A method for treating dye wastewater

Abstract

The present application relates to wastewater treatment technical field, specifically to a kind of dye wastewater treatment method.The present application overcomes the shortcomings of poor heavy metal ion removal ability and poor denitrification ability of the existing dye wastewater treatment method.In the present application, dye wastewater is treated in turn by adjusting tank, sedimentation tank, electrodialysis unit, hydrolysis acidification tank, pre-aeration tank, anoxic tank, aerobic MBR tank, electrolysis unit and sedimentation tank;Composite flocculants are added in the sedimentation tank, and the raw materials of the composite flocculants include acidified biochar, acidified diatomite and gel product;Composite slow-release carbon source fillers are added in the anoxic tank, and the raw materials of the composite slow-release carbon source fillers include polycaprolactone, sodium acetate, sodium humate and biochar;The composite slow-release carbon source fillers are distributed in layers in the anoxic tank;Through the coherent cooperation of the dye wastewater process, the effluent has low heavy metal content, low total nitrogen and ammonia nitrogen content, and good treatment effect.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically a method for treating dye wastewater. Background Technology

[0002] As a major industrial water user, the dyeing and printing industry generates dye wastewater characterized by its complex quality and diverse composition. This wastewater not only contains large amounts of organic dyes, auxiliaries, and sizing agents, but also often exhibits high salinity, high color, and high chemical oxygen demand (COD). If this wastewater is discharged directly without effective treatment, it will cause serious damage to natural aquatic ecosystems, such as increasing water color and reducing transparency, affecting the photosynthesis and respiration of aquatic organisms, thereby endangering the entire aquatic ecological balance. It will also have adverse effects on the surrounding soil environment and groundwater quality.

[0003] The high salinity of dye wastewater presents numerous challenges to wastewater treatment. Firstly, high salinity interferes with the hydrolysis and polymerization processes of flocculants, leading to unstable flocculant performance and difficulty in forming effective flocs. This significantly reduces the removal efficiency of suspended particles and colloidal substances in the wastewater. Secondly, heavy metal ions present in the wastewater, such as copper, zinc, and chromium, exhibit more complex chemical forms in high-salinity environments, interacting with other substances and increasing the difficulty of removal. Furthermore, high salinity strongly inhibits the growth and metabolism of microorganisms, hindering efficient biological denitrification. Under high salinity, microorganisms experience osmotic pressure imbalance and impaired enzyme activity, resulting in a significant decrease in their ability to convert nitrogen sources in wastewater, making it difficult to effectively convert nitrogenous 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 in heavy metal ion removal and biological denitrification in high-salinity environments, thereby achieving compliant discharge of dye wastewater and sustainable water resource utilization.

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

[0006] The purpose of this invention is to provide a method for treating dye wastewater. In this invention, the dye wastewater undergoes sequential treatment through an equalization 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. Specifically, a composite flocculant is added to the sedimentation tank; the raw materials for preparing the composite flocculant include acidified biochar, acidified diatomaceous earth, and gel products. A composite slow-release carbon source packing is added to the anoxic tank; the raw materials for preparing the composite slow-release carbon source packing include polycaprolactone, sodium acetate, sodium humate, and biochar, and the composite slow-release carbon source packing is distributed in layers within the anoxic tank. Through this continuous and coordinated treatment of the dye wastewater, the effluent has low heavy metal content, low total nitrogen and ammonia nitrogen content, and exhibits good treatment efficiency.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for treating dye wastewater, specifically including the following steps:

[0009] 1. A method for treating dye wastewater, characterized by comprising the following steps:

[0010] S1 introduces dye wastewater into an equalization tank to adjust the pH to neutral before introducing it into a sedimentation tank for further treatment. A composite flocculant is then added to the sedimentation tank.

[0011] S2 introduces the effluent from the sedimentation tank into the electrodialysis unit for desalination treatment. The salinity of the effluent from the electrodialysis unit is ≤5g / L.

[0012] S3 feeds the effluent from the electrodialysis unit into a hydrolysis 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 ozone accounting for 8-10% of the volume of the mixture.

[0013] S4 feeds the effluent from the pre-aeration tank into an anoxic tank, an aerobic MBR tank, and an electrolysis unit containing composite slow-release carbon source packing material. The effluent from the electrolysis unit is then treated in a sedimentation tank to obtain the discharge effluent.

[0014] The raw materials for preparing the composite flocculant include: acidified biochar, acidified diatomaceous earth, and gel products; the raw materials for preparing the gel products include: chitosan, glycidyltrimethylammonium chloride, corn starch, monochloroacetic acid, and 3-acrylamidopropanesulfonic acid.

[0015] The raw materials for preparing the composite slow-release carbon source filler include: polycaprolactone, sodium acetate, sodium humate, and biochar.

[0016] Preferably, the preparation method of the composite flocculant is as follows: 20-26 parts by mass of acidified biochar, 30-34 parts by mass of acidified diatomaceous earth, and 25-27 parts by mass of gel product are added to a 5% sodium dodecyl sulfonate solution and dispersed for 30 minutes at an ultrasonic power of 300W and a frequency of 40kHz to obtain a dispersion; 6 parts by mass of sodium alginate and 12 parts by mass of polyethylene oxide are dissolved in 300 parts by mass of 8% citric acid solution, stirred at 75℃ for 4 hours, the dispersion and 4 parts by mass of glutaraldehyde are added, and the mixture is reacted at 65℃ for 3 hours. After drying, the composite flocculant is prepared; the amount of composite flocculant added is 200-300 mg / L.

[0017] Preferably, the biochar obtained by carbonizing the biochar raw material is mixed with a 50% phosphoric acid solution at 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% sulfuric acid solution at a mass ratio of 1:5 and stirred at 80°C for 3 hours, then centrifuged, washed, and dried to obtain acidified diatomaceous earth.

[0018] Preferably, coconut shell is used as the raw material for biochar.

[0019] Preferably, 2 parts of chitosan are dissolved in a 5% (w / w) acetic acid solution, 2 parts of sodium montmorillonite and 1.2 parts of glycidyltrimethylammonium chloride are added, and the mixture is stirred at 60°C for 2 hours. After the reaction is completed, the pH is adjusted to 9, and the precipitate is allowed to stand, then centrifuged and dried to obtain the composite material. 13 parts of corn starch are mixed with a 30% (w / w) sodium hydroxide solution at a solid-liquid ratio of 1:4 and swelled for 1 hour. A 15% (w / w) monochloroacetic acid ethanol solution is added, with a corn starch to monochloroacetic acid molar ratio of 1:1.2. The mixture is reacted at 50°C for 4 hours, neutralized, washed with ethanol, and dried. Carboxymethyl starch was obtained by drying. 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 and reacted at 60°C for 4 hours. After evaporation, a 15% (w / w) sulfonated potassium polyacrylate solution was obtained. 4 parts of the composite material and 13 parts of carboxymethyl starch were added to 200 parts of deionized water and stirred to dissolve. The sulfonated potassium polyacrylate solution was then added. 0.005 parts of ammonium persulfate were added under a nitrogen atmosphere at 50°C and stirred for 40 minutes to obtain the initial product. The initial product was dried to obtain the gel product.

[0020] 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 extruded to obtain core particles; the core particles are immersed in a coating solution for 60 seconds, removed and allowed to stand for 20 minutes, and this process is repeated twice to obtain coated particles; the coated particles are immersed in a 2% sodium alginate solution for 30 seconds, removed and sprayed with a 5% calcium chloride solution for crosslinking for 10 minutes, and this 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 2-3% sodium alginate solution, centrifuged at 2000 rpm for 5 minutes, and dried to obtain the composite slow-release carbon source filler.

[0021] 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.

[0022] Preferably, the wastewater treatment method for the anoxic tank is as follows: the composite slow-release carbon source packing is loaded into the anoxic tank in three layers; the effluent from the pre-aeration tank enters from the lower inlet of the anoxic tank and flows out from the upper outlet.

[0023] Preferably, the particle size of the composite slow-release carbon source filler is 1-3 cm, and the three layers are a bottom layer, a middle layer, and a top 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 top layer is 1 cm.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. In this invention, for high-salt dye wastewater, a porous substrate is constructed through the synergistic adsorption of coconut shell activated carbon and acidified diatomaceous earth. The sulfonic acid groups of sulfonated potassium polyacrylate and the quaternary ammonium groups of quaternized chitosan form a bipolar charge system, which synergistically inhibits the charge imbalance under salt interference. The sulfonic acid groups repel interfering anions such as sulfate, while the quaternary ammonium groups directionally capture cationic pollutants such as copper ions, thus overcoming the shielding effect of salt on charge activity. Carboxymethyl starch and polyethylene oxide destroy the colloidal stability of the wastewater through molecular chain entanglement. Sodium alginate and glutaraldehyde crosslink to form a three-dimensional network to strengthen the floc structure, ultimately forming a salt-resistant composite flocculation system, which simultaneously achieves synergistic effects of dye decolorization, heavy metal removal, and salt interference inhibition.

[0026] 2. In this invention, ozone pretreatment directly oxidizes the sulfides generated during the hydrolysis and acidification stage into sulfates, eliminating odor and biotoxicity. Simultaneously, it attacks the azo bonds and conjugated systems in dye molecules, destroying chromophores and cleaving organic matter into small-molecule carboxylic acids. This process connects hydrolysis and acidification with subsequent biological treatment units, converting recalcitrant macromolecules into readily biodegradable substances. This not only alleviates the toxic effects of sulfides on MBR microorganisms but also enhances the mineralization efficiency of organic matter in the anoxic-aerobic MBR through chain scission reactions, forming a closed-loop synergistic purification process of oxidation pretreatment and biodegradation.

[0027] 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 remove ozone and free radicals, respectively. An outer gradient-coated calcium alginate layer controls the carbon source diffusion rate, and β-cyclodextrin encapsulates ascorbic acid to achieve long-term antioxidant protection. A biofilm forms on the surface of the biochar carrier, enriching denitrifying bacteria. During the ozone pre-aeration stage, recalcitrant organic matter decomposed is adsorbed by biochar in the packing layer. The core carbon source continuously releases and replenishes the electron donors required for denitrification. Sodium humate preferentially reduces residual ozone, and ascorbic acid neutralizes reactive oxygen free radicals. These three elements synergistically overcome the bottleneck of carbon and nitrogen metabolism imbalance under ozone interference, achieving simultaneous improvement in denitrifying bacteria activity protection and nitrogen removal efficiency in highly oxidizing wastewater environments.

[0028] 4. In this invention, the removal of heavy metal ions from dye wastewater using a composite flocculant resistant to high-salt environments, along with desalination during the electrodialysis stage, lays a solid foundation for subsequent biological treatment. Simultaneously, it reduces the pollutant load during the electrodialysis stage, improving treatment efficiency. In the effluent from the hydrolysis acidification tank, which contains a significant amount of sulfides, pre-aeration removes these sulfides and some recalcitrant organic matter, ensuring stable denitrification in the anoxic and aerobic MBR tanks. Finally, advanced treatment via an electrolysis unit further removes recalcitrant organic matter from the wastewater. Attached Figure Description

[0029] Figure 1 This is a process flow diagram for the treatment of dye wastewater according to the present invention. Detailed Implementation

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

[0031] Please see Figure 1 This invention provides a method for treating dye wastewater, the technical solution of which is as follows: Example 1

[0032] (I) Preparation of composite flocculants

[0033] Biochar raw material was carbonized at 850℃ for 2 hours at a rate of 10℃ / min to obtain carbonized product. The carbonized product was mixed with a 50% phosphoric acid solution at a mass ratio of 1:3 and reacted at 85℃ for 2 hours. The reaction product was washed, dried, and pulverized to 200 mesh to obtain acidified biochar. Diatomaceous earth was mixed with a 10% sulfuric acid solution at a mass ratio of 1:5 and reacted at 80℃ with stirring for 3 hours. After centrifugation, washing, and drying, acidified diatomaceous earth was obtained.

[0034] Two parts of chitosan were dissolved in a 5% acetic acid solution, two parts of sodium montmorillonite and 1.2 parts of glycidyltrimethylammonium chloride were added, and the mixture was stirred at 60°C for 2 hours. After the reaction was completed, sodium hydroxide solution was added dropwise to adjust the pH value to 9. After the precipitate was precipitated by standing, the mixture was centrifuged, freeze-dried and pulverized to 100 mesh to obtain the composite material.

[0035] 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 and reacted at 60°C for 4 hours. The mixture was then evaporated to obtain a concentrated solution with a mass fraction of 15%.

[0036] Thirteen parts of corn starch were mixed with 30% sodium hydroxide solution at a solid-liquid ratio of 1:4 and swelled for 1 hour. Then, 15% monochloroacetic acid ethanol solution was added. The molar ratio of starch to 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 and pulverized at 60°C to obtain carboxymethyl starch.

[0037] Four parts of the composite material and 13 parts of carboxymethyl starch were added to 200 parts of distilled water and stirred to dissolve. Then, sulfonated potassium polyacrylate solution was added. Under a nitrogen atmosphere at 50°C, 0.005 parts of ammonium persulfate were added and stirred for 40 minutes to obtain the initial product. The initial product was dried and pulverized to 100 mesh to obtain the gel product.

[0038] 20 parts of acidified biochar, 30 parts of acidified diatomaceous earth and 27 parts of gel product were added to 300 parts of sodium dodecyl sulfonate solution with a mass fraction of 5% and ultrasonically dispersed for 30 min at an ultrasonic power of 300 W and a frequency of 40 kHz to obtain a dispersion.

[0039] Six parts of sodium alginate and 12 parts of polyethylene oxide were dissolved in 300 parts of 8% citric acid solution, stirred at 75°C for 4 hours, then the dispersion and 4 parts of glutaraldehyde were added, and the mixture was reacted at 65°C for 3 hours. After drying, the composite flocculant was prepared.

[0040] (II) Preparation of composite slow-release packing

[0041] 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, processed at 180℃ and screw speed of 60 rpm, melt-blended, and extruded and granulated through a die to obtain core particles; the core particles are immersed in the coating solution for 60s, removed and allowed to stand for 20min, and the operation is repeated twice to obtain coated particles; the coated particles are immersed in a 2% sodium alginate solution for 30s, removed and sprayed with a 5% calcium chloride solution for crosslinking for 10min, and the coating-crosslinking operation is repeated three times to obtain outer coating particles; 110 parts of outer coating particles are mixed with 90 parts of biochar, immersed in a 2% sodium alginate solution, centrifuged at 2000 rpm for 5min, and dried to obtain the composite slow-release carbon source filler.

[0042] (III) Wastewater Treatment

[0043] S1 introduces dye wastewater into an equalization tank to adjust the pH to neutral before introducing it into a sedimentation tank for treatment. A composite flocculant is added to the sedimentation tank at a dosage of 200 mg / L, and the mixture is stirred for 30 minutes before settling.

[0044] S2 introduces the effluent from the sedimentation tank into the electrodialysis unit for desalination treatment, with a current density of 2.5 mA / cm³. 2 The operating voltage is 120V, the wastewater flow rate is 3cm / s, and the effluent salinity of the electrodialysis unit is ≤5g / L.

[0045] S3 feeds the effluent from the electrodialysis unit into the hydrolysis acidification tank for treatment. The hydraulic retention time is 8 hours. The effluent from the hydrolysis acidification tank is then fed into the pre-aeration tank. The pre-aeration tank uses a mixture of ozone and air for pre-aeration. The air-to-water ratio is 15:1, the pre-aeration time is 10 minutes, and the volume ratio of ozone to the mixed gas is 8%.

[0046] S4 feeds the effluent from the pre-aeration tank into an anoxic tank containing composite slow-release carbon source packing material. The anoxic tank is divided into three layers: a bottom layer, a middle layer, and a top layer. The bottom layer uses composite slow-release carbon source packing material with a particle size of 3 cm; the middle layer uses 2 cm; and the top layer uses 1 cm. Each layer occupies 40% of the total volume. The effluent from the anoxic tank is then fed into an aerobic MBR reactor for further treatment. The effluent then passes through an electrolysis unit under the following conditions: current density of 15 mA / cm², electrode spacing of 1 cm, and aeration and stirring. The effluent from the electrolysis unit is then treated in a sedimentation tank to obtain the final discharge effluent.

[0047] The difference between Example 2 and Example 1 is as follows: the amount of raw materials used in preparing the composite flocculant is different: 23 parts of acidified biochar, 32 parts of acidified diatomaceous earth, and 26 parts of gel product, with the amount of composite flocculant added being 250 mg / L; the amount of raw materials used in preparing the composite slow-release carbon source filler is different: 100 parts of outer coating particles and 100 parts of biochar, with the outer coating and biochar immersed in a 2.5% sodium alginate solution; and during the pre-aeration treatment, the proportion of ozone in the mixed gas is 9%.

[0048] The difference between Example 3 and Example 1 is as follows: the amount of raw materials used in preparing the composite flocculant is different: 26 parts of acidified biochar, 34 parts of acidified diatomaceous earth, and 27 parts of gel product, with the amount of composite flocculant added being 300 mg / L; the amount of raw materials used in preparing the composite slow-release carbon source filler is different: 90 parts of outer coating particles and 110 parts of biochar, with the outer coating and biochar immersed in a 3% sodium alginate solution; and during the pre-aeration treatment, the proportion of ozone in the mixed gas is 10%.

[0049] The difference between Example 4 and Example 1 is as follows: 23 parts of acidified biochar, 32 parts of acidified diatomaceous earth, and 26 parts of gel product were used; the amount of composite flocculant added was 300 mg / L; the raw material dosages were different when preparing the composite slow-release carbon source filler: 100 parts of outer coating particles and 100 parts of biochar were used; the outer coating and biochar were immersed in a 3% sodium alginate solution; and the proportion of ozone in the mixed gas was 10% during the pre-aeration treatment.

[0050] 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 was used in the sedimentation tank instead of the composite flocculant.

[0051] The only difference between Comparative Example 2 and Example 1 is that sulfonated potassium polyacrylate solution is not used in the preparation of the composite flocculant.

[0052] The only difference between Comparative Example 3 and Example 1 is that: sulfonated potassium polyacrylate solution is not used in the preparation of the composite flocculant; and glycidyltrimethylammonium chloride is not used when preparing the composite material in the preparation of the composite flocculant.

[0053] 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 AT&T Master-S28α salinity meter.

[0054] The only difference between Comparative Example 5 and Example 1 is that no pre-aeration is performed after the hydrolysis acidification tank treatment.

[0055] The only difference between Comparative Example 6 and Example 1 is that the pre-aeration after the hydrolysis acidification tank treatment uses only air.

[0056] The only difference between Comparative Example 7 and Example 1 is that the order of hydrolysis acidification and pre-aeration processes is reversed, that is, the effluent from the electrodialysis unit first enters the pre-aeration tank for treatment, and then enters the hydrolysis acidification tank for treatment.

[0057] The only difference between Comparative Example 8 and Example 1 is that no composite slow-release carbon source packing is added to the anoxic tank.

[0058] The only difference between Comparative Example 9 and Example 1 is that no coating solution is used and no sodium humate is added during the preparation of the composite slow-release carbon source filler.

[0059] The only difference between Comparative Example 10 and Example 1 is that the composite slow-release carbon source packing in the anoxic tank has only one layer and the particle size of the composite slow-release carbon source packing is 3 cm.

[0060] The only difference between Comparative Example 11 and Example 1 is that the composite slow-release carbon source packing in the anoxic tank has 3 layers: the bottom layer has a particle size of 1 cm; the middle layer has a particle size of 2 cm; and the top layer has a particle size of 3 cm.

[0061] Test case

[0062] The final dye wastewater effluent obtained under the treatment methods in Examples 1-4 and Comparative Examples 1-8 was tested.

[0063] Test method: COD was determined according to HJ-T399-2007 "Determination of Chemical Oxygen Demand in Water - Rapid Digestion Spectrophotometric Method";

[0064] Color determination shall be performed in accordance with GB11903-1989 "Determination of Color in Water".

[0065] The determination of ammonia nitrogen shall be in accordance with HJ535-2009 "Determination of Ammonia Nitrogen in Water - Nessler's Reagent Spectrophotometric Method";

[0066] Total nitrogen was determined according to HJ636-2012 "Determination of Total Nitrogen in Water - Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometric Method". The final test results are shown in Tables 1 and 2.

[0067] Table 1. Test results of COD, color, copper ion, and chromium ion in Examples 1-4 and Comparative Examples 1-11

[0068]

[0069] Under high salinity conditions with an influent salinity of 26 g / L, as shown in Table 1, the treatment effect on COD, color, copper ions, and chromium ions in wastewater was optimal under the conditions of Example 4.

[0070] In Comparative Example 1, the conventional flocculant lacked the bipolar charge system of sulfonic acid and quaternary ammonium groups. This prevented the sulfonic acid groups from repelling sulfate ions and interfering with anions, and the absence of the cation coordination effect of the quaternary ammonium groups led to a decrease in copper ion complexation. Simultaneously, the synergistic effect of the molecular chain entanglement between carboxymethyl starch and polyethylene oxide disrupting colloidal stability disappeared, resulting in colloid resolution and a poorer decolorization effect. In Comparative Example 2, the absence of potassium sulfonate caused the flocculant to lose the electrostatic repulsion of sulfate ions by the sulfonic acid groups. This resulted in sulfate ions in the salt competing with the quaternary ammonium groups for copper ions, weakening the coordination bond strength between the quaternary ammonium groups and copper ions. Furthermore, the charge neutralization effect of the sulfonic acid groups on the sulfonic acid groups in the dye molecules disappeared, causing redispersion of the dye molecules. In Comparative Example 3, the absence of glycidyltrimethylammonium chloride prevented chitosan from forming a quaternized structure, resulting in the loss of the ionic bond between the quaternary ammonium groups and copper ions. Simultaneously, the synergistic effect of the bipolar charge between the sulfonic acid and quaternary ammonium groups completely disappeared, causing copper ions to rely solely on physical adsorption and unable to form stable complexes.

[0071] Table 2. Test results of total nitrogen and ammonia nitrogen in Examples 1-4 and Comparative Examples 1-11

[0072]

[0073] As can be seen from Table 2, the treatment effect on total nitrogen and ammonia nitrogen in wastewater was the best under the conditions of Example 4.

[0074] In Comparative Example 4, after the effluent from the electrodialysis nitrogen source entered the biological treatment unit, the high-salinity environment inhibited the activity of acid-producing bacteria in the hydrolysis acidification tank, reducing the production of volatile fatty acids and leading to insufficient carbon source for subsequent denitrification. Simultaneously, the high salinity caused an osmotic pressure imbalance in the microbial cells of the aerobic MBR, reducing the activity of nitrifying and denitrifying enzymes, exacerbating nitrate nitrogen accumulation, and increasing the concentrations of total nitrogen and ammonia nitrogen. In Comparative Example 5, the lack of ozone pre-aeration resulted in the sulfides produced by hydrolysis acidification not being oxidized, inhibiting the activity of nitrifying bacteria in the aerobic MBR. The azo dye macromolecules were not broken down, leading to insufficient carbon source for denitrification, nitrate nitrogen accumulation, and increased concentrations of total nitrogen and ammonia nitrogen. In Comparative Example 6, although air aeration could remove some sulfides from the water or allow some sulfides to escape from the wastewater as hydrogen sulfide, reducing the mass concentration of sulfides in the wastewater, the reaction was incomplete due to the short pre-aeration time, causing sulfides to still affect the subsequent biological denitrification process. In Comparative Example 7, the reversed process sequence prevented the sulfides produced during hydrolysis and acidification from being oxidized by ozone. These sulfides directly entered the anoxic tank, inhibiting denitrifying enzyme activity and binding with nitrifying bacteria enzymes, thus hindering ammonia nitrogen conversion and leading to increased total nitrogen and ammonia nitrogen concentrations. In Comparative Example 8, without the addition of a composite slow-release carbon source packing, the denitrifying bacteria lacked a continuous carbon source, hindering nitrate reduction. Residual reactive oxygen species from ozone pre-aeration directly damaged denitrifying bacteria enzyme activity. The absence of sodium humate and ascorbic acid caused ozone oxidation to consume electron donors, preventing effective 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 a lack of β-cyclodextrin stabilizing effect on sodium humate. The absence of sodium humate prevented the neutralization of residual reactive oxygen species from ozone pre-aeration. Ozone caused denaturation and inactivation of denitrifying bacteria enzyme proteins; simultaneously, excessive carbon source release led to a reduction in carbon source in the later stages, weakening the nitrate nitrogen reduction reaction. Denitrifying bacteria activity was inhibited due to oxidative damage and an imbalance in carbon source supply, leading to increased total nitrogen and ammonia nitrogen concentrations in the effluent. In Comparative Example 10, the single-size packing material resulted in concentrated carbon source release in the early stages but insufficient release later. The insufficient surface area of ​​the biochar carrier reduced ozone removal efficiency, residual ozone inhibited denitrifying bacteria metabolism, and the locally supersaturated carbon source was oxidized and wasted, resulting in increased total nitrogen concentration in the effluent. In Comparative Example 11, the inverted packing layer and the poor shock resistance of the small-size packing material led to premature decomposition and failure to provide a slow-release effect. Rapid consumption of ascorbic acid prevented the neutralization of free radicals, residual ozone damaged the biofilm structure, and the mismatch between carbon source release and denitrification requirements caused fluctuations in nitrate reduction rates, resulting in increased total nitrogen.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for treating dye wastewater, characterized in that: Specifically, the steps include the following: S1 The dye wastewater is fed into an equalization tank to adjust the pH value to neutral before being fed into a sedimentation tank for treatment. A composite flocculant is added to the sedimentation tank. S2 introduces the effluent from the sedimentation tank into the electrodialysis unit for desalination treatment, wherein the salinity of the effluent from the electrodialysis unit is ≤5g / L; S3 The effluent from the electrodialysis unit is fed into a hydrolysis 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 ozone accounting for 8-10% of the volume of the mixture. S4 The effluent from the pre-aeration tank is fed into an anoxic tank, an aerobic MBR tank, and an electrolysis unit containing composite slow-release carbon source packing material. The effluent from the electrolysis unit is then treated in a sedimentation tank to obtain the discharge effluent. The raw materials for preparing the composite flocculant include: acidified biochar, acidified diatomaceous earth, and gel products; the raw materials for preparing the gel products include: chitosan, glycidyltrimethylammonium 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, characterized in that: The preparation method of the composite flocculant is as follows: 20-26 parts by mass of acidified biochar, 30-34 parts by mass of acidified diatomaceous earth, and 25-27 parts by mass of gel product are added to a 5% sodium dodecyl sulfonate solution and dispersed for 30 minutes at an ultrasonic power of 300W and a frequency of 40kHz to obtain a dispersion; 6 parts by mass of sodium alginate and 12 parts by mass of polyethylene oxide are dissolved in 300 parts by mass of 8% citric acid solution and stirred at 75℃ for 4 hours; the dispersion and 4 parts by mass of glutaraldehyde are added, and the mixture is reacted at 65℃ for 3 hours; after drying, the composite flocculant is obtained; the dosage of the composite flocculant is 200-300 mg / L.

3. The method for treating dye wastewater according to claim 2, characterized in that: Two parts of chitosan were dissolved in a 5% (w / w) acetic acid solution, and two parts of sodium montmorillonite and 1.2 parts of glycidyltrimethylammonium chloride were added. The mixture was stirred at 60°C for 2 hours. After the reaction was completed, the pH was adjusted to 9, and the precipitate was allowed to stand, centrifuged, and dried to obtain the composite material. Thirteen parts of corn starch were mixed with a 30% (w / w) sodium hydroxide solution at a solid-liquid ratio of 1:4 and swelled for 1 hour. A 15% (w / w) monochloroacetic acid ethanol solution was added, with the molar ratio of corn starch to monochloroacetic acid being 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, and 0.005 parts of ammonium persulfate were added under a nitrogen atmosphere and reacted at 60°C for 4 hours. After evaporation, a 15% (w / w) sulfonated potassium polyacrylate solution was obtained; 4 parts of the composite material and 13 parts of the carboxymethyl starch were added to 200 parts of deionized water and stirred to dissolve. Then, the sulfonated potassium polyacrylate solution was added, and 0.005 parts of the ammonium persulfate were added under a nitrogen atmosphere at 50°C and stirred for 40 minutes to obtain the initial product. The initial product was dried to obtain the gel product.

4. The method for treating dye wastewater according to claim 1, characterized in that: 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 extruded to obtain core particles; the core particles are immersed in a coating solution for 60 seconds, removed and allowed to stand for 20 minutes, and this process is repeated twice to obtain coated particles; the coated particles are immersed in a 2% sodium alginate solution for 30 seconds, removed and sprayed with a 5% calcium chloride solution for crosslinking for 10 minutes, and this 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 2-3% sodium alginate solution, centrifuged at 2000 rpm for 5 minutes, and dried to obtain the composite slow-release carbon source filler.

5. The method for treating dye wastewater according to claim 4, characterized in that: 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.

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

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

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