Dye wastewater treatment method

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a dye wastewater treatment method. The method provided by the invention overcomes the defects of poor heavy metal ion removal capability and poor denitrification capability of the existing dye wastewater treatment method. The dye wastewater is treated by a regulating tank, a sedimentation tank, an electrodialysis unit, a hydrolysis acidification tank, a pre-aeration tank, an anoxic tank, an aerobic MBR tank, an electrolysis unit and a sedimentation tank in sequence; wherein a composite flocculating agent is added into the sedimentation tank, and the composite flocculating agent is prepared from the following raw materials: acidified biochar, acidified diatomite and a gel product; a composite slow-release carbon source filler is added into the anoxic tank, the composite slow-release carbon source filler is prepared from polycaprolactone, sodium acetate, sodium humate, charcoal and the like, and the composite slow-release carbon source filler is distributed in the anoxic tank in a layered manner; through coherent cooperative treatment of the dye wastewater process, the content of heavy metals in effluent is low, the content of total nitrogen and ammonia nitrogen is low, and the treatment effect is good.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, in particular to a method for treating dye wastewater. Background Art

[0002] As a major industrial water consumer, the printing and dyeing industry discharges dye wastewater characterized by complex water quality and diverse composition. Dye wastewater not only contains large amounts of organic dyes, auxiliaries, and slurries, but also often exhibits high salinity, high color, and high chemical oxygen demand (COD). If discharged without effective treatment, this wastewater can severely damage natural aquatic ecosystems, such as increasing color and reducing transparency, affecting photosynthesis and respiration in aquatic organisms, and ultimately jeopardizing the overall aquatic ecological balance. It can also adversely affect the surrounding soil environment and groundwater quality.

[0003] The high salinity environment of dye wastewater poses many difficult problems to wastewater treatment. On the one hand, high salinity will interfere with the hydrolysis and polymerization process of flocculants, resulting in unstable flocculant performance and difficulty in forming effective flocs, which in turn greatly reduces the removal effect of suspended particles and colloidal substances in wastewater. On the other hand, heavy metal ions present in wastewater, such as copper, zinc, chromium, etc., have more complex chemical forms in high salinity environments and interact with other substances, increasing the difficulty of removal. In addition, high salinity environments have a strong inhibitory effect on the growth and metabolism of microorganisms, making it difficult for the biological denitrification process to proceed efficiently. Under high salinity, the cell osmotic pressure of microorganisms is unbalanced and the enzyme activity is affected, resulting in a significant decrease in their ability to convert nitrogen sources in wastewater, making it difficult to effectively convert nitrogen-containing pollutants such as ammonia nitrogen into harmless nitrogen gas for discharge.

[0004] In summary, existing dye wastewater treatment technologies suffer from poor heavy metal ion removal and denitrification capabilities when dealing with high-salinity dye wastewater. Therefore, there is an urgent need to develop a targeted, efficient, and stable dye wastewater treatment process to overcome the difficulties of heavy metal ion removal and biological denitrification in high-salinity environments, thereby achieving standard discharge of dye wastewater and sustainable utilization of water resources.

[0005] Therefore, a method for treating dye wastewater is proposed. Summary of the Invention

[0006] The present invention aims to provide a method for treating dye wastewater. The method comprises treating the dye wastewater sequentially through a regulating tank, a sedimentation tank, an electrodialysis unit, a hydrolysis-acidification tank, a pre-aeration tank, an anoxic tank, an aerobic MBR tank, an electrolysis unit, and a sedimentation tank. A composite flocculant, prepared from raw materials including acidified biochar, acidified diatomaceous earth, and a gel product, is added to the sedimentation tank. A composite slow-release carbon source filler, prepared from raw materials including polycaprolactone, sodium acetate, sodium humate, and biochar, is added to the anoxic tank, and the composite slow-release carbon source filler is distributed in layers within the anoxic tank. Through the sequential and coordinated treatment of the dye wastewater process, the effluent has low heavy metal content, low total nitrogen, and low ammonia nitrogen content, achieving excellent treatment results.

[0007] To achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for treating dye wastewater, which specifically comprises the following steps: 1. A method for treating dye wastewater, characterized in that it specifically comprises the following steps: S1 puts the dye wastewater into the regulating tank, adjusts the pH value to neutral, and then passes it into the sedimentation tank for treatment, adding composite flocculant in the sedimentation tank; S2 passes the effluent from the sedimentation tank into the electrodialysis unit for desalination treatment, and the salinity of the effluent from the electrodialysis unit is ≤5g / L; S3 passes the effluent from the electrodialysis unit into a hydrolysis and acidification tank for treatment and then into a pre-aeration tank. The pre-aeration tank uses a mixture of ozone and air for pre-aeration, with the volume ratio of ozone to the mixed gas being 8-10%; S4 passes the effluent from the pre-aeration tank into an anoxic tank containing a composite slow-release carbon source filler, an aerobic MBR tank, and an electrolysis unit for treatment. The effluent from the electrolysis unit is then treated in a sedimentation tank to obtain discharged effluent. The raw materials for preparing the composite flocculant include: acidified biochar, acidified diatomaceous earth, and gel product; the raw materials for preparing the gel product include: chitosan, glycidyl trimethylammonium chloride, corn starch, monochloroacetic acid, and 3-acrylamidopropanesulfonic acid; The raw materials for preparing the composite slow-release carbon source filler include: polycaprolactone, sodium acetate, sodium humate and biochar.

[0008] Preferably, the preparation method of the composite flocculant is as follows: by mass, 20-26 parts of acidified biochar, 30-34 parts of acidified diatomaceous earth, and 25-27 parts of gel product are added to a 5% by mass solution of sodium dodecylsulfonate, and dispersed for 30 minutes at an ultrasonic power of 300W and a frequency of 40kHz to obtain a dispersion; 6 parts of sodium alginate and 12 parts of polyethylene oxide are dissolved in 300 parts by mass of an 8% by mass citric acid solution, stirred at a constant temperature of 75°C for 4 hours, the dispersion and 4 parts of glutaraldehyde are added, reacted at 65°C for 3 hours, and dried to obtain a composite flocculant; the amount of composite flocculant added is 200-300 mg / L.

[0009] Preferably, the biochar obtained by carbonizing the biochar raw material is mixed with a 50% by mass phosphoric acid solution in a mass ratio of 1:3, and reacted at 85°C for 2 hours to obtain acidified biochar; diatomaceous earth is mixed with a 10% by mass sulfuric acid solution in a mass ratio of 1:5, stirred and reacted at 80°C for 3 hours, and then centrifuged, washed, and dried to obtain acidified diatomaceous earth.

[0010] Preferably, the biochar raw material is coconut shell.

[0011] Preferably, 2 parts of chitosan are dissolved in a 5% by mass acetic acid solution, 2 parts of sodium montmorillonite and 1.2 parts of glycidyl trimethylammonium chloride are added, and the mixture is stirred at 60°C for 2 hours. After the reaction is completed, the pH value is adjusted to 9, the mixture is allowed to stand for precipitation, and then centrifuged and dried to obtain a composite material; 13 parts of corn starch and 30% by mass sodium hydroxide solution are mixed at a solid-liquid ratio of 1:4 and swelled for 1 hour, 15% by mass monochloroacetic acid ethanol solution is added, and the molar ratio of corn starch to monochloroacetic acid is 1:1.2, and the mixture is reacted at 50°C for 4 hours. After neutralization, the mixture is washed with ethanol and dried. The method comprises the following steps: drying to obtain carboxymethyl starch; dissolving 6.8 parts of acrylic acid and 1.2 parts of 3-acrylamidopropanesulfonic acid in 200 parts of deionized water, adding 0.005 parts of ammonium persulfate under a nitrogen atmosphere, reacting at 60°C for 4 hours, and then evaporating to obtain a 15% by weight potassium sulfonated polyacrylate solution; adding 4 parts of the composite material and 13 parts of carboxymethyl starch to 200 parts of deionized water, stirring to dissolve, adding the sulfonated polyacrylate potassium solution, adding 0.005 parts of ammonium persulfate under a nitrogen atmosphere at 50°C, stirring to react for 40 minutes, obtaining a primary product, and drying the primary product to obtain a gel product.

[0012] Preferably, the preparation method of the composite slow-release carbon source filler is as follows: 70 parts of polycaprolactone, 30 parts of sodium acetate and 3 parts of sodium humate are mixed and then extruded and granulated to obtain core particles; the core particles are immersed in a coating liquid for 60 seconds, taken out and allowed to stand for 20 minutes, and repeated twice to obtain coated particles; the coated particles are immersed in a 2% sodium alginate solution for 30 seconds, taken out and sprayed with a 5% calcium chloride solution for cross-linking for 10 minutes, and repeated three times to obtain outer coating particles; 90-110 parts of the outer coating particles are mixed with 90-110 parts of biochar, immersed in a 2-3% sodium alginate solution, treated at 2000 rpm for 5 minutes by a centrifugal dehydrator, and dried to obtain a composite slow-release carbon source filler.

[0013] Preferably, the coating solution is prepared by dissolving 5 parts of β-cyclodextrin in 95 parts of deionized water, stirring until completely dissolved, and then adding 2 parts of ascorbic acid to obtain the coating solution.

[0014] Preferably, the wastewater treatment method of the anoxic tank is: loading the composite slow-release carbon source filler into the anoxic tank in three layers; and allowing the effluent from the pre-aeration tank to enter the anoxic tank from the lower water inlet and flow out from the upper water outlet.

[0015] Preferably, the particle size of the composite slow-release carbon source filler is 1-3 cm, and the three layers are the bottom layer, the middle layer, and the upper layer. The particle size of the composite slow-release carbon source filler in the bottom layer is 3 cm; the particle size of the composite slow-release carbon source filler in the middle layer is 2 cm; and the particle size of the composite slow-release carbon source filler in the upper layer is 1 cm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. In the present invention, for high-salt dye wastewater, a porous substrate is constructed through the synergistic adsorption of coconut shell activated carbon and acid-acidified diatomaceous earth. The sulfonic acid group of sulfonated potassium polyacrylate and the quaternary ammonium group of quaternized chitosan form a bipolar charge system, which synergistically suppresses the charge imbalance under salt interference. The sulfonic acid group repels interfering anions such as sulfate, and the quaternary ammonium group directionally captures cationic pollutants such as copper ions, breaking through the shielding effect of salt on charge activity; carboxymethyl starch and polyethylene oxide destroy the colloidal stability in the wastewater through molecular chain entanglement, and sodium alginate and glutaraldehyde cross-link to form a three-dimensional network to strengthen the floc structure, finally forming a salt-resistant composite flocculation system, which simultaneously achieves synergistic efficiencies in dye decolorization, heavy metal removal, and salt interference suppression.

[0017] 2. In this invention, ozone pretreatment directly oxidizes the sulfides generated during the hydrolysis and acidification phase into sulfates, eliminating odor and biotoxicity. It also attacks the azo bonds and conjugated systems in the dye molecules, destroying chromophores and cleaving organic matter into small carboxylic acids. This process connects the hydrolysis and acidification phase with the subsequent biological treatment unit, converting refractory macromolecules into readily biodegradable substances. This mitigates the toxic effects of sulfides on MBR microorganisms and, through chain scission reactions, improves the mineralization efficiency of organic matter in the anoxic-aerobic MBR, forming a closed-loop oxidation pretreatment-biodegradation synergistic purification system.

[0018] 3. In this invention, a polycaprolactone-sodium acetate core provides a slow-release carbon source, while sodium humate and ascorbic acid act as reducing agents to scavenge ozone and free radicals, respectively. A gradient-coated calcium alginate layer controls the carbon source diffusion rate, while β-cyclodextrin encapsulates ascorbic acid to provide long-lasting antioxidant protection. A biofilm forms on the surface of the biochar carrier, enriching the denitrifying bacteria. Refractory organic matter decomposed during the ozone pre-aeration phase is adsorbed by the biochar in the filler layer. The core carbon source continuously releases electrons to supplement denitrification. Sodium humate preferentially reduces residual ozone, while ascorbic acid neutralizes reactive oxygen species. These three factors work together to overcome the bottleneck of carbon-nitrogen metabolic imbalance caused by ozone interference, effectively protecting the activity of denitrifying bacteria and improving denitrification efficiency in highly oxidizing wastewater environments.

[0019] 4. In the present invention, the removal of heavy metal ions from dye wastewater and desalination in the electrodialysis stage by a composite flocculant resistant to high salt environments can lay a good foundation for subsequent biological treatment. At the same time, it can reduce the pollutant load in the electrodialysis stage and improve treatment efficiency. In the effluent after treatment in the hydrolysis and acidification tank, because the water contains a large amount of sulfide, the sulfide is removed after treatment in the pre-aeration tank. At the same time, some difficult-to-degrade organic matter can also be removed, ensuring the stable denitrification treatment effect of the wastewater in the anoxic tank and aerobic MBR tank. Finally, deep treatment is carried out in the electrolysis unit to further remove the difficult-to-degrade organic matter in the wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a process flow chart for dye wastewater treatment according to the present invention. DETAILED DESCRIPTION

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] See also Figure 1 The present invention provides a method for treating dye wastewater, and the technical solution is as follows: Example 1

[0023] (1) Preparation of composite flocculant The biochar raw material was heated to 850°C at a rate of 10°C / min and carbonized for 2 hours to obtain a carbonized product, the carbonized product was mixed with a 50% by mass phosphoric acid solution at a mass ratio of 1:3, the reaction product after being reacted at 85°C for 2 hours was washed and dried, and then pulverized to 200 mesh to obtain acidified biochar; diatomaceous earth was mixed with a 10% by mass sulfuric acid solution at a mass ratio of 1:5, stirred and reacted at 80°C for 3 hours, and then centrifuged, washed, and dried to obtain acidified diatomaceous earth; 2 parts of chitosan were dissolved in 5% by mass acetic acid solution, 2 parts of sodium montmorillonite and 1.2 parts of glycidyl trimethylammonium chloride were added, and the mixture was stirred at 60°C for 2 hours. After the reaction, sodium hydroxide solution was added dropwise to adjust the pH value to 9. The mixture was allowed to stand for precipitation and then centrifuged, freeze-dried and crushed into 100 mesh to obtain a composite material. 6.8 parts of acrylic acid and 1.2 parts of 3-acrylamidopropanesulfonic acid were dissolved in 200 parts of deionized water, 0.005 parts of ammonium persulfate were added under nitrogen atmosphere, reacted at 60°C for 4 hours, and then evaporated to obtain a concentrated solution with a mass fraction of 15%; 13 parts of corn starch and 30% sodium hydroxide solution by mass fraction were mixed at a solid-liquid ratio of 1:4 and swollen for 1 hour. Then, 15% monochloroacetic acid ethanol solution by mass fraction was added, and the molar ratio of starch to monochloroacetic acid was 1:1.2. The mixture was reacted at 50°C for 4 hours, neutralized, washed with ethanol, dried at 60°C and crushed to obtain carboxymethyl starch. 4 parts of the composite material and 13 parts of carboxymethyl starch were added to 200 parts of distilled water, stirred and dissolved, and then a sulfonated polyacrylate potassium solution was added. 0.005 parts of ammonium persulfate was added at 50° C. in a nitrogen atmosphere, and stirred for 40 minutes to obtain a primary product. The primary product was dried and crushed to 100 mesh to obtain a gel product. 20 parts of acidified biochar, 30 parts of acidified diatomaceous earth and 27 parts of the gel product were added to 300 parts of a 5% sodium dodecyl sulfate solution and ultrasonically dispersed for 30 minutes at an ultrasonic power of 300 W and a frequency of 40 kHz to obtain a dispersion. 6 parts of sodium alginate and 12 parts of polyethylene oxide were dissolved in 300 parts of 8% by mass citric acid solution, stirred at 75° C. for 4 hours, and then the dispersion liquid and 4 parts of glutaraldehyde were added, reacted at 65° C. for 3 hours, and dried to prepare the composite flocculant.

[0024] (2) Preparation of composite sustained-release fillers The preparation method of the composite slow-release carbon source filler is as follows: 70 parts of polycaprolactone, 30 parts of sodium acetate and 3 parts of sodium humate are added to a twin-screw extruder, melt-blended at a processing temperature of 180° C. and a screw speed of 60 rpm, and granulated through a die to obtain core particles; the core particles are immersed in the coating liquid for 60 seconds, taken out and allowed to stand for 20 minutes, and the operation is repeated twice to obtain coated particles; the coated particles are immersed in a sodium alginate solution with a mass fraction of 2% for 30 seconds, taken out and sprayed with a calcium chloride solution with a mass fraction for cross-linking for 10 minutes, and the coating-cross-linking operation is repeated three times to obtain outer coating particles; 110 parts of the outer coating particles are mixed with 90 parts of biochar, immersed in a 2% sodium alginate solution, treated at 2000 rpm for 5 minutes by a centrifugal dehydrator, and dried to obtain the composite slow-release carbon source filler.

[0025] (3) Wastewater treatment S1 puts the dye wastewater into the regulating tank, adjusts the pH to neutral and then passes it into the sedimentation tank for treatment. Add composite flocculant in the sedimentation tank at a dosage of 200 mg / L, stir for 30 minutes and then settle.

[0026] S2 passes the effluent from the sedimentation tank into the electrodialysis unit for desalination treatment with a current density of 2.5 mA / cm 2 , the operating voltage is 120V, the wastewater flow rate is 3cm / s, and the effluent salinity of the electrodialysis unit is ≦5g / L.

[0027] S3 passes the effluent from the electrodialysis unit into a hydrolysis and acidification tank for treatment with a hydraulic retention time of 8 hours. The effluent from the hydrolysis and acidification tank is then passed into a pre-aeration tank, which uses a mixture of ozone and air for pre-aeration with a gas-to-water ratio of 15:1 and a pre-aeration time of 10 minutes. The volume ratio of ozone to the mixed gas is 8%.

[0028] S4 passes the effluent from the pre-aeration tank into an anoxic tank containing a composite slow-release carbon source filler. The treatment area of the anoxic tank is divided into three layers: the bottom layer, the middle layer, and the upper layer. The particle size of the composite slow-release carbon source filler in the bottom layer is 3 cm; the particle size of the composite slow-release carbon source filler in the middle layer is 2 cm; and the particle size of the composite slow-release carbon source filler in the upper layer is 1 cm. The volume ratio of the filler in each layer is 40%. The effluent from the anoxic tank is then passed into the aerobic MBR reactor for treatment. The effluent is then treated in an electrolysis unit under the following conditions: a current density of 15 mA / cm², a plate spacing of 1 cm, and aeration and stirring. The effluent from the electrolysis unit is treated in a sedimentation tank and discharged.

[0029] Example 2 differs from Example 1 in that: the amounts of raw materials used in preparing the composite flocculant are different: 23 parts of acidified biochar, 32 parts of acidified diatomaceous earth, and 26 parts of gel product, and the amount of composite flocculant added is 250 mg / L; the amounts of raw materials used in preparing the composite slow-release carbon source filler are different: 100 parts of coated particles and 100 parts of biochar, and the coated particles and biochar are immersed in a sodium alginate solution with a mass fraction of 2.5%; during pre-aeration treatment, the proportion of ozone in the mixed gas is 9%.

[0030] Example 3 differs from Example 1 in that: the amounts of raw materials used in preparing the composite flocculant are different: 26 parts of acidified biochar, 34 parts of acidified diatomaceous earth, and 27 parts of gel product, and the amount of composite flocculant added is 300 mg / L; the amounts of raw materials used in preparing the composite slow-release carbon source filler are different: 90 parts of coated particles and 110 parts of biochar, and the coated particles and biochar are immersed in a sodium alginate solution with a mass fraction of 3%; during pre-aeration treatment, the proportion of ozone in the mixed gas is 10%.

[0031] Example 4 differs from Example 1 in that: 23 parts of acidified biochar, 32 parts of acidified diatomaceous earth, 26 parts of gel product, and the amount of composite flocculant added is 300 mg / L; the amount of raw materials used in preparing the composite slow-release carbon source filler is different: 100 parts of outer membrane particles and 100 parts of biochar, and the outer membrane and biochar are immersed in a sodium alginate solution with a mass fraction of 3%; during pre-aeration treatment, the proportion of ozone in the mixed gas is 10%.

[0032] The only difference between Comparative Example 1 and Example 1 is that a mixed flocculant of polyaluminum chloride and polyacrylamide at a mass ratio of 10:1 is used in the sedimentation tank instead of the composite flocculant.

[0033] The only difference between Comparative Example 2 and Example 1 is that the sulfonated potassium polyacrylate solution is not used in the preparation process of the composite flocculant.

[0034] Comparative Example 3 differs from Example 1 only in that: the sulfonated polyacrylate potassium solution is not used in the preparation of the composite flocculant; and glycidyl trimethyl ammonium chloride is not used in the preparation of the composite material.

[0035] The only difference between Comparative Example 4 and Example 1 is that the salinity of the effluent from the electrodialysis unit is 10 g / L, and the salinity is measured using an Atuo salt meter Master-S28α.

[0036] The only difference between Comparative Example 5 and Example 1 is that no pre-aeration is performed after the hydrolysis and acidification tank treatment.

[0037] The only difference between Comparative Example 6 and Example 1 is that only air is used for pre-aeration after the hydrolysis and acidification tank treatment.

[0038] The only difference between Comparative Example 7 and Example 1 is that the order of the hydrolysis and acidification processes and the pre-aeration processes are swapped, that is, the effluent from the electrodialysis unit first enters the pre-aeration tank for treatment and then enters the hydrolysis and acidification tank for treatment.

[0039] The only difference between Comparative Example 8 and Example 1 is that no composite slow-release carbon source filler is added to the anoxic tank.

[0040] The only difference between Comparative Example 9 and Example 1 is that during the preparation of the composite slow-release carbon source filler, no coating liquid was used for coating and no sodium humate was added.

[0041] The only difference between Comparative Example 10 and Example 1 is that there is only one layer of the composite slow-release carbon source filler in the anoxic tank, and the particle size of the composite slow-release carbon source filler is 3 cm.

[0042] The only difference between Comparative Example 11 and Example 1 is that there are three layers of composite slow-release carbon source filler in the anoxic tank, the particle size of the composite slow-release carbon source filler in the bottom layer is 1 cm; the particle size of the composite slow-release carbon source filler in the middle layer is 2 cm; and the particle size of the composite slow-release carbon source filler in the upper layer is 3 cm.

[0043] Test Case The final dye wastewater effluent obtained by the treatment methods in Examples 1-4 and Comparative Examples 1-8 was used for testing.

[0044] Test method: COD determination refers to HJ-T399-2007 "Water quality determination of chemical oxygen demand - rapid digestion spectrophotometry"; The determination of chromaticity shall refer to GB11903-1989 "Determination of chromaticity of water"; The determination of ammonia nitrogen refers to HJ535-2009 "Water quality - Determination of ammonia nitrogen - Nessler's reagent spectrophotometric method"; Total nitrogen was determined according to HJ636-2012, "Water Quality—Determination of Total Nitrogen—Alkaline Potassium Persulfate Digestion—UV Spectrophotometry." The final test results are shown in Tables 1 and 2.

[0045] Table 1 COD, chroma, copper ion, and chromium ion test results for Examples 1-4 and Comparative Examples 1-11

[0046] In a high salinity environment with an influent salinity of 26 g / L, it can be seen from Table 1 that under the conditions of Example 4, the treatment effects on COD, chroma, copper ions, and chromium ions in the wastewater are the best.

[0047] The conventional flocculant used in Comparative Example 1 lacks the bipolar charge system of sulfonic acid groups and quaternary ammonium groups, making it impossible to repel sulfate interference anions through the negative charge of the sulfonic acid groups. The lack of cationic coordination of the quaternary ammonium groups leads to a decrease in copper ion complexing ability. At the same time, the synergistic effect of the molecular chain entanglement of carboxymethyl starch and polyethylene oxide destroys the colloid stability, resulting in colloid redissolution and poor decolorization effect. The lack of sulfonated potassium polyacrylate in Comparative Example 2 causes the flocculant to lose the electrostatic repulsion of the sulfonic acid groups on sulfate groups, causing the sulfate groups in the salt to compete with the quaternary ammonium groups for copper ions, weakening the coordination bond strength of the quaternary ammonium groups and copper ions. At the same time, the charge neutralization effect of the sulfonic acid groups on the sulfonic acid groups in the dye molecules disappears, causing the dye molecules to redisperse. The lack of glycidyl trimethylammonium chloride in Comparative Example 3 prevents chitosan from forming a quaternized structure, and the quaternary ammonium groups lose their ionic bonding ability with copper ions. At the same time, the bipolar charge synergy of the sulfonic acid groups and the quaternary ammonium groups disappears completely, resulting in copper ions relying solely on physical adsorption and unable to form stable complexes.

[0048] Table 2 Total nitrogen and ammonia nitrogen test results of Examples 1-4 and Comparative Examples 1-11

[0049] It can be seen from Table 2 that under the conditions of Example 4, the treatment effect on total nitrogen and ammonia nitrogen in wastewater is the best.

[0050] In Comparative Example 4, after the electrodialysis nitrogen source effluent entered the biological treatment unit, the high salinity inhibited the activity of acid-producing bacteria in the hydrolysis and acidification tank, reducing volatile fatty acid production and resulting in insufficient carbon source for subsequent denitrification. Simultaneously, high salinity triggered an osmotic pressure imbalance in the microbial cells in the aerobic MBR, reducing nitrification and denitrification enzyme activities, exacerbating nitrate nitrogen accumulation, and increasing total nitrogen and ammonia nitrogen concentrations. In Comparative Example 5, ozone pre-aeration was omitted, resulting in unoxidized sulfides produced by hydrolysis and acidification, inhibiting the activity of nitrifying bacteria in the aerobic MBR. The macromolecules of the azo dye were not chain-scissioned, resulting in insufficient carbon source for denitrification, nitrate nitrogen accumulation, and increased total nitrogen and ammonia nitrogen concentrations. In Comparative Example 6, while air aeration could remove some sulfides from the water or allow some to escape from the wastewater as hydrogen sulfide, reducing its mass concentration in the wastewater, the shorter pre-aeration time resulted in an incomplete reaction, leading to sulfides still affecting the subsequent biological denitrification process. In Comparative Example 7, the reversed process order prevented the sulfide produced by hydrolysis and acidification from being oxidized by ozone. Sulfide directly entered the anoxic tank, inhibiting denitrifying enzyme activity and binding to nitrifying bacteria's enzymes, hindering ammonia nitrogen conversion, leading to increased total nitrogen and ammonia nitrogen concentrations. In Comparative Example 8, when no composite slow-release carbon source filler was added, the denitrifying bacteria were hindered from reducing nitrate due to lack of a continuous carbon source. Residual reactive oxygen radicals from ozone pre-aeration directly damaged denitrifying enzyme activity. The absence of sodium humate and ascorbic acid consumed electron donors for ozone oxidation, preventing efficient nitrate nitrogen conversion and increasing total nitrogen and ammonia nitrogen concentrations. In Comparative Example 9, the lack of a coating solution resulted in rapid carbon source release and the lack of β-cyclodextrin's stabilization of sodium humate. The absence of sodium humate prevented the neutralization of residual reactive oxygen radicals from ozone pre-aeration. Ozone denatured and inactivated denitrifying enzyme proteins. Furthermore, excessive carbon source release reduced carbon source availability in the later stages, weakening the nitrate nitrogen reduction reaction. Oxidative damage and an imbalance in carbon source supply inhibited the activity of denitrifying bacteria, leading to increased total nitrogen and ammonia nitrogen concentrations in the effluent. In Comparative Example 10, the use of a single-particle filler resulted in concentrated carbon source release in the early stages, followed by insufficient release in the later stages. The insufficient specific surface area of the biochar carrier reduced ozone removal efficiency, and residual ozone inhibited denitrifying bacteria metabolism. Locally oversaturated carbon sources were oxidized and wasted, leading to increased total nitrogen concentration in the effluent. In Comparative Example 11, the filler layer was inverted, and the small-particle filler had poor impact resistance, resulting in premature decomposition of the filler and failure to achieve a sustained-release effect. Rapid ascorbic acid consumption prevented free radical neutralization, and residual ozone damaged the biofilm structure. Carbon source release was misaligned with denitrification demand, causing fluctuations in the nitrate reduction rate and an increase in total nitrogen.

[0051] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for treating dye wastewater, characterized in that: The specific steps include: S1: the dye wastewater is passed into a regulating tank, the pH value is adjusted to neutral, and then passed into a sedimentation tank for treatment, and a composite flocculant is added into the sedimentation tank; S2: passing the effluent from the sedimentation tank into an electrodialysis unit for desalination treatment, wherein the effluent salinity of the electrodialysis unit is ≤5 g / L; S3: passing the effluent from the electrodialysis unit into a hydrolysis and acidification tank for treatment and then into a pre-aeration tank, wherein the pre-aeration tank uses a mixed gas of ozone and air for pre-aeration, wherein the volume ratio of the ozone to the mixed gas is 8-10%; S4: the effluent from the pre-aeration tank is passed through an anoxic tank containing a composite slow-release carbon source filler, an aerobic MBR tank, and an electrolysis unit for treatment; the effluent from the electrolysis unit is treated in a sedimentation tank to obtain discharged effluent; The raw materials for preparing the composite flocculant include: acidified biochar, acidified diatomaceous earth, and a gel product; the raw materials for preparing the gel product include: chitosan, glycidyl trimethylammonium chloride, corn starch, monochloroacetic acid, and 3-acrylamidopropanesulfonic acid; The raw materials for preparing the composite slow-release carbon source filler include: polycaprolactone, sodium acetate, sodium humate, and biochar.

2. The method for treating dye wastewater according to claim 1, wherein: The preparation method of the composite flocculant comprises the following steps: adding 20-26 parts by mass of acidified biochar, 30-34 parts by mass of acidified diatomaceous earth, and 25-27 parts by mass of a gel product to a 5% by mass sodium dodecylsulfonate solution, and dispersing the mixture for 30 minutes at an ultrasonic power of 300W and a frequency of 40kHz to obtain a dispersion; dissolving 6 parts by mass of sodium alginate and 12 parts by mass of polyethylene oxide in 300 parts by mass of an 8% by mass citric acid solution, stirring the mixture at a constant temperature of 75°C for 4 hours, adding the dispersion and 4 parts by mass of glutaraldehyde, reacting the mixture at 65°C for 3 hours, and drying the mixture to obtain the composite flocculant; and the addition amount of the composite flocculant is 200-300 mg / L.

3. The method for treating dye wastewater according to claim 2, wherein: 2 parts of chitosan were dissolved in 5% acetic acid solution, 2 parts of sodium montmorillonite and 1.2 parts of glycidyl trimethylammonium chloride were added, and the mixture was stirred at 60°C for 2 hours. After the reaction, the pH value was adjusted to 9, and the mixture was allowed to stand for precipitation, centrifuged, and dried to obtain a composite material. 13 parts of corn starch and 30% sodium hydroxide solution were mixed at a solid-liquid ratio of 1:4 and swelled for 1 hour. A 15% monochloroacetic acid ethanol solution was added, and the molar ratio of the corn starch to the monochloroacetic acid was 1:1.

2. The mixture was reacted at 50°C for 4 hours. After neutralization, the mixture was washed with ethanol and dried to obtain carboxymethyl starch; 6.8 parts of acrylic acid and 1.2 parts of 3-acrylamidopropanesulfonic acid were dissolved in 200 parts of deionized water, 0.005 parts of ammonium persulfate were added under a nitrogen atmosphere, the mixture was reacted at 60° C. for 4 hours, and then evaporated to obtain a 15% by weight potassium sulfonated polyacrylate solution; 4 parts of the composite material and 13 parts of the carboxymethyl starch were added to 200 parts of deionized water, stirred to dissolve, and then the sulfonated polyacrylate potassium solution was added, 0.005 parts of the ammonium persulfate was added under a nitrogen atmosphere at 50° C., stirred to react for 40 minutes to obtain a primary product, and the primary product was dried to obtain the gel product.

4. The method for treating dye wastewater according to claim 1, wherein: The preparation method of the composite slow-release carbon source filler is as follows: 70 parts of polycaprolactone, 30 parts of sodium acetate and 3 parts of sodium humate are mixed and then extruded and granulated to obtain core particles; the core particles are immersed in a coating liquid for 60 seconds, taken out and allowed to stand for 20 minutes, and the process is repeated twice to obtain coated particles; the coated particles are immersed in a sodium alginate solution with a mass fraction of 2% for 30 seconds, taken out and sprayed with a calcium chloride solution with a mass fraction for cross-linking for 10 minutes, and the process is repeated three times to obtain outer coating particles; 90-110 parts of the outer coating particles are mixed with 90-110 parts of biochar, immersed in a sodium alginate solution with a mass fraction of 2-3%, treated at 2000 rpm for 5 minutes by a centrifugal dehydrator, and dried to obtain the composite slow-release carbon source filler.

5. The method for treating dye wastewater according to claim 4, wherein: The coating liquid is prepared by dissolving 5 parts of β-cyclodextrin in 95 parts of deionized water, stirring until completely dissolved, and then adding 2 parts of ascorbic acid to obtain the coating liquid.

6. The method for treating dye wastewater according to claim 1, wherein: The wastewater treatment method of the anoxic tank is as follows: the composite slow-release carbon source filler is loaded into the anoxic tank in three layers; the effluent of the pre-aeration tank enters the anoxic tank from the lower water inlet and flows out from the upper water outlet.

7. The method for treating dye wastewater according to claim 6, wherein: The particle size of the composite slow-release carbon source filler is 1-3 cm, and the three layers are respectively a bottom layer, a middle layer, and an upper layer. The particle size of the composite slow-release carbon source filler in the bottom layer is 3 cm; the particle size of the composite slow-release carbon source filler in the middle layer is 2 cm; and the particle size of the composite slow-release carbon source filler in the upper layer is 1 cm.

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