A method for recycling erythritol nanofiltration membrane concentrated phase

Abstract

The present invention discloses a method for recycling the concentrated phase of an erythritol nanofiltration membrane, belonging to the technical field of concentrated phase treatment of erythritol nanofiltration membranes. The present invention discloses a method for recycling the concentrated phase of an erythritol nanofiltration membrane, comprising decolorization of the concentrated phase plate and frame of the erythritol nanofiltration membrane, ion exchange desalination, pH adjustment and addition of a saccharifying enzyme reaction, detection indicators, and re-matching and utilization. The present invention increases the transmittance of the concentrated phase of the erythritol nanofiltration membrane to more than 50% by means of decolorization, ion exchange desalination, saccharifying enzyme saccharification, etc., removes more than 95% of inorganic salts, and retains more than 90% of erythritol; converts more than 95% of reducing sugars into glucose, and increases the erythritol yield by more than 80g / L, thereby achieving secondary utilization of waste and cost savings.

Description

Technical Field

[0001] The invention relates to the technical field of erythritol nanofiltration membrane concentrated phase treatment, and more particularly to a method for recycling an erythritol nanofiltration membrane concentrated phase. Background Art

[0002] Nanofiltration is a crucial separation and purification step in the fermentation-based production of erythritol. Nanofiltration membranes have a specific molecular weight cutoff (MWCO), typically between 200 and 1000 Daltons. When the erythritol fermentation broth is eluted and filtered through the nanofiltration membrane, the portion of liquid retained by the membrane, unable to pass through, forms the nanofiltration concentrated phase. This phase contains macromolecular impurities from the fermentation broth that were not completely retained by the ceramic membrane, such as proteins and reducing sugars, as well as pigments and relatively large organic impurities. Reducing sugars include maltobiose and maltotriose, which are not saccharified to glucose during the starch sugar production process. The presence of these impurities can affect the purity and quality of the erythritol. If not effectively treated, they can negatively impact subsequent crystallization processes, such as crystallization difficulties and poor crystal quality. Inorganic salts in the fermentation broth can also accumulate in the nanofiltration concentrated phase. If these salts enter the subsequent erythritol product, they can affect its purity and taste, and may also corrode production equipment.

[0003] The concentrated phase of erythritol nanofiltration membrane is generally treated as waste sewage. Due to its high COD and conductivity, it often has an impact on the sewage treatment system, and also causes waste of reducing sugar and erythritol.

[0004] Therefore, providing a method for recycling the concentrated phase of erythritol nanofiltration membrane is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method for recycling the concentrated phase of an erythritol nanofiltration membrane.

[0006] The concentrated phase of the erythritol nanofiltration membrane has a soluble solids content of 20.0%-25.0%, a pH of 3.90-4.10, essentially zero transmittance, and a conductivity of 3.0-5.0 ms / cm. Reducing sugars account for 60.0%-70.0% of the soluble solids, and erythritol accounts for 15.0%-25.0%. By adding activated carbon for filtration and decolorization, and using an ion exchange system for desalination, impurities other than reducing sugars and erythritol can be effectively removed from the concentrated phase of the erythritol nanofiltration membrane. Adding a certain proportion of saccharifying enzymes can convert reducing sugars into glucose. The resulting glucose and erythritol mixture can be added back to the erythritol fermentation medium, enabling material reuse and cost savings.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for recycling an erythritol nanofiltration membrane concentrated phase comprises the following steps:

[0009] (1) Plate and frame decolorization of the dense phase of erythritol nanofiltration membrane: Detect the soluble solid content in the dense phase of erythritol nanofiltration membrane, add activated carbon in a certain proportion, and decolorize through the decolorization plate and frame after heating; the added proportion of the activated carbon is 1.5-2.0‰ of the soluble solid content in the dense phase of erythritol nanofiltration membrane; the heating temperature is 70-75℃, the plate and frame pressure is 0.3-0.4Mpa, and the filter cloth pore size is 300-400 mesh.

[0010] (2) Ion exchange desalination: The decolorized solution is desalted through the ion exchange system, and the conductivity is detected and recorded to determine the desalination effect; the discharge conductivity is controlled to be ≤200us / cm; the temperature of the decolorized solution passing through the ion exchange system is 50-55℃, and the flow rate is 6.0-8.0m 3 / h, the resin types used are macroporous strong acid cation resin and macroporous strong base anion resin.

[0011] (3) Adjusting pH and adding saccharifying enzyme for reaction: adding the desalted solution to the saccharification tank, adjusting the pH to 4.2-4.4, detecting the reducing sugar content, adding saccharifying enzyme according to the proportion, and carrying out saccharification reaction; the amount of the saccharifying enzyme added is 0.30-0.35 kg / ton of reducing sugar; the enzyme activity of the saccharifying enzyme is 150,000 u / ml-180,000 u / ml; the saccharification conditions are temperature 59.0-62.0°C, stirring speed 25-30 rpm, and saccharification time = 6-8 h.

[0012] (4) Detection indicators and back-mixing for utilization: After saccharification, the glucose content and erythritol content in the solution were detected, and the erythritol fermentation broth was back-mixed for utilization in a volume ratio of 1:2 between the erythritol fermentation broth and the concentrated phase of the treated nanofiltration membrane.

[0013] Furthermore, the instrument for detecting the soluble solid content in the concentrated phase of the erythritol nanofiltration membrane in step (1) is an Abbe refractometer.

[0014] Furthermore, in the concentrated phase of the erythritol nanofiltration membrane in step (1), the soluble solids content is 20.0%-25.0%, the pH is 3.90-4.10, the transmittance is 0-5%, and the conductivity is 3.0-5.0 ms / cm; the reducing sugar accounts for 60.0%-70.0% of the soluble solids content, and erythritol accounts for 15.0%-25.0% of the soluble solids content.

[0015] Furthermore, in step (4), the instrument for detecting the glucose content and erythritol content in the solution after saccharification is a high performance liquid chromatography, and the chromatographic column used is a hydrogen column.

[0016] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method for recycling the concentrated phase of erythritol nanofiltration membrane, which has the following beneficial effects:

[0017] (1) There are currently no relevant literature or patents on the secondary utilization of erythritol nanofiltration membrane in the concentrated phase. The present invention has strong creativity and practicality in this field.

[0018] (2) The present invention increases the concentrated phase transmittance of the erythritol nanofiltration membrane to more than 50% by means of decolorization, ion exchange desalination, saccharification by saccharifying enzymes, etc., removes more than 95% of inorganic salts, and retains more than 90% of erythritol; converts more than 95% of reducing sugar into glucose, and increases the erythritol production by more than 80g / L, thereby achieving secondary utilization of waste and cost savings. DETAILED DESCRIPTION

[0019] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0020] Source of erythritol nanofiltration membrane concentrated phase: See Patent 201710820906.1 A method for continuous extraction of erythritol, step (2) nanofiltration: filtering the ultrafiltration permeate through a continuous nanofiltration membrane to obtain a nanofiltration concentrate (erythritol nanofiltration membrane concentrated phase) and a nanofiltration permeate.

[0021] Example 1

[0022] A method for recycling an erythritol nanofiltration membrane concentrated phase comprises the following steps:

[0023] (1) Decolorization of the dense phase of the erythritol nanofiltration membrane using a plate and frame: The soluble solids content in the dense phase of the erythritol nanofiltration membrane was measured using an Abbe refractometer and was found to be 20.0%, with a pH of 3.90, a transmittance of 5%, and a conductivity of 3.0 ms / cm. The reducing sugar content was found to be 60.0% of the soluble solids content, and the erythritol content was found to be 15.0% of the soluble solids content. Activated carbon was added to the dense phase of the erythritol nanofiltration membrane at a ratio of 1.5‰, the temperature was raised to 70°C, and decolorization was performed using a plate and frame filter with a pore size of 300 mesh and a pressure of 0.3 MPa. The transmittance after decolorization was 54.0%.

[0024] (2) Ion exchange desalination: The temperature of the decolorized solution is controlled at 50°C and the flow rate is 6.0m 3 / h, desalination through the ion exchange system, the output conductivity is detected to be 122us / cm; the resin types used in the ion exchange system are macroporous strong acid cation resin and macroporous strong base anion resin.

[0025] (3) Adjusting pH and adding saccharifying enzyme for reaction: the desalted solution was added to the saccharification tank, the pH was adjusted to 4.2, the reducing sugar content was detected to be 12%, and saccharifying enzyme was added at a ratio of 0.30 kg saccharifying enzyme / ton reducing sugar for saccharification reaction; the enzyme activity of saccharifying enzyme was 150,000 u / ml; the saccharification conditions were a temperature of 59.0 °C, a stirring rate of 25 rpm, and a saccharification time of 8 h.

[0026] (4) Detection indicators, back-matching and utilization: After saccharification, the glucose content in the solution was 11.6% (g / 100g) and the erythritol content was 2.8% by high performance liquid chromatography; back-matching to the erythritol fermentation broth for utilization (after erythritol was fermented with glucose as a substrate, it was added to the fermentation broth in a ratio of 1:2 according to the volume of the fermentation broth: the volume of the concentrated phase of the treated nanofiltration membrane, and the fermentation was continued until the erythritol content no longer increased). Compared with the control group (erythritol was fermented with glucose as a substrate and no back-matching to the concentrated phase of the nanofiltration membrane), the erythritol production was increased by 85g / L.

[0027] Inorganic salt removal rate = (3000us / cm-122us / cm) / 3000us / cm*100%=95.93%.

[0028] Erythritol retention rate = 2.8% / (20%*15%)*100%=93.33%.

[0029] The yield of reducing sugar converted to glucose = 11.6% / (20%*60%)*100%=96.67%.

[0030] Example 2

[0031] A method for recycling an erythritol nanofiltration membrane concentrated phase comprises the following steps:

[0032] (1) Decolorization of the dense phase of the erythritol nanofiltration membrane using a plate and frame: The soluble solids content in the dense phase of the erythritol nanofiltration membrane was measured using an Abbe refractometer and was found to be 23.0%, with a pH of 4.00, a transmittance of 3%, and a conductivity of 4.0 ms / cm. The reducing sugar content was found to be 65.0% of the soluble solids content, and the erythritol content was found to be 20.0% of the soluble solids content. Activated carbon was added to the dense phase of the erythritol nanofiltration membrane at a ratio of 1.8‰, the temperature was raised to 73°C, and decolorization was performed using a plate and frame filter with a pore size of 350 mesh and a pressure of 0.35 MPa. The transmittance after decolorization was 52.0%.

[0033] (2) Ion exchange desalination: The temperature of the decolorized solution is controlled at 53°C and the flow rate is 7.0m 3 / h, desalination through the ion exchange system, the output conductivity is detected to be 156us / cm; the resin types used in the ion exchange system are macroporous strong acid cation resin and macroporous strong base anion resin.

[0034] (3) Adjusting pH and adding saccharifying enzyme for reaction: the desalted solution was added to the saccharification tank, and the pH was adjusted to 4.3. The reducing sugar content was detected to be 14.9%. Saccharifying enzyme was added at a ratio of 0.33 kg saccharifying enzyme / ton reducing sugar for saccharification reaction; the enzyme activity of saccharifying enzyme was 165,000 u / ml; the saccharification conditions were: temperature of 60.5 °C, stirring rate of 28 rpm, and saccharification time of 7 h.

[0035] (4) Detection indicators, back-matching and utilization: After saccharification, the glucose content in the solution was 14.3% and the erythritol content was 4.2% by high performance liquid chromatography; back-matching to the erythritol fermentation broth for utilization (after erythritol was fermented with glucose as a substrate, it was added to the fermentation broth in a ratio of 1:2, according to the volume of the fermentation broth: the volume of the treated nanofiltration membrane concentrated phase, and the fermentation was continued until the erythritol content no longer increased). Compared with the control group (erythritol was fermented with glucose as a substrate and no back-matching to the nanofiltration membrane concentrated phase), the erythritol production was increased by 90 g / L.

[0036] Inorganic salt removal rate = (4000us / cm-156us / cm) / 4000us / cm*100%=96.1%.

[0037] Erythritol retention rate = 4.2% / (23%*20%)*100%=91.3%.

[0038] The yield of reducing sugar converted to glucose = 14.3% / (23%*65%)*100%=95.65%.

[0039] Example 3

[0040] A method for recycling an erythritol nanofiltration membrane concentrated phase comprises the following steps:

[0041] (1) Decolorization of the dense phase of the erythritol nanofiltration membrane using a plate and frame: The soluble solids content in the dense phase of the erythritol nanofiltration membrane was detected using an Abbe refractometer and was found to be 25.0%, the pH to be 4.10, the transmittance to be 0%, and the conductivity to be 5.0 ms / cm. The reducing sugar content was found to be 70.0% of the soluble solids content, and the erythritol content was found to be 25.0% of the soluble solids content. Activated carbon was added to the dense phase of the erythritol nanofiltration membrane at a ratio of 2.0‰, the temperature was raised to 75°C, and decolorization was performed using a plate and frame filter with a pore size of 400 mesh and a pressure of 0.4 MPa. The transmittance after decolorization was 51.5%.

[0042] (2) Ion exchange desalination: The temperature of the decolorized solution is controlled at 55°C and the flow rate is 8.0m 3 / h, desalination through the ion exchange system, the output conductivity is detected to be 212us / cm; the resin types used in the ion exchange system are macroporous strong acid cation resin and macroporous strong base anion resin.

[0043] (3) Adjusting pH and adding saccharifying enzyme for reaction: adding the desalted solution to the saccharification tank, adjusting the pH to 4.4, detecting the reducing sugar content to be 17.5%, adding saccharifying enzyme at a ratio of 0.35 kg saccharifying enzyme / ton reducing sugar for saccharification reaction; the enzyme activity of the saccharifying enzyme is 180,000 u / ml; the saccharification conditions are a temperature of 62.0°C, a stirring rate of 30 rpm, and a saccharification time of 6 h.

[0044] (4) Detection indicators, back-matching and utilization: After saccharification, the glucose content in the solution was 16.8% and the erythritol content was 5.8% by high performance liquid chromatography; back-matching to the erythritol fermentation broth for utilization (after erythritol was fermented with glucose as a substrate, it was added to the fermentation broth in a ratio of 1:2, according to the volume of the fermentation broth: the volume of the treated nanofiltration membrane concentrated phase, and the fermentation was continued until the erythritol content no longer increased). Compared with the control group (erythritol was fermented with glucose as a substrate and no back-matching to the nanofiltration membrane concentrated phase), the erythritol production was increased by 96 g / L.

[0045] Inorganic salt removal rate = (5000us / cm-212us / cm) / 5000us / cm*100%=95.76%.

[0046] Erythritol retention rate = 5.8% / (25%*25%)*100%=92.8%.

[0047] The yield of reducing sugar converted to glucose = 16.8% / (25%*70%)*100%=96.0%.

[0048] Comparative Example 1 (concentrated phase is directly reconstituted into fermentation liquid for use)

[0049] A method for recycling an erythritol nanofiltration membrane concentrated phase comprises the following steps:

[0050] (1) Detection of concentrated phase indicators of erythritol nanofiltration membrane: The soluble solid content in the concentrated phase of erythritol nanofiltration membrane was detected by Abbe refractometer, which was 23.0%, pH was 4.00, transmittance was 3%, and conductivity was 4.0 ms / cm; the reducing sugar content was 65.0% of the soluble solid content, and the erythritol content was 20.0% of the soluble solid content.

[0051] (2) The concentrated phase of the erythritol nanofiltration membrane was directly mixed back into the erythritol fermentation broth (after the fermentation of erythritol with glucose as the substrate was completed, it was added to the fermentation broth in a ratio of 1:2 of fermentation broth volume to the concentrated phase of the nanofiltration membrane, and fermentation was continued until the erythritol content no longer increased). Compared with the control group (erythritol fermentation with glucose as the substrate and no mixed back into the concentrated phase of the nanofiltration membrane), the erythritol yield was increased by 5 g / L.

[0052] The inorganic salt removal rate was 0; the erythritol retention rate was 100%; and the yield of reducing sugar converted to glucose was 0.

[0053] Comparative Example 2 (without saccharifying enzyme treatment)

[0054] A method for recycling an erythritol nanofiltration membrane concentrated phase comprises the following steps:

[0055] (1) Decolorization of the dense phase of the erythritol nanofiltration membrane using a plate and frame: The soluble solids content in the dense phase of the erythritol nanofiltration membrane was measured using an Abbe refractometer and was found to be 23.0%, with a pH of 4.00, a transmittance of 3%, and a conductivity of 4.0 ms / cm. The reducing sugar content was found to be 65.0% of the soluble solids content, and the erythritol content was found to be 20.0% of the soluble solids content. Activated carbon was added to the dense phase of the erythritol nanofiltration membrane at a ratio of 1.8‰, the temperature was raised to 73°C, and decolorization was performed using a plate and frame filter with a pore size of 350 mesh and a pressure of 0.35 MPa. The transmittance after decolorization was 52.0%.

[0056] (2) Ion exchange desalination: The temperature of the decolorized solution is controlled at 53°C and the flow rate is 7.0m 3 / h, desalination through the ion exchange system, the output conductivity is detected to be 156us / cm; the resin types used in the ion exchange system are macroporous strong acid cation resin and macroporous strong base anion resin.

[0057] (3) Detection indicators, back-matching and utilization: After saccharification, the glucose content in the solution was 2.82% and the erythritol content was 4.2% by high performance liquid chromatography; back-matching to the erythritol fermentation broth for utilization (after erythritol was fermented with glucose as a substrate, it was added to the fermentation broth in a ratio of 1:2, according to the volume of the fermentation broth: the volume of the treated nanofiltration membrane concentrated phase, and the fermentation was continued until the erythritol content no longer increased). Compared with the control group (erythritol was fermented with glucose as a substrate and no back-matching to the nanofiltration membrane concentrated phase), the erythritol production was increased by 15 g / L.

[0058] Inorganic salt removal rate = (4000us / cm-156us / cm) / 4000us / cm*100%=96.1%.

[0059] Erythritol retention rate = 4.2% / (23%*20%)*100%=91.3%.

[0060] The yield of reducing sugar converted to glucose = 2.82% / (23%*65%)*100%=18.86%.

[0061] Comparative Example 3 (Adjusting Control Indicators)

[0062] A method for recycling an erythritol nanofiltration membrane concentrated phase comprises the following steps:

[0063] (1) Decolorization of the dense phase of the erythritol nanofiltration membrane using a plate and frame: The soluble solids content in the dense phase of the erythritol nanofiltration membrane was detected by an Abbe refractometer and was 20.0%, the pH was 3.90, the transmittance was 5%, and the conductivity was 3.0 ms / cm. The reducing sugar content was 60.0% of the soluble solids content, and the erythritol content was 15.0% of the soluble solids content. Activated carbon was added to the dense phase of the erythritol nanofiltration membrane at a ratio of 1.4‰, the temperature was raised to 68°C, and decolorization was performed using a plate and frame with a filter cloth aperture of 250 mesh and a pressure of 0.25 MPa. The transmittance after decolorization was 15.0%.

[0064] (2) Ion exchange desalination: The temperature of the decolorized solution is controlled at 48°C and the flow rate is 5.0m 3 / h, desalination through the ion exchange system, the output conductivity is detected to be 556us / cm; the resin types used in the ion exchange system are macroporous strong acid cation resin and macroporous strong base anion resin.

[0065] (3) Adjusting pH and adding saccharifying enzyme for reaction: the desalted solution was added to the saccharification tank, the pH was adjusted to 4.0, the reducing sugar content was detected to be 12%, and saccharifying enzyme was added at a ratio of 0.28 kg saccharifying enzyme / ton reducing sugar for saccharification reaction; the enzyme activity of saccharifying enzyme was 140,000 u / ml; the saccharification conditions were a temperature of 58.0 °C, a stirring rate of 20 rpm, and a saccharification time of 5 h.

[0066] (4) Detection indicators, back-matching and utilization: After saccharification, the glucose content in the solution was 6.8% (g / 100g) and the erythritol content was 2.1% by high performance liquid chromatography; back-matching to the erythritol fermentation broth for utilization (after erythritol was fermented with glucose as a substrate, it was added to the fermentation broth in a ratio of 1:2 according to the volume of fermentation broth: the volume of the treated nanofiltration membrane concentrated phase, and fermentation was continued until the erythritol content no longer increased). Compared with the control group (erythritol was fermented with glucose as a substrate and no back-matching to the nanofiltration membrane concentrated phase), the erythritol production was increased by 55 g / L.

[0067] Inorganic salt removal rate = (3000us / cm-556us / cm) / 3000us / cm*100%=81.47%.

[0068] Erythritol retention rate = 2.1% / (20%*15%)*100%=70.0%.

[0069] The yield of reducing sugar converted to glucose = 6.8% / (20%*60%)*100%=56.67%.

[0070] Comparative Example 4 (Adjusting Control Indicators)

[0071] A method for recycling an erythritol nanofiltration membrane concentrated phase comprises the following steps:

[0072] (1) Decolorization of the dense phase of the erythritol nanofiltration membrane using a plate and frame: The soluble solids content in the dense phase of the erythritol nanofiltration membrane was detected using an Abbe refractometer and was found to be 25.0%, pH 4.10, transmittance 0%, and conductivity 5.0 ms / cm. The reducing sugar content was found to be 70.0% of the soluble solids content, and the erythritol content was found to be 25.0% of the soluble solids content. Activated carbon was added to the dense phase of the erythritol nanofiltration membrane at a ratio of 2.5‰, the temperature was raised to 78°C, and decolorization was performed using a plate and frame filter with a pore size of 450 mesh and a pressure of 0.45 MPa. The transmittance after decolorization was 56.5%.

[0073] (2) Ion exchange desalination: The temperature of the decolorized solution is controlled at 57°C and the flow rate is 9.0m 3 / h, desalination through the ion exchange system, the output conductivity is detected to be 306us / cm; the resin types used in the ion exchange system are macroporous strong acid cation resin and macroporous strong base anion resin.

[0074] (3) Adjusting pH and adding saccharifying enzyme for reaction: the desalted solution was added to the saccharification tank, the pH was adjusted to 4.5, the reducing sugar content was detected to be 17.5%, and saccharifying enzyme was added at a ratio of 0.37 kg saccharifying enzyme / ton reducing sugar for saccharification reaction; the enzyme activity of saccharifying enzyme was 190,000 u / ml; the saccharification conditions were a temperature of 63.0 °C, a stirring rate of 35 rpm, and a saccharification time of 9 h.

[0075] (4) Detection indicators, back-matching and utilization: After saccharification, the glucose content in the solution was 12.3% and the erythritol content was 5.7% by high performance liquid chromatography; back-matching to the erythritol fermentation broth for utilization (after erythritol was fermented with glucose as a substrate, it was added to the fermentation broth in a ratio of 1:2, according to the volume of the fermentation broth: the volume of the treated nanofiltration membrane concentrated phase, and the fermentation was continued until the erythritol content no longer increased). Compared with the control group (erythritol was fermented with glucose as a substrate and no back-matching to the nanofiltration membrane concentrated phase), the erythritol production was increased by 86 g / L.

[0076] Inorganic salt removal rate = (5000us / cm-306us / cm) / 5000us / cm*100%=93.88%.

[0077] Erythritol retention rate = 5.7% / (25%*25%)*100%=91.2%.

[0078] The yield of reducing sugar converted to glucose = 12.3% / (25%*70%)*100%=70.29%.

[0079] Examples 1-3 and Comparative Examples 1-4 demonstrate that the method for recycling the concentrated phase of an erythritol nanofiltration membrane in Examples 1-3 can remove over 95% of inorganic salts from the concentrated phase of the erythritol nanofiltration membrane, retaining over 90% of the erythritol, and converting over 95% of reducing sugars into glucose. Examples 1-3 increase erythritol production by over 80 g / L. While Comparative Example 4 also increases erythritol production by over 80 g / L, the process is time-consuming and costly, making it unsuitable for practical production applications.

[0080] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for recycling the dense phase of erythritol nanofiltration membrane, characterized in that: The following steps are involved: (1) Plate-frame decolorization of the dense phase of erythritol nanofiltration membrane: Detect the soluble solid content in the dense phase of erythritol nanofiltration membrane, add activated carbon in a certain proportion, and decolorize through the decolorization plate-frame after heating; the amount of activated carbon added is 1.5-2.0‰ of the soluble solid content in the dense phase of erythritol nanofiltration membrane; the final temperature of the heating process is 70-75℃, the plate-frame pressure is 0.3-0.4Mpa, and the filter cloth pore size is 300-400 mesh; (2) Ion exchange desalination: The decolorized solution is desalted through the ion exchange system, and the discharge conductivity is controlled to be ≤200us / cm; the temperature of the decolorized solution passing through the ion exchange system is 50-55℃, and the flow rate is 6.0-8.0m 3 / h, the resin types used are macroporous strong acid cation resin and macroporous strong base anion resin; (3) Adjusting pH and adding saccharifying enzyme for reaction: adding the desalted solution to the saccharification tank, adjusting the pH to 4.2-4.4, detecting the reducing sugar content, adding saccharifying enzyme according to the proportion, and carrying out saccharification reaction; the amount of saccharifying enzyme added is 0.30-0.35 kg / ton reducing sugar; the enzyme activity of the saccharifying enzyme is 150,000 u / ml-180,000 u / ml; the conditions of the saccharification reaction are temperature 59.0-62.0°C, stirring speed 25-30 rpm, and saccharification time 6-8 h; (4) Detection indicators and re-use: Detect the glucose content and erythritol content in the solution after saccharification, and re-use it in the erythritol fermentation liquid.

2. The method for recycling the dense phase of erythritol nanofiltration membrane according to claim 1, characterized in that: The instrument for detecting the soluble solid content in the concentrated phase of the erythritol nanofiltration membrane in step (1) is an Abbe refractometer.

3. The method for recycling the dense phase of erythritol nanofiltration membrane according to claim 1, characterized in that: The soluble solids content in the concentrated phase of the erythritol nanofiltration membrane in step (1) is 20.0%-25.0%, the pH is 3.90-4.10, the transmittance is 0-5%, and the conductivity is 3.0-5.0 ms / cm; the reducing sugar accounts for 60.0%-70.0% of the soluble solids content, and erythritol accounts for 15.0%-25.0% of the soluble solids content.

4. The method for recycling the dense phase of erythritol nanofiltration membrane according to claim 1, characterized in that: In step (4), the instrument for detecting the glucose content and erythritol content in the solution after saccharification is a high performance liquid chromatography, and the chromatographic column used is a hydrogen column.