A synergistic treatment system for removing fluorine and heavy metals from photovoltaic wastewater and recycling heavy metals

Abstract

The present application belongs to the field of water pollution treatment, and relates to a photovoltaic wastewater fluorine and heavy metal recovery and removal synergistic treatment system, comprising a classification collection and adjustment system for classifying and collecting and adjusting the water quality of wastewater generated in the photovoltaic production process; a synergistic reaction treatment system for synergistically reacting and treating fluorine-containing adjusted water and ammonia-nitrogen-containing adjusted water to obtain synergistically treated water; an acid-alkali synergistic treatment system for synergistically reacting and treating acid adjusted water, alkali adjusted water and heavy metal-containing adjusted water to obtain acid-alkali synergistically treated water; a mixed treatment system for mixing and treating the synergistically treated water and the acid-alkali synergistically treated water and inducing crystallization to obtain mixed water; and a deep treatment system for deeply treating the mixed water to obtain regenerated water. The system has high pollutant removal efficiency, high effluent water quality, low treatment cost and low operation energy consumption, realizes the recycling and near-zero discharge of wastewater, and realizes the gradient recovery of multiple valuable resources.

Description

Technical Field

[0001] This invention belongs to the field of water pollution control, specifically relating to a synergistic treatment system for defluorination and heavy metal recovery of photovoltaic wastewater. Background Technology

[0002] The manufacturing process of photovoltaic products involves multiple steps, including silicon wafer cleaning, etching, diffusion, coating, and etching. This generates a large amount of complex industrial wastewater, including fluoride-containing wastewater, ammonia nitrogen-containing wastewater, acid and alkali wastewater, and wastewater containing heavy metals. This wastewater commonly contains fluoride ions, ammonia nitrogen, heavy metal ions (such as copper, nickel, and silver), and high concentrations of acidic and alkaline substances, requiring effective treatment before discharge. Currently, developing efficient and economical photovoltaic wastewater treatment and recycling technologies has become a key bottleneck restricting the green and sustainable development of the photovoltaic industry, and is also an important issue that urgently needs to be addressed in the environmental protection field.

[0003] Photovoltaic wastewater treatment technology has evolved from single pollutant removal to comprehensive treatment, and from end-of-pipe treatment to resource utilization. Early treatment of photovoltaic wastewater primarily employed traditional methods such as chemical precipitation, adsorption, and ion exchange. While these methods were effective at removing specific pollutants, they had significant limitations in terms of treatment efficiency, operational stability, and land area requirements. With the rapid development of membrane separation, advanced oxidation, and resource recovery technologies, photovoltaic wastewater treatment processes have gradually evolved towards diversification and integration. Specifically, in the treatment of fluoride-containing wastewater, chemical precipitation is currently the most widely used technique. Its principle involves adding calcium salts such as lime and calcium chloride, causing fluoride ions to react with calcium ions to form insoluble calcium fluoride precipitates, thereby removing fluoride ions. In the treatment of ammonia nitrogen-containing wastewater, biological nitrification / denitrification, air stripping, and membrane absorption technologies are all used to varying degrees. Regarding acid and alkali wastewater treatment, while traditional neutralization precipitation can adjust pH, it cannot achieve acid recovery and reuse, resulting in resource waste. In the treatment of heavy metal wastewater, flocculation and sedimentation are commonly used to remove and recover heavy metals.

[0004] However, the current photovoltaic wastewater treatment field generally faces the following technical challenges: First, existing technologies mostly focus on the treatment of single types of wastewater or single pollutants, lacking systematic methods for the synergistic treatment and recycling of multiple photovoltaic wastewaters, making it difficult to achieve resource complementarity and process coupling between different wastewaters; Second, existing technologies are significantly insufficient in the deep removal and resource utilization of pollutants, especially in the treatment efficiency of low-concentration pollutants such as fluoride, ammonia nitrogen, and heavy metals, which cannot meet increasingly stringent environmental protection requirements; Third, existing technical solutions generally suffer from system complexity, large equipment investment, and high operating costs, posing an economic feasibility challenge for their promotion and application in small and medium-sized photovoltaic enterprises; Fourth, existing technologies do not adequately consider the synergistic recovery of multiple valuable resources (such as fluoride, ammonia nitrogen, heavy metals, acids, and alkalis) in photovoltaic wastewater, failing to maximize the resource utilization of waste.

[0005] Therefore, how to propose a method for the synergistic treatment and recycling of photovoltaic wastewater that takes into account multiple performance aspects, while achieving fluoride removal and heavy metal recovery, and simultaneously realizing the synergistic treatment and resource integration of different types of photovoltaic wastewater, optimizing the recovery path of valuable resources, and reducing treatment costs and system complexity, has become a key challenge and an urgent technical problem to be solved. Summary of the Invention

[0006] To address the aforementioned problems in the existing technology, this invention provides a synergistic treatment system for fluoride removal and heavy metal recovery in photovoltaic wastewater. The technical problem to be solved by this invention is achieved through the following technical solution: This invention provides a synergistic treatment system for fluoride removal and heavy metal recovery in photovoltaic wastewater, comprising: The classified collection and regulation system is used to classify and collect wastewater containing fluoride, ammonia nitrogen, acidic wastewater, alkaline wastewater and heavy metal wastewater generated during the photovoltaic production process and to regulate water quality. A synergistic reaction treatment system, connected to the sorting and collection conditioning system, is used to synergistically react and treat fluoride-containing conditioning water and ammonia-nitrogen-containing conditioning water to obtain synergistically treated product water. An acid-base synergistic treatment system, connected to the sorting, collection, and regulation system, is used to synergistically treat acidic regulation water, alkaline regulation water, and heavy metal-containing regulation water to obtain acid-base synergistic product water. A mixed treatment system, connected to the synergistic reaction treatment system and the acid-base synergistic treatment system, is used to mix and induce crystallization of the synergistic treatment product water and the acid-base synergistic product water to obtain mixed product water; An advanced treatment system, connected to the mixed treatment system, is used to further treat the mixed permeate to obtain reclaimed water.

[0007] In one embodiment of the present invention, the classified collection and regulation system includes a fluoride-containing wastewater regulation unit, an ammonia-nitrogen-containing wastewater regulation unit, an acidic wastewater regulation unit, an alkaline wastewater regulation unit, and a heavy metal-containing wastewater regulation unit.

[0008] In one embodiment of the present invention, the fluoride-containing wastewater conditioning unit includes a first conditioning zone and a second conditioning zone connected to the first conditioning zone; the first conditioning zone is equipped with an aeration and stirring device, and the first conditioning zone adds lime slurry to cause some fluoride ions to react with calcium ions to form calcium fluoride precipitate; the second conditioning zone is equipped with a flow guide baffle to allow the wastewater to flow in a push flow manner, and the second conditioning zone adds sodium hydroxide solution to adjust the pH value to 6.0~8.0; The ammonia-nitrogen wastewater conditioning unit includes a pre-aeration zone, a main conditioning zone, and a stabilization zone arranged sequentially along the water flow direction. The pre-aeration zone is connected to the acid washing spray tower via a sealed cover and a tail gas collection device for recovering ammonia-containing tail gas. The main conditioning zone adjusts the pH value to 9.0~10.5 by adding sodium hydroxide solution. The stabilization zone is used to add buffers sodium carbonate and sodium bicarbonate when the pH value fluctuates beyond a set threshold. The acidic wastewater conditioning unit and the alkaline wastewater conditioning unit are arranged adjacently through a shared pool wall for non-contact heat exchange between acidic and alkaline wastewater. The shared pool wall is made of stainless steel corrugated plate. The heavy metal-containing wastewater conditioning unit includes a reaction zone, a solid-liquid separation component, and a conditioning zone. The reaction zone is used to add a heavy metal selective complexing agent to the heavy metal-containing wastewater to cause heavy metal ions to form insoluble chelate precipitates. The solid-liquid separation component is used to perform solid-liquid separation on the mixture in the reaction zone. The conditioning zone is used to monitor the pH of the separated clear liquid and adjust the pH value to 4.0~6.0.

[0009] In one embodiment of the present invention, the synergistic reaction processing system includes a first mixing reaction zone, a second mixing reaction zone, a slow growth zone, a flocculation zone, a first solid-liquid separation unit, and a second solid-liquid separation unit; The first mixing reaction zone is used to mix the fluoride-containing water with the added calcium salt and pH adjuster evenly through a high-shear homogenizing emulsifier to generate calcium fluoride crystal nuclei. After the reaction is completed, the effluent enters the first solid-liquid separation unit, the separated fluoride precipitate is discharged and recycled, and the clear liquid flows into the second mixing reaction zone. The second mixing reaction zone is used to mix the clear liquid from the first mixing reaction zone with ammonia nitrogen-adjusted water, while adding magnesium salt, phosphate and pH adjuster, and generating magnesium ammonium phosphate crystal nuclei under the action of a high shear homogenizing emulsifier; The stirring speed in the slow growth zone decreases gradually along the water flow direction, which is used to allow the magnesium ammonium phosphate crystal nuclei in the effluent of the second mixing reaction zone to continue to grow, so as to obtain crystal particles of a preset particle size. The flocculation zone is used to promote the flocculation and growth of the crystal particles to form flocs by adding flocculants; The second solid-liquid separation unit is used to separate the flocs obtained after flocculation from the water to obtain magnesium ammonium phosphate precipitate and supernatant as the co-processed water.

[0010] In one embodiment of the present invention, the acid-base synergistic treatment system includes an acid-base neutralization reaction tank, a heavy metal reaction tank, a flocculation reaction unit and a third solid-liquid separation unit arranged sequentially. The acid-base neutralization reaction tank includes a turbulent neutralization zone, a plug flow neutralization zone, and a stabilization zone arranged sequentially along the water flow direction. The turbulent neutralization zone is used to achieve turbulent mixing of acidic and alkaline conditioning water using the pressure of the inlet pipe. The plug flow neutralization zone is used to make the water flow in a plug flow manner through a baffle-type flow guide structure for neutralization. The stabilization zone is used to adjust the pH of the mixture to 7.5~9.0. The heavy metal reaction tank includes three precipitation zones arranged along the length of the tank. The first precipitation zone precipitates lead and silver ions by controlling the pH to 6.5-7.5, the second precipitation zone precipitates copper ions by controlling the pH to 7.5-8.5, and the third precipitation zone precipitates residual heavy metal ions by controlling the pH to 8.5-9.5. The flocculation reaction unit is used to promote the flocculation and growth of tiny precipitate particles in the effluent of the heavy metal reaction tank by adding flocculants. The third solid-liquid separation unit is used to separate the flocs after flocculation reaction from the water to obtain sludge sediment and supernatant as acid-base co-production water.

[0011] In one embodiment of the present invention, the mixing treatment system includes a mixing and conditioning tank, an induced crystallizer, and an intermediate sedimentation tank arranged sequentially. The mixing and regulating tank is equipped with an aeration and stirring system, which is used to mix the co-treated water and the acid-base co-treated water evenly through aeration and stirring. The induced crystallizer is filled with a packing material loaded with a nano-hydroxyapatite coating, which is used to induce the crystallization of residual ions in the mixed water on the surface of the packing material. The intermediate sedimentation tank is used to settle the effluent from the induced crystallizer to obtain bottom sediment and supernatant as mixed product water.

[0012] In one embodiment of the present invention, the induced crystallizer is provided with a combined air-water backwashing device, which is used to peel off and discharge the crystal layer when the crystal layer on the surface of the packing reaches a preset thickness.

[0013] In one embodiment of the present invention, the deep treatment system includes a pre-crystallization softening unit, a multi-media filtration unit, an ultrafiltration unit, a reverse osmosis unit, a disinfection unit, and a concentrate stage concentration-salt separation unit. The pre-crystallization softening unit is used to crystallize and precipitate residual calcium and magnesium in the water as calcium carbonate and magnesium hydroxide on the surface of the silica sand carrier. The multi-media filtration unit is used to filter the effluent from the pre-crystallization softening unit through a double layer of quartz sand and anthracite filter media. The ultrafiltration unit is used to filter the water effluent from the multi-media filtration unit through a cross-flow filtration method using a polyvinylidene fluoride hollow fiber membrane. The reverse osmosis unit is used to filter impurities in the effluent from the ultrafiltration unit through a polyamide composite membrane; The disinfection unit is used to disinfect the permeate from the reverse osmosis unit to obtain reclaimed water; The concentrate stage concentration-salt separation unit is used to perform stage concentration and salt separation treatment on the concentrate produced by the reverse osmosis unit.

[0014] In one embodiment of the present invention, the concentrated water staged concentration-salt separation unit includes a primary nanofiltration membrane system, a secondary reverse osmosis system, a first mechanical vapor recompression evaporator crystallizer, and a second mechanical vapor recompression evaporator crystallizer; The primary nanofiltration membrane system is used for salt separation of the concentrated water produced by the reverse osmosis unit; The secondary reverse osmosis system is used to further concentrate the permeate from the primary nanofiltration membrane system; the first mechanical vapor recompression evaporator is used to evaporate and crystallize the concentrate from the primary nanofiltration membrane system. The permeate from the secondary reverse osmosis system is returned to the mixing treatment system, and the concentrate from the secondary reverse osmosis system enters the second mechanical steam recompression evaporator crystallizer.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The synergistic treatment system of this invention achieves synergistic treatment and resource integration of photovoltaic wastewater by constructing a complete treatment chain including a classification collection and regulation system, a synergistic reaction treatment system, an acid-base synergistic treatment system, a mixing treatment system, and a deep treatment system. Fluoride-containing wastewater and ammonia-nitrogen-containing wastewater complete the precipitation and removal of fluoride ions and ammonia nitrogen in the synergistic reaction treatment system, and the neutralization reaction of acid-base wastewater provides an alkaline environment for heavy metal precipitation, realizing the synergistic effect of treating waste with waste. The system has high pollutant removal efficiency, high effluent quality, low treatment cost, and low operating energy consumption, realizing the recycling and near-zero discharge of wastewater and the cascade recovery of various valuable resources. Attached Figure Description

[0016] Figure 1 A schematic diagram of a synergistic treatment system for defluorination and heavy metal recovery of photovoltaic wastewater provided in an embodiment of the present invention; Figure 2 A schematic diagram of the synergistic reaction processing system provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the acid-base synergistic treatment system provided in an embodiment of the present invention; Figure 4 A schematic diagram of a hybrid processing system provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of a depth processing system provided in an embodiment of the present invention. Detailed Implementation

[0017] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0018] Example 1 Please see Figure 1 , Figure 1 This is a schematic diagram of a synergistic treatment system for defluorination and heavy metal recovery of photovoltaic wastewater provided in an embodiment of the present invention.

[0019] The synergistic treatment system for defluorination and heavy metal recovery of photovoltaic wastewater includes: a classification collection and conditioning system 100, used for classifying and collecting fluoride-containing wastewater, ammonia nitrogen-containing wastewater, acidic wastewater, alkaline wastewater, and heavy metal-containing wastewater generated during photovoltaic production and for water quality conditioning; a synergistic reaction treatment system 200, connected to the classification collection and conditioning system 100, used for synergistic reaction treatment of fluoride-containing conditioning water and ammonia nitrogen-containing conditioning water to obtain synergistically treated product water; an acid-base synergistic treatment system 300, connected to the classification collection and conditioning system 100, used for synergistic reaction treatment of acidic conditioning water, alkaline conditioning water, and heavy metal-containing conditioning water to obtain acid-base synergistic product water; a mixing treatment system 400, connected to the synergistic reaction treatment system 200 and the acid-base synergistic treatment system 300, used for mixing the synergistically treated product water and the acid-base synergistic product water and inducing crystallization to obtain mixed product water; and a deep treatment system 500, connected to the mixing treatment system 400, used for deep treatment of the mixed product water to obtain reclaimed water.

[0020] Specifically, the classified collection and regulation system 100 is connected to the fluoride-containing wastewater discharge outlet, ammonia-nitrogen-containing wastewater discharge outlet, acidic wastewater discharge outlet, alkaline wastewater discharge outlet, and heavy metal-containing wastewater discharge outlet of the photovoltaic production workshop through five independent inlet pipes. The outlets of the different types of wastewater from the classified collection and regulation system 100 are connected to the inlet of the co-reaction treatment system 200 and the acid-alkali co-treatment system 300 through pipes. The outlets of the co-reaction treatment system 200 and the acid-alkali co-treatment system 300 are connected to the inlet of the mixed treatment system 400 through pipes. The outlet of the mixed treatment system 400 is connected to the inlet of the advanced treatment system 500 through a pipe. The outlet of the advanced treatment system 500 is connected to the water-using process of the photovoltaic production workshop through a reuse pipe.

[0021] In one specific embodiment, the classification collection and regulation system 100 includes a fluoride-containing wastewater regulation unit 110, an ammonia-nitrogen-containing wastewater regulation unit 120, an acidic wastewater regulation unit 130, an alkaline wastewater regulation unit 140, and a heavy metal-containing wastewater regulation unit 150.

[0022] The fluoride-containing wastewater conditioning unit 110 includes a first conditioning zone and a second conditioning zone connected to the first conditioning zone; the first conditioning zone is equipped with an aeration and stirring device, and lime slurry is added to the first conditioning zone to cause some fluoride ions to react with calcium ions to form calcium fluoride precipitate; the second conditioning zone is equipped with a flow guide baffle to make the wastewater flow in a push flow manner, and the pH value is adjusted to 6.0~8.0 by adding a pH adjuster.

[0023] Hydrofluoric acid-containing wastewater generated during the texturing and cleaning processes in the photovoltaic production workshop is introduced into the fluoride-containing wastewater conditioning unit 110 through corrosion-resistant polyvinylidene fluoride (PVDF) pipes. The main characteristics of the fluoride-containing wastewater are: pH value 1.5~3.5, fluoride ion concentration 500~5000 mg / L, and small amounts of nitric acid and hydrochloric acid. The fluoride-containing wastewater conditioning unit 110 adopts a dual-zone design: the first conditioning zone is a coarse pH adjustment zone, and the second conditioning zone is a fine pH adjustment zone. In the first conditioning zone, the wastewater is vigorously agitated by a bottom-mounted aeration and stirring device, while lime slurry is added via a dosing device. During this process, calcium ions in the lime slurry react with fluoride ions to form calcium fluoride precipitate, removing some of the fluoride ions. In the second conditioning zone, a pH adjuster is added via a dosing device to adjust the pH to 6.0~8.0. The second conditioning zone is equipped with flow guide baffles to allow the wastewater to flow in a plug flow manner, with a hydraulic retention time of 30~60 minutes. After adjustment, fluoride-treated water is obtained, with the fluoride ion concentration reduced by about 15% to 30% and the pH value between 6.0 and 8.0.

[0024] The ammonia nitrogen wastewater conditioning unit 120 includes a pre-aeration zone, a main conditioning zone, and a stabilization zone arranged sequentially along the water flow direction. The pre-aeration zone is connected to the acid washing spray tower through a sealed cover and a tail gas collection device for recovering ammonia tail gas. The main conditioning zone adjusts the pH value to 9.0~10.5 by adding sodium hydroxide solution. The stabilization zone is used to add a buffer when the pH value fluctuates beyond the set threshold.

[0025] Ammonia-containing nitrogen wastewater discharged after ammonia cleaning or pH adjustment during photovoltaic production is introduced into the ammonia-containing nitrogen wastewater conditioning unit 120 via a separate pipeline. The main characteristics of this ammonia-containing nitrogen wastewater are: pH value 9.5~11.5, ammonia nitrogen concentration 200~2000 mg / L, and the presence of small amounts of fluoride ions and suspended solids. The ammonia-containing nitrogen wastewater conditioning unit 120 is divided into three zones along the water flow direction: a pre-aeration zone, a main conditioning zone, and a stabilization zone. The pre-aeration zone is equipped with a high-intensity aeration device that strips free ammonia from the wastewater through airlift. The stripped ammonia-containing tail gas is sent to an acid washing spray tower through a sealed cover and tail gas collection device. The acid washing spray tower uses dilute sulfuric acid as the absorbent to convert ammonia gas into ammonium sulfate solution; the ammonia nitrogen removal rate in the pre-aeration zone is approximately 15%~30%. The main adjustment zone automatically adds pH adjuster to 9.0-10.5 based on feedback from the online pH meter and online ammonia nitrogen analyzer, while simultaneously employing low-intensity intermittent aeration for homogenization. The stabilization zone is equipped with a buffer dosing device. When pH fluctuations exceed a set threshold (e.g., fluctuations exceeding ±0.15 around the target pH of 10.0), sodium carbonate and sodium bicarbonate buffers are added to stabilize the pH. After adjustment, ammonia nitrogen-containing adjusted water is obtained with a pH of 9.0-10.5, and pH fluctuations controlled within ±0.15.

[0026] Ammonia nitrogen in wastewater is mainly NH4+. + It exists in two forms, NH4+ and NH3, and their ratio is controlled by pH: when pH < 9.0, it exists in NH4+ form. + The primary ammonia component is NH3, with NH3 being dominant at pH > 10.5. This embodiment employs a gradient aeration design. In the pre-aeration zone, high-intensity aeration strips a large amount of free ammonia immediately upon the wastewater's entry into the equalization tank, reducing the ammonia nitrogen load in the main equalization zone and decreasing the treatment pressure on subsequent units. Intermittent aeration, rather than continuous aeration, is used in the main equalization zone to ensure uniform water quality while preventing excessive aeration that could lead to large-scale ammonia loss. A pH buffer dosing device is installed in the stabilization zone to ensure stable effluent pH during long-term operation, utilizing the buffer's pH-stabilizing effect.

[0027] The acidic wastewater conditioning unit 130 and the alkaline wastewater conditioning unit 140 are arranged adjacent to each other through a shared pool wall for non-contact heat exchange between the acidic and alkaline wastewater.

[0028] Acidic and alkaline wastewater generated from various processes in photovoltaic production are introduced into acidic wastewater conditioning unit 130 and alkaline wastewater conditioning unit 140 respectively through independent pipelines. The pH value of the acidic wastewater is 1.0~4.0, and the pH value of the alkaline wastewater is 10.0~13.0. Acidic wastewater conditioning unit 130 and alkaline wastewater conditioning unit 140 adopt a series buffer and heat exchange integrated design. The two conditioning units are arranged adjacent to each other in the pool structure through a shared pool wall. The shared pool wall is made of stainless steel corrugated plate with high thermal conductivity, utilizing the temperature difference between the acidic and alkaline wastewater for non-contact heat exchange, preheating the acidic wastewater and precooling the alkaline wastewater simultaneously. In acidic wastewater conditioning unit 130, the pH value is coarsely adjusted to 4.0~6.0 by adding sodium hydroxide or lime slurry. In alkaline wastewater conditioning unit 140, the pH value is coarsely adjusted to 8.0~10.0 by adding sulfuric acid or hydrochloric acid.

[0029] Photovoltaic alkaline wastewater is typically at a high temperature, while acidic wastewater is at a low temperature. In this embodiment, heat exchange is achieved through a heat-conducting corrugated plate. On the one hand, the residual heat of the alkaline wastewater is used to preheat the acidic wastewater, allowing the subsequent acid-base neutralization reaction to proceed quickly and increasing the reaction rate. On the other hand, the temperature of the alkaline wastewater is reduced, minimizing the corrosion of pipes, valves, pumps, and other components in the subsequent treatment unit caused by high temperatures.

[0030] The heavy metal wastewater conditioning unit 150 includes a reaction zone, a solid-liquid separation component, and a conditioning zone. The reaction zone is used to add a heavy metal selective complexing agent to cause heavy metal ions to form insoluble chelate precipitates. The solid-liquid separation component is used to perform solid-liquid separation on the mixture in the reaction zone. The conditioning zone is used to monitor the pH of the separated clear liquid and adjust the pH value to 4.0~6.0.

[0031] Wastewater from photovoltaic cell production, including cleaning and etching wastewater containing heavy metals such as silver, copper, and lead, is introduced into a heavy metal-containing wastewater conditioning unit 150 via a separate pipeline. The main characteristics of this wastewater are: pH value 2.0–6.0, and total heavy metal ion concentration 10–200 mg / L. The heavy metal-containing wastewater conditioning unit 150 consists of a reaction zone, a solid-liquid separation component, and a conditioning zone. In the reaction zone, sodium diethyldithiocarbamate (DDTC), a selective complexing agent for heavy metals, is added, causing heavy metal ions to react with DDTC to form stable, insoluble chelate precipitates. The mixture from the reaction zone is then piped into the solid-liquid separation component for solid-liquid separation. This component can be a tubular microfiltration membrane module, employing a cross-flow filtration method. The clarified liquid obtained after filtration by the tubular microfiltration membrane module enters the conditioning zone. The pH of the clarified liquid is monitored using an online pH meter, and sodium hydroxide solution is added to adjust the pH value to 4.0–6.0. After adjustment, water containing heavy metals is obtained, with a pH value of 4.0~6.0 and a total concentration of heavy metal ions reduced to 5~40 mg / L.

[0032] This embodiment performs complexation pre-separation on heavy metal-containing wastewater in the reaction zone, which can remove most of the heavy metal ions before the wastewater is mixed with other wastewater, significantly reducing the load on the heavy metal precipitation unit in the subsequent acid-base co-treatment system. Simultaneously, the pre-separated heavy metal-DDTC chelate precipitate has a high heavy metal content and small volume, facilitating subsequent recovery of valuable metals.

[0033] Please see Figure 2 , Figure 2 This is a schematic diagram of a synergistic reaction processing system provided in an embodiment of the present invention. The synergistic reaction processing system 200 includes a first mixing reaction zone 210, a second mixing reaction zone 220, a slow growth zone 230, a flocculation zone 240, a first solid-liquid separation unit 250, and a second solid-liquid separation unit 260.

[0034] The first mixing reaction zone 210 is used to uniformly mix fluoride-containing conditioning water with added calcium salt and pH adjuster through a high-shear homogenizing emulsifier to generate calcium fluoride crystal nuclei. After the reaction is completed, the effluent enters the first solid-liquid separation unit 250. The separated fluoride-containing precipitate is discharged and recycled, while the clear liquid flows into the second mixing reaction zone 220. The second mixing reaction zone 220 is used to mix the clear liquid from the first mixing reaction zone with ammonia nitrogen-containing conditioning water, and simultaneously add magnesium salt, phosphate and pH adjuster. Under the action of a high-shear homogenizing emulsifier, magnesium ammonium phosphate crystal nuclei are generated. In the slow growth zone 230, the stirring speed decreases gradually along the water flow direction to allow the magnesium ammonium phosphate crystal nuclei in the effluent of the second mixing reaction zone to continue to grow, obtaining crystal particles of a preset particle size. The flocculation zone 240 is used to promote the flocculation and growth of crystal particles to form flocs by adding flocculants. The second solid-liquid separation unit 260 is used to separate the flocs obtained after flocculation from the water to obtain magnesium ammonium phosphate precipitate and supernatant as co-processed permeate.

[0035] Specifically, the first mixing reaction zone 210 is used to uniformly mix the fluoride-containing adjusted water with the added calcium salt and pH adjuster through a high-shear homogenizing emulsifier, and control the reaction pH to 9.5~10.5 (achieved by automatically adding sodium hydroxide solution), so that fluoride ions and calcium ions can form calcium fluoride crystal nuclei. The hydraulic residence time is 2~5 minutes, the linear velocity of the high-shear homogenizing emulsifier is 15~25 m / s, and the calcium salt (calcium chloride) is added at a calcium-fluoride molar ratio of 1.2:1~1.5:1. After the reaction is completed, the effluent enters the first solid-liquid separation unit 250 (such as inclined tube sedimentation or tubular microfiltration). The separated fluoride-containing precipitate is discharged and recycled, while the clear liquid flows into the second mixing reaction zone 220.

[0036] The second mixing reaction zone 220 is used to mix the clarified liquid from the first mixing reaction zone 210 with ammonia nitrogen-adjusted water, while simultaneously adding magnesium salts, phosphates, and pH adjusters to control the reaction pH at 8.5-9.5 (automatic addition of dilute sulfuric acid or sodium hydroxide via online pH feedback). The molar ratio of magnesium:ammonia nitrogen:phosphate is 1.1:1:1.1. Under the action of a high-shear homogenizing emulsifier, magnesium ammonium phosphate crystal nuclei are rapidly generated. At this pH range, the precipitation efficiency of magnesium ammonium phosphate is the highest, and the residual calcium concentration in the clarified liquid is significantly reduced, effectively avoiding competitive side reactions of calcium phosphate. The effluent from the second mixing reaction zone 220 sequentially enters the slow growth zone 230 and the flocculation zone 240, allowing the magnesium ammonium phosphate crystal nuclei to continue to grow and flocculate. Subsequently, solid-liquid separation is performed through the second solid-liquid separation unit 260. The supernatant is the co-treated permeate, and the bottom sludge is high-purity magnesium ammonium phosphate precipitate, which can be recycled for use as slow-release fertilizer.

[0037] In the slow growth zone 230, the stirring speed decreases gradually along the water flow direction: 50-60 rpm at the inlet, 40-50 rpm in the middle, and less than 40 rpm at the outlet, with a hydraulic residence time of 20-30 minutes. Under staged stirring conditions, the crystal nuclei continuously grow into large crystal particles with a diameter of 50-100 μm in the slow growth zone 220.

[0038] In flocculation zone 240, flocculants, including polyaluminum chloride (PAC) and polyacrylamide (PAM), are added via metering pumps. The dosage of PAC is 10-30 mg / L, and the dosage of PAM is 1-3 mg / L, with a PAM mass concentration of 0.1%-0.2%. Flocculation zone 230 is equipped with a slow-speed agitator at a speed of 20-30 rpm and a hydraulic retention time of 10-15 minutes, allowing the crystal particles to flocculate and grow into flocs.

[0039] Both the first solid-liquid separation unit 250 and the second solid-liquid separation unit 260 employ inclined tube sedimentation tanks with a hydraulic retention time of 1.0 to 1.5 hours. The supernatant from the second solid-liquid separation unit 260 is the co-treatment permeable wastewater, which is transported to the mixed treatment system 400 via an effluent pipeline. Bottom sludge is discharged through a sludge discharge pipe. The water quality targets for the co-treatment permeable wastewater are: fluoride ion concentration ≤ 5 mg / L and ammonia nitrogen concentration ≤ 20 mg / L.

[0040] In this embodiment, a high-shear homogenizing emulsifier is used in the mixing zone, which enables the reagent and wastewater to be mixed rapidly at the microscale, generating a large number of uniformly sized crystal nuclei to provide seed crystals for subsequent crystal growth. The staged stirring strategy in the slow growth zone allows the crystals to continuously undergo a positive feedback cycle of "collision-agglomeration-growth-re-collision" during the flow process. The high-intensity stirring in the inlet section evenly disperses the crystal nuclei to prevent sedimentation, the moderate stirring in the middle section promotes collisional growth, and the gentle stirring in the outlet section protects the large crystals. During the sedimentation process, the large crystals become the traps for the small crystal nuclei, and the small crystal nuclei grow heterogeneously on the surface of the large crystals, ensuring the integrity and large particle size distribution of the discharged crystals.

[0041] This embodiment, through the combined setting of the second mixing reaction zone and the slow growth zone, increases the crystal particle size, improves the crystal sedimentation rate, enhances the ammonia nitrogen removal rate, and reduces the amount of reagent used, thus shortening the treatment time.

[0042] Please see Figure 3 , Figure 3 This is a schematic diagram of an acid-base synergistic treatment system provided in an embodiment of the present invention. The acid-base synergistic treatment system 300 includes an acid-base neutralization reaction tank 310, a heavy metal reaction tank 320, a flocculation reaction unit 330, and a third solid-liquid separation unit 340.

[0043] The inlet of the acid-base neutralization reaction tank 310 is connected to the outlets of the acidic wastewater conditioning unit and the alkaline wastewater conditioning unit via pipes and a booster pump, respectively. The inlet of the heavy metal reaction tank 320 is connected to the outlet of the heavy metal-containing wastewater conditioning unit via pipes and a booster pump, and is also connected to the outlet of the acid-base neutralization reaction tank 310 via pipes.

[0044] The acid-base neutralization reaction tank 310 includes a turbulent neutralization zone, a plug flow neutralization zone, and a stabilization zone arranged sequentially along the water flow direction. The turbulent neutralization zone is used to achieve turbulent mixing of acidic and alkaline conditioning water using the pressure of the inlet pipe. The plug flow neutralization zone is used to make the water flow in a plug flow manner through a baffle-type flow guide structure for neutralization. The stabilization zone is used to adjust the pH of the mixed solution to 7.5~9.0. The heavy metal reaction tank 320 includes three sedimentation zones arranged along the length of the tank. The first sedimentation zone controls the pH to 6. The first sedimentation zone has a pH of 0.5-7.5 to precipitate lead and silver ions; the second sedimentation zone has a pH of 7.5-8.5 to precipitate copper ions; and the third sedimentation zone has a pH of 8.5-9.5 to precipitate residual heavy metal ions. The flocculation reaction unit 330 is used to promote the flocculation and growth of tiny precipitate particles in the effluent of the heavy metal reaction tank by adding flocculants. The third solid-liquid separation unit 340 is used to separate the flocs after the flocculation reaction from the water to obtain sludge sediment and supernatant as acid-base co-processed water.

[0045] The acid-base neutralization reaction tank 310 is divided into three stages along the water flow direction. The first stage is the turbulent neutralization zone, equipped with a hydraulic jet mixer. Utilizing the pressure of the inlet pipe, it achieves high-intensity turbulent mixing of the acidic and alkaline conditioning water, where over 80% of the neutralization reaction is completed. The second stage is the plug flow neutralization zone, equipped with a baffle-type flow guide structure to ensure a plug flow, completing the remaining neutralization reaction. The third stage is the stabilization zone, equipped with an online pH meter and thermometer. An automatic dosing system precisely adjusts the pH of the mixed solution to 7.5~9.0. A spiral coil heat exchanger is installed at the bottom of the stabilization zone, recovering and utilizing the heat released during the neutralization reaction through circulating cooling water.

[0046] The effluent from the acid-base neutralization reaction tank 310 enters the heavy metal reaction tank 320. The heavy metal reaction tank 320 has three sedimentation zones along its length. The first sedimentation zone maintains a pH of 6.5–7.5, primarily precipitating lead and silver ions, with a hydraulic retention time of 10–15 minutes. The second sedimentation zone maintains a pH of 7.5–8.5, primarily precipitating copper ions, with a hydraulic retention time of 10–15 minutes. The third sedimentation zone maintains a pH of 8.5–9.5, precipitating residual heavy metal ions, with a hydraulic retention time of 10–15 minutes. pH is controlled in stages between sedimentation zones through automatic addition of pH adjusters. Each zone is equipped with an independent stirring device and an online pH meter. Each sedimentation zone has an independent sludge discharge port at its bottom.

[0047] The effluent from the heavy metal reaction tank 320 enters the flocculation reaction unit 330. In the flocculation reaction unit 330, PAC and PAM are added to promote the flocculation and growth of small precipitate particles. The dosage of PAC is 15-25 mg / L, and the dosage of PAM is 1-2 mg / L. After slow stirring, the effluent enters the third solid-liquid separation unit 340. The third solid-liquid separation unit 340 uses an inclined tube sedimentation tank with a hydraulic retention time of 1.0-2.0 hours. The supernatant from the inclined tube sedimentation tank is the acid-base co-processed wastewater, which is transported to the mixed treatment system 400 through the effluent pipeline. The water quality targets for the acid-base co-processed wastewater are: total heavy metal ion concentration ≤0.1 mg / L, and pH value 6.5-8.5.

[0048] This embodiment adopts a stepwise precipitation strategy. By precisely controlling the pH value of each precipitation zone, different heavy metal ions are precipitated step by step in their respective optimal pH ranges. The types of heavy metals in each precipitate are relatively simple, which facilitates subsequent classification, recycling and resource utilization.

[0049] Please see Figure 4 , Figure 4This is a schematic diagram of a mixing treatment system provided in an embodiment of the present invention. The mixing treatment system 400 includes a mixing and conditioning tank 410, an induced crystallizer 420, and an intermediate sedimentation tank 430 arranged sequentially. The first inlet of the mixing and conditioning tank 410 is connected to the outlet of the synergistic reaction treatment system 200 via a pipeline, and the second inlet is connected to the outlet of the acid-base synergistic treatment system 300 via a pipeline.

[0050] The co-treated permeate and the acid-base co-treated permeate are transported to the mixing and equalization tank 410 via pipeline at a volume ratio of 1:0.5 to 1:2. The mixing and equalization tank 410 is equipped with an aeration and stirring system to mix the co-treated permeate and the acid-base co-treated permeate evenly through aeration and stirring.

[0051] The effluent from the mixing and equalization tank 410 enters the induced crystallizer 420. The induced crystallizer 420 is filled with packing material coated with nano-hydroxyapatite (n-HAP) to induce the crystallization of residual ions in the mixed water on the surface of the packing material. Specifically, the induced crystallizer 420 is filled with modified quartz sand packing material, the surface of which is coated with a nano-hydroxyapatite (n-HAP) coating. The mixed water flows through the induced crystallizer at an upward flow rate of 0.5~2.0 m / h. The lattice constant of n-HAP has good lattice matching with CaF2 and MgNH4PO4·6H2O, allowing residual Ca... 2+ F - Mg 2+ NH 4+ PO4 3- Plasma induces crystallization on the surface of the packing material, generating mixed crystals of calcium fluoride and magnesium ammonium phosphate that are deposited on the packing surface.

[0052] Furthermore, the induced crystallizer is equipped with a combined air-water backwashing device, used to peel off and discharge the crystal layer when the crystal layer on the packing surface thickens to a preset thickness via combined air-water backwashing. The crystal thickness can be obtained using an ultrasonic thickness gauge. For example, the preset thickness of the crystal layer can be 2-3 mm. The crystal layer thickness on the packing surface typically reaches 2-3 mm in about 3 weeks, or it can be peeled off via combined air-water backwashing at 2-3 week intervals.

[0053] Intermediate sedimentation tank 430 is used to settle the effluent from the induced crystallizer, obtaining bottom sediment and supernatant as mixed permeate. The mixed permeate is transported to the advanced treatment system 500 through the effluent pipeline. The water quality targets for the mixed permeate are: fluoride ion ≤3mg / L, ammonia nitrogen ≤10mg / L, and total heavy metal concentration ≤0.05mg / L.

[0054] This embodiment further improves the removal rates of residual fluoride ions and residual ammonia nitrogen by setting up an induced crystallizer, thereby further enhancing the quality of the mixed product water.

[0055] Please see Figure 5 , Figure 5 This is a schematic diagram of a deep treatment system provided in an embodiment of the present invention. The deep treatment system 500 includes a pre-crystallization and softening unit 510, a multi-media filtration unit 520, an ultrafiltration unit 530, a reverse osmosis unit 540, a disinfection unit 550, and a concentrate stage concentration-salt separation unit 560, with each unit connected sequentially via pipelines.

[0056] The mixed permeate first enters the pre-crystallization softening unit 510. This unit causes residual calcium and magnesium in the water to crystallize and precipitate on the surface of the silica sand carrier in the form of calcium carbonate and magnesium hydroxide. The pre-crystallization softening unit 510 employs a fluidized bed reactor with an internal silica sand carrier. The mixed permeate enters from the bottom of the fluidized bed reactor, fluidizing the silica sand carrier. Sodium hydroxide and sodium carbonate solutions are added separately via metering pumps, causing residual calcium and magnesium hardness in the water to crystallize and precipitate on the silica sand carrier surface in the form of calcium carbonate and magnesium hydroxide. After pre-crystallization softening, the total hardness of the effluent is significantly reduced.

[0057] The effluent from the pre-crystallization softening unit 510 enters the multi-media filtration unit 520. The multi-media filtration unit 520 includes a multi-media filter filled with a dual-layer filter media of quartz sand and anthracite, which filters the effluent from the pre-crystallization softening unit.

[0058] The effluent from the multi-media filtration unit 520 enters the ultrafiltration unit 530. The ultrafiltration unit 530 includes an ultrafiltration membrane module 531. The ultrafiltration membrane is a polyvinylidene fluoride (PVDF) hollow fiber membrane. The ultrafiltration system adopts a cross-flow filtration method, filtering the effluent from the multi-media filtration unit through the PVDF hollow fiber membrane.

[0059] The effluent from the ultrafiltration unit 530 enters the reverse osmosis unit 540. The reverse osmosis unit 540 includes a reverse osmosis membrane module, and the reverse osmosis membrane is a polyamide composite membrane, which filters impurities in the effluent from the ultrafiltration unit.

[0060] The permeate from the reverse osmosis unit 540 is disinfected by the disinfection unit 550 to obtain reclaimed water.

[0061] The concentrate produced by the reverse osmosis unit 540 enters the concentrate stage concentration-salt separation unit 560. The concentrate stage concentration-salt separation unit 560 includes a primary nanofiltration membrane system, a secondary reverse osmosis system, a first mechanical vapor recompression (MVR) evaporator crystallizer, and a second mechanical vapor recompression (MVR) evaporator crystallizer. The primary nanofiltration membrane system separates the monovalent salts (NaCl) and divalent salts (Na₂SO₄, CaSO₄) from the reverse osmosis concentrate. The permeate from the primary nanofiltration membrane system (mainly containing NaCl) enters the secondary reverse osmosis system for further concentration under high pressure. The concentrate from the primary nanofiltration membrane system (mainly containing Na₂SO₄, CaSO₄) enters the first MVR evaporator crystallizer for evaporation and crystallization. The permeate from the secondary reverse osmosis system is returned to the front-end mixing treatment system 400. The concentrate from the secondary reverse osmosis system enters the second MVR evaporator crystallizer for evaporation and crystallization.

[0062] The synergistic treatment system of this invention achieves synergistic treatment and resource integration of photovoltaic wastewater by constructing a complete treatment chain including a classification collection and regulation system, a synergistic reaction treatment system, an acid-base synergistic treatment system, a mixing treatment system, and a deep treatment system. Fluoride-containing wastewater and ammonia-nitrogen-containing wastewater complete the precipitation and removal of fluoride ions and ammonia nitrogen in the synergistic reaction treatment system, and the neutralization reaction of acid-base wastewater provides an alkaline environment for heavy metal precipitation, realizing the synergistic effect of treating waste with waste. The system has high pollutant removal efficiency, high effluent quality, low treatment cost, and low operating energy consumption, realizing the recycling and near-zero discharge of wastewater and the cascade recovery of various valuable resources.

[0063] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A synergistic treatment system for defluoridation and heavy metal recovery of photovoltaic wastewater, characterized in that, include: The classified collection and regulation system is used to classify and collect wastewater containing fluoride, ammonia nitrogen, acidic wastewater, alkaline wastewater and heavy metal wastewater generated during the photovoltaic production process and to regulate water quality. A synergistic reaction treatment system, connected to the sorting and collection conditioning system, is used to synergistically react and treat fluoride-containing conditioning water and ammonia-nitrogen-containing conditioning water to obtain synergistically treated product water. An acid-base synergistic treatment system, connected to the sorting, collection, and regulation system, is used to synergistically treat acidic regulation water, alkaline regulation water, and heavy metal-containing regulation water to obtain acid-base synergistic product water. A mixed treatment system, connected to the synergistic reaction treatment system and the acid-base synergistic treatment system, is used to mix and induce crystallization of the synergistic treatment product water and the acid-base synergistic product water to obtain mixed product water; An advanced treatment system, connected to the mixed treatment system, is used to further treat the mixed permeate to obtain reclaimed water.

2. The synergistic treatment system for defluoridation and heavy metal recovery of photovoltaic wastewater according to claim 1, characterized in that, The classified collection and regulation system includes a fluoride-containing wastewater regulation unit, an ammonia-nitrogen-containing wastewater regulation unit, an acidic wastewater regulation unit, an alkaline wastewater regulation unit, and a heavy metal-containing wastewater regulation unit.

3. The synergistic treatment system for defluoridation and heavy metal recovery of photovoltaic wastewater according to claim 2, characterized in that, The fluoride-containing wastewater conditioning unit includes a first conditioning zone and a second conditioning zone connected to the first conditioning zone; the first conditioning zone is equipped with an aeration and stirring device, and lime slurry is added to the first conditioning zone to cause some fluoride ions to react with calcium ions to form calcium fluoride precipitate; the second conditioning zone is equipped with a flow guide baffle to make the wastewater flow in a push flow manner, and the second conditioning zone adjusts the pH value to 6.0~8.0; The ammonia-nitrogen wastewater conditioning unit includes a pre-aeration zone, a main conditioning zone, and a stabilization zone arranged sequentially along the water flow direction. The pre-aeration zone is connected to the acid washing spray tower via a sealed cover and a tail gas collection device for recovering ammonia-containing tail gas. The main conditioning zone adjusts the pH value to 9.0~10.5 by adding sodium hydroxide solution. The stabilization zone is used to add buffers sodium carbonate and sodium bicarbonate when the pH value fluctuates beyond a set threshold. The acidic wastewater conditioning unit and the alkaline wastewater conditioning unit are arranged adjacently through a shared pool wall for non-contact heat exchange between acidic and alkaline wastewater. The shared pool wall is made of stainless steel corrugated plate. The heavy metal-containing wastewater conditioning unit includes a reaction zone, a solid-liquid separation component, and a conditioning zone. The reaction zone is used to add a heavy metal selective complexing agent to the heavy metal-containing wastewater to cause heavy metal ions to form insoluble chelate precipitates. The solid-liquid separation component is used to perform solid-liquid separation on the mixture in the reaction zone. The conditioning zone is used to monitor the pH of the separated clear liquid and adjust the pH value to 4.0~6.

0.

4. The synergistic treatment system for defluoridation and heavy metal recovery of photovoltaic wastewater according to claim 1, characterized in that, The synergistic reaction processing system includes a first mixing reaction zone, a second mixing reaction zone, a slow growth zone, a flocculation zone, a first solid-liquid separation unit, and a second solid-liquid separation unit. The first mixing reaction zone is used to mix the fluoride-containing water with the added calcium salt and pH adjuster evenly through a high-shear homogenizing emulsifier to generate calcium fluoride crystal nuclei. After the reaction is completed, the effluent enters the first solid-liquid separation unit, the separated fluoride precipitate is discharged and recycled, and the clear liquid flows into the second mixing reaction zone. The second mixing reaction zone is used to mix the clear liquid from the first mixing reaction zone with ammonia nitrogen-adjusted water, while adding magnesium salt, phosphate and pH adjuster, and generating magnesium ammonium phosphate crystal nuclei under the action of a high shear homogenizing emulsifier; The stirring speed in the slow growth zone decreases gradually along the water flow direction, which is used to allow the magnesium ammonium phosphate crystal nuclei in the effluent of the second mixing reaction zone to continue to grow, so as to obtain crystal particles of a preset particle size. The flocculation zone is used to promote the flocculation and growth of the crystal particles to form flocs by adding flocculants; The second solid-liquid separation unit is used to separate the flocs obtained after flocculation from the water to obtain magnesium ammonium phosphate precipitate and supernatant as the co-processed water.

5. The synergistic treatment system for defluoridation and heavy metal recovery of photovoltaic wastewater according to claim 1, characterized in that, The acid-base synergistic treatment system includes an acid-base neutralization reaction tank, a heavy metal reaction tank, a flocculation reaction unit, and a third solid-liquid separation unit arranged in sequence. The acid-base neutralization reaction tank includes a turbulent neutralization zone, a plug flow neutralization zone, and a stabilization zone arranged sequentially along the water flow direction. The turbulent neutralization zone is used to achieve turbulent mixing of acidic and alkaline conditioning water using the pressure of the inlet pipe. The plug flow neutralization zone is used to make the water flow in a plug flow manner through a baffle-type flow guide structure for neutralization. The stabilization zone is used to adjust the pH of the mixture to 7.5~9.

0. The heavy metal reaction tank includes three precipitation zones arranged along the length of the tank. The first precipitation zone precipitates lead and silver ions by controlling the pH to 6.5-7.5, the second precipitation zone precipitates copper ions by controlling the pH to 7.5-8.5, and the third precipitation zone precipitates residual heavy metal ions by controlling the pH to 8.5-9.

5. The flocculation reaction unit is used to promote the flocculation and growth of tiny precipitate particles in the effluent of the heavy metal reaction tank by adding flocculants. The third solid-liquid separation unit is used to separate the flocs after flocculation reaction from the water to obtain sludge sediment and supernatant as acid-base co-production water.

6. The synergistic treatment system for defluoridation and heavy metal recovery of photovoltaic wastewater according to claim 1, characterized in that, The mixing system includes a mixing and conditioning tank, an induced crystallizer, and an intermediate sedimentation tank arranged in sequence. The mixing and regulating tank is equipped with an aeration and stirring system, which is used to mix the co-treated water and the acid-base co-treated water evenly through aeration and stirring. The induced crystallizer is filled with a packing material loaded with a nano-hydroxyapatite coating, which is used to induce the crystallization of residual ions in the mixed water on the surface of the packing material. The intermediate sedimentation tank is used to settle the effluent from the induced crystallizer to obtain bottom sediment and supernatant as mixed product water.

7. The synergistic treatment system for defluoridation and heavy metal recovery of photovoltaic wastewater according to claim 6, characterized in that, The induced crystallizer is equipped with a combined air-water backwashing device, which is used to peel off and discharge the crystal layer when the crystal layer on the surface of the packing reaches a preset thickness.

8. The synergistic treatment system for defluoridation and heavy metal recovery of photovoltaic wastewater according to claim 1, characterized in that, The advanced treatment system includes a pre-crystallization and softening unit, a multi-media filtration unit, an ultrafiltration unit, a reverse osmosis unit, a disinfection unit, and a concentrated water stage concentration-salt separation unit. The pre-crystallization softening unit is used to crystallize and precipitate residual calcium and magnesium in the water as calcium carbonate and magnesium hydroxide on the surface of the silica sand carrier. The multi-media filtration unit is used to filter the effluent from the pre-crystallization softening unit through a double layer of quartz sand and anthracite filter media. The ultrafiltration unit is used to filter the water effluent from the multi-media filtration unit through a cross-flow filtration method using a polyvinylidene fluoride hollow fiber membrane. The reverse osmosis unit is used to filter impurities in the effluent from the ultrafiltration unit through a polyamide composite membrane; The disinfection unit is used to disinfect the permeate from the reverse osmosis unit to obtain reclaimed water; The concentrate stage concentration-salt separation unit is used to perform stage concentration and salt separation treatment on the concentrate produced by the reverse osmosis unit.

9. The synergistic treatment system for defluorination and heavy metal recovery of photovoltaic wastewater according to claim 8, characterized in that, The concentrated water stage concentration-salt separation unit includes a primary nanofiltration membrane system, a secondary reverse osmosis system, a first mechanical vapor recompression evaporator crystallizer, and a second mechanical vapor recompression evaporator crystallizer. The primary nanofiltration membrane system is used for salt separation of the concentrated water produced by the reverse osmosis unit; The secondary reverse osmosis system is used to further concentrate the permeate from the primary nanofiltration membrane system; the first mechanical vapor recompression evaporator is used to evaporate and crystallize the concentrate from the primary nanofiltration membrane system. The permeate from the secondary reverse osmosis system is returned to the mixing treatment system, and the concentrate from the secondary reverse osmosis system enters the second mechanical steam recompression evaporator crystallizer.

Images