Treatment process of threonine waste liquid

Abstract

The invention relates to the technical field of wastewater treatment, in particular to a threonine waste liquid treatment process which comprises the following steps: firstly, adding a dicyandiamide-formaldehyde resin quaternary ammonium salt and nano-hydroxyapatite composite modifier, and adjusting the pH value to complete chelation and flocculation; the method comprises the following steps: firstly, carrying out light-enzyme synergistic degradation and electrochemical-ozone combined oxidation treatment on threonine, then converting threonine into short-chain fatty acid by using a microbial electric fermentation system, and finally recovering high-purity threonine and ammonium sulfate through nanofiltration-reverse osmosis membrane concentration in combination with vacuum cooling and melt crystallization, so as to realize pollutant removal and resource recovery. Through cooperation of multiple technologies, pollutants such as COD and ammonia nitrogen in the threonine waste liquid are efficiently removed, meanwhile, the recovery rate of threonine is increased, the product purity is high, and compared with a traditional process, the method has environment-friendly and economic values and is high in adaptability.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, in particular to a treatment process for threonine waste liquid. Background Art

[0002] Threonine, an essential amino acid, is widely used in medicine, food, and feed additives. Currently, threonine is primarily produced industrially through microbial fermentation. However, the wastewater generated after extraction and separation of the fermentation broth still contains significant amounts of organic matter, inorganic salts, and residual threonine. These wastewaters are characterized by high COD concentrations (10,000-30,000 mg / L), high ammonia nitrogen content (1,000-5,000 mg / L), and complex composition. Direct discharge of these wastewaters would not only cause severe environmental pollution but also waste resources.

[0003] Traditional methods for treating threonine wastewater mainly include physical, chemical and biological methods. Although the flocculation and sedimentation process in the physical method can remove some suspended matter and colloidal substances, it has limited effect on the removal of soluble organic matter; the evaporation crystallization method has high energy consumption and is prone to equipment scaling and corrosion. Although chemical methods such as Fenton oxidation and ozone oxidation can effectively degrade organic matter, they have problems such as large oxidant consumption and high operating costs. Biological methods have the advantages of low cost and environmental friendliness, but the high salt and high ammonia nitrogen characteristics in the wastewater will inhibit microbial activity, resulting in low treatment efficiency. In addition, traditional processes often focus on the removal of pollutants and ignore the recycling and utilization of threonine and other resources in the wastewater, resulting in a waste of resources.

[0004] In recent years, new technologies such as membrane separation, advanced oxidation, and microbial fuel cells have been increasingly applied to industrial wastewater treatment. However, single technologies still have limitations when treating threonine wastewater. For example, membrane separation is susceptible to concentration polarization and membrane fouling, resulting in reduced separation efficiency; advanced oxidation technologies are insufficient for the mineralization of certain recalcitrant organics; and while microbial fuel cells can achieve energy recovery, their electricity generation efficiency is low, making them difficult to meet industrial demand. Therefore, developing an efficient, cost-effective, and resource-recoverable threonine wastewater treatment process is of great practical significance. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a treatment process for threonine waste liquid.

[0006] A process for treating threonine waste liquid comprises the following steps: S1: Adding a composite modifier to the threonine wastewater, wherein the composite modifier is composed of dicyandiamide-formaldehyde resin quaternary ammonium salt and nano-hydroxyapatite in a mass ratio of 2:1, and adjusting the pH to 8.0 to 9.0; the dicyandiamide-formaldehyde resin quaternary ammonium salt forms electrostatic adsorption with the threonine molecules through the quaternary ammonium group, and the following chelation reaction occurs simultaneously: , S2: adding a composite photoenzyme system, wherein the composite photoenzyme system is an immobilized laccase-titanium dioxide nanotube array, the laccase loading amount is 50 to 80 mg / g, and the addition amount of titanium dioxide nanotubes is 1.0 to 1.8 g / L, and reacting under 365 nm ultraviolet light for 3 to 5 hours, and the ultraviolet light power density is 100 to 150 W / m²; S3: The wastewater is passed into a three-dimensional electrode reactor, with an IrO2-Ta2O5 / Ti mesh electrode as the anode and a nickel foam electrode as the cathode. Activated carbon particles are filled as the third electrode, and the particle size of the activated carbon particles is 0.5 to 1.0 mm. Ozone is introduced at the same time, with an ozone concentration of 15 to 20 mg / L and a flow rate of 3 to 5 L / min. The reaction is carried out at a current density of 20 to 30 mA / cm² and a pH of 10 to 11 for 45 to 75 minutes. S4: Connect the treated liquid to the microbial electrofermentation system, inoculate the electrogenic bacteria Geobactersulfurreducens at the anode, and add a mixed inoculum of nano-zero-valent iron and acid-producing bacteria Clostridium acetobutylicum at the cathode. The nano-zero-valent iron particle size is 50 to 100 nm. Connect an external 0.8 to 1.2 V DC power supply and run for 96 to 120 hours. S5: A nanofiltration-reverse osmosis two-stage membrane system is used for concentration. The nanofiltration molecular weight cutoff is 150 to 200 Da, and the reverse osmosis operating pressure is 3.0 to 5.0 MPa. The concentrate is subjected to a coupling process of vacuum cooling crystallization and melt crystallization to achieve synchronous separation of threonine product and ammonium sulfate by-product. The vacuum cooling crystallization pressure is 5 to 10 kPa, the temperature is 10 to 15°C, the melt crystallization heating rate is 2 to 5°C / h, and the melting point is 210 to 220°C.

[0007] Preferably, ultrasonic pretreatment is further included before S1: the waste liquid is placed in an ultrasonic device for treatment for 15 to 25 minutes, the ultrasonic device frequency is 40 kHz, and the power density is 0.5 to 1.0 W / cm², so as to destroy the colloidal structure in the waste liquid.

[0008] Preferably, magnetic nanoparticles Fe3O4 are introduced into the S2 light-enzyme synergistic degradation, the particle size of the magnetic nanoparticles is 10 to 20 nm, the addition amount is 0.2 to 0.5 g / L, and the rapid separation and recycling of the photoenzyme system is achieved by an external magnetic field, and the external magnetic field strength is 0.3 to 0.6T.

[0009] Preferably, in the S3 three-dimensional electrode reactor, the surface of the activated carbon particles is loaded with 5 to 10% MnO2 catalyst, which is prepared by an impregnation-calcination method, with an impregnation solution concentration of 0.1 to 0.3 mol / L and a calcination temperature of 400 to 500°C.

[0010] Preferably, 0.05 to 0.15 g / L of redox mediator methyl viologen is added to the cathode chamber of the S4 microbial electrofermentation system to promote electron transfer efficiency.

[0011] Preferably, the S5 nanofiltration membrane is a polypiperazineamide composite membrane prepared by interfacial polymerization, and the water contact angle of the membrane surface is 60 to 70°.

[0012] Preferably, an electro-Fenton enhancement step is added between S3 and S4: ferrous oxalate is added to the waste liquid in an amount of 0.3 to 0.8 g / L, the pH is adjusted to 3 to 4, and the reaction is carried out at a current density of 15 to 25 mA / cm² for 30 to 45 minutes.

[0013] Preferably, during the S5 vacuum cooling crystallization process, 0.01 to 0.03 g / L of seed crystals are added, the seed crystals are threonine crystals with a particle size of 100 to 200 μm, and the stirring speed is controlled to be 80 to 120 rpm.

[0014] Preferably, after the melt crystallization in S5, the threonine is further purified by molecular distillation technology to remove residual trace impurities, and the molecular distillation operation temperature is 180 to 200° C. and the pressure is 0.1 to 1 Pa.

[0015] Preferably, the dicyandiamide-formaldehyde resin quaternary ammonium salt in the S1 composite modifier is prepared by the following method: dicyandiamide and formaldehyde are mixed in a molar ratio of 1:3, reacted at 60 to 80° C. for 2 hours, trimethylamine is added for quaternization, trimethylamine accounts for 10 to 15% of the total mass of the reactants, and the mixture is spray-dried after reacting for 3 to 5 hours.

[0016] Compared with the existing technology, the beneficial effects of the present invention are: 1. The chelation-flocculation synergistic pretreatment process utilizes the synergistic effect of dicyandiamide-formaldehyde resin quaternary ammonium salt and nano-hydroxyapatite, which can not only effectively remove suspended matter and colloidal substances in the waste liquid, but also selectively recover part of the threonine through chelation, reducing the burden of subsequent treatment.

[0017] 2. The photo-enzyme synergistic degradation process combines the specificity of biocatalysis with the high efficiency of photocatalysis, achieving deep oxidative decomposition of refractory organic matter under mild conditions. The introduction of magnetic nanoparticles enables rapid separation and recovery of the photoenzyme system via a magnetic field, significantly reducing operating costs. The electrochemical-ozone combined oxidation process, through the synergistic effect of a three-dimensional electrode reactor and ozone, significantly increases the production of hydroxyl radicals, enhances the mineralization capacity of organic matter, and effectively reduces ammonia nitrogen content.

[0018] 3. The microbial electrofermentation recovery process combines electrogenic and acidogenic bacteria, not only further degrading organic matter in wastewater but also converting threonine into high-value-added short-chain fatty acids. The synergistic effect of applied voltage and redox mediators significantly improves electron transfer efficiency and fermentation yield. The membrane integration-crystallization coupled recovery process achieves efficient recovery and high-purity purification of threonine through fractional separation using nanofiltration and reverse osmosis, combined with vacuum cooling crystallization and melt crystallization. This process also produces ammonium sulfate as a byproduct, improving resource utilization.

[0019] 4. This process has the advantages of high treatment efficiency, high resource recovery rate, and environmental friendliness. In addition, the process has good adaptability and can flexibly adjust process parameters according to wastewater concentration and treatment requirements, providing threonine production enterprises with an efficient and sustainable wastewater treatment solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a process flow chart for treating threonine wastewater proposed by the present invention; Figure 2 3. It is a line comparison chart of total COD removal rate and ammonia nitrogen removal rate of the embodiment and the comparative example; Figure 3 3. It is a bar chart comparing the recovery rate and product purity of threonine in the embodiment and the comparative example; Figure 4 It is a radar comparison chart produced after unifying the dimensions of the performance data of the embodiment and the comparative example. DETAILED DESCRIPTION

[0021] according to Figures 1 to 4 , the specific implementation methods of the present invention are as follows: Example 1: Conventional threonine wastewater treatment S1: Chelation-flocculation synergistic pretreatment To a 5L sample of threonine wastewater from a fermentation plant (COD = 18,500 mg / L, ammonia nitrogen = 2,300 mg / L, threonine content 3.2 g / L), a composite modifier (dicyandiamide-formaldehyde resin quaternary ammonium salt with a molecular weight of 6,500 Da and nanohydroxyapatite with a particle size of 30-40 nm) was added at a dosage of 1.2 g / L. The pH was adjusted to 8.5 with 20% NaOH. The mixture was stirred at 300 rpm for 20 minutes, then reduced to 100 rpm and continued for another 15 minutes. After 30 minutes of settling, the COD of the supernatant decreased to 12,800 mg / L, and the turbidity dropped from 450 to 68 NTU.

[0022] S2: Photo-enzyme synergistic degradation The pretreated supernatant was transferred to a photocatalytic reactor, where 1.5 g / L of immobilized laccase-titanium dioxide nanotube arrays (laccase loading 65 mg / g, TiO2 tube diameter 90-100 nm) and 0.3 g / L of Fe3O4 magnetic nanoparticles were added. The reaction was conducted under a 365 nm UV lamp (power density 120 W / m²) at a constant temperature of 40°C and stirring at 150 rpm for 4 hours. After the reaction, the photoenzyme system was separated using a 0.5 T magnetic field. The COD decreased to 7200 mg / L, and the B / C ratio increased from 0.23 to 0.45.

[0023] S3: Electrochemical-Ozone Combined Oxidation The wastewater was pumped into a three-dimensional electrode reactor (effective volume 2L), equipped with an IrO2-Ta2O5 / Ti mesh electrode at the anode and a nickel foam electrode at the cathode, filled with activated carbon particles (particle size 0.8-1.0mm, loaded with 8% MnO2). Ozone (concentration 18mg / L, flow rate 4L / min) was introduced, with a current density of 25mA / cm², a pH of 10.5, and a constant temperature of 50°C for 60 minutes. After the reaction, COD dropped to 2800mg / L and ammonia nitrogen to 420mg / L.

[0024] S4: Microbial electrofermentation recovery The treated liquid was introduced into an MEC apparatus (anode chamber, 1 L; cathode chamber, 0.5 L). A Geobacter sulfurreducens culture (OD600 = 0.8) was inoculated at the anode, while a mixture of nano-zero-valent iron (70-80 nm) and Clostridium acetobutylicum was added to the cathode, along with 0.1 g / L of methyl viologen. The mixture was connected to a 1.0 V DC power supply and incubated at 35°C for 108 hours. At the end of fermentation, the concentration of acetic acid in the liquid phase reached 12.5 g / L, the concentration of propionic acid 4.3 g / L, and the residual threonine content decreased to 0.2 g / L.

[0025] S5: Membrane Integration-Crystallization Coupled Recovery The fermentation broth was passed through a two-stage membrane system: a NF membrane (molecular weight cut-off, 180 Da) operating at 1.8 MPa and a RO membrane operating at 4.0 MPa. The NF permeate was concentrated to a threonine concentration of 250 g / L via RO. The permeate then entered a vacuum-cooled crystallizer (pressure, 8 kPa, temperature, 12°C) with the addition of 0.02 g / L seed crystals (150 μm particle size). Crystallization proceeded at 100 rpm for 3 hours. After centrifugation, the crystals were purified by melt crystallization (heating rate, 3°C / h, melting point, 215°C) and molecular distillation (190°C, 0.5 Pa) to yield 15.8 g of threonine product with a purity of 99.2%. The mother liquor was concentrated and crystallized to recover 8.3 g of ammonium sulfate.

[0026] Example 2: Treatment of high-concentration threonine wastewater S1: Chelation-flocculation synergistic pretreatment Take 5L of high-concentration wastewater with a COD of 32,000mg / L, ammonia nitrogen of 4,100mg / L, and threonine content of 5.8g / L. Add 1.5g / L of the composite modifier and adjust the pH to 9.0 with 20% NaOH. Stir at 300rpm for 20 minutes, then reduce the speed to 100rpm and continue the reaction for 15 minutes. After settling for 30 minutes, the COD of the supernatant dropped to 21,500mg / L, and the turbidity was 75NTU.

[0027] S2: Photo-enzyme synergistic degradation The pretreated supernatant was transferred to a photocatalytic reactor, where 1.8 g / L of immobilized laccase-titanium dioxide nanotube arrays and 0.5 g / L of Fe₃O₄ magnetic nanoparticles were added. The reaction was conducted under a 365 nm UV lamp at a power density of 150 W / m², at a constant temperature of 40°C and with stirring at 150 rpm for 5 hours. After the reaction, the photoenzyme system was separated in a 0.5 T magnetic field. The COD decreased to 10,800 mg / L, and the B / C ratio increased to 0.48.

[0028] S3: Electrochemical-Ozone Combined Oxidation The wastewater was pumped into a three-dimensional electrode reactor with an effective volume of 2L. The anode was an IrO2-Ta2O5 / Ti mesh electrode, and the cathode was a nickel foam electrode filled with activated carbon particles with a particle size of 0.8-1.0mm and an 8% MnO2 loading. Ozone was introduced at a concentration of 20mg / L and a flow rate of 4L / min. The current density was adjusted to 30mA / cm², the pH was 10.5, and the reaction was carried out at a constant temperature of 50°C for 75 minutes. After the reaction, COD dropped to 4200mg / L and ammonia nitrogen to 580mg / L.

[0029] S4: Microbial electrofermentation recovery The treated liquid was introduced into an MEC apparatus with a 1L anode chamber and a 0.5L cathode chamber. The anode was inoculated with a strain of Geobacter sulfurreducens to an OD600 of 0.8. A mixture of nano-zero-valent iron and Clostridium acetobutylicum was added to the cathode, along with 0.15g / L methyl viologen. The system was connected to a 1.2V DC power supply and incubated at 35°C for 120 hours. At the end of fermentation, the liquid phase had acetic acid concentrations of 18.7g / L and propionic acid concentrations of 6.2g / L, with residual threonine reduced to 0.32g / L.

[0030] S5: Membrane Integration-Crystallization Coupled Recovery The fermentation broth was passed through a two-stage membrane system: the NF membrane operated at 1.8 MPa and the RO membrane operated at 5.0 MPa. The NF permeate was concentrated to a threonine concentration of 250 g / L via RO. The permeate then entered a vacuum cooling crystallizer at 5 kPa and 12°C, with 0.02 g / L seed crystals of 150 μm in size, and crystallized at 100 rpm for 3 hours. After centrifugation, the crystals were melt crystallized at a heating rate of 5°C / h to a melting point of 215°C, and purified by molecular distillation at 190°C and 0.5 Pa to yield 27.5 g of threonine product with a purity of 99.4%. The mother liquor was concentrated and crystallized to recover 14.2 g of ammonium sulfate.

[0031] Example 3: Treatment of low-concentration threonine wastewater S1: Chelation-flocculation synergistic pretreatment 5L of low-concentration wastewater with a COD of 9500mg / L, ammonia nitrogen of 1200mg / L, and threonine content of 1.5g / L was added with a composite modifier at a dosage of 0.8g / L. The pH was adjusted to 8.0 with 20% NaOH. The reaction was allowed to proceed at 300rpm for 20 minutes, then reduced to 100rpm and continued for 15 minutes. After 30 minutes of settling, the COD of the supernatant decreased to 6800mg / L, and the turbidity was 52NTU.

[0032] S2: Photo-enzyme synergistic degradation The pretreated supernatant was transferred to a photocatalytic reactor, where 1.0 g / L of immobilized laccase-titanium dioxide nanotube arrays and 0.2 g / L of Fe₃O₄ magnetic nanoparticles were added. The reaction was conducted under a 365 nm UV lamp at a power density of 120 W / m², at a constant temperature of 40°C and with stirring at 150 rpm for 3 hours. After the reaction, the photoenzyme system was separated in a 0.5 T magnetic field. The COD decreased to 3800 mg / L, and the B / C ratio increased to 0.42.

[0033] S3: Electrochemical-Ozone Combined Oxidation The wastewater was pumped into a three-dimensional electrode reactor with an effective volume of 2L. The anode was an IrO2-Ta2O5 / Ti mesh electrode, and the cathode was a nickel foam electrode filled with activated carbon particles with a particle size of 0.8-1.0mm and an 8% MnO2 loading. Ozone was introduced at a concentration of 15mg / L and a flow rate of 4L / min. The current density was adjusted to 20mA / cm², the pH was 10.5, and the reaction was carried out at a constant temperature of 50°C for 45 minutes. After the reaction, COD dropped to 1200mg / L and ammonia nitrogen to 180mg / L.

[0034] S4: Microbial electrofermentation recovery The treated liquid was introduced into an MEC apparatus with a 1L anode chamber and a 0.5L cathode chamber. The anode was inoculated with a strain of Geobacter sulfurreducens to an OD600 of 0.8. A mixture of nano-zero-valent iron and Clostridium acetobutylicum was added to the cathode, along with 0.05g / L methyl viologen. The system was connected to a 0.8V DC power supply and incubated at 35°C for 96 hours. At the end of fermentation, the liquid phase had acetic acid concentrations of 7.3g / L and propionic acid concentrations of 2.1g / L, with residual threonine reduced to 0.08g / L.

[0035] S5: Membrane Integration-Crystallization Coupled Recovery The fermentation broth was passed through a two-stage membrane system: the NF membrane operated at 1.8 MPa and the RO membrane operated at 3.0 MPa. The NF permeate was concentrated to a threonine concentration of 250 g / L via RO. The permeate then entered a vacuum cooling crystallizer at 10 kPa, 12°C, and 0.02 g / L seed crystals with a particle size of 150 μm were added. Crystallization was carried out at a stirring speed of 100 rpm for 3 hours. After centrifugation, the crystals were melt crystallized at a heating rate of 2°C / h to a melting point of 215°C, and purified by molecular distillation at 190°C and 0.5 Pa to yield 7.1 g of threonine product with a purity of 99.1%. The mother liquor was concentrated and crystallized to recover 3.6 g of ammonium sulfate.

[0036] Comparative example: traditional biochemical treatment process Flocculation precipitation: Take 5L of the same waste liquid, add 2g / L of polyaluminum chloride (PAC) and 0.05g / L of polyacrylamide (PAM), pH=7.5, and the COD drops to 14200mg / L after precipitation.

[0037] Anaerobic treatment: inoculate anaerobic sludge (MLSS=8000mg / L), react at 35℃ for 7 days, and the COD drops to 8500mg / L.

[0038] Aerobic treatment: inoculate activated sludge (MLSS=4000mg / L), aeration rate 1.5m³ / h, react for 48 hours, COD dropped to 3200mg / L.

[0039] Evaporation and crystallization: Concentrate to a threonine concentration of 200 g / L, and cool and crystallize to obtain 12.3 g of threonine product with a purity of 92.5%.

[0040] The performance comparison of the embodiment and the comparative example is shown in the following table: Table 1 .

[0041] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for treating threonine waste liquid, characterized in that: The following steps are involved: S1: Adding a composite modifier to the threonine wastewater, wherein the composite modifier is composed of dicyandiamide-formaldehyde resin quaternary ammonium salt and nano-hydroxyapatite in a mass ratio of 2:1, and adjusting the pH to 8.0 to 9.0; the dicyandiamide-formaldehyde resin quaternary ammonium salt forms electrostatic adsorption with the threonine molecules through the quaternary ammonium group, and the following chelation reaction occurs simultaneously: ， S2: adding a composite photoenzyme system, wherein the composite photoenzyme system is an immobilized laccase-titanium dioxide nanotube array, the laccase loading amount is 50 to 80 mg / g, and the addition amount of titanium dioxide nanotubes is 1.0 to 1.8 g / L, and reacting under 365 nm ultraviolet light for 3 to 5 hours, and the ultraviolet light power density is 100 to 150 W / m²; S3: The wastewater is passed into a three-dimensional electrode reactor, with an IrO2-Ta2O5 / Ti mesh electrode as the anode and a nickel foam electrode as the cathode. Activated carbon particles are filled as the third electrode, and the particle size of the activated carbon particles is 0.5 to 1.0 mm. Ozone is introduced at the same time, with an ozone concentration of 15 to 20 mg / L and a flow rate of 3 to 5 L / min. The reaction is carried out at a current density of 20 to 30 mA / cm² and a pH of 10 to 11 for 45 to 75 minutes. S4: Connect the treated liquid to the microbial electrofermentation system, inoculate the electrogenic bacteria Geobacter sulfurreducens at the anode, and add a mixed inoculum of nano-zero-valent iron and acid-producing bacteria Clostridium acetobutylicum at the cathode. The nano-zero-valent iron particle size is 50 to 100 nm. Connect an external 0.8 to 1.2 V DC power supply and operate for 96 to 120 hours. S5: A nanofiltration-reverse osmosis two-stage membrane system is used for concentration. The nanofiltration molecular weight cutoff is 150 to 200 Da, and the reverse osmosis operating pressure is 3.0 to 5.0 MPa. The concentrate is subjected to a coupling process of vacuum cooling crystallization and melt crystallization to achieve synchronous separation of threonine product and ammonium sulfate by-product. The vacuum cooling crystallization pressure is 5 to 10 kPa, the temperature is 10 to 15°C, the melt crystallization heating rate is 2 to 5°C / h, and the melting point is 210 to 220°C.

2. The process for treating threonine waste liquid according to claim 1, wherein It also includes ultrasonic pretreatment before S1: the waste liquid is placed in an ultrasonic device for 15 to 25 minutes, the ultrasonic device frequency is 40 kHz, and the power density is 0.5 to 1.0 W / cm² to destroy the colloidal structure in the waste liquid.

3. The process for treating threonine waste liquid according to claim 1, wherein It also includes the introduction of magnetic nanoparticles Fe3O4 in the S2 photo-enzyme synergistic degradation. The particle size of the magnetic nanoparticles is 10 to 20 nm, and the addition amount is 0.2 to 0.5 g / L. The rapid separation and recycling of the photoenzyme system is achieved through an external magnetic field with an external magnetic field strength of 0.3 to 0.6T.

4. The process for treating threonine waste liquid according to claim 1, wherein In the S3 three-dimensional electrode reactor, the surface of the activated carbon particles is loaded with 5 to 10% MnO2 catalyst, which is prepared by an impregnation-calcination method, with an impregnation solution concentration of 0.1 to 0.3 mol / L and a calcination temperature of 400 to 500°C.

5. The process for treating threonine waste liquid according to claim 1, wherein The cathode chamber of the S4 microbial electrofermentation system is added with 0.05 to 0.15 g / L of methyl viologen, a redox mediator, to promote electron transfer efficiency.

6. The process for treating threonine waste liquid according to claim 1, wherein The S5 nanofiltration membrane is a polypiperazineamide composite membrane prepared by interfacial polymerization, and the water contact angle of the membrane surface is 60 to 70 degrees.

7. The process for treating threonine waste liquid according to claim 1, wherein: An electro-Fenton enhancement step is added between S3 and S4: ferrous oxalate is added to the wastewater in an amount of 0.3 to 0.8 g / L, the pH is adjusted to 3 to 4, and the reaction is carried out at a current density of 15 to 25 mA / cm² for 30 to 45 minutes.

8. The process for treating threonine waste liquid according to claim 1, wherein: During the S5 vacuum cooling crystallization process, 0.01 to 0.03 g / L of seed crystals are added. The seed crystals are threonine crystals with a particle size of 100 to 200 μm. The stirring speed is controlled to be 80 to 120 rpm.

9. The process for treating threonine waste liquid according to claim 1, wherein: After S5 melt crystallization, molecular distillation technology is used to further purify threonine to remove residual trace impurities. The molecular distillation operating temperature is 180 to 200°C and the pressure is 0.1 to 1Pa.

10. The process for treating threonine waste liquid according to claim 1, wherein: The dicyandiamide-formaldehyde resin quaternary ammonium salt in the S1 composite modifier is prepared by the following method: dicyandiamide and formaldehyde are mixed in a molar ratio of 1:3, reacted at 60 to 80° C. for 2 hours, trimethylamine is added for quaternization, the trimethylamine accounts for 10 to 15% of the total mass of the reactants, and the mixture is spray-dried after reacting for 3 to 5 hours.

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