A printing and dyeing wastewater advanced treatment and salt control recycling process and system

Abstract

The application discloses a kind of printing and dyeing wastewater advanced treatment and salt control reuse process and system, belong to wastewater treatment technical field.The process is sequentially carried out on printing and dyeing wastewater grid interception, adjust homogeneity, coagulation and sedimentation pretreatment;Hydrolysis acidification and membrane biological reactor biochemical treatment;Ozone oxidation break and fluidized crystallization softening softening treatment;Nanofiltration separation obtains permeate and concentrated solution;Crystal seed fluidization descaling is carried out to concentrated solution;Again, nanofiltration permeate and descaling concentrated solution after membrane concentration are carried out by reverse osmosis, obtain sodium chloride and sodium sulfate concentrated solution;Finally, sludge and crystallization waste residue are evaporated and solidified treatment.The application is treated by multiple steps, realizes printing and dyeing wastewater advanced purification and salt efficient separation reuse, solves the problem that nanofiltration salt separation is not pure in prior art and system scaling risk is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wastewater treatment, and particularly relates to a dyeing wastewater advanced treatment and salt control recycling process and system. BACKGROUND

[0002] The dyeing wastewater has the characteristics of high chemical oxygen demand and high total dissolved solids content, and its advanced treatment and salt recycling have always been technical difficulties in the industry. The current mainstream treatment process uses a membrane bioreactor combined with reverse osmosis technology to realize water resource recycling, but the high-salt reverse osmosis concentrated water produced by the process has high salt concentration and complex composition, which becomes a key bottleneck restricting the near-zero discharge of wastewater. To solve this problem, the advanced treatment process uses a nanofiltration salt separation and reverse osmosis concentration technical route to realize the preliminary separation of sodium sulfate and sodium chloride and liquid recycling through the selective separation of monovalent salt and divalent salt by the nanofiltration membrane, thereby effectively reducing the treatment cost of the end evaporation crystallization.

[0003] However, the above-mentioned advanced process still has significant technical defects in actual application: the organic matter in the dyeing wastewater and the scale-forming ions such as calcium and magnesium easily form stable organic-inorganic complexes. The complexes not only hinder the directional precipitation of the scale-forming ions as crystallization inhibitors, but also wrap the calcium ions and magnesium ions to form a supersaturated system. In the existing process, even if resin deep dehardening means is used, it is still difficult to completely remove the scale-forming ions wrapped by the organic matter, resulting in a decrease in the selective separation efficiency of the membrane for monovalent salt and divalent salt in the nanofiltration salt separation process and insufficient salt separation purity. More importantly, when the recycling liquid containing supersaturated scale-forming ions encounters changes in temperature, pH value or flow rate during transportation and storage, the stable structure of the organic-inorganic complex is destroyed, and the supersaturated ions will precipitate disorderly on the surface of the pipeline and equipment, causing problems such as system blockage, membrane pollution and a decrease in heat transfer efficiency, which seriously affect the long-term stable operation of the recycling process.

[0004] In the prior art, the treatment of the organic-inorganic complex is mostly passive adsorption or single chemical precipitation, which cannot fundamentally destroy the complex structure and realize the directional removal of the scale-forming ions, resulting in impure nanofiltration salt separation and the risk of system scaling, which restricts the further development of the dyeing wastewater resource recycling technology. SUMMARY

[0005] The application overcomes the deficiencies of the prior art and provides a dyeing wastewater advanced treatment and salt control recycling process and system.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows: a dyeing wastewater advanced treatment and salt control recycling process, comprising the following steps:

[0007] Step S1: pretreating the printing and dyeing wastewater to obtain pretreated water; the pretreatment comprises sequentially performing grid interception treatment, adjustment homogenization treatment and coagulation sedimentation treatment on the printing and dyeing wastewater;

[0008] Step S2: biochemically treating the pretreated water to obtain biochemically treated water; the biochemical treatment comprises sequentially performing hydrolysis acidification treatment and membrane bioreactor treatment on the pretreated water;

[0009] Step S3: softening the biochemically treated water to obtain softening water; the softening treatment comprises sequentially performing oxidation breaking treatment and fluidized crystallization softening treatment on the biochemically treated water;

[0010] Step S4: performing nanofiltration separation treatment on the softening water to obtain nanofiltration permeate and nanofiltration concentrated liquid; the nanofiltration separation treatment is performed under pressure driving and utilizes a separation membrane to selectively separate the dissolved inorganic salt in the softening water;

[0011] Step S5: performing seed fluidized descaling treatment on the nanofiltration concentrated liquid to obtain descaled concentrated liquid; the seed fluidized descaling treatment induces preferential precipitation of the supersaturated scale-forming ions by adding seeds under fluidized conditions;

[0012] Step S6: performing membrane concentration treatment on the nanofiltration permeate and the descaled concentrated liquid to obtain sodium chloride concentrated liquid and sodium sulfate concentrated liquid; the membrane concentration treatment realizes salt purification and concentration through a reverse osmosis process;

[0013] Step S7: performing evaporation solidification treatment on the sludge and crystallization waste residue generated in the membrane concentration treatment process; the evaporation solidification treatment promotes water evaporation under heating and negative pressure conditions.

[0014] Further, in step S1, the grid gap width of the grid interception treatment is 1 mm to 5 mm.

[0015] Further, in step S1, the hydraulic retention time of the adjustment homogenization treatment is 6 h to 12 h, and the stirring rate is 30 r / min to 60 r / min.

[0016] Further, in step S1, the coagulation sedimentation treatment comprises adding 100 mg / L to 300 mg / L of polyaluminum chloride as a coagulant and 2 mg / L to 5 mg / L of polyacrylamide as a flocculant.

[0017] Further, in step S3, the oxidation breaking treatment uses ozone as an oxidizing agent, the ozone dosage is 50 mg / L to 80 mg / L, and the reaction time is 20 min to 30 min.

[0018] Further, in step S3, the fluidized crystallization softening treatment comprises adding sodium carbonate to adjust the pH to 9.0 to 10.0, and adding quartz sand seeds with a particle size of 0.2 mm to 0.5 mm, the seed adding concentration is 20 g / L to 50 g / L, the upflowing speed is controlled to be 20 m / h to 40 m / h, and the hydraulic retention time is 30 min to 60 min.

[0019] Further, in step S4, the operating pressure of the nanofiltration separation treatment is 1.0 MPa to 2.5 MPa, the nanofiltration membrane used has a molecular weight cut-off of 200 Da to 400 Da, and the recovery rate is controlled to be 70% to 80%.

[0020] Further, in step S5, the seed fluidized descaling treatment adds calcium sulfate seeds with a particle size of 5 μm to 50 μm, the seed adding concentration is 5 g / L to 10 g / L, the stirring speed is 100 rpm to 300 rpm, and the hydraulic retention time is 5 min to 15 min.

[0021] Further, in step S6, the operating pressure for reverse osmosis concentration of the nanofiltration permeate is 1.5 MPa to 4.0 MPa, and the operating pressure for disc-tube reverse osmosis concentration of the concentrated solution after descaling is 3.0 MPa to 8.0 MPa.

[0022] The present application provides another technical solution: a printing and dyeing wastewater advanced treatment and salt control recycling system for realizing the above process, comprising a grid, a regulating tank, a coagulation and sedimentation device, a hydrolysis acidification tank, a membrane bioreactor, an ozone oxidation tower, a fluidized bed crystallizer, a nanofiltration device, a seed fluidized reactor, a first reverse osmosis device, a second reverse osmosis device and an evaporator connected in sequence through pipelines and pumps.

[0023] The present application solves the defects in the background art, and has the following beneficial effects:

[0024] The printing and dyeing wastewater advanced treatment and salt control recycling process provided by the present application uses the strong oxidizing property of ozone to break the molecular chain of organic matter complexed with calcium and magnesium ions, destroys the stable structure of the organic-inorganic complex, and releases the wrapped scale-forming ions in the water body in a free state. The oxidation and breaking treatment significantly reduces the content of organic matter in the water body, eliminates the interference of organic matter on the subsequent crystallization process, and improves the precipitability of scale-forming ions. Compared with the direct softening treatment in the traditional process, the oxidation and breaking treatment effectively solves the problem of difficult release of scale-forming ions caused by organic matter wrapping, and improves the reaction efficiency of subsequent crystallization.

[0025] Further, the present application adopts fluidized crystallization softening treatment, immediately after oxidative breakage, sodium carbonate is added to adjust pH to 9.0-10.0, and 20 g / L to 50 g / L quartz sand seed with particle size of 0.2-0.5 mm is added, under the upflowing velocity of 20 m / h-40 m / h, the fluidized state is maintained, the free calcium ions are induced to form heterogeneous nucleation and growth on the surface of the seed in the form of calcium carbonate. The fluidized crystallization softening treatment avoids bed plugging, at the same time, the solid-liquid mass transfer process is strengthened, the directional crystallization and efficient separation of the scaling ions are realized. Compared with the traditional precipitation softening, the method significantly improves the hardness removal efficiency, greatly reduces the scaling and pollution risk of the subsequent nanofiltration membrane.

[0026] In particular, the timing coupling of the oxidative breakage treatment and the fluidized crystallization softening treatment, the ozone dosage is controlled at 65 mg / L to break the complex effectively without generating too much by-product, at the same time, the quartz sand seed concentration of 35 g / L is matched, sufficient nucleation sites are provided while the good fluidized state is maintained, the total hardness and total organic carbon in the softening effluent are significantly reduced, the separation selectivity of the nanofiltration membrane to the monovalent and divalent ions is effectively improved, the sulfate ion leakage is reduced, and the scaling tendency of the reverse osmosis concentration is controlled. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments described in the present application, and for those skilled in the art, other drawings can also be obtained without creative labor;

[0028] Figure 1 It is a kind of printing and dyeing wastewater advanced treatment and salt control reuse process flow chart;

[0029] Figure 2 It is a kind of printing and dyeing wastewater advanced treatment and salt control reuse system architecture diagram. DETAILED DESCRIPTION

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

[0031] In the following description, many specific details are set forth in order to provide a thorough understanding of the present application, but the present application can also be implemented in other ways different from those described herein, therefore, the protection scope of the present application is not limited by the specific embodiments disclosed below.

[0032] In the following, all starting materials can be obtained commercially or prepared by routine methods in the art, if not otherwise mentioned.

[0033] Exemplary method:

[0034] As shown in the accompanying drawings, a printing and dyeing wastewater advanced treatment and salt control recycling process comprises the following steps: Figure 1

[0035] Step S1: pretreating the printing and dyeing wastewater to obtain pretreated effluent;

[0036] Step S2: biochemically treating the pretreated effluent to obtain biochemically treated effluent;

[0037] Step S3: softening the biochemically treated effluent to obtain softened effluent;

[0038] Step S4: nanofiltration separating the softened effluent to obtain nanofiltration permeate and nanofiltration concentrate;

[0039] Step S5: fluidizing and descaling the nanofiltration concentrate by using seed crystals to obtain descaled concentrate;

[0040] Step S6: membrane concentrating the nanofiltration permeate and the descaled concentrate respectively to obtain sodium chloride concentrate and sodium sulfate concentrate;

[0041] Step S7: evaporating and solidifying the sludge and crystallization waste residue generated in the membrane concentrating process.

[0042] In the following, each step will be described in detail.

[0043] In Step S1, the pretreatment comprises successively grid intercepting the printing and dyeing wastewater, adjusting and homogenizing the printing and dyeing wastewater, and coagulating and precipitating the printing and dyeing wastewater.

[0044] Exemplarily, the method of grid intercepting the printing and dyeing wastewater comprises passing the printing and dyeing wastewater through a grid with a grid gap width of 1 mm to 5 mm. The grid intercepting treatment is based on the principle of physical screening, intercepts and removes fibers, fabric debris and scum in the printing and dyeing wastewater with a particle size greater than 1 mm, and prevents large-size suspended matter from entering the subsequent treatment link.

[0045] Exemplarily, the method of adjusting and homogenizing the printing and dyeing wastewater comprises stopping the printing and dyeing wastewater after grid intercepting treatment in an adjusting tank for 6 h to 12 h, and mechanically stirring at a speed of 30 r / min to 60 r / min, or stirring by introducing air. The adjusting and homogenizing treatment makes the printing and dyeing wastewater flowing in different time periods fully mixed, and outputs printing and dyeing wastewater with stable water quality and flow rate, thereby reducing the hydraulic and pollution load fluctuations in the subsequent treatment.

[0046] ​For example, the coagulation sedimentation method includes adding 100 mg / L to 300 mg / L of polyaluminum chloride as a coagulant to the adjusted and homogenized printing and dyeing wastewater. The polyaluminum chloride hydrolysis produces positively charged hydroxyl complexes, compresses the double electric layer of colloidal particles in the printing and dyeing wastewater through electrostatic neutralization, reduces the Zeta potential of colloidal particles, and destabilizes the colloidal particles. Then, 2 mg / L to 5 mg / L of polyacrylamide is added as a flocculant. The long molecular chains of polyacrylamide connect the destabilized colloidal particles and fine suspended solids through adsorption bridging, forming larger visible flocculation bodies.

[0047] After adding the polyaluminum chloride, rapid mixing is performed at a stirring rate of 200 r / min to 300 r / min for 2 min to 5 min to ensure rapid and uniform contact between the polyaluminum chloride and the printing and dyeing wastewater. After adding the polyacrylamide, slow stirring is performed at a stirring rate of 40 r / min to 60 r / min for 10 min to 15 min to promote the growth and increase of the flocculation bodies. Then, stirring is stopped, and settling and precipitation are performed for 1 h to 2 h. During the settling and precipitation process, the flocculation bodies settle to the bottom under the action of gravity, achieving solid-liquid separation. The supernatant is the pretreatment effluent, which contains significantly reduced turbidity, color, and colloidal organic matter.

[0048] In step S2, the biochemical treatment includes sequentially performing hydrolysis acidification treatment and membrane bioreactor treatment on the pretreatment effluent, utilizing microbial metabolism to degrade organic matter and achieve sludge-water separation.

[0049] For example, the hydrolysis acidification method includes performing a hydrolysis acidification reaction on the pretreatment effluent under anaerobic conditions. The dissolved oxygen concentration under anaerobic conditions is controlled at 0.2-0.5 mg / L by limiting aeration, the stirring rate is controlled at 30-50 r / min to maintain uniform suspension of the mixed liquor, the hydraulic retention time is controlled at 6 h to 12 h, the pH value is maintained at 5.5 to 6.5, and the temperature is maintained at 30°C to 38°C.

[0050] The hydrolysis acidification reaction is completed by an anaerobic bacterial community, which includes Clostridium (such as CICC 23847) and Bacteroides (such as CICC 24309) with a bacterial species ratio of 1:1. The anaerobic bacterial community is started by inoculating anaerobic digestion sludge from a municipal sewage treatment plant at an inoculation amount of 10%-15% of the effective volume. After inoculation, a 15-20 day acclimation culture stage is entered: initially, a mixture of 30% printing and dyeing wastewater and 70% clean water is used as the substrate, the proportion of printing and dyeing wastewater is increased by 10% per day, until the substrate is completely printing and dyeing wastewater, and acclimation is completed.

[0051] The extracellular enzymes secreted by the hydrolytic acidification bacteria group hydrolyze the refractory macromolecular organic matters in the pretreatment effluent into small molecular substances, and further ferment the small molecular substances into small molecular organic acids such as volatile fatty acids and alcohols, thereby improving the biodegradability of the pretreatment effluent and removing part of the chemical oxygen demand.

[0052] For example, the method for treating the membrane bioreactor includes biodegrading the pretreatment effluent treated by the hydrolytic acidification under aerobic conditions by the aerobic bacteria group, wherein the aeration intensity is controlled to be 0.3-0.6 Nm 3 / (m 2 ·h), the dissolved oxygen concentration is stably maintained at 2-4 mg / L, the mixed liquor sludge concentration is controlled to be 6000 mg / L to 10000 mg / L, the sludge age is 20-30 days, and the hydraulic retention time is 8 h to 12 h. The aerobic bacteria group utilizes the organic pollutants in the pretreatment effluent for metabolic activities, thereby greatly reducing the chemical oxygen demand and biochemical oxygen demand in the pretreatment effluent.

[0053] The aerobic bacteria group includes Pseudomonas (such as CICC 10351), Bacillus (such as CICC 10732) and nitrifying bacteria (such as CICC 10483), wherein the ratio of the number of Pseudomonas and Bacillus is 2:1, the total amount of the two is 70% of the total amount of the bacteria group, and the nitrifying bacteria accounts for 30% of the total amount of the bacteria group.

[0054] The aerobic bacteria group is started by inoculating the aerobic activated sludge of a municipal sewage treatment plant, and the inoculation amount is 15%-20% of the effective volume. After inoculation, the bacteria group enters the domestication stage: initially, the sludge load is 0.03 kgCOD / (kgMLSS·d), and every 3 days, the load is increased by 0.02 kgCOD / (kgMLSS·d) until the stable running load of 0.05-0.15 kgCOD / (kgMLSS·d) is reached, and the cultivation and domestication of the bacteria group are completed.

[0055] It should be noted that the anaerobic bacteria group and the aerobic bacteria group involved in step S2 are not limited to the specific strains and ratios described above. Any bacteria group that can hydrolyze and ferment refractory macromolecular organic matters under anaerobic conditions, improve the biodegradability of the pretreatment effluent, and remove part of the chemical oxygen demand, and any bacteria group that can efficiently degrade organic pollutants under aerobic conditions and greatly reduce the chemical oxygen demand and biochemical oxygen demand in the pretreatment effluent are suitable for the process.

[0056] After biodegradation, microfiltration or ultrafiltration treatment is performed to separate the sludge and water, the membrane pore size is controlled to be 0.1 μm to 0.4 μm, and the membrane flux is controlled to be 15 L / (m 2 ·h) to 25 L / (m 2• h). The membrane separation process completely intercepts suspended solids, bacteria and macromolecular substances to obtain the biochemical treatment effluent. The biochemical treatment effluent has low turbidity and is clear and transparent.

[0057] In step S3, the softening treatment includes sequentially performing oxidation breaking treatment and fluidized crystallization softening treatment on the biochemical treatment effluent.

[0058] For example, the method of oxidation breaking treatment includes adding ozone to the biochemical treatment effluent, and the ozone dosage is controlled to be 50 mg / L to 80 mg / L, and the reaction time is controlled to be 20 min to 30 min. The ozone molecule and the hydroxyl radical generated in the water body have strong oxidizing property, can effectively break the molecular chain of organic matter complexed with scale-forming ions such as calcium ions and magnesium ions, destroy the stable structure of organic-inorganic complex, and release the wrapped calcium ions and magnesium ions in free state into the water body, thereby eliminating the interference of organic matter on the subsequent crystallization process.

[0059] For example, the fluidized crystallization softening treatment is performed immediately after the oxidation breaking treatment, and the method includes adding sodium carbonate to the biochemical treatment effluent after the oxidation breaking treatment, and adjusting the pH value to 9.0 to 10.0. The addition of sodium carbonate provides carbonate ions, which react with free calcium ions in the water body to form calcium carbonate precipitate.

[0060] Subsequently, quartz sand with a particle size of 0.2 mm to 0.5 mm is added to the water body as a seed crystal, the quartz sand seed crystal dosage is controlled to be 20 g / L to 50 g / L, and the upward flow rate is controlled to be 20 m / h to 40 m / h, so that the quartz sand seed crystal is in a fluidized state, and the hydraulic retention time is controlled to be 30 min to 60 min.

[0061] Under the fluidized state, the calcium carbonate precipitate preferentially nucleates and grows on the surface of the quartz sand seed crystal in a heterogeneous phase, the fluidized condition avoids the blockage of the seed bed layer, strengthens the solid-liquid mass transfer efficiency, and realizes the directional crystallization and separation of scale-forming ions. The generated calcium carbonate crystals are periodically separated and discharged, and the total hardness of the effluent is controlled to be less than 50 mg / L (calculated as calcium carbonate). The supernatant is softening effluent, and the concentration of scale-forming ions in the softening effluent is significantly reduced, and the content of organic matter is further reduced.

[0062] In step S4, the nanofiltration separation treatment is performed under pressure driving, and the separation membrane is used to selectively separate the dissolved inorganic salt in the softening effluent.

[0063] For example, the method of nanofiltration separation treatment includes passing the softening effluent through a nanofiltration separation membrane with a molecular weight cut-off of 200 Da to 400 Da under an operating pressure of 1.0 MPa to 2.5 MPa, and controlling the recovery rate to be 70% to 80%, so as to balance the high permeability to monovalent salt and the high interception rate to divalent salt.

[0064] The nanofiltration separation membrane has high rejection rate for divalent and multivalent ions, and has partial permeability for monovalent ions. Under the action of operating pressure and membrane selectivity, the dissolved inorganic salts in the softened product water are separated.

[0065] The separation process obtains two streams, one is the nanofiltration permeate, and the main components of the nanofiltration permeate are sodium chloride and a small amount of monovalent ions; the other is the nanofiltration concentrate, and the main component of the nanofiltration concentrate is sodium sulfate, and contains trace amounts of residual calcium ions and sulfate ions.

[0066] In step S5, the seed fluidization descaling treatment is achieved by adding seed crystals and inducing preferential precipitation of supersaturated scale-forming ions under fluidization conditions to achieve deep removal of residual hardness ions.

[0067] For example, the method of seed fluidization descaling treatment includes adding calcium sulfate seed crystals with a particle size of 5 μm to 50 μm to the nanofiltration concentrate, and the seed crystal addition concentration is controlled to be 5 g / L to 10 g / L. Subsequently, the system is placed in a fluidized state at a stirring rate of 100 rpm to 300 rpm, and the hydraulic retention time is controlled to be 5 min to 15 min.

[0068] Under the condition of fluidization, the calcium sulfate seed crystals provide a large number of heterogeneous nucleation sites for the precipitation of calcium sulfate, induce the preferential precipitation of supersaturated calcium sulfate in the nanofiltration concentrate on the surface of the seed crystals, and avoid spontaneous homogeneous nucleation and scaling on the wall surface or membrane surface of the container. The fluid shear effect generated by mechanical stirring promotes the renewal and peeling of the precipitated crystals from the surface of the seed crystals, and maintains the activity of the seed crystal surface.

[0069] After the seed fluidization descaling treatment, a cyclone separation operation is performed, the underflow is discharged to precipitate calcium sulfate crystals, and the supernatant is the descaled concentrate, the calcium ion concentration in the descaled concentrate is controlled to be less than 20 mg / L, and the descaled concentrate has a low scaling tendency.

[0070] In step S6, the membrane concentration treatment is achieved by reverse osmosis process to purify and concentrate the salt.

[0071] For example, the method of membrane concentration treatment of the nanofiltration permeate includes performing reverse osmosis concentration operation on the nanofiltration permeate under an operating pressure of 1.5 MPa to 4.0 MPa. The reverse osmosis process selectively permeates water molecules and rejects dissolved salts, until the sodium chloride concentration in the concentrate reaches 60 g / L or more, to obtain a sodium chloride concentrate. The process simultaneously produces reverse osmosis product water with an electrical conductivity of less than 50 μS / cm.

[0072] Exemplarily, the method for performing the membrane concentration treatment on the descaling concentrated solution comprises performing a disc-tube reverse osmosis concentration operation on the descaling concentrated solution at an operating pressure of 3.0 MPa to 8.0 MPa. The high operating pressure is used to overcome the high osmotic pressure caused by the increase of the sodium sulfate concentration, so as to realize deep concentration until the sodium sulfate concentration in the concentrated solution reaches 80 g / L or more, and obtain the sodium sulfate concentrated solution.

[0073] In step S7, the evaporation solidification treatment is promoted by heating and negative pressure conditions.

[0074] Exemplarily, the method for performing the evaporation solidification treatment comprises heating the sludge generated in the membrane concentration treatment process and the crystallization waste residue at a temperature of 70°C to 90°C, and maintaining the system vacuum degree in the range of -0.06 MPa to -0.09 MPa. The negative pressure condition effectively reduces the boiling point of water, thereby accelerating the water evaporation process. The condensed water generated after the water evaporation is reused, and the residual solid is transported for disposal.

[0075] Exemplary system:

[0076] As shown in Figure 2 A dyeing wastewater deep treatment and salt control recycling system for realizing the above process comprises, in sequence, a grid, a regulating tank, a coagulation and sedimentation device, a hydrolysis acidification tank, a membrane bioreactor, an ozone oxidation tower, a fluidized bed crystallizer, a nanofiltration device, a seed fluidization reactor, a first reverse osmosis device, a second reverse osmosis device, and an evaporator, which are connected by pipes and pumps.

[0077] Exemplarily, the specific configuration of the system is as follows.

[0078] The grid is configured with a mechanical grid with a grid gap width of 1 mm to 5 mm; the water inlet of the grid is used to receive the dyeing wastewater, and the water outlet of the grid is connected to the water inlet of the regulating tank by a pipe.

[0079] The regulating tank is configured with a mechanical stirrer or an aeration device; the water outlet of the regulating tank is connected to the water inlet of the coagulation and sedimentation device by a pipe.

[0080] The coagulation and sedimentation device comprises a rapid mixing tank, a slow flocculation tank, and a sedimentation tank arranged in series; the rapid mixing tank is configured with a polyaluminum chloride dosing device and a stirrer with a rotating speed of 200 r / min to 300 r / min; the slow flocculation tank is configured with a polyacrylamide dosing device and a stirrer with a rotating speed of 40 r / min to 60 r / min; the hydraulic retention time of the sedimentation tank is set to 1 h to 2 h; the water outlet of the coagulation and sedimentation device is connected to the water inlet of the hydrolysis acidification tank by a pipe.

[0081] The hydrolysis acidification tank is configured with a pH control system and a temperature control system; the water outlet of the hydrolysis acidification tank is connected to the water inlet of the membrane bioreactor by a pipe.

[0082] The membrane bioreactor is configured with an aerobic biological reaction zone and a membrane separation zone, and the membrane separation zone is provided with a microfiltration or ultrafiltration membrane assembly with a pore size of 0.1 to 0.4 μm; a water outlet of the membrane bioreactor is connected to a water inlet of the ozone oxidation tower through a pipeline.

[0083] The ozone oxidation tower is configured with an ozone generator and a gas distribution system; a water outlet of the ozone oxidation tower is connected to a water inlet of the fluidized bed crystallizer through a pipeline.

[0084] The fluidized bed crystallizer is configured with a sodium carbonate feeding device, an on-line pH monitor, a quartz sand seed feeding port and a seed separation device, and the upflow velocity of the fluidized bed crystallizer is controlled to be 20 to 40 m / h; a water outlet of the fluidized bed crystallizer is connected to a water inlet of the nanofiltration device through a pipeline.

[0085] The nanofiltration device is configured with a nanofiltration membrane assembly with a molecular weight cut-off of 200 to 400 Da and a high-pressure pump; the nanofiltration device is provided with two water outlets, i.e., a nanofiltration permeate outlet and a nanofiltration concentrate outlet; the nanofiltration permeate outlet is connected to a water inlet of the first reverse osmosis device through a pipeline, and the nanofiltration concentrate outlet is connected to a water inlet of the seed fluidized reactor through a pipeline.

[0086] The seed fluidized reactor is configured with a calcium sulfate seed feeding device, a mechanical stirrer with a rotating speed of 100 to 300 rpm and a cyclone separator; a water outlet of the seed fluidized reactor is connected to a water inlet of the second reverse osmosis device through a pipeline.

[0087] The first reverse osmosis device is configured with a reverse osmosis membrane assembly; a concentrated water outlet of the first reverse osmosis device outputs a sodium chloride concentrate.

[0088] The second reverse osmosis device adopts a disc-and-tube reverse osmosis structure; a concentrated water outlet of the second reverse osmosis device outputs a sodium sulfate concentrate.

[0089] The evaporator is configured with a heating coil and a vacuum pump; a feed inlet of the evaporator is connected to a slag discharge port of the first and second reverse osmosis devices through a pipeline; a steam condensate water outlet of the evaporator is connected to a water reuse pipeline, and a solid material outlet is used for external transportation of solid waste.

[0090] In use, the printing and dyeing wastewater first enters the grid to remove large-size suspended solids; then enters the adjusting tank for water quality and quantity homogenization; the homogenized wastewater enters the coagulation and sedimentation equipment to remove colloidal substances by adding polyaluminum chloride and polyacrylamide; the coagulation and sedimentation effluent enters the hydrolysis acidification tank for hydrolysis acidification under anaerobic conditions to improve the biodegradability of the wastewater; then enters the membrane bioreactor for aerobic biological treatment and membrane separation to further remove organic substances.

[0091] The membrane bioreactor water production enters an ozone oxidation tower, and the organic-inorganic complex is destroyed by ozone oxidation; the water after oxidation enters a fluidized bed crystallizer, and calcium and magnesium ions are removed by adding sodium carbonate and quartz sand seeds under fluidization; the softened water is pumped into a nanofiltration device by a high-pressure pump, and a nanofiltration permeate mainly containing sodium chloride and a nanofiltration concentrate mainly containing sodium sulfate are separated.

[0092] The nanofiltration permeate enters a first reverse osmosis device to concentrate to obtain a sodium chloride concentrate; the nanofiltration concentrate enters a seed fluidized reactor, and after further removing residual hardness by adding calcium sulfate seeds, enters a second reverse osmosis device to concentrate to obtain a sodium sulfate concentrate; the sludge and crystallization waste slag produced by each reverse osmosis device enter an evaporator for evaporation and solidification, and the condensed water is recycled, and the solid waste is transported out.

[0093] The water quality composition and concentration of the raw wastewater used in the following examples and comparative examples include chemical oxygen demand 1200 mg / L, total dissolved solids 5800 mg / L, total hardness (calculated as calcium carbonate) 480 mg / L, calcium ion 120 mg / L, sulfate ion 1600 mg / L, chloride ion 1250 mg / L, and total organic carbon 185 mg / L, and the pH value is 8.2.

[0094] Example 1:

[0095] A dyeing wastewater advanced treatment and salt control recycling process, comprising the following steps:

[0096] Step S1: The dyeing wastewater is subjected to grid interception treatment by passing through a grid with a grid width of 3 mm; the dyeing wastewater subjected to the grid interception treatment is allowed to stay in a conditioning tank for 9 h and subjected to conditioning and homogenization treatment by mechanical stirring at a speed of 45 r / min; 200 mg / L of polyaluminum chloride is added to the dyeing wastewater subjected to the conditioning and homogenization treatment as a coagulant, and rapid mixing is performed at a stirring speed of 250 r / min for 3 min; then 3 mg / L of polyacrylamide is added as a flocculant, and slow stirring is performed at a stirring speed of 50 r / min for 12 min; after that, stirring is stopped, and standing and sedimentation are performed for 1.5 h, and the supernatant is the pretreatment water production.

[0097] Step S2: The pretreatment water production is subjected to hydrolysis acidification reaction under anaerobic conditions, the hydraulic retention time is controlled to be 9 h, the pH value is maintained at 6.0, and the temperature is maintained at 35℃; the pretreatment water production subjected to the hydrolysis acidification treatment is subjected to biodegradation under aerobic conditions, the mixed liquid sludge concentration is controlled to be 8000 mg / L, and the hydraulic retention time is 10 h; ultrafiltration treatment is performed to realize mud-water separation, the membrane pore size is controlled to be 0.2 μm, the membrane flux is controlled to be 20 L / (m 2 ·h), and the biochemical treatment water production is obtained.

[0098] Step S3: ozone was added into the biochemical treatment effluent, the ozone dosage was controlled at 65 mg / L, and the reaction time was controlled at 25 min for oxidation and complex breaking treatment; sodium carbonate was added into the biochemical treatment effluent subjected to the oxidation and complex breaking treatment, and the pH value was adjusted to 9.5; then quartz sand with a particle size of 0.3 mm was added into the water body as a seed crystal, the quartz sand seed crystal dosage was controlled at 35 g / L, and the upflow velocity was controlled at 30 m / h, so that the quartz sand seed crystal was in a fluidized state, and the hydraulic retention time was controlled at 45 min; the generated calcium carbonate crystals were separated and discharged periodically, and the supernatant was softening effluent.

[0099] Step S4: the softening effluent was subjected to nanofiltration separation membrane with a molecular weight cut-off of 300 Da at an operating pressure of 1.8 MPa, and the recovery rate was controlled at 75%, to obtain a nanofiltration permeate and a nanofiltration concentrate.

[0100] Step S5: calcium sulfate seed crystals with a particle size of 30 μm were added into the nanofiltration concentrate, and the seed crystal dosage was controlled at 7 g / L; the system was in a fluidized state at a stirring speed of 200 rpm, and the hydraulic retention time was controlled at 10 min; a cyclone separation operation was performed, the underflow was discharged to precipitate calcium sulfate crystals, and the supernatant was a descaled concentrate.

[0101] Step S6: the nanofiltration permeate was subjected to reverse osmosis concentration operation at an operating pressure of 2.5 MPa to obtain a sodium chloride concentrate; the descaled concentrate was subjected to a disc-tube reverse osmosis concentration operation at an operating pressure of 5.0 MPa to obtain a sodium sulfate concentrate.

[0102] Step S7: the sludge and the crystallization waste residue were heated at a temperature of 80 ℃, and the system vacuum degree was maintained at-0.07 MPa, the condensed water generated after water evaporation was reused, and the residual solid was transported and disposed.

[0103] Example 2:

[0104] The difference between this example and Example 1 is that in Step S3, the ozone dosage is controlled at 50 mg / L, and the quartz sand seed crystal dosage is controlled at 50 g / L; the other steps are consistent with Example 1.

[0105] Example 3:

[0106] The difference between this example and Example 1 is that in Step S3, the ozone dosage is controlled at 50 mg / L, and the quartz sand seed crystal dosage is controlled at 20 g / L; the other steps are consistent with Example 1.

[0107] Example 4:

[0108] The embodiment is different from example 1 in that: in step S3, the ozone dosage is controlled to be 65 mg / L, and the quartz sand seed dosage concentration is controlled to be 20 g / L; the remaining steps are consistent with example 1.

[0109] Example 5:

[0110] The embodiment is different from example 1 in that: in step S3, the ozone dosage is controlled to be 65 mg / L, and the quartz sand seed dosage concentration is controlled to be 35 g / L; the remaining steps are consistent with example 1.

[0111] Example 6:

[0112] The embodiment is different from example 1 in that: in step S3, the ozone dosage is controlled to be 65 mg / L, and the quartz sand seed dosage concentration is controlled to be 50 g / L; the remaining steps are consistent with example 1.

[0113] Example 7:

[0114] The embodiment is different from example 1 in that: in step S3, the ozone dosage is controlled to be 80 mg / L, and the quartz sand seed dosage concentration is controlled to be 20 g / L; the remaining steps are consistent with example 1.

[0115] Example 8:

[0116] The embodiment is different from example 1 in that: in step S3, the ozone dosage is controlled to be 80 mg / L, and the quartz sand seed dosage concentration is controlled to be 35 g / L; the remaining steps are consistent with example 1.

[0117] Example 9:

[0118] The embodiment is different from example 1 in that: in step S3, the ozone dosage is controlled to be 80 mg / L, and the quartz sand seed dosage concentration is controlled to be 50 g / L; the remaining steps are consistent with example 1.

[0119] Comparative example 1:

[0120] A printing and dyeing wastewater advanced treatment and salt control recycling process, comprising the following steps:

[0121] Step S1: The printing and dyeing wastewater was subjected to grid interception treatment by passing through a grid with a grid width of 3 mm; the printing and dyeing wastewater subjected to the grid interception treatment was subjected to adjustment and homogenization treatment by staying in an adjustment tank for 9 h and being subjected to mechanical stirring at a speed of 45 r / min; 200 mg / L of polyaluminum chloride was added to the printing and dyeing wastewater subjected to the adjustment and homogenization treatment as a coagulant, and rapid mixing was performed at a stirring speed of 250 r / min for 3 min; then, 3 mg / L of polyacrylamide was added as a flocculant, and slow stirring was performed at a stirring speed of 50 r / min for 12 min; after that, stirring was stopped, and standing and sedimentation were performed for 1.5 h, and the supernatant was the pretreatment effluent.

[0122] Step S2: The pretreatment effluent was subjected to hydrolysis acidification reaction under anaerobic conditions, the hydraulic retention time was controlled to be 9 h, the pH value was maintained at 6.0, and the temperature was maintained at 35℃; the pretreatment effluent subjected to the hydrolysis acidification treatment was subjected to biodegradation under aerobic conditions, the mixed liquid sludge concentration was controlled to be 8000 mg / L, and the hydraulic retention time was 10 h; the sludge and water were separated by ultrafiltration treatment, the membrane pore size was controlled to be 0.2 μm, and the membrane flux was controlled to be 20 L / (m 2 ·h), and the biochemical treatment effluent was obtained.

[0123] Step S3: Sodium carbonate was added to the biochemical treatment effluent to adjust the pH value to 9.5; then, quartz sand with a particle size of 0.3 mm was added to the water body as a seed crystal, the quartz sand seed crystal addition concentration was controlled to be 35 g / L, and the upward flow rate was controlled to be 30 m / h, so that the quartz sand seed crystal was in a fluidized state, and the hydraulic retention time was controlled to be 45 min; the generated calcium carbonate crystals were regularly separated and discharged, and the supernatant was the softening effluent.

[0124] Step S4: The softening effluent was subjected to nanofiltration separation membrane under an operating pressure of 1.8 MPa, the molecular weight cut-off was 300 Da, the recovery rate was controlled to be 75%, and the nanofiltration permeate and the nanofiltration concentrate were obtained.

[0125] Step S5: Calcium sulfate seed crystals with a particle size of 30 μm were added to the nanofiltration concentrate, the seed crystal addition concentration was controlled to be 7 g / L; the system was in a fluidized state at a stirring speed of 200 rpm, and the hydraulic retention time was controlled to be 10 min; cyclone separation operation was performed, the underflow was discharged to precipitate calcium sulfate crystals, and the supernatant was the descaled concentrate.

[0126] Step S6: The nanofiltration permeate was subjected to reverse osmosis concentration operation under an operating pressure of 2.5 MPa, and the sodium chloride concentrate was obtained; the descaled concentrate was subjected to disc-tube reverse osmosis concentration operation under an operating pressure of 5.0 MPa, and the sodium sulfate concentrate was obtained.

[0127] Step S7: The sludge and crystalline waste residue are heated at a temperature of 80℃, and the system is maintained at a vacuum degree of -0.07 MPa. The condensed water generated after evaporation of the moisture is reused, and the residual solid is transported out for disposal.

[0128] Comparative Example 2:

[0129] A printing and dyeing wastewater advanced treatment and salt control recycling process, comprising the following steps:

[0130] Step S1: The printing and dyeing wastewater is subjected to grid retention treatment by passing through a grid with a grid width of 3 mm. The printing and dyeing wastewater subjected to the grid retention treatment is allowed to stay in a conditioning tank for 9 h and subjected to conditioning and homogenization treatment by mechanical stirring at a speed of 45 r / min. 200 mg / L of polyaluminum chloride is added to the printing and dyeing wastewater subjected to the conditioning and homogenization treatment as a coagulant, and rapid mixing is performed at a stirring speed of 250 r / min for 3 min. Then, 3 mg / L of polyacrylamide is added as a flocculant, and slow stirring is performed at a stirring speed of 50 r / min for 12 min. After that, stirring is stopped, and the supernatant is obtained after standing and sedimentation for 1.5 h.

[0131] Step S2: The pretreated water is subjected to hydrolysis acidification reaction under anaerobic conditions, the hydraulic retention time is controlled to be 9 h, the pH value is maintained at 6.0, and the temperature is maintained at 35℃. The pretreated water subjected to the hydrolysis acidification treatment is subjected to biodegradation under aerobic conditions, the mixed liquor sludge concentration is controlled to be 8000 mg / L, and the hydraulic retention time is 10 h. Ultrafiltration treatment is performed to realize mud-water separation, the membrane pore size is controlled to be 0.2 μm, and the membrane flux is controlled to be 20 L / (m 2 ·h), to obtain the biochemical treatment effluent.

[0132] Step S3: Ozone is added to the biochemical treatment effluent, the ozone addition amount is controlled to be 65 mg / L, and the reaction time is controlled to be 25 min, to perform oxidation and breakage treatment, to obtain the oxidation and breakage effluent.

[0133] Step S4: The oxidation and breakage effluent is subjected to nanofiltration separation membrane under an operating pressure of 1.8 MPa, the molecular weight cut-off is 300 Da, and the recovery rate is controlled to be 75%, to obtain the nanofiltration permeate and the nanofiltration concentrated liquid.

[0134] Step S5: Calcium sulfate seed crystals with a particle size of 30 μm are added to the nanofiltration concentrated liquid, the seed crystal addition concentration is controlled to be 7 g / L, the system is in a fluidized state at a stirring speed of 200 rpm, and the hydraulic retention time is controlled to be 10 min. Cyclone separation operation is performed, the underflow is discharged to precipitate calcium sulfate crystals, and the supernatant is the descaled concentrated liquid.

[0135] Step S6: The nanofiltration permeate is subjected to reverse osmosis concentration operation at an operating pressure of 2.5 MPa to obtain a sodium chloride concentrate; the defouled concentrate is subjected to disc-tube reverse osmosis concentration operation at an operating pressure of 5.0 MPa to obtain a sodium sulfate concentrate.

[0136] Step S7: The sludge and the crystallization waste residue are heated at a temperature of 80°C, and the system is maintained at a vacuum degree of-0.07 MPa; the condensed water produced after evaporation of the moisture is reused, and the residual solid is transported out for disposal.

[0137] Experimental Example 1

[0138] Based on the dyeing wastewater advanced treatment and salt control recycling processes of Examples 1-9 and Comparative Examples 1-2, the following indexes are detected:

[0139] 1. The total hardness of the softened effluent is used to evaluate the overall removal effect of the fluidized crystallization softening treatment on the scale-forming ions. The softened effluent is taken as the test water sample, the test method refers to GB / T 7477-1987, the EDTA disodium standard titration solution is used to titrate the water sample, the total concentration of calcium and magnesium ions in the water sample is calculated according to the volume consumed, and the calculation result is expressed in milligrams per liter (mg / L) of calcium carbonate.

[0140] 2. The total organic carbon in the softened effluent is used to indirectly represent the degradation and mineralization degree of the organic matter by the oxidation and complex breaking treatment. The softened effluent is taken as the test water sample, the test method refers to HJ 501-2009, the total organic carbon analyzer is used, the water sample is high-temperature catalytic combustion, the generated carbon dioxide is detected by a non-dispersive infrared detector, and the total organic carbon concentration value is read out and recorded, with the unit of milligrams per liter (mg / L).

[0141] 3. The concentration of sulfate ions in the nanofiltration permeate is used to evaluate the selective separation effect of the nanofiltration membrane on divalent salts. The nanofiltration permeate outlet water sample is taken as the test water sample, the test method refers to GB / T 11899-1989, in hydrochloric acid medium, the sulfate ions in the water sample react with barium ions to generate barium sulfate precipitate, the precipitate is filtered and calcined to constant weight, and the concentration of sulfate ions is calculated according to the mass of the barium sulfate precipitate, with the unit of milligrams per liter (mg / L).

[0142] 4. The concentration of calcium ions in the defouled concentrate is used to evaluate the deep removal effect of the seed fluidized defouling treatment on residual hardness ions. The supernatant after cyclone separation (defouled concentrate) is taken as the test water sample, the test method refers to GB / T 11905-1989, the water sample is acidified with nitric acid, and the absorbance of calcium element is measured at a specific wavelength using an acetylene-air flame atomic absorption spectrophotometer. Through comparison with the calibration curve of the series of standard solutions, the concentration of calcium ions in the water sample is calculated, with the unit of milligrams per liter (mg / L).

[0143] 5. The scaling tendency of reverse osmosis system is used to comprehensively evaluate the scaling potential of the final concentrate from the perspective of thermodynamics, and the Langelier saturation index (LSI) is used as the evaluation basis. Sodium chloride concentrate and sodium sulfate concentrate are taken as test water samples respectively, and the test method refers to ASTM D3739-19. By measuring the pH value, total dissolved solids, calcium ion concentration, total alkalinity of the water sample and querying the corresponding constant of water temperature, LSI is calculated. LSI greater than 0 indicates that the water sample has a scaling tendency, and the larger the value, the higher the scaling risk; LSI equal to 0 indicates the equilibrium state; LSI less than 0 indicates a corrosion tendency.

[0144] The results are shown in the following table:

[0145] Table 1 Comparison of experimental results

[0146]

[0147] In Example 5, the process parameter combination of ozone dosage 65 mg / L and quartz sand seed dosage concentration 35 g / L is adopted, which specifically shows that: first, the ozone dosage of 65 mg / L effectively breaks the molecular chain of organic-inorganic complex, and releases the calcium ions and magnesium ions wrapped in the water body in the form of free state. At this dosage, the hydroxyl radicals produced by ozone in the water body have strong oxidizing property, which can efficiently destroy the stable complex structure formed by organic matter and scaling ions, so as to reduce the total organic carbon of softened water to 10.0 mg / L, thus creating low-interference water quality conditions for subsequent crystallization reaction. Second, the quartz sand seed dosage concentration of 35 g / L provides sufficient heterogeneous nucleation sites for calcium carbonate precipitation. In the fluidized state, the free calcium ions and the carbonate ions provided by the sodium carbonate dosage preferentially crystallize and grow on the surface of the seed, avoiding the scaling problem caused by homogeneous nucleation. At this concentration, the total hardness of the softened water is as low as 121 mg / L in terms of calcium carbonate, which significantly reduces the pollution risk of the subsequent nanofiltration membrane. Further, on the one hand, ozone destroys the complex structure to fully expose the scaling ions, and on the other hand, quartz sand seeds accelerate ion removal through heterogeneous nucleation, so that the oxidation and complex destruction process releases free calcium and magnesium ions, and the fluidized crystallization softening process forms a directional precipitation process, which forms a complement to each other. The combination of the two makes the concentration of sulfate ions in the nanofiltration permeate only 39 mg / L, and the concentration of calcium ions in the defouling concentrate is reduced to 9 mg / L, and the Langelier index LSI is 0.18, which is close to the equilibrium state, effectively controlling the scaling tendency.

[0148] Example 2 adopts ozone dosage 50 mg / L, quartz sand seed dosage concentration 50 g / L, due to insufficient ozone dosage, organic-inorganic complex is not completely broken, softened water total organic carbon is 22.8 mg / L, residual organic matter interferes with calcium carbonate crystallization, resulting in total hardness rising to 157 mg / L; although the quartz sand concentration is increased, but due to insufficient release of free calcium ions, the crystallization efficiency is not significantly improved, LSI 0.49, the scaling risk is obviously higher than that of example 5. Example 7 adopts ozone dosage 80 mg / L, quartz sand seed dosage concentration 20 g / L, although the excess ozone further degrades organic matter to total organic carbon 13.3 mg / L, but 20 g / L of quartz sand seed concentration is not enough to provide enough crystallization sites, resulting in softened water total hardness 145 mg / L, and the excess ozone increases the operation cost, and does not form an effective match with the seed concentration, LSI 0.37, and the excess ozone increases the operation cost, and does not form an effective match with the seed concentration.

[0149] Example 3 adopts ozone dosage 50 mg / L, quartz sand seed dosage concentration 20 g / L, insufficient ozone breakage leads to total organic carbon 21.4 mg / L, at the same time, insufficient seed concentration, double effect makes free calcium ions cannot be completely precipitated, total hardness reaches 151 mg / L, LSI 0.43, low seed concentration reduces the solid-liquid mass transfer efficiency under fluidized state, resulting in incomplete crystallization reaction. Example 6 adopts ozone dosage 65 mg / L, quartz sand seed dosage concentration 50 g / L, although the ozone breakage is sufficient to make total organic carbon 16.3 mg / L, but 50 g / L of quartz sand concentration makes the solid particles in the fluidized bed supersaturated, it is difficult to maintain the best upward flow rate of 30 m / h, resulting in calcium carbonate crystal growth being blocked, total hardness rising to 140 mg / L, LSI 0.33, and high concentration of seed increases the subsequent separation cost.

[0150] Example 4 adopts ozone dosage 65 mg / L, quartz sand seed dosage concentration 20 g / L, ozone breakage is sufficient but 20 g / L seed concentration is not enough to completely capture free calcium ions, total hardness is 147 mg / L, sulfate ion concentration in nanofiltration permeate is 80 mg / L, calcium ions still exist in free state, affecting the retention selectivity of nanofiltration membrane to divalent salt, LSI 0.38. Example 8 adopts ozone dosage 80 mg / L, quartz sand seed dosage concentration 35 g / L, excess ozone does not significantly improve the breakage effect, total organic carbon 12.5 mg / L, and 80 mg / L dose leads to residual oxidizing substances in water, which causes potential damage to the nanofiltration membrane, total hardness 134 mg / L, LSI 0.28, which does not further reduce the hardness. Example 9 adopts ozone dosage 80 mg / L, quartz sand seed dosage concentration 50 g / L, total hardness 143 mg / L, total organic carbon 15.4 mg / L, LSI 0.36, no additional advantage is shown.

[0151] Comparative Example 1 lacks the oxidation breaking treatment, and no ozone is added, so the organic-inorganic complex is not destroyed, and the scaling ions are still wrapped by the organic matter. The softening treatment is only carried out by adding sodium carbonate and quartz sand seeds, and the calcium ions are not fully dissociated, so the crystallization efficiency is very low, the total hardness of the softened water is as high as 225 mg / L, the concentration of sulfate ions in the nanofiltration permeate is 290 mg / L, the divalent salt rejection effect is poor, the unreleased calcium ions form a supersaturated solution with the sulfate ions, which causes the nanofiltration membrane surface to scale, the LSI index is 1.05, and the scaling risk is significantly higher than that of Example 5.

[0152] Comparative Example 2 lacks the fluidized crystallization softening treatment, and only the oxidation breaking treatment is carried out, without adding sodium carbonate and quartz sand seeds, so the dissociated calcium ions are not removed, the total hardness of the softened water is 206 mg / L, which is much higher than that of Example 5, and due to the lack of seed induction, the calcium ions still exist in the water body in the form of free ions. This makes the concentration of calcium ions in the nanofiltration concentrate high, and the concentration of calcium ions in the concentrate after descaling is 67 mg / L, and the LSI index is 0.88. Although calcium sulfate seeds are added in the subsequent seed fluidized descaling treatment, the calcium ions not removed in the early stage still form a supersaturated solution with the sulfate ions, and the reverse osmosis system has a significantly higher scaling tendency than Example 5.

[0153] The above is based on the ideal embodiment of the present application, and through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the contents of the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A process for advanced treatment and salt control and reuse of printing and dyeing wastewater, characterized in that, The method comprises the following steps: Step S1: pretreating the printing and dyeing wastewater to obtain pretreated water; The pretreatment comprises sequentially performing grid interception treatment, adjustment homogenization treatment and coagulation sedimentation treatment on the printing and dyeing wastewater; Step S2: performing biochemical treatment on the pretreated water to obtain biochemically treated water; the biochemical treatment comprises sequentially performing hydrolysis acidification treatment and membrane bioreactor treatment on the pretreated water; Step S3: performing softening treatment on the biochemically treated water to obtain softening water; the softening treatment comprises sequentially performing oxidation breaking treatment and fluidized crystallization softening treatment on the biochemically treated water; Step S4: performing nanofiltration separation treatment on the softening water to obtain nanofiltration permeate and nanofiltration concentrate; the nanofiltration separation treatment is performed under pressure driving, and a separation membrane is used to selectively separate the dissolved inorganic salt in the softening water; Step S5: performing crystal seed fluidized descaling treatment on the nanofiltration concentrate to obtain descaled concentrate; the crystal seed fluidized descaling treatment is performed by adding crystal seeds and inducing preferential precipitation of supersaturated scale-forming ions under fluidized conditions; Step S6: performing membrane concentration treatment on the nanofiltration permeate and the descaled concentrate to obtain sodium chloride concentrate and sodium sulfate concentrate; the membrane concentration treatment is achieved by a reverse osmosis process to purify and concentrate the salt; Step S7: performing evaporation solidification treatment on the sludge and crystallization waste residue generated in the membrane concentration treatment process; the evaporation solidification treatment is performed by heating and negative pressure conditions to promote water evaporation; In step S3, the oxidation breaking treatment uses ozone as the oxidant, the ozone dosage is 50 mg / L to 80 mg / L, and the reaction time is 20 min to 30 min; the fluidized crystallization softening treatment comprises adding sodium carbonate to adjust the pH to 9.0 to 10.0, adding quartz sand crystal seeds with a particle size of 0.2 mm to 0.5 mm, the crystal seed dosage is 20 g / L to 50 g / L, the upflow velocity is controlled to be 20 m / h to 40 m / h, and the hydraulic retention time is 30 min to 60 min; In step S5, the crystal seed fluidized descaling treatment adds calcium sulfate crystal seeds with a particle size of 5 μm to 50 μm, the crystal seed dosage is 5 g / L to 10 g / L, the stirring rate is 100 rpm to 300 rpm, and the hydraulic retention time is 5 min to 15 min.

2. The process according to claim 1, characterized in that, In step S1, the grid interception treatment has a grid gap width of 1 mm to 5 mm.

3. The process of claim 1, wherein, In step S1, the adjustment homogenization treatment has a hydraulic retention time of 6 h to 12 h and a stirring rate of 30 r / min to 60 r / min.

4. The process of claim 1, wherein, In step S1, the coagulation sedimentation treatment comprises adding 100 mg / L to 300 mg / L of polyaluminum chloride as a coagulant and 2 mg / L to 5 mg / L of polyacrylamide as a flocculant.

5. The process of claim 1, wherein, In step S4, the nanofiltration separation treatment has an operating pressure of 1.0 MPa to 2.5 MPa, the nanofiltration membrane used has a molecular weight cut-off of 200 Da to 400 Da, and the recovery rate is controlled to be 70% to 80%.

6. The process of claim 1, wherein, The operation pressure for the reverse osmosis concentration of the nanofiltration permeate in step S6 is 1.5 MPa to 4.0 MPa; and the operation pressure for the disc-tube reverse osmosis concentration of the concentrated solution after descaling is 3.0 MPa to 8.0 MPa.

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