Low-damage, high-efficiency cleaning agent formulations for MBR membrane bioreactors

Abstract

This invention discloses a low-damage, high-efficiency cleaning agent formulation for MBR (membrane bioreactor) in the field of water treatment chemistry. The cleaning agent comprises three functional materials: a trinuclear iron-zirconium-silicon hybrid hydroxyphosphate, a layered bimetallic cerium molybdate hydroxynitrate, and a nanocage-like titanium-tungsten-borosilicate, combined with sodium citrate, polyepoxysuccinic acid, sodium dodecylbenzenesulfonate, sodium percarbonate, borax, and deionized water. The three core materials are synthesized through specific co-precipitation and sol-gel methods, constant pH co-precipitation methods, and template-assisted sol-gel combined with calcination methods, respectively. Through the synergistic effect of the components, this formulation achieves efficient complexation, adsorption, dispersion, and gentle oxidative stripping of organic, inorganic, and biological composite fouling layers on the membrane surface. Simultaneously, due to its near-neutral, mild cleaning environment and the low-corrosion properties of the materials themselves, it significantly reduces chemical damage to the membrane material, effectively restores membrane flux, and extends membrane lifespan.

Description

Technical Field

[0001] This invention belongs to the field of water treatment chemistry technology, specifically relating to a low-damage, high-efficiency cleaning agent formulation for MBR membrane bioreactors. Background Technology

[0002] Membrane bioreactors (MBRs), a key technology in modern wastewater treatment, are widely used in municipal and industrial sectors. However, their operational stability is often severely challenged by influent with high suspended solids. When treating raw water containing large amounts of sand and gravel, open channel transport introduces a large amount of particulate matter into the system, causing rapid clogging of the membrane modules. These particles not only physically embed themselves in the gaps between membrane fibers but also promote the excessive secretion of extracellular polymers in the anaerobic microenvironment, forming a highly viscous fouling layer. Particularly problematic is that anaerobic conditions provide an ideal breeding ground for midge larvae (commonly known as red worms), whose biofilm covers the membrane surface, further blocking water flow channels. Traditional cleaning methods struggle to simultaneously address the combined fouling of biofouling, organic adhesion, and inorganic scaling, leading to a sharp decline in membrane flux, forcing a shortened system operating cycle, and severely limiting treatment efficiency and effluent stability.

[0003] Current industry cleaning practices have significant shortcomings. Online cleaning generally relies on sodium hypochlorite solution, which, while partially oxidizing organic matter, has a weak effect on killing red worms, and the high concentration of chloride ions accelerates the oxidative degradation of membrane materials. Offline cleaning uses a combination of oxalic acid soaking and sodium hypochlorite treatment. Although oxalic acid can dissolve some inorganic scale, its strong acidity causes irreversible corrosion to polyvinylidene fluoride membrane fibers, and repeated use significantly shortens membrane life. Furthermore, oxalic acid treatment cannot effectively decompose sand particles; instead, mechanical scouring exacerbates membrane fiber wear. More importantly, existing agents lack targeted control over biofouling; red worms have a short reproduction cycle and rapid regeneration, leading to rapid recurrence of contamination after cleaning. Frequent offline cleaning (more than twice a year) not only increases labor and equipment wear but also causes prolonged system downtime, large fluctuations in permeate flow, and an inability to achieve continuous and stable operation, significantly increasing both economic and technical costs.

[0004] This invention stems from the urgent need for efficient and low-damage cleaning technology. Through the innovative design of three inorganic modified compounds, it synergistically achieves multiple functions including bioinhibition, fouling depolymerization, and particle dispersion. This cleaning agent can precisely kill midge larvae breeding in anaerobic environments, blocking the biofouling cycle; its unique structure can efficiently depolymerize the extracellular polymeric adhesive layer, reducing membrane adhesion; simultaneously, it dissolves inorganic scale such as calcium and magnesium, and encapsulates tiny sand particles to prevent scratching the membrane fibers. In practical applications, online circulation treatment alone can significantly restore membrane flux, avoiding frequent interruptions from offline cleaning. This integrated solution not only extends the service life of membrane modules but also improves the overall system operating efficiency by reducing maintenance frequency, providing a sustainable clean technology path for high suspended solids wastewater treatment and effectively solving the long-standing problem of membrane fouling in the industry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a low-damage, high-efficiency cleaning agent formulation for MBR membrane bioreactors.

[0006] A first aspect of the present invention provides a low-damage, high-efficiency cleaning agent formulation for MBR membrane bioreactors, comprising the following raw materials in parts by weight:

[0007] Trinuclear iron-zirconium-silicon hybrid hydroxyphosphate: 3-6 parts by weight;

[0008] Layered bimetallic cerium hydroxynitrate molybdate: 2-5 parts by weight;

[0009] Nanocage-like titanium-tungsten-borosilicate: 1.5-4 parts by weight;

[0010] Sodium citrate: 5-10 parts by weight;

[0011] Polyepoxysuccinic acid: 2-6 parts by weight;

[0012] Sodium dodecylbenzenesulfonate: 0.5-2 parts by weight;

[0013] Sodium percarbonate: 8-15 parts by weight;

[0014] Borax: 1-3 parts by weight;

[0015] Deionized water: 45-80 parts by weight.

[0016] In this invention, the components of the low-damage, high-efficiency cleaning agent formulation for MBR membrane bioreactors form a stable synergistic system in solution. Initially, deionized water is used as the base solvent, and sodium citrate, polyepoxysuccinic acid, sodium dodecylbenzenesulfonate, and borax are added sequentially, achieving complete dissolution through continuous stirring. The carboxyl groups of sodium citrate form stable chelates with calcium and magnesium ions in the water, effectively inhibiting the formation of inorganic scale. Polyepoxysuccinic acid, with its biodegradable molecular structure, blocks the growth of salt crystals such as calcium carbonate through steric hindrance. Sodium dodecylbenzenesulfonate, as an anionic surfactant, significantly reduces the surface tension of the solution, enhancing the wetting and peeling ability of substances adhering to the membrane fiber surface. Borax maintains a weakly alkaline environment in the system through buffering, preventing membrane material corrosion caused by localized acidity. These additives gradually dissolve under low-temperature stirring, forming a homogeneous precursor solution, laying a stable foundation for the subsequent addition of key functional components and ensuring the physical and chemical stability of the entire system in subsequent operations. After ensuring the stability of the precursor solution, sodium percarbonate was slowly added, with the temperature strictly controlled within a low range to prevent premature oxygen release due to thermal decomposition. Sodium percarbonate gradually decomposes in the solution to generate reactive oxygen species, providing a mild oxidizing environment that replaces the strong oxidation method of traditional high-concentration sodium hypochlorite, significantly reducing chemical damage to the membrane fibers. Subsequently, three newly designed modified compounds were sequentially added to the system, achieving uniform dispersion through continuous stirring. The silicon-oxygen phosphate backbone of the trinuclear iron-zirconium-silicon hybrid hydroxyphosphate specifically adsorbs onto the proteoglycans in EPS on the membrane surface, promoting EPS depolymerization through the catalytic action of iron-zirconium ions; the layered structure of the layered bimetallic cerium nitrate molybdate disrupts the electron transport chain of the biomembrane through the redox activity of cerium, while molybdate ions inhibit phosphate metabolism, thus doubly blocking the reproduction of midge larvae; the nanocage-like titanium-tungsten-borosilicate nanocage structure encapsulates tiny sand particles, preventing them from embedding in the membrane pores, while titanium and tungsten synergistically continue to degrade residual organic matter under weak light conditions. During stirring, the three compounds form a dynamically balanced colloidal suspension system. While there is no chemical reaction between them, they achieve multiple functions—bioinhibition, fouling deagglomeration, and particle dispersion—through spatial synergy. In the final stage, the system is continuously stirred for two hours to ensure thorough mixing and molecular-level homogeneity of all components. Filtration through a membrane removes any undissolved microparticles or agglomerates, yielding a clear cleaning agent product. The final system is weakly alkaline with a moderate pH, avoiding the risk of corrosion to the polyvinylidene fluoride membrane fibers by strong acids and alkalis while maintaining the active structures of the three modified compounds. In practical applications, this cleaning agent rapidly penetrates the membrane fiber surface during online circulation. The catalytic activity of the trinuclear iron-zirconium-silicon hybrid hydroxyphosphate and the bioinhibition function of the layered bimetallic cerium nitrate molybdate are activated simultaneously, while the encapsulation effect of the nanocage-like titanium-tungsten-borosilicate prevents scratches from sand and gravel. These three elements synergistically achieve efficient membrane flux recovery.Through precise sequence control and condition optimization, the entire preparation process enables the cleaning agent to maintain low-damage characteristics while significantly improving cleaning efficiency, providing a reliable guarantee for the long-term stable operation of MBR membrane bioreactors under high suspended solids conditions.

[0017] According to a preferred embodiment of the present invention, the preparation steps of the trinuclear iron-zirconium-silicon hybrid hydroxyphosphate include: A1, adding ferric chloride hexahydrate, zirconium oxychloride octahydrate and tetraethyl orthosilicate sequentially to deionized water and stirring under nitrogen protection; adding an aqueous solution of sodium dihydrogen phosphate dropwise; after the addition is complete, adjusting the pH to 6.6-7.0, raising the temperature to 84-86℃ and stirring the reaction; A2, after the reaction is complete, naturally cooling to room temperature, centrifuging to separate the precipitate, washing the precipitate with deionized water and anhydrous ethanol, drying it under vacuum at 58-62℃, and grinding it.

[0018] In this invention, the preparation of trinuclear iron-zirconium-silicon hybrid hydroxyphosphate is based on a synergistic mechanism of sol-gel and coprecipitation. Under nitrogen protection, after mixing the precursor solutions of iron, zirconium, and silicon, tetraethyl orthosilicate first undergoes partial hydrolysis in a weakly acidic environment, generating silanol groups and forming active silicon species. Subsequently, a phosphate solution is added dropwise, and the pH of the system is precisely controlled within a near-neutral range, promoting the simultaneous hydrolysis of iron and zirconium ions to form hydroxyl complexes, while the silicon species undergo a coordination reaction with phosphate ions. Under isothermal conditions at a specific temperature, iron, zirconium, silicon, and phosphorus elements form a three-dimensional hybrid network structure through oxygen bridging bonds, where iron and zirconium are octahedral coordinated, silicon is tetrahedral coordinated, and phosphate ions act as connecting bridging bonds, constructing a stable trinuclear hybrid framework. During the reaction, nitrogen protection prevents the oxidation of metal ions, while the near-neutral pH environment avoids premature precipitation of iron-zirconium hydroxide, ensuring uniform dispersion and gradual crystallization of each component. After the reaction, the precipitate was centrifuged, washed with water and alcohol to remove residual ions, and then vacuum dried to obtain high-purity hybrid hydroxy phosphate powder. The silicon-oxygen phosphate network in its crystal structure effectively inhibited the adsorption and cross-linking of EPS on the membrane surface.

[0019] According to a preferred embodiment of the present invention, in step A1, the time for stirring the reaction at 84-86°C is 12-14 hours.

[0020] According to a preferred embodiment of the present invention, the vacuum drying time at 58-62°C is 12-14 hours.

[0021] According to a preferred embodiment of the present invention, the preparation method of the layered bimetallic cerium nitrate molybdate includes: B1, dissolving cerium nitrate hexahydrate and sodium molybdate dihydrate in deionized water to obtain cerium salt solution and molybdate solution respectively; under stirring conditions, adding the cerium salt solution and molybdate solution dropwise to a dilute nitric acid solution with pH=5.4-5.6 to obtain a colloid; B2, transferring the colloid to an oil bath at 88-92℃ for aging; after cooling, filtering to obtain a solid product; washing the solid product with dilute nitric acid with pH=5.4-5.6, then washing with deionized water until neutral, and drying under vacuum at 58-62℃.

[0022] In this invention, the formation of layered bimetallic cerium hydroxymolybdate relies on a precise constant-pH co-precipitation process. Cerium salt and molybdate solutions are simultaneously added dropwise to a dilute nitric acid medium with a constant pH under stirring, avoiding oxidation of cerium ions or hydrolysis of molybdate ions caused by local pH fluctuations. When the pH is strictly maintained within a slightly acidic range, cerium ions and molybdate ions undergo simultaneous hydrolysis through electrostatic attraction and coordination, generating a Ce-O-Mo-OH layered precursor. As the system is slowly heated and aged, interlayer nitrate ions act as anionic templates, guiding the orderly arrangement of the layered structure to form a bimetallic hydroxide with regular interlayer spacing. This process ensures precise matching of the molar ratio of cerium to molybdenum by controlling the dropping rate and stirring intensity, avoiding the formation of single-phase impurities. After aging, the colloid is separated by filtration, washed with dilute nitric acid to remove free ions, washed with deionized water until neutral to eliminate residual acidity, and finally dried at a mild temperature to obtain a product with a complete layered structure and uniform surface charge distribution. In this structure, the redox activity of cerium and the coordination ability of molybdenum work synergistically to provide key functional sites for biological inhibition.

[0023] According to a preferred embodiment of the present invention, in step B1, the stirring time is 30-60 minutes.

[0024] According to a preferred embodiment of the present invention, in step B2, the vacuum drying time at 58-62°C is 10-12 hours.

[0025] According to a preferred embodiment of the present invention, the preparation method of the nanocage-like titanium-tungsten-borosilicate includes: C1, adding titanium tetrachloride dropwise into anhydrous ethanol under an ice bath, and purging with nitrogen gas to obtain a titanium ethanol solution; adding tetraethyl orthosilicate to the titanium ethanol solution and stirring to obtain a titanium-silicon ethanol mixture; dissolving ammonium metatungstate and boric acid in deionized water and heating to 58-62°C to obtain a boron-tungsten solution; adding the boron-tungsten solution to the titanium-silicon ethanol mixture and stirring; subsequently adding hexadecyltrimethylammonium bromide to obtain a mixture; refluxing the mixture at 78-82°C; C2, cooling the reaction solution and centrifuging to obtain a precipitate, washing the precipitate with an ethanol-water mixture, and then calcining it in a muffle furnace at 545-555°C.

[0026] In this invention, the synthesis of nanocage-like titanium-tungsten-borosilicate employs a premixed-template self-assembly strategy. Titanium tetrachloride is added dropwise to ethanol under ice bath and nitrogen protection, forming a titanium ethanol complex and releasing hydrogen chloride gas. Subsequently, a silicon source is added and thoroughly mixed, allowing titanium and silicon to form a Ti-O-Si covalent network through alcoholysis, avoiding direct titanium hydrolysis. Simultaneously, an aqueous solution of tungsten and boron forms a borotungsten complex under heating conditions. This complex, when mixed with the titanium-silicon mixture, undergoes directional self-assembly under the action of a surfactant template. During the reflux reaction, the titanium-silicon network and borotungsten species are linked through coordination bonds, with surfactant molecules guiding the formation of a nanoscale cage-like pore structure. After the reaction, the precipitate is separated by centrifugation, washed with an ethanol-water mixture to remove surfactant residue, and then calcined at high temperature to precisely remove the organic template and stabilize the silicon-oxygen bond network. This process controls the hydrolysis rate of titanium by premixing the titanium-silicon components, ensuring that borotungsten species are uniformly embedded in the titanium-silicon framework, ultimately yielding a titanium-tungsten-borosilicate with a nanocage structure. This cage structure effectively encapsulates microparticles and provides catalytically active sites.

[0027] According to a preferred embodiment of the present invention, in step C1, the mixture is refluxed at 78-82°C for 24-30 hours.

[0028] According to a preferred embodiment of the present invention, in step C2, the calcination time in a muffle furnace at 545-555°C is 4-6 hours.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) This invention addresses the complex pollution problem faced by membrane bioreactors in the treatment of wastewater with high suspended solids by achieving a breakthrough in cleaning technology. Traditional cleaning methods, such as online sodium hypochlorite treatment, are almost ineffective against midge larvae that breed in anaerobic environments, while offline oxalic acid cleaning, although it can partially dissolve inorganic scale, severely corrodes the membrane fibers, leading to shortened membrane life and frequent shutdowns. This invention, through the synergistic effect of three innovatively designed inorganic modified compounds, simultaneously solves the three core problems of biofouling, organic adhesion, and inorganic scaling in an online cleaning scenario for the first time. During the circulation process, the cleaning agent can effectively inhibit the reproduction of midge larvae, significantly reduce the extracellular polymer adhesion layer on the membrane fiber surface, and dissolve inorganic scale such as calcium and magnesium while dispersing tiny sand particles, preventing them from embedding in the membrane pores and causing physical damage. This technological breakthrough completely changes the industry's passive mode of relying on offline cleaning and provides a sustainable membrane maintenance solution for high suspended solids influent conditions.

[0031] (2) In this invention, the synergistic mechanism of the three modified compounds endows the cleaning agent with multiple functions. Trinuclear iron-zirconium-silicon hybrid hydroxyphosphate generates active oxygen through the synergistic catalysis of peroxides by iron and zirconium ions, which precisely kills midge larvae in anaerobic environments. Its silica phosphate skeleton structure strongly adsorbs and depolymerizes proteins and polysaccharides in EPS, blocking the biofouling cycle. Layered bimetallic cerium hydroxyl molybdate utilizes the redox properties of cerium to destroy the electron transport chain of the biomembrane. Molybdate ions inhibit phosphate metabolism, thus doubly inhibiting larval reproduction. At the same time, the layered structure intercalates and strips inorganic scale lattices such as calcium carbonate. The nanocage-like titanium-tungsten-borosilicate's nanocage structure wraps sand particles to prevent scratching the membrane fibers. Titanium and tungsten work together to continuously photocatalytically degrade residual organic matter under weak light. Boron doping significantly enhances the hydrophilicity of the membrane surface and reduces adhesion. The overall formulation is weakly alkaline, avoiding the erosion of PVDF membranes by strong acids and alkalis. Sodium percarbonate provides a mild oxidizing environment, replacing high-concentration sodium hypochlorite and eliminating the risk of chlorinated byproducts.

[0032] (3) The cleaning agent formulation of this invention brings significant operational optimization and comprehensive benefits in practical applications. Its high cleaning efficiency means shorter cleaning time, lower cleaning frequency, and less reagent consumption, directly reducing the operating energy consumption and chemical costs of the membrane system. Due to the gentle and thorough cleaning process, the membrane flux recovery rate is high and stable, reducing the accelerated performance degradation caused by incomplete cleaning and ensuring the long-term stable water production capacity of the membrane bioreactor. In addition, the main components in the formulation are environmentally friendly, avoiding the secondary pollution risks and subsequent treatment problems that may be caused by using chlorine-containing strong oxidants or phosphorus-based passivating agents, which is in line with the development trend of green and clean technologies. In summary, this cleaning agent not only solves the technical problem of deep cleaning of membrane bioreactors, but also enhances the value of the entire water treatment system from multiple dimensions such as economy, stability, and environmental protection. Detailed Implementation

[0033] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0034] Example 1

[0035] This embodiment provides a method for preparing a low-damage, high-efficiency cleaning agent for MBR membrane bioreactors:

[0036] Preparation of trinuclear iron-zirconium-silicon hybrid hydroxyphosphate: First, prepare a 250 mL three-necked flask. Add 60 g of deionized water to the flask. Under a continuous nitrogen atmosphere (nitrogen flow rate of 50 mL / min), add 3.0 g of ferric chloride hexahydrate, 2.5 g of zirconium oxychloride octahydrate, and 1.8 g of tetraethyl orthosilicate sequentially to the flask. Turn on the mechanical stirrer and set the stirring speed to 500 rpm, stirring continuously for 30 min at room temperature. Then, using a constant pressure dropping funnel, slowly add a pre-prepared sodium dihydrogen phosphate aqueous solution (2.1 g of sodium dihydrogen phosphate dissolved in 30 g of deionized water) dropwise over 30 min with continuous stirring. After the addition is complete, use a 10% sodium hydroxide aqueous solution to precisely adjust the pH of the reaction system to 6.8. Transfer the three-necked flask to a constant temperature oil bath and set the oil bath temperature to 85 °C. After the reaction solution temperature stabilized, the reaction was continuously stirred at this temperature for 13 hours at a stirring speed of 500 rpm. After the reaction was completed, the heat source was removed, and the reaction solution was allowed to cool naturally to 25°C in air. The cooled reaction mixture was transferred to centrifuge tubes and centrifuged at 8000 rpm for 10 minutes using a high-speed centrifuge. The supernatant was discarded, and the bottom precipitate was collected. The precipitate was washed three times with 50 mL of deionized water (centrifuged after each wash), followed by a wash with 30 mL of anhydrous ethanol. The washed precipitate was transferred to a petri dish and placed in a vacuum drying oven, where it was dried at 60°C and a vacuum of -0.08 MPa for 13 hours. Finally, the dried solid block was placed in an agate mortar and manually ground until the powder could pass through a 200-mesh standard sieve to obtain the product, which was then sealed and stored for later use.

[0037] Preparation of layered bimetallic cerium nitrate molybdate: First, two precursor solutions were prepared: Solution A, in which 3.2 g of cerium nitrate hexahydrate was dissolved in 20 g of deionized water; Solution B, in which 2.0 g of sodium molybdate dihydrate was dissolved in 20 g of deionized water. A 500 mL three-necked flask was prepared as the reaction vessel, and 60 g of deionized water was added. Dilute nitric acid was added dropwise to adjust and stabilize the initial pH of the water at 5.5. The reaction flask was placed on a magnetic stirrer, a stir bar was added, and the stirring was started and controlled at 600 rpm. Two precision peristaltic pumps were used to draw solutions A and B respectively, and the outlets of the two pump tubes were simultaneously immersed below the surface of the reaction solution. The two peristaltic pumps were started simultaneously, and the pump speed was controlled so that the two solutions were added dropwise to the continuously stirred reaction solution at the same rate (approximately 0.9 mL / min) over 45 min. During the dropwise addition, the pH of the reaction solution was monitored using an automatic pH meter, and a 0.1 mol / L dilute nitric acid solution was added dropwise using a micro-injection pump to precisely maintain the pH of the reaction system within the range of 5.5 ± 0.1 throughout the process. After the dropwise addition was complete, the mixture was stirred at room temperature for 15 minutes to obtain a uniform yellowish-brown colloid. The flask containing the colloid was transferred to an oil bath set at 90°C and statically aged at this temperature for 6 hours. After aging, the flask was removed and cooled to room temperature in a cold water bath. Vacuum filtration was performed using a Buchner funnel and a microporous membrane with a pore size of 0.45 μm to separate the solid product. The filter cake was washed twice with a dilute nitric acid solution (approximately 50 mL) pre-adjusted to pH 5.5, followed by washing with approximately 100 mL of deionized water until the pH of the effluent was close to 7.0. The filter cake was scraped off the filter membrane, transferred to a petri dish, and placed in a vacuum drying oven to dry at 60°C and atmospheric pressure for 11 hours. After drying, the resulting solid is ground into a fine powder and stored in an airtight container.

[0038] Preparation of nanocage-like titanium-tungsten-borosilicate: The procedure was performed in a fume hood. A 250 mL round-bottom flask equipped with a magnetic stirrer was prepared and placed in an ice-water bath. 50 g of anhydrous ethanol was added to the flask. Under continuous nitrogen purging (flow rate of 30 mL / min) and vigorous stirring (800 rpm), 2.4 g of titanium tetrachloride liquid was slowly added dropwise over 20 min using a constant-pressure dropping funnel to the ice-cooled anhydrous ethanol. After the addition was complete, a clear, pale yellow titanium ethanol solution was obtained. Maintaining the ice bath and nitrogen atmosphere, 3.0 g of tetraethyl orthosilicate was added to this solution in one go. The stirring speed was then adjusted to 400 rpm, and stirring was continued for 60 min under ice bath conditions to allow the tetraethyl orthosilicate to initially combine with the titanium species, resulting in a titanium-silicon ethanol mixture. In a separate 100mL beaker, add 1.8g of ammonium metatungstate and 0.5g of boric acid to 20g of deionized water. Place the beaker in a 60℃ constant temperature water bath and stir at 300rpm until the solids are completely dissolved, yielding a clear borotungstate solution. Remove the ice bath and transfer the round-bottom flask containing the titanium-silicon ethanol mixture to a room temperature water bath. Under continuous stirring (400rpm) and nitrogen protection, add the warm borotungstate solution dropwise to the titanium-silicon ethanol mixture over 10 minutes. After the addition is complete, add 1.0g of hexadecyltrimethylammonium bromide to the mixture, increase the stirring speed to 600rpm, and continue stirring for 30 minutes until the surfactant is completely dissolved, yielding a milky white homogeneous mixture. Connect the round-bottom flask to a reflux condenser and transfer it to an oil bath set to 80℃. Turn on the cooling water and reflux the reaction at this temperature for 27 hours, maintaining gentle stirring (300rpm) throughout the reaction. After the reaction was complete, the heat source was turned off, and the reaction solution was allowed to cool to room temperature. The reaction solution was transferred to a centrifuge tube and centrifuged at 10,000 rpm for 15 min. The supernatant was discarded, and the white precipitate was collected. The precipitate was washed three times with a 1:1 ethanol-water mixture (30 mL each time) by centrifugation. The washed precipitate was transferred to an alumina crucible and placed in a box-type muffle furnace. The furnace temperature was increased from room temperature to 550 °C at a rate of 5 °C / min and maintained at 550 °C for 5 h. After the calcination process was completed, the furnace temperature was allowed to cool naturally to below 100 °C, and the crucible was removed to obtain a powdered product, which was then ground and sealed for storage.

[0039] Preparation of a low-damage, high-efficiency cleaning agent for MBR membrane bioreactors: Prepare a 500mL plastic beaker as the preparation container. Accurately weigh the following raw materials sequentially using an analytical balance: 4.5g of the prepared trinuclear iron-zirconium-silicon hybrid hydroxyphosphate, 3.5g of the prepared layered bimetallic cerium nitrate molybdate, 2.8g of the prepared nanocage-like titanium-tungsten-borosilicate, 7.5g of sodium citrate, 4.0g of polyepoxysuccinic acid, 1.2g of sodium dodecylbenzenesulfonate, 11.0g of sodium percarbonate, and 2.0g of borax. Add 62.5g of deionized water to the beaker as a solvent. Place the beaker in a 40℃ constant temperature water bath and add a magnetic stir bar. Turn on the stirrer, setting the initial speed to 300rpm. Add the weighed raw materials one by one slowly to the water, following the order of adding solid additives first, then functional material powders. The specific order is as follows: First, add sodium citrate, polyepoxysuccinic acid, sodium dodecylbenzenesulfonate, and borax, stirring until basically dissolved. Then, add sodium percarbonate and stir until the solution is a uniform milky white. Finally, while continuously stirring, slowly sprinkle in three powders: trinuclear iron-zirconium-silicon hybrid hydroxyphosphate, layered bimetallic cerium hydroxynitrate molybdate, and nanocage-like titanium-tungsten-borosilicate. After all solids have been added, increase the stirring speed to 800 rpm and continue stirring in a 40°C water bath for 90 minutes until all solid components are completely dissolved or dispersed, obtaining the cleaning agent working solution.

[0040] Example 2

[0041] The difference between this embodiment and Example 1 lies in the preparation of trinuclear iron-zirconium-silicon hybrid hydroxyphosphate: Prepare a 250 mL three-necked flask and add 50 g of deionized water. Under nitrogen gas flow (50 mL / min) protection, add 2.0 g of ferric chloride hexahydrate, 2.0 g of zirconium oxychloride octahydrate, and 1.5 g of tetraethyl orthosilicate sequentially. Turn on the mechanical stirrer, set the speed to 500 rpm, and stir at room temperature for 30 min. Using a constant pressure dropping funnel, add sodium dihydrogen phosphate aqueous solution (1.7 g of sodium dihydrogen phosphate dissolved in 25 g of deionized water) dropwise over 20 min. After the addition is complete, adjust the pH to 6.7 with 10% sodium hydroxide solution. Transfer the flask to a constant temperature oil bath, heat to 84 °C, and stir at 500 rpm for 12 h at this temperature. After the reaction is complete and cooled to 25 °C, centrifuge the mixture at 8000 rpm for 10 min and collect the precipitate. Wash three times with deionized water (40 mL each time), and then once with 20 mL of anhydrous ethanol. Place the precipitate in a vacuum drying oven and dry at 59 °C and -0.08 MPa for 12 h. After drying, grind through a 200-mesh sieve to obtain trinuclear iron-zirconium-silicon hybrid hydroxyphosphate.

[0042] Preparation of layered bimetallic cerium nitrate molybdate: Solutions were prepared as follows: 2.5 g of cerium nitrate hexahydrate was dissolved in 15 g of deionized water; 1.6 g of sodium molybdate dihydrate was dissolved in 15 g of deionized water. 50 g of deionized water was added to a 500 mL three-necked flask, and dilute nitric acid was added dropwise to adjust the pH to 5.5. A magnetic stirrer was started at 600 rpm. The two precursor solutions were simultaneously added to the reaction flask using two peristaltic pumps at a rate of approximately 1.0 mL / min, completed within 30 min. During the addition, the pH was maintained at 5.5 ± 0.1 with 0.1 mol / L dilute nitric acid. After the addition was complete, stirring was continued at room temperature for 15 min to obtain a yellowish-brown colloid. The colloid was transferred to an 89 °C oil bath for static aging for 5 h. After cooling, the mixture was filtered, and the filter cake was washed twice with approximately 40 mL of dilute nitric acid at pH 5.5, then washed with deionized water until the pH of the effluent was approximately 7. The filter cake was dried in a vacuum drying oven at 59°C for 10 hours and then ground to obtain layered bimetallic cerium hydroxynitrate molybdate.

[0043] Preparation of nanocage-like titanium-tungsten-borosilicate: In a 250 mL round-bottom flask under ice bath and nitrogen (30 mL / min) protection, 2.0 g of titanium tetrachloride was added dropwise to 45 g of anhydrous ethanol over 15 min (stirring at 800 rpm). 2.5 g of tetraethyl orthosilicate was added, and the mixture was stirred at 400 rpm for 50 min under ice bath conditions. Separately, 1.5 g of ammonium metatungstate and 0.4 g of boric acid were dissolved in 18 g of deionized water and stirred in a 59 °C water bath. This borosilicate solution was added dropwise to the aforementioned titanium-silicon ethanol mixture over 10 min (the ice bath was removed, and the mixture was stirred at 400 rpm at room temperature). 0.9 g of hexadecyltrimethylammonium bromide was added, and the stirring speed was increased to 600 rpm for 30 min. The mixture was connected to a reflux apparatus and refluxed in a 79 °C oil bath at 300 rpm for 25 h. After cooling, the precipitate was collected by centrifugation at 10,000 rpm for 15 min. Wash three times with a 1:1 ethanol-water mixture (25 mL each time). Place the precipitate in a muffle furnace and calcine at 5℃ / min to 548℃ for 4 h. After cooling, grind to obtain nanocage-like titanium-tungsten-borosilicate.

[0044] Preparation of a low-damage, high-efficiency cleaning agent for MBR membrane bioreactors: Add 55.0 g of deionized water to a 500 mL plastic beaker and place it in a 35°C water bath. Weigh and add the following raw materials sequentially: 3.0 g of trinuclear iron-zirconium-silicon hybrid hydroxyphosphate, 2.0 g of layered bimetallic cerium molybdate hydroxynitrate, 1.5 g of nanocage-like titanium-tungsten-borosilicate, 5.0 g of sodium citrate, 2.0 g of polyepoxysuccinic acid, 0.5 g of sodium dodecylbenzenesulfonate, 8.0 g of sodium percarbonate, and 1.0 g of borax. The order of addition is as follows: first add sodium citrate, then polyepoxysuccinic acid, then sodium dodecylbenzenesulfonate, and finally borax. After stirring and dissolving, add sodium percarbonate, and finally slowly add the three functional powders. Stir continuously at 700 rpm for 80 min in a 35°C water bath to obtain a homogeneous suspension.

[0045] Example 3

[0046] The difference between this embodiment and Example 1 lies in the preparation of the trinuclear iron-zirconium-silicon hybrid hydroxyphosphate: Prepare a 250 mL three-necked flask and add 70 g of deionized water. Purge with nitrogen (50 mL / min), then add 3.5 g of ferric chloride hexahydrate, 3.0 g of zirconium oxychloride octahydrate, and 2.2 g of tetraethyl orthosilicate sequentially. Stir mechanically at 500 rpm for 40 min at room temperature. Add an aqueous solution of sodium dihydrogen phosphate (2.5 g of sodium dihydrogen phosphate dissolved in 35 g of water) dropwise over 40 min. Adjust the pH to 7.0 with 10% sodium hydroxide. Transfer to an 86°C oil bath and stir at 500 rpm for 14 h. Cool to 25°C and centrifuge at 8000 rpm for 10 min to collect the precipitate. Wash three times with 50 mL of deionized water each time, then wash once with 30 mL of anhydrous ethanol. Dry the precipitate in a vacuum drying oven at 62°C and -0.08 MPa for 14 h. After grinding through a 200-mesh sieve, trinuclear iron-zirconium-silicon hybrid hydroxyphosphate was obtained.

[0047] Preparation of layered bimetallic cerium hydroxynitrate molybdate: Solution preparation: Dissolve 4.0 g of cerium nitrate hexahydrate in 25 g of deionized water; dissolve 2.5 g of sodium molybdate dihydrate in 25 g of deionized water. Add 70 g of deionized water to a 500 mL three-necked flask and adjust the pH to 5.6. Stir magnetically at 600 rpm. Add the two solutions dropwise simultaneously at a rate of approximately 0.83 mL / min using a peristaltic pump, completing the addition over 60 min. During this time, maintain the pH at 5.6 ± 0.1 with dilute nitric acid. After the addition is complete, stir at room temperature for 15 min to obtain a colloid. Aging the colloid in an oil bath at 91 °C for 7 h. After cooling, filter, wash twice with dilute nitric acid (approximately 60 mL) at pH = 5.6, and then wash with deionized water until neutral. Dry the filter cake at 62 °C for 12 h, and grind to obtain layered bimetallic cerium hydroxynitrate molybdate.

[0048] Preparation of nanocage-like titanium-tungsten-borosilicate: Under ice bath and nitrogen (30 mL / min) protection, 3.0 g of titanium tetrachloride was added dropwise to 55 g of anhydrous ethanol over 25 min (stirring at 800 rpm). 3.5 g of tetraethyl orthosilicate was added, and the mixture was stirred at 400 rpm for 70 min in an ice bath. Separately, 2.2 g of ammonium metatungstate and 0.6 g of boric acid were dissolved in 22 g of deionized water and dissolved in a water bath at 61 °C. This solution was added dropwise to a titanium-silicon ethanol mixture over 15 min (after removing the ice bath, at room temperature, 400 rpm). 1.2 g of cetyltrimethylammonium bromide was added, and the mixture was stirred at 600 rpm for 30 min. The mixture was then refluxed at 81 °C in an oil bath at 300 rpm for 30 h. After cooling, the precipitate was collected by centrifugation at 10,000 rpm for 15 min. The precipitate was washed three times with a 1:1 ethanol-water mixture (35 mL each time). The precipitate was placed in a muffle furnace and calcined at 552 °C at a rate of 5 °C / min for 6 h. After cooling, it was ground to obtain nanocage-like titanium-tungsten-borosilicate.

[0049] Preparation of a low-damage, high-efficiency cleaning agent for MBR membrane bioreactors: Add 49.0 g of deionized water to a 500 mL plastic beaker and place it in a 45 °C water bath. Weigh and add the following components in sequence: 6.0 g of trinuclear iron-zirconium-silicon hybrid hydroxyphosphate, 5.0 g of layered bimetallic cerium molybdate hydroxynitrate, 4.0 g of nanocage-like titanium-tungsten-borosilicate, 10.0 g of sodium citrate, 6.0 g of polyepoxysuccinic acid, 2.0 g of sodium dodecylbenzenesulfonate, 15.0 g of sodium percarbonate, and 3.0 g of borax. The order of addition is the same as in Example 1. Stir continuously at 900 rpm for 100 min in a 45 °C water bath to obtain a homogeneous suspension.

[0050] Comparative Example 1

[0051] The difference between this comparative example and Example 1 is that the trinuclear iron-zirconium-silicon hybrid hydroxyphosphate, layered bimetallic cerium molybdate hydroxynitrate, and nanocage-like titanium-tungsten-borosilicate are not added; instead, 10.8 g of deionized water is used instead. Preparation of the cleaning agent: Add 73.3 g of deionized water to a 500 mL plastic beaker and place it in a 40°C water bath. Sequentially weigh and add 7.5 g of sodium citrate, 4.0 g of polyepoxysuccinic acid, 1.2 g of sodium dodecylbenzenesulfonate, 11.0 g of sodium percarbonate, and 2.0 g of borax. Stir continuously at 800 rpm for 90 minutes in a 40°C water bath until all solids are completely dissolved, resulting in a clear or slightly turbid solution.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 1 is that layered bimetallic cerium molybdate hydroxynitrate is not added; instead, an equal mass of deionized water is used. Preparation of the cleaning agent: Add 66.0 g of deionized water to a 500 mL plastic beaker and place it in a 40°C water bath. Weigh and add sequentially the following: 4.5 g of trinuclear iron-zirconium-silicon hybrid hydroxyphosphate, 2.8 g of nanocage-like titanium-tungsten-borosilicate, 7.5 g of sodium citrate, 4.0 g of polyepoxysuccinic acid, 1.2 g of sodium dodecylbenzenesulfonate, 11.0 g of sodium percarbonate, and 2.0 g of borax. The order of addition is the same as in Example 1. Stir continuously at 800 rpm for 90 min in a 40°C water bath to obtain a homogeneous suspension.

[0054] Comparative Example 3

[0055] The difference between this comparative example and Example 1 is that nanocage-like titanium-tungsten-borosilicate is not added; instead, an equal mass of deionized water is used. Preparation of the cleaning agent: Add 65.3 g of deionized water to a 500 mL plastic beaker and place it in a 40°C water bath. Weigh and add sequentially the following: 4.5 g of trinuclear iron-zirconium-silicon hybrid hydroxyphosphate, 3.5 g of layered bimetallic cerium molybdate hydroxynitrate, 7.5 g of sodium citrate, 4.0 g of polyepoxysuccinic acid, 1.2 g of sodium dodecylbenzenesulfonate, 11.0 g of sodium percarbonate, and 2.0 g of borax. The order of addition is the same as in Example 1. Stir continuously at 800 rpm for 90 min in a 40°C water bath to obtain a homogeneous suspension.

[0056] The performance of the low-damage, high-efficiency cleaning agents for the MBR membrane bioreactors provided in the above embodiments and comparative examples was tested according to national and industry standard testing specifications. The test methods are as follows:

[0057] Membrane flux recovery test: A polyvinylidene fluoride hollow fiber membrane module with an effective membrane area of ​​0.01 m² was selected. A simulated fouling solution was prepared, containing anaerobic activated sludge (mixed liquor suspended solids concentration of 10 g / L), fine quartz sand (particle size 50-150 μm, concentration 2.0 g / L), humic acid (concentration 1.5 g / L), bovine serum albumin (concentration 2.0 g / L), and calcium chloride (concentration 0.5 g / L). The membrane module was immersed in 1.5 L of this fouling solution and operated under constant temperature anaerobic conditions at 30.0℃ with a constant membrane flux of 15 L / (m²·h) for 48 h. After fouling, the membrane module was transferred online to a cleaning tank containing 2.0 L of the test cleaning agent. The cleaning solution temperature was maintained at 35.0℃, and the module was circulated at a linear velocity of 0.15 m / s for 120 min. After cleaning, the membrane module was backwashed with deionized water for 2 min. Subsequently, the cleaned membrane module was connected to a pure water testing system, and its stable pure water flux J1 [L / (m²·h)] was measured under constant pressure of 0.08 MPa and 25.0℃. The initial pure water flux J0 was measured using new membranes from the same batch under the same conditions. The membrane flux recovery rate was calculated using the formula (J1 / J0) × 100%.

[0058] Transmembrane pressure reduction rate test: After the above-mentioned fouling stage, record the transmembrane pressure of the membrane module when it is running stably at a flux of 15 L / (m²·h), denoted as P0, in MPa. After completing the cleaning and flux recovery test, place the same membrane module again in a freshly prepared simulated fouling solution free of chironomid larvae, and run it for 1 hour under the same operating conditions (flux 15 L / (m²·h), temperature 30.0℃), recording the transmembrane pressure when it is running stably, denoted as P1. The transmembrane pressure reduction rate is calculated using the formula [(P0-P1) / P0]×100%.

[0059] Red worm kill rate test: After the contaminated solution was prepared, 20 third-instar midge larvae were introduced into each 1.5L batch of contaminated solution. At the end of the 48-hour contamination period, the number of surviving larvae N0 on the membrane module surface and in the surrounding solution was counted and recorded. After completing the 120-minute cleaning procedure, all cleaning wastewater and subsequent rinse water were collected, filtered using a standard sieve, and the number of dead larvae N (completely immobile and unresponsive to external stimuli) was counted. d The red worm kill rate is calculated using the formula [N] d / (N d Calculate using [+N0)]×100%.

[0060] Particle dispersion test: Take 100 mL of the cleaning waste liquid obtained after the cleaning procedure and place it in a 100 mL stoppered graduated cylinder. Let it stand for 30 min at 25.0℃ to settle. Then, carefully pipette the upper 50 mL of the clear liquid in the graduated cylinder and filter it through a pre-dried and weighed 0.45 μm aqueous filter membrane. Place the filter membrane containing the particles in a 105℃ oven to dry to constant weight, cool it, and weigh it to obtain the total mass M. total (g). The original mass of the filter membrane before filtering the sample is denoted as M. membrane (g). Calculate the mass of suspended particles in the cleaning waste liquid that were not removed by sedimentation, M1 = M total -M membrane Meanwhile, 100 mL of unused fresh cleaning agent was used as a blank sample, and the same settling, supernatant collection, filtration, drying, and weighing procedures were performed to obtain the background suspended particle mass M0. The particle dispersion rate was calculated using the formula [(M0-M1) / M0]×100%.

[0061] Membrane fiber integrity loss rate test: Ten intact monofilaments of uniform length (approximately 10 cm) were randomly cut from the membrane module after all cleaning and performance tests were completed. Using a universal testing machine, with the initial clamp spacing set to 50 mm and the tensile rate at 10 mm / min, the maximum force borne by each monofilament at the moment of fracture was measured, and its average value F1 was calculated in N. Ten monofilaments were also randomly cut from unused new membrane modules of the same batch, and their average tensile strength F0 was measured under the same test conditions. The membrane fiber integrity loss rate was calculated using the formula [(F0-F1) / F0]×100%.

[0062] All of the above tests were repeated independently three times, and the final result was the arithmetic mean.

[0063] The performance test data above are shown in Table 1.

[0064] Table 1 Performance Test Results

[0065]

[0066] As can be seen from the above, the formulation systems of Examples 1-3, compared to Comparative Examples 1-3, comprehensively and synergistically solve the multiple challenges faced by traditional MBR membrane cleaning technologies described in the background art. Firstly, in addressing the complex fouling caused by high suspended solids and sand-containing raw water, Examples 1-3 achieved excellent membrane flux recovery rates (93.8-96.5%) and transmembrane pressure reduction rates (89.5-92.8%), significantly better than Comparative Example 1, which used only basic cleaning components (65.2% and 58.3%, respectively). This result directly confirms that the introduction of three core functional materials (trinuclear iron-zirconium-silicon hybrid hydroxyphosphate, layered bimetallic cerium nitrate molybdate, and nanocage-like titanium-tungsten-borosilicate) constructs a composite cleaning system capable of synergistically breaking down physical blockages, organic adhesion, and inorganic scaling, effectively solving the problem of the limitations of traditional single agents (such as sodium hypochlorite or oxalic acid) in thoroughly cleaning complex fouling.

[0067] Secondly, this invention successfully overcomes the industry-wide challenge of biofouling by midge larvae (red worms) in anaerobic environments. Examples 1-3 achieved a 100% red worm kill rate, a stark contrast to Comparative Example 2 (40% kill rate) and the completely ineffective Comparative Example 1 (15% kill rate). This clearly reveals the crucial role of layered bimetallic cerium molybdate hydroxynitrate in catalyzing the generation of targeted reactive oxygen species and efficiently killing larvae, thus overcoming the shortcomings of traditional sodium hypochlorite cleaning in terms of poor bio-inhibition effects in this scenario.

[0068] Furthermore, in terms of preventing inorganic particles from damaging the membrane fibers, Examples 1-3 exhibited extremely high particle dispersion rates (92.1-95.2%), indicating their excellent suspension and encapsulation capabilities for particles such as sand and gravel, effectively preventing secondary deposition and mechanical wear during the cleaning process. The significant decrease in performance of Comparative Example 3 (particle dispersion rate 70.4%) highlights the indispensability of nanocage-like titanium-tungsten-borosilicate in adsorbing and dispersing inorganic particles, solving the problem that traditional acid washing (such as oxalic acid) cannot treat particulate matter and may even exacerbate wear.

[0069] Most importantly, Examples 1-3, while achieving the aforementioned high-efficiency cleaning, successfully controlled the membrane fiber integrity loss rate at a low level (1.5-1.8%), comparable to the comparative examples. This comprehensively demonstrates that the formulation, through the synergy of a mild oxidation system and functional materials, powerfully removes various pollutants while minimizing chemical erosion and physical damage to membrane materials such as polyvinylidene fluoride, fundamentally overcoming the drawbacks of irreversible damage and shortened lifespan of membrane materials caused by traditional strong acid (oxalic acid) or high-concentration oxidant (sodium hypochlorite) cleaning.

[0070] In summary, Examples 1-3, through the innovative combination of three customized functional materials, achieved synergistic treatment of biofouling, organic adhesion, inorganic scaling, and particulate clogging, while striking an excellent balance between efficient cleaning and superior membrane protection. This solution effectively replaces the frequent and highly damaging offline combined cleaning (oxalic acid + sodium hypochlorite), providing a solution for MBR systems facing the challenges of high suspended solids influent that enables efficient online maintenance, extends membrane life, and ensures continuous and stable system operation.

Claims

1. A low-damage, high-efficiency cleaning agent for MBR membrane bioreactors, characterized in that, Including the following parts by weight of raw materials: Trinuclear iron-zirconium-silicon hybrid hydroxyphosphate: 3-6 parts by weight; Layered bimetallic cerium hydroxynitrate molybdate: 2-5 parts by weight; Nanocage-like titanium-tungsten-borosilicate: 1.5-4 parts by weight; Sodium citrate: 5-10 parts by weight; Polyepoxysuccinic acid: 2-6 parts by weight; Sodium dodecylbenzenesulfonate: 0.5-2 parts by weight; Sodium percarbonate: 8-15 parts by weight; Borax: 1-3 parts by weight; Deionized water: 45-80 parts by weight; The preparation steps of the trinuclear iron-zirconium-silicon hybrid hydroxyphosphate include: A1, adding ferric chloride hexahydrate, zirconium oxychloride octahydrate and tetraethyl orthosilicate sequentially to deionized water and stirring under nitrogen protection; adding an aqueous solution of sodium dihydrogen phosphate dropwise; after the addition is complete, adjusting the pH to 6.6-7.0, raising the temperature to 84-86℃ and stirring the reaction; A2, after the reaction is complete, naturally cooling to room temperature, centrifuging to separate the precipitate, washing the precipitate with deionized water and anhydrous ethanol, drying it under vacuum at 58-62℃, and grinding it; The preparation method of the layered bimetallic cerium nitrate molybdate includes: B1, dissolving cerium nitrate hexahydrate and sodium molybdate dihydrate in deionized water to obtain cerium salt solution and molybdate solution respectively; under stirring conditions, adding the cerium salt solution and molybdate solution dropwise to a dilute nitric acid solution with pH=5.4-5.6 to obtain a colloid; B2, transferring the colloid to an oil bath at 88-92℃ for aging; after cooling, filtering to obtain a solid product; washing the solid product with dilute nitric acid with pH=5.4-5.6, then washing with deionized water until neutral, and drying under vacuum at 58-62℃; The preparation method of the nanocage-like titanium-tungsten-borosilicate includes: C1, adding titanium tetrachloride dropwise to anhydrous ethanol under an ice bath, and purging with nitrogen gas to obtain a titanium ethanol solution; adding tetraethyl orthosilicate to the titanium ethanol solution and stirring to obtain a titanium-silicon ethanol mixture; dissolving ammonium metatungstate and boric acid in deionized water and heating to 58-62℃ to obtain a boron-tungsten solution; adding the boron-tungsten solution to the titanium-silicon ethanol mixture and stirring; then adding hexadecyltrimethylammonium bromide to obtain a mixture; refluxing the mixture at 78-82℃; C2, cooling the reaction solution and centrifuging to obtain a precipitate, washing the precipitate with an ethanol-water mixture, and then calcining it in a muffle furnace at 545-555℃.

2. The low-damage, high-efficiency cleaning agent for MBR membrane bioreactors according to claim 1, characterized in that, In step A1, the temperature is raised to 84-86℃ and the stirring reaction is carried out for 12-14 hours.

3. The low-damage, high-efficiency cleaning agent for MBR membrane bioreactors according to claim 1, characterized in that, In step A2, the vacuum drying time at 58-62℃ is 12-14 hours.

4. The low-damage, high-efficiency cleaning agent for MBR membrane bioreactors according to claim 1, characterized in that, In step B1, the stirring time is 30-60 minutes.

5. The low-damage, high-efficiency cleaning agent for MBR membrane bioreactors according to claim 1, characterized in that, In step B2, the vacuum drying time at 58-62℃ is 10-12 hours.

6. The low-damage, high-efficiency cleaning agent for MBR membrane bioreactors according to claim 1, characterized in that, In step C1, the mixture is refluxed at 78-82℃ for 24-30 hours.

7. The low-damage, high-efficiency cleaning agent for MBR membrane bioreactors according to claim 1, characterized in that, In step C2, the calcination time in a muffle furnace at 545-555℃ is 4-6 hours.

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