Treatment process of photovoltaic cell production wastewater

Abstract

The invention discloses a treatment process of photovoltaic cell production wastewater, and relates to the technical field of industrial wastewater treatment. Comprising the following steps: treating dilute acid and dilute alkali through a reclaimed water recovery membrane system to obtain first produced water and reclaimed water concentrated water; treating the concentrated acid wastewater and the reclaimed concentrated water through a fluorine-calcium crystallization system to obtain defluorinated concentrated water and calcium fluoride crystals; treating the RO concentrated water and the defluorinated concentrated water by a hardness removal recycling system to obtain hardness-removed concentrated water and second produced water; treating the concentrated alkali wastewater through an alkali recovery membrane system to obtain purified alkali and alkali-removed concentrated water; hardness-removed concentrated water and alkali-removed concentrated water are treated by a comprehensive physicochemical system, and then are sequentially treated by a high-power concentration membrane system and a zero-discharge crystallization system to obtain solid wastes. The photovoltaic cell production wastewater treatment process provided by the invention achieves an economical and feasible zero-emission solution.

Description

Technical Field

[0001] The 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 terms of production volume. In the entire photovoltaic industry chain, the production of solar cells is the core process segment. Micron-level thin silicon wafers go through a series of chemical etching, soaking, chemical deposition, cleaning, and printing processes to become photovoltaic cells that can perform photoelectric conversion. In the production process of photovoltaic cells, a large amount of hydrofluoric acid, liquid alkali, ammonia, hydrogen peroxide and other chemicals are used. These chemicals do not enter the products of the solar cells, but are discharged as wastewater along with the cleaning. The wastewater from the photovoltaic cell production base is specifically divided into fluorine-containing dilute acid, dilute alkali, concentrated acid, and concentrated alkali wastewater, tail gas cleaning wastewater containing particulate matter, ammonia-containing silane wastewater, and domestic sewage and reverse osmosis (RO) concentrated water containing organic matter and salt. It is a complex wastewater source with many pollution factors, fluctuating water quality, and uneven water volume. The usual treatment method is to mix all the wastewater together and then add a large amount of reagents to treat the wastewater. However, due to the differences in the pH value and types of pollutants of various types of wastewater, the treatment process is cumbersome, and the effect after treatment is often not ideal, and it is impossible to meet the comprehensive emission requirements. There are also zero-emission treatment paths in the field of water treatment, but directly using them in photovoltaic wastewater will result in sky-high costs, which is not feasible from an economic perspective.

[0003] At present, the treatment of photovoltaic wastewater mostly adopts a combination of physical and chemical treatment and biochemical treatment. The physical and chemical system removes fluoride ions in wastewater through chemicals (mainly calcium salts), and the biochemical system uses biological denitrification (Anaerobic-Anoxic-Oxic, A / O) process or anaerobic ammonia oxidation process to remove ammonia nitrogen / chemical oxygen demand (Chemical Oxygen Demand, COD) in wastewater to achieve standard discharge. The traditional treatment process has a large amount of chemical dosage, a long process flow, and a large area. The most important thing is that the treated water can only be discharged as wastewater to the downstream sewage treatment plant, and it does not play a role in resource reuse. Hundreds of millions of tons of water are discharged from this industry every year, which is a great test for my country, where water resources are relatively uneven. Therefore, exploring a feasible solution to change the situation of large-scale wastewater discharge and bring economic value to enterprises and society is a work that requires 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: 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.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A photovoltaic cell production wastewater treatment process comprises at least the following steps: The diluted acid and alkali are treated by the reclaimed water recovery membrane system to obtain the first produced 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 de-alkali 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.

[0006] As a further solution of the present invention: the 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.

[0007] As a further solution of the present invention: 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, and the filtration pore size of the first-stage membrane is 10-20nm.

[0008] 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.

[0009] As a further solution of the present invention: 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 includes at least 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.

[0010] As a further solution 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.

[0011] As a further scheme 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 ultrafiltration membranes, calcium removal nanofiltration membranes and fluorine removal silicon nanofiltration membranes to filter and separate the RO concentrated water and the defluorination concentrated water, and returning part of the de-hardening concentrated water obtained to the fluorine calcium crystallization system.

[0012] 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.

[0013] 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 content of sodium hydroxide in the purified alkali is not less than 0.1%.

[0014] As a further solution of the present invention: the alkali recovery membrane system comprises an alkali-resistant nanofiltration membrane, an alkali-resistant layer is arranged on the alkali-resistant nanofiltration membrane, and the alkali-resistant layer comprises at least a hydrophilic furfuryl alcohol resin.

[0015] 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 to produce precipitated impurities and sodium salt concentrated water through solid-liquid separation, and the precipitant includes at least sodium carbonate and magnesium chloride.

[0016] 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.

[0017] As a further solution of the present invention: the high-concentration membrane system treatment at least includes using the first membrane unit and the second membrane unit to concentrate and filter the sodium salt concentrated water to obtain concentrated concentrated water and third produced water.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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 concentrated water.

[0022] Beneficial effects of the present invention: The treatment process of photovoltaic cell production wastewater proposed in this application treats the main pollutants by quality, stage and outlet, 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. 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 are set up. 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 systems, material separation and recovery are achieved, and waste is turned into treasure. Moreover, through the coupling process of special membrane and fluidized 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 enterprises is reduced, the reuse of wastewater is achieved and the cost of purchasing tap water for enterprises is reduced.

[0023] The reclaimed water reuse membrane system set in this application is provided with a first-level membrane, a second-level membrane and a third-level membrane. The first-level membrane intercepts fluorosilicate solids and colloidal silicon, and the second-level membrane and the third-level membrane intercept ionic pollution factors, thereby achieving a water reuse rate of more than 80%. The first-level membrane is modified with high hydrophilicity, and the filter pores are controlled at 10-20nm, which improves the interception efficiency of the first-level membrane for tiny particles or colloids. The second-level membrane and the third-level membrane are both modified with high hydrophilicity, have hydrophilic and anti-fouling effects, and strengthen the tolerance to silicon pollutants analyzed in part. This application concentrates dilute acid and dilute alkali through the reclaimed water reuse membrane system to obtain the first produced water and reclaimed water, and the concentration reaches 80-90%, that is, 7-10 times the concentration of pollution factors, which realizes further purification of reclaimed water and reduces the amount of water entering the subsequent system, thereby reducing the removal cost of the subsequent system. At the same time, the produced water can be used as the inlet water of the enterprise's power workshop, reducing the purchase of tap water by the enterprise and saving costs for the enterprise.

[0024] This application sets up a fluorine calcium crystallization system, sprays or injects the reclaimed water concentrate obtained by the reclaimed water reuse membrane system, the fluorine-containing concentrate returned by the de-hardening reuse system, and the concentrated acid wastewater into the crystallization tank of the fluorine calcium crystallization system, and by adding crystallizing agents such as calcium hydroxide or calcium chloride, and controlling the molar ratio of the calcium concentration in the crystallizing agent to the fluorine concentration in the wastewater between 0.6:1-1.5:1, the calcium ions and fluorine ions form calcium fluoride crystals (fluorite) that are insoluble in water, thereby removing most of the fluorine ions. After being treated by the fluorine calcium crystallization system, defluorinated concentrated water and calcium fluoride crystals are obtained, and the fluorine content in the defluorinated concentrated water is less than 100ppm, the defluorination efficiency is high, the fluorine removal rate can reach more than 95%, and the system can still maintain a very high defluorination efficiency after long-term operation. The purity of the obtained calcium fluoride crystals is greater than 90%, and the produced calcium fluoride will be sold as a product, realizing the rational disposal of waste and bringing economic benefits to the enterprise. In the fluorine calcium crystallization system provided in the present application, the water flow distribution is improved, the supersaturation of calcium fluoride in the reactor is reasonably regulated, and the fluoride ions are secondary concentrated by using the de-hardness reuse system and the reclaimed water reuse membrane system and then recycled into the crystallization, thereby realizing technical coupling and reducing the problems of large amount of reagent addition and large equipment footprint caused by one-step defluorination.

[0025] 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 provided with an ultrafiltration membrane, a decalcification nanofiltration membrane and a defluorinated silicon nanofiltration membrane. The defluorinated concentrated water and RO concentrated water 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 separation of impurity ions is achieved by filtering through a multi-layer membrane to obtain de-hardening concentrated water and second produced water. The de-hardening concentrated water contains 10-50% of fluorine-containing concentrated water, and the fluorine-containing concentrated water is refluxed to the fluorinated calcium crystallization system for treatment. The remaining de-hardening concentrated water enters the next system, and 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 defluorinated concentrated water introduced into the de-hardening and recycling system. The RO concentrated water and the defluorinated concentrated water are passed through the ultrafiltration membrane to remove impurities such as chloride ions, the decalcification nanofiltration membrane is used to remove impurities such as hard calcium remaining after being treated by the fluorinated calcium crystallization system, and the defluorinated silicon nanofiltration membrane is used to remove impurities such as fluorine and calcium. By setting up multiple layers of filtration membranes, impurities can be removed and concentrated step by step, avoiding the problem of membrane clogging or wear and tear caused by setting up only a single layer of filtration membrane, thereby improving the de-hardening efficiency.

[0026] The present application sets up an alkali recovery membrane system, and concentrated alkali wastewater enters this system for treatment and alkali removal. The present application also performs alkali-resistant modification on the traditional nanofiltration membrane, which can be used for a long time in an alkaline solution environment exceeding pH12. The alkali recovery membrane system set up in the present application separates the pollutants and purified alkali in the concentrated alkali wastewater, and the content of purified alkali is not less than 50% of the content of the concentrated alkali 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 the concentrated alkali wastewater, and after the concentrated alkali 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.

[0027] The present application sets up a comprehensive physical and chemical system, in which a sedimentation tank is set up. The hardened concentrated water and de-alkali concentrated water obtained after the treatment of the above-mentioned system are introduced into this system for treatment. By adding precipitants such as sodium carbonate and magnesium chloride, further calcium and silicon are removed respectively, and other impurities except sodium salt in the concentrated water are removed to obtain sodium salt concentrated water. Through the comprehensive physical and chemical system, the content of calcium and silicon in the concentrated water is reduced, and these two elements are prevented from causing scaling during the operation of the subsequent membrane system, resulting in an increase in the frequency of backwashing and even damage to the membrane and an increase in the operating costs of the enterprise.

[0028] The present application also sets up a high-concentration membrane system, and the sodium salt concentrated water after being treated by the comprehensive physical and chemical system is introduced into the high-concentration membrane system for concentration treatment to obtain concentrated concentrated water and the third produced water. The high-concentration membrane system is provided with a first membrane unit and a second membrane unit. The first membrane unit is a high desalination membrane unit, which adopts a high desalination and pollution-resistant membrane element to carry out the first step of concentration of concentrated water. When the extremely high osmotic pressure is reached and the first membrane unit cannot effectively produce water, the water enters the second membrane unit. The second membrane unit is a high permeability membrane unit, which adopts a loose membrane element, which 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 part of the second membrane unit can return to the inlet water again to balance the ion concentration of the incoming water. Through the combined process of the first membrane unit and the second membrane unit, the concentration of the concentrated water of the second membrane unit, that is, the concentrated concentrated water, reaches 80g / L, and the content of the third produced water accounts for at least 50% of the content of the sodium salt concentrated water introduced into the high-concentration membrane system, achieving the maximum reduction of water volume, further reducing the water volume before evaporation, and reducing the subsequent evaporation cost. In this system, the water production channel is coated with epoxy material. The epoxy-coated dense water production channel is used as a key auxiliary material for high-pressure membrane products, thereby improving the problem of dense bonding between the membrane and the channel under high-pressure environment.

[0029] 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, 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 content 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.

[0030] In summary, the present invention treats the production wastewater and domestic sewage of the photovoltaic production area through reverse osmosis membranes and nanofiltration membranes with different characteristics. Compared with the traditional treatment pool, the floor space is greatly reduced. Zero discharge is achieved through the coordination and combination of seven systems, which realizes the reuse of wastewater for enterprises, saves the consumption of tap water, the addition of reagents and the consumption of electric energy, 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 one system of the traditional process. It can be adjusted in real time according to 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 the reuse of produced water in the reclaimed water reuse membrane system, the de-hardening reuse system, the high-concentration water membrane system and the zero-discharge crystallization system, which greatly reduces the production cost of the enterprise. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0032] Figure 1 This is a process flow chart for treating photovoltaic cell production wastewater in one embodiment.

[0033] Figure 2 A conventional treatment process flow chart of photovoltaic cell production wastewater is shown in Figure 2. DETAILED DESCRIPTION

[0034] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments of the present invention. Obviously, the described embodiments 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.

[0035] The treatment process of photovoltaic cell production wastewater includes the following steps: like Figure 1As shown, dilute acid and 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, and the second-stage membrane and the third-stage membrane are provided with a polyvinyl alcohol coating, which is sequentially processed by the first-stage membrane, the second-stage membrane and the third-stage membrane of the reclaimed water recovery membrane system to obtain reclaimed water, concentrated water and first produced water. In this embodiment, the content of the reused first produced water is 80% of the content of the dilute acid and alkali, thereby achieving the concentration of the pollution factors.

[0036] like Figure 1 As shown, concentrated acid wastewater, concentrated reclaimed water treated by a reclaimed water recovery membrane system, and fluorine-containing concentrated water returned by a de-hardening and reuse system are sprayed or injected into a crystallization tank of a fluorine-calcium crystallization system for treatment, and a crystallizing agent such as calcium hydroxide or calcium chloride is added to the concentrated water. The molar ratio of the calcium concentration in the crystallizing agent to the fluorine concentration in the concentrated acid wastewater, the reclaimed water, and the 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, and the occurrence of crystal nuclei is induced to accelerate the precipitation and outflow of calcium fluoride crystals, remove most of the fluoride ions, and introduce the defluorinated concentrated water into the next system.

[0037] like Figure 1 As shown, RO concentrated water and defluorinated concentrated water treated by the fluorine-calcium crystallization system are introduced into the de-hardening recycling system for treatment, and impurities are removed step by step through the ultrafiltration membrane, decalcification nanofiltration membrane and defluorination silicon nanofiltration membrane provided in the de-hardening recycling system to achieve separation of calcium ions, thereby obtaining de-hardening concentrated water and second produced water, wherein the second produced water is reused, 30% of the fluorine-containing concentrated water produced 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 comprehensive physical and chemical system for treatment, and 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 recycling system; like Figure 1 As shown, 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 de-alkali concentrated water. The produced water containing purified alkali is recycled, and the de-alkali 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%.

[0038] like Figure 1 As shown, the de-hardened concentrated water and de-alkali concentrated water treated by the de-hardening and reuse system are introduced into the comprehensive physical and chemical system for treatment, and the concentrated water is injected into the sedimentation tank for further decalcification and desiliconization by adding sodium carbonate and magnesium chloride, so that the sodium salt concentrated water containing only sodium salt enters the next system for treatment.

[0039] like Figure 1 As shown, the sodium salt concentrate 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 part of the ions to pass through the membrane layer and balance the osmotic pressure on both sides of the membrane to slow down the accumulation of osmotic pressure on the membrane surface. The permeate of the second membrane unit can return to the influent again to balance the ion concentration of the incoming water, and finally concentrated concentrate and the third produced water are obtained. The concentrated concentrate enters the next system, and the third produced water is reused. In this embodiment, the measured concentration of the concentrate reaches 90g / L, and the content of the third produced water accounts for 60% of the content of the sodium salt concentrate flowing into the high-concentration membrane system.

[0040] like Figure 1 As shown, the concentrated brine produced after high-concentration by the high-concentration membrane system is introduced into the zero-discharge crystallization system, and is evaporated and crystallized by the evaporator. The fourth produced water produced by evaporation is used for reuse, and the solid waste produced by evaporation is transported out for treatment, thereby completing the zero-discharge treatment of photovoltaic cell production wastewater. In this embodiment, the content of the reused fourth produced water accounts for 90% of the concentrated brine content.

[0041] The conventional treatment process of photovoltaic cell production wastewater includes at least the following steps: like Figure 2 As shown, concentrated acid wastewater, concentrated alkali wastewater, dilute acid wastewater and dilute alkali wastewater are collected in respective wastewater collection tanks, added into a neutralization regulating tank and mixed evenly.

[0042] like Figure 2 As shown, the effluent from the concentrated acid wastewater collection tank and the effluent from the concentrated alkali wastewater collection tank are introduced into the pH adjustment tank, the pH is adjusted to 8-9, and then introduced into the primary reaction tank, calcium hydroxide and calcium chloride are added, polyaluminium chloride and polyacrylamide are added after forming a precipitate, and the effluent is introduced into the primary sedimentation tank after the reaction forms alum flowers; the mud and water are separated in the primary sedimentation tank, the upper wastewater enters the secondary reaction tank, the fluoride ions are reduced to below 80mg / L, and the lower sludge enters the sludge tank; calcium hydroxide and calcium chloride are added to the wastewater in the secondary reaction tank, the precipitate is formed, polyaluminium chloride and polyacrylamide are added, the effluent is introduced into the secondary sedimentation tank after the reaction forms alum flowers; the mud and water are separated in the secondary sedimentation tank, liquid alkali is added to the upper clear liquid to adjust the pH to 7-9, the effluent is introduced into the discharge tank, the fluoride ions are reduced to below 5mg / L, and the lower sludge enters the sludge tank; the sludge collected in the sludge tank is concentrated and introduced into the sludge filter press, cationic polyacrylamide is added and mixed, and then the filtrate is filtered by gravity into the primary reaction tank, and the mud cake is transported out for treatment.

[0043] like Figure 2As shown, 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 concentrated acid and concentrated alkali treatment process.

[0044] like Figure 2 As shown, 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 and 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, and 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.

[0045] The water quality and water volume of photovoltaic cell production wastewater to be treated in the embodiments and comparative examples are shown in Table 1 below: Table 1 Water quality and water quantity of wastewater to be treated in the examples and comparative examples

[0046] The water quality and water quantity of the treated wastewater in the embodiments and comparative examples are shown in Table 2 below: Table 2 Water quality of produced water in the embodiment and water in the discharge pool in the comparative example

[0047] 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 produced during the treatment process, including the first water production, the second water production, the third water production and the fourth water production, 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 sewage treatment effect of the sewage treatment process provided in the present application, and the production water 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 of 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 discharge of wastewater.

[0048] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation 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 produced 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 de-alkali 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. A photovoltaic cell production wastewater treatment process according to claim 1, characterized in that: The treatment of the reclaimed water recovery membrane system includes concentrating the dilute acid and alkali using a fluorine-silicon concentrating membrane, and the content of the first produced water accounts for at least 50% of the content of the dilute acid and alkali.

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

5. A 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 defluorination concentrated water is less than 100 ppm.

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

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

10. A 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 arranged on the alkali-resistant nanofiltration membrane, and the alkali-resistant layer comprises at least a hydrophilic furfuryl alcohol resin.

11. A 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 to produce 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. A 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 produced 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 accounts for at least 50% of the content of the sodium salt brine.

15. A 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. A 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 concentrated water.

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