Coking wastewater zero discharge treatment process

Abstract

This application discloses a zero-discharge treatment process for coking wastewater, comprising the following steps: a. Coagulation pretreatment: coking wastewater is introduced into a coagulation reaction tank, a coagulating precipitant is added and rapidly stirred. The coagulating precipitant includes at least a main flocculant and an adsorbent. The stirring is then slowed, and the mixture is allowed to settle. b. Biological treatment: the coagulated wastewater is transported to a biological treatment system for sequential anaerobic and aerobic reactions. c. Advanced oxidation treatment: the biologically treated wastewater is introduced into an advanced treatment system, where a composite nanocatalyst is added for photo-Fenton advanced oxidation. d. Membrane treatment. e. Sludge and byproduct treatment. This process is highly systematic. The pretreatment process uses a specially formulated coagulating precipitant to efficiently and stably remove high-concentration suspended solids and colloids. Combined with specific advanced oxidation treatment, efficient oxidative decomposition is achieved. Finally, membrane treatment achieves deep purification. The sludge undergoes concentration and dewatering, and the wastewater is recycled, achieving the zero-discharge target.

Description

Technical Field

[0001] This application relates to a zero-discharge treatment process for coking wastewater, belonging to the field of wastewater treatment technology. Background Technology

[0002] Coking wastewater is a complex industrial wastewater generated during coke production. It is characterized by high concentrations of organic matter, color, and toxic substances such as polycyclic aromatic hydrocarbons, phenolic compounds, and ammonia nitrogen. These pollutants not only pose a threat to the environment but also have potential hazards to human health.

[0003] Existing technologies for treating coking wastewater mainly include physical methods such as sedimentation and filtration, primarily used to remove suspended solids and some large organic molecules. Chemical methods, such as coagulation and flocculation, can further remove suspended solids and some dissolved substances. Membrane treatment is also an option. However, the final treatment effect is limited, and there is no systematic process.

[0004] Chinese patent application CN116395876A discloses a zero-discharge pretreatment process for coking wastewater. The process involves adding lime, coagulant aid, and magnesium agent to fully react and clarify the wastewater. The coking wastewater, after passing through an immersion ultrafiltration membrane to remove residual suspended solids and colloids, enters a resin softener to remove residual calcium and magnesium hardness, thus ensuring that the pretreated product water meets the requirements for subsequent membrane concentration feed water. However, the coagulant effect is generally limited, and the flocculation effect is limited in practical applications.

[0005] Chinese patent application CN 104609632 A - A zero-discharge treatment process for coking wastewater discloses activated carbon adsorption and microwave activated carbon adsorption, which are regenerable. The softening crystallizer can remove hardness from the water and eliminate scaling factors, but its efficiency in degrading recalcitrant organic matter and toxic substances in coking wastewater is relatively low. Summary of the Invention

[0006] To address the aforementioned issues, this application proposes a zero-discharge treatment process for coking wastewater. This process is highly systematic. The pretreatment process utilizes a specially formulated coagulation and precipitant to efficiently and stably remove high concentrations of suspended solids and colloids, significantly reducing the load on subsequent biochemical treatment. Simultaneously, combined with specific advanced oxidation treatment, pollutants such as polycyclic aromatic hydrocarbons and phenolic compounds are efficiently oxidized and decomposed under the action of composite nanocatalysts. Finally, membrane treatment achieves deep purification of the coking wastewater, producing high-quality reclaimed water. The sludge undergoes concentration and dewatering treatment, and the wastewater is recycled, achieving the goal of zero discharge.

[0007] According to one aspect of this application, a zero-discharge treatment process for coking wastewater is provided, comprising the following steps:

[0008] a. Coagulation pretreatment: The coking wastewater is introduced into the coagulation reaction tank, a coagulation precipitant is added and rapidly stirred. The coagulation precipitant includes at least the main flocculant and the adsorbent. Then the stirring is slow and the mixture is allowed to settle.

[0009] b. Biochemical treatment: The coking wastewater after coagulation pretreatment is transported to the biochemical treatment system, where it undergoes anaerobic and aerobic reactions in sequence;

[0010] c. Advanced oxidation treatment: The wastewater after biochemical treatment is introduced into an advanced treatment system, and a composite nanocatalyst is added for photo-Fenton advanced oxidation;

[0011] d. Membrane treatment: The wastewater that has undergone deep oxidation treatment is passed through an ultrafiltration system. The wastewater after ultrafiltration enters a reverse osmosis system. The pure water produced is reused, and the reverse osmosis wastewater is returned to the coagulation reaction tank in step a.

[0012] e. Sludge and by-product treatment: Collect the sludge generated during coagulation pretreatment and biochemical treatment, dewater the sludge by pressure filtration, return the filtrate to the coagulation reaction tank in step a, and dispose of the filter cake formed by pressure filtration as solid waste.

[0013] Specifically, in step a, the dosage of the coagulant / precipitant is 200 mg / L, the rapid stirring rate is 300 rpm, and the time is 3 min to ensure that the coagulant and water are fully mixed and to promote the formation of flocs. The slow stirring rate is 50 rpm, and the time is 30 min to promote the growth and sedimentation of flocs and prevent them from breaking down. The settling time is 1 h.

[0014] In step e, sludge dewatering is performed using a filter press with an operating pressure of 3-6 Bar.

[0015] Optionally, the coagulation and precipitating agent in step a includes a primary flocculant, an adsorbent, and a flocculant aid, in a weight ratio of 1:(0.2-0.4):(0.1-0.3).

[0016] Optionally, the main flocculant is polyaluminum chloride and polyaluminum iron oxide in a ratio of 1:(0.1-0.4); the flocculant aid is a polysilicate flocculant.

[0017] Optionally, the adsorbent is a compound modified polyacrylamide, including carboxyl-modified polyacrylamide and sulfonated polyacrylamide, in a weight ratio of 1:(1-1.5).

[0018] Specifically, by using polyaluminum chloride and polyaluminum iron oxide as the main flocculant and limiting the proportion, the polynuclear complexes and hydrophobic aluminum hydroxyl clusters generated by hydrolysis in water can effectively neutralize the surface charge of suspended particles, promote particle aggregation, increase the weight and size of particles, and accelerate their sedimentation. The synergistic effect of the two can enhance the coagulation effect and more effectively remove suspended particles and some organic matter.

[0019] Furthermore, the adsorbent used is a compound modified polyacrylamide (PAM) (carboxyl-modified PAM and sulfonated PAM). By introducing specific functional groups and performing surface modification, the modified PAM can more effectively form chemical bonds or exhibit stronger physical adsorption with specific organic pollutants and heavy metal ions, thereby improving removal efficiency. Simultaneously, mild cross-linking increases the connections between molecular chains, improving the material's stability and durability, and adapting it to complex wastewater treatment environments. Through the polar effect of the carboxyl groups, the adsorption of organic matter, especially polycyclic aromatic hydrocarbons and phenolic compounds, is enhanced. The sulfate groups, through forming strong ionic bonds or chelation, effectively remove heavy metal ions from water, enhance floc stability during coagulation, improve suspended solids removal efficiency, and exhibit stronger adsorption capacity for specific organic pollutants.

[0020] Specifically, using polysilicate flocculants as flocculants can increase the strength and settling velocity of flocs, improve treatment efficiency, and enhance coagulation performance under low temperature or low turbidity conditions. Polysilicate flocculants strengthen the structure of flocs by providing additional bridging, making them more stable and easier to settle, and offering additional opportunities to capture small particles or suspended solids that are difficult to remove.

[0021] Optionally, the preparation method of carboxyl-modified polyacrylamide is as follows: dissolve polyacrylamide in water, add acrylic acid, use potassium persulfate as an initiator, react at 60-70℃ for 2-4 hours, and then purify and dry to obtain the product.

[0022] The preparation method of sulfonated modified polyacrylamide is as follows: dissolve polyacrylamide in water, add 2-acryloyl-2-methylpropanesulfonic acid, use potassium persulfate as an initiator, react at 60-70℃ for 1-3 hours, and then purify and dry to obtain the product.

[0023] Specifically, the preparation of the polyacrylamide solution is as follows: polyacrylamide concentration: 1-3%, solvent: deionized water.

[0024] Acrylic acid dosage: Based on the mass of polyacrylamide, the amount of acrylic acid added is 10-20% of the mass of polyacrylamide. Addition method: Add slowly dropwise to avoid localized over-reaction. Initiator (potassium persulfate) dosage: Based on the mass of acrylic acid, the amount of potassium persulfate added is 1-2% of the mass of acrylic acid. Addition method: Mix thoroughly to ensure complete reaction.

[0025] Purification and drying: Purification method: remove unreacted monomers and byproducts by centrifugation; Drying method: freeze drying to obtain a powdered product.

[0026] Purification centrifugation parameters: centrifugation speed: 6000 rpm, centrifugation time: 30 min.

[0027] Freeze-drying parameters: temperature -20℃, time 5h, maintaining low vacuum pressure 0.3mBar.

[0028] In the preparation method of sulfonated modified polyacrylamide, the amount of 2-acryloyl-2-methylpropanesulfonic acid added is 10% of the mass of polyacrylamide, and the other steps are the same as above.

[0029] Optionally, in step b, an anaerobic reaction is carried out first, with the temperature controlled at 35-37℃, the pH at 6.5-7.5, and the hydraulic retention time at 12-24h.

[0030] Then, an aerobic reaction is carried out, with the temperature controlled at 20-30℃, dissolved oxygen at 2-4 mg / L, pH at 6.8-7.5, and hydraulic retention time at 6-12 hours.

[0031] Optionally, in step b, the aerobic reactor is connected to an aeration system, which can adjust the aeration rate according to the biochemical oxygen demand and chemical oxygen demand of the wastewater.

[0032] Optionally, step c, the advanced treatment system, involves advanced oxidation treatment using a photo-Fenton process in a continuous flow reactor at a pH of 3-4 for a reaction time of 1-2 hours.

[0033] Optionally, the concentration of the composite nanocatalyst in step c is 0.5-1 g / L, including a photocatalyst and a Fenton catalyst, with a weight ratio of (4-6):1;

[0034] The photocatalyst is titanium dioxide nanoparticles, and the Fenton catalyst is iron-based nanoparticles.

[0035] Preferably, the iron-based nanoparticles are Fe2O3 or Fe3O4.

[0036] Specifically, the photo-Fenton process parameters are: pH 3-4, with a suitable acidic environment favoring the Fenton reaction; reaction time 1-2 hours, adjusted in actual production based on wastewater characteristics and pollutant quality.

[0037] Light source: ultraviolet lamp, wavelength 254nm, to stimulate the photocatalytic activity of TiO2.

[0038] Photocatalyst: Titanium dioxide (TiO2) nanoparticles. Particle size: 20-50 nm; smaller particle size helps improve photocatalytic efficiency. Morphology: Isotropic to ensure maximum light exposure area and reaction activity.

[0039] Fenton catalyst: Iron-based nanoparticles, Fe2O3 or Fe3O4. Particle size: 10-30 nm; smaller particle size helps increase the reaction surface area and reaction rate. Concentration: 0.5-1 g / L, adjusted according to the characteristics of the wastewater. Oxidant: Hydrogen peroxide, dosage adjusted according to pollutant concentration, 100-200 mg / L.

[0040] Optionally, in step d, the ultrafiltration system uses a polysulfone or polyimide-based ultrafiltration membrane with a pore size of 0.01-0.1 μm, an operating pressure of 1-3 Bar, and a flow rate of 20-60 L / m. 2 ·h.

[0041] The beneficial effects that this application may produce include, but are not limited to:

[0042] 1. The zero-discharge treatment process for coking wastewater provided in this application employs a specific coagulant-precipitant. Through charge neutralization and adsorption bridging, the coagulant-precipitant aggregates tiny suspended particles into larger flocs, facilitating sedimentation and removal. The combination of the main flocculant and adsorbent enhances treatment efficiency, particularly in the removal of fine suspended particles and certain dissolved organic matter. It rapidly removes a large amount of suspended solids and some macromolecular organic matter, significantly reducing the load on subsequent treatment processes and decreasing the concentration of harmful substances such as heavy metals and certain organic pollutants, thus creating more suitable conditions for subsequent biochemical treatment.

[0043] 2. The zero-discharge treatment process for coking wastewater provided in this application, wherein the two modification methods of adsorbent compound modified polyacrylamide can significantly enhance the performance of PAM in coking wastewater treatment, especially in the targeted removal of recalcitrant organic matter (polycyclic aromatic hydrocarbons and phenolic compounds) and heavy metal ions, providing important support for the overall effect of the coagulation system.

[0044] 3. The zero-discharge treatment process for coking wastewater provided in this application mainly targets recalcitrant organic matter in the anaerobic reaction during biochemical treatment. Through the anaerobic metabolism of microorganisms, these organic matter is converted into intermediate products that are easily degraded by aerobic reactions. The aerobic reaction further degrades these intermediate products, converting them into CO2 and H2O through the metabolic action of microorganisms. By degrading organic matter through microorganisms, the concentration of organic pollutants is significantly reduced, especially for pollutants with good biodegradability. At the same time, the combination of anaerobic and aerobic reactions achieves more comprehensive and efficient degradation of organic matter.

[0045] 4. The coking wastewater zero-discharge treatment process provided in this application involves TiO2 nanoparticles generating highly reactive free radicals under ultraviolet light excitation during the photo-Fenton reaction in the deep oxidation treatment. These free radicals can efficiently attack and destroy the chemical bonds of organic matter, thereby achieving rapid degradation. Iron-based nanoparticles catalyze hydrogen peroxide to generate additional free radicals in the Fenton reaction, further enhancing the oxidation degradation effect. The deep oxidation process significantly improves the effluent quality, providing a cleaner water source for subsequent membrane treatment or reuse.

[0046] 5. The zero-discharge treatment process for coking wastewater provided in this application utilizes ultrafiltration membranes to effectively remove suspended particles and some large organic molecules, serving as a pretreatment step before reverse osmosis and reducing the risk of reverse osmosis membrane fouling. The reverse osmosis membrane effectively removes dissolved salts, small organic molecules, and inorganic substances, producing pure water. This achieves deep purification of coking wastewater, removing fine suspended particles, dissolved substances, and certain heavy metal ions, generating high-quality reclaimed water, reducing wastewater discharge, and achieving the zero-discharge goal.

[0047] 6. The zero-discharge treatment process for coking wastewater provided in this application significantly reduces the volume of sludge after thickening and dewatering, making it easier to transport and dispose of. The filtrate is returned to the coagulation reaction tank, reducing the demand for fresh water and improving the efficiency of water resource utilization. Attached Figure Description

[0048] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0049] Figure 1 This is a schematic diagram of the zero-discharge treatment process for coking wastewater involved in the embodiments of this application; Detailed Implementation

[0050] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods in the art or as per the product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described in this patent are for illustrative purposes only.

[0052] In this application, the polysilicate flocculant, polyaluminum ferric silicate, has a content of 36% and is manufactured by Guangzhou Anbi Chemical Technology Co., Ltd.; the polyaluminum chloride has a content of 28%; and the polyaluminum ferric oxide has an alumina content of 26% and an iron content of 2.5% and is manufactured by Fengxiang Water Treatment Materials Co., Ltd.

[0053] The bacterial strains and equipment used in the biochemical treatment are all commercially available products. Specific dosages and processes can be found in existing technologies or product manuals. Anaerobic treatment bacterial strains: Strain types: Methanogenic archaea (Methanosaeta), sulfur-reducing bacteria (Desulfovibrio). Operating parameters: Temperature range: 35-37℃. pH range: 6.5-7.5. Anaerobic conditions: Ensure an oxygen-free or extremely low oxygen concentration within the reactor.

[0054] Aerobic treatment bacteria: Bacterial type: Nitrifying bacteria (Nitrosomonas, Nitrobacter). Operating parameters: Temperature range: 20-30℃. pH range: 6.8-7.5. Dissolved oxygen (DO): Maintained at 2-4 mg / L. Aerobic reactor aeration system operating parameters: Dissolved oxygen (DO): Maintained at 2-4 mg / L. Aeration rate: Adjusted according to reactor size and wastewater load, 3-5 L / min / m³. 3 Continue to monitor dissolved oxygen levels to ensure they meet the requirements for aerobic reactions, and adjust the aeration rate according to the biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of the wastewater.

[0055] Example 1

[0056] The zero-discharge treatment process for coking wastewater includes the following steps:

[0057] a. Coagulation pretreatment: The coking wastewater is introduced into the coagulation reaction tank, coagulation precipitant is added and the mixture is stirred rapidly, then the stirring is slow and the mixture is allowed to settle.

[0058] b. Biochemical treatment: The coking wastewater after coagulation pretreatment is transported to the biochemical treatment system, where it undergoes anaerobic and aerobic reactions in sequence;

[0059] c. Advanced oxidation treatment: The wastewater after biochemical treatment is introduced into an advanced treatment system, and a composite nanocatalyst is added for photo-Fenton advanced oxidation;

[0060] d. Membrane treatment: The wastewater that has undergone deep oxidation treatment is passed through an ultrafiltration system. The wastewater after ultrafiltration enters a reverse osmosis system. The pure water produced is reused, and the reverse osmosis wastewater is returned to the coagulation reaction tank in step a.

[0061] e. Sludge and by-product treatment: Collect the sludge generated during coagulation pretreatment and biochemical treatment, dewater the sludge by pressure filtration, return the filtrate to the coagulation reaction tank in step a, and dispose of the filter cake formed by pressure filtration as solid waste.

[0062] In step a, the coagulation and precipitating agent includes a main flocculant and an adsorbent in a weight ratio of 1:0.3; the main flocculant is polyaluminum chloride and polyaluminum iron in a ratio of 1:0.2. The adsorbent is a compound modified polyacrylamide, including carboxyl-modified polyacrylamide and sulfonated polyacrylamide in a weight ratio of 1:1.2. The preparation method of carboxyl-modified polyacrylamide is as follows: dissolve polyacrylamide in water, add acrylic acid, use potassium persulfate as an initiator, react at 65°C for 3 hours, and then purify and dry to obtain the product; the preparation method of sulfonated polyacrylamide is as follows: dissolve polyacrylamide in water, add 2-acryloyl-2-methylpropanesulfonic acid, use potassium persulfate as an initiator, react at 65°C for 2 hours, and then purify and dry to obtain the product.

[0063] In step b, an anaerobic reaction is first carried out, with the temperature controlled at 36℃, pH at 7, and hydraulic retention time at 16h; then an aerobic reaction is carried out, with the temperature controlled at 25℃, dissolved oxygen at 3mg / L, pH at 7, and hydraulic retention time at 10h. In step b, the aerobic reactor is connected to an aeration system, which can adjust the aeration rate according to the biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of the wastewater.

[0064] Step c, the advanced treatment system, involves a photo-Fenton process in a continuous flow reactor for advanced oxidation treatment at pH 3 for 1 hour. The concentration of the composite nanocatalyst in step c is 1 g / L, comprising a photocatalyst and a Fenton catalyst in a weight ratio of 5:1. The photocatalyst is titanium dioxide nanoparticles, and the Fenton catalyst is iron-based nanoparticles. The iron-based nanoparticles are Fe₂O₃.

[0065] In step d, the ultrafiltration system uses a polysulfone or polyimide-based ultrafiltration membrane with a pore size of 0.05 μm, an operating pressure of 2 Bar, and a flow rate of 40 L / m³. 2 ·h.

[0066] In step e, sludge dewatering is performed using a filter press with an operating pressure of 5 Bar.

[0067] Example 2

[0068] The difference between Example 2 and Example 1 is that:

[0069] In step a, the coagulation and precipitating agent includes a primary flocculant, an adsorbent, and a flocculant aid, with a weight ratio of 1:0.2:0.1. The primary flocculant is polyaluminum chloride and polyaluminum iron, with a ratio of 1:0.1; the flocculant aid is a polysilicate flocculant. The adsorbent is a compound modified polyacrylamide, including carboxyl-modified polyacrylamide and sulfonated polyacrylamide, with a weight ratio of 1:1. The preparation method of carboxyl-modified polyacrylamide is as follows: dissolve polyacrylamide in water, add acrylic acid, use potassium persulfate as an initiator, react at 70°C for 2 hours, and then purify and dry to obtain the product. The preparation method of sulfonated modified polyacrylamide is as follows: dissolve polyacrylamide in water, add 2-acryloyl-2-methylpropanesulfonic acid, use potassium persulfate as an initiator, react at 70°C for 1 hour, and then purify and dry to obtain the product.

[0070] In step b, an anaerobic reaction is first carried out, with the temperature controlled at 35℃, pH at 6.5, and hydraulic retention time at 12h; then an aerobic reaction is carried out, with the temperature controlled at 20℃, dissolved oxygen at 4mg / L, pH at 6.8, and hydraulic retention time at 6h. In step b, the aerobic reactor is connected to an aeration system, which can adjust the aeration rate according to the biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of the wastewater.

[0071] Step c, the advanced treatment system, involves a photo-Fenton process in a continuous flow reactor for advanced oxidation treatment at pH 4 for 2 hours. The concentration of the composite nanocatalyst in step c is 1 g / L, comprising a photocatalyst and a Fenton catalyst in a weight ratio of 4:1. The photocatalyst is titanium dioxide nanoparticles, and the Fenton catalyst is iron-based nanoparticles. The iron-based nanoparticles are Fe3O4.

[0072] In step d, the ultrafiltration system uses a polysulfone or polyimide-based ultrafiltration membrane with a pore size of 0.1 μm, an operating pressure of 3 Bar, and a flow rate of 60 L / m³. 2 ·h.

[0073] In step e, sludge dewatering is performed using a filter press with an operating pressure of 5 Bar.

[0074] Example 3

[0075] The difference between Example 3 and Example 1 is that:

[0076] In step a, the coagulation and precipitating agent includes a primary flocculant, an adsorbent, and a flocculant aid, with a weight ratio of 1:0.4:0.3. The primary flocculant is polyaluminum chloride and polyaluminum iron oxide, with a ratio of 1:0.4; the flocculant aid is a polysilicate flocculant. The adsorbent is a compound modified polyacrylamide, including carboxyl-modified polyacrylamide and sulfonated polyacrylamide, with a weight ratio of 1:1.5. The preparation method of carboxyl-modified polyacrylamide is as follows: dissolve polyacrylamide in water, add acrylic acid, use potassium persulfate as an initiator, react at 60°C for 4 hours, and then purify and dry to obtain the product. The preparation method of sulfonated polyacrylamide is as follows: dissolve polyacrylamide in water, add 2-acryloyl-2-methylpropanesulfonic acid, use potassium persulfate as an initiator, react at 60°C for 3 hours, and then purify and dry to obtain the product.

[0077] In step b, an anaerobic reaction is first carried out, with the temperature controlled at 37℃, pH at 7.5, and hydraulic retention time at 24 h; then an aerobic reaction is carried out, with the temperature controlled at 28℃, dissolved oxygen at 4 mg / L, pH at 7.3, and hydraulic retention time at 10 h. In step b, the aerobic reactor is connected to an aeration system, which can adjust the aeration rate according to the biochemical oxygen demand (BOD) and chemical oxygen demand (COD) of the wastewater.

[0078] Step c, the advanced treatment system, involves a photo-Fenton process in a continuous flow reactor for advanced oxidation treatment at pH 4 for 2 hours. The concentration of the composite nanocatalyst in step c is 1 g / L, comprising a photocatalyst and a Fenton catalyst in a weight ratio of 6:1. The photocatalyst is titanium dioxide nanoparticles, and the Fenton catalyst is iron-based nanoparticles. The iron-based nanoparticles are Fe₂O₃.

[0079] In step d, the ultrafiltration system uses a polysulfone or polyimide-based ultrafiltration membrane with a pore size of 0.01 μm, an operating pressure of 2 Bar, and a flow rate of 20 L / m³. 2 ·h.

[0080] In step e, sludge dewatering is performed using a filter press with an operating pressure of 5 Bar.

[0081] Comparative Example 1

[0082] The difference between Comparative Example 1 and Example 3 is that the pretreatment in Comparative Example 1 uses an activated carbon adsorption tower, which is a technology in the prior art.

[0083] Comparative Example 2

[0084] The difference between Comparative Example 2 and Example 3 is that no adsorbent is used in Comparative Example 2.

[0085] Comparative Example 3

[0086] The difference between Comparative Example 3 and Example 3 is that the adsorbent in Comparative Example 3 is unmodified polyacrylamide.

[0087] Comparative Example 4

[0088] The difference between Comparative Example 4 and Example 3 is that the deep oxidation treatment in Comparative Example 4 uses a single light treatment instead of Fenton treatment.

[0089] Experimental Example

[0090] Coking wastewater treatment tests were conducted according to the processes of Examples 1-3 and Comparative Examples 1-4, respectively.

[0091] 1. Test items:

[0092] COD removal rate: Chemical oxygen demand (COD) is an important indicator for measuring the concentration of organic matter in water.

[0093] BOD removal rate: Biochemical oxygen demand (BOD) reflects the amount of biodegradable organic matter in water.

[0094] Suspended solids removal rate: Evaluates the removal efficiency of suspended particulate matter in water.

[0095] Total nitrogen and total phosphorus removal rates: These measures the efficiency of removing nutrients such as nitrogen and phosphorus.

[0096] Heavy metal removal rate: Evaluation of the removal effect of heavy metals in water.

[0097] 2. Experimental Methods:

[0098] COD / BOD: The determination was carried out in accordance with GB 11914-89 "Determination of Chemical Oxygen Demand in Water".

[0099] Suspended solids: determined according to GB 11901-89.

[0100] Total nitrogen / total phosphorus: determined by spectroscopic methods. Heavy metals: determined by atomic absorption spectrometry.

[0101] 3. The original water quality parameters of the coking wastewater are shown in Table 1, and the experimental results are shown in Tables 2 and 3.

[0102] Table 1. Original water quality of coking wastewater

[0103] parameter Original water quality (mg / L) COD 800 suspended matter 200 Total nitrogen 80 Total phosphorus 10 Heavy metals (as Pb) 5

[0104] Table 2 Water quality data for Examples 1-3 and Comparative Examples 1-4

[0105]

[0106] Table 3 shows the removal rates of various items in Examples 1-3 and Comparative Examples 1-4.

[0107]

[0108] As can be seen from the above, the zero-discharge treatment process for coking wastewater defined in this application can control the COD of the treated coking wastewater to below 50 mg / L and the total nitrogen removal rate to above 88%. It has a significant effect on removing organic pollutants from water and is also excellent in reducing heavy metal pollution in water, thus achieving deep purification of coking wastewater.

[0109] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0110] The above description is merely an embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A coking wastewater zero liquid discharge treatment process characterized by, Includes the following steps: a. Coagulation pretreatment: The coking wastewater is introduced into the coagulation reaction tank, coagulation precipitant is added and the mixture is stirred rapidly, then the stirring is slow and the mixture is allowed to settle. The coagulation and precipitating agent comprises a primary flocculant, an adsorbent, and a flocculant aid, in a weight ratio of 1:(0.2-0.4):(0.1-0.3); the primary flocculant is polyaluminum chloride and polyaluminum iron oxide in a ratio of 1:(0.1-0.4); the flocculant aid is a polysilicate flocculant; and the adsorbent is a compound modified polyacrylamide, including carboxyl-modified polyacrylamide and sulfonated polyacrylamide, in a weight ratio of 1:(1-1.5). The preparation method of carboxyl-modified polyacrylamide is as follows: dissolve polyacrylamide in water, add acrylic acid, use potassium persulfate as an initiator, react at 60-70℃ for 2-4 hours, and then purify and dry to obtain the product; The preparation method of sulfonated modified polyacrylamide is as follows: dissolve polyacrylamide in water, add 2-acryloyl-2-methylpropanesulfonic acid, use potassium persulfate as an initiator, react at 60-70℃ for 1-3 hours, and then purify and dry to obtain the product; b. Biochemical treatment: The coking wastewater after coagulation pretreatment is transported to the biochemical treatment system, where anaerobic and aerobic reactions are carried out sequentially; among them, the anaerobic reaction is carried out first, with the temperature controlled at 35-37℃, the pH at 6.5-7.5, and the hydraulic retention time at 12-24h. c. Advanced oxidation treatment: The wastewater after biochemical treatment is introduced into an advanced treatment system, and a composite nanocatalyst is added for photo-Fenton advanced oxidation; The concentration of the composite nanocatalyst is 0.5-1 g / L, including photocatalyst and Fenton catalyst, with a weight ratio of (4-6):1; The photocatalyst is titanium dioxide nanoparticles with a particle size of 20-50 nm; the Fenton catalyst is iron-based nanoparticles with a particle size of 10-30 nm. d. Membrane treatment: The wastewater that has undergone deep oxidation treatment is passed through an ultrafiltration system. The wastewater after ultrafiltration enters a reverse osmosis system. The pure water produced is reused, and the reverse osmosis wastewater is returned to the coagulation reaction tank in step a. e. Sludge and by-product treatment: Collect the sludge generated during coagulation pretreatment and biochemical treatment, dewater the sludge by pressure filtration, return the filtrate to the coagulation reaction tank in step a, and dispose of the filter cake formed by pressure filtration as solid waste.

2. The zero-discharge treatment process for coking wastewater according to claim 1, characterized in that, In step b, the aerobic reaction temperature is controlled at 20-30℃, dissolved oxygen at 2-4 mg / L, pH at 6.8-7.5, and hydraulic retention time at 6-12h.

3. The zero-discharge treatment process for coking wastewater according to claim 2, characterized in that, In step b, the aerobic reactor is connected to the aeration system, which can adjust the aeration rate according to the biochemical oxygen demand and chemical oxygen demand of the wastewater.

4. The zero-discharge treatment process for coking wastewater according to claim 1, characterized in that, Step c, the advanced treatment system, involves advanced oxidation treatment using a photo-Fenton process in a continuous flow reactor at a pH of 3-4 for a reaction time of 1-2 hours.

5. The zero-discharge treatment process for coking wastewater according to claim 1, characterized in that, The iron-based nanoparticles are Fe2O3 or Fe3O4.

6. The zero-discharge treatment process for coking wastewater according to claim 1, characterized in that, In step d, the ultrafiltration system uses a polysulfone or polyimide-based ultrafiltration membrane with a pore size of 0.01-0.1 μm, an operating pressure of 1-3 Bar, and a flow rate of 20-60 L / m²·h.

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