Method for purifying and recycling sprout vegetable production wastewater and energy saving circulation

Abstract

The present application relates to the field of wastewater reuse, and discloses a kind of sprout production wastewater purification reuse and energy saving circulation method, steps are as follows: (1) the impurities of sprout production wastewater are removed, then enter the conditioning tank homogenization;(2) remove organic pollutants by biochemical treatment device;(3) into flocculation reaction sedimentation tank and carry out coagulation and flocculation reaction;(4) the effluent of flocculation reaction sedimentation tank enters sand filter tank, after turbidity removal, through pipeline type ultraviolet sterilizer sterilization, and is discharged into reuse water temporary storage tank, and adds sodium hypochlorite disinfectant to ensure that residual chlorine reaches standard, to obtain reuse water;(5) the reuse water is recycled to sprout production workshop as the supplement of spray water source, to realize energy saving circulation.The effluent quality of the present application is stable, disinfection is thorough, and when reuse as the spray water of sprout production, it will not affect the quality of sprout, and improves the utilization rate of water resources;And in the process of treatment, a large amount of energy is not consumed, and the energy saving circulation of sprout wastewater can be realized.

Description

Technical Field

[0001] This invention relates to the field of wastewater reuse technology, and in particular to a method for purifying, reusing, and energy-saving recycling of wastewater from sprout production. Background Technology

[0002] Sprouts, a highly nutritious, pollution-free, and additive-free green vegetable, are generally produced using vertical soilless cultivation technology. The production process includes "washing and selecting beans - soaking beans - rinsing - watering and hatching - cleaning the finished product," which consumes a large amount of water. Especially during the watering stage, the respiration heat generated during bean germination needs to be dissipated through rinsing; otherwise, the sprouts are highly susceptible to rotting and spoilage. During the sprout hatching process, the rinsing water, soaking water, and washing water are discharged intermittently in large quantities.

[0003] Statistics show that 1 kg of mung beans can produce 7-8 kg of mung bean sprouts, with an incubation period of 8 days and a water consumption of approximately 350 L per production cycle; 1 kg of soybeans can produce 11-13 kg of soybean sprouts, with an incubation period of 6 days and a water consumption of approximately 450 L per production cycle. To ensure vegetable quality, the water used for sprout production complies with the "Standards for Drinking Water Quality" (GB5749-2022), with residual chlorine levels controlled below 0.02 mg / L. In areas with abundant groundwater reserves, purified deep well water is used as the production water.

[0004] During the production of sprouts, besides the water consumed by the sprouts themselves during growth, the combined wastewater from soaking, rinsing, and washing processes has a pollution concentration below the limit set by the "Water Quality Standard for Wastewater Discharge into Urban Sewers" (GB / T 31962-2015), and can be directly discharged into urban sewers. Taking a daily sprout production of 150 tons as an example, the daily wastewater discharge is approximately 8750 m³. 3 Of the total daily wastewater discharge, approximately 2% comes from water used for soaking beans and washing vegetables. This wastewater is high in organic pollutants, with measured COD concentrations of approximately 280–500 mg / L, ammonia nitrogen concentrations of approximately 6–10 mg / L, and turbidity of 60–100 NTU. The remaining 98% comes from rinsing wastewater, which is low in organic pollutants, with measured COD concentrations of approximately 25–50 mg / L, ammonia nitrogen concentrations of approximately 0.3–1.5 mg / L, and turbidity of 10–40 NTU. This wastewater is directly discharged into urban sewers, placing pressure on end-of-pickled wastewater treatment plants and resulting in significant water waste and high water costs for sprout vegetable producers. If the wastewater from sprout vegetable production could be purified and recycled, water resources could be greatly saved.

[0005] To ensure that recycled water meets the standards for sprout production, existing technologies generally require membrane treatment such as reverse osmosis to reuse sprout production wastewater. For example, a method for treating bean sprout wastewater for reuse, disclosed in Chinese patent literature (publication number CN111807548A), includes the following steps: coagulation and chemical addition; air flotation; membrane filtration; and reverse osmosis. However, membrane treatment systems such as reverse osmosis require operation under high pressure and regular replacement of membrane modules, cleaning, and maintenance, resulting in high operating and maintenance costs. Furthermore, the water production is low, generating a large amount of concentrated wastewater, which is detrimental to water resource reuse. Summary of the Invention

[0006] This invention aims to overcome the problems of high water consumption and ineffective recycling in the sprout hatching process in existing technologies. It provides a method for purifying, reusing, and energy-saving recycling wastewater generated during sprout production. The wastewater is purified through conditioning, biochemical treatment, sedimentation, flocculation, filtration, ultraviolet sterilization, and sodium hypochlorite disinfection to meet reuse standards. Then, through energy-saving recycling technology, the water resources in the sprout production process are reused.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for purifying, reusing, and energy-saving recycling wastewater from sprout production includes the following steps:

[0009] (1) The wastewater from sprout production is passed through an arc screen to remove impurities, and then enters the equalization tank for water volume adjustment and water quality balancing.

[0010] (2) The effluent from the equalization tank is lifted into the biochemical treatment device to remove organic pollutants and total nitrogen. The wastewater after biochemical treatment enters the sedimentation tank for mud-water separation.

[0011] (3) The effluent (supernatant) from the sedimentation tank enters the flocculation reaction sedimentation tank, where coagulant and flocculant are added for coagulation and flocculation reaction, followed by sedimentation for solid-liquid separation.

[0012] (4) The effluent (supernatant) from the flocculation reaction sedimentation tank enters the sand filter tank. After turbidity removal, it is sterilized by a pipeline ultraviolet sterilizer and then enters the recycled water storage tank. Sodium hypochlorite disinfectant is added to ensure that the residual chlorine meets the standard, thus obtaining recycled water.

[0013] (5) Recycle the recycled water to the sprout production workshop as a supplementary water source for spraying, so as to achieve energy-saving recycling.

[0014] This invention first removes impurities such as bean husks and vegetable roots from sprout production wastewater using an arc-shaped screen. Then, after water volume adjustment and quality balancing in a regulating tank, most organic pollutants are removed through biochemical treatment. Suspended solids are then removed through coagulation and flocculation reactions, followed by turbidity removal via sand filtration. Finally, a combined ultraviolet light and sodium hypochlorite disinfection method ensures sterility of the recycled water. This invention utilizes a pipeline-type ultraviolet sterilizer, achieving a sterilization rate of over 99.9%, with rapid and efficient disinfection, without introducing impurities into the water, ensuring the water's physicochemical properties remain largely unchanged, and producing no disinfection byproducts. Using this method to treat sprout production wastewater results in stable effluent quality and thorough disinfection, consistently meeting the "Standards for Drinking Water Quality" (GB5749-2022). When reused as rinsing water for sprout production, it does not affect the quality of the sprouts, improving water resource utilization and significantly reducing production costs for enterprises. Furthermore, the treatment process does not consume large amounts of energy, achieving energy-saving recycling of sprout wastewater.

[0015] Preferably, in step (1), the wastewater from sprout production is collected separately. The vegetable washing water and bean soaking water, after removing impurities, enter the first regulating tank, while the rinsing water, after removing impurities, enters the second regulating tank. The effluent from the first and second regulating tanks is mixed for biochemical treatment in step (2). The wastewater flow rate in the first regulating tank is 20–80 t / d, with a retention time of 12–36 h; the wastewater flow rate in the second regulating tank is 3000–8000 t / d, with a retention time of 1–2 h. This invention collects wastewater separately, allowing wastewater of different properties generated during sprout production to be conditioned in different regulating tanks, which is beneficial for the stable operation of the biochemical treatment device.

[0016] Preferably, the biochemical treatment device in step (2) includes a hydrolysis acidification unit and a biological contact oxidation unit. The biochemical treatment device adopts a gravity flow two-stage tower structure, with the hydrolysis acidification unit located above the contact oxidation unit. The effluent from the equalization tank enters from the top of the biochemical treatment device. The residence time in the hydrolysis acidification unit is 40–80 min, and the residence time in the contact oxidation unit is 1.5–2.5 h. The biochemical treatment of this invention uses hydrolysis acidification + contact oxidation, which facilitates microbial biofilm formation, produces clean water, and has a low content of participating microorganisms, which is beneficial for subsequent disinfection. Furthermore, the device adopts a gravity flow two-stage tower structure, so the effluent from the equalization tank only needs to be lifted once and flow by gravity to different biochemical treatment units, which can save power consumption.

[0017] Preferably, the residence time in the sedimentation tank in step (2) is 1 to 1.5 hours.

[0018] Preferably, the coagulant in step (3) is PAC, and the amount of coagulant added is 40-60 ppm; the flocculant is PAM, and the amount of flocculant added is 2-4 ppm.

[0019] Preferably, the flocculation reaction sedimentation tank in step (3) includes a pre-reaction zone and a sedimentation zone; coagulant and flocculant are added sequentially in the pre-reaction zone and mechanically stirred, and after coagulation and flocculation reaction, the wastewater enters the sedimentation zone for solid-liquid separation; the residence time in the pre-reaction zone is 8 to 12 minutes; the residence time in the sedimentation zone is 1 to 2 hours.

[0020] Preferably, modified quartz sand is used as the filter media in the sand filter tank of step (4), and the method for preparing the modified quartz sand is as follows:

[0021] A) Quartz sand with a particle size of 0.5-1.5 mm is soaked in 0.1-0.5 mol / L hydrochloric acid solution for 12-24 hours, filtered and washed to obtain pretreated quartz sand;

[0022] B) Dissolve ferric chloride in DMF, then add terephthalic acid and stir until homogeneous to obtain a mixed solution; the molar ratio of ferric chloride to terephthalic acid is 1:1 to 1.2; add pretreated quartz sand to the mixed solution and disperse it evenly by ultrasonication to obtain a dispersion; the mass ratio of the added quartz sand to ferric chloride is 2 to 3:1.

[0023] C) The dispersion was subjected to hydrothermal reaction at 130-150℃ for 24-48h. The product was separated, washed, and dried to obtain Fe-MOF coated quartz sand.

[0024] D) The Fe-MOF-coated quartz sand was calcined at 700-800℃ for 3-4 hours in an inert atmosphere to obtain the modified quartz sand.

[0025] This invention modifies quartz sand for use as a filter media in sand filtration. The modification process involves first pretreating the surface of the quartz sand with hydrochloric acid to remove surface impurities; then, Fe... 3+ As a metal ion, terephthalic acid serves as a ligand, enabling the in-situ growth of an iron-containing metal-organic framework (Fe-MOF) on the surface of quartz sand via a hydrothermal reaction. The Fe-MOF material possesses high porosity and a large specific surface area. After calcination in step D), a composite of porous carbon and nano-iron oxide can be obtained on the quartz sand surface. The loading of nano-iron oxide can impart a positive charge to the quartz sand surface under neutral pH conditions, which is beneficial for the removal of negatively charged impurity particles from wastewater. Meanwhile, the coating of porous carbon significantly increases the specific surface area of ​​the quartz sand, and its porous structure allows for the adsorption and removal of pollutants from wastewater, significantly improving the turbidity removal efficiency of the sand filtration process and enabling the effluent to meet reuse standards.

[0026] Preferably, the filter media height in the sand filter tank is 1–1.5 m, the filtration rate is 7–9 m / h, and the backwashing intensity is 12–15 L / m. 2S, backwashing time 3-5 minutes.

[0027] Preferably, the pipeline-type ultraviolet sterilizer used in step (4) employs a medium-pressure multi-spectral ultraviolet system with a wavelength range of 200–400 nm. This invention uses a medium-pressure multi-spectral ultraviolet system for ultraviolet sterilization, achieving a sterilization efficiency of 4 Log. One lamp tube can replace the effect of more than a dozen low-pressure ultraviolet lamp tubes, resulting in low energy consumption and ensuring disinfection effectiveness while saving energy. Furthermore, the medium-pressure multi-spectral ultraviolet system in this invention uses a quartz fiber optic transmission method for ultraviolet light disinfection. Utilizing a high-power medium-pressure ultraviolet lamp source, the ultraviolet light is uniformly transmitted through the diffused light points on the quartz fiber to kill bacteria in the water, effectively avoiding the photoreactivation of microorganisms after low-pressure ultraviolet disinfection. The medium-pressure multi-spectral ultraviolet system in this invention is an advanced water optical disinfection technology. It integrates a UVT (ultraviolet transmittance) sensor to continuously monitor ultraviolet light transmittance and intelligently control the number of ultraviolet lamp tubes online. Real-time monitoring can address fluctuations in water volume and changes in water quality.

[0028] As a preferred option, the residual chlorine in step (4) after adding sodium hypochlorite disinfectant is controlled below 0.02 mg / L to ensure that there is no adverse effect on the shape, freshness, expansion ratio and shelf life of the sprouts; and to ensure that the water has a continuous bactericidal ability after ultraviolet disinfection.

[0029] Preferably, in step (5), when the recycled water is used as spray water in the sprout production workshop, an intelligent temperature control system and a pressure-stabilized water supply system are installed. The intelligent temperature control system can control the temperature of the recycled water at a suitable temperature of 20-25℃ for sprout growth; the pressure-stabilized water supply system can ensure the stable and reliable production of sprouts.

[0030] Therefore, the present invention has the following beneficial effects:

[0031] (1) The method of the present invention is used to treat the wastewater of sprout production. The effluent quality is stable and the disinfection is thorough. It can stably meet the "Standards for Drinking Water Quality" (GB5749-2022). When it is reused as rinsing water for sprout production, it will not affect the quality of sprouts. It improves the utilization rate of water resources and greatly reduces the production cost of enterprises. Moreover, the treatment process does not consume a lot of energy, and can realize the energy-saving recycling of sprout wastewater.

[0032] (2) Modified quartz sand is used as filter media during sand filtration, which can significantly improve the turbidity removal effect of sand filtration process and make the effluent meet the reuse standards. Attached Figure Description

[0033] Figure 1 This is a flowchart of the wastewater purification, reuse, and energy-saving recycling process for sprout production, as described in this invention. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments.

[0035] In this invention, unless otherwise specified, all raw materials are available from the market or commonly used in the industry. The methods in the following embodiments are conventional methods in the field unless otherwise specified.

[0036] General Implementation Examples:

[0037] A method for purifying, reusing, and energy-saving recycling wastewater from sprout production includes the following steps:

[0038] (1) The wastewater from sprout production is collected separately. The vegetable washing water and bean soaking water are filtered through an arc screen to remove impurities and then enter the first equalization tank for water flow adjustment and homogenization. The rinsing water is filtered through an arc screen to remove impurities and then enters the second equalization tank for water flow adjustment and homogenization. The wastewater flow rate in the first equalization tank is 20-80 t / d and the retention time is 12-36 h. The wastewater flow rate in the second equalization tank is 3000-8000 t / d and the retention time is 1-2 h.

[0039] (2) The effluent from the first and second equalization tanks is mixed and enters the biological treatment device to remove organic pollutants and total nitrogen. The biological treatment device includes a hydrolysis acidification unit and a biological contact oxidation unit. The biological treatment device adopts a gravity flow two-stage tower structure, with the hydrolysis acidification unit located above the contact oxidation unit. The effluent from the equalization tank enters from the top of the biological treatment device. The residence time in the hydrolysis acidification unit is 40-80 min, and the residence time in the contact oxidation unit is 1.5-2.5 h. The wastewater after biological treatment enters the sedimentation tank for mud-water separation. The residence time in the sedimentation tank is 1-1.5 h.

[0040] (3) The effluent from the sedimentation tank enters the flocculation reaction sedimentation tank, which includes a pre-reaction zone and a sedimentation zone. In the pre-reaction zone, coagulant PAC and flocculant PAM are added sequentially and mechanically stirred. The amount of coagulant added is 40-60 ppm. The flocculant is PAM, and the amount of flocculant added is 2-4 ppm. After coagulation and flocculation reaction, the wastewater enters the sedimentation zone for solid-liquid separation. The residence time in the pre-reaction zone is 8-12 min. The residence time in the sedimentation zone is 1-2 h.

[0041] (4) The effluent from the flocculation reaction sedimentation tank enters the sand filter tank. After turbidity removal, it is sterilized by a pipeline ultraviolet sterilizer and then discharged into the recycled water storage tank. Sodium hypochlorite disinfectant is added to control the residual chlorine below 0.02 mg / L to obtain recycled water. Modified quartz sand is used as the filter media in the sand filter tank. The filter media height is 1-1.5 m, the filtration rate is 7-9 m / h, and the backwashing intensity is 12-15 L / m. 2 · S, backwashing time 3-5 min; pipeline UV sterilizer adopts medium pressure multi-spectral UV system, wavelength range 200-400nm;

[0042] The method for preparing the modified quartz sand is as follows:

[0043] A) Quartz sand with a particle size of 0.5-1.5 mm is soaked in 0.1-0.5 mol / L hydrochloric acid solution for 12-24 hours, filtered and washed to obtain pretreated quartz sand;

[0044] B) Dissolve ferric chloride in DMF, then add terephthalic acid and stir until homogeneous to obtain a mixed solution; the molar ratio of ferric chloride to terephthalic acid is 1:1 to 1.2; add pretreated quartz sand to the mixed solution and ultrasonically disperse until homogeneous to obtain a dispersion; the mass ratio of added quartz sand to ferric chloride is 2 to 3:1.

[0045] C) The dispersion was subjected to hydrothermal reaction at 130-150℃ for 24-48h. The product was separated, washed, and dried to obtain Fe-MOF coated quartz sand.

[0046] D) Calcine the Fe-MOF-coated quartz sand at 700-800℃ for 3-4 hours in an inert atmosphere to obtain the modified quartz sand.

[0047] (5) An intelligent temperature control system and a pressure-stabilized water supply system are installed to recycle the recycled water to the sprout production workshop as a supplementary water source for spraying, achieving energy-saving recycling. The operating cost of the wastewater purification and reuse system is 0.45 yuan / ton of water, achieving a 90% reuse rate and reducing the company's production costs by 10%.

[0048] Example 1:

[0049] A method for purifying, reusing, and energy-saving recycling wastewater from sprout production includes the following steps:

[0050] (1) The wastewater from sprout production is collected separately. The vegetable washing water and bean soaking water are filtered through an arc screen to remove impurities and then enter the first equalization tank for water flow adjustment and homogenization. The rinsing water is filtered through an arc screen to remove impurities and then enters the second equalization tank for water flow adjustment and homogenization. The wastewater flow rate of the first equalization tank is 40t / d and the retention time is 24h. The wastewater flow rate of the second equalization tank is 4280t / d and the retention time is 1.5h.

[0051] (2) The effluent from the first and second equalization tanks is pumped and mixed before entering the biochemical treatment device to remove organic pollutants and total nitrogen. The biochemical treatment device includes a hydrolysis acidification unit and a biological contact oxidation unit. The biochemical treatment device adopts a gravity flow two-stage tower structure, with the hydrolysis acidification unit located above the contact oxidation unit. The effluent from the equalization tank enters from the top of the biochemical treatment device. The residence time in the hydrolysis acidification unit is 1 hour, and the residence time in the contact oxidation unit is 2 hours. The wastewater after biochemical treatment flows by gravity into a vertical flow inclined tube sedimentation tank for mud-water separation. The residence time in the sedimentation tank is 1.25 hours.

[0052] (3) The effluent from the sedimentation tank enters the flocculation reaction sedimentation tank, which includes a pre-reaction zone and a sedimentation zone. In the pre-reaction zone, coagulant PAC and flocculant PAM are added sequentially and mechanically stirred. The amount of coagulant added is 50 ppm. The flocculant is PAM, and the amount of flocculant added is 3 ppm. After coagulation and flocculation reaction, the wastewater enters the sedimentation zone for solid-liquid separation. The residence time in the pre-reaction zone is 10 min. The residence time in the sedimentation zone is 1.5 h.

[0053] (4) The supernatant from the flocculation reaction sedimentation tank flows by gravity into the intermediate water tank, is pumped into the sand filter tank, and after turbidity removal, is sterilized by a pipeline ultraviolet sterilizer before being discharged into the recycled water storage tank. Sodium hypochlorite disinfectant is added to control the residual chlorine below 0.02 mg / L to obtain recycled water. Modified quartz sand is used as the filter media in the sand filter tank, with a filter height of 1.1 m, a filtration rate of 8 m / h, and a backwash intensity of 13 L / m. 2 • S, backwashing time 4 min; the pipeline UV sterilizer adopts a medium-pressure multi-spectral UV system with a wavelength range of 300 nm; the preparation method of the modified quartz sand is as follows:

[0054] A) Quartz sand with a particle size of 1 mm was soaked in 0.2 mol / L hydrochloric acid solution for 18 h, filtered and washed to obtain pretreated quartz sand;

[0055] B) Dissolve ferric chloride in DMF, then add terephthalic acid and stir until homogeneous to obtain a mixed solution; the molar ratio of ferric chloride to terephthalic acid is 1:1.1; add pretreated quartz sand to the mixed solution and ultrasonically disperse until homogeneous to obtain a dispersion; the mass ratio of added quartz sand to ferric chloride is 2.5:1.

[0056] C) The dispersion was hydrothermally reacted at 140℃ for 36h, and the product was separated, washed and dried to obtain Fe-MOF coated quartz sand;

[0057] D) The Fe-MOF-coated quartz sand was calcined at 750°C for 3.5 h in a nitrogen atmosphere to obtain the modified quartz sand.

[0058] (5) An electric valve is installed in the recycled water storage tank. Through the intelligent temperature control system and the pressure stabilizing water supply system, the recycled water is circulated to the sprout production workshop as a supplementary water source for spraying water, so as to achieve energy-saving recycling.

[0059] Example 2:

[0060] A method for purifying, reusing, and energy-saving recycling wastewater from sprout production includes the following steps:

[0061] (1) The wastewater from sprout production is collected separately. The vegetable washing water and bean soaking water are filtered through an arc screen to remove impurities and then enter the first equalization tank for water flow adjustment and homogenization. The rinsing water is filtered through an arc screen to remove impurities and then enters the second equalization tank for water flow adjustment and homogenization. The wastewater flow rate in the first equalization tank is 25t / d and the retention time is 24h. The wastewater flow rate in the second equalization tank is 3590t / d and the retention time is 1.5h.

[0062] (2) The effluent from the first and second equalization tanks is pumped and mixed before entering the biochemical treatment device to remove organic pollutants and total nitrogen. The biochemical treatment device includes a hydrolysis acidification unit and a biological contact oxidation unit. The biochemical treatment device adopts a gravity flow two-stage tower structure, with the hydrolysis acidification unit located above the contact oxidation unit. The effluent from the equalization tank enters from the top of the biochemical treatment device. The residence time in the hydrolysis acidification unit is 1 hour, and the residence time in the contact oxidation unit is 2 hours. The wastewater after biochemical treatment flows by gravity into a vertical flow inclined tube sedimentation tank for mud-water separation. The residence time in the sedimentation tank is 1.25 hours.

[0063] (3) The effluent from the sedimentation tank enters the flocculation reaction sedimentation tank, which includes a pre-reaction zone and a sedimentation zone. In the pre-reaction zone, coagulant PAC and flocculant PAM are added sequentially and mechanically stirred. The amount of coagulant added is 50 ppm. The flocculant is PAM, and the amount of flocculant added is 3 ppm. After coagulation and flocculation reaction, the wastewater enters the sedimentation zone for solid-liquid separation. The residence time in the pre-reaction zone is 10 min. The residence time in the sedimentation zone is 1.5 h.

[0064] (4) The supernatant from the flocculation reaction sedimentation tank flows by gravity into the intermediate water tank, is pumped into the sand filter tank, and after turbidity removal, is sterilized by a pipeline ultraviolet sterilizer before being discharged into the recycled water storage tank. Sodium hypochlorite disinfectant is added to control the residual chlorine below 0.02 mg / L to obtain recycled water. Modified quartz sand is used as the filter media in the sand filter tank, with a filter height of 1.1 m, a filtration rate of 8 m / h, and a backwash intensity of 13 L / m. 2 • S, backwashing time 4 min; the pipeline UV sterilizer adopts a medium-pressure multi-spectral UV system with a wavelength range of 300 nm; the preparation method of the modified quartz sand is as follows:

[0065] A) Quartz sand with a particle size of 1 mm was soaked in 0.1 mol / L hydrochloric acid solution for 24 h, filtered and washed to obtain pretreated quartz sand;

[0066] B) Dissolve ferric chloride in DMF, then add terephthalic acid and stir until homogeneous to obtain a mixed solution; the molar ratio of ferric chloride to terephthalic acid is 1:1; add pretreated quartz sand to the mixed solution and ultrasonically disperse until homogeneous to obtain a dispersion; the mass ratio of added quartz sand to ferric chloride is 2:1.

[0067] C) The dispersion was hydrothermally reacted at 130℃ for 48h. The product was separated, washed, and dried to obtain Fe-MOF coated quartz sand.

[0068] D) The Fe-MOF-coated quartz sand was calcined at 700°C for 4 hours in a nitrogen atmosphere to obtain the modified quartz sand.

[0069] (5) An electric valve is installed in the recycled water storage tank. Through the intelligent temperature control system and the pressure stabilizing water supply system, the recycled water is circulated to the sprout production workshop as a supplementary water source for spraying water, so as to achieve energy-saving recycling.

[0070] Example 3:

[0071] A method for purifying, reusing, and energy-saving recycling wastewater from sprout production includes the following steps:

[0072] (1) The wastewater from sprout production is collected separately. The vegetable washing water and bean soaking water are filtered through an arc screen to remove impurities and then enter the first equalization tank for water flow adjustment and homogenization. The rinsing water is filtered through an arc screen to remove impurities and then enters the second equalization tank for water flow adjustment and homogenization. The wastewater flow rate of the first equalization tank is 80t / d and the retention time is 24h. The wastewater flow rate of the second equalization tank is 7560t / d and the retention time is 1.5h.

[0073] (2) The effluent from the first and second equalization tanks is pumped and mixed before entering the biochemical treatment device to remove organic pollutants and total nitrogen. The biochemical treatment device includes a hydrolysis acidification unit and a biological contact oxidation unit. The biochemical treatment device adopts a gravity flow two-stage tower structure, with the hydrolysis acidification unit located above the contact oxidation unit. The effluent from the equalization tank enters from the top of the biochemical treatment device. The residence time in the hydrolysis acidification unit is 1 hour, and the residence time in the contact oxidation unit is 2 hours. The wastewater after biochemical treatment flows by gravity into a vertical flow inclined tube sedimentation tank for mud-water separation. The residence time in the sedimentation tank is 1.25 hours.

[0074] (3) The effluent from the sedimentation tank enters the flocculation reaction sedimentation tank, which includes a pre-reaction zone and a sedimentation zone. In the pre-reaction zone, coagulant PAC and flocculant PAM are added sequentially and mechanically stirred. The amount of coagulant added is 50 ppm. The flocculant is PAM, and the amount of flocculant added is 3 ppm. After coagulation and flocculation reaction, the wastewater enters the sedimentation zone for solid-liquid separation. The residence time in the pre-reaction zone is 10 min. The residence time in the sedimentation zone is 1.5 h.

[0075] (4) The supernatant from the flocculation reaction sedimentation tank flows by gravity into the intermediate water tank, is pumped into the sand filter tank, and after turbidity removal, is sterilized by a pipeline ultraviolet sterilizer before being discharged into the recycled water storage tank. Sodium hypochlorite disinfectant is added to control the residual chlorine below 0.02 mg / L to obtain recycled water. Modified quartz sand is used as the filter media in the sand filter tank, with a filter height of 1.1 m, a filtration rate of 8 m / h, and a backwash intensity of 13 L / m. 2 • S, backwashing time 4 min; the pipeline UV sterilizer adopts a medium-pressure multi-spectral UV system with a wavelength range of 300 nm; the preparation method of the modified quartz sand is as follows:

[0076] A) Quartz sand with a particle size of 1 mm was soaked in 0.5 mol / L hydrochloric acid solution for 12 h, filtered and washed to obtain pretreated quartz sand;

[0077] B) Dissolve ferric chloride in DMF, then add terephthalic acid and stir until homogeneous to obtain a mixed solution; the molar ratio of ferric chloride to terephthalic acid is 1:1.2; add pretreated quartz sand to the mixed solution and disperse it evenly by ultrasonication to obtain a dispersion; the mass ratio of added quartz sand to ferric chloride is 3:1.

[0078] C) The dispersion was hydrothermally reacted at 150℃ for 24h, and the product was separated, washed and dried to obtain Fe-MOF coated quartz sand.

[0079] D) The Fe-MOF-coated quartz sand was calcined at 800°C for 4 hours in a nitrogen atmosphere to obtain the modified quartz sand.

[0080] (5) An electric valve is installed in the recycled water storage tank. Through the intelligent temperature control system and the pressure stabilizing water supply system, the recycled water is circulated to the sprout production workshop as a supplementary water source for spraying water, so as to achieve energy-saving recycling.

[0081] Comparative Example 1 (without UV sterilization):

[0082] In step (4) of Comparative Example 1, the effluent from the sand filter tank directly enters the recycled water storage tank and sodium hypochlorite disinfectant is added, without passing through the pipeline ultraviolet sterilizer for ultraviolet sterilization; the rest is the same as in Example 1.

[0083] Comparative Example 2 (without sodium hypochlorite sterilization):

[0084] In Comparative Example 2, sodium hypochlorite disinfectant was not added in step (4), and all other steps were the same as in Example 1.

[0085] Comparative Example 3:

[0086] The difference between Comparative Example 3 and Example 1 is that unmodified quartz sand is used as the filter media in the sand filter tank, while the rest is the same as in Example 1.

[0087] Comparative Example 4 (without calcination):

[0088] The difference between Comparative Example 4 and Example 1 is that the method for preparing the modified quartz sand in the sand filter tank is as follows:

[0089] A) Quartz sand with a particle size of 1 mm was soaked in 0.2 mol / L hydrochloric acid solution for 18 h, filtered and washed to obtain pretreated quartz sand;

[0090] B) Dissolve ferric chloride in DMF, then add terephthalic acid and stir until homogeneous to obtain a mixed solution; the molar ratio of ferric chloride to terephthalic acid is 1:1.1; add pretreated quartz sand to the mixed solution and ultrasonically disperse until homogeneous to obtain a dispersion; the mass ratio of added quartz sand to ferric chloride is 2.5:1.

[0091] C) The dispersion was subjected to hydrothermal reaction at 140°C for 36 hours. The product was then separated, washed, and dried to obtain the modified quartz sand. The rest was the same as in Example 1.

[0092] Comparative Example 5 (Fe oxide only):

[0093] The difference between Comparative Example 5 and Example 1 is that the method for preparing the modified quartz sand in the sand filter tank is as follows:

[0094] A) Quartz sand with a particle size of 1 mm was soaked in 0.2 mol / L hydrochloric acid solution for 18 h, filtered and washed to obtain pretreated quartz sand;

[0095] B) Add quartz sand to a 2.5 mol / L ferric chloride aqueous solution and stir until homogeneous. The mass ratio of quartz sand to ferric chloride is 2.5:1. Then evaporate and dehydrate in an oil bath at 120°C, dry in an oven at 110°C for 10 hours, and calcine at 600°C for 3 hours to obtain the modified quartz sand.

[0096] Everything else is the same as in Example 1.

[0097] Comparative Example 6 (first loading iron oxide then coating porous carbon):

[0098] The difference between Comparative Example 6 and Example 1 is that the method for preparing the modified quartz sand in the sand filter tank is as follows:

[0099] A) Quartz sand with a particle size of 1 mm was soaked in 0.2 mol / L hydrochloric acid solution for 18 h, filtered and washed to obtain pretreated quartz sand;

[0100] B) Add quartz sand to a 2.5 mol / L ferric chloride aqueous solution and stir until homogeneous. The mass ratio of quartz sand to ferric chloride is 2.5:1. Then evaporate and dehydrate in an oil bath at 120℃, dry in an oven at 110℃ for 10 hours, and then calcine at 600℃ for 3 hours to obtain quartz sand coated with iron oxide.

[0101] C) Add iron oxide-coated quartz sand to a 2 wt% starch solution. The mass ratio of iron oxide-coated quartz sand to starch is 2.5:1. After stirring for 2 hours, dry the product and then calcine it at 750°C for 3.5 hours in a nitrogen atmosphere to obtain the modified quartz sand. The rest is the same as in Example 1.

[0102] The water quality of the purified reclaimed water obtained in the above embodiments and comparative examples was tested, and the results are shown in Table 1.

[0103] Table 1: Test results of recycled water quality.

[0104]

[0105] (Note: * represents the permanganate index, expressed as O2)

[0106] As can be seen from Table 1, the recycled water obtained by the method of the present invention in Examples 1 to 3 has stable water quality, thorough disinfection, meets the "Standards for Drinking Water Quality" (GB5749-2022), and can be recycled for spraying water in sprout production.

[0107] In Comparative Example 1, no ultraviolet sterilization was performed, and only sodium hypochlorite was used for disinfection. The sterilization effect was poor, and the sterility of the reclaimed water could not be guaranteed. In Comparative Example 2, only ultraviolet sterilization was performed without the addition of sodium hypochlorite, and the sterilization effect was also not good. In Comparative Example 3, unmodified quartz sand was used for sand filtration, resulting in a decrease in the filter media's ability to retain pollutants and a significant decrease in turbidity removal compared to Example 1. In Comparative Example 4, quartz sand was coated with Fe-MOF but not calcined, thus failing to generate iron oxide and porous carbon structures, leading to a decrease in turbidity removal. In Comparative Example 5, only iron oxide was coated on the surface of the quartz sand, lacking the function of porous carbon, resulting in a decrease in the specific surface area of ​​the filter media, reduced adsorption capacity for pollutants, and increased turbidity in the reclaimed water, failing to meet standards. In Comparative Example 6, iron oxide was first coated on the surface of the quartz sand, followed by a carbon layer formed by starch carbonization. Compared to the porous carbon layer formed by calcining MOF in this invention, the carbon layer formed by organic carbonization has a significantly lower porosity, resulting in decreased adsorption capacity for pollutants. Furthermore, the carbon layer coating also affects the function of iron oxide, making it difficult to improve the surface charge of the quartz sand, thus increasing the turbidity of the reclaimed water compared to Example 1.

Claims

1. A method for purifying and recycling the wastewater from sprout production and saving energy, characterized in that, Includes the following steps: (1) The wastewater from sprout production is passed through an arc screen to remove impurities, and then enters the equalization tank for water volume adjustment and homogenization; (2) The effluent from the equalization tank enters the biochemical treatment device to remove organic pollutants and total nitrogen. The wastewater after biochemical treatment enters the sedimentation tank for mud-water separation. (3) The effluent from the sedimentation tank enters the flocculation reaction sedimentation tank, where coagulant and flocculant are added for coagulation and flocculation reaction, followed by sedimentation for solid-liquid separation. (4) The effluent from the flocculation reaction sedimentation tank enters the sand filter tank. After turbidity removal, it is sterilized by a pipeline ultraviolet sterilizer and then discharged into the recycled water storage tank. Sodium hypochlorite disinfectant is added to ensure that the residual chlorine meets the standard, thus obtaining recycled water. Modified quartz sand is used as the filter media in the sand filter tank. During modification, the surface of the quartz sand is first pretreated with hydrochloric acid to remove surface impurities. Then Fe 3+ As a metal ion, terephthalic acid serves as a ligand, and an iron-containing metal-organic framework is grown in situ on the surface of quartz sand via a hydrothermal reaction. Finally, a composite of porous carbon and nano-iron oxide is obtained on the surface of quartz sand through calcination. (5) Recycle the recycled water to the sprout production workshop as a supplementary water source for spraying, so as to achieve energy-saving recycling.

2. The method according to claim 1, wherein the method is characterized by, In step (1), the wastewater from the sprout production is collected separately. The vegetable washing water and bean soaking water are removed of impurities and then enter the first regulating tank. The rinsing water is removed of impurities and then enters the second regulating tank. The effluent from the first and second regulating tanks is mixed and subjected to biochemical treatment in step (2). The wastewater flow rate of the first regulating tank is 20~80t / d and the retention time is 12~36h. The wastewater flow rate of the second regulating tank is 3000~8000t / d and the retention time is 1~2h.

3. The method according to claim 1, wherein the method is characterized in that, The biochemical treatment device in step (2) includes a hydrolysis acidification unit and a biological contact oxidation unit. The biochemical treatment device adopts a gravity flow two-stage tower structure, with the hydrolysis acidification unit located above the contact oxidation unit. The effluent from the equalization tank enters from the top of the biochemical treatment device. The residence time in the hydrolysis acidification unit is 40-80 min, and the residence time in the contact oxidation unit is 1.5-2.5 h.

4. The method according to claim 1 or 3, wherein the method is characterized in that, The residence time in the sedimentation tank in step (2) is 1~1.5h.

5. The method according to claim 1, wherein the method is characterized in that, The coagulant mentioned in step (3) is PAC, and the amount of coagulant added is 40~60ppm; the flocculant mentioned is PAM, and the amount of flocculant added is 2~4ppm.

6. The method according to claim 1 or 5, wherein the method is characterized in that, The flocculation reaction sedimentation tank in step (3) includes a pre-reaction zone and a sedimentation zone. Coagulant and flocculant are added sequentially in the pre-reaction zone and mechanically stirred. After coagulation and flocculation reaction, the wastewater enters the sedimentation zone for solid-liquid separation. The residence time in the pre-reaction zone is 8-12 minutes, and the residence time in the sedimentation zone is 1-2 hours.

7. The method according to claim 1, wherein the method is characterized in that, The method for preparing the modified quartz sand in step (4) is as follows: A) Quartz sand with a particle size of 0.5~1.5mm is soaked in 0.1~0.5mol / L hydrochloric acid solution for 12~24h, filtered and washed to obtain pretreated quartz sand; B) Dissolve ferric chloride in DMF, then add terephthalic acid and stir until homogeneous to obtain a mixed solution; the molar ratio of ferric chloride to terephthalic acid is 1:1~1.2; add pretreated quartz sand to the mixed solution and ultrasonically disperse until homogeneous to obtain a dispersion; the mass ratio of added quartz sand to ferric chloride is 2~3:

1. C) The dispersion was subjected to hydrothermal reaction at 130~150℃ for 24~48h. The product was separated, washed and dried to obtain Fe-MOF coated quartz sand. D) Calcine the Fe-MOF-coated quartz sand at 700-800℃ for 3-4 hours in an inert atmosphere to obtain the modified quartz sand.

8. The method according to claim 7, wherein the method is characterized by, The filter material height in the sand filter tank is 1-1.5 m, the filter speed is 7-9 m / h, and the backwashing intensity is 12-15 L / m 2 . S, and the backwashing time is 3-5 min.

9. The method according to claim 1, wherein the method is characterized by, The pipeline type ultraviolet sterilizer used in step (4) adopts a medium pressure multi-spectrum ultraviolet system with a wavelength range of 200-400 nm; and the residual chlorine is controlled to be below 0.02 mg / L after adding sodium hypochlorite disinfectant.

10. The method according to claim 1, wherein the method is characterized by, In step (5), when the recycled water is circulated to the sprout vegetable production workshop as spraying water, an intelligent temperature control system and a stable pressure water supply system are arranged.

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