Printing and dyeing wastewater advanced treatment and salt control recycling process and system

Abstract

The invention discloses a printing and dyeing wastewater advanced treatment and salt control recycling process and system, and belongs to the technical field of wastewater treatment. According to the process, the printing and dyeing wastewater is sequentially subjected to pretreatment of grating interception, adjustment and homogenization, and coagulating sedimentation; carrying out hydrolytic acidification and biochemical treatment in a membrane bioreactor; softening treatment of ozone oxidation complex breaking and fluidization crystallization softening; carrying out nanofiltration separation to obtain a permeate and a concentrated solution; carrying out seed crystal fluidization descaling on the concentrated solution; respectively carrying out membrane concentration on the nanofiltration permeate and the descaled concentrated solution through reverse osmosis to obtain sodium chloride and sodium sulfate concentrated solutions; and finally, carrying out evaporation curing treatment on the sludge and the crystallized waste residues. Through multi-step cooperative treatment, deep purification of the printing and dyeing wastewater and efficient separation and recycling of salt are realized, and the problems of impure nanofiltration salt separation and high system scaling risk in the prior art are solved.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a process and system for deep treatment and salt control and reuse of dyeing and printing wastewater. Background Technology

[0002] Due to its high chemical oxygen demand (COD) and total dissolved solids (TDS) content, advanced treatment and salt recovery of dyeing and printing wastewater have always been technical challenges in the industry. Current mainstream treatment processes utilize a combination of membrane bioreactors and reverse osmosis for water reuse. However, the high-salt reverse osmosis concentrate produced by this process, with its high salt concentration and complex composition, has become a key bottleneck restricting near-zero wastewater discharge. To address this issue, advanced treatment processes employ a nanofiltration-based salt separation and reverse osmosis concentration approach. By selectively separating monovalent and divalent salts through nanofiltration membranes, preliminary separation and liquid recovery of sodium sulfate and sodium chloride are achieved, effectively reducing the treatment costs associated with end-of-pipe evaporation and crystallization.

[0003] However, the aforementioned advanced processes still have significant technical drawbacks in practical applications: organic matter in dyeing and printing wastewater easily forms stable organic-inorganic complexes with scale-forming ions such as calcium and magnesium. These complexes not only act as crystallization inhibitors, hindering the directional precipitation of scale-forming ions, but also encapsulate calcium and magnesium ions, forming a supersaturated system. In existing processes, even with methods such as deep resin hardening, it is still difficult to completely remove scale-forming ions encapsulated by organic matter. This leads to a decrease in the selective separation efficiency of the membrane for monovalent and divalent salts during nanofiltration desalination, resulting in insufficient salt purity. More importantly, when the recycled liquid containing supersaturated scale-forming ions encounters changes in temperature, pH, or flow rate during transportation and storage, the stable structure of the organic-inorganic complex is disrupted. Supersaturated ions will precipitate disorderly on the surfaces of pipes and equipment, causing problems such as system blockage, membrane fouling, and decreased heat transfer efficiency, seriously affecting the long-term stable operation of the recycling process.

[0004] In existing technologies, the treatment of organic-inorganic complexes mostly adopts passive adsorption or single chemical precipitation methods, which cannot fundamentally destroy the complex structure and achieve targeted removal of scale-forming ions. As a result, the risks of impure salt separation by nanofiltration and scaling of the system have not been effectively resolved, which has restricted the further development of dyeing and printing wastewater resource reuse technology. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a process and system for deep treatment and salt control and reuse of dyeing and printing wastewater.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a process for deep treatment and salt control of dyeing and printing wastewater, comprising the following steps: Step S1: Pre-treat the dyeing and printing wastewater to obtain pre-treated wastewater; the pre-treatment includes sequentially treating the dyeing and printing wastewater with screen interception, conditioning and homogenization, and coagulation and sedimentation. Step S2: Perform biochemical treatment on the pretreated wastewater to obtain biochemically treated wastewater; the biochemical treatment includes sequentially performing hydrolysis acidification treatment and membrane bioreactor treatment on the pretreated wastewater. Step S3: Soften the biochemical treatment permeate to obtain softened permeate; the softening treatment includes sequentially performing oxidation complex-breaking treatment and fluidized crystallization softening treatment on the biochemical treatment permeate. Step S4: Perform nanofiltration separation treatment on the softened product water to obtain nanofiltration permeate and nanofiltration concentrate; the nanofiltration separation treatment is carried out under pressure and uses a separation membrane to selectively separate dissolved inorganic salts in the softened product water. Step S5: Perform seed fluidization descaling treatment on the nanofiltration concentrate to obtain a descaled concentrate; the seed fluidization descaling treatment involves adding seed crystals and inducing the preferential precipitation and separation of supersaturated scale-forming ions under fluidization conditions; Step S6: The nanofiltration permeate and the descaling concentrate are respectively subjected to membrane concentration treatment to obtain sodium chloride concentrate and sodium sulfate concentrate; the membrane concentration treatment achieves salt purification and concentration through reverse osmosis. Step S7: Evaporate and solidify the sludge and crystallized waste generated during the membrane concentration process; the evaporation and solidification process promotes water evaporation through heating and negative pressure conditions.

[0007] Furthermore, in step S1, the grid gap width of the grid interception process is 1mm to 5mm.

[0008] Furthermore, in step S1, the hydraulic residence time of the homogenization treatment is adjusted to 6h to 12h, and the stirring rate is adjusted to 30r / min to 60r / min.

[0009] Further, in step S1, the coagulation and sedimentation treatment includes 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.

[0010] Furthermore, in step S3, ozone is used as the oxidant in the oxidation and complex-breaking treatment, with an ozone dosage of 50 mg / L to 80 mg / L and a reaction time of 20 min to 30 min.

[0011] Further, in step S3, the fluidized crystallization softening treatment includes adding sodium carbonate to adjust the pH to 9.0 to 10.0, adding quartz sand seed crystals with a particle size of 0.2 mm to 0.5 mm, with a seed crystal concentration of 20 g / L to 50 g / L, controlling the upward flow rate to 20 m / h to 40 m / h, and the hydraulic retention time to 30 min to 60 min.

[0012] Furthermore, in step S4, the operating pressure of the nanofiltration separation process is 1.0 MPa to 2.5 MPa, the molecular weight cutoff of the nanofiltration membrane used is 200 Da to 400 Da, and the recovery rate is controlled at 70% to 80%.

[0013] Furthermore, in step S5, the seed crystals added in the seed fluidization descaling treatment are calcium sulfate seed crystals with a particle size of 5μm to 50μm, the seed crystal concentration is 5g / L to 10g / L, the stirring rate is 100rpm to 300rpm, and the hydraulic retention time is 5min to 15min.

[0014] Furthermore, 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 descaling concentrate is 3.0 MPa to 8.0 MPa.

[0015] Another technical solution provided by the present invention is a deep treatment and salt control reuse system for dyeing and printing wastewater, used to realize the above process, including a bar screen, equalization tank, coagulation sedimentation equipment, hydrolysis acidification tank, membrane bioreactor, ozone oxidation tower, fluidized bed crystallizer, nanofiltration device, seed fluidized reactor, first reverse osmosis device, second reverse osmosis device and evaporator connected in sequence by pipelines and pumps.

[0016] This invention addresses the shortcomings of the prior art and has the following beneficial effects: The advanced treatment and salt-controlled reuse process for dyeing and printing wastewater provided by this invention involves adding 50 mg / L to 80 mg / L of ozone to the biochemically treated wastewater through an oxidation-complex-breaking treatment. The strong oxidizing properties of ozone break down the molecular chains of organic matter complexed with calcium and magnesium ions, disrupting the stable structure of the organic-inorganic complex and releasing the encapsulated scale-forming ions into the water in a free state. This oxidation-complex-breaking treatment significantly reduces the organic matter content in the water, eliminating interference from organic matter in the subsequent crystallization process, thereby improving the precipitability of scale-forming ions. Compared to the traditional method of direct softening, this oxidation-complex-breaking treatment effectively solves the problem of scale-forming ions being difficult to release due to organic matter encapsulation, thus improving the efficiency of the subsequent crystallization reaction.

[0017] Furthermore, this invention employs fluidized bed crystallization softening treatment. Immediately after oxidation and complex breaking, sodium carbonate is added to adjust the pH to 9.0-10.0, and 20 g / L to 50 g / L of quartz sand seed crystals with a particle size of 0.2-0.5 mm are added. The fluidization state is maintained at an upward flow rate of 20 m / h-40 m / h, inducing free calcium ions to nucleate and grow heterogeneously on the seed crystal surface in the form of calcium carbonate. Fluidized bed crystallization softening treatment avoids bed clogging while enhancing the solid-liquid mass transfer process, achieving directional crystallization and efficient separation of scale-forming ions. Compared with traditional precipitation softening, this method significantly improves hardness removal efficiency and greatly reduces the risk of scaling and fouling of subsequent nanofiltration membranes.

[0018] In particular, the sequential coupling of oxidation complex-breaking treatment and fluidized crystallization softening treatment, with ozone dosage controlled at 65 mg / L for efficient complex breaking without generating excessive byproducts, combined with a quartz sand seed concentration of 35 g / L, provides sufficient nucleation sites while maintaining good fluidization, significantly reducing the total hardness and total organic carbon in the softened effluent, effectively improving the nanofiltration membrane's selectivity for separating monovalent and divalent ions, reducing sulfate ion leakage, and controlling the scaling tendency of reverse osmosis concentration. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is a process flow diagram for the deep treatment and salt control reuse of dyeing and printing wastewater. Figure 2 This is a system architecture diagram for advanced treatment and salt control of dyeing and printing wastewater. Detailed Implementation

[0020] 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.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0022] Unless otherwise specified, all raw materials described below may be commercially available or prepared using conventional methods in the art.

[0023] Exemplary method: like Figure 1 As shown, a process for advanced treatment and salt control of dyeing and printing wastewater includes the following steps: Step S1: Pre-treat the dyeing and printing wastewater to obtain pre-treated wastewater; Step S2: Perform biochemical treatment on the pretreated wastewater to obtain biochemically treated wastewater; Step S3: Soften the biochemical treatment wastewater to obtain softened wastewater; Step S4: Perform nanofiltration separation treatment on the softened permeate to obtain nanofiltration permeate and nanofiltration concentrate; Step S5: Perform seeding fluidization descaling treatment on the nanofiltration concentrate to obtain a descaled concentrate; Step S6: Perform membrane concentration treatment on the nanofiltration permeate and the descaling concentrate to obtain sodium chloride concentrate and sodium sulfate concentrate, respectively. Step S7: Evaporate and solidify the sludge and crystallized waste generated during the membrane concentration process.

[0024] Below, each step will be explained in detail.

[0025] In step S1, the pretreatment includes sequentially treating the dyeing and printing wastewater with a screen, adjusting and homogenizing it, and coagulating and settling it.

[0026] For example, a method for screen retention treatment includes passing dyeing and printing wastewater through a screen with a mesh width of 1 mm to 5 mm. Screen retention treatment is based on the principle of physical sieving, intercepting and removing fibers, fabric debris, and scum with a particle size greater than 1 mm from the dyeing and printing wastewater, preventing large suspended solids from entering subsequent treatment stages.

[0027] For example, the method of conditioning and homogenization treatment includes retaining the dyeing and printing wastewater that has been treated by screen interception in a conditioning tank for 6 to 12 hours, and mechanically stirring it at a rate of 30 to 60 r / min, or stirring it by introducing air. Conditioning and homogenization treatment fully mixes the dyeing and printing wastewater that flows in at different times and has fluctuations in water quality and flow rate, and outputs dyeing and printing wastewater with stable water quality and flow rate, thereby reducing the fluctuations in hydraulic and pollution loads in subsequent treatment.

[0028] For example, a coagulation and sedimentation treatment method includes adding 100 mg / L to 300 mg / L of polyaluminum chloride as a coagulant to homogenized and conditioned dyeing wastewater. Polyaluminum chloride hydrolyzes to produce positively charged hydroxyl complexes, which compress the electric double layer of colloidal particles in the dyeing wastewater through charge neutralization, reducing the zeta potential of the colloidal particles and destabilizing them. Subsequently, 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 flocs visible to the naked eye.

[0029] After adding polyaluminum chloride, mix rapidly at a stirring rate of 200 to 300 rpm for 2 to 5 minutes to ensure rapid and uniform contact between the polyaluminum chloride and the dyeing wastewater. After adding polyacrylamide, stir slowly at a stirring rate of 40 to 60 rpm for 10 to 15 minutes to promote floc growth. Then stop stirring and allow to settle for 1 to 2 hours. During settling, the flocs settle to the bottom under gravity, achieving solid-liquid separation. The supernatant is the pretreated wastewater, which contains significantly reduced turbidity, color, and colloidal organic matter.

[0030] In step S2, the biochemical treatment includes sequentially hydrolyzing and acidifying the pretreated water and then treating it with a membrane bioreactor, utilizing the metabolic activity of microorganisms to degrade organic matter and achieve mud-water separation.

[0031] For example, the hydrolysis-acidification treatment method includes performing a hydrolysis-acidification reaction on pretreated permeate 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 mixture, 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.

[0032] The hydrolysis and acidification reaction is carried out by anaerobic bacteria, which consist of Clostridium (e.g., CICC 23847) and Bacteroides (e.g., CICC 24309) in a 1:1 ratio. The anaerobic bacteria are initiated by inoculating anaerobic digested sludge from a municipal wastewater treatment plant at a rate of 10%-15% of the effective volume. After inoculation, a 15-20 day acclimatization period is initiated: initially using a mixture of 30% dyeing wastewater and 70% clean water as the substrate, the proportion of dyeing wastewater is increased by 10% daily until the substrate is entirely dyeing wastewater, thus completing the acclimatization process.

[0033] The hydrolytic acidifying bacteria secrete extracellular enzymes to hydrolyze the recalcitrant macromolecular organic matter in the pretreated wastewater into smaller molecules, and further ferment these smaller molecules into volatile fatty acids, alcohols, and other small organic acids, thereby improving the biodegradability of the pretreated wastewater and removing some of the chemical oxygen demand.

[0034] For example, a membrane bioreactor treatment method includes biodegrading pretreated wastewater that has undergone hydrolysis and acidification under aerobic conditions using aerobic bacteria, wherein the aeration intensity is controlled at 0.3-0.6 Nm³. 3 / (m 2 The dissolved oxygen concentration was maintained at 2-4 mg / L, the mixed liquor sludge concentration was controlled at 6000 mg / L to 10000 mg / L, the sludge age was 20-30 days, and the hydraulic retention time was 8-12 hours. Aerobic bacteria utilized the organic pollutants in the pretreated permeate for metabolic activities, significantly reducing the chemical oxygen demand (COD) and biochemical oxygen demand (BOD) in the pretreated permeate.

[0035] The aerobic bacterial community consists of Pseudomonas (e.g., CICC 10351), Bacillus (e.g., CICC 10732), and Nitrifying Bacteria (e.g., CICC 10483). The ratio of Pseudomonas to Bacillus species is 2:1, and the two together account for 70% of the total bacterial community. Nitrifying Bacteria account for 30% of the total bacterial community.

[0036] The aerobic microbial community is started by inoculating aerobic activated sludge from a municipal wastewater treatment plant. The inoculation amount is 15%-20% of the effective volume. After inoculation, the community enters the acclimatization stage: initially, it operates at a sludge load of 0.03 kg COD / (kg MLSS·d), and the load is gradually increased by 0.02 kg COD / (kg MLSS·d) every 3 days until a stable operating load of 0.05-0.15 kg COD / (kg MLSS·d) is reached, thus completing the microbial community cultivation and acclimatization.

[0037] It should be noted that the anaerobic and aerobic bacteria involved in step S2 are not limited to the specific species and ratios mentioned above. Any bacteria that can complete the hydrolysis and fermentation of recalcitrant macromolecular organic matter under anaerobic conditions, improve the biodegradability of pretreated water and remove some chemical oxygen demand, as well as bacteria that can efficiently degrade organic pollutants under aerobic conditions and significantly reduce the chemical oxygen demand and biochemical oxygen demand in pretreated water, are all applicable to this process.

[0038] After biodegradation, the material undergoes microfiltration or ultrafiltration to achieve mud-water separation. 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 / (m²). 2 •h) to 25L / (m 2(h). This membrane separation process completely removes suspended solids, bacteria, and macromolecules, yielding biochemically treated permeate. The biochemically treated permeate has low turbidity and is clear and transparent.

[0039] In step S3, the softening treatment includes sequentially performing oxidation and complex-breaking treatment and fluidized crystallization softening treatment on the biochemical treatment product water.

[0040] For example, the oxidation-based complex-breaking treatment method includes adding ozone to the biologically treated wastewater, with the ozone dosage controlled at 50 mg / L to 80 mg / L and the reaction time controlled at 20 min to 30 min. Ozone molecules and the hydroxyl radicals they generate in water have strong oxidizing properties, which can effectively break the molecular chains of organic matter complexed with scale-forming ions such as calcium and magnesium ions, destroy the stable structure of organic-inorganic complexes, and release the encapsulated calcium and magnesium ions into the water in a free state, eliminating the interference of organic matter on the subsequent crystallization process.

[0041] For example, fluidized bed crystallization softening treatment is carried out immediately after oxidative complex-breaking treatment, and the method includes adding sodium carbonate to the biochemically treated wastewater that has undergone oxidative complex-breaking treatment to adjust the pH to 9.0 to 10.0. The addition of sodium carbonate provides carbonate ions, which react with free calcium ions in the water to form calcium carbonate precipitate.

[0042] Subsequently, quartz sand with a particle size of 0.2 mm to 0.5 mm was added to the water as seed crystals. The concentration of the quartz sand seed crystals was controlled at 20 g / L to 50 g / L, and the upward flow velocity was controlled at 20 m / h to 40 m / h to keep the quartz sand seed crystals in a fluidized state. The hydraulic retention time was controlled at 30 min to 60 min.

[0043] Under fluidized bed conditions, calcium carbonate precipitates preferentially nucleate and grow heterogeneously on the surface of quartz sand seed crystals. Fluidized conditions prevent clogging of the seed bed, enhance solid-liquid mass transfer efficiency, and achieve directional crystallization and separation of scale-forming ions. The generated calcium carbonate crystals are periodically separated and discharged, controlling the total hardness of the effluent to below 50 mg / L (calculated as calcium carbonate). The supernatant is softened permeate, in which the concentration of scale-forming ions is significantly reduced, and the organic matter content is further decreased.

[0044] In step S4, nanofiltration separation is performed under pressure, using a separation membrane to selectively separate dissolved inorganic salts in the softened product water.

[0045] For example, a nanofiltration separation treatment method includes passing softened permeate through a nanofiltration membrane with a molecular weight cutoff of 200 Da to 400 Da at an operating pressure of 1.0 MPa to 2.5 MPa, controlling the recovery rate to 70% to 80%, and balancing the high permeability to monovalent salts with the high rejection rate to divalent salts.

[0046] Nanofiltration membranes exhibit high rejection rates for divalent and multivalent ions, while allowing partial permeability to monovalent ions. Under the combined effects of operating pressure and membrane selectivity, dissolved inorganic salts in softened permeate are separated.

[0047] The separation process yields two streams: one is the nanofiltration permeate, whose main components are sodium chloride and a small amount of monovalent ions; the other is the nanofiltration concentrate, whose main component is sodium sulfate and contains trace amounts of residual calcium and sulfate ions.

[0048] In step S5, the seed fluidization descaling treatment involves adding seed crystals and inducing supersaturated scale-forming ions to preferentially precipitate and separate under fluidization conditions, thereby achieving deep removal of residual hardness ions.

[0049] For example, the method of seed fluidized bed descaling includes adding calcium sulfate seed crystals with a particle size of 5 μm to 50 μm to the nanofiltration concentrate, with the seed crystal concentration controlled at 5 g / L to 10 g / L. The system is then fluidized at a stirring rate of 100 rpm to 300 rpm, and the hydraulic residence time is controlled at 5 min to 15 min.

[0050] Under fluidized conditions, calcium sulfate seed crystals provide numerous heterogeneous nucleation sites for calcium sulfate precipitation, inducing supersaturated calcium sulfate in the nanofiltration concentrate to preferentially precipitate and grow on the seed crystal surface, thus preventing spontaneous homogeneous nucleation and scaling of calcium sulfate on the container wall or membrane surface. The fluid shearing action generated by mechanical stirring promotes the renewal and peeling of precipitated crystals from the seed crystal surface, maintaining the activity of the seed crystal surface.

[0051] After the seed fluidization descaling treatment, a cyclone separation operation is performed. The precipitated calcium sulfate crystals are discharged from the underflow, and the supernatant is the descaling concentrate. The calcium ion concentration in the descaling concentrate is controlled to be below 20 mg / L to ensure that the descaling concentrate has a low scaling tendency.

[0052] In step S6, the membrane concentration process achieves salt purification and concentration through reverse osmosis.

[0053] An exemplary method for membrane concentration of nanofiltration permeate includes performing reverse osmosis concentration on the nanofiltration permeate at an operating pressure of 1.5 MPa to 4.0 MPa. The reverse osmosis process selectively permeates water molecules while retaining dissolved salts until the sodium chloride concentration in the concentrate reaches 60 g / L or higher, yielding a sodium chloride concentrate. This process simultaneously produces reverse osmosis permeate with a conductivity of less than 50 μS / cm.

[0054] For example, a method for membrane concentration of the descaling concentrate includes performing disc-tube reverse osmosis concentration at an operating pressure of 3.0 MPa to 8.0 MPa. The higher operating pressure overcomes the high osmotic pressure caused by the increased sodium sulfate concentration, achieving deep concentration until the sodium sulfate concentration in the concentrate reaches 80 g / L or higher, thus obtaining a sodium sulfate concentrate.

[0055] In step S7, the evaporation curing process promotes moisture evaporation through heating and negative pressure conditions.

[0056] For example, the evaporation solidification method includes heating the sludge and crystallization residue generated during membrane concentration at a temperature of 70°C to 90°C, while maintaining a system vacuum in the range of -0.06 MPa to -0.09 MPa. The negative pressure effectively lowers the boiling point of water, thereby accelerating the water evaporation process. The condensate generated after water evaporation is reused, and the remaining solids are transported off-site for disposal.

[0057] Exemplary system: like Figure 2 As shown, a deep treatment and salt control reuse system for dyeing and printing wastewater is used to realize the above-mentioned process. It includes a bar screen, an equalization tank, a coagulation 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, which are connected in sequence by pipelines and pumps.

[0058] For example, the specific configuration of this system is as follows.

[0059] The bar screen is equipped with a mechanical bar screen with a mesh width of 1mm to 5mm; the inlet of the bar screen is used to receive dyeing and printing wastewater, and the outlet of the bar screen is connected to the inlet of the equalization tank through a pipe.

[0060] The equalization tank is equipped with a mechanical agitator or aeration device; the outlet of the equalization tank is connected to the inlet of the coagulation and sedimentation equipment via a pipeline.

[0061] The coagulation and sedimentation equipment includes a rapid mixing tank, a slow flocculation tank, and a sedimentation tank arranged in series. The rapid mixing tank is equipped with a polyaluminum chloride dosing device and a stirrer with a rotation speed of 200 r / min to 300 r / min. The slow flocculation tank is equipped with a polyacrylamide dosing device and a stirrer with a rotation 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 outlet of the coagulation and sedimentation equipment is connected to the inlet of the hydrolysis acidification tank through a pipeline.

[0062] The hydrolysis acidification tank is equipped with a pH control system and a temperature control system; the outlet of the hydrolysis acidification tank is connected to the inlet of the membrane bioreactor via a pipe.

[0063] The membrane bioreactor is equipped with an aerobic biological reaction zone and a membrane separation zone. The membrane separation zone is equipped with microfiltration or ultrafiltration membrane modules with a pore size of 0.1μm to 0.4μm. The product water outlet of the membrane bioreactor is connected to the inlet of the ozone oxidation tower through a pipeline.

[0064] The ozone oxidation tower is equipped with an ozone generator and a gas distribution system; the outlet of the ozone oxidation tower is connected to the inlet of the fluidized bed crystallizer via a pipeline.

[0065] The fluidized bed crystallizer is equipped with a sodium carbonate dosing device, an online pH monitor, a quartz sand seed inlet, and a seed separation device. The upward flow velocity of the fluidized bed crystallizer is controlled to be 20 m / h to 40 m / h. The outlet of the fluidized bed crystallizer is connected to the inlet of the nanofiltration unit through a pipeline.

[0066] The nanofiltration unit is equipped with nanofiltration membrane modules with a molecular weight cutoff of 200 Da to 400 Da and a high-pressure pump. The nanofiltration unit has two outlets, namely the nanofiltration permeate outlet and the nanofiltration concentrate outlet. The nanofiltration permeate outlet is connected to the inlet of the first reverse osmosis unit through a pipeline, and the nanofiltration concentrate outlet is connected to the inlet of the seed fluidized reactor through a pipeline.

[0067] The seed fluidized bed reactor is equipped with a calcium sulfate seed dosing device, a mechanical stirrer with a rotation speed of 100 rpm to 300 rpm, and a hydrocyclone separator; the outlet of the seed fluidized bed reactor is connected to the inlet of the second reverse osmosis unit through a pipeline.

[0068] The first reverse osmosis unit is equipped with a reverse osmosis membrane module; the concentrate outlet of the first reverse osmosis unit outputs sodium chloride concentrate.

[0069] The second reverse osmosis unit adopts a disc tube reverse osmosis structure; the concentrate outlet of the second reverse osmosis unit outputs sodium sulfate concentrate.

[0070] The evaporator is equipped with a heating coil and a vacuum pump; the feed inlet of the evaporator is connected to the slag discharge outlet of the first and second reverse osmosis units via a pipeline; the steam condensate outlet of the evaporator is connected to a recycled water pipeline, and the solid material outlet is used for transporting solid waste.

[0071] In operation, the dyeing and printing wastewater first enters the screen to remove large suspended solids; then it enters the equalization tank for water quality and quantity homogenization; the homogenized wastewater enters the coagulation sedimentation equipment, where polyaluminum chloride and polyacrylamide are added for coagulation and sedimentation to remove colloidal substances; the effluent from the coagulation sedimentation enters the hydrolysis acidification tank for hydrolysis and acidification under anaerobic conditions to improve the biodegradability of the wastewater; then it enters the membrane bioreactor for aerobic biological treatment and membrane separation to further remove organic matter.

[0072] The permeate from the membrane bioreactor enters the ozone oxidation tower, where ozone oxidation breaks down organic-inorganic complexes. The effluent after oxidation enters the fluidized bed crystallizer, where calcium and magnesium ions are removed by adding sodium carbonate and quartz sand seed crystals in a fluidized state. The softened effluent is then pumped by a high-pressure pump into a nanofiltration unit, where nanofiltration permeate, mainly composed of sodium chloride, and nanofiltration concentrate, mainly composed of sodium sulfate, are separated.

[0073] The nanofiltration permeate enters the first reverse osmosis unit for concentration to obtain sodium chloride concentrate; the nanofiltration concentrate enters the seed fluidized bed reactor, and after further removal of residual hardness by adding calcium sulfate seed crystals, it enters the second reverse osmosis unit for concentration to obtain sodium sulfate concentrate; the sludge and crystallized waste generated by each reverse osmosis unit enter the evaporator for evaporation and solidification, the condensate is reused, and the solid waste is transported off-site.

[0074] The water composition and concentrations of the original wastewater used in the following examples and comparative examples include chemical oxygen demand (COD) of 1200 mg / L, total dissolved solids (TDS) of 5800 mg / L, total hardness (calculated as calcium carbonate) of 480 mg / L, calcium ions of 120 mg / L, sulfate ions of 1600 mg / L, chloride ions of 1250 mg / L, and total organic carbon of 185 mg / L, with a pH of 8.2.

[0075] Example 1: A process for advanced treatment and salt control of dyeing and printing wastewater for reuse includes the following steps: Step S1: Pass the dyeing and printing wastewater through a 3mm mesh screen for interception treatment; let the screened wastewater remain in an equalization tank for 9 hours and mechanically stir at 45r / min for homogenization treatment; add 200mg / L of polyaluminum chloride as a coagulant to the homogenized wastewater and mix rapidly at 250r / min for 3 minutes; then add 3mg / L of polyacrylamide as a flocculant and stir slowly at 50r / min for 12 minutes; then stop stirring and let it stand for 1.5 hours to settle, and the supernatant is the pretreated product water.

[0076] Step S2: The pretreated effluent is subjected to hydrolysis and acidification under anaerobic conditions, with a hydraulic retention time of 9 hours, pH maintained at 6.0, and temperature maintained at 35°C. The pretreated effluent after hydrolysis and acidification is then subjected to biodegradation under aerobic conditions, with the mixed liquor sludge concentration controlled at 8000 mg / L and a hydraulic retention time of 10 hours. Ultrafiltration is then performed to achieve sludge-water separation, with the membrane pore size controlled at 0.2 μm and the membrane flux controlled at 20 L / (m³). 2 ·h), to obtain biochemically treated wastewater.

[0077] Step S3: Add ozone to the biochemical treatment permeate at a dosage of 65 mg / L and a reaction time of 25 min for oxidation and complex breaking treatment; add sodium carbonate to the biochemical treatment permeate after oxidation and complex breaking treatment to adjust the pH to 9.5; then add 0.3 mm quartz sand as seed crystals to the water at a concentration of 35 g / L and an upward flow velocity of 30 m / h to keep the quartz sand seed crystals in a fluidized state, with a hydraulic retention time of 45 min; periodically separate and discharge the generated calcium carbonate crystals, and the supernatant is softened permeate.

[0078] Step S4: The softened permeate is passed through a nanofiltration membrane with a molecular weight cutoff of 300 Da at an operating pressure of 1.8 MPa, and the recovery rate is controlled at 75% to obtain nanofiltration permeate and nanofiltration concentrate.

[0079] Step S5: Add calcium sulfate seed crystals with a particle size of 30 μm to the nanofiltration concentrate, and control the concentration of the seed crystals at 7 g / L; keep the system in a fluidized state by stirring at 200 rpm, and control the hydraulic residence time at 10 min; perform hydrocyclone separation, discharge the precipitated calcium sulfate crystals from the underflow, and the supernatant is the concentrate after descaling.

[0080] Step S6: The nanofiltration permeate is concentrated by reverse osmosis at an operating pressure of 2.5 MPa to obtain sodium chloride concentrate; the descaling concentrate is concentrated by disc tube reverse osmosis at an operating pressure of 5.0 MPa to obtain sodium sulfate concentrate.

[0081] Step S7: The sludge and crystallized waste residue are heated at 80°C while maintaining the system vacuum at -0.07MPa. The condensate produced after the water evaporates is reused, and the residual solids are transported off-site for disposal.

[0082] Example 2:

[0083] The difference between this embodiment and Embodiment 1 is that in step S3, the ozone dosage is controlled at 50 mg / L and the concentration of quartz sand seed crystals is controlled at 50 g / L; the remaining steps are the same as in Embodiment 1.

[0084] Example 3:

[0085] The difference between this embodiment and Embodiment 1 is that in step S3, the ozone dosage is controlled at 50 mg / L and the concentration of quartz sand seed crystals is controlled at 20 g / L; the remaining steps are the same as in Embodiment 1.

[0086] Example 4:

[0087] The difference between this embodiment and Embodiment 1 is that in step S3, the ozone dosage is controlled at 65 mg / L and the concentration of quartz sand seed crystals is controlled at 20 g / L; the remaining steps are the same as in Embodiment 1.

[0088] Example 5:

[0089] The difference between this embodiment and Embodiment 1 is that in step S3, the ozone dosage is controlled at 65 mg / L and the concentration of quartz sand seed crystals is controlled at 35 g / L; the remaining steps are the same as in Embodiment 1.

[0090] Example 6:

[0091] The difference between this embodiment and Embodiment 1 is that in step S3, the ozone dosage is controlled at 65 mg / L and the concentration of quartz sand seed crystals is controlled at 50 g / L; the remaining steps are the same as in Embodiment 1.

[0092] Example 7:

[0093] The difference between this embodiment and Embodiment 1 is that in step S3, the ozone dosage is controlled at 80 mg / L and the concentration of quartz sand seed crystals is controlled at 20 g / L; the remaining steps are the same as in Embodiment 1.

[0094] Example 8:

[0095] The difference between this embodiment and Embodiment 1 is that in step S3, the ozone dosage is controlled at 80 mg / L and the concentration of quartz sand seed crystals is controlled at 35 g / L; the remaining steps are the same as in Embodiment 1.

[0096] Example 9:

[0097] The difference between this embodiment and Embodiment 1 is that in step S3, the ozone dosage is controlled at 80 mg / L and the concentration of quartz sand seed crystals is controlled at 50 g / L; the remaining steps are the same as in Embodiment 1.

[0098] Comparative Example 1: A process for advanced treatment and salt control of dyeing and printing wastewater for reuse includes the following steps: Step S1: Pass the dyeing and printing wastewater through a 3mm mesh screen for interception treatment; let the screened wastewater remain in an equalization tank for 9 hours and mechanically stir at 45r / min for homogenization treatment; add 200mg / L of polyaluminum chloride as a coagulant to the homogenized wastewater and mix rapidly at 250r / min for 3 minutes; then add 3mg / L of polyacrylamide as a flocculant and stir slowly at 50r / min for 12 minutes; then stop stirring and let it stand for 1.5 hours to settle, and the supernatant is the pretreated product water.

[0099] Step S2: The pretreated effluent is subjected to hydrolysis and acidification under anaerobic conditions, with a hydraulic retention time of 9 hours, pH maintained at 6.0, and temperature maintained at 35°C. The pretreated effluent after hydrolysis and acidification is then subjected to biodegradation under aerobic conditions, with the mixed liquor sludge concentration controlled at 8000 mg / L and a hydraulic retention time of 10 hours. Ultrafiltration is then performed to achieve sludge-water separation, with the membrane pore size controlled at 0.2 μm and the membrane flux controlled at 20 L / (m³). 2 ·h), to obtain biochemically treated wastewater.

[0100] Step S3: Add sodium carbonate to the biochemical treatment permeate to adjust the pH to 9.5; then add 0.3 mm quartz sand as seed crystals to the water, with the concentration of quartz sand seed crystals controlled at 35 g / L and the upward flow rate controlled at 30 m / h to keep the quartz sand seed crystals in a fluidized state, and the hydraulic retention time controlled at 45 min; periodically separate and discharge the generated calcium carbonate crystals, and the supernatant is softened permeate.

[0101] Step S4: The softened permeate is passed through a nanofiltration membrane with a molecular weight cutoff of 300 Da at an operating pressure of 1.8 MPa, and the recovery rate is controlled at 75% to obtain nanofiltration permeate and nanofiltration concentrate.

[0102] Step S5: Add calcium sulfate seed crystals with a particle size of 30 μm to the nanofiltration concentrate, and control the concentration of the seed crystals at 7 g / L; keep the system in a fluidized state by stirring at 200 rpm, and control the hydraulic residence time at 10 min; perform hydrocyclone separation, discharge the precipitated calcium sulfate crystals from the underflow, and the supernatant is the concentrate after descaling.

[0103] Step S6: The nanofiltration permeate is concentrated by reverse osmosis at an operating pressure of 2.5 MPa to obtain sodium chloride concentrate; the descaling concentrate is concentrated by disc tube reverse osmosis at an operating pressure of 5.0 MPa to obtain sodium sulfate concentrate.

[0104] Step S7: The sludge and crystallized waste residue are heated at 80°C while maintaining the system vacuum at -0.07MPa. The condensate produced after the water evaporates is reused, and the residual solids are transported off-site for disposal.

[0105] Comparative Example 2: A process for advanced treatment and salt control of dyeing and printing wastewater for reuse includes the following steps: Step S1: Pass the dyeing and printing wastewater through a 3mm mesh screen for interception treatment; let the screened wastewater remain in an equalization tank for 9 hours and mechanically stir at 45r / min for homogenization treatment; add 200mg / L of polyaluminum chloride as a coagulant to the homogenized wastewater and mix rapidly at 250r / min for 3 minutes; then add 3mg / L of polyacrylamide as a flocculant and stir slowly at 50r / min for 12 minutes; then stop stirring and let it stand for 1.5 hours to settle, and the supernatant is the pretreated product water.

[0106] Step S2: The pretreated effluent is subjected to hydrolysis and acidification under anaerobic conditions, with a hydraulic retention time of 9 hours, pH maintained at 6.0, and temperature maintained at 35°C. The pretreated effluent after hydrolysis and acidification is then subjected to biodegradation under aerobic conditions, with the mixed liquor sludge concentration controlled at 8000 mg / L and a hydraulic retention time of 10 hours. Ultrafiltration is then performed to achieve sludge-water separation, with the membrane pore size controlled at 0.2 μm and the membrane flux controlled at 20 L / (m³). 2 ·h), to obtain biochemically treated wastewater.

[0107] Step S3: Add ozone to the biochemical treatment product water, with the ozone dosage controlled at 65 mg / L and the reaction time controlled at 25 min, to carry out oxidation and complex-breaking treatment and obtain oxidation and complex-breaking effluent.

[0108] Step S4: The oxidized and broken complex effluent is passed through a nanofiltration membrane with a molecular weight cutoff of 300 Da under an operating pressure of 1.8 MPa, and the recovery rate is controlled at 75% to obtain nanofiltration permeate and nanofiltration concentrate.

[0109] Step S5: Add calcium sulfate seed crystals with a particle size of 30 μm to the nanofiltration concentrate, and control the concentration of the seed crystals at 7 g / L; keep the system in a fluidized state by stirring at 200 rpm, and control the hydraulic residence time at 10 min; perform hydrocyclone separation, discharge the precipitated calcium sulfate crystals from the underflow, and the supernatant is the concentrate after descaling.

[0110] Step S6: The nanofiltration permeate is concentrated by reverse osmosis at an operating pressure of 2.5 MPa to obtain sodium chloride concentrate; the descaling concentrate is concentrated by disc tube reverse osmosis at an operating pressure of 5.0 MPa to obtain sodium sulfate concentrate.

[0111] Step S7: The sludge and crystallized waste residue are heated at 80°C while maintaining the system vacuum at -0.07MPa. The condensate produced after the water evaporates is reused, and the residual solids are transported off-site for disposal.

[0112] Experimental Example 1: Based on the advanced treatment and salt-controlled reuse processes for dyeing and printing wastewater in Examples 1-9 and Comparative Examples 1-2, the following indicators were tested: 1. Total hardness of softened water is used to evaluate the overall removal effect of fluidized bed crystallization softening treatment on scale-forming ions. Softened permeate is used as the test sample. The test method follows GB / T 7477-1987, using EDTA disodium standard titration solution to titrate the water sample. The total concentration of calcium and magnesium ions in the water sample is calculated based on the volume consumed, and the result is expressed as milligrams per liter (mg / L) of calcium carbonate.

[0113] 2. Total organic carbon in softened effluent is used to indirectly characterize the degree of degradation and mineralization of organic matter by oxidative complex-breaking treatment. Softened effluent is used as the test sample. The test method follows HJ 501-2009. A total organic carbon analyzer is used, and the water sample is subjected to 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 and recorded in milligrams per liter (mg / L).

[0114] 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. A sample of the nanofiltration permeate outlet water is taken as the test water sample. The test method follows GB / T 11899-1989. In hydrochloric acid medium, sulfate ions in the water sample react with barium ions to form barium sulfate precipitate. After filtration and ignition to constant weight, the concentration of sulfate ions is calculated based on the mass of the barium sulfate precipitate, expressed in milligrams per liter (mg / L).

[0115] 4. The calcium ion concentration in the concentrate after descaling is used to evaluate the deep removal effect of seed fluidized bed descaling on residual hardness ions. The supernatant after hydrocyclone separation (the concentrate after descaling) is taken as the test water sample. The test method follows GB / T11905-1989. After acidifying the water sample with nitric acid, the absorbance of calcium is measured at a specific wavelength using an acetylene-air flame atomic absorption spectrophotometer. The concentration of calcium ions in the water sample is calculated by comparing it with a series of standard solution calibration curves, expressed in milligrams per liter (mg / L).

[0116] 5. Scaling tendency of reverse osmosis systems: This parameter is used to comprehensively assess the scaling potential of the final concentrate from a thermodynamic perspective, using the Langelinie Saturation Index (LSI) as the evaluation criterion. Sodium chloride concentrate and sodium sulfate concentrate are used as test water samples. The test method follows ASTM D3739-19. The LSI is calculated by measuring the pH, total dissolved solids, calcium ion concentration, and total alkalinity of the water samples and referring to the constants corresponding to the water temperature. An LSI greater than 0 indicates a scaling tendency, with a higher value indicating a higher scaling risk; an LSI of 0 indicates an equilibrium state; and an LSI less than 0 indicates a corrosion tendency.

[0117] The results are shown in the table below: Table 1 Comparison of Experimental Results

[0118] Example 5 employs a process parameter combination of 65 mg / L ozone dosage and 35 g / L quartz sand seed crystal concentration. Specifically: First, the 65 mg / L ozone dosage effectively breaks the molecular chains of the organic-inorganic complex, releasing the encapsulated calcium and magnesium ions into the water in a free state. At this dosage, the hydroxyl radicals generated by ozone in the water have strong oxidizing properties, efficiently destroying the stable complex structure formed by organic matter and scale-forming ions, reducing the total organic carbon in the softened effluent to 10.0 mg / L, creating low-interference water quality conditions for subsequent crystallization reactions. Second, the 35 g / L quartz sand seed crystal concentration provides sufficient heterogeneous nucleation sites for calcium carbonate precipitation. Under fluidized conditions, free calcium ions and carbonate ions provided by sodium carbonate preferentially crystallize and grow on the seed crystal surface, avoiding scaling problems caused by homogeneous nucleation. At this concentration, the total hardness of the softened effluent is as low as 121 mg / L (calculated as calcium carbonate), significantly reducing the risk of fouling by the subsequent nanofiltration membrane. Furthermore, on the one hand, ozone destroys the complex structure, allowing scale-forming ions to be fully exposed; on the other hand, quartz sand seeds accelerate ion removal through heterogeneous nucleation. This makes the free calcium and magnesium ions released by the oxidation and complex-breaking treatment complementary to the directional precipitation process of the fluidized crystallization softening treatment. The combination of these two factors results in a sulfate ion concentration of only 39 mg / L in the nanofiltration permeate and a calcium ion concentration of 9 mg / L in the concentrate after descaling. The Langelier index (LSI) is 0.18, which is close to the equilibrium state, effectively controlling the scaling tendency.

[0119] Example 2 used an ozone dosage of 50 mg / L and a quartz sand seed concentration of 50 g / L. Due to insufficient ozone dosage, the organic-inorganic complex was not completely broken down, resulting in a total organic carbon content of 22.8 mg / L in the softened water. The residual organic matter interfered with calcium carbonate crystallization, leading to a total hardness increase to 157 mg / L. Although the quartz sand concentration was increased, the crystallization efficiency was not significantly improved due to insufficient release of free calcium ions, resulting in an LSI of 0.49. The risk of scaling was significantly higher than in Example 5. Example 7 used an ozone dosage of 80 mg / L and a quartz sand seed concentration of 20 g / L. Although the excess ozone further degraded organic matter to a total organic carbon of 13.3 mg / L, the 20 g / L quartz sand seed concentration was insufficient to provide enough crystallization sites, resulting in a total hardness of 145 mg / L in the softened effluent. Furthermore, the excess ozone increased operating costs and did not effectively match the seed concentration, with an LSI of 0.37.

[0120] Example 3 used an ozone dosage of 50 mg / L and a quartz sand seed concentration of 20 g / L. Insufficient ozone complex disruption resulted in a total organic carbon (TOC) of 21.4 mg / L. Simultaneously, the insufficient seed concentration, a combined effect, prevented complete precipitation of free calcium ions, leading to a total hardness of 151 mg / L and an LSI of 0.43. The low seed concentration reduced the solid-liquid mass transfer efficiency under fluidized bed conditions, resulting in incomplete crystallization. Example 6 used an ozone dosage of 65 mg / L and a quartz sand seed concentration of 50 g / L. Although ozone complex disruption resulted in a TOC of 16.3 mg / L, the 50 g / L quartz sand concentration caused supersaturation of solid particles in the fluidized bed, making it difficult to maintain the optimal upward flow rate of 30 m / h. This hindered calcium carbonate crystal growth, increasing the total hardness to 140 mg / L and the LSI to 0.33. Furthermore, the high seed concentration increased subsequent separation costs.

[0121] Example 4 used an ozone dosage of 65 mg / L and a quartz sand seed concentration of 20 g / L. While ozone effectively broke down the complex, the 20 g / L seed concentration was insufficient to completely capture free calcium ions, resulting in a total hardness of 147 mg / L. The sulfate ion concentration in the nanofiltration permeate was 80 mg / L, meaning calcium ions remained in a free state, affecting the nanofiltration membrane's selectivity for divalent salts (LSI 0.38). Example 8 used an ozone dosage of 80 mg / L and a quartz sand seed concentration of 35 g / L. Excess ozone did not significantly improve the complex-breaking effect, resulting in a total organic carbon concentration of 12.5 mg / L. Furthermore, the 80 mg / L dosage left residual oxidizing substances in the water, potentially damaging the nanofiltration membrane. The total hardness was 134 mg / L (LSI 0.28), and no further reduction in hardness was achieved. Example 9 used an ozone dosage of 80 mg / L and a quartz sand seed concentration of 50 g / L, resulting in a total hardness of 143 mg / L, a total organic carbon of 15.4 mg / L, and an LSI of 0.36, without showing any additional advantages.

[0122] Comparative Example 1 lacked oxidation and complex-breaking treatment and ozone was not added. The organic-inorganic complex was not destroyed, and scale-forming ions remained encapsulated by organic matter. Softening treatment was carried out solely by adding sodium carbonate and quartz sand seed crystals. Due to insufficient release of calcium ions, the crystallization efficiency was extremely low, resulting in a total hardness of 225 mg / L in the softened effluent. The sulfate ion concentration in the nanofiltration permeate was 290 mg / L, indicating poor divalent salt retention. Unreleased calcium ions and sulfate ions formed a supersaturated solution, leading to scaling on the nanofiltration membrane surface. The LSI index was 1.05, and the scaling risk was significantly higher than in Example 5.

[0123] Comparative Example 2 lacked fluidized bed crystallization softening treatment and only underwent oxidation and complex-breaking treatment without the addition of sodium carbonate and quartz sand seeds. Free calcium ions were not directionally removed, resulting in a total hardness of 206 mg / L in the softened effluent, significantly higher than in Example 5. Due to the lack of seed induction, calcium ions remained in a free state in the water. This led to a high calcium ion concentration in the nanofiltration concentrate, reaching 67 mg / L after descaling, with an LSI index of 0.88. Although calcium sulfate seeds were added during subsequent fluidized bed descaling treatment, the unremoved calcium ions from the initial treatment still formed a supersaturated solution with sulfate ions, resulting in a significantly higher scaling tendency in the reverse osmosis system compared to Example 5.

[0124] Based on the preferred embodiments of the present invention described above, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A process for deep treatment and salt control of dyeing and printing wastewater, characterized in that, Includes the following steps: Step S1: Pre-treat the dyeing and printing wastewater to obtain pre-treated product water; The pretreatment includes sequentially treating the dyeing and printing wastewater with a screen interception treatment, a conditioning and homogenization treatment, and a coagulation and sedimentation treatment. Step S2: Perform biochemical treatment on the pretreated wastewater to obtain biochemically treated wastewater; the biochemical treatment includes sequentially performing hydrolysis acidification treatment and membrane bioreactor treatment on the pretreated wastewater. Step S3: Soften the biochemical treatment wastewater to obtain softened wastewater; the softening treatment includes sequentially performing oxidation complex-breaking treatment and fluidized crystallization softening treatment on the biochemical treatment wastewater. Step S4: Perform nanofiltration separation treatment on the softened product water to obtain nanofiltration permeate and nanofiltration concentrate; the nanofiltration separation treatment is carried out under pressure and uses a separation membrane to selectively separate dissolved inorganic salts in the softened product water. Step S5: Perform seed fluidization descaling treatment on the nanofiltration concentrate to obtain a descaled concentrate; the seed fluidization descaling treatment involves adding seed crystals and inducing the preferential precipitation and separation of supersaturated scale-forming ions under fluidization conditions; Step S6: The nanofiltration permeate and the descaling concentrate are respectively subjected to membrane concentration treatment to obtain sodium chloride concentrate and sodium sulfate concentrate; the membrane concentration treatment achieves salt purification and concentration through reverse osmosis. Step S7: Evaporate and solidify the sludge and crystallized waste generated during the membrane concentration process; the evaporation and solidification process promotes water evaporation through heating and negative pressure conditions.

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

3. The process according to claim 1, characterized in that, In step S1, the hydraulic retention time of the homogenization process is adjusted to be 6h to 12h, and the stirring rate is 30r / min to 60r / min.

4. The process according to claim 1, characterized in that, In step S1, the coagulation and sedimentation treatment includes 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 according to claim 1, characterized in that, In step S3, the oxidation and complex-breaking treatment uses ozone as an oxidant, with an ozone dosage of 50 mg / L to 80 mg / L and a reaction time of 20 min to 30 min.

6. The process according to claim 1, characterized in that, In step S3, the fluidized crystallization softening treatment includes adding sodium carbonate to adjust the pH to 9.0 to 10.0, adding quartz sand seed crystals with a particle size of 0.2 mm to 0.5 mm, with a seed crystal concentration of 20 g / L to 50 g / L, controlling the upward flow rate to 20 m / h to 40 m / h, and the hydraulic retention time to 30 min to 60 min.

7. The process according to claim 1, characterized in that, In step S4, the operating pressure of the nanofiltration separation process is 1.0 MPa to 2.5 MPa, the molecular weight cutoff of the nanofiltration membrane used is 200 Da to 400 Da, and the recovery rate is controlled at 70% to 80%.

8. The process according to claim 1, characterized in that, In step S5, the seed crystals added in the seed fluidization descaling treatment are calcium sulfate seed crystals with a particle size of 5μm to 50μm, the seed crystal concentration is 5g / L to 10g / L, the stirring rate is 100rpm to 300rpm, and the hydraulic retention time is 5min to 15min.

9. The process according to claim 1, characterized in that, In step S6, the operating pressure for reverse osmosis concentration of nanofiltration permeate is 1.5 MPa to 4.0 MPa; the operating pressure for disc tube reverse osmosis concentration of descaling concentrate is 3.0 MPa to 8.0 MPa.

10. A system for deep treatment and salt control of dyeing and printing wastewater, used to implement the process described in any one of claims 1 to 9, characterized in that, It includes a screen, equalization tank, coagulation sedimentation equipment, hydrolysis acidification tank, membrane bioreactor, ozone oxidation tower, fluidized bed crystallizer, nanofiltration device, seed fluidized reactor, first reverse osmosis device, second reverse osmosis device and evaporator connected in sequence by pipes and pumps.

Images