Method and system for treating waste liquid absorbed by lithium iron phosphate production kiln tail gas

Abstract

The application provides a treatment method and system for waste liquid of lithium iron phosphate production kiln tail gas absorption, and belongs to the wastewater treatment field. In the application, the waste liquid is flocculated and precipitated, the waste liquid is filtered by using a filter cake layer made of biochemical sludge and lime, anaerobic treatment and aerobic treatment are performed after adjusting the pH value of the filtrate, and the clear liquid meeting the discharge standard is obtained through solid-liquid separation, and the biochemical sludge can be recycled. After the waste liquid is filtered through the filter cake layer, the COD is greatly reduced, the water quality becomes colorless and transparent, there is no foul odor, and the biodegradability is significantly improved. The application greatly shortens the waste liquid treatment process, saves energy consumption and reagents, significantly reduces the biochemical system treatment load, ensures the stable operation of the biochemical system and the discharge of waste liquid meeting the standard, is good in economy, and is conducive to environmental protection.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a method and system for treating waste liquid absorbed by the tail gas of lithium iron phosphate production kilns. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage markets, the demand for lithium iron phosphate batteries continues to grow. During the production process, the amount of waste liquid emitted from the tail gas absorption of lithium iron phosphate production kilns has increased significantly. This waste liquid is characterized by high organic content, high color, high suspended solids, foul odor, difficulty in degradation, and biotoxicity, which seriously affects the environment and organisms.

[0003] Existing wastewater treatment technologies mainly include physical, chemical, and biological methods. These methods have the following shortcomings when treating wastewater: 1. Physical methods, such as flocculation, sedimentation, and filtration, have limited treatment effects and are difficult to remove organic matter and biotoxic substances from wastewater; 2. Chemical methods, such as advanced oxidation, neutralization, and adsorption, have long treatment processes, high energy consumption, large amounts of reagents, and high treatment costs; 3. Biological methods, such as activated sludge and biofilm methods, are not effective in treating high-concentration organic wastewater and are difficult to degrade biotoxic substances.

[0004] In view of this, it is necessary to design a method and system for treating waste liquid absorbed by the tail gas of lithium iron phosphate production kiln in order to solve the above problems. Summary of the Invention

[0005] In view of the technical problems existing in the background art, this application provides a method and system for treating waste liquid absorbed by the tail gas of lithium iron phosphate production kiln, aiming to solve the technical problems of long treatment process, poor treatment effect, high load of biochemical system, unstable biochemical effluent and high operating cost of traditional kiln tail gas absorption waste liquid treatment.

[0006] In a first aspect, embodiments of this application provide a method for treating waste liquid absorbed by the tail gas of a lithium iron phosphate production kiln, comprising the following steps:

[0007] S1. Collect the waste liquid absorbed by the kiln tail gas, add flocculant, stir and mix to obtain pretreated wastewater and flocculated precipitate;

[0008] S2. Add lime and flocculant to the biochemical sludge, and obtain a first filter cake layer after pressure filtration. Add the flocculated precipitate obtained in step S1 above the first filter cake layer, and obtain a second filter cake layer above the first filter cake layer after pressure filtration.

[0009] S3. Using the first filter cake layer and the second filter cake layer as filter media, the pretreated wastewater obtained in step S1 is subjected to pressure filtration to obtain filtrate;

[0010] S4. Add a pH adjuster to the filtrate obtained in step S3 to adjust the pH value to a predetermined range, and then perform anaerobic treatment and aerobic treatment in sequence.

[0011] S5. The mixed liquid after aerobic treatment in step S4 is subjected to solid-liquid separation. The clear liquid is discharged, and the biochemical sludge is returned to step S2 for reuse.

[0012] In the technical solution of this application embodiment, by adding flocculants to pretreat the tail gas absorption wastewater, suspended solids and some organic matter in the wastewater can be effectively aggregated and removed, improving the efficiency of subsequent treatment. Using biochemical sludge and lime to prepare a filter cake layer not only treats the biochemical sludge but also transforms it into a useful filter medium, achieving resource utilization. Pressure filtration further purifies the pretreated wastewater, resulting in filtrate with lower pollutant content, which is beneficial for subsequent biochemical treatment. After pH adjustment, the filtrate undergoes anaerobic and aerobic treatment, effectively degrading organic pollutants in the wastewater and reducing COD (chemical oxygen demand) and BOD (biochemical oxygen demand). Solid-liquid separation yields a clear liquid that meets emission standards, reducing environmental impact. The aerobic-treated biochemical sludge is returned to step S2 for reuse, forming a closed treatment cycle, reducing treatment costs and improving the operating efficiency of the treatment system.

[0013] This application features a short water treatment process with high efficiency; the use of biochemical sludge cake filter media provides excellent filtration, effectively adsorbing organic matter with a high organic removal rate and low equipment load; the system has low energy consumption, low reagent consumption, and low overall operating costs; and low sludge production and low solid waste treatment costs.

[0014] In some embodiments, in step S1, the flocculant includes an inorganic polymeric flocculant and a polyacrylamide coagulant aid. The inorganic polymeric flocculant is one or more of polyaluminum ferric silicate, polyaluminum ferric chloride, polyaluminum chloride, and polyferric sulfate, and the dosage is 400-1000 ppm; and / or, the polyacrylamide coagulant aid is one or more of anionic polyacrylamide, cationic polyacrylamide, and nonionic polyacrylamide, and the dosage is 5-20 ppm; and / or, the stirring time is 10-20 min.

[0015] In this embodiment, the inorganic polymeric flocculant has strong charge neutralization and adsorption bridging effects, effectively aggregating suspended particles and colloidal substances in wastewater to form flocs. The preferred dosage of the inorganic polymeric flocculant is 400–1000 ppm, within which settling performance is optimal. Increasing the dosage decreases settling performance and produces excessive sludge; decreasing the dosage further reduces settling performance, or even prevents sedimentation altogether. The polyacrylamide coagulant further enhances the flocculation effect. Through flocculation, fine particles aggregate into larger flocs, significantly increasing their settling velocity and facilitating subsequent solid-liquid separation.

[0016] In some embodiments, in step S2, the amount of lime used is 0.5-2%; and / or, the flocculant is one or more of anionic polyacrylamide, cationic polyacrylamide and nonionic polyacrylamide, and the amount used is 5-20 ppm.

[0017] In this embodiment, lime, as a skeleton material, increases the mechanical strength of the filter cake, making it less prone to breakage during pressure filtration, thereby improving filtration performance and reducing solid particles in the filtrate. An appropriate amount of flocculant helps fine particles in the sludge aggregate into larger flocs, increasing sludge modification and settling velocity.

[0018] In some embodiments, in step S4, the pH adjuster is sodium hydroxide, and the predetermined pH range is 7-8. The anaerobic sludge concentration is 2-4 g / L, and the retention time is 8-24 h. The aerobic sludge concentration is 2-4 g / L, the dissolved oxygen is 2-4 mg / L, and the retention time is 40-120 h.

[0019] In this embodiment, by adjusting the pH value to a predetermined range of 7-8, a suitable growth environment is provided for anaerobic and aerobic microorganisms, thereby improving the efficiency of biological treatment. The biological treatment parameters can maintain the activity of the sludge and enhance its ability to treat pollutants. By precisely controlling the parameters of the biological treatment, the stability of the effluent quality can be ensured, water quality fluctuations can be reduced, and discharge standards can be met. At the same time, suitable sludge concentration and retention time can improve the biological system's resistance to wastewater load fluctuations and maintain stable system operation.

[0020] In some embodiments, in step S5, the COD of the clarified liquid is less than 500 mg / L.

[0021] In this embodiment, the treated wastewater can meet the discharge standards.

[0022] Secondly, embodiments of this application provide a treatment system for waste liquid absorbed by tail gas from lithium iron phosphate production kilns. The system uses the treatment method for waste liquid absorbed by tail gas from lithium iron phosphate production kilns described in the first aspect to treat the waste liquid absorbed by tail gas from lithium iron phosphate production kilns. The system includes a wastewater pretreatment device, a filtration device, a biochemical treatment device, a solid-liquid separation device, and a sludge treatment device connected in sequence.

[0023] In the technical solution of this application embodiment, the tail gas absorption waste liquid generated during the lithium iron phosphate production process is efficiently treated through the synergistic effect of each processing unit, ensuring that the waste liquid meets environmental emission standards. Waste generation is reduced and resource utilization is optimized through the recycling of sludge. This system is easy to operate, has low maintenance costs, and exhibits good economic efficiency and reliability.

[0024] In some embodiments, the biochemical treatment apparatus includes a neutralization tank, an anaerobic reactor, and an aerobic reactor connected in sequence, with the outlet of the aerobic reactor connected to the inlet of the solid-liquid separation apparatus.

[0025] In this embodiment, continuous treatment of wastewater is achieved by sequentially connecting a neutralization tank, an anaerobic reactor, and an aerobic reactor, thereby improving treatment efficiency. The combination of anaerobic and aerobic treatment more effectively decomposes organic matter in the wastewater, increasing COD removal rate. Subsequent solid-liquid separation ensures that the discharged clarified liquid meets environmental standards, reducing environmental impact.

[0026] In some embodiments, the filtration device includes a pressing device and a first filter cake layer and a second filter cake layer disposed inside the pressing device.

[0027] In this embodiment, the combination of the compression device and two filter cake layers creates a highly efficient filtration interface, improving the removal rate of pollutants. The design of the compression device simplifies the replacement and maintenance of the filter media.

[0028] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0030] Figure 1 A schematic diagram of the process for treating waste liquid absorbed by the tail gas of a lithium iron phosphate production kiln provided in this application embodiment;

[0031] Figure 2 A schematic diagram of the filtration device structure of the treatment system for the absorption of waste liquid from the tail gas of a lithium iron phosphate production kiln provided in this application embodiment.

[0032] Explanation of reference numerals in the attached drawings: 1. Compressing device; 2. First filter cake layer; 3. Second filter cake layer; 4. Pre-treated wastewater inlet; 5. Filtrate outlet. Detailed Implementation

[0033] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0035] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0036] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0037] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0038] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0039] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0040] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0041] The wastewater from the tail gas absorption of lithium iron phosphate production kilns is characterized by high organic content, high color, high suspended solids, malodor, recalcitrant degradation, and biotoxicity, causing serious impacts on the environment and organisms. Existing wastewater treatment technologies mainly include physical, chemical, and biological methods. These methods have the following shortcomings: 1. Physical methods, such as flocculation, sedimentation, and filtration, have limited treatment effects and are difficult to remove organic matter and biotoxic substances from the wastewater; 2. Chemical methods, such as advanced oxidation, neutralization, and adsorption, have long processing flows, high energy consumption, large reagent usage, and high treatment costs; 3. Biological methods, such as activated sludge and biofilm methods, are ineffective in treating high-concentration organic wastewater and are difficult to degrade biotoxic substances.

[0042] To address the technical problems of traditional kiln tail gas absorption wastewater treatment processes, such as long processing times, poor treatment efficiency, high load on the biological system, unstable effluent, and high operating costs, this application provides a method and system for treating wastewater from lithium iron phosphate production kilns. The method involves flocculating and settling the wastewater, using a filter cake layer made of biological sludge and lime for filtration, adjusting the pH of the filtrate, and then subjecting it to anaerobic and aerobic treatment. After solid-liquid separation, a clear liquid meeting emission standards is obtained, and the biological sludge can be recycled. This application enhances filtration efficiency, improves biological treatment conditions, achieves resource recycling, reduces treatment costs, minimizes environmental impact, and improves system stability and reliability. It is economical, environmentally friendly, and conducive to clean production and sustainable development.

[0043] Please refer to Figure 1 In a first aspect, embodiments of this application provide a method for treating waste liquid absorbed by the tail gas of a lithium iron phosphate production kiln, comprising the following steps:

[0044] S1. Collect the waste liquid absorbed by the kiln tail gas, add flocculant, stir and mix to obtain pretreated wastewater and flocculated precipitate;

[0045] S2. Add lime and flocculant to the biochemical sludge, and obtain the first filter cake layer after pressure filtration. Add the flocculated precipitate obtained in step S1 above the first filter cake layer, and obtain the second filter cake layer above the first filter cake layer after pressure filtration.

[0046] S3. Using the first and second filter cake layers as filter media, the pretreated wastewater obtained in step S1 is subjected to pressure filtration to obtain filtrate.

[0047] S4. Add a pH adjuster to the filtrate obtained in step S3 to adjust the pH value to a predetermined range, and then perform anaerobic treatment and aerobic treatment in sequence.

[0048] S5. The mixed liquid after aerobic treatment in step S4 is subjected to solid-liquid separation. The clear liquid is discharged, and the biochemical sludge is returned to step S2 for reuse.

[0049] In this embodiment, after adding flocculant to the waste liquid, the suspended solids, colloids, and some organic matter in the waste liquid are captured by the flocculant and form flocs, which settle to the bottom of the container to form flocculated precipitate, while the upper layer is relatively clear pretreated wastewater. Lime can increase the pH value of the sludge, promote the flocculation of organic matter in the sludge, and at the same time, lime, as a skeleton material, can increase the mechanical strength of the filter cake, making it less prone to breakage during the pressure filtration process, thereby improving filtration performance. After adding flocculant, the fine particles in the sludge aggregate into larger flocs, and through pressure filtration in a pressing device, water is squeezed out to form a first filter cake layer. The pressing device can be a plate and frame filter or other solid-liquid separation equipment. The flocculated precipitate is added above the first filter cake layer and pressure filtration is performed again to form a second filter cake layer. Using the first and second filter cake layers as filter media, when the pretreated wastewater passes through the filter media, the suspended solids and flocs are intercepted, thereby obtaining a clear filtrate. pH is a crucial factor affecting microbial activity. By adding a pH adjuster, the pH of the filtrate is adjusted to a suitable range for microbial growth. Anaerobic treatment, under anaerobic conditions, utilizes anaerobic microorganisms to decompose complex organic matter into simpler organic matter. Aerobic treatment, under aerobic conditions, utilizes aerobic microorganisms to further decompose organic matter, converting it into carbon dioxide and water. Simultaneously, pollutants in the waste liquid are removed through microbial metabolism. The mixed liquor after aerobic treatment contains a large amount of microbial flocs (biological sludge) and treated water (clarified liquid). Through solid-liquid separation, the clarified liquid can meet discharge standards, while the biological sludge is returned to step S2, mixed with newly added lime and flocculant, and subjected to further filtration and utilization, achieving the resource recycling of sludge.

[0050] Further, in some embodiments, in step S1, the flocculant includes an inorganic polymeric flocculant and a polyacrylamide coagulant aid. The inorganic polymeric flocculant is one or more of polyaluminum ferric silicate, polyaluminum ferric chloride, polyaluminum chloride, and polyferric sulfate, and the dosage is 400-1000 ppm; and / or, the polyacrylamide coagulant aid is one or more of anionic polyacrylamide, cationic polyacrylamide, and nonionic polyacrylamide, and the dosage is 5-20 ppm; and / or, the stirring time is 10-20 min.

[0051] In the technical solution of this application embodiment, the flocculant is preferably polyaluminum ferric silicate, and the coagulant aid is preferably anionic polyacrylamide. These methods offer the best flocculation effect, minimize reagent consumption, and eliminate the need to adjust the pH value of the wastewater from the kiln exhaust gas, thus reducing the reagents used for pH adjustment. The resulting flocs are larger, have better settling properties, and produce a clear and transparent supernatant. This process significantly reduces suspended solids in the wastewater.

[0052] Furthermore, in some embodiments, in step S2, the amount of lime used is 0.5-2%; and / or, the flocculant is one or more of anionic polyacrylamide, cationic polyacrylamide and nonionic polyacrylamide, and the amount used is 5-20 ppm.

[0053] In the technical solution of this application embodiment, lime and polyacrylamide (any of cationic, anionic, or nonionic) are used to condition the biological sludge to obtain sludge with good filter press performance. Simultaneously, a pressing device is used to press the conditioned sludge, forming a first filter cake layer with relatively large pores on the pressing device. The first filter cake layer accounts for 1 / 2 to 2 / 3 of the total filter cake layer thickness. The specific feeding time and pressing operation are determined based on actual experiments, or theoretical values ​​can be calculated based on sludge concentration detection, and fine adjustments can be made during specific implementation.

[0054] The flocculated precipitate obtained in step S1 is fed into a compaction device for filtration, forming a dense second filter cake layer above the first filter cake layer. The second filter cake layer is mainly composed of a viscous substance formed from polyaluminum ferric silicate and polyacrylamide, exhibiting strong adsorption capacity and effectively intercepting impurities in the wastewater. The second filter cake layer occupies 1 / 3 to 1 / 2 of the total filter cake layer thickness. The specific feeding time and compaction operation are determined based on actual experiments, or theoretical values ​​can be calculated based on sludge concentration detection and fine-tuned during implementation. The first filter cake layer acts as a supporting bridge for the second filter cake layer, improving the overall permeability of the filter cake layer.

[0055] The pretreated wastewater obtained in step S1 is fed into a pressing device for filtration. At this time, the clarified liquid needs to pass through the second filter cake layer and the first filter cake layer in sequence. The second filter cake layer ensures efficient interception of organic components in the clarified liquid, while the first filter cake layer ensures filtration performance, avoids clogging of the filter cloth, and increases the dirt-holding capacity of the entire filter cake layer.

[0056] After the above steps, the COD concentration of the exhaust gas absorption wastewater is significantly reduced, harmful substances are almost completely intercepted, and biodegradability is greatly improved. Subsequent treatment using a combined anaerobic (hydrolysis acidification) and aerobic biological system can stably meet the standards. Traditional treatment methods require the addition of a high-quality carbon source to condition the wastewater, and a certain proportion of carbon source needs to be added, resulting in high organic concentration and high load on the biological system.

[0057] Furthermore, in some embodiments, in step S4, the pH adjuster is sodium hydroxide, and the predetermined pH range is 7–8. The anaerobic sludge concentration is 2–4 g / L, and the retention time is 8–24 h. The aerobic sludge concentration is 2–4 g / L, the dissolved oxygen is 2–4 mg / L, and the retention time is 40–120 h.

[0058] In the technical solution of this application embodiment, the pH value of the wastewater is adjusted to a predetermined range to provide a suitable environment and ensure the smooth progress of the subsequent biological treatment process. A pH value that is too high or too low will affect the activity of microorganisms. Anaerobic treatment is a process in which anaerobic microorganisms convert organic matter in wastewater into methane and carbon dioxide under oxygen-free conditions. The sludge concentration ensures sufficient microorganisms to participate in the decomposition of organic matter, and the retention time ensures that the organic matter is fully decomposed by microorganisms, degrading organic pollutants in the wastewater and reducing COD and BOD. Aerobic treatment utilizes aerobic microorganisms to decompose organic matter in wastewater under aerobic conditions. The sludge concentration ensures sufficient microorganisms for biodegradation, the dissolved oxygen concentration is to maintain the activity of microorganisms, as aerobic microorganisms require oxygen for metabolism, and the retention time ensures that the organic matter in the wastewater is fully decomposed. Aerobic treatment further degrades organic pollutants, reducing the COD and BOD of the wastewater. Through the metabolic activities of microorganisms, organic matter is converted into harmless carbon dioxide and water.

[0059] The mixed liquid after aerobic treatment was subjected to solid-liquid separation, and the resulting clear liquid had a COD of less than 500 mg / L, which met the emission standards.

[0060] Secondly, embodiments of this application provide a treatment system for waste liquid absorbed by tail gas from lithium iron phosphate production kilns. The system uses the treatment method for waste liquid absorbed by tail gas from lithium iron phosphate production kilns described in the first aspect to treat the waste liquid absorbed by tail gas from lithium iron phosphate production kilns. The system includes a wastewater pretreatment device, a filtration device, a biochemical treatment device, a solid-liquid separation device, and a sludge treatment device connected in sequence.

[0061] Among them, by combining physical, chemical and biological methods, the waste liquid absorbed by the tail gas of lithium iron phosphate production kiln is efficiently treated to meet environmental emission standards and realize resource recovery and recycling.

[0062] Furthermore, in some embodiments, the biochemical treatment apparatus includes a neutralization tank, an anaerobic reactor, and an aerobic reactor connected in sequence, with the outlet of the aerobic reactor connected to the inlet of the solid-liquid separation device.

[0063] In the technical solution of this application embodiment, the biochemical treatment device and the filtration device can work together efficiently to effectively treat the waste liquid absorbed by the tail gas of the lithium iron phosphate production kiln, ensuring that the treated wastewater meets the discharge standards, and at the same time realize the resource utilization of sludge.

[0064] Please refer to Figure 2 The filtration device includes a pressing device 1 and a first filter cake layer 2 and a second filter cake layer 3 disposed inside the pressing device 1. The top of the pressing device 1 is provided with a pre-treated wastewater inlet 4 and the bottom is provided with a filtrate outlet 5.

[0065] In the technical solutions of this application embodiment, there are many devices capable of achieving filtration, such as plate and frame filter presses. A filter cloth is provided below the first filter cake layer 2. The filter cloth, as an important filtration material, is used to intercept sludge particles, forming a porous filter cake layer on the filter cloth. This porous filter cake layer is composed of lime and PAM-modified biochemical sludge, providing favorable conditions for the formation of a dense filter cake layer and improving water permeability. The dense filter cake layer is a highly viscous substance, i.e., flocculated sediment, formed by the reaction of wastewater flocculants and coagulants. It has extremely high adsorption capacity. Simultaneously, due to its high viscosity, the filter cake layer has a dense structure, resulting in higher filtration accuracy and significantly reducing the interception of harmful substances in wastewater. The dense filter cake layer is also the core of this device for COD removal.

[0066] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0067] Example

[0068] This embodiment provides a method for treating waste liquid absorbed by the tail gas of a lithium iron phosphate production kiln, such as... Figure 1 and Figure 2 As shown, it includes the following steps:

[0069] S1. Wastewater Collection and Adjustment: Collect the wastewater from the kiln exhaust gas in the adjustment tank to regulate the water quality and quantity fluctuations, ensuring the stability of subsequent treatment processes. Add 500 ppm of polyaluminum ferric silicate and 10 ppm of anionic polyacrylamide to the wastewater. These agents help remove organic matter and suspended solids from the wastewater. Stir for 15 minutes to obtain pretreated wastewater and flocculated precipitate.

[0070] S2. Filter cake layer preparation: 1% lime and 10ppm anionic polyacrylamide are added to the biochemical sludge in the sludge conditioning tank. After plate and frame filtration, the first filter cake layer 2 is obtained. Flocculated sediment is added above the first filter cake layer 2, and after filtration, the second filter cake layer 3 is obtained above the first filter cake layer 2. This step aims to improve the adsorption and filtration performance of the sludge.

[0071] S3. Activated sludge filtration: Using the two-layer filter cake prepared in step S2 as the filter medium, employing as follows... Figure 2 The filtration device shown performs pressure filtration on the pretreated wastewater from step S1 to obtain filtrate. This step further reduces the organic concentration and suspended solids content of the wastewater.

[0072] S4. pH adjustment: Add sodium hydroxide to the filtrate obtained in step S3 to adjust its pH value to 8 to meet the requirements of subsequent biochemical treatment.

[0073] S5. Anaerobic Treatment: The wastewater obtained in step S4 is fed into an anaerobic reactor for anaerobic treatment. The sludge concentration in the anaerobic reactor is 3 g / L, and the retention time is 12 h.

[0074] S6. Aerobic Treatment: The waste liquid obtained in step S5 is fed into an aerobic reactor for aerobic treatment. The sludge concentration in the aerobic reactor is 3 g / L, the retention time is 40 h, and the dissolved oxygen is controlled at 3 mg / L.

[0075] S7. Sedimentation and Discharge: The effluent from step S6 is fed into a sedimentation tank for solid-liquid separation. The COD of the clarified liquid is less than 200 mg / L, meeting the wastewater discharge standards for the battery industry, and can be directly discharged into the sewer system. The sludge in the sedimentation tank is sent to step S2 for reuse.

[0076] S8. Sludge treatment: The filter media in step S3 is replaced 3 times a day, and the sludge removed is transported off-site as solid waste for treatment.

[0077] In this embodiment, the initial pH of the wastewater absorbed by the kiln tail gas is 3.5, and the COD is 16000 mg / L. After treatment by the method of this application, the pH of the filtrate obtained in step S3 is 6.2, and the COD is reduced to 3000 mg / L; the pH of the supernatant in the sedimentation tank in step S7 is 7.2, and the COD is less than 200 mg / L, meeting the emission standards. This application uses activated sludge as the adsorbent material and lime as the framework to make the filter cake layer for filtering wastewater, thoroughly purifying toxic and harmful substances in the wastewater, with an organic removal rate of up to 80% and a color removal rate of up to 90%.

[0078] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for treating waste liquid absorbed by the tail gas of a lithium iron phosphate production kiln, characterized in that, Includes the following steps: S1. Collect the waste liquid absorbed by the kiln tail gas, add flocculant, stir and mix to obtain pretreated wastewater and flocculated precipitate; S2. Add lime and flocculant to the biochemical sludge, and obtain a first filter cake layer after pressure filtration. Add the flocculated precipitate obtained in step S1 above the first filter cake layer, and obtain a second filter cake layer above the first filter cake layer after pressure filtration. S3. Using the first filter cake layer and the second filter cake layer as filter media, the pretreated wastewater obtained in step S1 is subjected to pressure filtration, so that the clear liquid in the pretreated wastewater passes through the second filter cake layer and the first filter cake layer in sequence to obtain filtrate; S4. Add a pH adjuster to the filtrate obtained in step S3 to adjust the pH value to a predetermined range, and then perform anaerobic treatment and aerobic treatment in sequence. S5. The mixed liquor after aerobic treatment in step S4 is subjected to solid-liquid separation. The clear liquid obtained is discharged, and the biochemical sludge is returned to step S2 for reuse. In step S1, the flocculant includes an inorganic polymeric flocculant and a polyacrylamide coagulant aid. The inorganic polymeric flocculant is one or more of polyaluminum ferric silicate, polyaluminum ferric chloride, polyaluminum chloride, and polyferric sulfate, and the dosage is 400~1000 ppm. The polyacrylamide coagulant is one or more of anionic polyacrylamide, cationic polyacrylamide and nonionic polyacrylamide, and the dosage is 5~20 ppm; The stirring time is 10-20 minutes; In step S2, the amount of lime used is 0.5-2%; The flocculant is one or more of anionic polyacrylamide, cationic polyacrylamide, and nonionic polyacrylamide, and the dosage is 5~20 ppm.

2. The method for treating waste liquid absorbed by the tail gas of lithium iron phosphate production kiln according to claim 1, characterized in that, In step S4, the pH adjuster is sodium hydroxide, and the predetermined range of the pH value is 7-8.

3. The method for treating waste liquid absorbed by the tail gas of lithium iron phosphate production kiln according to claim 2, characterized in that, The sludge concentration in the anaerobic treatment is 2-4 g / L, and the retention time is 8-24 h.

4. The method for treating waste liquid absorbed by the tail gas of lithium iron phosphate production kiln according to claim 3, characterized in that, The aerobic treatment involves sludge concentrations of 2-4 g / L, dissolved oxygen concentrations of 2-4 mg / L, and retention times of 40-120 h.

5. The method for treating waste liquid absorbed by the tail gas of lithium iron phosphate production kiln according to claim 1, characterized in that, In step S5, the COD of the clarified liquid is less than 500 mg / L.

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