Composite spiral-wound membrane element and winding method thereof

Abstract

The invention relates to the technical field of membrane separation, in particular to a composite spiral-wound membrane element and a winding method thereof. The membrane element is rolled by the method. The method comprises the following steps: winding a first fresh water diversion net on a central water collecting pipe for at least one circle by taking one end in the length direction as a starting point; a composite dechlorination and water purification membrane layer is arranged on the first fresh water flow guide net in an adhesion mode and then wound on the central water collecting pipe along with the first fresh water flow guide net by at least one circle; winding the staggered folded membranes and the second fresh water guide net on the central water collecting pipe along with the first fresh water guide net to form a prefabricated spiral-wound membrane element; and shaping the appearance protection film wound on the prefabricated spiral-wound membrane element to obtain the composite spiral-wound membrane element. According to the invention, the composite spiral-wound membrane element with high removal rate of residual chlorine in produced water and low bacterial content can be prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and particularly relates to a composite spiral wound membrane element and a winding method thereof. Background Art

[0002] The conventional winding method for spiral wound membrane elements is as follows: A membrane sheet (such as a reverse osmosis membrane sheet) is folded in half along the length direction to form an N shape, and a concentrated water spacer is placed in the middle of the N shape; A fresh water spacer is placed on the folded membrane sheet, and resin sealant is applied to the three open connecting edges of the membrane sheet to adhere the fresh water spacer to the membrane sheet; The membrane sheet is wound around a central product water pipe in a spiral manner to form a spiral wound membrane element. When applying this spiral wound membrane element, the pure water filtered by the membrane sheet is directly connected to the fresh water spacer and converges onto the central collecting pipe, and is collected and produced by the central collecting pipe. However, the pure water produced by this spiral wound membrane element has problems of low residual chlorine removal rate and high bacterial content.

[0003] In summary, it is necessary to develop a composite spiral wound membrane element and a winding method thereof to solve the problems of low residual chlorine removal rate and high bacterial content in the pure water produced by the existing spiral wound membrane elements. Summary of the Invention

[0004] The purpose of the present invention is to provide a composite spiral wound membrane element and a winding method thereof, and the specific technical solutions are as follows:

[0005] In a first aspect, the present invention provides a winding method for a composite spiral wound membrane element, including:

[0006] Step S1: Starting from one end of the first fresh water diversion net in its length direction, wind it around the central collecting pipe for at least one week;

[0007] Step S2: Adhere and set the composite chlorine-removing and water-purifying membrane layer on the first fresh water diversion net, and then wind it around the central collecting pipe along with the first fresh water diversion net for at least one week;

[0008] Step S3: Fold the membrane sheet in a staggered manner along the length direction to form a staggered folded membrane sheet, and place the concentrated water spacer in the middle of the staggered folded membrane sheet; Stack multiple staggered folded membrane sheets containing the concentrated water spacer on the first fresh water diversion net in a staggered manner in sequence, and adhere and set a second fresh water diversion net between every two adjacent staggered folded membrane sheets; The staggered folded membrane sheet in contact with the first fresh water diversion net is adhered and set on the first fresh water diversion net;

[0009] When stacking in a staggered manner, the non-opening ends of the staggered folded membrane sheets are sequentially away from the central collecting pipe, and the short membrane sheet pages in each staggered folded membrane sheet are closer to the first fresh water diversion net than the long membrane sheet pages;

[0010] Each of the misaligned folding membrane sheets and the second fresh water diversion net are wound around the central water collecting pipe together with the first fresh water diversion net to form a prefabricated spiral membrane element;

[0011] Step S4: Wind an appearance protection film around the prefabricated spiral membrane element for shaping to obtain a composite spiral membrane element; wherein, a water inlet and a water outlet are reserved on the appearance protection film.

[0012] Optionally, the composite chlorine-removing and water-purifying membrane layer includes a carbon fiber membrane layer and an antibacterial membrane layer arranged in a stacked manner, or includes a carbon fiber membrane layer and an antibacterial membrane layer arranged at intervals along the length direction of the first fresh water diversion net;

[0013] When the carbon fiber membrane layer and the antibacterial membrane layer are arranged at intervals along the length direction of the first fresh water diversion net, both the carbon fiber membrane layer and the antibacterial membrane layer are wound around the central water collecting pipe together with the first fresh water diversion net for at least one turn.

[0014] Optionally, in step S2, a first sealant line is coated on the first fresh water diversion net; there are two first sealant lines, and they are arranged in parallel at both ends along the wide side direction of the first fresh water diversion net; the composite chlorine-removing and water-purifying membrane layer is adhered to the first fresh water diversion net through the first sealant line;

[0015] Or, a first sealant line is coated on the composite chlorine-removing and water-purifying membrane layer; there are two first sealant lines, and they are arranged in parallel at both ends along the wide side direction of the composite chlorine-removing and water-purifying membrane layer; the first fresh water diversion net is adhered to the composite chlorine-removing and water-purifying membrane layer through the first sealant line;

[0016] The length of the first sealant line is equal to the length of the composite chlorine-removing and water-purifying membrane layer.

[0017] Optionally, the shortest distance between the first sealant line and the end of the wide side direction of the first fresh water diversion net is 10 - 25 mm; the width of the first sealant line is 4 - 8 mm.

[0018] Optionally, in step S3, a second sealant line is coated on the outer surfaces of the three open ends of each of the misaligned folding membrane sheets; each of the second sealant lines encloses a U-shaped structure.

[0019] Optionally, the sealants used for the first sealant line and the second sealant line both include polyurethane glue.

[0020] Optionally, a plurality of water collecting holes are arranged at intervals on the pipe wall along the length direction of the central water collecting pipe, and are all covered by the composite chlorine-removing and water-purifying membrane layer wound around the central water collecting pipe.

[0021] Optionally, the length of the first fresh water diversion net is greater than the length of the second fresh water diversion net;

[0022] The length of the second fresh water diversion net is greater than or equal to the length of the long membrane sheet in the offset folded membrane sheet.

[0023] In a second aspect, the present invention provides a composite spiral wound membrane element, which is wound by using the winding method of the composite spiral wound membrane element.

[0024] Optionally, the composite spiral wound membrane element includes any one of a reverse osmosis spiral wound membrane element, a nanofiltration spiral wound membrane element, and an ultrafiltration spiral wound membrane element.

[0025] Applying the technical solution of the present invention has at least the following beneficial effects:

[0026] The winding method of the composite spiral wound membrane element provided by the present invention can prepare a composite spiral wound membrane element with a high chlorine removal rate of the produced water and a low bacteria content. Specifically, the present invention first uses an offset folded membrane sheet with a concentrated water spacer to complete the preliminary purification of the water body; then uses a combination of a first fresh water diversion net, a second fresh water diversion net, and a composite chlorine-removing and water-purifying membrane layer to complete the sufficient adsorption and purification of the water body, so that the chlorine removal rate of the produced water is high and the bacteria content is low. Among them, in step S1 of the present invention, the first fresh water diversion net is wound around the central collecting pipe for at least one week. On the one hand, it increases the contact area for water purification for the composite chlorine-removing and water-purifying membrane layer wound around the central collecting pipe in step S2 subsequently, and on the other hand, it effectively improves the water flow permeability; the composite chlorine-removing and water-purifying membrane layer wound around the central collecting pipe in step S2 is wound for at least one week to ensure that all water bodies can pass through the composite chlorine-removing and water-purifying membrane layer for purification; in step S3, the offset folded membrane sheets and the offset folded membrane sheets are sequentially arranged in an offset manner to increase the effective membrane area that can be used for water purification after the offset folded membrane sheets are wound; in step S4, the appearance protection film is used to press the prefabricated spiral wound membrane element to ensure the structural stability of the prefabricated spiral wound membrane element during water purification.

[0027] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The present invention will be further described in detail below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0029] Figure 1 is a schematic structural diagram before winding the composite chlorine-removing and water-purifying membrane layer on the first fresh water diversion net in Example 1;

[0030] Figure 2 It is a schematic structural diagram before winding in Embodiment 1, where each misaligned folded membrane sheet is sequentially and misaligned stacked on the first fresh water diversion net (the arrow direction in the figure indicates the winding direction).

[0031] Among them, 1 is the first fresh water diversion net, 2 is the central water collecting pipe, 3 is the composite chlorine-removing and water-purifying membrane layer, 4 is the misaligned folded membrane sheet, 5 is the concentrated water separation net, 6 is the second fresh water diversion net, 7 is the first sealant line, and 8 is the second sealant line. Specific Embodiment

[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0033] Embodiment 1:

[0034] See Figures 1 - 2 , a winding method for a composite spiral wound membrane element, including:

[0035] Step S1: Wind the first fresh water diversion net 1 (made of polyethylene terephthalate) around the central water collecting pipe 2 (with a diameter of 17 mm and a length of 298 mm) at least once starting from one end in its length direction; on the one hand, it increases the contact area for water purification of the composite chlorine-removing and water-purifying membrane layer 3 wound around the central water collecting pipe 2 in Step S2 subsequently, and on the other hand, it effectively improves the water flow permeability;

[0036] Step S2: Adhere the composite chlorine-removing and water-purifying membrane layer 3 to the first fresh water diversion net 1, and then wind it around the central water collecting pipe 2 along with the first fresh water diversion net 1, and wind it at least once to ensure that all water bodies can be purified by the composite chlorine-removing and water-purifying membrane layer 3;

[0037] Step S3: Fold the membrane sheet in half in a misaligned manner along the length direction to form a misaligned folded membrane sheet 4, and arrange the concentrated water separation net 5 (made of polypropylene) in the middle of the misaligned folded membrane sheet 4; sequentially and misaligned stack 1 to 20 (specifically 2) misaligned folded membrane sheets 4 containing the concentrated water separation net 5 on the first fresh water diversion net 1, and adhesively arrange a second fresh water diversion net 6 (made of polyethylene terephthalate) between every two adjacent misaligned folded membrane sheets 4; the misaligned folded membrane sheet 4 in contact with the first fresh water diversion net 1 is adhesively arranged on the first fresh water diversion net 1;

[0038] When arranged in a staggered stack, the non-opening ends of the staggered folding diaphragm sheets 4 are successively away from the central water collecting pipe 2, and the short diaphragm sheets in each of the staggered folding diaphragm sheets 4 are closer to the first fresh water diversion net 1 than the long diaphragm sheets;

[0039] Each of the staggered folding diaphragm sheets 4 and the second fresh water diversion net 6 are wound around the central water collecting pipe 2 together with the first fresh water diversion net 1 to form a prefabricated spiral membrane element;

[0040] The use of the staggered folding diaphragm sheets 4 and the successive staggered stack arrangement of the staggered folding diaphragm sheets 4 is to increase the effective membrane area that can be used for water purification after the staggered folding diaphragm sheets 4 are wound;

[0041] Step S4: Shape the prefabricated spiral membrane element by winding an appearance protection film (made of biaxially oriented polypropylene film; not shown in the figure) to obtain a composite spiral membrane element; wherein, an inlet and an outlet are reserved on the appearance protection film. The appearance protection film is used to press the prefabricated spiral membrane element to ensure the structural stability of the prefabricated spiral membrane element during water purification.

[0042] The composite chlorine-removing water purification membrane layer 3 includes a carbon fiber membrane layer (specifically, activated carbon fiber felt) and an antibacterial membrane layer (specifically, an antibacterial membrane made of quaternary ammonium salt) arranged in a stack, or includes a carbon fiber membrane layer and an antibacterial membrane layer arranged at intervals along the length direction of the first fresh water diversion net 1. Wherein, when the carbon fiber membrane layer and the antibacterial membrane layer are arranged in a stack, the carbon fiber membrane layer is closer to the first fresh water diversion net 1 than the antibacterial membrane layer, or the antibacterial membrane layer is closer to the first fresh water diversion net 1 than the carbon fiber membrane layer; in this embodiment, it is selected that the carbon fiber membrane layer is closer to the first fresh water diversion net 1 than the antibacterial membrane layer. When the carbon fiber membrane layer and the antibacterial membrane layer are arranged at intervals along the length direction of the first fresh water diversion net 1, the carbon fiber membrane layer is closer to the central water collecting pipe 2 than the antibacterial membrane layer, or the antibacterial membrane layer is closer to the central water collecting pipe 2 than the carbon fiber membrane layer, and the carbon fiber membrane layer and the antibacterial membrane layer are wound around the central water collecting pipe 2 together with the first fresh water diversion net 1 for at least one turn to ensure that all water bodies can be purified by the composite chlorine-removing water purification membrane layer 3.

[0043] In step S2, a first sealing glue line 7 is coated on the first fresh water diversion net 1; there are two first sealing glue lines 7, and they are arranged in parallel at both ends along the width direction of the first fresh water diversion net 1; the composite chlorine-removing water purification membrane layer 3 is adhered to the first fresh water diversion net 1 through the first sealing glue line 7;

[0044] Or, a first sealing glue line 7 is coated on the composite chlorine-removing water purification membrane layer 3; there are two first sealing glue lines 7, and they are arranged in parallel at both ends along the width direction of the composite chlorine-removing water purification membrane layer 3; the first fresh water diversion net 1 is adhered to the composite chlorine-removing water purification membrane layer 3 through the first sealing glue line 7;

[0045] The length of the first sealant line 7 is equal to the length of the composite chlorine-removing water purification membrane layer 3, ensuring that both ends of the composite chlorine-removing water purification membrane layer 3 in the width direction are effectively sealed, so as to fully adsorb and purify the water body subsequently.

[0046] The shortest distance between the first sealant line 7 and the end of the wide side of the first fresh water diversion net 1 is 10 - 25 mm (specifically, 20 mm can be selected), ensuring the maximization of the effective membrane area; the width of the first sealant line 7 is 4 - 8 mm (specifically, 6 mm can be selected), ensuring firm bonding between the composite chlorine-removing water purification membrane layer 3 and the first fresh water diversion net 1, achieving a sealing effect, and ensuring that the water body purified by the combination of the composite chlorine-removing water purification membrane layer 3 and the first fresh water diversion net 1 converges into the central water collecting pipe 2 after passing through the sealed area surrounded by the first sealant line 7.

[0047] In step S3, a second sealant line 8 is coated on the outer surfaces of the three open ends of each of the misaligned folded membrane sheets 4; each of the second sealant lines 8 encloses a U-shaped structure, ensuring that the water body preliminarily purified by the misaligned folded membrane sheets 4 flows into the U-shaped structure, and the preliminarily purified water body is directionally diverted to the sealed area combined by the first fresh water diversion net 1, the first sealant line 7 and the composite chlorine-removing water purification membrane layer 3 through the sealing effect of the edge of the U-shaped structure for full adsorption and purification.

[0048] The sealants used for the first sealant line 7 and the second sealant line 8 are both polyurethane adhesives (i.e., polyurethane resin). The polyurethane adhesive not only has a good penetration rate for the misaligned folded membrane sheets 4, the first fresh water diversion net 1, the second fresh water diversion net 6 and the composite chlorine-removing water purification membrane layer 3, ensuring the adhesion strength, but also has a certain fluidity to reduce the winding difficulty.

[0049] A plurality of (specifically, eleven) water collecting holes are arranged at intervals on the pipe wall along the length direction of the central water collecting pipe 2, and all are covered by the composite chlorine-removing water purification membrane layer 3 wound around the central water collecting pipe 2, ensuring that all water bodies can be purified by the composite chlorine-removing water purification membrane layer 3.

[0050] The length of the first fresh water diversion net 1 is greater than the length of the second fresh water diversion net 6, ensuring the smooth completion of the winding operation;

[0051] The length of the second fresh water diversion net 6 is greater than or equal to the length of the long membrane sheet in the misaligned folded membrane sheets 4, ensuring that the misaligned folded membrane sheets 4 can be completely covered by the second fresh water diversion net 6 when the second fresh water diversion net 6 and the misaligned folded membrane sheets 4 are stacked, facilitating the effective purification of the water body.

[0052] The composite spiral wound membrane element includes any one of a reverse osmosis spiral wound membrane element, a nanofiltration spiral wound membrane element, and an ultrafiltration spiral wound membrane element. When the membrane sheet is a reverse osmosis membrane, the composite spiral wound membrane element is a reverse osmosis spiral wound membrane element. When the membrane sheet is a nanofiltration membrane, the composite spiral wound membrane element is a nanofiltration spiral wound membrane element. When the membrane sheet is an ultrafiltration membrane, the composite spiral wound membrane element is an ultrafiltration spiral wound membrane element. In Example 1, the composite spiral wound membrane element is a reverse osmosis spiral wound membrane element.

[0053] The operation principle of the composite spiral wound membrane element prepared in Example 1 for purifying water is as follows: First, the water body is preliminarily purified by using the misaligned folded membrane sheet 4 with the concentrated water spacer 5; then, the first fresh water diversion net 1, the second fresh water diversion net 6, and the composite chlorine-removing and water-purifying membrane layer 3 are combined to complete the sufficient adsorption and purification of the water body, so that the produced water has a high chlorine removal rate and a low bacteria content.

[0054] Comparative Example 1:

[0055] Different from Example 1, the composite chlorine-removing and water-purifying membrane layer 3 is not provided.

[0056] Comparative Example 2:

[0057] Different from Example 1, the composite chlorine-removing and water-purifying membrane layer 3 is replaced by a carbon fiber membrane layer, and the length of the carbon fiber membrane layer is less than one week around the winding center collecting pipe 2; in addition, a carbon fiber membrane layer stacked with the concentrated water spacer 5 is also provided in the misaligned folded membrane sheet 4.

[0058] The composite spiral wound membrane elements prepared in Example 1 and Comparative Examples 1-2 are respectively subjected to water production performance and water quality tests. The test results are shown in Table 1. The water production performance test method is as follows:

[0059] Control the pre-membrane pressure to 60 Psi, rinse the composite spiral wound membrane element with pure water for 20 min, and then run the composite spiral wound membrane element with the test solution (i.e., Zhuzhou municipal tap water) for 10 min to measure the initial flow rate and the initial desalination rate; subsequently, continuously run the composite spiral wound membrane element with the test solution for 30 days, and then measure the initial flow rate after 30 days and the desalination rate after 30 days. Among them, the model of each composite spiral wound membrane element is 1812 (“18” represents 1.8 inches; “12” represents 12 inches.); the recovery rate of the composite spiral wound membrane element in Example 1 is 50% - 55%; the recovery rate of the composite spiral wound membrane element in Comparative Example 1 is 50% - 55%; the recovery rate of the composite spiral wound membrane element in Comparative Example 2 is 50% - 55%; the recovery rate = water production ÷ (water production + waste water) × 100%; the flow rate decay rate = (1 - flow rate after 30 days / initial flow rate) × 100%.

[0060] The water quality test includes the produced water colony test and the chlorine removal rate test.

[0061] The test method for the colonies in the produced water was completed with reference to "GB / T 5750.12-2006 Standard Test Methods for Drinking Water - Microbiological Indicators".

[0062] The test method for the chlorine removal rate was completed with reference to "GB 11896-89 Water Quality - Determination of Chloride - Silver Nitrate Titration Method". Among them, the chlorine removal rate = (1 - chloride ion content in the produced water / chloride ion content in the test solution) × 100%.

[0063] Table 1 Test Results of Produced Water Performance and Water Quality

[0064]

[0065] As can be seen from Table 1, compared with Example 1, the composite spiral wound membrane elements prepared in Comparative Example 1 and Comparative Example 2 both had the problem of unqualified microorganisms in the produced water after operation. This is because the antibacterial film layer was not set in both Comparative Example 1 and Comparative Example 2.

[0066] Compared with Example 1 and Comparative Example 1, the composite spiral wound membrane element prepared in Comparative Example 2 not only had a significant decrease in the initial flow rate after operation, but also had a problem of a further decrease in the flow rate after 30 days. This is because a carbon fiber membrane layer stacked with the concentrated water spacer 5 was also set in the misaligned folded membrane sheet 4, which increased the inlet resistance, reduced the water inflow per unit time, and made the initial flow rate of Comparative Example 2 significantly decrease; with the blocking effect of the carbon fiber membrane layer stacked with the concentrated water spacer 5, the impurities in the inlet water body were blocked at the inlet end of the concentrated water spacer 5, resulting in a further decrease in the flow rate of the composite spiral wound membrane element prepared in Comparative Example 2 after 30 days of operation.

[0067] Compared with Example 1, the chlorine removal rate of the produced water of the composite spiral wound membrane element prepared in Comparative Example 2 was relatively lower than that of Example 1 after operation. This is because the length of the carbon fiber membrane layer in Comparative Example 2 was less than one week around the central collecting pipe 2, so that the carbon fiber membrane layer could not completely cover the central collecting pipe 2, resulting in poor adsorption and purification effect of the produced water in the area where the central collecting pipe 2 was not covered by the carbon fiber membrane layer, and the residual chlorine in the water body could not be fully adsorbed and removed by the carbon fiber membrane layer, resulting in a relatively lower chlorine removal rate of the produced water than that of Example 1.

[0068] The composite spiral wound membrane elements prepared in Example 1 and Comparative Examples 1-2 were respectively subjected to the national standard GB 34914-2021 water efficiency water test to measure the initial flow rate and initial desalination rate. The test results are shown in Table 2. The test results also include the residual chlorine removal rate (the residual chlorine removal rate test was completed with reference to "GB 11896-89 Determination of Chloride in Water Quality - Silver Nitrate Titration Method"). Among them, the pressure before the membrane was controlled at 100 Psi; the model of each composite spiral wound membrane element was 4012 ("40" represents 4.0 inches; "12" represents 12 inches.); the recovery rate of the composite spiral wound membrane element in Example 1 was 70% - 75%; the recovery rate of the composite spiral wound membrane element in Comparative Example 1 was 70% - 75%; the recovery rate of the composite spiral wound membrane element in Comparative Example 2 was 70% - 75%; the recovery rate is the percentage of the ratio of the water production to the water intake.

[0069] Table 2 Water Efficiency Water Test Results and Residual Chlorine Removal Rate Test Results

[0070] Grouping Initial flow rate mL / min Initial desalination rate % Residual chlorine removal rate % Comparative Example 1 2174 93.2 87.4 Comparative Example 2 1851 92.8 98.6 Example 1 4972 93.3 99.2

[0071] As can be seen from Table 2, compared with Comparative Example 1, the composite spiral wound membrane elements prepared in Example 1 and Comparative Example 2 have relatively high residual chlorine removal rates in the produced water after operation. This is because carbon fiber membrane layers were used in both Example 1 and Comparative Example 2, which can fully adsorb and remove the residual chlorine in the water body.

[0072] Furthermore, compared with Example 1, the residual chlorine removal rate of the composite spiral wound membrane element prepared in Comparative Example 2 in the produced water after operation is relatively lower than that of Example 1. The reason is the same as the data analysis in Table 1.

[0073] Compared with Example 1 and Comparative Example 1, the initial flow rate of the composite spiral wound membrane element prepared in Comparative Example 2 decreased significantly after operation. The reason is the same as the data analysis in Table 1.

[0074] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for rolling a composite rolled membrane element, characterized in that: include: Step S1, winding the first fresh water diversion net (1) around the central water collecting pipe (2) for at least one circle starting from one end in the length direction; Step S2, bonding the composite dechlorination water purification membrane layer (3) on the first fresh water diversion net (1), and then winding the composite dechlorination water purification membrane layer (3) on the central water collecting pipe (2) along with the first fresh water diversion net (1), and winding the composite dechlorination water purification membrane layer (3) for at least one cycle; Step S3, folding the membrane sheet in half in a staggered manner along the length direction to form a staggered folded membrane sheet (4), and arranging a concentrated water separator (5) in the middle of the staggered folded membrane sheet (4); A plurality of the offset folded membrane sheets (4) containing the concentrated water separation net (5) are sequentially stacked and offset on the first fresh water diversion net (1), and a second fresh water diversion net (6) is adhesively arranged between each two adjacent offset folded membrane sheets (4); the offset folded membrane sheets (4) in contact with the first fresh water diversion net (1) are adhesively arranged on the first fresh water diversion net (1); When the staggered layers are stacked, the non-open ends of the staggered folded membrane sheets (4) are sequentially away from the central water collecting pipe (2), and the short membrane sheets in the staggered folded membrane sheets (4) are closer to the first fresh water diversion network (1) than the long membrane sheets; Each of the offset folded membrane sheets (4) and the second fresh water guide net (6) are wound on the central water collecting pipe (2) along with the first fresh water guide net (1) to form a prefabricated rolled membrane element; Step S4, winding the prefabricated rolled membrane element with an appearance protective film to shape it, so as to obtain a composite rolled membrane element; wherein a water inlet and a water outlet are reserved on the appearance protective film.

2. The method for rolling a composite wound membrane element according to claim 1, characterized in that: The composite dechlorination water purification membrane layer (3) comprises a carbon fiber membrane layer and an antibacterial membrane layer which are stacked, or comprises a carbon fiber membrane layer and an antibacterial membrane layer which are spaced apart along the length direction of the first fresh water diversion net (1); When the carbon fiber membrane layer and the antibacterial membrane layer are arranged at intervals along the length direction of the first fresh water diversion net (1), the carbon fiber membrane layer and the antibacterial membrane layer are wound around the central water collecting pipe (2) along with the first fresh water diversion net (1) for at least one cycle.

3. The method for rolling a composite wound membrane element according to claim 1, characterized in that: In step S2, a first sealant line (7) is applied on the first fresh water diversion net (1); the first sealant lines (7) are two and are arranged in parallel along the two ends of the width direction of the first fresh water diversion net (1); the composite dechlorination water purification membrane layer (3) is adhered to the first fresh water diversion net (1) through the first sealant lines (7); Alternatively, a first sealant line (7) is coated on the composite dechlorination water purification membrane layer (3); the first sealant line (7) is two and is arranged in parallel at both ends along the width direction of the composite dechlorination water purification membrane layer (3); the first fresh water guide net (1) is adhered to the composite dechlorination water purification membrane layer (3) via the first sealant line (7); The length of the first sealant line (7) is equal to the length of the composite chlorine removal and water purification membrane layer (3).

4. The method for rolling a composite wound membrane element according to claim 3, characterized in that: The shortest distance between the first sealant line (7) and the end of the first freshwater diversion net (1) in the wide side direction is 10 to 25 mm; the width of the first sealant line (7) is 4 to 8 mm.

5. The method for rolling a composite wound membrane element according to claim 3, characterized in that: In step S3, a second sealing glue line (8) is coated on the outer surface of the three open ends of each of the offset folded membrane sheets (4); each of the second sealing glue lines (8) forms a U-shaped structure.

6. The method for rolling a composite wound membrane element according to claim 5, characterized in that: The sealants used in the first sealant line (7) and the second sealant line (8) both include polyurethane sealant.

7. The method for rolling a composite wound membrane element according to claim 1, characterized in that: A plurality of water collection holes are arranged at intervals on the pipe wall along the length direction of the central water collection pipe (2), and are all covered by the composite dechlorination and water purification membrane layer (3) wound on the central water collection pipe (2).

8. The method for rolling a composite wound membrane element according to any one of claims 1 to 7, characterized in that: The length of the first fresh water diversion net (1) is greater than the length of the second fresh water diversion net (6); The length of the second fresh water guide net (6) is greater than or equal to the length of the long membrane leaf in the offset folded membrane (4).

9. A composite spiral membrane element, characterized in that: The composite rolled membrane element is rolled using the rolling method as described in claim 8.

10. The composite spiral membrane element according to claim 9, characterized in that: The composite rolled membrane element includes any one of a reverse osmosis rolled membrane element, a nanofiltration rolled membrane element and an ultrafiltration rolled membrane element.

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