Method for recycling leaching water in production of sprouting vegetables

Abstract

The invention relates to the technical field of wastewater reuse, and discloses a sprouting vegetable production leaching water reuse method, which comprises: collecting sprouting vegetable production leaching water into a microfiltration device, carrying out microfiltration treatment to prepare microfiltration water, feeding the microfiltration water into a regulation and storage tank, carrying out water quality and water quantity regulation to prepare regulation water, the adjusting water enters an MBR biological membrane treatment device to be subjected to microbial biochemical treatment and ultrafiltration treatment to prepare ultrafiltration water, the ultrafiltration water is subjected to ultraviolet sterilization treatment to prepare sterilized water, the sterilized water enters a temporary storage tank to prepare reuse water, and the reuse water is sent to a sprouting vegetable production line to be reused as a supplementary water source of spray water; according to the method, microfiltration treatment, MBR biological membrane treatment and ultraviolet sterilization treatment are adopted for treating leaching water in sprouting vegetable production, reuse water obtained through treatment meets the standard value of the GB5749-2022 sanitary standard for drinking water and can serve as a supplementary water source for sprouting vegetable leaching, and the method is simple in process, low in cost and high in efficiency.

Description

A method for reusing rinsing water from sprout production Technical Field

[0001] This invention relates to the field of wastewater reuse technology, and in particular to a method for reusing rinsing water from sprout production. Background Technology

[0002] Sprouts are vegetables consumed as young, tender parts of plants. Rich in vitamins, minerals, and dietary fiber, they are a green and healthy food. Currently, sprout production mainly uses hydroponics, which consumes a large amount of water. Therefore, developing water-saving technologies for sprout production is of great significance. Currently disclosed wastewater treatment methods for sprout production primarily employ membrane treatment and a combination of biochemical / physicochemical treatment. For example, CN111807548A discloses a method for treating bean sprout wastewater reuse, which uses chemical flocculation, flotation, membrane filtration, and reverse osmosis processes. Another example is CN117682690A, which discloses a method for purifying, reusing, and energy-saving recycling wastewater from sprout production. This method uses an arc screen, a hydrolysis acidification / biological contact oxidation tank, a secondary sedimentation tank, a flocculation reaction sedimentation tank, sand filtration, ultraviolet disinfection, and sodium hypochlorite disinfection.

[0003] This invention, through analysis of existing technologies, reveals that the common practice of collecting and combining wastewater from various sprout production processes for combined treatment in sprout vegetable production is characterized by lengthy processes, numerous modules, low efficiency, and high operation and maintenance costs. Further analysis of the wastewater generated during sprout vegetable production reveals that it primarily originates from processes such as bean washing, bean soaking, rinsing and hatching, and finished product cleaning. The rinsing and hatching process accounts for over 98% of the total wastewater, making it the main component of sprout vegetable production wastewater. Furthermore, testing of pollutants in the wastewater from each production process shows that the rinsing wastewater is less polluted and relatively cleaner than wastewater from other processes. Therefore, rinsing wastewater can be treated separately, which helps reduce treatment costs and increase economic benefits. Summary of the Invention

[0004] This invention addresses the problems of high cost and low efficiency in the centralized treatment of wastewater from various processes in sprout production in existing technologies. It provides a method for reusing rinsing water from sprout production. This method uses microfiltration pretreatment, MBR biofilm treatment, and ultraviolet sterilization to treat the rinsing water from sprout production. The treated effluent meets the standard values ​​of "GB5749-2022 Standard for Drinking Water Quality" and can be reused as a supplementary water source for sprout rinsing water. This method is simple, low-cost, and highly efficient.

[0005] The specific technical solution of the present invention is as follows: a method for reusing rinsing water from sprout production, comprising the following steps: (1) collecting rinsing water from sprout production into a microfiltration device and processing it into microfiltration water; (2) adjusting the water quality and quantity of the microfiltration water in a storage tank to produce conditioning water; (3) processing the conditioning water into an MBR biofilm treatment device for microbial biochemical treatment and ultrafiltration treatment to produce ultrafiltration water; (4) sterilizing the ultrafiltration water by ultraviolet sterilization treatment; (5) storing the sterilized water in a temporary storage tank to produce recycled water; and (6) sending the recycled water to the sprout production line as a supplementary source of spray water.

[0006] This invention provides a method for reusing rinsing water from sprout production. Since wastewater from sprout washing accounts for over 98% of the total wastewater in sprout production, and is relatively cleaner than wastewater from other processes, combining this relatively clean and predominantly high-volume rinsing wastewater with other process wastewater would significantly increase treatment costs and waste resources. Therefore, this invention collects and treats the wastewater from the sprout washing process separately using microfiltration, MBR biofilm treatment, and ultraviolet sterilization to obtain reclaimed water that meets the "GB5749-2022 Standard for Drinking Water Quality". The treatment process is simple, low-cost, and highly efficient. The resulting reclaimed water can be used as a supplementary source for rinsing water without affecting the quality of the sprouts.

[0007] Preferably, the filtration accuracy of the microfiltration process is ≥0.5 mm.

[0008] This invention employs an internal flow microfilter for microfiltration treatment, which can remove particulate impurities such as bean skins and bean tendrils from the rinsing water, thus performing preliminary impurity removal on the rinsing wastewater.

[0009] Preferably, in step (2), the retention time of the microfiltered water in the storage tank is 0.5~1 h, and the water flow rate in the storage tank is 5000~10000 t / d. Perforated aeration pipes are installed in the storage tank for air agitation to balance the water quality and ensure the stable operation of the subsequent biochemical treatment device.

[0010] Preferably, the time for microbial biochemical treatment in step (3) is 1~2 h.

[0011] Preferably, the filtration accuracy of the ultrafiltration process in step (3) is 30 μm.

[0012] The microbial treatment of the present invention uses an MBR biofilm treatment device, which consists of a high-efficiency biological pool unit and a membrane separation unit. The high-efficiency biological pool unit adopts a baffled reactor to ensure that the microorganisms are in full contact with the wastewater and effectively degrade pollutants. The membrane separation component adopts a PVDF ultrafiltration membrane.

[0013] Preferably, the SS of the ultrafiltered water is <3 mg / L, and the turbidity of the ultrafiltered water is ≤1 NTU.

[0014] Preferably, the wavelength of the ultraviolet sterilization treatment is 200~400 nm.

[0015] Preferably, the ultraviolet sterilization treatment uses a pipeline ultraviolet sterilizer.

[0016] The ultraviolet sterilization treatment of the present invention is carried out by a pipeline ultraviolet sterilizer. The pipeline ultraviolet sterilizer adopts a medium-pressure ultraviolet system with a wavelength of 200~400 nm, which has broad-spectrum sterilization and a sterilization rate of more than 4 Log. It does not require the addition of chlorine and has no adverse effect on the quality of sprouts.

[0017] Preferably, the ultrafiltration process in step (3) uses a nano zinc oxide PVDF membrane. The preparation steps of the nano zinc oxide PVDF membrane include: placing the PVDF membrane in a sodium hydroxide solution to react and prepare a pretreated PVDF membrane; then placing the pretreated PVDF membrane in an aminosilane coupling agent solution to react and prepare an amino-modified PVDF membrane; and placing the amino-modified PVDF membrane, zinc salt solution, ammonia water and polyethylene glycol in a hydrothermal reaction vessel to conduct a hydrothermal reaction and prepare a nano zinc oxide PVDF membrane.

[0018] Since the concentration of pollutants in the rinsing water of sprouts is low, after microbial degradation, only the microbial cells and metabolites need to be retained. Therefore, the ultrafiltration of this invention uses a PVDF membrane with a filtration accuracy of 30~50 μm. This large-pore membrane can retain particulate matter and has a large output. However, this type of membrane cannot completely retain microorganisms in the water. Therefore, this invention sets up an ultraviolet sterilizer at the outlet pipe after ultrafiltration to inactivate the microorganisms in the water.

[0019] To enhance the inactivation effect on microorganisms in water, this invention uses a nano zinc oxide ultrafiltration membrane. The nano zinc oxide ultrafiltration membrane is made by loading nano zinc oxide onto the surface and pore walls of a PVDF membrane. The nano zinc oxide crystals can destroy the cells of microorganisms passing through the membrane surface, thereby killing microorganisms in the water during filtration. The small amount of microorganisms remaining can be completely inactivated by an ultraviolet sterilizer, ensuring the output water volume of the filtered water.

[0020] The nano-zinc oxide ultrafiltration membrane of the present invention is prepared by first modifying the surface and inner wall of the PVDF membrane with an alkaline solution. The OH content of the alkaline solution... -The process involves replacing the fluorine (F) groups on the PVDF membrane surface to graft hydroxyl groups onto the PVDF membrane surface; then, an aminosilane coupling agent is used to react with the hydroxyl-modified PVDF membrane, grafting the aminosilane coupling agent onto the PVDF surface, thus grafting amino groups onto the PVDF membrane. Amino groups can act as complexing agents for nano-zinc oxide crystals. In this invention, after grafting amino groups onto the PVDF membrane, they can serve as targeted sites for the growth of nano-zinc oxide crystals, thereby loading nano-zinc oxide onto the PVDF membrane. Because PVDF has poor high-temperature resistance and also requires loading nano-zinc oxide onto the inner pore walls of the PVDF membrane, this invention uses a hydrothermal method to grow nano-zinc oxide on the surface of the PVDF and on the inner pore walls of the PVDF.

[0021] In addition, different nano zinc oxide crystals have different destructive effects on cells. Irregularly shaped nano zinc oxide crystals are more destructive to microbial cells than spherical nano zinc oxide crystals. Therefore, obtaining a large number of irregularly shaped nano zinc oxide crystals can enhance the filtration and sterilization effect. During the preparation of nano zinc oxide, complexing agents, zinc salts, additives and hydrothermal conditions have a significant impact on its appearance and particle size.

[0022] Preferably, the PVDF filter membrane has a pore size of 30~50 μm.

[0023] Preferably, the alkaline solution is sodium hydroxide, and the concentration of the alkaline solution is 1~10 mol / L.

[0024] Preferably, the aminosilane coupling agent is γ-aminopropyltriethoxysilane.

[0025] Preferably, the zinc salt is one of zinc sulfate, zinc chloride, and zinc acetate, and the concentration of the zinc salt is 0.1~1 mol / L.

[0026] Preferably, the ammonia concentration is 2~5 mol / L.

[0027] Preferably, the hydrothermal reaction conditions include: temperature 110~130 ℃ and time 10~15 h.

[0028] Compared with the prior art, this application has the following technical effects: (1) The method uses microfiltration, MBR biofilm treatment and ultraviolet sterilization to treat the rinsing water in the production of sprouts. The treated effluent meets the standard value of "GB5749-2022 Standard for Drinking Water Quality" and can be reused as a supplementary water source for sprout rinsing water. The method is simple, low in cost and highly efficient; (2) The ultrafiltration treatment of this invention uses a nano zinc oxide ultrafiltration membrane. The ultrafiltration membrane is loaded with nano zinc oxide crystals on the PVDF membrane and pore wall. Using the nano zinc oxide ultrafiltration membrane can initially kill microorganisms in the water while filtering large particles. It can significantly reduce the content of live bacteria in the effluent while ensuring the effluent volume and improve the killing efficiency. In addition, there will be no microbial growth on the surface of the nano zinc oxide ultrafiltration membrane, which significantly increases durability and can also avoid the problem of microbial growth covering the filter membrane and reducing the filter membrane filtration performance. Attached Figure Description

[0029] Figure 1 is a process flow diagram of the method for reusing rinsing water in the production of sprout vegetables according to the present invention.

[0030] Figure 2 is a schematic diagram of the apparatus for the method of reusing rinsing water in the sprout vegetable industry according to the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to embodiments.

[0032] Example 1: A method for reusing rinsing water from sprout vegetable production, comprising the following steps: (1) Collecting the rinsing water from sprout vegetable production separately and injecting it into an internal flow microfilter (filtration accuracy of 0.5 mm) for microfiltration treatment to remove impurities such as bean skins and bean tendrils to produce microfiltered water; (2) Injecting the microfiltered water into a regulating tank to adjust the water quality and quantity to produce regulating water. The water flow rate in the regulating tank is 8000 t / d, the retention time is 1 h, and the aeration intensity in the regulating tank is 0.5 m. 3 / m 2 ·h; (3) The regulating water in the storage tank is lifted to the MBR biofilm treatment system by a centrifugal pump. The regulating water first enters the high-efficiency biological tank unit for microbial biochemical treatment, and then enters the membrane separation unit for ultrafiltration treatment to produce ultrafiltration water. The high-efficiency biological tank unit adopts a folded plate reactor, and the membrane separation unit adopts a nano zinc oxide ultrafiltration membrane. The ultrafiltration water produced has SS < 3 mg / L and turbidity ≤ 1 NTU; (4) The ultrafiltration water is injected into a pipeline ultraviolet sterilizer for ultraviolet treatment to produce sterilized water. The wavelength range of ultraviolet disinfection is 200~400 nm; (5) The sterilized water is injected into a temporary storage tank for later use; (6) The effluent is sent to the sprout production workshop for reuse as spray water. An intelligent temperature control system and a pressure-stabilized water supply system are set up. The intelligent temperature control system controls the water temperature at 22~25 ℃, and the pressure-stabilized water supply system ensures the stability and reliability of sprout production.

[0033] The preparation method of nano-zinc oxide ultrafiltration membrane includes the following steps: S1: PVDF filter membrane (pore size 30~50 μm) is placed in alkaline solution (5 mol / L NaOH solution) and soaked at 50℃ for 6 h to prepare hydroxyl-modified PVDF filter membrane. The hydroxyl-modified PVDF filter membrane is then washed with deionized water until neutral. S2: The hydroxyl-modified PVDF filter membrane is then placed in an amino coupling agent (8% γ-aminopropyltriethoxysilane ethanol solution) and soaked at 50℃ for 11 h to obtain amino-modified PVDF filter membrane. The amino-modified PVDF filter membrane is then washed and dried with anhydrous ethanol to remove the ethanol. S3: The amino-modified PVDF filter membrane is soaked in deionized water for full wetting. The soaked amino-modified PVDF filter membrane is then placed in a hydrothermal reactor. Polyethylene glycol (0.05 mol / L) and zinc salt solution (0.5 mol / L) are added. A 3 mol / L solution of zinc sulfate was added to a hydrothermal reactor to immerse the amino-modified PVDF membrane. The mixture was stirred for 20 min to allow the zinc salt to fully complex with the amino groups on the PVDF surface. Ammonia water (3 mol / L) was added, and stirring was continued to increase the complexation effect. The hydrothermal reactor was then sealed and reacted at 120 °C for 12 h to produce a nano-zinc oxide ultrafiltration membrane. The nano-zinc oxide ultrafiltration membrane was washed with deionized water until no sulfate ions were present (a barium chloride solution was used to test for sulfate ions). The washed nano-zinc oxide ultrafiltration membrane was then placed in an oven and dried to constant weight.

[0034] Example 2: A method for reusing rinsing water from sprout vegetable production, comprising the following steps: (1) Collecting the rinsing water from sprout vegetable production separately and injecting it into an internal flow microfilter (filtration accuracy of 0.5 mm) for microfiltration treatment to remove impurities such as bean skins and bean tendrils to produce microfiltered water; (2) Injecting the microfiltered water into a regulating tank to adjust the water quality and quantity to produce regulating water. The water flow rate in the regulating tank is 5000 t / d, the retention time is 0.5 h, and the aeration intensity in the regulating tank is 0.5 m. 3 / m 2·h; (3) The regulating water in the storage tank is lifted to the MBR biofilm treatment system by a centrifugal pump. The regulating water first enters the high-efficiency biological tank unit for microbial biochemical treatment, and then enters the membrane separation unit for ultrafiltration treatment to produce ultrafiltration water. The high-efficiency biological tank unit uses a folded plate reactor, and the membrane separation unit uses a PVDF ultrafiltration membrane with a filtration accuracy of 30 μm. The ultrafiltration water produced has SS < 3 mg / L and turbidity ≤ 1 NTU; (4) The ultrafiltration water is injected into a pipeline ultraviolet sterilizer for ultraviolet treatment to produce sterilized water. The wavelength range of ultraviolet disinfection is 200~400 nm; (5) The sterilized water is injected into a temporary storage tank for later use; (6) The effluent is sent to the sprout production workshop for reuse as spray water. An intelligent temperature control system and a pressure-stabilized water supply system are set up. The intelligent temperature control system controls the water temperature at 18~20℃, and the pressure-stabilized water supply system ensures the stable and reliable production of sprouts.

[0035] The preparation method of nano-zinc oxide ultrafiltration membrane includes the following steps: S1: A PVDF filter membrane (pore size 30-50 μm) is immersed in an alkaline solution (1 mol / L NaOH solution) at 30°C for 8 h to prepare a hydroxyl-modified PVDF filter membrane. The hydroxyl-modified PVDF filter membrane is then washed with deionized water until neutral. S2: The hydroxyl-modified PVDF filter membrane is then immersed in an amino coupling agent (5% γ-aminopropyltriethoxysilane ethanol solution) at 60°C for 10 h to obtain an amino-modified PVDF filter membrane. The amino-modified PVDF filter membrane is then washed and dried with anhydrous ethanol to remove the ethanol. S3: The amino-modified PVDF filter membrane is fully immersed in deionized water. The immersed amino-modified PVDF filter membrane is then placed in a hydrothermal reactor. Polyethylene glycol (0.01 mol / L) and zinc salt solution (0.1 mol / L) are added. A 2 mol / L solution of zinc sulfate was added to a hydrothermal reactor to immerse the amino-modified PVDF membrane. The mixture was stirred for 20 min to allow the zinc salt to fully complex with the amino groups on the PVDF surface. Ammonia water (2 mol / L concentration) was added, and stirring was continued to increase the complexation effect. The hydrothermal reactor was sealed and reacted at 130 °C for 15 h to produce a nano-zinc oxide ultrafiltration membrane. The nano-zinc oxide ultrafiltration membrane was washed with deionized water until no sulfate ions were present (the sulfate ion concentration was tested using barium chloride solution). The washed nano-zinc oxide ultrafiltration membrane was then dried in an oven to constant weight.

[0036] Example 3: A method for reusing rinsing water from sprout vegetable production, comprising the following steps: (1) Collecting the rinsing water from sprout vegetable production separately and injecting it into an internal flow microfilter (filtration accuracy of 0.5 mm) for microfiltration treatment to remove impurities such as bean skins and bean tendrils to produce microfiltered water; (2) Injecting the microfiltered water into a regulating tank to adjust the water quality and quantity to produce regulating water. The water flow rate in the regulating tank is 10,000 t / d, the retention time is 1 h, and the aeration intensity in the regulating tank is 0.5 m. 3 / m 2 ·h; (3) The regulating water in the storage tank is lifted to the MBR biofilm treatment system by a centrifugal pump. The regulating water first enters the high-efficiency biological tank unit for microbial biochemical treatment, and then enters the membrane separation unit for ultrafiltration treatment to produce ultrafiltration water. The high-efficiency biological tank unit uses a folded plate reactor, and the membrane separation unit uses a PVDF ultrafiltration membrane with a filtration accuracy of 30 μm. The ultrafiltration water produced has SS < 3 mg / L and turbidity ≤ 1 NTU; (4) The ultrafiltration water is injected into a pipeline ultraviolet sterilizer for ultraviolet treatment to produce sterilized water. The wavelength range of ultraviolet disinfection is 200~400 nm; (5) The sterilized water is injected into a temporary storage tank for later use; (6) The recycled water is sent to the sprout production workshop for reuse as spray water. An intelligent temperature control system and a pressure-stabilized water supply system are set up. The intelligent temperature control system controls the water temperature at 23~25 ℃, and the pressure-stabilized water supply system ensures the stable and reliable production of sprouts.

[0037] The preparation method of nano-zinc oxide ultrafiltration membrane includes the following steps: S1: PVDF filter membrane (pore size 30~50 μm) is immersed in alkaline solution (10 mol / L NaOH solution) at 60℃ for 5 h to prepare hydroxyl-modified PVDF filter membrane, and then washed with deionized water until neutral; S2: The hydroxyl-modified PVDF filter membrane is then immersed in amino coupling agent (10% γ-aminopropyltriethoxysilane ethanol solution) at 40℃ for 12 h to obtain amino-modified PVDF filter membrane, and then washed and dried with anhydrous ethanol to remove the ethanol; S3: The amino-modified PVDF filter membrane is fully immersed in deionized water, and then the immersed amino-modified PVDF filter membrane is placed in a hydrothermal reactor, and polyethylene glycol (concentration 0.1) is added. A 5 mol / L ammonia solution and a zinc salt solution (zinc sulfate) were mixed thoroughly and added to a hydrothermal reactor to immerse the amino-modified PVDF filter membrane. The mixture was stirred for 20 min to allow the zinc salt to fully complex with the amino groups on the PVDF surface. Ammonia solution (5 mol / L) was added, and stirring continued to increase the complexation effect. The hydrothermal reactor was then sealed and reacted at 110 °C for 15 h to produce a nano-zinc oxide ultrafiltration membrane. The nano-zinc oxide ultrafiltration membrane was washed with deionized water until no sulfate ions were present (sulfate ions were tested using barium chloride solution). The washed nano-zinc oxide ultrafiltration membrane was then dried in an oven to constant weight.

[0038] Example 4: A method for reusing rinsing water from sprout vegetable production, comprising the following steps: (1) Collecting the rinsing water from sprout vegetable production separately and injecting it into an internal flow microfilter (filtration accuracy of 0.5 mm) for microfiltration treatment to remove impurities such as bean skins and bean tendrils to produce microfiltered water; (2) Injecting the microfiltered water into a regulating tank to adjust the water quality and quantity to produce regulating water. The water flow rate in the regulating tank is 5000 t / d, the retention time is 1 h, and the aeration intensity in the regulating tank is 0.5 m. 3 / m 2·h; (3) The regulating water in the storage tank is lifted to the MBR biofilm treatment system by a centrifugal pump. The regulating water first enters the high-efficiency biological tank unit for microbial biochemical treatment, and then enters the membrane separation unit for ultrafiltration treatment to produce ultrafiltration water. The high-efficiency biological tank unit uses a folded plate reactor, and the membrane separation unit uses a PVDF ultrafiltration membrane with a filtration accuracy of 30 μm. The ultrafiltration water produced has SS < 3 mg / L and turbidity ≤ 1 NTU; (4) The ultrafiltration water is injected into a pipeline ultraviolet sterilizer for ultraviolet treatment to produce sterilized water. The wavelength range of ultraviolet disinfection is 200~400 nm; (5) The sterilized water is injected into a temporary storage tank for later use; (6) The recycled water is sent to the sprout production workshop for reuse as spray water. An intelligent temperature control system and a pressure-stabilized water supply system are set up. The intelligent temperature control system controls the water temperature at 21~23 ℃, and the pressure-stabilized water supply system ensures the stable and reliable production of sprouts.

[0039] The preparation method of nano-zinc oxide ultrafiltration membrane includes the following steps: S1: A PVDF filter membrane (pore size 30~50 μm) is immersed in an alkaline solution (3 mol / L NaOH solution) at 40℃ for 6 h to prepare a hydroxyl-modified PVDF filter membrane. The hydroxyl-modified PVDF filter membrane is then washed with deionized water until neutral. S2: The hydroxyl-modified PVDF filter membrane is then immersed in an amino coupling agent (5% γ-aminopropyltriethoxysilane ethanol solution) at 60℃ for 10 h to obtain an amino-modified PVDF filter membrane. The amino-modified PVDF filter membrane is then washed and dried with anhydrous ethanol to remove the ethanol. S3: The amino-modified PVDF filter membrane is fully immersed in deionized water. The immersed amino-modified PVDF filter membrane is then placed in a hydrothermal reactor. Polyethylene glycol (0.04 mol / L) and zinc salt solution (0.5 mol / L) are added. A 3 mol / L solution of zinc sulfate was added to a hydrothermal reactor to immerse the amino-modified PVDF membrane. The mixture was stirred for 20 min to allow the zinc salt to fully complex with the amino groups on the PVDF surface. Ammonia water (3 mol / L) was added, and stirring was continued to increase the complexation effect. The hydrothermal reactor was then sealed and reacted at 120 °C for 12 h to produce a nano-zinc oxide ultrafiltration membrane. The nano-zinc oxide ultrafiltration membrane was washed with deionized water until no sulfate ions were present (a barium chloride solution was used to test for sulfate ions). The washed nano-zinc oxide ultrafiltration membrane was then placed in an oven and dried to constant weight.

[0040] Example 5: A method for reusing rinsing water from sprout vegetable production, comprising the following steps: (1) Collecting the rinsing water from sprout vegetable production separately and injecting it into an internal flow microfilter (filtration accuracy of 0.5 mm) for microfiltration treatment to remove impurities such as bean skins and bean tendrils to produce microfiltered water; (2) Injecting the microfiltered water into a regulating tank to adjust the water quality and quantity to produce regulating water. The water flow rate in the regulating tank is 5000 t / d, the retention time is 1 h, and the aeration intensity in the regulating tank is 0.5 m. 3 / m 2 ·h; (3) The regulating water in the storage tank is lifted to the MBR biofilm treatment system by a centrifugal pump. The regulating water first enters the high-efficiency biological tank unit for microbial biochemical treatment, and then enters the membrane separation unit for ultrafiltration treatment to produce ultrafiltration water. The high-efficiency biological tank unit uses a folded plate reactor, and the membrane separation unit uses a PVDF ultrafiltration membrane with a filtration accuracy of 30 μm. The ultrafiltration water produced has SS < 3 mg / L and turbidity ≤ 1 NTU; (4) The ultrafiltration water is injected into a pipeline ultraviolet sterilizer for ultraviolet treatment to produce sterilized water. The wavelength range of ultraviolet disinfection is 200~400 nm; (5) The sterilized water is injected into a temporary storage tank for later use; (6) The recycled water is sent to the sprout production workshop for reuse as spray water. An intelligent temperature control system and a pressure-stabilized water supply system are set up. The intelligent temperature control system controls the water temperature at 20~23 ℃, and the pressure-stabilized water supply system ensures the stable and reliable production of sprouts.

[0041] The preparation method of nano-zinc oxide ultrafiltration membrane includes the following steps: S1: PVDF filter membrane (pore size 30~50 μm) is immersed in alkaline solution (8 mol / L NaOH solution) at 50℃ for 7 h to prepare hydroxyl-modified PVDF filter membrane, and then washed with deionized water until neutral; S2: The hydroxyl-modified PVDF filter membrane is then immersed in amino coupling agent (3% γ-aminopropyltriethoxysilane ethanol solution) at 50℃ for 11 h to obtain amino-modified PVDF filter membrane, and then washed and dried with anhydrous ethanol to remove the ethanol; S3: The amino-modified PVDF filter membrane is fully immersed in deionized water, and then the immersed amino-modified PVDF filter membrane is placed in a hydrothermal reactor, and polyethylene glycol (0.02 mol / L) and zinc salt solution (0.8 mol / L) are added. Ammonia (4 mol / L) solution was added to a hydrothermal reactor to immerse the amino-modified PVDF membrane. The mixture was stirred for 20 min to allow the zinc salt to fully complex with the amino groups on the PVDF surface. Ammonia (4 mol / L) solution was added, and stirring continued to increase the complexation effect. The hydrothermal reactor was then sealed and reacted at 120 °C for 13 h to produce a nano-zinc oxide ultrafiltration membrane. The nano-zinc oxide ultrafiltration membrane was washed with deionized water until no sulfate ions were present (a barium chloride solution was used to test for sulfate ions). The washed nano-zinc oxide ultrafiltration membrane was then dried in an oven to constant weight.

[0042] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that no ultraviolet treatment was performed, while all other conditions were the same as in Example 1.

[0043] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that the ultraviolet treatment was replaced by disinfection of the water in the temporary storage tank with sodium hypochlorite, and all other conditions were the same as in Example 1.

[0044] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that a common PVDF ultrafiltration membrane (30~50μm) was used for ultrafiltration treatment, and all other conditions were the same as in Example 1.

[0045] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that lead acetate was used as the zinc salt, while all other conditions were the same as in Example 1.

[0046] Comparative Example 5: The difference between Comparative Example 5 and Example 1 is that lead chloride was used as the zinc salt, while all other conditions were the same as in Example 1.

[0047] Comparative Example 6: The difference between Comparative Example 6 and Example 1 is that the hydrothermal reaction time is 24 h, while the other conditions are the same as those in Example 1.

[0048] Comparative Example 7: The difference between Comparative Example 6 and Example 1 is that the hydrothermal reaction time is 3 hours, while the other conditions are the same as in Example 1.

[0049] Test examples: The quality of reclaimed water and the microbial content of filter membrane effluent prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were tested; the reclaimed water quality test items included: COD, turbidity, free chlorine, total coliforms, Escherichia coli and total colony count, and the test methods were carried out in accordance with the contents disclosed in GB5749-2022 Standard for Drinking Water Quality; the test results are shown in Table 1.

[0050] Table 1 Test Results As shown in Table 1, the recycled water prepared in Examples 1 to 5 had a COD of 1.21~1.25 mg / L, a turbidity of 0.51~0.53 MPa, a free chlorine of 0 mg / L, and no detectable total coliforms, Escherichia coli, or total bacterial count. According to the content disclosed in GB / T 5749-2022 Standard for Drinking Water Quality, the recycled water prepared by this invention meets the requirements of the standard and can be used as supplementary backup water for spraying water in sprout production.

[0051] In Comparative Example 1, no ultraviolet treatment was used, and the results showed that total coliforms and Escherichia coli were detected in the water, which did not meet the standards of "GB / T 5749-2022 Standard for Drinking Water Quality" and could not be used.

[0052] In Comparative Example 2, sodium hypochlorite was used to disinfect the water in the temporary storage tank. The results showed that the free chlorine content in the water reached 0.35 mg / L, which does not meet the standard value of "GB / T 5749-2022 Standard for Drinking Water Quality" and therefore cannot be used.

[0053] Comparative Example 3 used a common PVDF membrane. The results showed that the microbial content in the effluent from the membrane of Comparative Example 3 was relatively high. Furthermore, even after subsequent ultraviolet disinfection, the microorganisms in the recycled water could not be completely eliminated.

[0054] Comparative Examples 4 and 5 used different zinc salts. The results showed that when different zinc salts were used as substrates for zinc oxide growth, the resulting nano-zinc oxide ultrafiltration membranes all had a certain killing effect on bacteria, but the killing effect varied. After analysis, it was found that the morphology of the nano-zinc oxide grown by different zinc oxides was quite different. Zinc acetate was more likely to form spherical nano-zinc oxide, while zinc chloride was more likely to form polygonal nano-zinc oxide, and zinc sulfate could form irregular shapes with spikes. These different shapes also had different effects on the disruption of microbial cells in water. In this invention, it was found that the killing effect of different zinc salts on microorganisms in water was, in descending order, that of zinc sulfate, zinc chloride, and zinc acetate.

[0055] The hydrothermal reaction time was investigated in Comparative Examples 6 and 7. The results showed that if the hydrothermal reaction time was too short, nano-zinc oxide crystals could not be effectively grown on the PVDF surface. If the hydrothermal time was too long, the nano-zinc oxide crystals in the PVDF pores would be too large, resulting in a small water output from the filter membrane.

[0056] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for reusing rinsing water from sprout production, characterized in that, Includes the following steps: (1) Collect the rinsing water from sprout production into a microfiltration device and process it into microfiltration water through a microfiltration machine; (2) The microfiltration water enters the storage tank for water quality and quantity adjustment to make conditioning water; (3) The conditioning water enters the MBR biofilm treatment device for microbial biochemical treatment and ultrafiltration treatment to make ultrafiltration water; (4) The ultrafiltration water is treated with ultraviolet sterilization to make sterilized water; (5) The sterilized water enters the temporary storage tank to make recycled water; (6) The recycled water is sent to the sprout production line as a supplementary source of rinsing water.

2. The method according to claim 1, characterized in that, The microfiltration process has a filtration accuracy of 0.5 mm.

3. The method according to claim 1, characterized in that, In step (2), the residence time of the micro-filtered water in the storage tank is 0.5~1 h, and the water flow rate in the storage tank is 5000~10000 t / d.

4. The method according to claim 1, characterized in that, The time for microbial biochemical treatment in step (3) is 1~2 h.

5. The method according to claim 1, characterized in that, In step (3), ultrafiltration is performed using a nano zinc oxide PVDF membrane. The preparation steps of the nano zinc oxide PVDF membrane include: placing the PVDF membrane in a sodium hydroxide solution to react and prepare a pretreated PVDF membrane. The pretreated PVDF membrane was then reacted in an aminosilane coupling agent solution to prepare an amino-modified PVDF membrane. The amino-modified PVDF membrane, zinc salt solution, ammonia water and polyethylene glycol were placed in a hydrothermal reaction vessel to prepare a nano zinc oxide PVDF membrane.

6. The method according to claim 5, characterized in that, The PVDF membrane has a pore size of 30~50μm.

7. The method according to claim 5, characterized in that, The zinc salt solution is a zinc sulfate solution.

8. The method according to claim 5, characterized in that, The conditions for the hydrothermal reaction include: temperature 110~120℃, time 10~15h.

9. The method according to claim 1, characterized in that, The ultraviolet sterilization treatment uses a pipeline ultraviolet sterilizer.

10. The method according to claim 1 or 9, characterized in that, The wavelength of the ultraviolet sterilization treatment is 200~400nm.

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