A method for treating wastewater from a steel plant

Abstract

This application relates to the technical field of wastewater treatment, specifically disclosing a method for treating steel plant wastewater. The disclosed method includes the following steps: pretreatment: wastewater is treated by passing it through a screen and equalization tank; main treatment: coagulation and sedimentation are performed by adding a coagulant; deep filtration is performed using a membrane separation unit; the coagulant, based on wastewater volume, consists of the following components at the following concentrations: polyaluminum chloride 50-85 mg / L, polyferric sulfate 40-60 mg / L, polyacrylamide 0.2-1 mg / L, and coagulant aid 3-10 mg / L; the coagulant aid is prepared by mixing a cross-linked network polymer with an enzyme-modified polysaccharide; post-treatment: disinfection. Using the method provided in this application, steel plant wastewater is treated; the process is simple and has excellent wastewater treatment effects.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, and particularly relates to a steel plant wastewater treatment method. BACKGROUND

[0002] The steel industry is one of the important basic industries in China, but a large amount of wastewater containing heavy metals, suspended solids, oils and other pollutants is generated in the production process. With the increasingly stringent environmental protection requirements, the wastewater treatment technology of steel plants has become the focus of the industry. At present, physical and chemical methods, biological treatment methods and other technical means are generally used for wastewater treatment in the industry, but these methods still have many challenges in treatment efficiency, operation cost and the like.

[0003] In recent years, new treatment processes such as membrane separation technology and advanced oxidation technology have been gradually applied to the field of steel wastewater treatment, but a mature technical system has not yet been formed. SUMMARY

[0004] In order to solve the above technical problems, the present application provides a steel plant wastewater treatment method.

[0005] The present application provides a steel plant wastewater treatment method, which specifically comprises the following steps in sequence:

[0006] (1) Pretreatment: wastewater is treated in a grid and a regulating tank;

[0007] (2) Main treatment: a coagulant is added for coagulation and sedimentation; a membrane separation assembly is used for deep filtration;

[0008] The coagulant consists of the following components in the following concentrations: polyaluminum chloride 50-85 mg / L, polyferric sulfate 40-60 mg / L, polyacrylamide 0.2-1 mg / L, and coagulant aid 3-10 mg / L, based on the amount of wastewater;

[0009] The preparation method of the coagulant aid is as follows: cross-linked network structure polymers are prepared from acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid and acryloyloxyethyltrimethylammonium chloride in a molar ratio of 2.5-3.5:3.5-4.5:2.5-3.5 by using an initiator and a cross-linking agent; chitosan is modified using laccase and cellulase to obtain enzyme-modified polysaccharides;

[0010] Then, the cross-linked network structure polymers and the enzyme-modified polysaccharides are mixed in a weight ratio of 3-5:1-2 to obtain the coagulant aid.

[0011] (3) Post-treatment: disinfection treatment.

[0012] The technical solution provided in this application adopts a process route of "pretreatment of wastewater through a screen and equalization tank" - "main treatment of coagulation and sedimentation by adding coagulant and deep filtration by membrane separation components" - "posttreatment of disinfection". At the same time, the composition of the coagulant is screened and optimized during the coagulation and sedimentation process, thereby treating steel plant wastewater and achieving excellent wastewater treatment effect.

[0013] The coagulant is obtained by mixing a cross-linked network polymer with an enzyme-modified polysaccharide. The cross-linked network polymer uses acrylic acid to provide carboxylic acid groups, 2-acrylamide-2-methylpropanesulfonic acid to provide sulfonic acid groups, and acryloyloxyethyltrimethylammonium chloride to provide quaternary ammonium groups. An initiator enables the free radical polymerization of monomers to form a zwitterionic copolymer, which is then cross-linked and cured by the addition of a cross-linking agent to obtain the cross-linked network polymer. This cross-linked network polymer can form dynamic ion clusters through alternating positive and negative charges, automatically adjusting the charge distribution in wastewater (e.g., quaternary ammonium groups dominate under acidic conditions, and sulfonic acid groups are exposed under alkaline conditions). The three-dimensional network structure encapsulates flocs, reducing secondary floc formation, preventing secondary breakage, and improving settling speed, achieving excellent treatment effects on pollutants and heavy metals in wastewater. In enzyme-modified polysaccharides, the short-chain polysaccharide fragments produced by chitosan enzymatic hydrolysis expose more hydroxyl groups, forming hydrogen bonds with hydroxyl groups on the colloidal surface; laccase catalyzes the oxidation of phenolic substances on the colloidal surface to generate quinone groups, which crosslink with the amino / carboxyl groups of polysaccharides, forming a covalent-physical complex adsorption; particles (such as iron oxide and humic acid) are captured through hydroxyl / quinone covalent bonds; and enzyme-modified polysaccharides can enhance the removal of metal colloids through biomineralization, further improving the treatment effect on wastewater.

[0014] Preferably, the bar screen treatment step is as follows: wastewater is fed into a mechanical automatic slag removal bar screen, and solid suspended matter, particulate matter and sediment are removed by using a coarse bar screen with a spacing of 50-100mm and a fine bar screen with a spacing of 5-10mm.

[0015] Preferably, based on wastewater volume, the coagulant consists of the following components at the following concentrations: polyaluminum chloride 60-70 mg / L, polyferric sulfate 45-55 mg / L, polyacrylamide 0.4-0.8 mg / L, and coagulant aid 5-8 mg / L.

[0016] In one specific implementation, the coagulant, based on wastewater volume, comprises the following components at concentrations: 65 mg / L polyaluminum chloride, 50 mg / L polyferric sulfate, 0.6 mg / L polyacrylamide, and 7 mg / L coagulant aid.

[0017] Preferably, the preparation method of the cross-linked network structure polymer in the coagulant is as follows: acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and acryloyloxyethyltrimethylammonium chloride are dissolved in water at a molar ratio of 2.5-3.5:3.5-4.5:2.5-3.5, the pH is adjusted to 6.5-7.0, N2 protection is provided, and ammonium persulfate initiator with a concentration of 0.8-1.2 wt% of the reaction system is added at 55-65°C. The reaction is carried out for 5-8 hours to form a zwitterionic copolymer. Then, N,N'-methylenebisacrylamide cross-linking agent with a concentration of 0.3-0.7 wt% of the reaction system is added, and the reaction is continued for 2-4 hours. After freeze-drying, the mixture is ground through a 200-mesh sieve to obtain the cross-linked network structure polymer.

[0018] In one specific embodiment, the preparation method of the cross-linked network structure polymer in the coagulant is as follows: acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and acryloyloxyethyltrimethylammonium chloride are dissolved in water at a molar ratio of 3:4:3, the pH is adjusted to 6.8, N2 protection is applied, and 1 wt% of ammonium persulfate initiator is added at 60°C. The reaction is carried out for 6 hours to form a zwitterionic copolymer. Then, 0.5 wt% of N,N'-methylenebisacrylamide cross-linking agent is added, and the reaction is continued for 3 hours. After freeze-drying, the mixture is ground through a 200-mesh sieve to obtain the cross-linked network structure polymer.

[0019] Preferably, the preparation method of the enzyme-modified chitosan is as follows: chitosan is dissolved in 0.08-0.12 mol / L acetic acid solution at a concentration of 2-4% w / v, and magnetically stirred for 2-4 h. Then, laccase of chitosan at 8-12 U / g and cellulase of chitosan at 3-6 U / g are added, the pH is adjusted to 4-5, and the reaction is carried out at 45-55℃ with shaking for 3-5 h to obtain an enzymatic hydrolysate. 2-3% v / v glutaraldehyde is added to the enzymatic hydrolysate, and crosslinking is carried out at room temperature for 2-4 h. The mixture is then dried to obtain the enzyme-modified chitosan.

[0020] Preferably, the preparation method of the enzyme-modified chitosan is as follows: chitosan is dissolved in 0.08-0.12 mol / L acetic acid solution at a concentration of 2.5-3.5% w / v, and magnetically stirred for 2-4 h. Then, 9-11 U / g laccase and 4-5 U / g cellulase of chitosan are added, the pH is adjusted to 4-5, and the reaction is carried out at 45-55℃ with shaking for 3-5 h to obtain an enzymatic hydrolysate. 2-3% v / v glutaraldehyde is added to the enzymatic hydrolysate, and crosslinking is carried out at room temperature for 2-4 h. The mixture is then dried to obtain the enzyme-modified chitosan.

[0021] In one specific embodiment, the preparation method of the enzyme-modified chitosan is as follows: chitosan is dissolved in 0.1 mol / L acetic acid solution at a concentration of 3% w / v, magnetically stirred for 3 h, 10 U / g chitosan laccase and 4.5 U / g chitosan cellulase are added, the pH is adjusted to 4.5, and the reaction is carried out at 50℃ with shaking for 4 h to obtain an enzymatic hydrolysate; 2.5% v / v glutaraldehyde is added to the enzymatic hydrolysate, crosslinked at room temperature for 3 h, and vacuum dried at 80℃ to obtain enzyme-modified chitosan.

[0022] Preferably, the coagulant is obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 3.5-4.5:1.2-1.8.

[0023] Preferably, the membrane separation module employs tubular ultrafiltration, with a membrane tube inner diameter of 5 mm, a membrane tube length of 3 m, a membrane pore size of 30 nm, and a membrane material of PVDF; the operating pressure is 0.1-0.3 MPa, and the membrane flux is 20-60 L / (m³). 2 h).

[0024] Preferably, the disinfection device process involves: using a wavelength of 254 nm and a dosage of 60-90 mJ / cm². 2 Disinfect with ultraviolet light until the total bacterial count is ≤5 CFU / mL.

[0025] Preferably, the steel plant wastewater treatment method utilizes a wastewater treatment system to treat the wastewater, the wastewater treatment system comprising: a pretreatment unit, a main treatment unit, and a post-treatment unit; the pretreatment unit consists of a bar screen and an equalization tank; the main treatment unit includes a coagulation sedimentation device and a membrane separation component; the post-treatment unit is a disinfection device; each unit is connected sequentially through pipelines to form a continuous treatment process.

[0026] In summary, the technical solution of this application has the following effects:

[0027] The technical solution provided in this application adopts a process route of "pretreatment of wastewater through a screen and equalization tank" - "main treatment of coagulation and sedimentation by adding coagulant and deep filtration by membrane separation components" - "posttreatment of disinfection". At the same time, the composition of the coagulant is screened and optimized during the coagulation and sedimentation process, thereby treating steel plant wastewater and achieving excellent wastewater treatment effect. Detailed Implementation

[0028] The present application will be further described in detail below with reference to embodiments, comparative examples and performance test results. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0029] The wastewater in the examples and comparative examples came from a steel company in Tianjin, with a flow rate of 40 t / h. The measured values ​​were: pH 7.7, suspended solids (SS) 4060 mg / L, COD 4515 mg / L, TDS 4890 mg / L, total nitrogen 178 mg / L, and heavy metal Cr... 6+ The concentration was 48.2 mg / L, Cu 2+ It is 9.3 mg / L, Ni 2+ It is 5.2 mg / L.

[0030] Example

[0031] Example 1

[0032] Example 1 provides a method for treating wastewater from a steel plant.

[0033] The steel plant wastewater treatment system includes: a pretreatment unit, a main treatment unit, and a post-treatment unit; the pretreatment unit consists of a bar screen and an equalization tank; the main treatment unit includes a coagulation sedimentation device, a bioreactor, and a membrane separation assembly; the post-treatment unit is a disinfection device; each unit is connected sequentially through pipelines to form a continuous treatment process.

[0034] The wastewater treatment method for steel plants in the above embodiments is as follows.

[0035] (1) Preprocessing

[0036] (1.1) Bar screen treatment: Wastewater enters the mechanical automatic slag removal bar screen, where solid suspended matter, large particles and sediments (such as iron oxide scale, slag, debris, etc.) entering the pipeline are intercepted by interception plates with different aperture sizes; Among them, the coarse bar screen has a spacing of 50-100mm and is mechanically cleaned to intercept large debris; the fine bar screen has a spacing of 5-10mm and adopts a rotary type to remove smaller particles and prevent them from entering the downstream.

[0037] (1.2) Equalization Tank Treatment: The effluent from the screen enters the equalization tank to balance water quality and quantity fluctuations and reduce the impact on subsequent processes; the hydraulic retention time is 6 hours, and a stirring device is installed in the tank to prevent sedimentation; pH, COD, and conductivity are monitored online, and lime or sulfuric acid is added to stabilize the wastewater pH at 7.5-8.5; the effluent quality is as follows: suspended solids (SS) 2003 mg / L, COD 4326 mg / L, total nitrogen 167 mg / L, and heavy metal Cr... 6+ It is 46.7 mg / L, Cu 2+ It is 9.1 mg / L, Ni 2+ It is 5.1 mg / L.

[0038] (2) Main Processing

[0039] (2.1) Coagulation and sedimentation treatment: Based on the wastewater volume, add coagulant, which consists of the following components at the following concentrations: 65 mg / L polyaluminum chloride, 50 mg / L polyferric sulfate, 0.6 mg / L polyacrylamide, and 7 mg / L coagulant aid (the coagulant aid is obtained by mixing a cross-linked network structure polymer and an enzyme-modified polysaccharide in a weight ratio of 4:1.5).

[0040] Stir at 500 rpm for 25 min, then stir at 100 rpm for 20 min. Let it stand in a sedimentation tank to remove 80-90% of suspended solids and some heavy metals. The wastewater will then proceed to the next stage.

[0041] The specific preparation method of the cross-linked network structure polymer is as follows: acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, and acryloyloxyethyltrimethylammonium chloride are dissolved in water at a molar ratio of 3:4:3 in 10 times their weight of the material system. The pH is adjusted to 6.8, and N2 protection is provided. At 60°C, 1 wt% of the initiator ammonium persulfate is added, and the reaction is carried out for 6 hours to form a zwitterionic copolymer. Then, 0.5 wt% of the cross-linking agent N,N'-methylenebisacrylamide is added, and the reaction is continued for 3 hours. After freeze-drying, the polymer is ground through a 200-mesh sieve to obtain the cross-linked network structure polymer.

[0042] The specific preparation method of enzyme-modified chitosan is as follows: chitosan is dissolved in 0.1 mol / L acetic acid solution at a concentration of 3% w / v, and magnetically stirred for 3 h. Then, 10 U / g chitosan laccase and 4.5 U / g chitosan cellulase are added, the pH is adjusted to 4.5, and the reaction is carried out at 50℃ with shaking for 4 h to obtain the enzymatic hydrolysate. 2.5% v / v glutaraldehyde is added to the enzymatic hydrolysate, crosslinking is carried out at room temperature for 3 h, and the mixture is vacuum dried at 80℃ to obtain enzyme-modified chitosan.

[0043] The effluent quality was as follows: suspended solids (SS) 213 mg / L, COD 1521 mg / L, total nitrogen 145 mg / L, and heavy metal Cr... 6+ It is 3.6 mg / L, Cu 2+ It is 0.83 mg / L, Ni 2+ The concentration was 0.35 mg / L.

[0044] (2.2) Membrane separation module treatment: Tubular ultrafiltration is used, with an inner diameter of 5 mm, a length of 3 m, a pore size of 30 nm, and PVDF as the membrane material; operating pressure is 0.2 MPa, and membrane flux is 40 L / (m³). 2 h).

[0045] The effluent quality was as follows: suspended solids (SS) 9.5 mg / L, COD 223 mg / L, total nitrogen 0.9 mg / L, and heavy metals Cr... 6+ The concentration was 3.5 mg / L, Cu 2+It is 0.79 mg / L, Ni 2+ It is 0.34 mg / L.

[0046] (3) Post-processing

[0047] Disinfection device treatment: using a wavelength of 254nm and a dosage of 75mJ / cm² 2 Disinfect with ultraviolet light until the total bacterial count is ≤5 CFU / mL.

[0048] Examples 2-5

[0049] Examples 2-5 each provide a method for treating wastewater from a steel plant.

[0050] The difference between the above embodiments and Embodiment 1 is that the concentration of the coagulant added is different, as shown below.

[0051] In Example 2: Based on the wastewater volume, a coagulant was added. The coagulant consisted of the following components at the following concentrations: 60 mg / L polyaluminum chloride, 55 mg / L polyferric sulfate, 0.4 mg / L polyacrylamide, and 8 mg / L coagulant aid (the coagulant aid was obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 4:1.5).

[0052] In Example 3: Based on the wastewater volume, a coagulant was added. The coagulant consisted of the following components at the following concentrations: 70 mg / L polyaluminum chloride, 45 mg / L polyferric sulfate, 0.8 mg / L polyacrylamide, and 5 mg / L coagulant aid (the coagulant aid was obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 4:1.5).

[0053] In Example 4: Based on the wastewater volume, a coagulant was added. The coagulant consisted of the following components at the following concentrations: 50 mg / L polyaluminum chloride, 60 mg / L polyferric sulfate, 0.1 mg / L polyacrylamide, and 10 mg / L coagulant aid (the coagulant aid was obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 4:1.5).

[0054] In Example 5: Based on the wastewater volume, a coagulant was added. The coagulant consisted of the following components at the following concentrations: 80 mg / L polyaluminum chloride, 40 mg / L polyferric sulfate, 1 mg / L polyacrylamide, and 3 mg / L coagulant aid (the coagulant aid was obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 4:1.5).

[0055] All other process parameters in the above embodiments are the same as those in Embodiment 1.

[0056] Examples 6-12

[0057] Examples 6-12 provide a method for treating wastewater from a steel plant.

[0058] The difference between the above embodiments and Embodiment 1 is that the preparation methods of the coagulant are different, as shown below.

[0059] In Example 6: The coagulant was obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 3:2.

[0060] In Example 7: The coagulant was obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 5:1.

[0061] In Example 8: the coagulant was obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 3.5:1.8.

[0062] In Example 9: The coagulant was obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 4.5:1.2.

[0063] In Example 10, the preparation method of enzyme-modified chitosan is as follows: chitosan is dissolved in 0.1 mol / L acetic acid solution at a concentration of 3% w / v, and magnetically stirred for 3 h. Then, 10 U / g chitosan laccase and 4.5 U / g chitosan cellulase are added, the pH is adjusted to 4.5, and the reaction is carried out at 50°C with shaking for 4 h to obtain the enzymatic hydrolysate. The enzymatic modified chitosan is obtained by vacuum drying at 80°C.

[0064] In Example 11: The preparation method of enzyme-modified chitosan in the coagulant is as follows: chitosan is dissolved in 0.1 mol / L acetic acid solution at a concentration of 3% w / v, magnetically stirred for 3 h, laccase of chitosan (8 U / g) and cellulase of chitosan (6 U / g) are added, the pH is adjusted to 4.5, and the reaction is carried out at 50°C with shaking for 4 h to obtain an enzymatic hydrolysate; 2.5% v / v glutaraldehyde is added to the enzymatic hydrolysate, crosslinked at room temperature for 3 h, and vacuum dried at 80°C to obtain enzyme-modified chitosan.

[0065] In Example 12: The preparation method of enzyme-modified chitosan in the coagulant is as follows: Chitosan is dissolved in 0.1 mol / L acetic acid solution at a concentration of 3% w / v, and magnetically stirred for 3 h. Laccase of chitosan at 12 U / g and cellulase of chitosan at 3 U / g are added, the pH is adjusted to 4.5, and the reaction is carried out at 50°C with shaking for 4 h to obtain an enzymatic hydrolysate. 2.5% v / v glutaraldehyde is added to the enzymatic hydrolysate, crosslinking is carried out at room temperature for 3 h, and vacuum drying is carried out at 80°C to obtain enzyme-modified chitosan.

[0066] All other process parameters in the above embodiments are the same as those in Embodiment 1.

[0067] Comparative Example

[0068] Comparative Examples 1-5

[0069] Comparative Examples 1-5 each provide a method for treating wastewater from a steel plant.

[0070] The difference between the above comparative examples and Example 1 lies in the composition or preparation method of the coagulant, as detailed below.

[0071] In Comparative Example 1: Based on wastewater volume, a coagulant was added. The coagulant consisted of the following components at the following concentrations: 65 mg / L polyaluminum chloride, 50 mg / L polyferric sulfate, and 0.6 mg / L polyacrylamide (no coagulant aid was added).

[0072] In Comparative Example 2: Based on the wastewater volume, a coagulant was added. The coagulant consisted of the following components at the following concentrations: 50 mg / L polyaluminum chloride, 65 mg / L polyferric sulfate, 0.1 mg / L polyacrylamide, and 1 mg / L coagulant aid.

[0073] In Comparative Example 3: the coagulant was obtained by mixing a cross-linked network polymer and an enzyme-modified polysaccharide in a weight ratio of 1.5:4.

[0074] In Comparative Example 4: The preparation method of the cross-linked network structure polymer in the coagulant is as follows: acrylic acid, sodium methacrylate sulfonate, and acryloyloxyethyltrimethylammonium chloride are dissolved in water at a molar ratio of 3:4:3 in 10 times their weight of the material system. The pH is adjusted to 6.8, and N2 protection is provided. At 60°C, 1 wt% of the initiator ammonium persulfate is added, and the reaction is carried out for 6 hours to form a zwitterionic copolymer. Then, 0.5 wt% of the cross-linking agent N,N'-methylenebisacrylamide is added, and the reaction is continued for 3 hours. After freeze-drying, the polymer is ground through a 200-mesh sieve to obtain the cross-linked network structure polymer.

[0075] In Comparative Example 5: The preparation method of enzyme-modified chitosan in the coagulant is as follows: chitosan is dissolved in 0.1 mol / L acetic acid solution at a concentration of 3% w / v, and magnetically stirred for 3 h. Xylanase of chitosan and glucose oxidase of chitosan are added, the pH is adjusted to 4.5, and the reaction is carried out at 50℃ with shaking for 4 h to obtain the enzymatic hydrolysate. 2.5% v / v glutaraldehyde is added to the enzymatic hydrolysate, crosslinking is carried out at room temperature for 3 h, and vacuum drying is carried out at 80℃ to obtain enzyme-modified chitosan.

[0076] All other process parameters in the above comparative examples are the same as those in Example 1.

[0077] Performance testing

[0078] The wastewater treatment methods in the examples and comparative examples were used to test the quality of the effluent after coagulation and sedimentation treatment.

[0079] Test results are shown in Table 1.

[0080] Table 1. Water quality test results of effluent treated by coagulation and sedimentation in the examples and comparative examples.

[0081]

[0082] As can be seen from the test results in the table above, the technical solution provided in this application adopts a process route of "pretreatment of wastewater through a screen and equalization tank" - "main treatment of coagulation and sedimentation by adding coagulant and deep filtration by membrane separation components" - "posttreatment of disinfection". At the same time, the composition of the coagulant is screened and optimized during the coagulation and sedimentation process, thereby treating steel plant wastewater and achieving excellent wastewater treatment effect.

[0083] No coagulant was added in Comparative Example 1. In Comparative Example 2, the coagulant consisted of 50 mg / L polyaluminum chloride, 65 mg / L polyferric sulfate, 0.1 mg / L polyacrylamide, and 1 mg / L coagulant. In Comparative Example 3, the coagulant was obtained by mixing a cross-linked network polymer with an enzyme-modified polysaccharide in a weight ratio of 1.5:4. In Comparative Example 4, the coagulant was prepared by using acrylic acid, sodium methacrylate sulfonate, and acryloyloxyethyltrimethylammonium chloride in a molar ratio of 3:4:3 with an initiator and a cross-linking agent to obtain a cross-linked network polymer. In Comparative Example 5, the coagulant was obtained by modifying chitosan with xylanase and glucose oxidase to obtain enzyme-modified chitosan, which was then applied to the coagulation and sedimentation process, but the wastewater treatment effect was poor.

[0084] In contrast, this application improves wastewater treatment efficiency by controlling the composition of the coagulant to consist of 50-85 mg / L polyaluminum chloride, 40-60 mg / L polyferric sulfate, 0.2-1 mg / L polyacrylamide, and 3-10 mg / L coagulant aid, and by mixing the cross-linked network polymer with enzyme-modified polysaccharide at a weight ratio of 3-5:1-2.

[0085] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for treating steel mill wastewater, characterized by, Specifically comprising the following steps in sequence: (1) Pretreatment: wastewater is treated in quality in a grid and a regulating tank; (2) Main treatment: a coagulant is added for coagulation and sedimentation; a membrane separation assembly is used for deep filtration; The coagulant consists of the following components at the following concentrations based on the amount of wastewater: 50-85 mg / L of polyaluminum chloride, 40-60 mg / L of polyferric sulfate, 0.2-1 mg / L of polyacrylamide, and 3-10 mg / L of a coagulant aid; The preparation method of the coagulant aid is as follows: acrylic acid, 2-acrylamide-2-methylpropanesulfonic acid, and acryloyloxyethyltrimethylammonium chloride are dissolved in water at a molar ratio of 2.5-3.5:3.5-4.5:2.5-3.5, the pH is adjusted to 6.5-7.0, N2 protection is used, 0.8-1.2 wt% of initiator ammonium persulfate is added to the reaction system at 55-65 ℃, and reaction is carried out for 5-8 h to form a zwitterionic copolymer; then 0.3-0.7 wt% of crosslinking agent N,N'-methylenebisacrylamide is added to the reaction system, and reaction is continued for 2-4 h, followed by freeze-drying and grinding through a 200-mesh screen to obtain a crosslinked network structure polymer; Chitosan is dissolved in an acetic acid solution at a concentration of 2-4% w / v, magnetic stirring is carried out for 2-4 h, 8-12 U / g of chitosan of laccase and 3-6 U / g of chitosan of cellulase are added, the pH is adjusted to 4-5, and oscillation reaction is carried out at 45-55 ℃ for 3-5 h to obtain an enzymatic hydrolysate; 2-3% v / v glutaraldehyde is added to the enzymatic hydrolysate, crosslinking is carried out at room temperature for 2-4 h, and drying is carried out to obtain enzyme-modified chitosan; Then the crosslinked network structure polymer and the enzyme-modified chitosan are mixed at a weight ratio of 3-5:1-2 to obtain the coagulant aid; (3) Post-treatment: disinfection treatment.

2. The steel mill wastewater treatment method according to claim 1, characterized in that, The grid treatment step is as follows: wastewater is fed into a mechanical automatic slag grid, and coarse grids with a spacing of 50-100 mm and fine grids with a spacing of 5-10 mm are used to remove solid suspended matter, particulate matter, and precipitates.

3. The steel mill wastewater treatment method of claim 1, wherein, The coagulant consists of the following components at the following concentrations based on the amount of wastewater: 60-70 mg / L of polyaluminum chloride, 45-55 mg / L of polyferric sulfate, 0.4-0.8 mg / L of polyacrylamide, and 5-8 mg / L of a coagulant aid.

4. The steel mill wastewater treatment method of claim 1, wherein The preparation method of the enzyme-modified chitosan is as follows: chitosan is dissolved in an acetic acid solution at a concentration of 2.5-3.5% w / v, magnetic stirring is carried out for 2-4 h, 9-11 U / g of chitosan of laccase and 4-5 U / g of chitosan of cellulase are added, the pH is adjusted to 4-5, and oscillation reaction is carried out at 45-55 ℃ for 3-5 h to obtain an enzymatic hydrolysate; 2-3% v / v glutaraldehyde is added to the enzymatic hydrolysate, crosslinking is carried out at room temperature for 2-4 h, and drying is carried out to obtain enzyme-modified chitosan.

5. The steel mill wastewater treatment method of claim 1, wherein, The coagulant aid is obtained by mixing the crosslinked network structure polymer and the enzyme-modified chitosan at a weight ratio of 3.5-4.5:1.2-1.

8.

6. The steel mill wastewater treatment method of claim 1, wherein, The membrane separation assembly adopts tubular ultrafiltration in the treatment, the inner diameter of the membrane tube is 5 mm, the length of the membrane tube is 3 m, the membrane pore size is 30 nm, the membrane material is PVDF; the operating pressure is 0.1-0.3 MPa, the membrane flux is 20-60 L / (m 2 h).

7. The steel mill wastewater treatment method of claim 1, wherein, The disinfection treatment step is as follows: ultraviolet light with a wavelength of 254 nm and a dose of 60-90 mJ / cm² is used for disinfection treatment until the total number of bacteria is ≤5 CFU / mL.

8. The steel mill wastewater treatment method according to any one of claims 1 to 7, characterized in that, The steel plant wastewater treatment method utilizes a wastewater treatment system to treat wastewater, and the wastewater treatment system comprises a pretreatment unit, a main treatment unit and a post-treatment unit; the pretreatment unit is composed of a grid and a regulating tank; the main treatment unit comprises a coagulation sedimentation device and a membrane separation assembly; the post-treatment unit is a disinfection device; each unit is sequentially connected through a pipeline to form a continuous treatment process.

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