Bipolar plate cleaning waste liquid recovery device and process

Abstract

The invention discloses a bipolar plate cleaning waste liquid recovery device. The bipolar plate cleaning waste liquid recovery device comprises a curing tank, a plate filter, a diaphragm pump and a storage tank, the output end of the curing tank is sequentially connected with a diaphragm pump and the liquid inlet end of the plate filter; and the liquid outlet end of the plate filter is connected with the liquid conveying end of the storage tank through another diaphragm pump. According to the method, the organic infiltration resin in the waste liquid is separated in a curing-separating mode, meanwhile, the separated cleaning liquid can be recycled, the production cost is greatly reduced, and remarkable environmental protection benefits are generated.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a bipolar plate cleaning waste liquid recovery device and process. Background Art

[0002] Hydrogen fuel cells are composed of bipolar plates, membrane electrodes, gas diffusion layers, catalysts, etc. The bipolar plates serve as current collectors in the stack system, distributing air and hydrogen. At the same time, the flow channels on both sides can drain gas and cooling water to discharge heat.

[0003] Flexible graphite sheets are used for sealing between bipolar plates and other components (such as membrane electrode assemblies), providing the battery with air tightness and thermal conductivity, avoiding gas leakage, and ensuring the smooth flow of reaction gases in the battery. Flexible graphite sheets are currently widely studied and reported for their advantages such as low price, light texture, and corrosion resistance, especially in terms of volume power density compared to graphite machined sheets. Preparation process of flexible graphite sheets: natural expandable graphite powder is used, and is made through high-temperature expansion, rolling, molding, vacuum impregnation, and cleaning. Among them, the traditional water cleaning process requires the use of a large amount of water and surfactants to remove excess impregnation resin on the surface of the plate. The organic wastewater generated contains a large amount of harmful substances such as polymer resins and organic surfactants, which makes the wastewater treatment process complicated and significantly reduces the competitiveness of the product.

[0004] Therefore, it is necessary to propose a new bipolar plate cleaning waste liquid recovery device and process to solve the problem of excessive harmful substances in the existing organic wastewater. Summary of the invention

[0005] The purpose of the present invention is to provide a bipolar plate cleaning waste liquid recovery device and process to solve the problem of excessive harmful substances in organic wastewater.

[0006] To achieve this object, the present invention adopts the following technical solutions: A bipolar plate cleaning waste liquid recovery device, the bipolar plate cleaning waste liquid recovery device comprises a curing tank, a plate filter, a diaphragm pump and a storage tank; the output end of the curing tank is connected to a diaphragm pump and a liquid inlet end of the plate filter in sequence; the liquid outlet end of the plate filter is connected to the infusion end of the storage tank through another diaphragm pump.

[0007] Furthermore, the curing tank also includes a tank cover circulating water tank; the tank cover of the curing tank is in communication with the tank cover circulating water tank.

[0008] Furthermore, a liquid level sensor and a temperature sensor are provided in the curing tank; the liquid level sensor and the temperature sensor are both electrically connected to the tank cover circulating water tank.

[0009] Furthermore, the curing tank also includes a heating and curing section; the tank cover of the curing tank is a condensing section; the heating and curing section includes a plurality of heating rods which are arranged at the bottom of the curing tank and are spaced at a preset distance.

[0010] Furthermore, the operating pressure of the plate filter is 0.3-0.6 .

[0011] A bipolar plate cleaning waste liquid recovery process, the specific process comprises the following steps: S1. Mix the cleaning waste liquid transferred to the curing tank with an appropriate amount of curing agent and mix them evenly; S2, heating the stirred and mixed cleaning wastewater to a preset temperature, and turning on a condensation device to solidify the impregnated resin in the wastewater; S3. Use a plate filter to perform solid-liquid separation on the solid-liquid mixture.

[0012] Furthermore, in step S1, the curing agent is one or more of azobisisobutyronitrile, azobisisovaleronitrile, and dibenzoyl peroxide.

[0013] Furthermore, in step S2, the cleaning waste liquid is heated to 75°C to 80°C and kept at a constant temperature for 1 hour to 3 hours.

[0014] Furthermore, the step S1 further includes step S0: S0, pre-clean the waste liquid through the pore size of 50-100 The filter is filtered through a mesh to remove large particles of impurities.

[0015] Furthermore, the step S3 further includes a step S4: S4. When the conductivity of the separated liquid is ≤100 , it is judged to be reusable.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The solidification-separation method is adopted to separate the organic impregnation resin in the waste liquid. At the same time, the separated cleaning liquid can be recycled, which greatly reduces the production cost and produces significant environmental benefits. Through precise curing agent ratio, temperature control and filtration operation, the quality of the recovered liquid is higher, and the preset liquid conductivity can confirm its reuse, thereby reducing the cost of waste liquid treatment and achieving the dual goals of environmental protection and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0018] The structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention.

[0019] Figure 1 A schematic diagram of an embodiment of a bipolar plate cleaning waste liquid recovery device and process of the present invention; Figure 2 A schematic diagram of the structure of a curing tank of an embodiment of a bipolar plate cleaning waste liquid recovery device of the present invention; Figure 3 The present invention is a flow chart of a bipolar plate cleaning waste liquid recovery process.

[0020] Illustrations: 100, curing tank; 200, plate filter; 300, diaphragm pump; 400, storage tank; 110, tank cover; 120, tank body; 130, heating and curing section; 140, stirring device; 150, tank cover circulating water tank. DETAILED DESCRIPTION

[0021] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In the description of the present invention, it should be understood that the terms "upper", "lower", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention. It should be noted that when a component is considered to be "connected" to another component, it may be directly connected to the other component or there may be a centrally arranged component at the same time.

[0023] The technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0024] Figure 1 A schematic diagram of an embodiment of a bipolar plate cleaning waste liquid recovery device and process of the present invention; Figure 2 A schematic diagram of the structure of a curing tank of an embodiment of a bipolar plate cleaning waste liquid recovery device of the present invention; Figure 3 The present invention is a flow chart of a bipolar plate cleaning waste liquid recovery process.

[0025] Embodiment 1: The embodiment of the present invention provides a bipolar plate cleaning waste liquid recovery device, which can significantly reduce the generation of waste liquid discharge, has the characteristics of low cost, safe and reliable process, etc.

[0026] like Figure 1 As shown, a bipolar plate cleaning waste liquid recovery device comprises a curing tank 100, a plate filter 200, a diaphragm pump 300 and a storage tank 400; the output end of the curing tank 100 is connected to a diaphragm pump 300 and a liquid inlet end of the plate filter 200 in sequence; the liquid outlet end of the plate filter 200 is connected to the infusion end of the storage tank 400 through another diaphragm pump 300.

[0027] It should be noted that the diaphragm pump 300 connected to the curing tank 100 is denoted as the first diaphragm pump, and the diaphragm pump 300 connected to the storage tank 400 is denoted as the second diaphragm pump. The diaphragm pumps 300 at the two locations play different roles due to the different processing conditions. The first diaphragm pump pumps the waste liquid (mixture containing solid particles) after the resin curing in the curing tank 100 to the plate filter 200 to ensure that the high viscosity or solid-containing fluid enters the filtration system smoothly. Secondly, it also provides a stable inlet pressure (usually 0.3-0.6 ), forcing the fluid to pass through the filter medium to improve the solid-liquid separation efficiency. It can avoid material retention in the solidification tank 100 and prevent secondary agglomeration; optimize the filtration rate through pressure control and reduce energy consumption. The second diaphragm pump extracts the separated filtrate (liquid detergent or water) from the outlet of the plate filter 200, overcomes the resistance of the filter material and the pressure drop of the pipeline, ensures that the filtrate is completely discharged, and also reduces the cavity pressure of the plate filter 200 through suction to avoid filtrate backflow or residue, while providing transportation power for the storage tank 400. Improve the filtrate recovery rate (up to more than 95%); reduce the moisture content of the filter cake and reduce the subsequent processing costs.

[0028] The dual pumps regulate the pressure in stages to avoid overloading of a single pump (for example, using only a single pump may result in insufficient pressure at the front end or insufficient suction at the back end); reduce overall energy consumption through segmented pressure management (experimental data show that the dual pump system saves 15% to 20% energy compared to a single pump); and prevent the solid-liquid mixture from clogging the filter (the first diaphragm pump pushes the pressure) and the filtrate remains (the second diaphragm pump sucks the negative pressure). Through the collaborative design of the two diaphragm pumps 300, the device achieves efficient and stable operation of the entire process from solidification to separation, and is particularly suitable for the high-standard recovery requirements of waste liquid from fuel cell bipolar plate washing.

[0029] Further, such as Figure 2 As shown, the curing tank 100 further includes a tank cover 110 , a tank body 120 , a heating and curing section 130 , and a stirring device 140 ; ​​the tank cover 110 of the curing tank 100 is in communication with the tank cover circulating water tank 150 .

[0030] Furthermore, a liquid level sensor and a temperature sensor are provided in the curing tank 100 ; the liquid level sensor and the temperature sensor are both electrically connected to the tank cover circulating water tank 150 .

[0031] Furthermore, the curing tank 100 also includes a heating and curing section 130; the tank cover 110 of the curing tank 100 is a condensing section; the heating and curing section 130 includes a plurality of heating rods which are arranged at the bottom of the curing tank 100 and are spaced at a preset distance.

[0032] Preferably, the stirring device 140 preferably uses a stirring fan arranged at the side end of the tank body 120, and adopts dynamic variable speed stirring. In the first stage (first 5 minutes): when the waste liquid is heated to 75°C~80°C, it is stirred at a high speed of 500 rpm to accelerate the dispersion of the curing agent and the start of the reaction; in the second stage (subsequent constant temperature for 1h~3h): maintain the temperature at 75°C~80°C, switch to low-speed stirring at 200 rpm to maintain the uniformity of the reaction and reduce bubbles; wherein, nitrogen is injected throughout the stirring process, the gas flow rate is 0.5-1.0 L / min, and the pressure is 0.05-0.1 , covering the liquid surface to form an inert environment. High-speed stirring matches the high-activity reaction requirements in the heating stage, and low-speed stirring avoids local overheating caused by too fast resin curing during the constant temperature period; secondly, nitrogen protection effectively blocks oxygen contact at high temperatures to prevent resin oxidation degradation); dynamic stirring and coordinated control of the temperature curve improve the uniformity of curing agent dispersion.

[0033] Furthermore, the operating pressure of the plate filter 200 is 0.3-0.6 .

[0034] It should be noted that the plate filter 200 preferably uses a plate and frame filter press or a chamber filter press. It is recommended to choose 316L stainless steel material, which has stronger corrosion resistance. The filtering principle of the plate filter 200 is that the medium set on the filter plate is intercepted, and the pressure difference on both sides of the medium is added to complete the separation. The plate filter 200 is mainly composed of a plurality of filter plates, which are closely arranged. The filter plates usually have specific textures or grooves on the surface of the filter plates. A filter chamber is formed between adjacent filter plates. When the solid-liquid mixture enters the filter, it will be distributed in the space formed by these filter plates, creating conditions for solid-liquid separation; the filter plate is covered with a filter medium, such as a common filter cloth, etc. The filter medium has a certain pore size. When the solid-liquid mixture flows through the filter cloth, the liquid can penetrate through the tiny pores of the filter cloth, and the solid particles are trapped on the surface of the filter cloth because the particle size is larger than the pore size of the filter cloth. As the filtering process proceeds, the solid particles gradually accumulate on the surface of the filter cloth to form a filter cake. The filter cake also plays a certain filtering role, further blocking smaller solid particles and improving the solid-liquid separation effect; the pressure difference is formed by a diaphragm pump The equipment such as 300 delivers the solid-liquid mixture to the plate filter 200 at a certain pressure, so that the mixture flows to one side of the filter cloth under the action of pressure, thereby prompting the liquid to pass through the filter cloth and the solid to be retained. The greater the pressure difference, the faster the filtration speed is relatively, but the pressure needs to be controlled within a reasonable range to avoid damaging the filter cloth due to excessive pressure or causing solid particles to be embedded too deeply in the filter cloth, affecting the filtration effect and filter cloth cleaning; the separation result is achieved by draining and slag discharge, and the liquid that penetrates the filter cloth is gathered in a specific channel and flows out from the liquid outlet of the plate filter 200 to become the separated liquid; and the solid particles retained on the surface of the filter cloth are discharged with the filter cake as the filter cake thickens to a certain extent, and the filter cake is discharged by opening the slag discharge port of the filter machine using gravity or mechanical assistance (such as vibration, etc.), completing the whole process of solid-liquid separation.

[0035] Embodiment 2: like Figure 3 As shown, a bipolar plate cleaning waste liquid recovery process, the specific process includes the following steps: S1, mixing the cleaning waste liquid transferred to the curing tank 100 and an appropriate amount of curing agent evenly; S2, heating the stirred and mixed cleaning wastewater to a preset temperature, and turning on a condensation device to solidify the impregnated resin in the wastewater; S3. Use a plate filter to perform solid-liquid separation on the solid-liquid mixture.

[0036] Furthermore, the curing agent is one or more of azobisisobutyronitrile, azobisisovaleronitrile, and dibenzoyl peroxide.

[0037] Furthermore, azobisisobutyronitrile, also known as AIBN, has good thermal stability and a high decomposition temperature, generally between 60-80°C, which is suitable for medium and low temperature curing processes; free radicals are released when AIBN decomposes, which can effectively start polymerization or cross-linking reactions, and are suitable for curing organic resins; the decomposition rate of AIBN can be adjusted at different temperatures, which has good process flexibility. However, compared with other peroxides, the decomposition rate of AIBN is relatively low, and higher temperatures or longer reaction times may be required; and, despite its good thermal stability, higher temperatures are usually required to fully decompose it, which may not be suitable for some temperature-sensitive materials.

[0038] Azobisisovaleronitrile, also known as AIPN, has a low decomposition temperature. AIPN usually decomposes at a low temperature of 50-60°C, which is suitable for low-temperature curing processes. AIPN can quickly generate free radicals and start cross-linking reactions quickly, which is suitable for processes that require fast curing. Compared with AIBN, AIPN has stronger selectivity and can adapt to different types of resin systems. However, although it decomposes faster at low temperatures, this may also lead to unstable or uncontrollable reactions, especially in some high-temperature sensitive materials; and at high temperatures, the decomposition products of AIPN (such as nitrogen) may have adverse effects on the environment.

[0039] Benzoyl peroxide, also known as BPO, has a moderate decomposition temperature, usually between 70-100°C, which is suitable for medium and high temperature curing processes and can ensure uniform curing of the resin; it can start the curing reaction in a relatively short time, which is suitable for applications that require rapid curing; it can adapt to a variety of resin systems, especially in the curing of thermosetting resins. However, its high temperature may cause side reactions. When BPO is used at higher temperatures, it may cause side reactions in the resin system, affecting the final curing effect; it releases more heat during decomposition, which may have an adverse effect on temperature-sensitive resins or materials.

[0040] In short, the choice of using a single curing agent or a combination of multiple curing agents depends on the specific application requirements, resin type and curing conditions. If a milder curing process is required, AIBN or AIPN can be selected; if a faster reaction is required, BPO can be selected. When mixing, the proportion of each curing agent and the process conditions need to be carefully controlled to avoid adverse side reactions and ensure the quality of the final product.

[0041] As a more preferred embodiment, 100 ml of the cleaning waste liquid is transferred to a flask, about 0.4% of a curing agent (azobisisobutyronitrile and azobisisovaleronitrile mass ratio is 1:1) is added, stirred evenly, heated to 75 ° C in an oil bath, maintained for 2 hours, a white flocculent substance appears, and then a filter is used for solid-liquid separation to obtain a white solid and a cleaning liquid, respectively.

[0042] As a more preferred embodiment, 100 ml of the cleaning waste liquid is transferred to a flask, about 0.4% of a curing agent (azobisisobutyronitrile and azobisisovaleronitrile mass ratio is 1:1) is added, stirred evenly, heated to 80 ° C in an oil bath pot, maintained for 2 hours, a white flocculent substance appears, and then a filter is used for solid-liquid separation to obtain a white solid and a cleaning liquid, respectively.

[0043] As a more preferred embodiment, 100 ml of the cleaning waste liquid is transferred to a flask, about 0.4% of a curing agent (azobisisobutyronitrile and azobisisovaleronitrile mass ratio is 1:1) is added, stirred evenly, heated to 80 ° C in an oil bath, maintained for 1 hour, and no white flocculent substance appears.

[0044] Furthermore, the cleaning waste liquid is heated to 75°C to 80°C and kept at this temperature for 1h to 3h.

[0045] It should be noted that precise temperature control allows the impregnation resin (such as epoxy resin, acrylic resin, etc.) in the cleaning waste liquid to undergo a heat-induced cross-linking reaction under the action of the curing agent to form stable solid particles, which are convenient for subsequent solid-liquid separation; specifically, the starting temperature: room temperature (about 25°C) or the temperature of the waste liquid after pretreatment (such as 40°C if preheated); heating rate: 2-5°C / min (to avoid excessively fast heating that may cause local overheating or resin decomposition); target temperature: 75°C~80°C, and the temperature of the curing tank 100 is monitored in real time by a temperature sensor, and the temperature is maintained when the target temperature is reached.

[0046] The specific method of the condensation section is well known to those skilled in the art and will not be specifically expanded in this embodiment. It can convert the volatile gas into liquid, mainly to recover and condense the evaporated harmful gas or solvent, help solidify the resin in the wastewater, and avoid the emission of harmful gases. It also helps to concentrate the wastewater and remove excess water. In this way, the condensation device not only helps to improve the waste liquid treatment efficiency, but also reduces environmental pollution. It is more preferred to use a spiral-shaped pipe so that the gas has a longer contact time when flowing in the pipe and effectively exchanges heat with the external cooling medium.

[0047] Furthermore, the curing time is related to the resin concentration. Specifically, 1 hour of curing is suitable for low-concentration resin (such as 3% to 5%) or highly active curing agent (such as peroxide), 2 hours of curing is suitable for the equilibrium time of medium-concentration resin (5% to 8%), and the curing rate can reach more than 95%. 3 hours of curing is suitable for high-concentration resin (8% to 10%) or when the curing agent has low activity to ensure complete curing.

[0048] Furthermore, at least three temperature measurement points (center, edge, and bottom) are set to avoid local overheating.

[0049] Furthermore, the step S1 further includes step S0: S0, pre-clean the waste liquid through the pore size of 50-100 The filter is filtered through a mesh to remove large particles of impurities.

[0050] It should be noted that due to the complexity of its sources, cleaning waste liquid may contain various solid particles, impurities or sediments (such as dust, oil stains, metal chips, sludge, etc.). If these solid substances are not filtered, they will affect the subsequent treatment process or equipment, causing equipment blockage, corrosion or damage; if the solid impurities in the cleaning waste liquid are not removed in time, the pollution load in the wastewater will increase, resulting in the subsequent treatment process requiring more resources (such as chemicals, energy, etc.) to remove soluble pollutants. Filtration treatment can effectively reduce the content of solid matter, thereby reducing the burden of subsequent treatment and improving overall resource utilization efficiency; certain solid particles will react with the chemicals added during the recycling process to produce toxic gases that cannot meet emission standards; some cleaning waste liquids may contain recyclable solid substances (such as metal particles, precious metals or oils). Through filtration treatment, these recyclable resources can be effectively collected and reused, which not only helps to reduce waste but also reduces costs.

[0051] Furthermore, the step S3 further includes a step S4: S4. When the conductivity of the separated liquid is ≤100 , it is judged to be reusable.

[0052] When the conductivity of the separated liquid is ≤100 When , it means that there are fewer soluble substances in the liquid, the water quality is purer, and it is more suitable for reuse in industry or other applications, such as cleaning, cooling or as process water. It also means that the water quality meets more stringent discharge or reuse standards, is easier to pass environmental protection testing, and reduces the risk of environmental pollution. This helps to reduce interference with subsequent processes, reduce corrosion risks, meet environmental standards, save resources and costs, and improve the safety and controllability of reused water.

[0053] The waste liquid generated by the traditional bipolar plate cleaning process brings tremendous pressure to environmental protection and industrial production costs. The present invention adopts a solidification-separation method to separate the organic impregnation resin in the waste liquid. At the same time, the separated cleaning liquid can be recycled, which greatly reduces the production cost and produces significant environmental benefits.

[0054] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A bipolar plate cleaning waste liquid recovery device, characterized in that: The bipolar plate cleaning waste liquid recovery device comprises a curing tank, a plate filter, a diaphragm pump and a storage tank; The output end of the curing tank is connected to a diaphragm pump and a liquid inlet end of a plate filter in sequence; The liquid outlet end of the plate filter is connected to the liquid infusion end of the storage tank through another diaphragm pump.

2. The bipolar plate cleaning waste liquid recovery device according to claim 1, characterized in that: The curing tank also includes a tank cover circulating water tank; The tank cover of the solidification tank is communicated with the tank cover circulating water tank.

3. The bipolar plate cleaning waste liquid recovery device according to claim 2, characterized in that: A liquid level sensor and a temperature sensor are provided in the curing tank; The liquid level sensor and the temperature sensor are both electrically connected to the tank cover circulating water tank.

4. The bipolar plate cleaning waste liquid recovery device according to claim 1, characterized in that: The curing tank also includes a heating and curing section; The tank cover of the solidification tank is a condensation section; The heating and curing section comprises a plurality of heating rods which are arranged at the bottom end of the curing tank and are spaced at a preset distance.

5. The bipolar plate cleaning waste liquid recovery device according to claim 1, characterized in that: The operating pressure of the plate filter is 0.3-0.6 .

6. A process for recovering waste liquid from bipolar plate cleaning, characterized in that: The specific process includes the following steps: S1. Mix the cleaning waste liquid transferred to the curing tank with an appropriate amount of curing agent and mix them evenly; S2, heating the stirred and mixed cleaning wastewater to a preset temperature, and turning on a condensation device to solidify the impregnated resin in the wastewater; S3. Use a plate filter to perform solid-liquid separation on the solid-liquid mixture.

7. The process for recycling bipolar plate cleaning waste liquid according to claim 6, characterized in that: In step S1, the curing agent is one or more of azobisisobutyronitrile, azobisisovaleronitrile, and dibenzoyl peroxide.

8. The process for recycling bipolar plate cleaning waste liquid according to claim 7, characterized in that: In step S2, the cleaning waste liquid is heated to 75°C-80°C and kept at this temperature for 1 hour to 3 hours.

9. The process for recycling waste liquid from bipolar plate cleaning according to claim 6, characterized in that: The step S1 also includes step S0: S0, pre-clean the waste liquid through the pore size of 50-100 The filter is filtered through a mesh to remove large particles of impurities.

10. The process for recycling bipolar plate cleaning waste liquid according to claim 6, characterized in that: The step S3 further includes a step S4: S4. When the conductivity of the separated liquid is ≤100 , it is judged to be reusable.

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