A continuous membrane filtration system and filtration method for erythritol fermentation broth

Abstract

The present invention relates to a continuous membrane filtration system for erythritol fermentation liquid, comprising a continuous ceramic membrane filtration subsystem, a continuous nanofiltration membrane filtration subsystem, a continuous reverse osmosis membrane concentration subsystem and a low-concentration dialyzate recycling subsystem. After the erythritol fermentation liquid is filtered and treated by the continuous ceramic membrane filtration subsystem, a high-concentration ceramic membrane permeate, a medium-concentration ceramic membrane permeate, a low-concentration ceramic membrane permeate and a ceramic membrane concentrate are obtained respectively. After the erythritol fermentation liquid is filtered and treated by the continuous nanofiltration membrane filtration subsystem, a high-concentration nanofiltration permeate, a medium-concentration nanofiltration permeate, a low-concentration nanofiltration permeate and a nanofiltration concentrate are obtained respectively. After the continuous reverse osmosis membrane concentration subsystem is treated, a reverse osmosis membrane concentrate and permeate water are obtained. The present invention also discloses a filtration method using the system. The present invention collects and utilizes dialyzates of various concentrations respectively, ensures the stability of the discharging material, and reduces the subsequent evaporation of water.

Description

Technical Field

[0001] The invention belongs to the technical field of erythritol preparation, and particularly relates to a continuous membrane filtration system and a filtration method for erythritol fermentation liquid. Background Art

[0002] Erythritol is a bulk sweetener, a four-carbon sugar alcohol with a molecular formula of C4H 10 O4 is a white crystalline powder with a mild cool feeling when dissolved in the mouth. The sweetness of erythritol is about 70% of sucrose. Since it is non-hygroscopic, it has good fluidity. Erythritol has been widely used in food, beverage and other industries due to its low calorie, good stability and no caries. At present, the industrial preparation method of erythritol is mostly to use glucose as raw material through microbial fermentation, and then separate and purify the fermentation broth through various separation and purification processes to obtain the finished erythritol.

[0003] Separation and purification of erythritol from fermentation broth first requires membrane processing. For example, patent No. 200710115541.9 discloses a method for separation and purification of erythritol from fermentation broth, the purification process includes fermentation broth bacterial separation, fermentation broth clarification and preliminary purification, fermentation broth decolorization and purification, fermentation broth concentration crystallization and recrystallization to prepare pure erythritol, etc., using ceramic membrane to remove protein and other impurities with large molecular weight, and using nanofiltration separation to introduce separation and purification of erythritol, which can save decolorization and ion exchange processes and reduce sewage discharge, but the patent has the problems of low extraction efficiency, large amount of water added, and large fluctuation of discharge concentration. Patent No. ZL201710820906.1 discloses a method for continuous extraction of erythritol. Through ultrafiltration, nanofiltration, diafiltration, concentration, evaporation and crystallization, impurities in the erythritol solution are removed, the content and transmittance of erythritol are increased, and the yield reaches 99%. However, this patent adopts a post-ultrafiltration water washing process, which consumes a large amount of water. At the same time, the permeates of each level of ultrafiltration are collected into nanofiltration separately, and all are collected into the subsequent evaporation process. The discharge concentration is low and the evaporation energy consumption is large. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a continuous membrane filtration system and a filtration method for erythritol fermentation broth, which can stabilize the discharge concentration of the erythritol membrane filtration process, improve the yield of erythritol, reduce water consumption, and reduce production costs.

[0005] The present invention is implemented in this way, providing a continuous membrane filtration system for erythritol fermentation broth, including a continuous ceramic membrane filtration subsystem, a continuous nanofiltration membrane filtration subsystem, a continuous reverse osmosis membrane concentration subsystem and a low-concentration dialysate recycling subsystem, wherein the continuous ceramic membrane filtration subsystem includes a ceramic membrane front-stage filtration group, a ceramic membrane middle-stage filtration group and a ceramic membrane rear-stage filtration group respectively composed of multiple groups of ceramic membrane filters connected in sequence through pipelines, the continuous nanofiltration membrane filtration subsystem includes a nanofiltration membrane front-stage filtration group, a nanofiltration membrane middle-stage filtration group and a nanofiltration membrane rear-stage filtration group respectively composed of multiple groups of nanofiltration membrane filters connected in sequence through pipelines, the continuous reverse osmosis membrane concentration subsystem includes a plurality of groups of The reverse osmosis membrane filters connected in sequence by pipelines respectively form a reverse osmosis membrane front-end concentration group, a reverse osmosis membrane middle-end concentration group and a reverse osmosis membrane rear-end concentration group, the low-concentration dialysate recycling subsystem comprises a low-concentration ceramic membrane permeate recycling tank, a low-concentration nanofiltration permeate recycling tank and a permeate water recycling tank; in the continuous ceramic membrane filtration subsystem, an erythritol fermentation liquid inlet pipe, a high-concentration ceramic membrane permeate outlet pipe, a medium-concentration ceramic membrane permeate outlet pipe, a low-concentration ceramic membrane permeate outlet pipe, a ceramic membrane concentrated liquid outlet pipe, a middle-section low-concentration ceramic membrane permeate recycling inlet pipe, a ceramic membrane middle-section permeate water recycling inlet pipe and a ceramic membrane rear-section permeate water recycling inlet pipe are respectively arranged. The liquid inlet end of the permeate re-jacket tank is connected with the low-concentration ceramic membrane permeate outlet pipe, and the liquid outlet end is connected with the re-jacket inlet pipe of the middle-section low-concentration ceramic membrane permeate, and the ceramic membrane middle-section permeate water re-jacket inlet pipe and the ceramic membrane rear-section permeate water re-jacket inlet pipe are respectively connected with the outlet end of the permeate water re-jacket tank; in the continuous nanofiltration membrane filtration subsystem, a nanofiltration membrane inlet pipe, a high-concentration nanofiltration permeate outlet pipe, a medium-concentration nanofiltration permeate outlet pipe, a low-concentration nanofiltration permeate outlet pipe, a nanofiltration concentrated liquid outlet pipe, a middle-section low-concentration nanofiltration permeate re-jacket inlet pipe, a nanofiltration membrane middle-section permeate water re-jacket inlet pipe and a nanofiltration membrane rear-section permeate water re-jacket inlet pipe are respectively arranged, and the liquid inlet end of the low-concentration nanofiltration permeate re-jacket tank is connected with the low The concentration nanofiltration permeate outlet pipe is connected, and its outlet end is connected to the return jacket inlet pipe of the middle section low concentration nanofiltration permeate, and the nanofiltration membrane middle section permeate return jacket inlet pipe and the nanofiltration membrane rear section permeate return jacket inlet pipe are respectively connected to the outlet end of the permeate return jacket tank; the reverse osmosis membrane inlet pipe, the reverse osmosis membrane concentrated liquid outlet pipe and the permeate water collecting pipe are respectively arranged in the continuous reverse osmosis membrane concentration subsystem, the reverse osmosis membrane inlet pipe is respectively connected to the medium concentration ceramic membrane permeate outlet pipe and the medium concentration nanofiltration permeate outlet pipe, the reverse osmosis membrane concentrated liquid outlet pipe is connected to the high concentration ceramic membrane permeate outlet pipe and then connected to the nanofiltration membrane inlet pipe, and the permeate water collecting pipe is connected to the inlet end of the permeate return jacket tank.

[0006] The present invention is implemented by providing a continuous membrane filtration method for erythritol fermentation broth, which uses the continuous membrane filtration system for erythritol fermentation broth as described above, and the filtration method comprises the following steps:

[0007] Step 1, continuous ceramic membrane filtration, filtering and clarifying the erythritol fermentation broth through a continuous ceramic membrane filtration subsystem, and continuously adding water for filtration, to obtain a high-concentration ceramic membrane permeate, a medium-concentration ceramic membrane permeate, a low-concentration ceramic membrane permeate and a ceramic membrane concentrate, respectively;

[0008] Step 2, continuous nanofiltration membrane filtration, the high-concentration ceramic membrane permeate and the reverse osmosis membrane concentrate obtained in the subsequent step 3 are mixed and then enter the continuous nanofiltration membrane filtration subsystem, and water is continuously added for filtration, to obtain high-concentration nanofiltration permeate, medium-concentration nanofiltration permeate, low-concentration nanofiltration permeate and nanofiltration concentrate respectively;

[0009] Step 3, continuous reverse osmosis membrane concentration, mixing the medium-concentration ceramic membrane permeate obtained in step 1 and the medium-concentration nanofiltration permeate obtained in step 2 into a continuous reverse osmosis membrane concentration subsystem to obtain reverse osmosis membrane concentrate and permeate water, respectively;

[0010] Step 4: Reuse of low-concentration dialysate. The low-concentration ceramic membrane permeate obtained in step 1 is collected and then recycled to the ceramic membrane middle filtration group for use as erythritol ceramic membrane filtration. The low-concentration nanofiltration permeate obtained in step 2 is collected and then recycled to the nanofiltration membrane middle filtration group for use as erythritol nanofiltration membrane filtration. The permeate water obtained by reverse osmosis membrane filtration in step 3 is recycled to the ceramic membrane middle filtration group, the ceramic membrane rear filtration group, the nanofiltration membrane middle filtration group and the nanofiltration membrane rear filtration group, respectively, for use as water for washing the ceramic membrane and the nanofiltration membrane.

[0011] Compared with the prior art, the continuous membrane filtration system and filtration method of the erythritol fermentation broth of the present invention have the following characteristics:

[0012] (1) A continuous membrane filtration process is adopted, which is simple to operate and fully automatic. A ceramic membrane is used to remove mycelium and visible protein impurities in the erythritol fermentation broth, and a nanofiltration membrane is used to remove pigment impurities in the erythritol fermentation broth. The erythritol content can be increased from 93% to 95% to more than 97% to 99%, and the transmittance is more than 90%. The yields of the continuous ceramic membrane filtration subsystem and the continuous nanofiltration membrane filtration subsystem are both above 99%, which is at least 2% higher than the existing technology.

[0013] (2) According to the concentration difference between the effluent from the ceramic membrane and the nanofiltration dialysis, the dialysis fluids of various concentrations are collected and utilized respectively. The high-concentration dialysis fluid directly enters the next process, the medium-concentration dialysis fluid is collected and then enters the continuous reverse osmosis membrane concentration subsystem, and then returns to the previous process after concentration. The low-concentration dialysis fluid is directly recycled and used, which effectively ensures the stability of the effluent from the erythritol fermentation liquid after filtration through the ceramic membrane and the nanofiltration membrane, solves the problem of large fluctuations in the effluent concentration caused by the dialysis process of the ceramic membrane and the nanofiltration membrane, ensures the stability of the subsequent process operation, reduces the amount of subsequent evaporation water, and reduces the operating cost.

[0014] (3) The continuous ceramic membrane, the continuous nanofiltration membrane and the continuous reverse osmosis membrane are combined in the operation mode, so that the erythritol yield can be increased by more than 2% by increasing the amount of water for filtration during the operation of the continuous membrane filtration system. The increased filtration water is finally recovered by dialysis through the continuous reverse osmosis membrane concentration subsystem. Compared with the present system, the consumption of fresh water is not increased, but the consumption of fresh water is reduced by more than 20% overall. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The figure is a schematic diagram of the structural principle of a preferred embodiment of the continuous membrane filtration system for erythritol fermentation broth of the present invention. DETAILED DESCRIPTION

[0016] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0017] Please refer to Figure 1 As shown, a preferred embodiment of the continuous membrane filtration system of erythritol fermentation broth of the present invention comprises a continuous ceramic membrane filtration subsystem 1, a continuous nanofiltration membrane filtration subsystem 2, a continuous reverse osmosis membrane concentration subsystem 3 and a low-concentration dialysate recycling subsystem 4. The arrow direction in the figure indicates the flow direction of the liquid material (such as erythritol fermentation broth, pure water, etc.) of the system.

[0018] The continuous ceramic membrane filtration subsystem 1 includes a ceramic membrane front-end filtration group 12, a ceramic membrane middle-end filtration group 13 and a ceramic membrane rear-end filtration group 14, which are respectively composed of multiple groups of ceramic membrane filters 11 connected in sequence through pipelines. The continuous nanofiltration membrane filtration subsystem 2 includes a nanofiltration membrane front-end filtration group 22, a nanofiltration membrane middle-end filtration group 23 and a nanofiltration membrane rear-end filtration group 24, which are respectively composed of multiple groups of nanofiltration membrane filters 21 connected in sequence through pipelines. The continuous reverse osmosis membrane concentration subsystem 3 includes a reverse osmosis membrane front-end concentration group 32, a reverse osmosis membrane middle-end concentration group 33 and a reverse osmosis membrane rear-end concentration group 34, which are respectively composed of multiple groups of reverse osmosis membrane filters 31 connected in sequence through pipelines. The low-concentration dialysate recycling subsystem 4 includes a low-concentration ceramic membrane permeate recycling tank 41, a low-concentration nanofiltration permeate recycling tank 42 and a permeate water recycling tank 43.

[0019] In the continuous ceramic membrane filtration subsystem 1, an erythritol fermentation liquid inlet pipe 15, a high-concentration ceramic membrane permeate outlet pipe 16, a medium-concentration ceramic membrane permeate outlet pipe 17, a low-concentration ceramic membrane permeate outlet pipe 18, a ceramic membrane concentrated liquid outlet pipe 19, a middle-section low-concentration ceramic membrane permeate return jacket inlet pipe 110, a ceramic membrane middle-section permeate return jacket inlet pipe 111, and a ceramic membrane rear-section permeate return jacket inlet pipe 112 are respectively arranged. After the erythritol fermentation liquid is filtered and treated by the continuous ceramic membrane filtration subsystem 1, a high-concentration ceramic membrane permeate, a medium-concentration ceramic membrane permeate, a low-concentration ceramic membrane permeate, and a ceramic membrane concentrated liquid are obtained.

[0020] The liquid inlet end of the low-concentration ceramic membrane permeate return jacket tank 41 is connected to the low-concentration ceramic membrane permeate liquid outlet pipe 18, and its liquid outlet end is connected to the middle section low-concentration ceramic membrane permeate return jacket inlet pipe 110. The ceramic membrane middle section permeate return jacket inlet pipe 111 and the ceramic membrane rear section permeate return jacket inlet pipe 112 are respectively connected to the water outlet end of the permeate return jacket tank 43. The ceramic membrane concentrate is discharged through the ceramic membrane concentrate outlet pipe 19 for other use.

[0021] In the continuous nanofiltration membrane filtration subsystem 2, a high-concentration dialysate tank 213, a high-concentration dialysate tank inlet pipe 214, a nanofiltration membrane inlet pipe 25, a high-concentration nanofiltration permeate outlet pipe 26, a medium-concentration nanofiltration permeate outlet pipe 27, a low-concentration nanofiltration permeate outlet pipe 28, a nanofiltration concentrate outlet pipe 29, a middle-section low-concentration nanofiltration permeate return inlet pipe 210, a nanofiltration membrane middle-section permeate return inlet pipe 211, and a nanofiltration membrane rear-section permeate return inlet pipe 212 are respectively arranged. After the high-concentration dialysate (including the high-concentration ceramic membrane permeate obtained after filtration treatment by the continuous ceramic membrane filtration subsystem 1 and the reverse osmosis membrane concentrate obtained after filtration treatment by the continuous reverse osmosis membrane concentration subsystem 3) is filtered and treated by the continuous nanofiltration membrane filtration subsystem 2, a high-concentration nanofiltration permeate, a medium-concentration nanofiltration permeate, a low-concentration nanofiltration permeate and a nanofiltration concentrate are obtained.

[0022] The liquid inlet of the low-concentration nanofiltration permeate return tank 42 is connected to the low-concentration nanofiltration permeate outlet pipe 28, and its liquid outlet is connected to the middle-section low-concentration nanofiltration permeate return inlet pipe 210, and the nanofiltration membrane middle section permeate return inlet pipe 211 and the nanofiltration membrane rear section permeate return inlet pipe 212 are respectively connected to the outlet of the permeate return tank 43. The high-concentration nanofiltration permeate is discharged for other use through the high-concentration nanofiltration permeate outlet pipe 26. The nanofiltration concentrate is discharged for other use through the nanofiltration concentrate outlet pipe 29.

[0023] The liquid inlet end of the high-concentration dialysate tank 213 is connected to the high-concentration ceramic membrane permeate outlet pipe 16 of the continuous ceramic membrane filtration subsystem 1 and the reverse osmosis membrane concentrated liquid outlet pipe 36 of the continuous reverse osmosis membrane concentration subsystem 3 through the high-concentration dialysate tank inlet pipe 214, and its liquid outlet end is connected to each nanofiltration membrane filter 21 in the continuous nanofiltration membrane filtration subsystem 2 through the nanofiltration membrane inlet pipe 25.

[0024] A medium-concentration dialysate tank 38, a medium-concentration dialysate tank inlet pipe 39, a reverse osmosis membrane inlet pipe 35, a reverse osmosis membrane concentrate outlet pipe 36 and a permeate water collection pipe 37 are respectively arranged in the continuous reverse osmosis membrane concentration subsystem 3. The medium-concentration dialysate (including the medium-concentration ceramic membrane permeate obtained after filtration treatment by the continuous ceramic membrane filtration subsystem 1 and the medium-concentration nanofiltration permeate obtained after filtration treatment by the continuous nanofiltration membrane filtration subsystem 2) is filtered and treated by the continuous reverse osmosis membrane concentration subsystem 3 to obtain reverse osmosis membrane concentrate and permeate water respectively.

[0025] The liquid inlet end of the medium-concentration dialysate tank 38 is connected to the medium-concentration ceramic membrane permeate outlet pipe 17 of the continuous ceramic membrane filtration subsystem 1 and the medium-concentration nanofiltration permeate outlet pipe 27 of the continuous nanofiltration membrane filtration subsystem 2 through the medium-concentration dialysate tank inlet pipe 39, and its liquid outlet end is connected to each reverse osmosis membrane filter 31 in the continuous reverse osmosis membrane concentration subsystem 3 through the reverse osmosis membrane inlet pipe 35.

[0026] The medium-concentration ceramic membrane permeate outlet pipe 17 and the medium-concentration nanofiltration permeate outlet pipe 27 are respectively connected to the medium-concentration dialysis fluid tank inlet pipe 39 and then connected to the inlet end of the medium-concentration dialysis fluid tank 38. The reverse osmosis membrane concentrate outlet pipe 36 and the high-concentration ceramic membrane permeate outlet pipe 16 are respectively connected to the high-concentration dialysis fluid tank inlet pipe 214 and then connected to the inlet end of the high-concentration dialysis fluid tank 213. The permeate water collection pipe 37 is connected to the water inlet end of the permeate water return tank 43.

[0027] A pure water inlet pipe 44 is also provided at the water inlet end of the permeate water return tank 43 .

[0028] The continuous ceramic membrane filtration subsystem 1 includes five groups of ceramic membrane filters 11, wherein the ceramic membrane front section filtration group 12 and the ceramic membrane middle section filtration group 13 are respectively provided with two groups of ceramic membrane filters 11, and the ceramic membrane rear section filtration group 14 is provided with one group of ceramic membrane filters 11. The first two groups of ceramic membrane filters 11 constitute the ceramic membrane front section filtration group 12, the last group of ceramic membrane filters 11 is the ceramic membrane rear section filtration group 14, and the middle two groups of ceramic membrane filters 11 constitute the ceramic membrane middle section filtration group 13.

[0029] The continuous nanofiltration membrane filtration subsystem 2 includes five groups of nanofiltration membrane filters 21, wherein the nanofiltration membrane front section filtration group 22 and the nanofiltration membrane middle section filtration group 23 are respectively provided with two groups of nanofiltration membrane filters 21, and the nanofiltration membrane rear section filtration group 24 is provided with one group of nanofiltration membrane filters 21. The first two groups of nanofiltration membrane filters 21 constitute the nanofiltration membrane front section filtration group 22, the second group of nanofiltration membrane filters 21 is the nanofiltration membrane rear section filtration group 24, and the middle two groups of nanofiltration membrane filters 21 constitute the nanofiltration membrane middle section filtration group 23.

[0030] The continuous reverse osmosis membrane concentration subsystem 3 includes three groups of reverse osmosis membrane filters 31, wherein the reverse osmosis membrane front section concentration group 32, the reverse osmosis membrane middle section concentration group 33 and the reverse osmosis membrane rear section concentration group 34 are each provided with a group of reverse osmosis membrane filters 31. The reverse osmosis membrane filter 31 located in the front is the reverse osmosis membrane front section concentration group 32, the reverse osmosis membrane filter 31 in the middle is the reverse osmosis membrane middle section concentration group 33, and the last reverse osmosis membrane filter 31 is the reverse osmosis membrane rear section concentration group 34.

[0031] The present invention also discloses a method for continuous membrane filtration of erythritol fermentation broth, which uses the continuous membrane filtration system of erythritol fermentation broth as described above. The filtration method comprises the following steps:

[0032] Step 1, continuous ceramic membrane filtration, filtering and clarifying the erythritol fermentation broth through the continuous ceramic membrane filtration subsystem 1, and continuously adding water for filtration, to obtain high-concentration ceramic membrane permeate, medium-concentration ceramic membrane permeate, low-concentration ceramic membrane permeate and ceramic membrane concentrate respectively.

[0033] Step 2, continuous nanofiltration membrane filtration, the high-concentration ceramic membrane permeate and the reverse osmosis membrane concentrated liquid obtained in the subsequent step 3 are mixed and enter the continuous nanofiltration membrane filtration subsystem 2, and water is continuously added for washing to obtain high-concentration nanofiltration permeate, medium-concentration nanofiltration permeate, low-concentration nanofiltration permeate and nanofiltration concentrated liquid respectively.

[0034] Step 3, continuous reverse osmosis membrane concentration, the medium-concentration ceramic membrane permeate obtained in step 1 and the medium-concentration nanofiltration permeate obtained in step 2 are mixed and enter into the continuous reverse osmosis membrane concentration subsystem 3 to obtain reverse osmosis membrane concentrate and permeate water respectively.

[0035] Step 4: Reuse of low-concentration dialysate. The low-concentration ceramic membrane permeate obtained in step 1 is collected and then recycled to the ceramic membrane middle filter group 13 for use as erythritol ceramic membrane filtration. The low-concentration nanofiltration permeate obtained in step 2 is collected and then recycled to the nanofiltration membrane middle filter group 23 for use as erythritol nanofiltration. The permeate obtained by reverse osmosis membrane filtration in step 3 is recycled to the ceramic membrane middle filter group 13, the ceramic membrane rear filter group 14, the nanofiltration membrane middle filter group 23 and the nanofiltration membrane rear filter group 24, respectively, for use as water for washing the ceramic membrane and the nanofiltration membrane.

[0036] Specifically, the continuous membrane filtration method of the erythritol fermentation broth comprises the following steps:

[0037] Step (1), transporting erythritol fermentation liquid with a concentration of 16% to 22% to a continuous ceramic membrane filtration subsystem 1, wherein the continuous ceramic membrane filtration subsystem 1 includes five groups of ceramic membrane filters 11. The pore size of the ceramic membrane is preferably 15KD~600KD, the operating pressure of the ceramic membrane is 3bar~6bar, and the operating temperature is 30℃~65℃. The first two groups of ceramic membrane filters 11 are not diluted with water, and the erythritol fermentation broth is filtered through the ceramic membrane front-stage filter group 12 to obtain a high-concentration ceramic membrane permeate with a concentration of 16%~22%, and the high-concentration ceramic membrane permeate accounts for 70%~85% of the total feed amount; the third group of ceramic membrane filters 11 is washed with the low-concentration ceramic membrane permeate with a concentration of 1.0%~2.5% to obtain a first-level medium-concentration ceramic membrane permeate with a concentration of 6%~9%, the fourth group of ceramic membrane filters 11 is washed with permeate water or pure water obtained by reverse osmosis membrane filtration to obtain a second-level medium-concentration ceramic membrane permeate with a concentration of 3%~6%, and the fifth group of ceramic membrane filters 11 is further washed with permeate water or pure water obtained by reverse osmosis membrane filtration to obtain a low-concentration ceramic membrane permeate and a ceramic membrane concentrate with a concentration of 1.0%~2.5%.

[0038] Step (2), mixing the high-concentration ceramic membrane permeate with a concentration of 16% to 22% obtained in step (1) and the reverse osmosis membrane concentrate with a concentration of 16% to 22% obtained in step (3) and then transporting them to the continuous nanofiltration membrane filtration subsystem 2, the continuous nanofiltration membrane filtration subsystem 2 includes five groups of nanofiltration membrane filters 21, the membrane pore size of the nanofiltration membrane is 250Da to 500Da, the operating pressure of the nanofiltration membrane is 25bar to 45bar, and the operating temperature is 30°C to 50°C, wherein the first two groups of nanofiltration membrane filters 21 are not diluted with water, and the high-concentration nanofiltration with a concentration of 16% to 22% is obtained after filtration through the nanofiltration membrane filter front-stage concentration group 22. Membrane permeate, high-concentration nanofiltration membrane permeate accounts for 70%~85% of the total feed; the third group of nanofiltration membrane filters 21 uses the low-concentration nanofiltration membrane permeate with a concentration of 1.0%~2.5% to wash filter, and obtain a first-level medium-concentration nanofiltration membrane permeate with a concentration of 6%~9%. The fourth group of nanofiltration membrane filters 21 uses the permeate water or pure water obtained by reverse osmosis membrane filtration to wash filter, and obtain a second-level medium-concentration nanofiltration membrane permeate with a concentration of 3%~6%. The fifth group of nanofiltration membrane filters 21 uses the permeate water or pure water obtained by reverse osmosis membrane filtration to further wash filter, and obtain a low-concentration nanofiltration membrane permeate and nanofiltration membrane concentrate with a concentration of 1.0%~2.5%.

[0039] Step (3), mixing the primary and secondary medium-concentration ceramic membrane permeates obtained in step (1) and the primary and secondary medium-concentration nanofiltration permeates obtained in step (2) into the continuous reverse osmosis membrane concentration subsystem 3, the concentration of the mixed solution is 5%~8%, the pore size of the reverse osmosis membrane is 0.1nm~0.5nm, the operating pressure is 35bar~50bar, the operating temperature is 30℃~50, and the reverse osmosis membrane concentrate and permeate water with a concentration of 16%~22% are obtained.

[0040] Step (4), after collecting the low-concentration ceramic membrane permeate with a concentration of 1.0% to 2.5% obtained in step (1), the permeate is returned to the third group of ceramic membrane filters 11 for use as erythritol ceramic membrane washing; after collecting the low-concentration nanofiltration permeate with a concentration of 1.0% to 2.5% obtained in step (2), the permeate is returned to the third group of nanofiltration membrane filters 21 for use as erythritol nanofiltration membrane washing; the permeate obtained in step (3) is returned to the fourth group and the fifth group of the continuous ceramic membrane filtration subsystem 1 and the continuous nanofiltration membrane filtration subsystem 2, respectively, as water for washing the ceramic membrane and the nanofiltration membrane, and the insufficient part is supplemented with pure water.

[0041] The filtration method of continuous membrane filtration of erythritol fermentation broth of the present invention is further described below in conjunction with specific examples.

[0042] Example 1

[0043] Step 11, conveying 20% ​​concentration erythritol fermentation broth (wherein the erythritol content in the fermentation broth dry basis is 94.2%) to the continuous ceramic membrane filtration subsystem 1 at 40m³ / h, wherein the continuous ceramic membrane filtration subsystem 1 is composed of five groups of ceramic membrane filters 11. The pore size of the ceramic membrane in this embodiment is selected to be 300KD, the operating pressure of the ceramic membrane is 3bar~3.5bar, and the operating temperature is 45°C. The first two groups of ceramic membrane filters 11 are not diluted with water, and the erythritol fermentation broth is filtered through the front-stage filtration group 12 to obtain a high-concentration ceramic membrane permeate of 32m³ / h with a concentration of 20%; the third group of ceramic membrane filters 11 is washed with a low-concentration ceramic membrane permeate of 12m³ / h with a concentration of 1.4% to obtain a first-level medium-concentration ceramic membrane permeate of 12m³ / h with a concentration of 8.8%, the fourth group of ceramic membrane filters 11 is washed with permeate water or pure water obtained by reverse osmosis membrane filtration to obtain a second-level medium-concentration ceramic membrane permeate of 12m³ / h with a concentration of 3.5%, and the fifth group of ceramic membrane filters 11 is further washed with permeate water or pure water obtained by reverse osmosis membrane filtration to obtain a low-concentration ceramic membrane permeate of 12m³ / h with a concentration of 1.4% and a ceramic membrane concentrate of 8m³ / h.

[0044] Discharge conditions: The high-concentration ceramic membrane permeate, medium-concentration ceramic membrane permeate and low-concentration ceramic membrane permeate are all clear solutions. No mycelium is observed with the naked eye. There is no sediment after centrifugation for 6 minutes at 8000r / min in a high-speed centrifuge.

[0045] Step 12, the high-concentration ceramic membrane permeate 32m³ / h with a concentration of 20% obtained in step 11 and the reverse osmosis membrane concentrate 16m³ / h with a concentration of 20% obtained in step 13 are mixed and transported to the continuous nanofiltration membrane filtration subsystem 2, which is composed of five groups of nanofiltration membrane filters 21. The pore size of the nanofiltration membrane in this embodiment is selected to be 300Da, the operating pressure of the nanofiltration membrane is 30bar~35bar, and the operating temperature is 45°C. The first two groups of nanofiltration membrane filters 21 are not diluted with water. After filtering through the front-end concentration group 22 of the nanofiltration membrane filter, a high-concentration nanomembrane permeate 38.8m³ / h with a concentration of 20% is obtained, and the erythritol content in the dry basis of the permeate is 97.8%. The third group of nanofiltration membrane filters 21 is washed with a low-concentration nanofiltration membrane permeate 14.4m³ / h with a concentration of 1.4%. The first-stage medium-concentration nanofiltration membrane permeate of 14.4 m³ / h with a concentration of 8.8% is obtained by filtering with the permeate water or pure water obtained by the reverse osmosis membrane of the fourth group of nanofiltration membrane filters 21, and the second-stage medium-concentration nanofiltration membrane permeate of 14.4 m³ / h with a concentration of 3.5% is obtained by further filtering with the permeate water or pure water obtained by the reverse osmosis membrane of the fifth group of nanofiltration membrane filters 21, and the low-concentration nanofiltration membrane permeate of 14.4 m³ / h with a concentration of 1.4% and the nanofiltration membrane concentrate of 9.6 m³ / h are obtained.

[0046] Discharge conditions: The transmittance of the high-concentration nanofiltration membrane permeate was detected to be 90% (wavelength 420nm), and the transmittance of the medium-concentration nanofiltration membrane permeate and the low-concentration nanofiltration membrane permeate was 91% (wavelength 420nm).

[0047] Step 13: After mixing the first-level medium-concentration ceramic membrane permeate 12m³ / h with a concentration of 8.8% and the second-level medium-concentration ceramic membrane permeate 12m³ / h with a concentration of 3.5% obtained in step 11, and the first-level medium-concentration nanofiltration permeate 14.4m³ / h with a concentration of 8.8% and the second-level medium-concentration nanofiltration permeate 14.4m³ / h with a concentration of 3.5% obtained in step 12, a mixed solution with a flow rate of 52.8m³ / h and a concentration of 6.15% is obtained, and enters the continuous reverse osmosis membrane concentration subsystem 3. The reverse osmosis membrane pore size of this example is 0.2nm, the operating pressure is 45bar, and the operating temperature is 45°C, and a reverse osmosis membrane concentrate with a concentration of 20% and 36.8m³ / h of permeate water are obtained.

[0048] Step 14: After collecting the 12m³ / h low-concentration ceramic membrane permeate with a concentration of 1.4% obtained in step 11, it is returned to the ceramic membrane middle filter group 13 for use as erythritol ceramic membrane filtration. After collecting the 14.4m³ / h low-concentration nanofiltration permeate with a concentration of 1.4% obtained in step 12, it is returned to the nanofiltration membrane middle filter group 23 for use as erythritol nanofiltration membrane filtration. The 36.8m³ / h of permeate obtained in step 13 is returned to the ceramic membrane middle filter group 13, the ceramic membrane rear filter group 14, the nanofiltration membrane middle filter group 23 and the nanofiltration membrane rear filter group 24, respectively, as water for washing the ceramic membrane and nanofiltration membrane. The insufficient part is supplemented with pure water, and about 16m³ / h of pure water is required every hour.

[0049] Finally, the continuous ceramic membrane filtration subsystem 1 had a yield of 99.05%, the continuous nanofiltration membrane filtration subsystem 2 had a yield of 99.10%, and 4 m3 of water was saved per hour. 3 / h.

[0050] Example 2

[0051] Step 21, conveying 18% concentration erythritol fermentation broth (wherein the erythritol content in the fermentation broth dry basis is 93.4%) to the continuous ceramic membrane filtration subsystem 1 at 40m³ / h, wherein the continuous ceramic membrane filtration subsystem 1 is composed of five groups of ceramic membrane filters 11. The pore size of the ceramic membrane of this embodiment is selected to be 60KD, the operating pressure of the ceramic membrane is 3.5bar~4.5bar, and the operating temperature is 45°C. The first two groups of ceramic membrane filters 11 are not diluted with water, and the erythritol fermentation broth is filtered through the front-stage filtration group 12 to obtain a high-concentration ceramic membrane permeate of 32m³ / h with a concentration of 18%; the third group of ceramic membrane filters 11 is washed with a low-concentration ceramic membrane permeate of 12m³ / h with a concentration of 1.27% to obtain a first-level medium-concentration ceramic membrane permeate of 12m³ / h with a concentration of 7.96%, the fourth group of ceramic membrane filters 11 is washed with permeate water or pure water obtained by reverse osmosis membrane filtration to obtain a second-level medium-concentration ceramic membrane permeate of 12m³ / h with a concentration of 3.18%, and the fifth group of ceramic membrane filters 11 is further washed with permeate water or pure water obtained by reverse osmosis membrane filtration to obtain a low-concentration ceramic membrane permeate of 12m³ / h with a concentration of 1.27% and a ceramic membrane concentrate of 8m³ / h.

[0052] Discharge conditions: The high-concentration ceramic membrane permeate, medium-concentration ceramic membrane permeate and low-concentration ceramic membrane permeate are all clear solutions. No mycelium is observed with the naked eye. There is no sediment after centrifugation for 6 minutes at 8000r / min in a high-speed centrifuge.

[0053] Step 22, the high-concentration ceramic membrane permeate 32m³ / h with a concentration of 18% obtained in step 21 and the reverse osmosis membrane concentrate 16m³ / h with a concentration of 18% obtained in step 13 are mixed and transported to the continuous nanofiltration membrane filtration subsystem 2, which is composed of five groups of nanofiltration membrane filters 21. The pore size of the nanofiltration membrane in this embodiment is selected to be 300Da, the operating pressure of the nanofiltration membrane is 30bar~35bar, and the operating temperature is 45°C. The first two groups of nanofiltration membrane filters 21 are not diluted with water. After filtering through the front-end concentration group 22 of the nanofiltration membrane filter, a high-concentration nanomembrane permeate 38.8m³ / h with a concentration of 18% is obtained, and the erythritol content in the dry basis of the permeate is 97.2%. The third group of nanofiltration membrane filters 21 is washed with a low-concentration nanofiltration membrane permeate 14.4m³ / h with a concentration of 1.27% , and a first-level medium-concentration nanofiltration membrane permeate of 14.4m³ / h with a concentration of 7.96% was obtained. The fourth group of nanofiltration membrane filters 21 was filtered with permeate water or pure water obtained by reverse osmosis membrane filtration to obtain a second-level medium-concentration nanofiltration membrane permeate of 14.4m³ / h with a concentration of 3.18%. The fifth group of nanofiltration membrane filters 21 was further filtered with permeate water or pure water obtained by reverse osmosis membrane filtration to obtain a low-concentration nanofiltration membrane permeate of 14.4m³ / h with a concentration of 1.27% and a nanofiltration membrane concentrate of 9.6m³ / h.

[0054] Discharge conditions: The transmittance of the high-concentration nanofiltration membrane permeate was detected to be 90% (wavelength 420nm), and the transmittance of the medium-concentration nanofiltration membrane permeate and the low-concentration nanofiltration membrane permeate was 91% (wavelength 420nm).

[0055] Step 23, after mixing the first-level medium-concentration ceramic membrane permeate 12m³ / h with a concentration of 7.96% and the second-level medium-concentration ceramic membrane permeate 12m³ / h with a concentration of 3.18% obtained in step 21, and the first-level medium-concentration nanofiltration permeate 14.4m³ / h with a concentration of 7.96% and the second-level medium-concentration nanofiltration permeate 14.4m³ / h with a concentration of 3.18% obtained in step 22, a mixed solution with a flow rate of 52.8m³ / h and a concentration of 5.57% is obtained, and enters the continuous reverse osmosis membrane concentration subsystem 3. The reverse osmosis membrane pore size of this example is 0.2nm, the operating pressure is 45bar, and the operating temperature is 45°C, and 16m³ / h of reverse osmosis membrane concentrate with a concentration of 18% and 36.8m³ / h of permeate water are obtained.

[0056] Step 24, after collecting the low-concentration ceramic membrane permeate 12m³ / h with a concentration of 1.27% obtained in step 21, return it to the ceramic membrane middle filter group 13 for use as erythritol ceramic membrane filtration. After collecting the low-concentration nanofiltration permeate 14.4m³ / h with a concentration of 1.27% obtained in step 22, return it to the nanofiltration membrane middle filter group 23 for use as erythritol nanofiltration membrane filtration. The permeate water 36.8m³ / h obtained in step 23 is returned to the ceramic membrane middle filter group 13, the ceramic membrane rear filter group 14, the nanofiltration membrane middle filter group 23 and the nanofiltration membrane rear filter group 24, respectively, as water for washing the ceramic membrane and nanofiltration membrane, and the insufficient part is supplemented with pure water, and about 16m³ / h of pure water is required every hour.

[0057] Finally, the continuous ceramic membrane filtration subsystem 1 had a yield of 99.11%, the continuous nanofiltration membrane filtration subsystem 2 had a yield of 99.14%, and 4m3 of water was saved per hour. 3 / h.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A continuous membrane filtration system for erythritol fermentation broth, characterized in that: The invention comprises a continuous ceramic membrane filtration subsystem, a continuous nanofiltration membrane filtration subsystem, a continuous reverse osmosis membrane concentration subsystem and a low-concentration dialysate recycling subsystem, wherein the continuous ceramic membrane filtration subsystem comprises a ceramic membrane front section filtration group, a ceramic membrane middle section filtration group and a ceramic membrane rear section filtration group respectively composed of a plurality of groups of ceramic membrane filters which are sequentially connected through pipelines, the continuous nanofiltration membrane filtration subsystem comprises a nanofiltration membrane front section filtration group, a nanofiltration membrane middle section filtration group and a nanofiltration membrane rear section filtration group respectively composed of a plurality of groups of nanofiltration membrane filters which are sequentially connected through pipelines, the continuous reverse osmosis membrane concentration subsystem comprises a reverse osmosis membrane filter which is sequentially connected through pipelines, the ... The invention discloses a front-end membrane concentration group, a middle-end reverse osmosis membrane concentration group and a rear-end reverse osmosis membrane concentration group. The low-concentration dialysate recycling subsystem comprises a low-concentration ceramic membrane permeate recycling tank, a low-concentration nanofiltration permeate recycling tank and a permeate recycling tank. The continuous ceramic membrane filtration subsystem is provided with an erythritol fermentation liquid inlet pipe, a high-concentration ceramic membrane permeate outlet pipe, a medium-concentration ceramic membrane permeate outlet pipe, a low-concentration ceramic membrane permeate outlet pipe, a ceramic membrane concentrated liquid outlet pipe, a middle-end low-concentration ceramic membrane permeate recycling inlet pipe, a ceramic membrane middle-end permeate recycling water recycling water inlet pipe and a ceramic membrane rear-end permeate recycling water recycling water inlet pipe. The low-concentration ceramic membrane permeate recycling tank is connected to the low-concentration ceramic membrane by a liquid inlet end and a liquid outlet end of the low-concentration ceramic membrane permeate recycling tank. The membrane permeate outlet pipe is connected, and its outlet end is connected to the return jacket inlet pipe of the middle low-concentration ceramic membrane permeate, and the ceramic membrane middle section permeate water return jacket inlet pipe and the ceramic membrane rear section permeate water return jacket inlet pipe are respectively connected to the outlet end of the permeate water return jacket tank; in the continuous nanofiltration membrane filtration subsystem, a nanofiltration membrane inlet pipe, a high-concentration nanofiltration permeate outlet pipe, a medium-concentration nanofiltration permeate outlet pipe, a low-concentration nanofiltration permeate outlet pipe, a nanofiltration concentrated liquid outlet pipe, a middle section low-concentration nanofiltration permeate return jacket inlet pipe, a nanofiltration membrane middle section permeate water return jacket inlet pipe and a nanofiltration membrane rear section permeate water return jacket inlet pipe are respectively arranged, and the liquid inlet end of the low-concentration nanofiltration permeate return jacket tank is connected to the low-concentration nanofiltration permeate outlet pipe. The liquid pipe is connected, and its liquid outlet end is connected with the return jacket inlet pipe of the middle section low-concentration nanofiltration permeate, and the return jacket inlet pipe of the middle section permeate water of the nanofiltration membrane and the return jacket inlet pipe of the rear section permeate water of the nanofiltration membrane are respectively connected with the water outlet end of the permeate water return jacket tank; in the continuous reverse osmosis membrane concentration subsystem, a reverse osmosis membrane inlet pipe, a reverse osmosis membrane concentrated liquid outlet pipe and a permeate water collecting pipe are respectively arranged, and the reverse osmosis membrane inlet pipe is respectively connected with the medium-concentration ceramic membrane permeate liquid outlet pipe and the medium-concentration nanofiltration permeate liquid outlet pipe, and the reverse osmosis membrane concentrated liquid outlet pipe is connected with the high-concentration ceramic membrane permeate liquid outlet pipe and then connected with the nanofiltration membrane inlet pipe, and the permeate water collecting pipe is connected with the water inlet end of the permeate water return jacket tank.

2. The continuous membrane filtration system for erythritol fermentation broth according to claim 1, characterized in that: A pure water inlet pipe is also arranged at the water inlet end of the permeate water return tank.

3. The continuous membrane filtration system for erythritol fermentation broth according to claim 1, characterized in that: The continuous ceramic membrane filtration subsystem includes five groups of ceramic membrane filters, wherein the ceramic membrane front section filtration group and the ceramic membrane middle section filtration group are respectively provided with two groups of ceramic membrane filters, and the ceramic membrane rear section filtration group is provided with one group of ceramic membrane filters.

4. The continuous membrane filtration system for erythritol fermentation broth according to claim 1, characterized in that: The continuous nanofiltration membrane filtration subsystem includes five groups of nanofiltration membrane filters, wherein the nanofiltration membrane front section filtration group and the nanofiltration membrane middle section filtration group are respectively provided with two groups of nanofiltration membrane filters, and the nanofiltration membrane rear section filtration group is provided with one group of nanofiltration membrane filters.

5. The continuous membrane filtration system for erythritol fermentation broth according to claim 1, characterized in that: The continuous reverse osmosis membrane concentration subsystem comprises three groups of reverse osmosis membrane filters, wherein the reverse osmosis membrane front section concentration group, the reverse osmosis membrane middle section concentration group and the reverse osmosis membrane rear section concentration group are each provided with a group of reverse osmosis membrane filters.

6. The continuous membrane filtration system for erythritol fermentation broth according to claim 1, characterized in that: A high-concentration dialysate tank is arranged on the nanofiltration membrane liquid inlet pipe.

7. The continuous membrane filtration system for erythritol fermentation broth according to claim 1, characterized in that: A medium-concentration dialysate tank is arranged on the reverse osmosis membrane liquid inlet pipe.

8. A method for continuous membrane filtration of erythritol fermentation broth, characterized in that: It uses the continuous membrane filtration system of erythritol fermentation broth as claimed in any one of claims 1 to 7, and the filtration method comprises the following steps: Step 1, continuous ceramic membrane filtration, filtering and clarifying the erythritol fermentation broth through a continuous ceramic membrane filtration subsystem, and continuously adding water for filtration, to obtain a high-concentration ceramic membrane permeate, a medium-concentration ceramic membrane permeate, a low-concentration ceramic membrane permeate and a ceramic membrane concentrate, respectively; Step 2, continuous nanofiltration membrane filtration, the high-concentration ceramic membrane permeate and the reverse osmosis membrane concentrate obtained in the subsequent step 3 are mixed and then enter the continuous nanofiltration membrane filtration subsystem, and water is continuously added for filtration, to obtain high-concentration nanofiltration permeate, medium-concentration nanofiltration permeate, low-concentration nanofiltration permeate and nanofiltration concentrate respectively; Step 3, continuous reverse osmosis membrane concentration, mixing the medium-concentration ceramic membrane permeate obtained in step 1 and the medium-concentration nanofiltration permeate obtained in step 2 into a continuous reverse osmosis membrane concentration subsystem to obtain reverse osmosis membrane concentrate and permeate water, respectively; Step 4: Reuse of low-concentration dialysate. The low-concentration ceramic membrane permeate obtained in step 1 is collected and then recycled to the ceramic membrane middle filtration group for use as erythritol ceramic membrane filtration. The low-concentration nanofiltration permeate obtained in step 2 is collected and then recycled to the nanofiltration membrane middle filtration group for use as erythritol nanofiltration membrane filtration. The permeate water obtained by reverse osmosis membrane filtration in step 3 is recycled to the ceramic membrane middle filtration group, the ceramic membrane rear filtration group, the nanofiltration membrane middle filtration group and the nanofiltration membrane rear filtration group, respectively, for use as water for washing the ceramic membrane and the nanofiltration membrane.

9. The method for continuous membrane filtration of erythritol fermentation broth according to claim 8, characterized in that: The steps include: Step (1), conveying the erythritol fermentation liquid with a concentration of 16% to 22% to a continuous ceramic membrane filtration subsystem, the continuous ceramic membrane filtration subsystem comprising five groups of ceramic membrane filters, the ceramic membrane pore size is 15KD to 600KD, the ceramic membrane operating pressure is 3bar to 6bar, and the operating temperature is 30°C to 65°C, wherein the first two groups of ceramic membrane filters are not diluted with water, and the erythritol fermentation liquid is filtered through the ceramic membrane front section filtration group to obtain a high-concentration ceramic membrane permeate with a concentration of 16% to 22%, and the high-concentration ceramic membrane permeate accounts for 70% of the total feed amount ~85%; the third group of ceramic membrane filters uses the low-concentration ceramic membrane permeate with a concentration of 1.0%~2.5% to perform diafiltration to obtain a first-level medium-concentration ceramic membrane permeate with a concentration of 6%~9%, the fourth group of ceramic membrane filters uses the permeate water or pure water obtained by reverse osmosis membrane filtration to perform diafiltration to obtain a second-level medium-concentration ceramic membrane permeate with a concentration of 3%~6%, and the fifth group of ceramic membrane filters uses the permeate water or pure water obtained by reverse osmosis membrane filtration to further perform diafiltration to obtain a low-concentration ceramic membrane permeate and ceramic membrane concentrate with a concentration of 1.0%~2.5%; Step (2), mixing the high-concentration ceramic membrane permeate with a concentration of 16% to 22% obtained in step (1) and the reverse osmosis membrane concentrate with a concentration of 16% to 22% obtained in step (3), and then transporting them to a continuous nanofiltration membrane filtration subsystem, the continuous nanofiltration membrane filtration subsystem comprising five groups of nanofiltration membrane filters, the membrane pore size of the nanofiltration membrane is 250Da to 500Da, the operating pressure of the nanofiltration membrane is 25bar to 45bar, and the operating temperature is 30°C to 50°C, wherein the first two groups of nanofiltration membrane filters are not diluted with water, and a high-concentration nanofiltration membrane with a concentration of 16% to 22% is obtained after filtration through the front-end concentration group of the nanofiltration membrane filter. The permeate of the high-concentration nanofiltration membrane permeate accounts for 70% to 85% of the total feed; the third group of nanofiltration membrane filters uses the low-concentration nanofiltration membrane permeate of the concentration of 1.0% to 2.5% to wash filter, and obtain the first-level medium-concentration nanofiltration membrane permeate of the concentration of 6% to 9%. The fourth group of nanofiltration membrane filters uses the permeate water or pure water obtained by reverse osmosis membrane filtration to wash filter, and obtain the second-level medium-concentration nanofiltration membrane permeate of the concentration of 3% to 6%. The fifth group of nanofiltration membrane filters uses the permeate water or pure water obtained by reverse osmosis membrane filtration to further wash filter, and obtain the low-concentration nanofiltration membrane permeate and nanofiltration membrane concentrate of the concentration of 1.0% to 2.5%. Step (3), mixing the primary and secondary medium-concentration ceramic membrane permeates obtained in step (1) and the primary and secondary medium-concentration nanofiltration permeates obtained in step (2) into a continuous reverse osmosis membrane concentration subsystem, wherein the concentration of the mixed solution is 5% to 8%, the pore size of the reverse osmosis membrane is 0.1 nm to 0.5 nm, the operating pressure is 35 bar to 50 bar, and the operating temperature is 30° C. to 50° C., to obtain a reverse osmosis membrane concentrate and permeate water with a concentration of 16% to 22%; Step (4), after collecting the low-concentration ceramic membrane permeate with a concentration of 1.0% to 2.5% obtained in step (1), returning it to the third group of ceramic membrane filters for use as erythritol ceramic membrane washing; after collecting the low-concentration nanofiltration permeate with a concentration of 1.0% to 2.5% obtained in step (2), returning it to the third group of nanofiltration membrane filters for use as erythritol nanofiltration membrane washing; the permeate obtained in step (3) is returned to the fourth group and the fifth group of the continuous ceramic membrane filtration subsystem and the continuous nanofiltration membrane filtration subsystem, respectively, as water for washing the ceramic membrane and the nanofiltration membrane, and the insufficient part is supplemented with pure water.

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