wastewater (i.e., MBR permeate) before entering the sand filtration system are shown in Table 1:

[0059] Table 1

[0060]

[0061] (1) Pretreatment and Precise pH Control: MBR permeate (COD 410 mg / L) enters the sand filtration system. Through interlocking control of an online pH analyzer and dosing device, 30% hydrochloric acid is precisely added to adjust the pH to 6.5, effectively preventing scale formation from silicates, calcium, and magnesium, and avoiding irreversible damage to downstream membrane systems caused by MBR membrane leakage. This lays a solid foundation for downstream nanofiltration high-concentration. Backwash water is reused in the MBR feed tank, and the sand filtration permeate has an SDI of 2.8. (For a 12000m³...) 3 The permeate from the MBR (Mechanical Batch Reactor) is pumped by a sand filter transfer pump to the primary sand filter system. The permeate from the primary sand filter system then enters the secondary sand filter system, and finally, the permeate from the secondary sand filter system enters the sand filter permeate tank. The sand filter permeate tank / reservoir has a volume of approximately 1000 m³. 3 As a buffer, the sand filtration system operates at a pressure of 0.2~0.3MPa. An online monitoring and analysis instrument is installed in the main pipe of the secondary sand filtration permeate to monitor the pH, conductivity, and turbidity of the permeate in real time, ensuring stable influent conditions to meet the high-concentration requirements of the downstream nanofiltration system.

[0062] (2) Customized Nanofiltration Desalination: Pretreated wastewater is fed into a customized nanofiltration system, employing a "three-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow" operation mode. This ensures a continuous and stable desalination process while significantly reducing operating costs; the concentration ratio is ≥20 times, achieving preliminary separation of monovalent and polyvalent salts and retaining the vast majority of COD. Approximately 12,000 m³ / day. 3 The sand filtration permeate is pumped to the security filter via a nanofiltration transfer pump, then pressurized by a nanofiltration high-pressure pump before being delivered to the nanofiltration unit. Each nanofiltration unit strictly follows the above operating mode, producing approximately 11,400 m³ of nanofiltration permeate. 3 / d Enters the nanofiltration permeate tank / bottle, with a matching nanofiltration permeate tank / bottle volume of approximately 1000m³. 3 As a buffer tank; nanofiltration concentrate approximately 600m³ 3 / d Enters the nanofiltration concentrate tank / bottle, with a matching nanofiltration concentrate tank / tank volume of approximately 100m³. 3 As a buffer tank, the nanofiltration system has a first-stage pressure of 1.2 MPa, a second-stage pressure of 1.5 MPa, and a third-stage pressure of 2.0 MPa. Online conductivity meters and flow meters are installed in the nanofiltration system's concentrate and permeate main pipes to detect changes in the conductivity of the nanofiltration system's permeate and concentrate, and to record the daily concentrate and permeate volumes. Bactericides and scale inhibitors are added online to the nanofiltration permeate main pipe to meet the high-concentration requirements of the downstream ultra-high pressure RO system.

[0063] (3) Ultra-high pressure RO deep desalination and reuse: Nanofiltration permeate is fed into the ultra-high pressure RO system, adopting a "four-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow" operation mode to ensure stable permeate production and reduce energy consumption. The No. 1 / No. 2 three-stage membrane system operates at a pressure of 6MPa, and the RO membranes retain more than 98% of dissolved salts, heavy metals, and other harmful substances. Approximately 11,400 m³ / day. 3 The nanofiltration permeate is pumped to a security filter via an RO transfer pump, then pressurized by an RO high-pressure pump before entering an ultra-high-pressure RO unit. Each ultra-high-pressure RO unit operates in the above mode, with a concentration ratio ≥20 times and an RO permeate volume of approximately 10830 m³ / d. 3 / d Enters the RO permeate tank / compartment, with a matching RO permeate tank / compartment volume of approximately 1000m³. 3 As a buffer tank; RO concentrate approximately 570 ml 3 / d Enters the RO concentrate tank / compartment, with a matching RO concentrate tank / compartment volume of approximately 100m³. 3 As a buffer tank, the first three stages of the ultra-high pressure RO system operate at pressures of 4~9MPa, while the fourth stage of ultra-high pressure RO concentrate reaches a maximum pressure of 12MPa. Online conductivity meters are installed in the main concentrate pipe of the ultra-high pressure RO system and the permeate branch pipes of each RO unit to detect changes in the conductivity of permeate and concentrate. At the same time, flow meters are installed to record the daily concentrate and permeate flow rates.

[0064] (4) Membrane concentrate treatment: approximately 600 m³ / day 3 / d Nanofiltration concentrate is pumped to the alkali-adjusting flocculation tank / box (approximately 15m³) 3 After the pH is adjusted and stabilized by adding 30wt% hydrochloric acid, the solution is pumped to the KMPR membrane tank via the KMPR feed pump. Then, under negative pressure, the KMPR permeate pump pumps the permeate to the KMPR permeate tank, achieving a concentration ratio of ≥20 times. The NF concentrate and KMPR permeate are approximately 570m³. 3 / d enters the NF concentrate KMPR permeate tank / reservoir, with a capacity of approximately 50m³. 3 As a buffer tank; the NF concentrate KMPR system has approximately 30m³ of concentrate. 3 The sludge is pumped by a screw pump to a sludge thickening tank and then enters a plate and frame filter press system, where concentrated sludge is produced. The operating pressure of the NF concentrate KMPR system is -0.02 to -0.05 MPa. The No. 1 KMPR system treats the primary membrane concentrate (permeate water hardness ≤ 5 mg / L), and the No. 2 KMPR system treats the secondary membrane concentrate. The subsequent ultrafiltration decolorization system continues the "three-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow" mode to ensure continuous and stable decolorization. In the step-by-step pressurization of ultrafiltration decolorization, the first stage pressure is 1.0 MPa, the second stage pressure is 1.2 MPa, and the third stage pressure is 1.5 MPa. After decolorization by the No. 2 ozone system, the sludge enters a multi-stage evaporation and crystallization process, ultimately producing divalent salts (purity 99.2%) and monovalent salts (purity 99.5%).

[0065] (5) Resource recovery: Condensate is reused in the production system, the recycling rate of reclaimed water (RO permeate) reaches 96.8%, and the calorific value utilization rate of concentrated slag incineration is 98%; salt resources are classified and reused in the production process, realizing the dual resource recovery of water and salt resources, and the operating cost is reduced by more than 30% compared with the traditional process.

[0066] Table 2 Water quality indicators of RO permeate

[0067] Comparative Example

[0068] Conventional greywater reuse systems employ a combination of high-density sedimentation tanks, multi-stage membrane processes, and multi-effect evaporation crystallization systems.

[0069] The high-density sedimentation tank mainly functions to remove calcium, magnesium, and other hardness substances before the membrane enters the membrane, and then concentrates the membrane through a multi-stage membrane combination.

[0070] The multi-stage membrane combination process generally adopts two-stage or higher concentration processes such as NF+RO. The membrane operating pressure generally does not exceed 6MPa, the concentration ratio does not exceed 15 times, the membrane element is frequently blocked, and it cannot operate continuously for a long time. The maximum water reuse rate does not exceed 90%. The water quality indicators of the generated water are shown in Table 3 below, and the amount of concentrated water generated is large. Under the same conditions, the amount of wastewater that needs to enter the evaporation system will exceed 25%.

[0071] The evaporation system described is a multi-effect evaporation system, which has low evaporation efficiency and high energy consumption. The mixed salts produced by the concentrated crystallization cannot be directly reused in production to achieve recycling.

[0072] Table 3

[0073]

[0074] As can be seen from the above embodiments, the present invention provides a near-zero discharge treatment method for cotton textile dyeing wastewater, including the following steps: (1) the cotton textile dyeing wastewater to be treated is subjected to primary sand filtration and secondary sand filtration, and the pH value is adjusted to 6.4~6.6; (2) the wastewater after treatment in step (1) is subjected to nanofiltration treatment in a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization and simultaneous inflow and outflow mode to obtain nanofiltration concentrate and nanofiltration permeate; (3) the nanofiltration permeate obtained in step (2) is subjected to ultra-high pressure reverse osmosis treatment to obtain RO concentrate and RO permeate; (4) the nanofiltration concentrate and RO concentrate are subjected to KMPR hardening purification, ultrafiltration decolorization and ozone deep decolorization treatment respectively, and then subjected to multi-stage evaporation crystallization to obtain salt; (5) the RO permeate is reused in cotton dyeing production, and the evaporated condensate is incorporated into the reuse system. This method adjusts the pH value to 6.4-6.6 before the wastewater enters the membrane, and combines this with a "three-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow" mode to achieve near-zero discharge of cotton textile dyeing wastewater and resource-based reuse of water and salt. The produced salt has high purity and reduces costs. Experimental results show that the salt purity is over 99%, the greywater recycling rate is as high as 96.8%, and the operating cost is reduced by more than 30% compared to traditional processes.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for treating near-zero discharge of cotton textile dyeing wastewater, comprising the following steps: (1) The cotton textile dyeing wastewater to be treated is subjected to primary sand filtration and secondary sand filtration, and the pH value is adjusted to 6.4~6.6; (2) The wastewater after step (1) is treated by nanofiltration in a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization and simultaneous inflow and outflow mode to obtain nanofiltration concentrate and nanofiltration permeate. (3) The nanofiltration permeate obtained in step (2) is subjected to ultra-high pressure reverse osmosis treatment to obtain RO concentrate and RO permeate; (4) The nanofiltration concentrate and RO concentrate are subjected to KMPR hardening purification, ultrafiltration decolorization and ozone deep decolorization treatment respectively, and then subjected to multi-stage evaporation and crystallization to obtain salt; (5) The RO permeate is reused in cotton printing and dyeing production, and the evaporated condensate is incorporated into the reuse system.

2. The processing method according to claim 1, characterized in that, Both the primary and secondary sand filters are equipped with 7 sand filter tanks, using a 6-in-1-out-of-service mode. The sand filter tank uses a dual logic backwashing system based on differential pressure and fixed time. The secondary sand filtration permeate main pipe is equipped with an online pH meter, conductivity meter, and turbidity analyzer.

3. The processing method according to claim 1, characterized in that, The nanofiltration process uses 8 sets of three-stage continuous concentration membrane skid-mounted units, employing a 7-use-1-clean mode. Each three-stage continuous concentration membrane skid-mounted unit adopts a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow mode.

4. The processing method according to claim 3, characterized in that, Concentration factor ≥ 20 times; Nanofiltration membranes have a divalent ion rejection rate of ≥90%; The mass ratio of monovalent salts to polyvalent salts in nanofiltration permeate is higher than that in nanofiltration concentrate. The pressure of the first stage of the step-by-step pressurization is 1.2 MPa, the pressure of the second stage is 1.5 MPa, and the pressure of the third stage is 2.0 MPa.

5. The processing method according to claim 1, characterized in that, The ultra-high pressure reverse osmosis treatment uses 4 sets of RO skid-mounted units, adopting a 3-use-1-wash mode; Each RO skid-mounted unit adopts a four-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow mode.

6. The processing method according to claim 5, characterized in that, The concentration factor is ≥20 times; After 3 years, the water quality and quantity fluctuations of the RO membrane are less than 3%. The water quality of RO permeate should meet the following requirements: COD≤50mg / L, TDS≤500mg / L, total hardness≤20mg / L, color 2~3 times, and pH 7~8.

7. The processing method according to claim 1, characterized in that, The KMPR hardness removal and purification system includes a nanofiltration concentrate KMPR system and an RO concentrate KMPR system. The nanofiltration concentrate KMPR system is equipped with 3 membrane tanks, and the RO concentrate KMPR system is equipped with 2 membrane tanks. It adopts an automatic online backwashing system with an operating pressure of -0.02 to -0.05 MPa and can withstand influent suspended solids of 1000 to 10000 mg / L.

8. The processing method according to claim 1, characterized in that, The ultrafiltration decolorization adopts a three-stage continuous concentration, step-by-step circulation, step-by-step pressurization, and simultaneous inflow and outflow mode, with a total concentration factor of ≥10.

9. The processing method according to claim 8, characterized in that, In the stepwise pressurization process of ultrafiltration decolorization, the first stage pressure is 1.0 MPa, the second stage pressure is 1.2 MPa, and the third stage pressure is 1.5 MPa.

10. The processing method according to claim 1, characterized in that, The reaction residence time for ozone deep decolorization treatment is 55~65min, the decolorization rate of dyeing and printing wastewater is ≥93%, and the effluent color is <50 times.

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