Method for treating photovoltaic panel cleaning wastewater

Abstract

The invention discloses a photovoltaic panel cleaning wastewater treatment method which comprises the following steps: firstly, adding a coagulant and a coagulant aid into wastewater, stirring, standing and precipitating, and separating out supernate and sludge; enabling the supernate to sequentially pass through an ultrafiltration membrane and a reverse osmosis membrane to obtain reverse osmosis produced water and reverse osmosis concentrated water which can be reused for a photovoltaic panel cleaning system; concentrated water is electrolyzed, metal elementary substances such as lead are recycled at the cathode, and the recovery rate reaches 95% or above; and evaporating and crystallizing the electrolytic residual liquid to obtain the mixed industrial salt. According to the method, the transformation from'treatment 'to'resource recovery' is realized, and economic value is created. Through a multi-stage process, water, heavy metals and total dissolved solids in the wastewater are converted into reuse water, metal products and industrial salts, so that efficient cyclic utilization of resources is realized. The treatment process is tightly coupled and progressive layer by layer, near-zero emission is realized, environmental risks are eliminated, a membrane concentration and rotational flow electrolysis process is adopted for the lead-containing wastewater, and an economic, environment-friendly and efficient scheme is provided for the field.

Description

Technical Field

[0001] This invention pertains to the operation and maintenance of photovoltaic power plants and wastewater treatment, and relates to a method for treating wastewater from photovoltaic panel cleaning. Background Technology

[0002] Against the backdrop of a global push for clean energy development, photovoltaic (PV) power generation, as a highly promising form of renewable energy, is experiencing rapid expansion. With the large-scale construction and operation of PV power plants, ensuring power generation efficiency has become crucial, making the regular cleaning of PV panels an increasingly important aspect of operation and maintenance. Accumulated dust and dirt on the surface of PV panels significantly reduces the efficiency of sunlight absorption and conversion, thus affecting overall power generation. Therefore, regular cleaning is essential for maintaining the efficient and stable operation of PV systems.

[0003] Currently, photovoltaic panel cleaning mainly relies on water washing. However, this seemingly conventional cleaning process brings new problems—generating a large amount of complex cleaning wastewater. This wastewater is not ordinary "pure water"; it contains a variety of harmful substances. From a physical perspective, there is physical dust formed by particulate matter such as silicates, calcium and magnesium salts, and iron oxides from the environment. From a chemical perspective, it mainly originates from the aging and precipitation of the photovoltaic modules themselves, especially heavy metals such as lead (Pb) and cadmium (Cd) in solder ribbons and encapsulation material additives, as well as possible fluorides. If chemical cleaning agents are used, exogenous chemical substances such as surfactants, complexing agents, acids, and alkalis will also remain in the wastewater.

[0004] Faced with such complex wastewater, current treatment methods are rather crude. In most cases, wastewater is simply discharged after sedimentation or outsourced for treatment. This approach has many serious drawbacks. On the one hand, it poses environmental pollution risks. Once heavy metals and other toxic substances in the wastewater enter the environment, they accumulate in the soil, damaging soil structure and fertility, and affecting plant growth. They can also enter water bodies with the flow of water, polluting rivers and lakes, threatening the survival of aquatic life, and harming human health through the food chain. On the other hand, it causes serious waste of water resources. In water-scarce areas, water resources are already precious, and the direct discharge of cleaning wastewater without effective treatment fails to achieve recycling, exacerbating the contradiction between water supply and demand. Furthermore, it leads to the failure to recover resources. Valuable metals such as lead contained in the wastewater, which could be recycled and reused through reasonable technologies, are treated as waste along with the wastewater, failing to achieve effective resource recycling and resulting in resource waste.

[0005] Therefore, developing a treatment method that can simultaneously achieve wastewater purification and reuse, heavy metal resource recovery, and ultimately achieve near-zero emissions has become a critical technical challenge that the photovoltaic industry urgently needs to overcome in order to achieve green development. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for treating photovoltaic panel cleaning wastewater, thereby solving the technical problems of complex wastewater generated by photovoltaic panel washing, crude treatment methods, environmental pollution risks, water waste, and failure to recover valuable metal resources. The aim is to achieve water resource recycling and effective recovery of heavy metals, ultimately achieving near-zero discharge of cleaning wastewater.

[0007] This invention is achieved through the following technical solution: A method for treating photovoltaic panel cleaning wastewater includes the following steps: S1: Add coagulant and coagulant aid to the photovoltaic panel cleaning wastewater to be treated, stir and let it settle to separate the supernatant and sludge. S2: The supernatant is passed sequentially through an ultrafiltration membrane and a reverse osmosis membrane to obtain reverse osmosis permeate and reverse osmosis concentrate; the reverse osmosis permeate is recycled for the photovoltaic panel cleaning system; S3: Electrolyze the reverse osmosis concentrate to recover elemental metals at the cathode; S4: Evaporate and crystallize the residual liquid after electrolysis to obtain mixed industrial salt, thus completing the photovoltaic panel cleaning wastewater treatment.

[0008] Preferably, the coagulant is polyaluminum chloride or polyferric sulfate.

[0009] Preferably, the coagulant is polyacrylamide.

[0010] Preferably, the sludge, after dewatering, is used as a building material additive or soil conditioner.

[0011] Preferably, the pore size of the ultrafiltration membrane is 0.01-0.1 μm.

[0012] Preferably, the reverse osmosis membrane has a molecular weight cutoff of less than 100 Da.

[0013] Preferably, during electrolytic treatment, the cathode is a stainless steel mesh electrode or a carbon fiber electrode, and the anode is a titanium-coated ruthenium-iridium electrode.

[0014] Preferably, the current density during electrolytic treatment is 50-200 A / m. 2 The water flow velocity is 0.5-2.0 m / s.

[0015] Preferably, in step S4, a mechanical vapor recompression evaporator is used for evaporation and crystallization.

[0016] A system for implementing the above-described method for treating photovoltaic panel cleaning wastewater includes, in sequence, the photovoltaic panel cleaning wastewater to be treated, a coagulation sedimentation tank, an ultrafiltration device, a reverse osmosis device, a cyclone electrochemical device, and an evaporator crystallizer. The coagulation sedimentation tank is used to remove suspended particles and colloidal substances from wastewater; Ultrafiltration and reverse osmosis units are used to separate reverse osmosis permeate and concentrate heavy metals; The cyclone electrochemical device is used to electrolyze and recover heavy metals from reverse osmosis concentrate; An evaporator crystallizer is used for solid-liquid separation of the final residue to obtain industrial salt.

[0017] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for treating photovoltaic panel cleaning wastewater, which represents a significant shift from traditional "treatment" to "resource recycling," creating considerable economic value. This method utilizes a multi-stage treatment process to convert water, heavy metals, and total dissolved solids in the wastewater into reclaimed water, metal products, and industrial salt, respectively, achieving efficient resource recycling. In the treatment process, coagulation and sedimentation are first used to remove most suspended particles and colloidal substances, reducing the difficulty of subsequent treatment. Then, ultrafiltration and reverse osmosis membrane separation technologies are used to obtain high-quality permeate that can be reused for photovoltaic panel cleaning, significantly saving water resources. Electrolysis of the reverse osmosis concentrate allows for the precise recovery of heavy metals, such as lead, with a recovery rate exceeding 95%, effectively realizing the reuse of heavy metal resources. Finally, the electrolytic residue is evaporated and crystallized to obtain industrial salt that can be recycled, further improving the comprehensive utilization rate of resources. The entire treatment process is tightly coupled, with each step progressing in turn. This not only achieves near-zero wastewater discharge, fundamentally eliminating the potential pollution risks posed by wastewater to the environment, but also addresses the special case of lead-containing photovoltaic panel cleaning wastewater by employing a "membrane concentration + cyclone electrolysis" process. This process is characterized by high efficiency and high selectivity, maximizing resource recycling and reuse, and providing an economical, environmentally friendly, and efficient solution for the treatment of photovoltaic panel cleaning wastewater.

[0018] Furthermore, the coagulant is polyaluminum chloride or polyferric sulfate. These two coagulants have good coagulation effects, can effectively remove suspended solids and colloids in wastewater, improve coagulation and sedimentation efficiency, and enhance the effect of subsequent treatment.

[0019] Furthermore, the coagulant is polyacrylamide, which can enhance the bridging effect of the coagulant, making it easier for colloidal particles to aggregate and precipitate, thereby further improving the precipitation effect and reducing the impurity content in the supernatant.

[0020] Furthermore, the sludge, after dewatering, can be used as a building material additive or soil conditioner, realizing the resource utilization of sludge, avoiding secondary pollution of sludge, reducing treatment costs, and increasing economic benefits.

[0021] Furthermore, the pore size of the ultrafiltration membrane is 0.01-0.1 μm. This pore size range can effectively intercept macromolecular substances, bacteria and some colloids in the wastewater, ensuring the quality of the ultrafiltration permeate and providing good feed water conditions for subsequent reverse osmosis treatment.

[0022] Furthermore, the reverse osmosis membrane has a molecular weight cutoff of less than 100 Da, which can efficiently remove small molecules and ions from wastewater to obtain high-quality reverse osmosis permeate, meeting the requirements for water used for photovoltaic panel cleaning.

[0023] Furthermore, during electrolytic treatment, the cathode is a stainless steel mesh electrode or a carbon fiber electrode, and the anode is a titanium-coated ruthenium-iridium electrode. These electrode materials have good conductivity and corrosion resistance, which can improve electrolysis efficiency and ensure the stable operation of the electrolysis process.

[0024] Furthermore, during electrolytic treatment, the current density is 50-200 A / m. 2 The water flow velocity is 0.5-2.0 m / s. Appropriate current density and water flow velocity can improve the recovery efficiency of heavy metals, while ensuring the uniformity and stability of the electrolysis reaction.

[0025] Furthermore, in step S4, a mechanical vapor recompression evaporator is used for evaporation and crystallization. This equipment has the characteristics of low energy consumption and high evaporation efficiency, which can effectively reduce the energy consumption of the evaporation and crystallization process and improve the yield and quality of industrial salt.

[0026] A system for treating photovoltaic panel cleaning wastewater, as described above, offers significant environmental and economic benefits. This system, through the sequential connection of a coagulation sedimentation tank, an ultrafiltration unit, a reverse osmosis unit, a cyclone electrochemical unit, and an evaporator crystallizer, achieves multi-stage wastewater treatment and efficient resource recovery. The coagulation sedimentation tank effectively removes suspended particles and colloidal substances from the wastewater, reducing turbidity and the content of some pollutants, creating favorable conditions for subsequent treatment. The ultrafiltration and reverse osmosis units work closely together; ultrafiltration further traps impurities such as large molecules, while reverse osmosis separates the water into high-quality permeate and concentrate. The permeate can be reused for photovoltaic panel cleaning, while the concentrate is processed in the next stage, achieving efficient water resource recycling. The cyclone electrochemical unit precisely recovers heavy metals from the reverse osmosis concentrate, employing specific electrode materials and suitable process parameters, exhibiting high efficiency and selectivity. The recovery rate of heavy metals such as lead can reach over 95%, maximizing the reuse of heavy metal resources. The evaporator crystallizer separates the electrolytic residue into solid and liquid components, obtaining industrial salt that can be recycled, further improving the comprehensive utilization rate of resources. The entire system is tightly coupled, with each link progressing step by step, achieving near-zero wastewater discharge. This fundamentally eliminates the potential pollution risks of wastewater to the environment, providing strong protection for ecological and environmental protection. At the same time, it creates considerable economic value through resource recycling, and has broad application prospects in the field of photovoltaic panel cleaning wastewater treatment. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a process flow diagram of a method for treating photovoltaic panel cleaning wastewater according to the present invention.

[0029] The components include: 1. Photovoltaic panel cleaning wastewater to be treated; 2. Coagulation sedimentation tank; 3. Ultrafiltration device; 4. Reverse osmosis device; 5. Cyclone electrochemical device; and 6. Evaporator crystallizer. Detailed Implementation

[0030] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0031] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0032] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0033] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0034] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0035] This invention provides a method for treating photovoltaic panel cleaning wastewater, comprising the following steps: S1: Coagulation and sedimentation pretreatment: Add coagulant and coagulant aid to the photovoltaic panel cleaning wastewater to be treated, stir and let it settle to separate the supernatant and sludge. The coagulant is polyaluminium chloride (PAC) or polyferric sulfate (PFS). The coagulant is polyacrylamide (PAM). In addition, the sludge produced by sedimentation can be dewatered and utilized as a building material additive or soil conditioner for resource recovery.

[0036] In the treatment process of photovoltaic panel cleaning wastewater, coagulation and sedimentation pretreatment is a crucial first step. Specifically, coagulants and coagulant aids need to be precisely added to the photovoltaic panel cleaning wastewater. Polyaluminum chloride (PAC) or polyferric sulfate (PFS) are selected as coagulants, as these two coagulants effectively promote the aggregation of suspended particles and colloids in the wastewater. Polyacrylamide (PAM) is used as the coagulant aid, which further enhances the flocculation effect, resulting in larger and denser flocs. After adding the agents, thorough stirring is performed to ensure complete mixing and reaction between the agents and the wastewater, followed by settling. After a period of time, impurities in the wastewater settle to the bottom, forming sludge, while the clear upper layer becomes the supernatant, achieving solid-liquid separation. The sludge produced by sedimentation is not simply discarded; after dewatering, it can be used as a building material additive to improve building material performance or as a soil conditioner to regulate soil structure, achieving resource utilization of the sludge, reducing treatment costs and environmental pollution.

[0037] S2: Membrane separation and concentration: The supernatant obtained from coagulation and sedimentation is sequentially processed through an ultrafiltration membrane and a reverse osmosis membrane to obtain reverse osmosis permeate and reverse osmosis concentrate; the reverse osmosis permeate is recycled for the photovoltaic panel cleaning system; The ultrafiltration membrane has a pore size of 0.01-0.1 μm, and the reverse osmosis membrane has a molecular weight cutoff of less than 100 Da.

[0038] Specifically, in the photovoltaic panel cleaning wastewater treatment process, the membrane separation and concentration stage plays a crucial role. The supernatant obtained after coagulation and sedimentation pretreatment is sequentially introduced into ultrafiltration and reverse osmosis membrane systems for further treatment. Ultrafiltration membranes have a specific pore size range, between 0.01 and 0.1 μm. Within this pore size, they effectively trap large molecules, bacteria, viruses, and some colloids in the water, allowing relatively pure water to pass through. The water treated by the ultrafiltration membrane then enters the reverse osmosis membrane system. The reverse osmosis membrane has a molecular weight cutoff of less than 100 Da, meaning it can further remove even smaller dissolved salts and small organic molecules. After reverse osmosis treatment, two types of water with different properties are produced: reverse osmosis permeate and reverse osmosis concentrate. The reverse osmosis permeate has excellent water quality, meeting the water requirements of the photovoltaic panel cleaning system. Therefore, it can be directly reused in the system, achieving water resource recycling. This not only saves a significant amount of fresh water resources but also reduces the environmental pressure caused by wastewater discharge. The reverse osmosis concentrate will then enter subsequent treatment stages to further recover useful substances and achieve final treatment of wastewater to meet standards.

[0039] S3: Electrochemical recovery of heavy metals: The reverse osmosis concentrate obtained by membrane separation and concentration is sent to a cyclone electrochemical device for electrolytic treatment, and the elemental metals are recovered at the cathode. The cathode of the cyclone electrochemical device is a stainless steel mesh electrode or a carbon fiber electrode, and the anode is a titanium-coated ruthenium-iridium electrode; the current density of the electrolysis treatment is 50-200 A / m², and the water flow velocity is 0.5-2.0 m / s.

[0040] In the complete process of photovoltaic panel cleaning wastewater treatment, the electrochemical recovery of heavy metals is a key step in achieving resource reuse. The reverse osmosis concentrate obtained after membrane separation and concentration contains a certain amount of heavy metal ions. Direct discharge of this concentrate would not only waste resources but also cause serious environmental pollution. Therefore, this reverse osmosis concentrate needs to be sent to a specialized cyclone electrochemical device for electrolytic treatment.

[0041] The cyclone electrochemical device features a unique electrode design, with either a stainless steel mesh electrode or a carbon fiber electrode as the cathode. The stainless steel mesh electrode offers excellent conductivity and corrosion resistance, ensuring stable electrolysis. The carbon fiber electrode, with its larger specific surface area, increases the contact area with the solution, thereby improving electrolysis efficiency. The anode is a titanium-coated ruthenium-iridium electrode, which exhibits excellent electrochemical performance and corrosion resistance, maintaining stability during prolonged electrolysis.

[0042] Strict requirements are placed on process parameters during electrolytic treatment. The current density is controlled between 50-200 A / m³. 2 During this process, a suitable current density ensures that heavy metal ions are fully reduced at the cathode, forming elemental metals for recovery. Simultaneously, a water flow rate set between 0.5 and 2.0 m / s ensures uniform solution flow within the device, preventing localized high or low concentrations and guaranteeing the uniformity and efficiency of the electrolysis reaction. Through this electrolysis process, heavy metal ions in the reverse osmosis concentrate are reduced to elemental metals at the cathode, achieving heavy metal resource recovery. This reduces environmental pollution and creates considerable economic benefits for the company.

[0043] S4: Evaporation and crystallization: The residual liquid after electrolysis is evaporated and crystallized to obtain mixed industrial salt.

[0044] In this step, a mechanical vapor recompression evaporator can be used for evaporation and crystallization.

[0045] Specifically, in the complete process chain of photovoltaic panel cleaning wastewater treatment, the evaporation and crystallization stage is the key step to ultimately achieve deep wastewater treatment and resource recycling. Even after electrochemical recovery of heavy metals, the residual liquid still contains a certain amount of dissolved salts. Direct discharge of this liquid would not only waste resources but also potentially have adverse effects on surrounding water bodies and soil environments. Therefore, these residual liquids need to undergo evaporation and crystallization treatment.

[0046] In practice, mechanical vapor recompression evaporators can be used for evaporation and crystallization. A mechanical vapor recompression evaporator is a highly efficient and energy-saving evaporation device. Its working principle involves compressing the secondary steam generated during evaporation using a compressor, increasing its temperature and pressure, and then reintroducing it as heating steam into the evaporator, achieving heat recycling. This method significantly reduces dependence on external steam, lowers energy consumption, and offers substantial economic advantages and environmental benefits compared to traditional evaporation equipment.

[0047] When the residual liquid enters the mechanical vapor recompression evaporator, the water gradually evaporates under heating, and the salt concentration in the solution continuously increases until it reaches a supersaturated state, at which point the salt precipitates out in the form of crystals. As evaporation continues, the crystals grow, eventually forming mixed industrial salts. These mixed industrial salts can serve as important chemical raw materials and are widely used in various industrial fields, such as chemicals, building materials, and metallurgy. This achieves the effective recovery and reuse of salt resources from wastewater, further enhancing the economic value and environmental benefits of the entire wastewater treatment process and providing strong support for the sustainable development of the photovoltaic industry.

[0048] Meanwhile, this invention discloses a processing system for implementing the above-mentioned processing method, comprising: connected sequentially via pipes: Photovoltaic panel cleaning wastewater 1, i.e., raw water tank, to be treated.

[0049] Coagulation sedimentation tank 2 is used to remove suspended particles and colloidal substances from wastewater; Ultrafiltration unit 3 and reverse osmosis unit 4, including ultrafiltration unit and reverse osmosis unit, are used to separate product water and concentrate heavy metals; 5. A cyclone electrochemical device is used to electrolyze and recover heavy metals from concentrated water. Evaporator crystallizer 6 is used for solid-liquid separation of the final residue to obtain industrial salt.

[0050] Specifically, this invention ingeniously discloses a treatment system for implementing the above-mentioned photovoltaic panel cleaning wastewater treatment method. This system is like a highly efficient "resource purification and recycling production line", with each component closely connected in sequence through pipelines to collaboratively complete the entire process from wastewater treatment to resource recycling.

[0051] The system starts with the photovoltaic panel cleaning wastewater 1, also known as the raw water tank. This tank collects various types of wastewater generated during the photovoltaic panel cleaning process, containing pollutants such as suspended particles, colloidal substances, heavy metal ions, and various dissolved salts. It is the source of subsequent treatment.

[0052] Wastewater from the raw water tank is piped to coagulation sedimentation tank 2. In this crucial treatment unit, precise addition of coagulants and flocculants, coupled with thorough agitation, promotes the collision and aggregation of suspended particles and colloidal substances in the wastewater, forming larger, easily settling flocs. After settling, these flocs gradually sink to the bottom of the tank to form sludge, while the relatively clear supernatant flows smoothly through pipes to the next treatment stage, effectively removing most of the suspended impurities from the wastewater.

[0053] Next, the supernatant flows into the membrane filtration unit, which consists of ultrafiltration unit 3 and reverse osmosis unit 4. Ultrafiltration unit 3, with its membrane of specific pore size, acts like a fine sieve, trapping large molecules, bacteria, viruses, and some colloids in the water, further purifying the water. The water treated by ultrafiltration then flows into reverse osmosis unit 4, whose membrane has an even finer separation capability, separating the water into product water and concentrated water containing heavy metals. The product water is of excellent quality and can be reused in the photovoltaic panel cleaning system, achieving water resource recycling; while the concentrated water carries a large number of heavy metal ions and enters the subsequent treatment unit.

[0054] In the cyclone electrochemical device 5, concentrated water enters and undergoes electrolysis under specific electrode and current density conditions. At the cathode, heavy metal ions are reduced to elemental metals, thereby achieving the recovery of heavy metal resources.

[0055] Finally, the residual liquid after electrolysis enters the evaporator crystallizer 6. Through advanced mechanical vapor recompression technology, the heat of the secondary steam is used to continuously evaporate the residual liquid. The salt in the solution gradually reaches a supersaturated state and crystallizes out, ultimately achieving solid-liquid separation and obtaining mixed industrial salt that can be applied to multiple industrial fields, thus completing the effective recovery of salt resources from wastewater.

[0056] This invention represents a significant breakthrough in the treatment of photovoltaic panel cleaning wastewater, achieving a shift from the traditional "treatment" model to a "resource recycling" model, truly turning waste into treasure and creating considerable economic value. During the treatment process, the system ingeniously converts water, heavy metals, and total dissolved solids in the wastewater into reclaimed water, metal products, and industrial salt, respectively, realizing the efficient recycling of resources.

[0057] This treatment process exhibits significant near-zero emissions and environmental friendliness. Through the tight coupling of multiple processes, from coagulation and sedimentation to membrane filtration, then to cyclone electrochemical recovery and evaporation crystallization, each step is progressively advanced, ultimately producing only a small amount of resource-recoverable solid products. This achievement greatly reduces wastewater discharge, achieving near-zero wastewater discharge and fundamentally eliminating the potential pollution risks posed by wastewater to the environment, thus providing strong protection for ecological and environmental protection.

[0058] Meanwhile, this process is highly targeted and boasts extremely high recovery efficiency. Considering the special case of lead-containing photovoltaic panel cleaning wastewater, an innovative "membrane concentration + cyclone electrolysis" process is adopted. This process can precisely recover heavy metals such as lead, exhibiting high efficiency and selectivity, with a recovery rate of over 95%, maximizing resource recycling and reuse.

[0059] Furthermore, the water-saving effect is also significant. The reverse osmosis permeate water is of excellent quality, fully meeting the water requirements of the photovoltaic panel cleaning system, and can be directly reused in the cleaning system, greatly reducing the new water consumption of the photovoltaic power station. This characteristic is particularly important in water-scarce areas, effectively alleviating local water resource pressure.

[0060] It is worth mentioning that this process system also possesses enormous potential for intelligent and automated operation. It easily integrates online monitoring and automatic control technologies, and can automatically adjust operating parameters according to fluctuations in influent water quality, ensuring the stability of treatment results. This lays a solid foundation for the modernization and intelligent development of photovoltaic panel cleaning wastewater treatment.

[0061] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0062] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0063] Example 1 At a photovoltaic power station in a certain region, clean water is used daily to clean the photovoltaic panels, and the wastewater after cleaning is collected. This wastewater is turbid, and after testing, its pH value is 7.5, the lead (Pb) concentration reaches 2.5 mg / L, and the total dissolved solids (TDS) content is 1200 mg / L.

[0064] For this wastewater, S1 coagulation and sedimentation pretreatment was first performed. The wastewater was pumped into a coagulation and sedimentation tank, and 50 mg / L of polyaluminium chloride (PAC) and 1 mg / L of polyacrylamide (PAM) were added. Then, rapid stirring and slow stirring were performed, followed by settling for 1 hour. After this series of operations, the lead concentration in the supernatant was significantly reduced to 0.1 mg / L, and the turbidity was less than 5 NTU.

[0065] Next, S2 membrane separation and concentration were carried out. The supernatant was first filtered through ultrafiltration (UF) to remove large molecules and some impurities, and then entered the reverse osmosis (RO) unit. The recovery rate of the RO system was set at 85%. After treatment, RO permeate, accounting for 85% of the total volume, was obtained with a TDS of less than 50 mg / L and no detectable lead. This permeate was stored in the recycled water tank for the next photovoltaic panel cleaning. The lead concentration in the approximately 15% RO concentrate was concentrated to approximately 15 mg / L.

[0066] Then, S3 heavy metal electrochemical recovery was performed. RO concentrate was pumped into a cyclone electrochemical device using a stainless steel cathode. The current density was set at 100 A / m², and the water flow velocity at 1.0 m / s. After 30 minutes of electrolysis, lead foil was successfully recovered from the cathode surface, with a total lead recovery rate as high as 96%.

[0067] Finally, S4 evaporation and crystallization occurs. The residual liquid after electrolysis enters a mechanical vapor recompression (MVR) evaporator and crystallizer. After processing, a white mixed industrial salt is finally obtained, whose main components are sodium sulfate and sodium chloride, which can be sold as an industrial raw material.

[0068] Example 2 Near an industrial park, there is a sizable photovoltaic power station. Due to frequent industrial activity and a relatively complex environmental condition in the area, the photovoltaic panels accumulate large amounts of dust, oil, and other stubborn stains during long-term operation. To achieve a good cleaning effect, the power station uses a cleaning agent containing surfactants to clean the photovoltaic panels. However, this cleaning method results in extremely complex wastewater composition. Professional testing revealed that the lead (Pb) concentration in the wastewater was as high as 5.0 mg / L, and the chemical oxygen demand (COD) was 150 mg / L, posing a significant challenge to subsequent wastewater treatment.

[0069] To address this issue, coagulation and sedimentation are first performed in the initial stage (S1) of wastewater treatment. By adding appropriate amounts of coagulants and flocculants to the wastewater, and after thorough stirring and sedimentation, most suspended particles and colloidal substances are removed. Subsequently, an innovative advanced oxidation pretreatment step is added, specifically by adding ozone / persulfate to the coagulated and sedimented wastewater. Under the combined action of ozone and persulfate, organic pollutants in the wastewater undergo oxidative decomposition, successfully reducing COD to below 50 mg / L. Simultaneously, this process effectively breaks down the complexes formed between heavy metals and organic matter, making it easier for heavy metals such as lead to be removed by subsequent treatment processes.

[0070] After completing the advanced oxidation pretreatment, the subsequent wastewater treatment steps remained consistent with those in Example 1. Through a series of refined processes, including membrane separation and concentration, electrochemical recovery of heavy metals, and evaporation crystallization, satisfactory results were achieved. Not only was an 85% water reuse rate achieved, effectively conserving water resources and reducing the power plant's water costs, but the lead recovery rate also reached 92%, maximizing the recycling and reuse of heavy metal resources. Furthermore, mixed industrial salt suitable for industrial production was obtained, truly realizing the resource-based treatment of wastewater and turning waste into treasure.

[0071] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for treating photovoltaic panel cleaning wastewater, characterized in that, Includes the following steps: S1: Add coagulant and coagulant aid to the photovoltaic panel cleaning wastewater to be treated, stir and let it settle to separate the supernatant and sludge. S2: The supernatant is passed sequentially through an ultrafiltration membrane and a reverse osmosis membrane to obtain reverse osmosis permeate and reverse osmosis concentrate; the reverse osmosis permeate is recycled for the photovoltaic panel cleaning system; S3: Electrolyze the reverse osmosis concentrate to recover elemental metals at the cathode; S4: Evaporate and crystallize the residual liquid after electrolysis to obtain mixed industrial salt, thus completing the photovoltaic panel cleaning wastewater treatment.

2. The method for treating photovoltaic panel cleaning wastewater according to claim 1, characterized in that, The coagulant is polyaluminum chloride or polyferric sulfate.

3. The method for treating photovoltaic panel cleaning wastewater according to claim 1, characterized in that, The coagulant is polyacrylamide.

4. The method for treating photovoltaic panel cleaning wastewater according to claim 1, characterized in that, The sludge, after dewatering, is used as a building material additive or soil conditioner.

5. The method for treating photovoltaic panel cleaning wastewater according to claim 1, characterized in that, The pore size of the ultrafiltration membrane is 0.01-0.1 μm.

6. The method for treating photovoltaic panel cleaning wastewater according to claim 1, characterized in that, The reverse osmosis membrane has a molecular weight cutoff of less than 100 Da.

7. The method for treating photovoltaic panel cleaning wastewater according to claim 1, characterized in that, During electrolytic treatment, the cathode is a stainless steel mesh electrode or a carbon fiber electrode, and the anode is a titanium-coated ruthenium-iridium electrode.

8. A method for treating photovoltaic panel cleaning wastewater according to claim 1, characterized in that, During electrolytic treatment, the current density is 50-200 A / m 2 The water flow velocity is 0.5-2.0 m / s.

9. The method for treating photovoltaic panel cleaning wastewater according to claim 1, characterized in that, In step S4, a mechanical vapor recompression evaporator is used for evaporation and crystallization.

10. A system for implementing the method for treating photovoltaic panel cleaning wastewater according to any one of claims 1 to 9, characterized in that, The system includes, in sequence, the photovoltaic panel cleaning wastewater to be treated (1), the coagulation sedimentation tank (2), the ultrafiltration device (3), the reverse osmosis device (4), the cyclone electrochemical device (5), and the evaporator crystallizer (6). The coagulation sedimentation tank (2) is used to remove suspended particles and colloidal substances from wastewater; The ultrafiltration unit (3) and the reverse osmosis unit (4) are used to separate reverse osmosis permeate and concentrate heavy metals; The cyclone electrochemical device (5) is used to electrolyze and recover heavy metals from reverse osmosis concentrate; An evaporator crystallizer (6) is used for solid-liquid separation of the final residue to obtain industrial salt.

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