Treatment method and system for lithium iron phosphate production kiln tail gas absorption waste liquid

Abstract

The invention provides a treatment method and system for lithium iron phosphate production kiln tail gas absorption waste liquid, and belongs to the field of wastewater treatment. According to the application, the waste liquid is flocculated and precipitated, the filter cake layer is prepared from biochemical sludge and lime to filter the waste liquid, the pH value of the filtrate is adjusted, anaerobic treatment and aerobic treatment are carried out, solid-liquid separation is carried out to obtain the clear liquid meeting the emission standard, and the biochemical sludge can be recycled. After the waste liquid is filtered by the filter cake layer, the COD (Chemical Oxygen Demand) is greatly reduced, the water becomes colorless and transparent and has no foul smell, and the biodegradability is obviously improved. On one hand, the waste liquid treatment process is greatly shortened, energy consumption and chemicals are saved, on the other hand, the treatment load of a biochemical system is remarkably reduced, stable operation of the biochemical system and standard discharge of waste liquid are guaranteed, the economical efficiency is good, and environmental protection is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a method and system for treating waste liquid absorbed by tail gas from a lithium iron phosphate production kiln. Background Art

[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 discharge of waste liquid absorbed by tail gas from lithium iron phosphate production kilns has increased significantly. This type of waste liquid has the characteristics of high organic content, high chroma, high suspended solids, odor, difficulty in degradation and biological toxicity, which has a serious impact on the environment and organisms.

[0003] Existing waste liquid treatment technologies mainly include physical methods, chemical methods and biological methods. These methods have the following shortcomings when treating waste liquid: 1. Physical methods, such as flocculation, sedimentation, filtration, etc., have limited treatment effects and are difficult to remove organic matter and biological toxic substances in waste liquid; 2. Chemical methods, such as advanced oxidation, neutralization, adsorption, etc., have long treatment processes, high energy consumption, large amounts of chemicals used, and high treatment costs; 3. Biological methods, such as activated sludge method and biofilm method, have poor treatment effects on high-concentration organic waste liquid and are difficult to degrade biological toxic substances.

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

[0005] In view of the technical problems existing in the background technology, the present application provides a method and system for treating waste liquid absorbed by exhaust gas from lithium iron phosphate production kilns, aiming to solve the technical problems of long treatment process of waste liquid absorbed by exhaust gas from traditional kilns, poor treatment effect, high load of biochemical system, unstable biochemical effluent and high operating costs.

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

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

[0008] S2. adding lime and flocculant to the biochemical sludge, and obtaining a first filter cake layer after filter pressing, adding the flocculated precipitate obtained in step S1 to the top of the first filter cake layer, and obtaining a second filter cake layer on the top of the first filter cake layer after filter pressing;

[0009] S3. Using the first filter cake layer and the second filter cake layer as filter media, filter the pretreated wastewater obtained in step S1 by filter press to obtain a filtrate;

[0010] S4. Adding a pH adjusting agent to the filtrate obtained in step S3 to adjust the pH value to a predetermined range, followed by anaerobic treatment and aerobic treatment;

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

[0012] In the technical scheme of the embodiment of the present application, by adding a flocculant to pre-treat the tail gas absorption waste liquid, the suspended solids and some organic matter in the wastewater can be effectively aggregated and removed, thereby improving the efficiency of subsequent treatment. The use of biochemical sludge and lime to prepare the filter cake layer not only treats the biochemical sludge, but also converts it into a useful filter medium, thereby realizing resource utilization. The pretreated wastewater is further purified by filter press filtration, and the obtained filtrate has a lower pollutant content, which is conducive to subsequent biochemical treatment. The filtrate after pH adjustment is subjected to anaerobic and aerobic treatment, which can effectively degrade organic pollutants in the wastewater and reduce COD (chemical oxygen demand) and BOD (biochemical oxygen demand). Through solid-liquid separation, a clear liquid that meets the emission standards is obtained, reducing the impact on the environment. The biochemical sludge after aerobic treatment 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] The water treatment process of this application is short and the treatment efficiency is high; the use of biochemical sludge cake filter material has good filtration treatment effect, can effectively adsorb organic matter, has a high organic removal rate, and has a low equipment load; the system has low energy consumption, low chemical consumption, and low overall operating cost; the sludge output is low and the solid waste treatment cost is low.

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

[0015] In this embodiment, the inorganic polymer flocculant has a strong charge neutralization and adsorption bridging effect, and can effectively aggregate suspended particles and colloidal substances in wastewater to form flocs. The dosage of the inorganic polymer flocculant is preferably 400-1000ppm. The sedimentation performance is best within this range. When the dosage is increased, the sedimentation performance decreases, and there is too much sludge; when the dosage is reduced, the sedimentation performance decreases, or even no sedimentation occurs. The polyacrylamide coagulant further improves the flocculation effect. Through flocculation, fine particles aggregate into larger flocs, and their sedimentation rate is significantly increased, which is convenient for 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 can increase the mechanical strength of the filter cake, making it less likely to break during the filter pressing process, thereby improving the filtration performance and reducing the solid particles in the filtrate. An appropriate amount of flocculant helps the fine particles in the sludge to aggregate into larger flocs, increasing the sludge modification and sedimentation rate.

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

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

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

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

[0022] In the second aspect, an embodiment of the present application provides a system for treating waste liquid absorbed by exhaust gas from a lithium iron phosphate production furnace, which adopts the method for treating waste liquid absorbed by exhaust gas from a lithium iron phosphate production furnace described in the first aspect to treat the waste liquid absorbed by exhaust gas from a lithium iron phosphate production furnace, and 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 the embodiment of the present application, the tail gas absorption waste liquid generated in the production process of lithium iron phosphate is efficiently treated through the synergistic effect of each processing unit to ensure that the waste liquid meets the environmental emission standards. The recycling of sludge reduces waste generation and optimizes resource utilization. The system is easy to operate, has low maintenance costs, and has good economy and reliability.

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

[0025] In this embodiment, by sequentially connecting the neutralization tank, the anaerobic reactor and the aerobic reactor, the waste liquid is continuously treated and the treatment efficiency is improved. By combining anaerobic and aerobic treatment, the organic matter in the waste water can be more effectively decomposed and the COD removal rate can be improved. Through the subsequent solid-liquid separation device, it can be ensured that the discharged clear liquid meets the environmental protection standards and reduces the impact on the environment.

[0026] In some embodiments, the filtering 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, through the cooperation of the pressing device and the two filter cake layers, a high-efficiency filtering interface can be formed to improve the removal rate of pollutants. The design of the pressing device makes the replacement and maintenance of the filter medium easier.

[0028] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solution of the present application, the following is a brief introduction to the drawings used in the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0030] Figure 1 A schematic flow chart of a method for treating waste liquid absorbed from tail gas in a lithium iron phosphate production kiln provided in an embodiment of the present application;

[0031] Figure 2 A schematic diagram of the structure of a filtering device for a treatment system of waste liquid absorbed by tail gas from a lithium iron phosphate production kiln provided in an embodiment of the present application;

[0032] Explanation of the accompanying drawings: 1. Compression device; 2. First filter cake layer; 3. Second filter cake layer; 4. Pre-treated wastewater inlet; 5. Filtrate outlet. DETAILED DESCRIPTION

[0033] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0035] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0036] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0037] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0038] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0039] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0040] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0041] The waste liquid absorbed by the tail gas of lithium iron phosphate production kilns has the characteristics of high organic content, high chroma, high suspended solids, malodor, difficulty in degradation and biological toxicity, which has serious impacts on the environment and organisms. Existing waste liquid treatment technologies mainly include physical methods, chemical methods and biological methods, etc. These methods have the following shortcomings when treating waste liquid: 1. Physical methods, such as flocculation, precipitation, filtration, etc., have limited treatment effects and are difficult to remove organic matter and biological toxic substances in waste liquid; 2. Chemical methods, such as advanced oxidation, neutralization, adsorption, etc., have long treatment processes, high energy consumption, large amounts of reagents used, and high treatment costs; 3. Biological methods, such as activated sludge method and biofilm method, have poor treatment effects on high-concentration organic waste liquid and are difficult to degrade biological toxic substances.

[0042] In order to solve the technical problems of the long treatment process of traditional kiln tail gas absorption waste liquid, poor treatment effect, high biochemical system load, unstable biochemical effluent, and high operating costs, the present application provides a method and system for treating the tail gas absorption waste liquid of lithium iron phosphate production kiln, wherein the waste liquid is flocculated and precipitated, and a filter cake layer is made of biochemical sludge and lime for waste liquid filtration, and the filtrate pH value is adjusted to perform anaerobic treatment and aerobic treatment, and solid-liquid separation is performed to obtain a clear liquid that meets the emission standards, and the biochemical sludge can be recycled. The present application enhances the filtering effect, improves the biochemical treatment conditions, realizes the recycling of resources, and at the same time reduces the treatment cost, reduces the environmental impact, improves the stability and reliability of the system, is economical and environmentally friendly, and is conducive to achieving clean production and sustainable development.

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

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

[0045] S2. adding lime and flocculant to the biochemical sludge, and obtaining a first filter cake layer after filter pressing, adding the flocculated precipitate obtained in step S1 to the top of the first filter cake layer, and obtaining a second filter cake layer on the top of the first filter cake layer after filter pressing;

[0046] S3. Using the first filter cake layer and the second filter cake layer as filter media, filter the pretreated wastewater obtained in step S1 by filter press to obtain a filtrate;

[0047] S4. Adding a pH adjusting agent to the filtrate obtained in step S3 to adjust the pH value to a predetermined range, followed by anaerobic treatment and aerobic treatment;

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

[0049] In this embodiment, after adding flocculants to the waste liquid, the suspended matter, colloids and some organic matter in the waste liquid are captured by the flocculants and form flocs through stirring and mixing, and settle to the bottom of the container to form flocculated precipitates, while the upper layer is relatively clear pretreated wastewater. Lime can increase the pH value of the sludge and promote the flocculation of organic matter in the sludge. At the same time, lime, as a skeleton material, can increase the mechanical strength of the filter cake, making it difficult to break during the filter pressing process, thereby improving the filtering performance. After adding the flocculant, the fine particles in the sludge gather into larger flocs, and the water is squeezed out by filter pressing in the pressing device to form a first filter cake layer. The pressing device can be a plate frame or other solid-liquid separation equipment. The flocculated precipitate is added above the first filter cake layer, and filter pressing is performed again to form a second filter cake layer. The first filter cake layer and the second filter cake layer are used as filter media. When the pretreated wastewater passes through the filter media, the suspended matter and flocs therein are intercepted, thereby obtaining a clear filtrate. pH value is an important factor affecting microbial activity. By adding a pH regulator, the pH value of the filtrate is adjusted to a range suitable for microbial growth. Anaerobic treatment is the use of anaerobic microorganisms to decompose complex organic matter into simple organic matter under anaerobic conditions, while aerobic treatment is the use of aerobic microorganisms to further decompose organic matter under aerobic conditions, converting it into carbon dioxide and water, and removing pollutants in the waste liquid through the metabolism of microorganisms. The mixed liquor after aerobic treatment contains a large amount of microbial flocs (biochemical sludge) and treated water (clear liquid). Through solid-liquid separation, the clear liquid can meet the discharge standards, and the biochemical sludge is returned to step S2, mixed with the newly added lime and flocculant, and filtered and utilized again, realizing the resource recycling of sludge.

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

[0051] In the technical solution of the embodiment of the present application, the flocculant is preferably polyaluminium ferric silicate, and the coagulant is preferably anionic polyacrylamide, which has the best flocculation effect, the least reagent consumption, and no need to adjust the pH value of the waste liquid absorbed by the kiln tail gas, which can reduce the reagents used for pH adjustment, and the alum flowers formed are larger, the sedimentation performance is better, and the supernatant is clear and transparent. This process greatly reduces the suspended matter 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 the embodiment of the present application, lime and polyacrylamide (any one of cation, anion, and non-ion) are used to condition the biochemical sludge to obtain sludge with good filter pressing performance. At the same time, a pressing device is used to filter the conditioned sludge, and a first filter cake layer with large gaps is formed on the pressing device. The first filter cake layer accounts for 1 / 2 to 2 / 3 of the thickness of the entire filter cake layer. The specific feeding time and pressing operation are determined according to actual experiments, and the theoretical value can also be calculated according to the sludge concentration detection, and fine-tuned during the specific implementation process.

[0054] The flocculated precipitate obtained in step S1 is driven into a compacting device for filtration, and a dense second filter cake layer is formed above the first filter cake layer. The main component of the second filter cake layer is a viscous substance formed by polyaluminum ferrosilicate and polyacrylamide, which has a strong adsorption capacity and can effectively intercept impurities in wastewater. The second filter cake layer accounts for 1 / 3 to 1 / 2 of the thickness of the entire filter cake layer. The specific feeding time and compacting operation are determined according to actual experiments, and the theoretical value can also be calculated based on the sludge concentration detection, and fine-tuned during the specific implementation process. The first filter cake layer acts as a supporting bridge for the second filter cake layer, thereby improving the water permeability of the entire filter cake layer.

[0055] The pretreated wastewater obtained in step S1 is pumped into a compacting device for filtration, and the clear 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 clear liquid, and the first filter cake layer ensures filtering performance, avoids clogging of the filter cloth, and increases the pollution-receiving capacity of the entire filter cake layer.

[0056] After the above steps, the COD concentration of the tail gas absorption waste liquid is greatly reduced, the harmful substances are almost completely intercepted, and the biodegradability is greatly improved. The subsequent direct use of the anaerobic (hydrolysis acidification) + aerobic combination biochemical system treatment can stably meet the standards. The traditional treatment method requires the addition of high-quality carbon sources to condition the wastewater, and a certain proportion of carbon sources needs to be added, resulting in high organic concentration and high load on the biochemical system.

[0057] Further, in some embodiments, in step S4, the pH regulator is sodium hydroxide, and the predetermined range of pH value is 7 to 8. The sludge concentration of anaerobic treatment is 2 to 4 g / L, and the retention time is 8 to 24 hours. The sludge concentration of aerobic treatment is 2 to 4 g / L, the dissolved oxygen is 2 to 4 mg / L, and the retention time is 40 to 120 hours.

[0058] In the technical solution of the embodiment of the present application, the pH value of the wastewater is adjusted to a predetermined range to provide a suitable environment to ensure that the subsequent biological treatment process can proceed smoothly. Too high or too low a pH value will affect the activity of microorganisms. Anaerobic treatment is the process of converting organic matter in wastewater into methane and carbon dioxide using anaerobic microorganisms in the absence of oxygen. The sludge concentration can ensure that there are enough microorganisms to participate in the decomposition of organic matter. The residence time is to ensure that the organic matter can be fully decomposed by microorganisms, degrade organic pollutants in wastewater, and reduce COD and BOD. Aerobic treatment is the use of aerobic microorganisms to decompose organic matter in wastewater under aerobic conditions. The sludge concentration ensures that there are enough microorganisms for biodegradation. The dissolved oxygen concentration is to maintain the activity of microorganisms, because aerobic microorganisms need oxygen for metabolism, and the residence time is to ensure that the organic matter in the wastewater can be fully decomposed. Organic pollutants are further degraded by aerobic treatment to reduce the COD and BOD of wastewater. Through the metabolic activities of microorganisms, organic matter is converted into harmless carbon dioxide and water.

[0059] The mixed liquid after aerobic treatment is subjected to solid-liquid separation, and the COD of the obtained clear liquid is less than 500 mg / L, meeting the discharge standard.

[0060] In the second aspect, an embodiment of the present application provides a system for treating waste liquid absorbed by exhaust gas from a lithium iron phosphate production furnace, which adopts the method for treating waste liquid absorbed by exhaust gas from a lithium iron phosphate production furnace described in the first aspect to treat the waste liquid absorbed by exhaust gas from a lithium iron phosphate production furnace, and 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, through the combination of physical, chemical and biological methods, efficient treatment of lithium iron phosphate production kiln exhaust gas absorption waste liquid is achieved, meeting environmental protection emission standards, and realizing resource recovery and recycling.

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

[0063] In the technical solution of the embodiment of the present application, the biochemical treatment device and the filtration device can work together efficiently to achieve effective treatment of the exhaust gas absorption waste liquid of the lithium iron phosphate production kiln, ensure that the treated wastewater meets the emission standards, and realize the resource utilization of sludge.

[0064] Please refer to Figure 2 The filtering device includes a pressing device 1 and a first filter cake layer 2 and a second filter cake layer 3 arranged 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 solution of the embodiment of the present application, there are many devices that can realize the filtering function, such as a plate and frame filter press. A filter cloth is provided below the first filter cake layer 2. The filter cloth is used as an important filtering material to intercept mud cake particles and form a porous filter cake layer on the filter cloth. The porous filter cake layer is composed of biochemical sludge modified by lime and PAM. On the one hand, it provides favorable conditions for the formation of a dense filter cake layer, and on the other hand, it improves the water permeability. The dense filter cake layer is a highly viscous substance formed by the reaction of sewage flocculants and coagulants, that is, flocculated precipitates, which have extremely high adsorption capacity. At the same time, due to its high viscosity, when the filter cake layer is formed, the filter cake layer has a dense structure and higher filtration accuracy, which can greatly intercept harmful substances in sewage. The dense filter cake layer is also the core of the device for removing COD.

[0066] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. The reagents or instruments used without specifying the manufacturer are all conventional products that can be obtained commercially.

[0067] Example

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

[0069] S1. Waste liquid collection and regulation: Collect the waste liquid absorbed by the kiln tail gas in the regulating tank to regulate the water quality and water volume fluctuations of the wastewater to ensure the stability of the subsequent treatment process. Add 500ppm of polyaluminum ferrosilicate and 10ppm of anionic polyacrylamide to the wastewater. These agents help to remove organic matter and suspended matter in the wastewater. Stir for 15 minutes to obtain pretreated wastewater and flocculated precipitate.

[0070] S2. Preparation of filter cake layer: 1% lime and 10ppm anionic polyacrylamide are added to the biochemical sludge in the sludge conditioning tank, and the first filter cake layer 2 is obtained after plate and frame filtration, and the flocculated precipitate 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 is intended to improve the adsorption and filtration performance of the sludge.

[0071] S3. Activated sludge filtration: Use the two filter cake layers prepared in step S2 as the filtration medium, using Figure 2 The filtration device shown performs filter press filtration on the wastewater pretreated in step S1 to obtain a filtrate. This step further reduces the organic concentration and suspended matter content of the wastewater.

[0072] S4. pH adjustment: sodium hydroxide is added 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 connected to an anaerobic reactor for anaerobic treatment. The sludge concentration in the anaerobic reactor is 3 g / L, and the residence time is 12 h.

[0074] S6. Aerobic treatment: The waste liquid obtained in step S5 is connected to an aerobic reactor for aerobic treatment. The sludge concentration in the aerobic reactor is 3 g / L, the residence 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 connected to a sedimentation tank for solid-liquid separation. The COD of the clear liquid is less than 200 mg / L, which meets the wastewater discharge standards of the battery industry and can be directly discharged into the sewer. The sludge in the sedimentation tank is sent to step S2 for reuse.

[0076] S8. Sludge treatment: The filter medium in step S3 is replaced three times a day, and the replaced sludge is transported out as solid waste.

[0077] In this embodiment, the initial pH of the waste liquid absorbed by the kiln tail gas is 3.5, and the COD is 16000 mg / L. After the treatment 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, which meets the emission standards. This application uses activated sludge as an adsorption material and lime as a skeleton to make a filter cake layer for filtering wastewater, and thoroughly purifies toxic and harmful substances in the wastewater, with an organic removal rate of up to 80% and a chromaticity removal rate of up to 90%.

[0078] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for treating waste liquid absorbed by tail gas from a lithium iron phosphate production kiln, characterized in that: The following steps are involved: S1. Collect the waste liquid absorbed by the kiln exhaust gas, add a flocculant, stir and mix, and obtain pretreated wastewater and flocculated precipitate; S2. adding lime and flocculant to the biochemical sludge, and obtaining a first filter cake layer after filter pressing, adding the flocculated precipitate obtained in step S1 to the top of the first filter cake layer, and obtaining a second filter cake layer on the top of the first filter cake layer after filter pressing; S3. Using the first filter cake layer and the second filter cake layer as filter media, filter the pretreated wastewater obtained in step S1 by filter press to obtain a filtrate; S4. Adding a pH adjusting agent to the filtrate obtained in step S3 to adjust the pH value to a predetermined range, followed by anaerobic treatment and aerobic treatment; S5. The mixed liquid after aerobic treatment in step S4 is subjected to solid-liquid separation, the obtained clear liquid is discharged, and the biochemical sludge is returned to step S2 for reuse.

2. The method for treating waste liquid absorbed by tail gas from lithium iron phosphate production kiln according to claim 1, characterized in that: In step S1, the flocculant includes an inorganic polymer flocculant and a polyacrylamide coagulant aid, wherein the inorganic polymer flocculant is one or more of polyaluminium ferric silicate, polyaluminium ferric chloride, polyaluminium 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 to 20 ppm; And / or, the stirring time is 10 to 20 minutes.

3. The method for treating waste liquid absorbed by tail gas from lithium iron phosphate production kiln according to claim 1, characterized in that: 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 dosage is 5-20 ppm.

4. The method for treating waste liquid absorbed by tail gas from 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.

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

6. The method for treating waste liquid absorbed by tail gas from lithium iron phosphate production kiln according to claim 5, characterized in that: The sludge concentration of the aerobic treatment is 2-4 g / L, the dissolved oxygen is 2-4 mg / L, and the residence time is 40-120 h.

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

8. A system for treating waste liquid absorbed from tail gas of a lithium iron phosphate production furnace, which uses the method for treating waste liquid absorbed from tail gas of a lithium iron phosphate production furnace as described in any one of claims 1 to 7, characterized in that: The invention comprises a wastewater pretreatment device, a filtering device, a biochemical treatment device, a solid-liquid separation device and a sludge treatment device which are connected in sequence.

9. The lithium iron phosphate production kiln tail gas absorption waste liquid treatment system according to claim 8, characterized in that: The biochemical treatment device comprises a neutralization tank, an anaerobic reactor and an aerobic reactor which are connected in sequence, and the outlet of the aerobic reactor is connected to the inlet of the solid-liquid separation device.

10. The lithium iron phosphate production kiln tail gas absorption waste liquid treatment system according to claim 8, characterized in that: The filtering device comprises a pressing device and a first filter cake layer and a second filter cake layer arranged inside the pressing device.

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