Treatment process for photovoltaic cell production wastewater

Abstract

The present invention relates to the technical field of industrial wastewater treatment. Disclosed is a treatment process for photovoltaic cell production wastewater. The process comprises the following steps: treating a dilute acid or a dilute alkali by means of a reclaimed water recovery membrane system, so as to obtain first produced water and reclaimed water concentrated water; treating concentrated acid wastewater and the reclaimed water concentrated water by means of a fluorine-calcium crystallization system, so as to obtain defluorinated concentrated water and calcium fluoride crystals; treating RO concentrated water and the defluorinated concentrated water by means of a hardness-removal recycling system, so as to obtain hardness-removed concentrated water and second produced water; treating concentrated alkali wastewater by means of an alkali recovery membrane system, so as to obtain a purified alkali and alkali-removed concentrated water; and treating the hardness-removed concentrated water and the alkali-removed concentrated water by means of a comprehensive physicochemical system, and then sequentially treating same by means of a high-concentration membrane system and a zero-discharge crystallization system, so as to obtain solid waste. The treatment process for photovoltaic cell production wastewater provided in the present application achieves an economical and feasible zero-emission solution.

Description

A treatment process for photovoltaic cell production wastewater Technical Field

[0001] The present invention relates to the technical field of industrial wastewater treatment, and in particular to a treatment process for photovoltaic cell production wastewater. Background Art

[0002] my country's photovoltaic industry ranks first in the world in production volume. Cell production is the core process in the entire photovoltaic industry chain. Micron-thin silicon wafers undergo a series of chemical etching, soaking, chemical deposition, cleaning, and printing steps to become photovoltaic cells capable of photoelectric conversion. The photovoltaic cell production process uses large quantities of chemicals such as hydrofluoric acid, liquid caustic soda, ammonia, and hydrogen peroxide. These chemicals do not enter the finished cell product but are discharged as wastewater during cleaning. The wastewater from photovoltaic cell production bases can be categorized as fluorine-containing dilute acid, dilute alkali, concentrated acid, and concentrated alkali wastewater; exhaust cleaning wastewater containing particulate matter; silane wastewater containing ammonia; and domestic sewage and reverse osmosis (RO) concentrate containing organic matter and salt. These wastewater sources are complex, characterized by numerous pollutants, fluctuating water quality, and uneven water supply. The typical treatment method involves mixing all wastewater together and then adding a large amount of chemicals to treat it. However, due to the varying pH levels and pollutant types of various wastewaters, the treatment process is cumbersome, and the results are often less than ideal, failing to meet comprehensive emission requirements. Zero-emission treatment pathways also exist in the water treatment field, but their direct application to photovoltaic wastewater would incur prohibitive costs, making them uneconomical.

[0003] Currently, photovoltaic wastewater treatment mostly relies on a combination of physical, chemical, and biochemical treatment. Physical-chemical systems use chemicals (primarily calcium salts) to remove fluoride ions from the wastewater, while biochemical systems use biological denitrification (A / O) or anaerobic ammonium oxidation (ANAMOX) processes to remove ammonia nitrogen and chemical oxygen demand (COD) from the wastewater, achieving standard discharge. Traditional treatment processes require large chemical dosages, lengthy process flows, and require significant floor space. Most importantly, the treated water can only be discharged as wastewater to downstream sewage treatment plants, failing to achieve resource recovery. The hundreds of millions of tons of water discharged annually from this industry pose a significant challenge to my country, a country with relatively uneven water resources. Therefore, exploring feasible solutions that can address the high volume of wastewater discharged while also generating economic value for businesses and society is a critical area of ​​innovation and breakthroughs in the photovoltaic industry. Summary of the Invention

[0004] The purpose of the present invention is to provide a treatment process for photovoltaic cell production wastewater to solve the following technical problems:

[0005] The existing photovoltaic cell production wastewater treatment process has problems such as poor wastewater treatment effect, large equipment production area, high cost and waste of water resources.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A process for treating photovoltaic cell production wastewater comprises at least the following steps:

[0008] The diluted acid and alkali are treated by the reclaimed water recovery membrane system to obtain the first product water and reclaimed water concentrate;

[0009] The concentrated acid wastewater and the concentrated water are treated by a fluoride-calcium crystallization system to obtain defluorinated concentrated water and calcium fluoride crystals;

[0010] The RO concentrated water and the defluorinated concentrated water are treated by a de-hardening and recycling system to obtain de-hardening concentrated water and secondary produced water;

[0011] The concentrated alkali wastewater is treated by an alkali recovery membrane system to obtain purified alkali and dealkali concentrated water;

[0012] The de-hardened concentrated water and the de-alkali concentrated water are treated by a comprehensive physical and chemical system, and then sequentially treated by a high-concentration membrane system and a zero-discharge crystallization system to obtain solid waste.

[0013] As a further solution of the present invention: the reclaimed water recovery membrane system treatment includes using a fluorine-silicon concentration membrane to concentrate the dilute acid and alkali, and the content of the first produced water accounts for at least 50% of the content of the dilute acid and alkali.

[0014] As a further solution of the present invention: the fluorine-silicon concentrating membrane includes at least a first-stage membrane, a second-stage membrane and a third-stage membrane, the first-stage membrane includes at least one of sulfonated polysulfone, polysulfone or polyethersulfone, and the filtration pore size of the first-stage membrane is 10-20nm.

[0015] As a further solution of the present invention: a hydrophilic layer is provided on the second-stage membrane and the third-stage membrane, and the hydrophilic layer is a polyvinyl alcohol coating.

[0016] As a further solution of the present invention: the fluorine-calcium crystallization system treatment at least includes adding a crystallizing agent to the water in the fluorine-calcium crystallization system, generating the calcium fluoride crystals and the defluoridated concentrated water through solid-liquid separation, the crystallizing agent at least includes calcium hydroxide and calcium chloride, and the molar ratio of the calcium concentration in the crystallizing agent to the fluorine concentration in the wastewater introduced into the fluorine-calcium crystallization system is controlled between 0.6:1 and 1.5:1.

[0017] As a further embodiment of the present invention, the purity of the calcium fluoride crystals is greater than 90%, and the fluorine content in the defluorination concentrated water is less than 100 ppm.

[0018] As a further solution of the present invention: A photovoltaic cell production wastewater treatment process according to claim 1 is characterized in that the de-hardening and reuse system treatment includes at least using one or more of an ultrafiltration membrane, a calcium removal nanofiltration membrane and a fluorine-silicon removal nanofiltration membrane to filter and separate the RO concentrated water and the defluorination concentrated water, and returning part of the obtained de-hardening concentrated water to the fluorine-calcium crystallization system.

[0019] As a further solution of the present invention: the content of the second produced water accounts for at least 50% of the content of the RO concentrated water and the defluorination concentrated water, and part of the dehardening concentrated water refluxed to the fluorine-calcium crystallization system is fluorine-containing concentrated water, and the content of the fluorine-containing concentrated water accounts for at least 10-50% of the content of the dehardening concentrated water.

[0020] As a further solution of the present invention: the alkali recovery membrane system treatment at least includes using an alkali-resistant nanofiltration membrane to filter and recover the concentrated alkali wastewater, the content of the purified alkali accounts for at least 50% of the concentrated alkali wastewater, and the sodium hydroxide content in the purified alkali is not less than 0.1%.

[0021] As a further solution of the present invention: the alkali recovery membrane system includes an alkali-resistant nanofiltration membrane, an alkali-resistant layer is provided on the alkali-resistant nanofiltration membrane, and the alkali-resistant layer at least includes a hydrophilic furfuryl alcohol resin.

[0022] As a further solution of the present invention: the integrated physicochemical system treatment at least includes adding a precipitant to water in the integrated physicochemical system, generating precipitated impurities and sodium salt concentrated water through solid-liquid separation, and the precipitant includes at least sodium carbonate and magnesium chloride.

[0023] As a further solution of the present invention: a precipitation tank is provided in the integrated physicochemical system, and the precipitated impurities at least include silicon-containing or calcium-containing impurities.

[0024] As a further solution of the present invention: the high-concentration membrane system treatment at least includes using a first membrane unit and a second membrane unit to concentrate and filter the sodium salt concentrated water to obtain concentrated concentrated water and third product water.

[0025] As a further solution of the present invention: the concentration of the concentrated brine is at least 80 g / L, and the content of the third produced water accounts for at least 50% of the content of the sodium salt brine.

[0026] As a further solution of the present invention: the first membrane unit is a high desalination membrane unit, and the second membrane unit is a high permeability membrane unit.

[0027] As a further solution of the present invention: the zero-discharge crystallization system treatment at least includes evaporating and crystallizing the concentrated water to obtain the solid waste and the fourth produced water.

[0028] As a further solution of the present invention: the content of the fourth produced water accounts for at least 90% of the content of the concentrated water.

[0029] Beneficial effects of the present invention:

[0030] The treatment process for photovoltaic cell production wastewater proposed in this application separates the main pollutants by quality, stage and outlet for treatment, so as to achieve the purpose of fluorine and alkali recovery and water reuse. This application is different from the common treatment process in which a large number of treatment tanks such as reaction tanks, sedimentation tanks or flocculation tanks are set up. It sets up a reclaimed water recovery membrane system, a fluorine calcium crystallization system, a de-hardening and reuse system, an alkali recovery membrane system, a comprehensive physical and chemical system, a high-concentration membrane system and a zero-discharge crystallization system. The photovoltaic cell production wastewater is divided into RO concentrated water, dilute acid and dilute alkali, concentrated acid wastewater and concentrated alkali wastewater, which enter different systems for treatment and reuse, reducing the floor space of the treatment equipment. No mud is generated during the wastewater treatment process. Through the cooperation between the various systems, material separation and recovery are achieved, turning waste into treasure. Moreover, through the coupling process of special membranes and fluidized bed crystallization, the wastewater recovery rate can reach 80-90%, fully recovering water resources. While treating wastewater, the amount of pure water produced is increased, the amount of tap water purchased by the enterprise is reduced, the reuse of wastewater is achieved and the cost of purchasing tap water for the enterprise is reduced.

[0031] The reclaimed water reuse membrane system set up in this application is provided with a first-stage membrane, a second-stage membrane and a third-stage membrane. The first-stage membrane intercepts fluorosilicate solids and colloidal silicon, and the second-stage membrane and the third-stage membrane intercept ionic pollutants, thereby achieving a water reuse rate of more than 80%. The first-stage membrane is modified with high hydrophilicity to control the filter pores at 10-20nm, which improves the interception efficiency of the first-stage membrane for tiny particles or colloids. The second-stage membrane and the third-stage membrane are both modified with high hydrophilicity, have a hydrophilic and anti-fouling effect, and enhance the tolerance to partially analyzed silicon pollutants. This application concentrates dilute acids and dilute alkalis through the reclaimed water reuse membrane system to obtain first produced water and reclaimed water concentrate, with a concentration of 80-90%, that is, 7-10 times the concentration of pollutants, achieving further purification of reclaimed water, reducing the amount of water entering the subsequent system, and thus reducing the removal cost of the subsequent system. At the same time, the produced water can be used as the water inlet of the enterprise's power workshop, reducing the enterprise's purchase of tap water and saving costs for the enterprise.

[0032] This application utilizes a calcium fluoride crystallization system. Reclaimed water concentrate obtained through a reclaimed water reuse membrane system, fluoride-containing concentrate returned from a de-hardening and reuse system, and concentrated acid wastewater are sprayed or injected into the crystallization tank of the calcium fluoride crystallization system. By adding a crystallizing agent such as calcium hydroxide or calcium chloride, and controlling the molar ratio of calcium concentration in the crystallizer to fluoride concentration in the wastewater to between 0.6:1 and 1.5:1, the calcium ions react with fluoride ions to form water-insoluble calcium fluoride crystals (fluorite), thereby removing the majority of the fluoride ions. After treatment in the calcium fluoride crystallization system, defluorinated concentrate and calcium fluoride crystals are obtained. The fluoride content in the defluorinated concentrate is less than 100 ppm, resulting in a high fluoride removal efficiency of over 95%. This high fluoride removal efficiency is maintained even after long-term operation. The resulting calcium fluoride crystals have a purity exceeding 90%. The produced calcium fluoride will be sold as a product, achieving efficient waste disposal and generating economic benefits for the enterprise. In the calcium fluoride crystallization system provided in the present application, water flow distribution is improved, the supersaturation of calcium fluoride in the reactor is rationally regulated, and fluoride ions are secondary concentrated using a de-hardness reuse system and a reclaimed water reuse membrane system before being recycled into the crystallization process, thereby achieving technical coupling and reducing the problems of large reagent addition amounts and large equipment footprint caused by one-step fluoride removal.

[0033] The present application sets up a de-hardening and recycling system, and introduces RO concentrated water and defluorinated concentrated water into the de-hardening and recycling system. The de-hardening and recycling system is equipped with an ultrafiltration membrane, a decalcification nanofiltration membrane, and a defluorination silicon nanofiltration membrane. The defluorination concentrated water and RO concentrated water after being treated by the calcium fluoride crystallization system contain a large amount of calcium ions, dissolved silicon, total silicon, and a small amount of fluoride ions. The impurity ions are separated by filtration through a multi-layer membrane to obtain de-hardening concentrated water and a second produced water. The de-hardening concentrated water contains 10-50% fluoride-containing concentrated water. The fluoride-containing concentrated water is returned to the calcium fluoride crystallization system for treatment. The remaining de-hardening concentrated water enters the next system. The second produced water can be reused, and the content of the second produced water is not less than 50% of the content of the RO concentrated water and defluorination concentrated water introduced into the de-hardening and recycling system. The RO concentrated water and defluorination concentrated water are passed through the ultrafiltration membrane to remove impurities such as chloride ions, the decalcification nanofiltration membrane to remove impurities such as hard calcium remaining after treatment by the calcium fluoride crystallization system, and the defluorination silicon nanofiltration membrane to remove impurities such as fluoride and calcium. By setting up multiple layers of filter membranes, impurities can be removed and concentrated step by step, avoiding the problems of membrane clogging or wear and tear caused by setting up only a single layer of filter membrane, and improving the de-hardening efficiency.

[0034] The present application sets up an alkali recovery membrane system, and concentrated alkaline wastewater enters this system for treatment and alkali removal. The present application also performs alkali-resistant modification on traditional nanofiltration membranes, which can be used for a long time in an alkaline solution environment with a pH exceeding 12. The alkali recovery membrane system set up in the present application separates pollutants and purified alkali in concentrated alkaline wastewater, and the content of purified alkali is not less than 50% of the content of concentrated alkaline wastewater introduced into the alkali recovery system, and the content of sodium hydroxide in the purified alkali is not less than 0.1%. The recycled alkali is used in the treatment process, which can save the purchase cost of liquid alkali for the enterprise. At the same time, the alkali recovery membrane system set up in the present application can also remove impurities such as fluorine and silicon in concentrated alkaline wastewater, and after the concentrated alkaline wastewater is filtered twice by the alkali recovery membrane system, the fluoride ion concentration can be reduced to 1ppm, and the silicon dioxide content can be reduced to 200ppm.

[0035] This application utilizes a comprehensive physicochemical system, including a sedimentation tank. The de-hardened and de-alkali concentrated water obtained after treatment in the aforementioned systems is introduced into this system for further treatment. Precipitants such as sodium carbonate and magnesium chloride are added for further decalcification and desiliconization, respectively, removing impurities other than sodium salts from the concentrated water to produce sodium salt concentrated water. This comprehensive physicochemical system reduces the calcium and silicon content in the concentrated water, preventing these two elements from causing scaling during subsequent membrane system operation, leading to increased backwash frequency, membrane damage, and increased operating costs.

[0036] This application also provides a high-concentration membrane system. After sodium salt concentrate has been treated by the integrated physicochemical system, it is introduced into the high-concentration membrane system for concentration, producing concentrated concentrate and tertiary product water. The high-concentration membrane system comprises a first membrane unit and a second membrane unit. The first membrane unit is a high-desalination membrane unit, utilizing high-desalination and pollution-resistant membrane elements, which perform the initial concentration of the concentrate. When the osmotic pressure reaches extremely high levels and the first membrane unit is unable to effectively produce water, the water enters the second membrane unit. The second membrane unit is a high-permeability membrane unit, utilizing loose-type membrane elements. This allows for the partial ion permeation of the membrane layer, balancing the osmotic pressure across the membrane and slowing the accumulation of osmotic pressure on the membrane surface. The permeate from the second membrane unit can then be returned to the influent to balance the ion concentration of the incoming water. Through the combined process of the first and second membrane units, the concentration of the second membrane unit concentrate, i.e., the concentrated concentrate, reaches 80 g / L. The tertiary product water comprises at least 50% of the sodium salt concentrate introduced into the high-concentration membrane system, achieving maximum water volume reduction. This further reduces the water volume before evaporation, reducing subsequent evaporation costs. In this system, the water production channel is coated with epoxy material. By using the epoxy-coated dense water production channel as a key auxiliary material for high-pressure membrane products, the problem of dense bonding between the membrane and the channel under high-pressure environment is improved.

[0037] The present application is also provided with a zero-discharge crystallization system. The concentrated water treated by the high-concentration membrane system enters the zero-discharge crystallization system. After passing through the evaporator, the fourth produced water and solid waste are generated. The fourth produced water is used for reuse, and the content of the fourth produced water is at least 90% of the concentrated water entering the zero-discharge crystallization system. The solid waste needs to be transported out for treatment to complete the treatment of photovoltaic cell production wastewater.

[0038] In summary, the present invention treats the production wastewater and domestic sewage in the photovoltaic production area through reverse osmosis membranes and nanofiltration membranes with different characteristics. Compared with traditional treatment pools, the floor space is greatly reduced, and zero discharge is achieved through the coordination and combination of seven systems, which enables the reuse of wastewater for enterprises, saves the consumption of tap water, the addition of reagents and the consumption of electricity, and maximizes the cost reduction and efficiency improvement for enterprises. The seven systems in this application cooperate with each other, rather than being completed by a single system as in traditional processes. They can be adjusted in real time according to local conditions based on the huge changes in water quality and water volume of photovoltaic enterprises, thereby improving the efficiency of wastewater treatment. The coordination of multiple systems can reuse valuable substances in wastewater separately, such as calcium fluoride produced in the fluorine calcium crystallization system, purified alkali produced in the alkali recovery membrane system, and water reuse in the reclaimed water reuse membrane system, de-hardening reuse system, high-concentration water membrane system and zero-discharge crystallization system, which greatly reduces the production cost of the enterprise. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. 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 creative work.

[0040] FIG1 is a flow chart of a treatment process for photovoltaic cell production wastewater according to an embodiment.

[0041] Figure 2 is a flow chart of the traditional treatment process for photovoltaic cell production wastewater. DETAILED DESCRIPTION

[0042] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0043] The treatment process of photovoltaic cell production wastewater includes the following steps:

[0044] As shown in Figure 1, dilute acid and dilute alkali are introduced into the reclaimed water recovery membrane system, and the reclaimed water recovery membrane system is provided with a first-stage membrane, a second-stage membrane and a third-stage membrane. In this embodiment, the first-stage membrane includes sulfonated polysulfone, and the filtration pore size of the first-stage membrane is 10-20nm. The second-stage membrane and the third-stage membrane are provided with a polyvinyl alcohol coating. After being processed in sequence by the first-stage membrane, the second-stage membrane and the third-stage membrane of the reclaimed water recovery membrane system, reclaimed water concentrate and first produced water are obtained. In this embodiment, the content of the reused first produced water is 80% of the content of the dilute acid and dilute alkali, thereby achieving the concentration of pollution factors.

[0045] As shown in Figure 1, concentrated acid wastewater, concentrated reclaimed water treated by the reclaimed water recovery membrane system, and fluorine-containing concentrated water returned by the de-hardening and reuse system are sprayed or injected into the crystallization tank of the fluorine-calcium crystallization system for treatment. Crystallizing agents such as calcium hydroxide or calcium chloride are added to the concentrated water. The molar ratio of calcium concentration in the crystallizing agent to fluorine concentration in the concentrated acid wastewater, reclaimed water, and fluorine-containing concentrated water is controlled to be between 0.6:1 and 1.5:1. Calcium fluoride crystals that are insoluble in water are formed by calcium ions and fluoride ions. Crystallization is induced by crystal nuclei, which accelerates the precipitation and outflow of calcium fluoride crystals, removes most of the fluoride ions, and the defluorinated concentrated water is introduced into the next system.

[0046] As shown in FIG1 , RO concentrated water and defluorinated concentrated water treated by the fluorine-calcium crystallization system are introduced into the de-hardening and reuse system for treatment. Impurities are removed step by step through the ultrafiltration membrane, decalcification nanofiltration membrane, and defluorination silicon nanofiltration membrane provided in the de-hardening and reuse system to achieve separation of calcium ions, thereby obtaining de-hardening concentrated water and second produced water. In the second produced water, 30% of the fluorine-containing concentrated water generated in the de-hardening concentrated water is introduced into the fluorine-calcium crystallization system for defluorination, and the remaining de-hardening concentrated water is introduced into the integrated physical and chemical system for treatment. In this embodiment, the content of the second produced water for reuse is 55% of the content of the concentrated water introduced into the de-hardening and reuse system.

[0047] As shown in Figure 1, concentrated alkaline wastewater is introduced into an alkali recovery membrane system for treatment. In this embodiment, an alkali-resistant coating of a hydrophilic furfuryl alcohol resin is formed on the nanofiltration membrane in the alkali recovery membrane system. The nanofiltration membrane containing the alkali-resistant coating filters the concentrated alkaline wastewater to obtain produced water containing purified alkali and dealkali concentrated water. The produced water containing purified alkali is recycled and the dealkali concentrated water is introduced into the next system. In this embodiment, the content of purified alkali produced accounts for 50% of the concentrated alkaline wastewater, and the content of sodium hydroxide in the purified alkali is not less than 0.1%.

[0048] As shown in Figure 1, the de-hardened concentrated water and de-alkali concentrated water treated by the de-hardening and reuse system are introduced into the integrated physical and chemical system for treatment. The concentrated water is injected into the sedimentation tank and further decalcified and desiliconized by adding sodium carbonate and magnesium chloride, respectively, so that the sodium salt concentrated water containing only sodium salt enters the next system for treatment.

[0049] As shown in Figure 1, the sodium salt concentrate after being treated by the integrated physical and chemical system is introduced into the high-concentration membrane system. The first membrane unit in the high-concentration membrane system first concentrates the concentrate. When the concentrate reaches an extremely high osmotic pressure and the first membrane unit cannot effectively produce water, the concentrate will enter the second membrane unit. The second membrane unit further concentrates the concentrate. The second membrane unit can control some ions to pass through the membrane layer, balance the osmotic pressure on both sides of the membrane, and slow down the accumulation of osmotic pressure on the membrane surface. The permeate of the second membrane unit can return to the influent to balance the ion concentration of the incoming water, and finally obtain concentrated concentrate and tertiary produced water. The concentrated concentrate enters the next system, and the tertiary produced water is reused. In this embodiment, the measured concentration of the concentrate reaches 90g / L, and the content of the tertiary produced water accounts for 60% of the content of the sodium salt concentrate flowing into the high-concentration membrane system.

[0050] As shown in FIG1 , the concentrated brine produced after high-concentration by the high-concentration membrane system is introduced into a zero-discharge crystallization system, and is evaporated and crystallized by an evaporator. The fourth-product water produced by evaporation is reused, and the solid waste produced by evaporation is transported for treatment, thereby completing the zero-discharge treatment of photovoltaic cell production wastewater. In this embodiment, the content of the reused fourth-product water accounts for 90% of the content of the concentrated brine.

[0051] The conventional treatment process for photovoltaic cell production wastewater includes at least the following steps:

[0052] As shown in FIG2 , concentrated acid wastewater, concentrated alkali wastewater, dilute acid wastewater and dilute alkali wastewater are collected in their respective wastewater collection tanks and added to a neutralization and regulating tank for uniform mixing.

[0053] As shown in Figure 2, the effluent from the concentrated acid wastewater collection tank and the effluent from the concentrated alkaline wastewater collection tank are passed into a pH adjustment tank to adjust the pH to 8-9. The water is then passed into the primary reaction tank, where calcium hydroxide and calcium chloride are added to form a precipitate. Polyaluminium chloride and polyacrylamide are then added to react to form alum flocs, and the effluent is then discharged to the primary sedimentation tank. The mud and water are separated in the primary sedimentation tank, and the upper layer of wastewater enters the secondary reaction tank, where the fluoride ion content is reduced to below 80 mg / L. The lower layer of sludge enters the sludge tank. Calcium hydroxide and calcium chloride are added to the wastewater in the secondary reaction tank to form a precipitate. Polyaluminium chloride and polyacrylamide are then added to react to form alum flocs, and the effluent is then discharged to the secondary sedimentation tank. The mud and water are separated in the secondary sedimentation tank, and liquid caustic soda is added to the upper layer of the clear liquid to adjust the pH to 7-9. The effluent is then discharged to a discharge tank, where the fluoride ion content is reduced to below 5 mg / L. The lower layer of sludge enters the sludge tank. The sludge collected in the sludge tank is concentrated and passed into a sludge filter press. Cationic polyacrylamide is added, mixed, and filtered. The filtrate flows by gravity into the primary reaction tank, and the mud cake is transported for treatment.

[0054] As shown in FIG2 , the effluent from the dilute acid wastewater collection pool and the effluent from the dilute alkali wastewater collection pool are introduced into a pH adjustment pool to adjust the pH to 7-9. The subsequent treatment process is the same as the above-mentioned treatment process for concentrated acid and concentrated alkali.

[0055] As shown in Figure 2, the ammonia nitrogen wastewater is passed into the biochemical blending tank, a carbon source is added for denitrification reaction, and then the effluent is sent to the anaerobic ammonia oxidation system, sodium bicarbonate is added for A / O biochemical reaction, and the effluent after the reaction is sent to the secondary sedimentation tank for mud-water separation. The effluent from the secondary sedimentation tank is sent to the biochemical effluent tank, and after treatment in the biochemical effluent tank, the effluent is sent to the discharge tank. The sludge in the secondary sedimentation tank is regularly returned to the denitrification tank and the anaerobic ammonia oxidation system to supplement the bacteria. The remaining sludge enters the biochemical sludge storage tank, cationic polyacrylamide is added to the mixture, and then filtered. The filtrate flows into the corresponding water distribution tank by gravity, and the mud cake is transported out for treatment, completing the traditional treatment process of photovoltaic cell production wastewater.

[0056] The water quality and water quantity of photovoltaic cell production wastewater to be treated in the examples and comparative examples are shown in Table 1 below:

[0057] Table 1 Water quality and water quantity of wastewater to be treated in Examples and Comparative Examples

[0058] Dilute acid Dilute alkali Concentrated acid Concentrated alkali PH 2.91 11.64 2.93 13.25 F2 14.08 22.32 45 39.72 17.21 TDS 119 7.54 100 8.78 182 17.26 150 43.64 Total silicon (as Si) 37.77 30 9.86 45 7.54 80 0 0.00 Dissolved silicon (as SiO2) 18.98 230.76 418.68 67 66.88 Cl 44.44 15.07 20 44.92 7.80 Water content (m 3 / d)600033001200500

[0059] The water quality and water quantity of the treated wastewater in the examples and comparative examples are shown in Table 2 below:

[0060] Table 2 Water quality of the produced water in the embodiment and the water in the discharge pool in the comparative example

[0061] Example Comparative Example Conductivity (us / cm) ≤20 ≤50 PH6-86-9 Fluoride ion (mg / L) ≤1 ≤5 Silicon (mg / L) ≤2 ≤10

[0062] As can be seen from Tables 1 and 2, the photovoltaic cell production wastewater treatment process provided in the embodiment of the present application achieves zero discharge of the production wastewater after treatment, and a large amount of water is generated during the treatment process, including the first water, the second water, the third water and the fourth water, which are used for reuse, saving water resources, and can also produce purified alkali and calcium fluoride crystals, greatly reducing the production cost of the enterprise. In the comparative example, the photovoltaic cell production wastewater is treated by the traditional wastewater treatment process, and the wastewater treatment effect is far inferior to the treatment effect of the sewage treatment process provided in this application, and the water production reuse cannot be achieved. In addition, by the photovoltaic cell production wastewater treatment process provided in this embodiment, only the first unit of the reclaimed water reuse is used, which can achieve a 46% reduction in tap water consumption for 10,000 batteries, a 15% reduction in the amount of crystallizer added, a 10% reduction in tap water costs, and a 50% reduction in wastewater treatment load. After all the process units are implemented, the battery factory achieves zero wastewater discharge.

[0063] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A process for treating photovoltaic cell production wastewater, characterized in that: At least the following steps are included: The diluted acid and alkali are treated by the reclaimed water recovery membrane system to obtain the first product water and reclaimed water concentrate; The concentrated acid wastewater and the concentrated water are treated by a fluoride-calcium crystallization system to obtain defluorinated concentrated water and calcium fluoride crystals; The RO concentrated water and the defluorinated concentrated water are treated by a de-hardening and recycling system to obtain de-hardening concentrated water and secondary produced water; The concentrated alkali wastewater is treated by an alkali recovery membrane system to obtain purified alkali and dealkali concentrated water; The de-hardened concentrated water and the de-alkali concentrated water are treated by a comprehensive physical and chemical system, and then sequentially treated by a high-concentration membrane system and a zero-discharge crystallization system to obtain solid waste.

2. The photovoltaic cell production wastewater treatment process according to claim 1, characterized in that: The reclaimed water recovery membrane system treatment includes using a fluorine-silicon concentration membrane to concentrate the dilute acid and dilute alkali, and the content of the first produced water accounts for at least 50% of the content of the dilute acid and dilute alkali.

3. The photovoltaic cell production wastewater treatment process according to claim 2, characterized in that: The fluorine-silicon concentrating membrane comprises at least a first-stage membrane, a second-stage membrane and a third-stage membrane. The first-stage membrane comprises at least one of sulfonated polysulfone, polysulfone or polyethersulfone. The filtration pore size of the first-stage membrane is 10-20 nm.

4. The photovoltaic cell production wastewater treatment process according to claim 3, characterized in that: A hydrophilic layer is provided on the second-stage membrane and the third-stage membrane, and the hydrophilic layer is a polyvinyl alcohol coating.

5. The photovoltaic cell production wastewater treatment process according to claim 1, characterized in that: The fluorine-calcium crystallization system treatment at least includes adding a crystallizing agent to water in the fluorine-calcium crystallization system, generating the calcium fluoride crystals and the defluoridated concentrated water through solid-liquid separation, the crystallizing agent at least includes calcium hydroxide and calcium chloride, and the molar ratio of the calcium concentration in the crystallizing agent to the fluorine concentration in the wastewater introduced into the fluorine-calcium crystallization system is controlled between 0.6:1 and 1.5:

1.

6. A photovoltaic cell production wastewater treatment process according to claim 5, characterized in that: The purity of the calcium fluoride crystals is greater than 90%, and the fluorine content in the defluoridation concentrated water is less than 100 ppm.

7. The photovoltaic cell production wastewater treatment process according to claim 1, characterized in that: The de-hardening and reuse system treatment includes at least using one or more of an ultrafiltration membrane, a calcium removal nanofiltration membrane, and a fluorine-silicon removal nanofiltration membrane to filter and separate the RO concentrated water and the defluoridation concentrated water, and returning part of the obtained de-hardening concentrated water to the fluorine-calcium crystallization system.

8. The photovoltaic cell production wastewater treatment process according to claim 7, characterized in that: The content of the second produced water accounts for at least 50% of the content of the RO concentrated water and the defluorination concentrated water, and part of the dehardening concentrated water returned to the fluorine-calcium crystallization system is fluorine-containing concentrated water, and the content of the fluorine-containing concentrated water accounts for at least 10-50% of the content of the dehardening concentrated water.

9. The photovoltaic cell production wastewater treatment process according to claim 1, characterized in that: The alkali recovery membrane system treatment at least includes using an alkali-resistant nanofiltration membrane to filter and recover the concentrated alkali wastewater, the content of the purified alkali accounts for at least 50% of the concentrated alkali wastewater, and the sodium hydroxide content in the purified alkali is not less than 0.1%.

10. The photovoltaic cell production wastewater treatment process according to claim 9, characterized in that: The alkali recovery membrane system comprises an alkali-resistant nanofiltration membrane, an alkali-resistant layer is provided on the alkali-resistant nanofiltration membrane, and the alkali-resistant layer comprises at least a hydrophilic furfuryl alcohol resin.

11. The photovoltaic cell production wastewater treatment process according to claim 1, characterized in that: The integrated physicochemical system treatment at least includes adding a precipitant to water in the integrated physicochemical system, generating precipitated impurities and sodium salt concentrated water through solid-liquid separation, and the precipitant at least includes sodium carbonate and magnesium chloride.

12. A photovoltaic cell production wastewater treatment process according to claim 11, characterized in that: The integrated physicochemical system is provided with a sedimentation tank, and the precipitated impurities at least include silicon-containing or calcium-containing impurities.

13. The photovoltaic cell production wastewater treatment process according to claim 11, characterized in that: The high-concentration membrane system treatment at least includes using a first membrane unit and a second membrane unit to concentrate and filter the sodium salt concentrated water to obtain concentrated concentrated water and third product water.

14. A photovoltaic cell production wastewater treatment process according to claim 13, characterized in that: The concentration of the concentrated brine is at least 80 g / L, and the content of the third produced water is at least 50% of the content of the sodium salt brine.

15. The photovoltaic cell production wastewater treatment process according to claim 13, characterized in that: The first membrane unit is a high desalination membrane unit, and the second membrane unit is a high permeability membrane unit.

16. The photovoltaic cell production wastewater treatment process according to claim 13, characterized in that: The zero-discharge crystallization system treatment at least includes evaporating and crystallizing the concentrated water to obtain the solid waste and the fourth produced water.

17. A photovoltaic cell production wastewater treatment process according to claim 16, characterized in that: The content of the fourth produced water accounts for at least 90% of the content of the concentrated water.

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