A treatment process for photovoltaic cell production wastewater

Abstract

The present invention discloses a treatment process for photovoltaic cell production wastewater, which relates to the technical field of industrial wastewater treatment. The process includes the following steps: treating dilute acid and dilute alkali through a reclaimed water recovery membrane system to obtain first-stage produced water and reclaimed water concentrate; treating concentrated acid wastewater and reclaimed water concentrate through a fluorine-calcium crystallization system to obtain defluorinated concentrate and calcium fluoride crystals; treating RO concentrate and defluorinated concentrate through a hardness removal and reuse system to obtain hardness-removed concentrate and second-stage produced water; treating concentrated alkali wastewater through an alkali recovery membrane system to obtain purified alkali and alkali-removed concentrate; treating hardness-removed concentrate and alkali-removed concentrate through a comprehensive physical and chemical treatment system, and then successively through a high-concentration membrane system and a zero-discharge crystallization system to obtain solid waste. The treatment process for photovoltaic cell production wastewater provided by this application achieves an economically feasible zero-discharge 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:

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

[0006] The object of the present invention can be achieved by the following technical solutions:

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

[0008] Treat dilute acid and dilute alkali through a reclaimed water reuse membrane system to obtain first-stage product water and reclaimed water concentrate.

[0009] Treat concentrated acid wastewater and the reclaimed water concentrate through a fluorine-calcium crystallization system to obtain defluorinated concentrate and calcium fluoride crystals.

[0010] Treat RO concentrate and the defluorinated concentrate through a dehardening and reuse system to obtain dehardened concentrate and second-stage product water.

[0011] Treat concentrated alkali wastewater through an alkali recovery membrane system to obtain purified alkali and alkali-removed concentrate.

[0012] Treat the dehardened concentrate and the alkali-removed concentrate through a comprehensive physical and chemical system, and then successively through 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 treatment by the reclaimed water reuse membrane system includes concentrating the dilute acid and dilute alkali using a fluorosilicon concentration membrane, and the content of the first-stage product water accounts for at least 50% of the content of the dilute acid and dilute alkali.

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

[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 treatment by the fluorine-calcium crystallization system at least includes adding a crystallization agent to water in the fluorine-calcium crystallization system, and performing solid-liquid separation to produce the calcium fluoride crystals and the defluorinated concentrate. The crystallization agent at least includes calcium hydroxide and calcium chloride, and the molar ratio of the calcium concentration in the crystallization agent to the fluorine concentration in the wastewater introduced into the fluorine-calcium crystallization system is controlled between 0.6:1 - 1.5:1.

[0017] 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 defluorinated concentrate is less than 100 ppm.

[0018] As a further aspect of the present invention: The treatment of the hardening removal and recycling system at least includes filtering and separating the RO concentrated water and the defluorinated concentrated water by using one or more of an ultrafiltration membrane, a calcium-removing nanofiltration membrane, and a fluorine-silicon-removing nanofiltration membrane, and recycling a part of the obtained hardening removal concentrated water to the fluorine-calcium crystallization system.

[0019] As a further aspect 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 defluorinated concentrated water, and a part of the hardening removal concentrated water recycled 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 hardening removal concentrated water.

[0020] As a further aspect of the present invention: The treatment of the alkali recovery membrane system at least includes filtering and recovering the concentrated alkali wastewater by using an alkali-resistant nanofiltration membrane, 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 aspect of the present invention: The alkali recovery membrane system includes an alkali-resistant nanofiltration membrane, and an alkali-resistant layer is provided on the alkali-resistant nanofiltration membrane, and the alkali-resistant layer at least includes hydrophilic furfuryl alcohol resin.

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

[0023] As a further aspect of the present invention: A sedimentation tank is provided in the comprehensive physical and chemical system, and the precipitated impurities at least include silicon-containing or calcium-containing impurities.

[0024] As a further aspect of the present invention: The treatment of the high-fold concentration membrane system at least includes concentrating and filtering the sodium salt concentrated water by using a first membrane unit and a second membrane unit to obtain concentrated concentrated water and third produced water.

[0025] As a further aspect of the present invention: The concentration of the concentrated concentrated water 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 concentrated water.

[0026] As a further aspect 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 aspect of the present invention: The treatment of the zero-discharge crystallization system at least includes evaporating and crystallizing the concentrated concentrated water to obtain the solid waste and fourth produced water.

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

[0029] Advantages of the present invention:

[0030] The treatment process for photovoltaic cell production wastewater proposed in this application treats the main pollutants by quality, stage, and outlet, achieving the purpose of fluorine and alkali recovery and water reuse. Different from the conventional treatment process that sets a large number of treatment ponds such as reaction ponds, sedimentation ponds, or flocculation ponds, this application sets up a reclaimed water reuse membrane system, a fluorine-calcium crystallization system, a hardness removal 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 concentrate, dilute acid and alkali, concentrated acid wastewater, and concentrated alkali wastewater and enters different systems for treatment and reuse respectively, reducing the floor area of the treatment equipment. No sludge is generated during the wastewater treatment process. Through the cooperation between systems, material separation and recovery are realized, turning waste into treasure. And through the coupling process of special membranes and fluidized crystallization, the wastewater recovery rate can reach 80-90%, fully recovering water resources. While treating wastewater, the production of pure water is increased, the amount of tap water purchased by the enterprise is reduced, the reuse of wastewater is realized, and the cost of purchasing tap water by the enterprise is reduced.

[0031] The reclaimed water reuse membrane system set in this application, by setting the first-stage membrane, the second-stage membrane, and the 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 pollution factors, thus achieving a water reuse rate of more than 80%. The first-stage membrane is modified with high hydrophilicity, controlling the filtration pores at 10-20 nm, improving the interception efficiency of the first-stage membrane for fine particles or colloids. The second-stage membrane and the third-stage membrane are both modified with high hydrophilicity, having hydrophilic and anti-fouling effects, and strengthening the tolerance to partially precipitated silicon pollutants. This application concentrates dilute acid and alkali through the reclaimed water reuse membrane system to obtain the first produced water and the reclaimed water concentrate, with a concentration of 80-90%, that is, a 7-10-fold concentration of pollution factors, realizing the further purification of reclaimed water, reducing the amount of water entering the subsequent systems, and thus reducing the removal cost of the subsequent systems. At the same time, the produced water can be used as the inlet water for the enterprise's power workshop, reducing the enterprise's procurement of tap water and saving costs for the enterprise.

[0032] This application sets up a fluorite crystallization system. The intermediate water concentrate obtained through the intermediate water reuse membrane system, the fluorine-containing concentrate refluxed from the dehardening reuse system, and the concentrated acid wastewater are sprayed or injected into the crystallization tank of the fluorite crystallization system. By adding crystallization agents such as calcium hydroxide or calcium chloride, and controlling the molar ratio of calcium concentration in the crystallization agent to fluorine concentration in the wastewater to be between 0.6:1 and 1.5:1, calcium ions and fluoride ions form calcium fluoride crystals (fluorite) that are insoluble in water, thereby removing most of the fluoride ions. After being treated by the fluorite crystallization system, defluorinated concentrate and calcium fluoride crystals are obtained. The fluorine content in the defluorinated concentrate is less than 100 ppm, 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%. The produced calcium fluoride will be sold as a product, realizing the reasonable disposal of waste and bringing economic benefits to the enterprise. In the fluorite crystallization system provided in this application, the water flow distribution is improved, the supersaturation of calcium fluoride in the reactor is reasonably regulated, and after the fluoride ions are secondarily concentrated by the dehardening reuse system and the intermediate water reuse membrane system and then recycled into crystallization, technical coupling is achieved, reducing the problems of large amounts of chemical agents added and large floor area of equipment caused by one-step defluorination.

[0033] This application sets up a dehardening reuse system. The RO concentrate and the defluorinated concentrate are introduced into the dehardening reuse system. The dehardening reuse system is equipped with an ultrafiltration membrane, a decalcifying nanofiltration membrane, and a defluorinated silicon nanofiltration membrane. The defluorinated concentrate and the RO concentrate after being treated by the fluorite 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 through the filtration of multiple layers of membranes, obtaining dehardened concentrate and secondary product water. The dehardened concentrate contains 10 - 50% of fluorine-containing concentrate, and the fluorine-containing concentrate is refluxed to the fluorite crystallization system for treatment. The remaining dehardened concentrate enters the next system. The secondary product water can be reused, and the content of the secondary product water is not less than 50% of the content of the RO concentrate and the defluorinated concentrate introduced into the dehardening reuse system. The RO concentrate and the defluorinated concentrate remove impurities such as chloride ions through the ultrafiltration membrane, remove residual hard calcium and other impurities after being treated by the fluorite crystallization system through the decalcifying nanofiltration membrane, and remove impurities such as fluorine and calcium through the defluorinated silicon nanofiltration membrane. By setting up multiple layers of filtration membranes and removing and concentrating impurities step by step, the problem of membrane blockage or abrasion and rupture caused by only setting a single layer of filtration membrane is avoided, and the dehardening efficiency is improved.

[0034] This application sets up an alkali recovery membrane system, and concentrated alkaline wastewater enters this system for alkali removal treatment. This application also modifies traditional nanofiltration membranes to be alkali-resistant, enabling them to be used for a long time in an alkaline solution environment with a pH exceeding 12. The alkali recovery membrane system set up in this application separates the pollutants and purified alkali in the concentrated alkaline wastewater. The content of the purified alkali is not less than 50% of the content of the 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 enterprise the cost of purchasing liquid alkali. At the same time, the alkali recovery membrane system set up in this application can also remove impurities such as fluorine and silicon in the concentrated alkaline wastewater. After the concentrated alkaline wastewater is filtered twice by the alkali recovery membrane system, the fluoride ion concentration can be reduced to 1 ppm, and the silica content can be reduced to 200 ppm.

[0035] This application sets up a comprehensive physical and chemical system. A sedimentation tank is set up in the comprehensive physical and chemical system. The dehardened concentrated water and alkali-removed concentrated water obtained after the treatment of the previous system are introduced into this system for treatment. By adding precipitants such as sodium carbonate and magnesium chloride, further calcium and silicon removal are carried out respectively to remove other impurities in the concentrated water except sodium salts, and sodium salt concentrated water is obtained. Through the comprehensive physical and chemical system, the contents of calcium and silicon in the concentrated water are reduced, avoiding the scaling during the operation of the subsequent membrane system caused by these two elements, which may increase the backwashing frequency, even damage the membrane and increase the operation cost of the enterprise.

[0036] This application also sets up a high-concentration membrane system. The sodium salt concentrated water 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 uses high-desalination and pollution-resistant membrane elements to perform the first-step concentration on the 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 uses loose-type membrane elements and can control the permeation of some ions through the membrane layer to balance the osmotic pressure on both sides of the membrane, so as to slow down the accumulation of osmotic pressure on the membrane surface. Part of the permeate of the second membrane unit can be returned 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 80 g / 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, realizing the maximum reduction of water volume, further reducing the water volume before evaporation, and reducing the subsequent evaporation cost. And in this system, the water production flow channel is coated with epoxy material. By using the dense water production flow channel coated with epoxy as the key auxiliary material of the high-pressure membrane product, the problem of the dense combination of the membrane and the channel under the high-pressure environment is improved.

[0037] This application is also provided with a zero-discharge crystallization system. The concentrated brine 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 content of the concentrated brine entering the zero-discharge crystallization system. The solid waste needs to be transported out for treatment, completing the treatment of the 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 the traditional treatment tank, the floor area is greatly reduced. Zero discharge is achieved through the cooperation and joint use of seven systems, realizing the reuse of wastewater for enterprises, saving the consumption of tap water, the addition of chemicals, and the consumption of electric energy for enterprises, and maximizing cost reduction and efficiency increase for enterprises. The seven systems in this application cooperate with each other, rather than being completed by a single system in the traditional process, and can be adjusted in a timely manner according to the huge changes in water quality and water volume of photovoltaic enterprises, improving the wastewater treatment efficiency. The cooperation of multiple systems can respectively reuse valuable substances in the wastewater. For example, calcium fluoride produced in the fluorine-calcium crystallization system, purified alkali produced in the alkali recovery membrane system, and the produced water reuse in the reclaimed water reuse membrane system, the hardening removal reuse system, the high-concentration brine membrane system, and the zero-discharge crystallization system, greatly reducing the production cost of enterprises. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0040] Figure 1 It is a process flow chart for treating photovoltaic cell production wastewater in an embodiment.

[0041] Figure 2 It is a traditional process flow chart for treating photovoltaic cell production wastewater in a comparative example. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention.

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

[0044] As Figure 1As shown in the figure, dilute acid and dilute alkali are introduced into the reclaimed water membrane system. In the reclaimed water membrane system, there are 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 - 20 nm. The second-stage membrane and the third-stage membrane are provided with polyvinyl alcohol coatings. After passing through the first-stage membrane, the second-stage membrane, and the third-stage membrane of the reclaimed water membrane system in sequence, reclaimed water concentrate and first-stage produced water are obtained. In this embodiment, the content of the first-stage produced water for reuse is 80% of the content of the dilute acid and dilute alkali, realizing the concentration of pollution factors.

[0045] As Figure 1 shown in the figure, concentrated acid wastewater, the reclaimed water concentrate treated and concentrated by the reclaimed water membrane system, and the fluorine-containing concentrate refluxed by the dehardening and reuse system are sprayed or injected into the crystallization tank of the fluorite crystallization system for treatment. A crystallization agent such as calcium hydroxide or calcium chloride is added to the concentrated water, and the molar ratio of calcium concentration in the crystallization agent to fluorine concentration in the concentrated acid wastewater, reclaimed water concentrate, and fluorine-containing concentrated water is controlled between 0.6:1 - 1.5:1. Calcium fluoride crystals that are insoluble in water are formed by calcium ions and fluorine ions. Through the induction of crystal nuclei, the precipitation of calcium fluoride crystals flows out more quickly, removing most of the fluorine ions, and the defluorinated concentrated water is introduced into the next system.

[0046] As Figure 1 shown in the figure, RO concentrated water and the defluorinated concentrated water treated by the fluorite crystallization system are introduced into the dehardening and reuse system for treatment. Through the ultrafiltration membrane, decalcifying nanofiltration membrane, and defluorinating and desiliconizing nanofiltration membrane set in the dehardening and reuse system, impurities are removed step by step to realize the separation of calcium ions, obtaining dehardening concentrated water and second-stage produced water. Among them, the second-stage produced water is reused, 30% of the fluorine-containing concentrated water generated in the dehardening concentrated water is introduced into the fluorite crystallization system for defluorination, and the remaining dehardening concentrated water is introduced into the comprehensive physical and chemical system for treatment. In this embodiment, the content of the second-stage produced water for reuse is 55% of the content of the concentrated water introduced into the dehardening and reuse system;

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

[0048] As Figure 1 shown in the figure, the dehardening concentrated water and the alkali-removing concentrated water treated by the dehardening and reuse system are introduced into the comprehensive physical and chemical system for treatment. The concentrated water is injected into the sedimentation tank, and further calcium removal and silicon removal are carried out by adding sodium carbonate and magnesium chloride respectively, so that only the sodium salt concentrated water containing sodium salts enters the next system for treatment.

[0049] As Figure 1 shown, the concentrated sodium salt water after being treated by the comprehensive 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 concentrated water. When the concentrated water reaches an extremely high osmotic pressure and the first membrane unit cannot effectively produce water, the concentrated water will enter the second membrane unit. The second membrane unit further concentrates the concentrated water. The second membrane unit can control the passage of some ions through the membrane layer to balance the osmotic pressure on both sides of the membrane, so as to slow down the accumulation of osmotic pressure on the membrane surface. Part of the permeate of the second membrane unit can return to the influent water again to balance the ion concentration of the influent water. Finally, concentrated concentrated water and the third produced water are obtained. The concentrated concentrated water enters the next system, and the third produced water is recycled. And in this embodiment, the concentration of the concentrated water measurement reaches 90 g / L, and the content of the third produced water accounts for 60% of the content of the sodium salt concentrated water flowing into the high-concentration membrane system.

[0050] As Figure 1 shown, the concentrated concentrated water produced after high-concentration by the high-concentration membrane system is introduced into the zero-discharge crystallization system, and evaporation crystallization is carried out through an evaporator. The fourth produced water generated by evaporation is used for recycling, and the solid waste generated by evaporation is transported out for treatment, completing the zero-discharge treatment of photovoltaic cell production wastewater. And in this embodiment, the content of the recycled fourth produced water accounts for 90% of the content of the concentrated concentrated water.

[0051] Comparative example The traditional treatment process of photovoltaic cell production wastewater at least includes the following steps:

[0052] As Figure 2 shown, the concentrated acid wastewater, concentrated alkali wastewater, dilute acid wastewater and dilute alkali wastewater are collected in their respective wastewater collection tanks and mixed evenly in the neutralization adjustment tank.

[0053] As Figure 2 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 first reaction tank. Calcium hydroxide and calcium chloride are added. After forming a precipitate, polyaluminum chloride and polyacrylamide are added. After the reaction forms flocs, the water flows out to the first sedimentation tank; the mud and water are separated in the first sedimentation tank, the upper-layer wastewater enters the second reaction tank, and the fluoride ion is reduced to below 80 mg / L. The lower-layer sludge enters the sludge tank; calcium hydroxide and calcium chloride are added to the wastewater in the second reaction tank. After forming a precipitate, polyaluminum chloride and polyacrylamide are added. After the reaction forms flocs, the water flows out to the second sedimentation tank; the mud and water are separated in the second sedimentation tank. Liquid alkali is added to the upper-layer clear liquid to adjust the pH to 7-9, and the water flows out to the discharge tank, and the fluoride ion is reduced to below 5 mg / L. The lower-layer sludge enters the sludge tank; the sludge collected in the sludge tank is concentrated and then introduced into the sludge filter press, and cationic polyacrylamide is added and mixed for filtration. The filtrate flows into the first reaction tank by itself, and the filter cake is transported out for treatment.

[0054] AsFigure 2 As shown, the effluent from the dilute acid wastewater collection tank and the effluent from the dilute alkali wastewater collection tank are introduced into the pH adjustment tank to adjust the pH to 7-9, and the subsequent treatment process is the same as the treatment process for concentrated acid and concentrated alkali above.

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

[0056] The water quality and quantity of the 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 quantity of the wastewater to be treated in the examples and comparative examples

[0058]

[0059] The water quality and 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 examples and the water in the discharge tank in the comparative examples

[0061]

[0062] As can be seen from Table 1 and Table 2, the treated production wastewater of the photovoltaic cell production wastewater treatment process provided in the examples of the present application achieves zero discharge, and a large amount of produced water is generated during the treatment process, including the first produced water, the second produced water, the third produced water and the fourth produced water, which is 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 that of the sewage treatment process provided in the present application, and the produced water cannot be reused. In addition, through the photovoltaic cell production wastewater treatment process provided in this example, only by using the intermediate water reuse of the first unit, the tap water consumption per 10,000 pieces of batteries can be reduced by 46%, the dosage of the crystallization agent can be reduced by 15%, the tap water cost can be reduced by 10%, and the wastewater treatment load can be reduced by 50%. After all the overall process units are implemented, the battery factory achieves zero discharge of wastewater.

[0063] The above has described in detail an embodiment of the present invention, but the above content is only a preferred embodiment of the present invention and cannot be considered as defining the scope of implementation of the present invention. All equivalent changes and improvements made according to the scope of the application of the present invention should still fall within the scope covered by the patent 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 reuse 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; Among them, the reclaimed water reuse membrane system treatment includes using a fluorine-silicon concentrating membrane to concentrate the dilute acid and alkali, 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, 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 hydrophilic layer, and the hydrophilic layer is a polyvinyl alcohol coating.

2. A photovoltaic cell production wastewater treatment process according to claim 1, characterized in that: The content of the first produced water is at least 50% of the content of the dilute acid and dilute alkali.

3. 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.

4. A photovoltaic cell production wastewater treatment process according to claim 3, 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.

5. 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.

6. A photovoltaic cell production wastewater treatment process according to claim 5, 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.

7. 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%.

8. A photovoltaic cell production wastewater treatment process according to claim 7, 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.

9. 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.

10. A photovoltaic cell production wastewater treatment process according to claim 9, 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.

11. A photovoltaic cell production wastewater treatment process according to claim 9, 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.

12. A photovoltaic cell production wastewater treatment process according to claim 11, 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.

13. A photovoltaic cell production wastewater treatment process according to claim 11, characterized in that: The first membrane unit is a high desalination membrane unit, and the second membrane unit is a high permeability membrane unit.

14. 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.

15. A photovoltaic cell production wastewater treatment process according to claim 14, 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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