Photovoltaic cell production wastewater perfluorine recovery process and treatment system

Abstract

The invention discloses a photovoltaic cell production wastewater perfluorine recovery process and a treatment system, concentrated alkaline water and dilute alkaline water are mixed, suspended solids, organic matters and particulate impurities are removed through a pretreatment system, fine particles are removed through an ultrafiltration membrane system, and then the mixture enters a nanofiltration membrane system to intercept silicon and other ions with more than two valence, so that the perfluorine recovery process is realized. Water produced by the nanofiltration membrane system enters a neutralization adjusting tank to be neutralized with part of dilute acid water until the pH is 5-8, fine particles in the solution are removed through a first precision filter, fluoride is intercepted through a two-stage RO membrane, and a concentrated sodium fluoride solution is obtained; sodium fluoride solution concentrated acid water and residual dilute acid water are mixed and then subjected to a crystallization reaction with a lime solution and a calcium chloride solution in a fluorine recovery and crystallization reactor to obtain a calcium fluoride crystal product, and effluent of the fluorine recovery and crystallization reactor enters a fluorine removal system and then is discharged after reaching the standard. 99% of fluorine elements are recycled as high-purity calcium fluoride, the sludge amount is small, and the medicament cost is very low.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and in particular to a process and treatment system for the recovery of perfluorinated wastewater from photovoltaic cell production. Background Technology

[0002] The production of photovoltaic cells involves the use of large quantities of hydrofluoric acid and alkalis (sodium hydroxide and potassium hydroxide) for texturing, etching, and cleaning, generating significant amounts of wastewater. Wastewater from the photovoltaic cell manufacturing industry is generally classified into four categories: concentrated acid, dilute acid, concentrated alkali, and dilute alkali wastewater. Concentrated acid and dilute acid wastewater are fluoride-containing wastewater, with fluoride ion concentrations typically ranging from several hundred to tens of thousands of mg / L. Dilute and concentrated alkali wastewater contain several hundred to several thousand mg / L of silicon, exhibiting strong alkalinity.

[0003] Currently, the photovoltaic cell industry generally treats the above four types of wastewater together. The treatment of fluoride mainly employs chemical precipitation, which involves adding calcium salts (such as simple lime or calcium chloride and calcium hydroxide) to react calcium ions with fluorides in the water to form calcium fluoride precipitate. While this method is simple to operate, it has significant limitations: the resulting sludge has a small particle size, making dewatering difficult and resulting in a large sludge production volume. Furthermore, the sludge contains a high concentration of silicon, leading to low sludge purity (50%-80%), significantly reducing the resource value of fluoride-containing sludge and hindering the effective recovery of fluoride resources.

[0004] To improve the fluoride recovery rate and value of wastewater, some companies separate concentrated acid wastewater containing fluoride from other wastewater to increase the purity of calcium fluoride produced from wastewater treatment, thereby recovering some high-purity calcium fluoride with a purity of up to 90%. The recovered effluent is then combined with dilute acid wastewater and alkaline water for comprehensive treatment. However, the fluoride resources in the dilute acid water still cannot be recovered, and the overall fluoride recovery rate to obtain high-purity calcium fluoride products is only 70%-80%.

[0005] Chinese patent CN120364886A, a resource-based treatment system and process for photovoltaic acid and alkaline wastewater, proposes mixing concentrated acid and alkaline water to a pH range of 6-9 to remove silica and generate high-purity silica gel. The filtrate from this step is then mixed with the remaining concentrated acid, and calcium chloride and lime are added to react and remove fluoride, producing high-purity calcium fluoride. While this method can obtain high-purity calcium fluoride for fluoride recovery and fully utilizes the alkalinity of the concentrated alkaline water, a large amount of fluoride in the dilute acid wastewater remains unrecovered.

[0006] Chinese patent CN120172421B, "A Method for Removing Impurities from Multi-Source Photovoltaic Wastewater and Synergistically Preparing Fluorine Products in a Staged Process," proposes a method for the staged treatment of concentrated acid and alkaline solutions to recover fluorine and silicon resources. In the first stage, magnesium chloride is added to concentrated alkaline solution to recover silicon via magnesium silicate. In the second stage, barium chloride is added to concentrated acid solution along with cryolite and sodium aluminate to recover fluorine via cryolite. In the third stage, calcium fluoride seed crystals and calcium chloride are added to the secondary waste liquid to recover fluorine via calcium fluoride. While this method can effectively recover fluorine and silicon, it requires numerous external reagents, is complex to operate, and is costly. Furthermore, it only uses concentrated acid and alkaline solutions; dilute acid and alkaline solutions are not recovered. Summary of the Invention

[0007] To overcome the above-mentioned defects, the present invention provides a process and system for the recovery of perfluorinated wastewater from photovoltaic cell production. This process and system can treat all four types of wastewater from the photovoltaic industry and obtain high-purity calcium fluoride products.

[0008] The technical solution adopted by this invention to solve its technical problem is: a process for recovering perfluorinated wastewater from photovoltaic cell production, the specific steps of which are as follows:

[0009] Step 1: Mix concentrated and dilute alkaline solutions and pump them into the pretreatment system to remove suspended solids, organic matter, and particulate impurities from the mixed alkaline solution;

[0010] Step 2: The effluent from the pretreatment system is fed into the ultrafiltration membrane system to remove fine particles;

[0011] Step 3: The permeate from the ultrafiltration membrane system is fed into the nanofiltration membrane system to intercept silicon and other divalent or higher ions. By intercepting divalent and higher ions in the water through nanofiltration, SiO3 in alkaline water can be blocked. 2- The water enters the concentrate side, achieving the effect of removing silicon from the alkaline water. The permeate from the nanofiltration membrane system enters the neutralization and equalization tank.

[0012] Step 4: Inject some dilute acid water into the neutralization and conditioning tank and mix it with the water produced by the nanofiltration membrane system. Control the pH of the acid-base mixture between 5 and 8. Adjust the acid-base mixture to a pH range suitable for RO membrane operation to prevent damage to the RO membrane. The pH of the acid-base mixture is controlled by the amount of dilute acid water injected.

[0013] Step 5: The prepared solution in the neutralization and conditioning tank is fed into the first precision filter to intercept fine particles in the solution;

[0014] Step Six: The effluent from the precision filter is fed into a two-stage RO membrane system. After treatment by the two-stage reverse osmosis membranes, fluoride in the water is removed. The concentrate side of the two-stage RO membrane system yields a sodium fluoride solution with a content of more than 2%. Salt is intercepted by the reverse osmosis membranes on the concentrate side. At this point, the main components of the water are fluoride ions and sodium ions. The primary concentrate produced by the primary RO membrane is then fed into the secondary RO membrane for further concentration. The sodium fluoride solution concentration in the secondary concentrate produced by the secondary RO membrane can be concentrated to more than 2%, thereby reducing the volume of fluoride-containing wastewater for use in the fluoride recovery system. Both the primary and secondary permeate water from the two-stage RO membrane system are sent to the reverse osmosis permeate tank for reuse.

[0015] Step 7: The concentrated water, concentrated acid water, and residual dilute acid water from the two-stage RO membrane system are mixed to form mixed acid water. The mixed acid water, lime solution, and calcium chloride solution are then fed into the fluoride recovery crystallization reactor. The pH of the liquid in the fluoride recovery crystallization reactor is controlled between 4 and 7. The pH of the mixed solution in the fluoride recovery crystallization reactor is regulated by controlling the flow rate of the lime solution. The total calcium-fluoride molar ratio of the liquid in the fluoride recovery crystallization reactor is controlled between 0.5 and 0.6. The total calcium-fluoride molar ratio of the mixed solution in the fluoride recovery crystallization reactor is controlled by controlling the flow rate of the calcium chloride solution.

[0016] Step 8: After the calcium fluoride crystals in the fluoride recovery crystallization reactor are periodically discharged, they are dehydrated to obtain calcium fluoride crystal products. The effluent from the fluoride recovery crystallization reactor enters the defluorination system and is discharged after meeting the standards.

[0017] In the fluoride recovery crystallization reactor, fluoride in the mixed acidic water combines with calcium source at a certain pH to form calcium fluoride crystals, which significantly reduces the fluoride content in the effluent. The calcium fluoride crystals grow continuously in the system and are periodically discharged from the system as high-purity calcium fluoride products. The purity of the dehydrated calcium fluoride crystal products is over 90%, which has certain economic value. The fluoride ion content in the effluent from the fluoride recovery crystallization reactor is around 100 mg / L, and the effluent meets the discharge standards after entering the subsequent defluorination system.

[0018] As a further improvement of the present invention, in step seven, the mass percentage concentration of the lime solution is 3%-5%, the mass percentage concentration of the calcium chloride solution is 10-30%, the lime solution is prepared by mixing lime and water in a lime pool, and the calcium chloride solution is prepared by mixing calcium chloride and water in a calcium chloride pool.

[0019] As a further improvement of the present invention, in step one, concentrated alkaline water and dilute alkaline water are first transported to an alkaline water equalization tank for homogenization treatment. The homogenized mixed alkaline water is then pumped into a pretreatment system. An agitator can be installed in the alkaline water equalization tank to stir the mixed alkaline water, thereby achieving rapid homogenization treatment.

[0020] As a further improvement of the present invention, in step one, the pretreatment system intercepts suspended solids and adsorbs and removes organic matter in the mixed alkaline water through carbon filtration, and intercepts fine particles in the mixed alkaline water through precision filtration to reduce the turbidity of the mixed alkaline water. The mixed alkaline water undergoes carbon filtration and precision filtration treatment in sequence so as not to clog the subsequent RO membrane.

[0021] As a further improvement of the present invention, the concentrate from the ultrafiltration membrane system in step two is returned to the alkaline water conditioning tank, and the concentrate from the nanofiltration membrane system in step three is a high-concentration sodium silicate solution. The concentrate from the nanofiltration membrane system is collected in a nanofiltration concentrate tank and recycled as a raw material for water glass production.

[0022] As a further improvement of the present invention, in step six, the permeate from the two-stage RO membrane system is collected by the reverse osmosis permeate tank and used as recycled water at the production end.

[0023] As a further improvement of the present invention, in step seven, the concentrated water, concentrated acid water and residual dilute acid water of the two-stage RO membrane system are mixed and homogenized in the acid water conditioning tank, and then fed into the fluorine recovery crystallization reactor. A stirrer can be installed in the acid water conditioning tank to stir the mixed acid water, thereby achieving rapid homogenization.

[0024] A perfluoride recovery and treatment system for photovoltaic cell production wastewater includes an alkaline water equalization tank, a pretreatment system, an ultrafiltration membrane system, a nanofiltration membrane system, a neutralization equalization tank, a first precision filter, a two-stage RO membrane system, an acid water equalization tank, a lime tank, a calcium chloride tank, a fluoride recovery crystallization reactor, a dehydration device, a subsequent defluorination system, a first pH meter, a second pH meter, several booster pumps, and a control system. The alkaline water equalization tank is used to contain and mix concentrated and dilute alkaline water. The booster pumps can pump the homogenized mixed alkaline water from the alkaline water equalization tank into the pretreatment system. The pretreatment system can... The pretreatment system removes suspended solids, organic matter, and particulate impurities from the mixed alkaline water. The effluent from the pretreatment system is then pumped into the ultrafiltration membrane system via a booster pump. The effluent from the ultrafiltration membrane system is then pumped into the nanofiltration membrane system, which performs nanofiltration treatment on the mixed alkaline water. The permeate from the nanofiltration membrane system enters a neutralization and equalization tank through pipelines. This tank contains and mixes the permeate from the nanofiltration membrane system and a portion of the dilute acid water. A first pH meter is installed in the neutralization and equalization tank to monitor the pH value of the mixed liquid in real time and feeds the result back to the control system. The prepared solution in the equalization tank is pumped into the first precision filter via a booster pump. The first precision filter intercepts fine particles in the solution. The effluent from the first precision filter is then pumped into a two-stage RO membrane system. This system removes fluoride from the solution through a two-stage reverse osmosis membrane treatment. The concentrate from the two-stage RO membrane system enters the acid water equalization tank through pipes. This tank contains and homogenizes the concentrate, concentrated acid water, and remaining dilute acid water from the two-stage RO membrane system to form a mixed acid water. The acid water equalization tank contains the homogenized mixed acid water, the lime solution prepared in the lime tank, and chlorine... The calcium chloride solution prepared in the calcium chloride tank is pumped into the fluoride recovery crystallization reactor through a booster pump. The second pH meter is installed in the fluoride recovery crystallization reactor. The first pH meter can detect the pH value of the mixed liquid in the fluoride recovery crystallization reactor in real time and feed the detection result back to the control system in real time. The crystal discharge port of the fluoride recovery crystallization reactor is connected to the inlet of the dehydration device through a pipeline. The water outlet of the fluoride recovery crystallization reactor is connected to the subsequent defluorination system through a pipeline. The control system controls the start and stop of each booster pump and the dehydration device, and controls the opening and closing of the crystal discharge port of the fluoride recovery crystallization reactor at regular intervals.

[0025] As a further improvement of the present invention, the dewatering device is a plate and frame filter press, and the filter water of the plate and frame filter press is pumped into the subsequent defluorination system by a booster pump. In addition to the plate and frame filter press, other dewatering equipment can also be used for dewatering.

[0026] As a further improvement of the present invention, a concentrated acid water storage tank, a dilute acid water storage tank, a concentrated alkali water storage tank, a dilute alkali water storage tank, a nanofiltration concentrate tank, and a reverse osmosis permeate tank are also provided. The concentrated acid water storage tank, dilute acid water storage tank, concentrated alkali water storage tank, and dilute alkali water storage tank are respectively used to hold concentrated acid water, dilute acid water, concentrated alkali water, and dilute alkali water. The nanofiltration concentrate tank is used to hold the concentrate water of the nanofiltration membrane system, and the reverse osmosis permeate tank is used to hold the permeate water of the two-stage RO membrane system. The pretreatment system includes a carbon filter tank and a second precision filter. The outlet of the carbon filter tank is connected to the inlet of the second precision filter, and the mixed alkali water can pass through the carbon filter tank and the precision filter sequentially.

[0027] The beneficial effects of this invention are as follows: This invention concentrates large volumes of dilute acidic water with low fluoride content to a certain fluoride concentration via a membrane, then introduces it together with concentrated acidic water into a fluoride recovery crystallization reactor to generate calcium fluoride for resource recovery. Ultimately, only 100 ppm of fluoride is discharged, and a very small amount of fluoride ions enters subsequent treatment devices to generate sludge, significantly reducing the amount of sludge. It recovers 99% of the fluoride element in photovoltaic industry wastewater into high-purity calcium fluoride. This invention can treat all four types of wastewater from the photovoltaic industry and remove a large amount of silicon from traditional calcium fluoride sludge through membrane treatment, obtaining a high-purity calcium fluoride product. Simultaneously, the nanofiltration concentrate after silicon removal can be recycled as water glass. This invention uses dilute alkaline water for pH adjustment of mixed alkaline water, saving acid and alkali usage. Furthermore, the entire process only requires common calcium sources, lime and calcium chloride, resulting in very low reagent costs. The fluoride recovery crystallization reactor of this invention can produce high-purity calcium fluoride crystals, which has certain economic value and realizes the resource recovery and treatment of fluoride. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the present invention;

[0029] Figure 2 This is a comparative process flow diagram. Detailed Implementation

[0030] Example:

[0031] The wastewater indicators of a certain photovoltaic industry are shown in Table 1:

[0032] Wastewater type <![CDATA[Water volume m 3 / d]]> Fluoride ions mg / L silicon mg / L concentrated acid water 131 21537 19 dilute acid water 4587 367 11 concentrated alkaline water 457 34.2 4847 dilute alkaline water 2940 7.58 123

[0033] Table 1

[0034] The specific steps of the perfluoride recovery process for photovoltaic cell production wastewater using the present invention are as follows:

[0035] 1. Collect concentrated acid water, dilute acid water, concentrated alkali water and dilute alkali water into concentrated acid water storage tank, dilute acid water storage tank, concentrated alkali water storage tank and dilute alkali water storage tank respectively, and homogenize the water quality;

[0036] 2. Solid lime is prepared into a 5% lime solution in a lime pool, and solid calcium chloride is prepared into a 15% calcium chloride solution in a calcium chloride pool;

[0037] 3. The concentrated alkaline water in the concentrated alkaline water storage tank and the dilute alkaline water in the dilute alkaline water storage tank are pumped into the alkaline water equalization tank by a booster pump for homogenization, and then pumped into the pretreatment system by a booster pump. The water passes through the carbon filter tank and the second precision filter in sequence. The effluent from the pretreatment system enters the ultrafiltration membrane system. The permeate from the ultrafiltration membrane system enters the nanofiltration membrane system. The concentrate from the ultrafiltration membrane system is returned to the alkaline water equalization tank. The permeate from the nanofiltration membrane system enters the neutralization equalization tank. The concentrate from the nanofiltration membrane system enters the nanofiltration concentrate tank. The solution in the nanofiltration concentrate tank is a high-concentration sodium silicate solution. The nanofiltration recovery rate in this step is above 75%, and the silicon concentration in the nanofiltration permeate is below 20 mg / L.

[0038] 4. Dilute acid water is pumped from the dilute acid water storage tank into the neutralization and conditioning tank, where it mixes with the permeate from the nanofiltration membrane system. The pH of the mixed solution in the neutralization and conditioning tank is controlled within the range of 6-8 by the pH control module of the control system. The solution in the neutralization and conditioning tank is then pumped sequentially into the first precision filter and the two-stage RO membrane system. Finally, the concentrate from the two-stage RO membrane system enters the acid water conditioning tank, and the permeate from the two-stage RO membrane system enters the reverse osmosis permeate tank. In this stage, the fluoride ion concentration in the permeate from the two-stage RO membrane system is below 3 mg / L, and the fluoride ion concentration in the concentrate from the two-stage RO membrane system is above 20,000 mg / L.

[0039] 5. Concentrated acid water and residual dilute acid water are pumped into the acid water conditioning tank through a booster pump, and mixed and homogenized with the concentrated water from the two-stage RO membrane system. After homogenization, the fluoride ion concentration of the solution is above 10000 mg / L. The mixed acid water, lime solution, and calcium chloride solution are pumped into the fluoride recovery crystallization reactor in a certain proportion. At this time, the pH in the fluoride recovery crystallization reactor is controlled between 5.5 and 6 by the pH control module of the control system. The total calcium-fluoride molar ratio added in the reactor is between 0.55 and 0.6. The residence time in the crystallization reactor is 40-60 minutes. The fluoride ion content in the effluent from the fluoride recovery crystallization reactor is about 55 mg / L, and it enters the subsequent defluorination device for treatment until it meets the discharge standards.

[0040] 6. Crystals in the fluorine recovery reactor are periodically discharged into a plate and frame filter press. After dehydration and separation, 12.2 tons of calcium fluoride product are obtained, and the purity of the calcium fluoride product is measured to be 92.1%.

[0041] Comparative example:

[0042] The concentrated acidic wastewater containing fluoride is treated using a primary chemical defluorination and precipitation method. High-purity calcium fluoride sludge is recovered. The effluent enters a comprehensive equalization tank, where it is mixed and adjusted with dilute acid wastewater, dilute alkaline water, and concentrated alkaline water before undergoing a secondary chemical defluorination and precipitation process to achieve the required standards. The specific steps are as follows:

[0043] 1. Concentrated acid water is collected in a fluoride-containing wastewater equalization tank, homogenized, and then introduced into a primary reaction tank along with lime solution. The pH of the solution in the primary reaction tank is controlled within the range of 7-8. After flocculation and sedimentation by adding PAM, it enters the primary sedimentation tank. The sludge at the bottom of the primary sedimentation tank enters the calcium fluoride sludge collection tank. The effluent from the primary sedimentation tank enters the comprehensive equalization tank. The fluoride ion concentration in the effluent from the primary sedimentation tank is within the range of 200-300 mg / L.

[0044] 2. The sludge in the calcium fluoride sludge tank is separated into sludge and water by a dewatering device. The filtrate enters the comprehensive equalization tank, and the resulting solid is calcium fluoride product with a purity of about 87.2%.

[0045] 3. The effluent from the primary sedimentation tank and the concentrated alkaline water, dilute alkaline water and dilute acid water are collected in the comprehensive equalization tank. After equalization and homogenization, they enter the secondary reaction tank and lime solution, calcium chloride solution, PAC solution and PAM solution are added in sequence. The effluent from the comprehensive equalization tank enters the secondary sedimentation tank, the sludge at the bottom of the secondary sedimentation tank enters the low purity sludge tank, and the effluent from the secondary sedimentation tank enters the buffer tank.

[0046] 4. The low-purity sludge in the low-purity sludge tank is separated into sludge filter cake by a dewatering device. The purity of calcium fluoride is 64.2%. The filtrate is returned to the integrated equalization tank, and the sludge filter cake is outsourced for treatment.

[0047] In the comparative example, the calcium fluoride precipitate formed after the fluoride ions in the wastewater react with the lime solution contains a large number of impurities that cannot be recycled and are all converted into sludge. The amount of sludge is very large. In order to ensure that the fluoride ions react fully, an excessive amount of lime, as well as a large amount of flocculant, coagulant and sulfuric acid solution, are required.

[0048] Comparing the embodiments of the present invention with the comparative examples, the present invention has obvious advantages in terms of dosage, crystal yield, and resource utilization effect.

[0049] Table 2 shows a comparison of the processing effects of the embodiments of the present invention with those of conventional technical solutions:

[0050]

[0051] Table 2

[0052] From the two implementation methods, the present invention has obvious advantages in terms of dosage, sludge production, and resource utilization effect.

Claims

1. A process for recovering perfluorinated wastewater from photovoltaic cell manufacturing, characterized in that: The specific steps are as follows: Step one: mix concentrated alkali water and dilute alkali water, and then pump into the pretreatment system to remove suspended solids, organic matter and particulate impurities in the mixed alkali water; Step two: pump the effluent of the pretreatment system into the ultrafiltration membrane system to remove fine particles; Step three: pump the effluent of the ultrafiltration membrane system into the nanofiltration membrane system to intercept silicon and other divalent or higher valence ions, and then pump the effluent of the nanofiltration membrane system into the neutralization and adjustment tank; Step four: pump part of the dilute acid water into the neutralization and adjustment tank to mix with the effluent of the nanofiltration membrane system, and control the pH of the mixed acid and alkali solution to be between 5 and 8; Step five: pump the solution prepared in the neutralization and adjustment tank into the first precision filter to intercept fine particles in the solution; Step six: pump the effluent of the precision filter into the two-stage RO membrane system, pass the effluent through the two-stage reverse osmosis membrane to remove fluoride in the water, and obtain a sodium fluoride solution with a content of more than 2% from the concentrated water side of the two-stage RO membrane system; Step seven: mix the concentrated water of the two-stage RO membrane system, concentrated acid water and remaining dilute acid water to form mixed acid water, and then pump the mixed acid water, lime solution and calcium chloride solution into the fluorine recovery crystallization reactor, control the pH of the liquid in the fluorine recovery crystallization reactor to be between 4 and 7, and control the total calcium fluoride molar ratio in the fluorine recovery crystallization reactor to be between 0.5 and 0.6; Step eight: after the calcium fluoride crystals in the fluorine recovery crystallization reactor are periodically discharged, the calcium fluoride crystals are dehydrated to obtain calcium fluoride crystal products, and the effluent of the fluorine recovery crystallization reactor is discharged after reaching the standard of the defluorination system.

2. The photovoltaic cell production wastewater perfluoro-recovery process according to claim 1, characterized in that: The mass percentage concentration of the lime solution in step seven is 3%-5%, and the mass percentage concentration of the calcium chloride solution is 10-30%.

3. The photovoltaic cell production wastewater perfluoro-recovery process of claim 1, wherein: In step one, the concentrated alkali water and the dilute alkali water are first transported to the alkali water adjustment tank for homogenization treatment, and then the mixed alkali water after the homogenization treatment is pumped into the pretreatment system.

4. The photovoltaic cell production wastewater perfluoro-recovery process according to claim 1 or 3, characterized in that: In step one, the pretreatment system intercepts suspended solids in the mixed alkali water by carbon filtration and removes organic matter by adsorption, and intercepts fine particles in the mixed alkali water by precision filtration to reduce the turbidity of the mixed alkali water.

5. The photovoltaic cell production wastewater perfluoro-recovery process of claim 3, wherein: In step two, the concentrated water of the ultrafiltration membrane system is returned to the alkali water adjustment tank, and in step three, the concentrated water of the nanofiltration membrane system is a high-concentration sodium silicate solution, which is collected in the nanofiltration concentrated water tank and recycled as a raw material for water glass production.

6. The photovoltaic cell production wastewater perfluoro-recovery process of claim 1, wherein: In step six, the effluent of the two-stage RO membrane system is collected in the reverse osmosis effluent tank and used as production end recycled water.

7. The photovoltaic cell production wastewater perfluoro-recovery process of claim 1, wherein: In step seven, the concentrated water of the two-stage RO membrane system, the concentrated acid water and the remaining dilute acid water are mixed and homogenized in the acid water adjustment tank, and then pumped into the fluorine recovery crystallization reactor.

8. A treatment system for use in a process for recovering perfluorinated compounds from photovoltaic cell production wastewater according to any one of claims 1 to 7, characterized in that it comprises: The alkali water adjusting tank is used for containing and uniformly mixing concentrated alkali water and dilute alkali water, and a lifting pump can pump the mixed alkali water after uniform treatment in the alkali water adjusting tank into the pretreatment system; the pretreatment system can remove suspended solids, organic matter and particulate impurities in the mixed alkali water; the water outlet of the pretreatment system can be pumped into the ultrafiltration membrane system through a lifting pump; the water outlet of the ultrafiltration membrane system can be pumped into the nanofiltration membrane system through a lifting pump; the nanofiltration membrane system can perform nanofiltration treatment on the mixed alkali water; the water produced by the nanofiltration membrane system enters the neutralization adjusting tank through a pipeline; the neutralization adjusting tank can contain and uniformly mix the water produced by the nanofiltration membrane system and part of the dilute acid water; a first pH meter is installed in the neutralization adjusting tank; the first pH meter can detect the pH value of the mixed liquid in the neutralization adjusting tank in real time and feed back the detection result to the control system in real time; the prepared solution in the neutralization adjusting tank is pumped into the first precision filter through a lifting pump; the first precision filter can intercept small particles in the solution; the water outlet of the first precision filter is pumped into the two-stage RO membrane system through a lifting pump; the two-stage RO membrane system can remove fluoride in the solution through a two-stage reverse osmosis membrane; the concentrated water of the two-stage RO membrane system enters the acid water adjusting tank through a pipeline; the acid water adjusting tank can contain and uniformly mix the concentrated water of the two-stage RO membrane system, concentrated acid water and residual dilute acid water to form mixed acid water; the uniformly mixed acid water in the acid water adjusting tank, the prepared lime solution in the lime tank and the prepared calcium chloride solution in the calcium chloride tank are respectively pumped into the fluoride recovery crystallization reactor through lifting pumps; a second pH meter is installed in the fluoride recovery crystallization reactor; the first pH meter can detect the pH value of the mixed liquid in the fluoride recovery crystallization reactor in real time and feed back the detection result to the control system in real time; the crystal discharge port of the fluoride recovery crystallization reactor is communicated with the dehydration device inlet through a pipeline; the water outlet of the fluoride recovery crystallization reactor is communicated with the subsequent defluorination system through a pipeline; the control system controls the start and stop of each lifting pump and the dehydration device, and controls the opening and closing of the crystal discharge port of the fluoride recovery crystallization reactor.

9. The photovoltaic cell production wastewater perfluoro-recovery treatment system according to claim 8, characterized in that: The dehydration device is a plate and frame filter press, and the filter pressing water of the plate and frame filter press is pumped into the subsequent defluorination system through a lifting pump.

10. The photovoltaic cell production wastewater perfluoro-recovery treatment system according to claim 8, characterized in that: A concentrated acid water storage tank, a dilute acid water storage tank, a concentrated alkali water storage tank, a dilute alkali water storage tank, a nanofiltration concentrated water tank and a reverse osmosis water tank are further provided; the concentrated acid water storage tank, the dilute acid water storage tank, the concentrated alkali water storage tank and the dilute alkali water storage tank are respectively used for containing concentrated acid water, dilute acid water, concentrated alkali water and dilute alkali water; the nanofiltration concentrated water tank is used for containing the concentrated water of the nanofiltration membrane system; the reverse osmosis water tank is used for containing the water produced by the two-stage RO membrane system; the pretreatment system comprises a carbon filter tank and a second precision filter; the water outlet of the carbon filter tank is communicated with the water inlet of the second precision filter; and the mixed alkali water can sequentially pass through the carbon filter tank and the precision filter.

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