Printing and dyeing wastewater resourceful treatment method

Abstract

The invention relates to the technical field of printing and dyeing wastewater treatment, in particular to a printing and dyeing wastewater resourceful treatment method which comprises the following steps: S1, conveying to-be-treated printing and dyeing wastewater to a flocculating settling unit through a pipeline, adding a flocculating agent, stirring, mixing and reacting to aggregate suspended solids, colloids and part of dye molecules into flocs, and filtering to obtain a filtrate; after settling, collecting upper-layer clarified liquor to obtain pretreated wastewater; s2, feeding the pretreated wastewater into a carbon discharge unit, and removing inorganic carbon in the wastewater to obtain carbon-discharged wastewater; and S3, introducing the carbon-discharged wastewater into a micro-electrolysis unit, adding an oxidizing agent, and generating hydroxyl radicals under the action of a catalyst to obtain oxidative degradation wastewater. The flocculation-microelectrolysis-nanofiltration-electrodialysis coupling technology is adopted, efficient removal of organic matter, salt resource recycling and acid-alkali co-production are achieved, the added value of products is increased, obtained acid and alkali can be directly reused for cloth dyeing, and the service life of a membrane is prolonged.

Description

Technical Field

[0001] This invention relates to the field of dyeing and printing wastewater treatment technology, and more specifically, to a method for the resource-based treatment of dyeing and printing wastewater. Background Technology

[0002] Dyeing and printing wastewater is a challenging type of industrial wastewater due to its complex composition, high color, high organic matter content, and high salt content. Traditional treatment methods, such as biochemical methods, ozone oxidation, and coagulation sedimentation, can remove some pollutants to a certain extent, but they still suffer from problems such as incomplete degradation of organic matter, high treatment costs, and low resource recovery rates.

[0003] In the prior art, patent publication number CN110697960A proposes a method for separating salt from dyeing and printing wastewater using electrodialysis technology, achieving the separation and reuse of salt and organic matter. However, this process does not perform sufficient pretreatment for organic matter degradation in the wastewater, and the direct entry of organic matter into the electrodialysis system can easily lead to membrane fouling, seriously affecting membrane life and current efficiency.

[0004] Patent publication number CN109896685B discloses a system and method for the harmless treatment of high-concentration dyeing and printing wastewater. This patent proposes a system combining ozone oxidation, Fenton reaction, filtration, and electrodialysis to treat high-concentration dyeing and printing wastewater, ultimately obtaining sodium chloride through evaporation and crystallization. While this process achieves a certain degree of resource recovery, it relies on energy-intensive MVR evaporators and has low added value for the products, resulting in poor economic efficiency.

[0005] Therefore, there is an urgent need to develop a new method for treating dyeing and printing wastewater that can efficiently degrade organic matter, recover salt resources, reduce treatment costs, and increase the added value of products. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, embodiments of the present invention provide a method for the resource-based treatment of dyeing and printing wastewater to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for resource-based treatment of dyeing and printing wastewater, comprising the following steps:

[0008] Step S1: The dyeing and printing wastewater to be treated is transported to the flocculation and sedimentation unit through pipelines, flocculant is added, and after stirring and mixing, the suspended solids, colloids and some dye molecules are aggregated into flocs. After sedimentation, the upper clear liquid is collected to obtain pretreated wastewater.

[0009] Step S2: Send the pretreated wastewater into the carbon removal unit to remove inorganic carbon from the wastewater, and obtain the carbon-removed wastewater;

[0010] Step S3: Introduce the wastewater after carbon removal into the micro-electrolysis unit, add oxidant and generate hydroxyl radicals under the action of catalyst, oxidize and degrade the difficult-to-decompose organic matter, and obtain oxidized and degraded wastewater.

[0011] Step S4: The oxidative degradation wastewater is fed into the nanofiltration unit, where the nanofiltration membrane retains organic matter and divalent ions, separating the qualified permeable water and the concentrated water enriched with pollutants.

[0012] Step S5: Introduce nanofiltration permeate into the homogeneous membrane electrodialysis unit, and separate anions and cations through the ion exchange membrane under the action of a DC electric field to obtain concentrated water and fresh water;

[0013] Step S6: Pass the concentrated water into the bipolar membrane electrodialysis unit, utilizing the water dissociation produced by the bipolar membrane. and Combined with the separation effect of ion exchange membranes, the solute is converted into acid, alkaline solutions and low-salinity brine.

[0014] In a preferred embodiment, the salt content of the dyeing and printing wastewater to be treated is 0.5wt% to 20wt%, and the TOC (total organic carbon) is 1000 mg / L to 2000 mg / L; the impurities include , , , , , One or more ions in it.

[0015] In a preferred embodiment, the low-salinity brine produced by the bipolar membrane electrodialysis unit is returned to the electrodialysis unit for cyclic concentration treatment, and the concentration of the brine is 5wt% to 7wt%.

[0016] In a preferred embodiment, in step S1, 200 mg / L to 300 mg / L of polyaluminum chloride and 2 mg / L to 4 mg / L of polyacrylamide are added, the pH is controlled at 3 to 12, the reaction time is 0.5 h to 2 h, and the flocculated sludge is sent to a solid waste treatment company after being filtered by plate and frame filter press.

[0017] In a preferred embodiment, dilute hydrochloric acid is added in step S2 for carbon removal treatment, the pH is controlled at 2-5, the concentration of dilute hydrochloric acid is 3mol / L-8mol / L, and the reaction time is 0.5h-2h.

[0018] In a preferred embodiment, in step S3, the micro-electrolysis packing particle size is 3cm to 5cm, the pH is controlled at 3.0 to 3.5, the hydraulic retention time is 1h to 2h, the TOC removal rate is >85%, and the effluent TOC is <500mg / L.

[0019] In a preferred embodiment, in step S4, the nanofiltration membrane has a molecular weight cutoff of 150 Da to 300 Da, an operating pressure of 1.8 MPa to 4.5 MPa, a TOC rejection rate of >80%, and a product water TOC of <50 mg / L.

[0020] In a preferred embodiment, the electrodialysis treatment conditions in step S5 are: constant current operation, current density of 20 mA / cm² to 40 mA / cm², feed flow rate of 20 L / h to 100 L / h, final distillate concentration of 0.5 wt% to 5 wt%, and final concentrate concentration of 12 wt% to 25 wt%.

[0021] A monovalent cation-selective permeable cation membrane is preferred.

[0022] In a preferred embodiment, the bipolar membrane electrodialysis treatment conditions in step S6 are: constant current operation, current density 40 mA / cm²~90 mA / cm².

[0023] The technical effects and advantages of this invention are as follows:

[0024] 1. Through multi-stage synergy of flocculation, micro-electrolysis, and nanofiltration, the TOC removal rate is high and the organic matter content in the effluent is significantly reduced;

[0025] 2. Pretreatment effectively removes colloids, suspended solids and macromolecular organic matter, significantly reducing fouling of subsequent nanofiltration and electrodialysis membranes and extending membrane lifespan;

[0026] 3. By coupling electrodialysis with bipolar membranes, salt recovery and acid-alkali co-production can be achieved. The acid and alkali products can be directly recycled in the printing and dyeing process, improving economic benefits.

[0027] 4. Low energy consumption and low cost: It avoids the high energy consumption problem of traditional evaporation crystallization, and the overall process is compact with low operating costs;

[0028] 5. Environmentally friendly: The sludge is incinerated after being filtered, and the wastewater is thoroughly treated, with no secondary pollution, which meets the requirements of green manufacturing. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process flow structure of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] A method for resource-based treatment of dyeing and printing wastewater includes the following steps:

[0032] The salt content of the dyeing and printing wastewater to be treated is 0.5–20 wt%, and the TOC is 1000–2000 mg / L; the impurities include , , , , , One or more ions in it;

[0033] Step S1: The dyeing and printing wastewater to be treated is transported to the flocculation and sedimentation unit through pipelines. Flocculant is added, and after stirring and mixing, the suspended solids, colloids and some dye molecules aggregate into flocs. After sedimentation, the upper clear liquid is collected to obtain pretreated wastewater. In step S1, 200mg / L to 300mg / L of polyaluminum chloride and 2mg / L to 4mg / L of polyacrylamide are added. The pH is controlled at 3 to 12, and the reaction time is 0.5h to 2h. The flocculated sludge is sent to the solid waste treatment company after being filtered by plate and frame filter press.

[0034] Step S2: Send the pretreated wastewater into the carbon removal unit, add dilute hydrochloric acid for carbon removal treatment, control the pH at 2-5, the concentration of dilute hydrochloric acid at 3mol / L-8mol / L, and the reaction time at 0.5h-2h.

[0035] Step S3: The wastewater after carbon discharge is introduced into the micro-electrolysis unit, and an oxidant is added to generate hydroxyl radicals under the action of a catalyst, which oxidizes and degrades the recalcitrant organic matter, resulting in oxidized and degraded wastewater; in step S3, the micro-electrolysis packing particle size is 3cm to 5cm, the pH is controlled at 3.0 to 3.5, the hydraulic retention time is 1h to 2h, the TOC removal rate is >85%, and the effluent TOC is <500mg / L;

[0036] Step S4: The oxidative degradation wastewater is fed into a nanofiltration unit, where the nanofiltration membrane retains organic matter and divalent ions, separating compliant permeate and concentrated wastewater enriched with pollutants. In step S4, the nanofiltration membrane has a molecular weight cutoff of 150 Da to 300 Da, an operating pressure of 1.8 MPa to 4.5 MPa, a TOC rejection rate of >80%, and a permeate TOC of <50 mg / L.

[0037] Step S5: The nanofiltration permeate is introduced into the homogeneous membrane electrodialysis unit. Under the action of a DC electric field, anions and cations are separated through the ion exchange membrane to obtain concentrated water and desalinated water. The electrodialysis treatment conditions in step S5 are: constant current operation, current density 20mA / cm²~40mA / cm², feed flow rate 20L / h~100L / h, final desalinated water concentration 0.5wt%~5wt%, and final concentrated water concentration 12wt%~25wt%.

[0038] The preferred method is to use a monovalent cation-selective permeable cation membrane;

[0039] Step S6: Pass the concentrated water into the bipolar membrane electrodialysis unit, utilizing the water dissociation produced by the bipolar membrane. and Combined with the separation effect of ion exchange membrane, the solute is converted into acid, alkaline solutions and low salinity brine; the bipolar membrane electrodialysis treatment conditions in step S6 are: constant current operation, current density 40mA / cm²~90mA / cm².

[0040] The low-salinity brine produced by the bipolar membrane electrodialysis unit is returned to the electrodialysis unit for cyclic concentration treatment, and the concentration of the brine is 5wt% to 7wt%.

[0041] Example

[0042] Reference Figure 1 :

[0043] Example 1: The dyeing wastewater from a fine chemical plant has a salt content of about 12wt% to 13wt%, and contains a large amount of mixed salts, high-valence ions and organic matter, with a TOC of 1805 mg / L.

[0044] Step S1: The dyeing and printing wastewater is subjected to flocculation pretreatment, in which the amount of PAC added is 100mg / L and the amount of PAM added is 2mg / L. The pH of the wastewater is adjusted to 8, the reaction is carried out for 1 hour, and the supernatant is taken to obtain the pretreated wastewater.

[0045] Step S2: Perform carbon removal treatment on the pretreated wastewater, adjust the pH to 3.5, the concentration of dilute hydrochloric acid to 6 mol / L, and react for 1 hour to obtain the carbon-removed wastewater.

[0046] Step S3: Micro-electrolysis degradation of the wastewater after carbon removal. The micro-electrolysis packing particle size is 3cm, the pH is controlled at 3.5, the hydraulic retention time (HRT) is 1h, and the TOC is 271mg / L.

[0047] Step S4: The degraded wastewater is treated by nanofiltration. A nanofiltration membrane with a molecular weight cutoff of 200 Do is selected. The pressure is 4.5 MPa, the pH of the influent is 8, the NaCl content in the product water is 98.5%, and the TOC is 41 mg / L.

[0048] Step S5: Introduce the nanofiltration permeate into the electrodialysis unit (ED) for selective electrodialysis treatment. Specific conditions include: constant current operation, current density 30 mA / cm³. 2 The feed flow rate was 40 L / h; the temperature was 25 °C; the final distillate concentration was adjusted to 1.1 wt%; and the concentrate concentration was adjusted to 14.8 wt%.

[0049] Step S6: The ED concentrate from the electrodialysis unit enters the bipolar membrane unit (hereinafter referred to as BPED) for bipolar membrane electrodialysis treatment, under the following conditions: constant current operation, current density 80 mA / cm³. 2 The temperature is 30℃; brine, acid and alkali are prepared, with acid concentration of 7.9wt%, alkali concentration of 8.2wt%, and brine concentration of 6wt%, which can achieve resource recovery.

[0050] Example 2: The dyeing wastewater in a certain industrial park has a salt content of about 12wt% to 13wt%, and contains a large amount of mixed salts, high-valence ions and organic matter, with a TOC of 2160 mg / L.

[0051] Step S1: Perform the above wastewater treatment according to steps 1-2 of Implementation Case 1 to obtain wastewater after carbon removal.

[0052] Step S2: The wastewater after carbon removal is subjected to micro-electrolysis degradation. The micro-electrolysis packing particle size is 3cm, the pH is controlled at 3.0, the hydraulic retention time (HRT) is 1h, and the TOC is 324mg / L.

[0053] Step S3: The degraded wastewater is treated by nanofiltration. A nanofiltration membrane with a molecular weight cutoff of 150 Do is selected. The pressure is 4.5 MPa, the pH of the influent is 8, the NaCl content in the product water is 99.1%, and the TOC is 45 mg / L.

[0054] Step S4: Introduce the nanofiltration permeate into the electrodialysis unit (ED) for selective electrodialysis treatment. Specific conditions include: constant current operation, current density 35 mA / cm³. 2 The feed flow rate was 40 L / h; the temperature was 25 °C; the final distillate concentration was adjusted to 1.0 wt%; and the concentrate concentration was adjusted to 15.1 wt%.

[0055] Step S5: The ED concentrate from the electrodialysis unit enters the bipolar membrane unit (hereinafter referred to as BPED) for bipolar membrane electrodialysis treatment, under the following conditions: constant current operation, current density 80 mA / cm². 2 The temperature is 30℃; brine, acid and alkali are prepared, with acid concentration of 8.0wt%, alkali concentration of 8.1wt% and brine concentration of 6wt%, which can realize resource recycling.

[0056] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for resourceful treatment of printing and dyeing wastewater, characterized in that; The method comprises the following steps: Step S1: the printing and dyeing wastewater to be treated is transported to a flocculation and sedimentation unit through a pipeline, a flocculant is added, and after stirring, mixing and reaction, suspended solids, colloids and part of dye molecules are aggregated into flocs, the upper clear liquid is collected after sedimentation, and pretreated wastewater is obtained; Step S2: the pretreated wastewater is sent to a carbon removal unit to remove inorganic carbon in the wastewater, and carbon-removed wastewater is obtained; Step S3: the carbon-removed wastewater is introduced into a micro-electrolysis unit, an oxidant is added, and hydroxyl radicals are generated under the action of a catalyst to oxidatively degrade refractory organic matter, and oxidatively degraded wastewater is obtained; Step S4: the oxidatively degraded wastewater is sent to a nanofiltration unit, and organic matter and divalent ions are intercepted by a nanofiltration membrane, and standard water and concentrated water rich in pollutants are separated; Step S5: the nanofiltration water is introduced into a homogeneous membrane electrodialysis unit, and under the action of a direct current electric field, anions and cations are separated by an ion exchange membrane to obtain concentrated water and dilute water; Step S6: passing the concentrated water into the bipolar membrane electrodialysis unit, using the water dissociation by the bipolar membrane to produce and , in combination with the separation effect of ion exchange membranes, to convert the solutes into acid, base solutions and low salinity brine.

2. The printing and dyeing wastewater resourceful treatment method according to claim 1, characterized in that: The salt content of the printing and dyeing wastewater to be treated is 0.5wt%-20wt%, and the TOC is 1000mg / L-2000mg / L; the mixed salt includes one or more ions of 、 、 、 、 、 .

3. The printing and dyeing wastewater resourceful treatment method according to claim 1, characterized in that: The low-salinity brine produced by the bipolar membrane electrodialysis unit is returned to the electrodialysis unit for recycling and concentration treatment, and the concentration of the brine is 5wt%-7wt%.

4. The printing and dyeing wastewater resourceful treatment method according to claim 1, characterized in that: In step S1, 200mg / L-300mg / L of polyaluminum chloride and 2mg / L-4mg / L of polyacrylamide are added, the pH is controlled at 3-12, the reaction time is 0.5h-2h, and the flocculated sludge is sent to a solid waste treatment company after being filtered by a plate and frame filter.

5. The printing and dyeing wastewater resourceful treatment method according to claim 1, characterized in that: In step S2, dilute hydrochloric acid is added for carbon removal treatment, the pH is controlled at 2-5, the concentration of the dilute hydrochloric acid is 3mol / L-8mol / L, and the reaction time is 0.5h-2h.

6. The printing and dyeing wastewater resourceful treatment method according to claim 1, characterized in that: In step S3, the particle size of the micro-electrolysis filler is 3cm-5cm, the pH is controlled at 3.0-3.5, the hydraulic retention time is 1h-2h, the TOC removal rate is >85%, and the TOC of the effluent is <500mg / L.

7. The printing and dyeing wastewater resourceful treatment method according to claim 1, characterized in that: In step S4, the molecular weight cut-off of the nanofiltration membrane is 150Da-300Da, the operating pressure is 1.8MPa-4.5MPa, the TOC removal rate is >80%, and the TOC of the product water is <50mg / L.

8. The printing and dyeing wastewater resourceful treatment method according to claim 1, characterized in that: In step S5, the electrodialysis treatment conditions are as follows: constant current operation, current density 20mA / cm²-40mA / cm², feed liquid flow rate 20L / h-100L / h, final dilute water concentration 0.5wt%-5wt%, and final concentrated water concentration 12wt%-25wt%. A monovalent cation-selective positive membrane is preferably used.

9. The printing and dyeing wastewater resourceful treatment method according to claim 1, characterized in that: In step S6, the bipolar membrane electrodialysis treatment conditions are as follows: constant current operation, current density 40mA / cm²-90mA / cm².

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