Separation and concentration device suitable for organic wastewater treatment

Abstract

The invention discloses a separation and concentration device suitable for organic wastewater treatment, which comprises a demulsification reaction tank fixed on a base, an ultrafiltration membrane assembly and a nanofiltration membrane assembly, the top of the base is communicated with a wastewater inlet pipe, the wastewater inlet pipe is internally provided with a grid filter screen, the demulsification reaction tank is internally provided with a stirring structure, and the stirring structure is internally provided with an ultrafiltration membrane. And the stirring structure reciprocates in the demulsification reaction tank in the axial direction of the demulsification reaction tank, the grid filter screen slides in the wastewater inlet pipe along with the stirring structure, and when the stirring structure upwards moves to the highest position in the demulsification reaction tank, the grid filter screen moves out of the wastewater inlet pipe. The grating filter screen is lifted and rotated through linkage of the stirring structure, and when the stirring shaft ascends to the highest position, the grating filter screen is exposed out of the wastewater inlet pipe, so that quick cleaning is facilitated; meanwhile, the stirring structure moves in the demulsification reaction tank along the axial direction, so that the demulsification efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, in particular to a separation and concentration device suitable for treating organic wastewater. Background Art

[0002] Organic wastewater comes from a wide range of sources. Industries like food processing, chemical production, and pharmaceuticals all generate large quantities of it. This type of wastewater contains high concentrations of organic matter and suspended solids, and direct discharge can cause serious environmental pollution. Currently, the treatment of organic wastewater typically requires separation and concentration to reduce the wastewater volume and recover useful substances, followed by advanced treatment of the concentrated wastewater. Currently, wastewater treatment generally involves pre-filtering the wastewater through a grid filter assembly. The filtered wastewater then enters a demulsification reactor for demulsification, followed by separation of suspended organic matter and colloids through an ultrafiltration membrane, and finally further concentration through a nanofiltration membrane.

[0003] However, the existing processing device still has the following problems:

[0004] (1) The grid filter components are mostly fixed structures, which are easily clogged by large particles of impurities and require frequent shutdowns for cleaning. In addition, the inner wall of the liquid inlet pipe cannot be cleaned synchronously, affecting the wastewater flow efficiency.

[0005] (2) The stirring structure in the demulsification reaction tank is mostly of fixed height, which makes it difficult to achieve sufficient mixing of the reagent and wastewater, especially the uneven treatment of emulsions at different heights in the tank, resulting in incomplete demulsification.

[0006] Therefore, there is an urgent need for an organic wastewater separation and concentration device that integrates efficient pretreatment and enhanced demulsification reaction to solve the above technical defects. Summary of the Invention

[0007] In order to solve the technical problems existing in the above-mentioned prior art, the present invention provides a separation and concentration device suitable for treating organic wastewater.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solutions: a separation and concentration device suitable for organic wastewater treatment, comprising a demulsification reaction tank, an ultrafiltration membrane assembly and a nanofiltration membrane assembly fixed on a base, a wastewater inlet pipe connected to the top of the base, a grid filter provided inside the wastewater inlet pipe, a stirring structure provided inside the demulsification reaction tank, and the stirring structure reciprocates along its axial direction inside the demulsification reaction tank, the grid filter slides inside the wastewater inlet pipe following the stirring structure, and when the stirring structure moves upward to the highest position inside the demulsification reaction tank, the grid filter moves outside the wastewater inlet pipe.

[0009] Preferably, the stirring structure includes a motor fixed to the top of the outer side of the demulsification reaction tank, a first stirring shaft is fixedly connected to the motor shaft of the motor, the first stirring shaft extends downward to the inside of the demulsification reaction tank and is then sleeved with a second stirring shaft, and an array of first stirring paddles are distributed on the circumferential surface of the second stirring shaft;

[0010] At least two ribs are arranged along the axial direction on the outer circumferential surface of the first stirring shaft, and a rib groove adapted to the first stirring shaft is formed inside the second stirring shaft. The first stirring shaft and the second stirring shaft can only slide relative to each other along the axial direction through the cooperation of the ribs and the rib grooves, and they rotate synchronously in the circumferential direction.

[0011] Preferably, a connecting plate is rotatably sleeved on the outer circumferential surface of the top of the second stirring shaft. The connecting plate is distributed in the horizontal direction, and its end is fixedly connected to the cylinder piston end fixed to the outside of the demulsification reaction tank.

[0012] Preferably, a support rod is fixedly connected to the center of the bottom of the grid filter in the vertical direction, and a fixed ring is fixed to the connecting point between the wastewater inlet pipe and the demulsification reaction tank through several support rods. The support rod passes through the fixed ring and is slidably connected thereto.

[0013] Preferably, the outside of the second stirring shaft is fixedly connected to the limit ring through several connecting rods, and the inside of the limit ring is provided with a 360° annular guide groove along its circumference. The top of the guide groove is open and connected to the outside of the limit ring. A pulley is rotatably installed at the bottom end of the support rod, and the pulley is embedded in the guide groove and slidably connected thereto.

[0014] Preferably, the width of the guide groove opening is smaller than the width of the interior of the groove body, and the width of the interior of the groove body is adapted to the diameter of the pulley.

[0015] Preferably, a plurality of arc-shaped liquid leakage grooves are provided at the bottom of the guide groove.

[0016] Preferably, a plurality of small blades are evenly distributed on the outer circumferential surface of the limiting ring.

[0017] Preferably, a first sprocket is fixedly sleeved on the outside of the support rod, a second sprocket is fixedly sleeved on the outside of the second stirring shaft, and a chain is sleeved between the second sprocket and the first sprocket.

[0018] Preferably, the bottom of the demulsification reaction tank is connected to the interior of the ultrafiltration membrane assembly through a first liquid pipe, the first permeate output pipe of the ultrafiltration membrane assembly is connected to an external clean water collection box, the concentrate output pipe is connected to the nanofiltration membrane assembly, the permeate outlet of the nanofiltration membrane assembly is connected to a second permeate output pipe, the second permeate output pipe is connected to the middle of the first liquid pipe, and the concentrate outlet of the nanofiltration membrane assembly is connected to an external concentrated liquid collection box.

[0019] Compared with the prior art, the present invention provides a separation and concentration device suitable for organic wastewater treatment, which has the following beneficial effects:

[0020] (1) The screen filter is lifted and rotated by the linkage of the stirring structure. When the stirring shaft rises to the highest position, the screen filter is exposed to the outside of the wastewater inlet pipe, which is convenient for quick cleaning. At the same time, the rotating screen filter can scrape off impurities attached to the inner wall of the inlet pipe to avoid blockage, reduce downtime for maintenance, and improve pretreatment efficiency.

[0021] (2) The motor drives the second stirring shaft to rotate, and the cylinder drives it to rise and fall along the axial direction, cooperating with the first stirring paddle and the small blade on the limit ring to fully stir the wastewater at different heights and different areas in the demulsification reaction tank, so that the demulsifier and the emulsion are evenly mixed, thereby improving the demulsification efficiency.

[0022] (3) The lifting and lowering of the screen filter and the movement of the agitator shaft are mechanically linked through limit rings, pulleys, sprockets and other structures, without the need for an additional power source, thus reducing energy consumption. At the same time, the rotation speed of the screen filter is optimized through the sprocket transmission ratio, which can effectively scrape off impurities while avoiding energy waste caused by excessively high rotation speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0024] Figure 1 Schematic diagram of the three-dimensional structure of the entire device in the embodiment;

[0025] Figure 2 Schematic diagram of the three-dimensional structure inside the demulsification reaction tank in the embodiment;

[0026] Figure 3 This is a schematic front cross-sectional view of the interior of the demulsification reaction tank in the embodiment;

[0027] Figure 4 Schematic diagram of the structure of the limiting ring in the embodiment;

[0028] Figure 5 Schematic diagram of the distribution of the grille filter, the first sprocket and the pulley on the support rod in the embodiment.

[0029] In the figure: 1. base; 2. demulsification reaction tank; 3. first liquid pipe; 4. ultrafiltration membrane assembly; 5. circulation pump; 6. first permeate output pipe; 7. nanofiltration membrane assembly; 8. second permeate output pipe; 9. motor; 10. wastewater inlet pipe; 11. cylinder; 12. first stirring shaft; 13. connecting plate; 14. second stirring shaft; 15. first stirring paddle; 16. limiting ring; 17. small blade; 18. support rod; 19. fixing collar; 20. first sprocket; 21. second sprocket; 22. chain; 23. rib groove; 24. guide groove; 25. arc leakage groove; 26. connecting rod; 27. grid filter; 28. pulley. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the 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. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0031] like Figure 1-5 As shown, this embodiment proposes a separation and concentration device suitable for organic wastewater treatment, including a demulsification reaction tank 2, an ultrafiltration membrane assembly 4 and a nanofiltration membrane assembly 7 fixed on a base 1, wherein the top of the base 1 is connected to a wastewater inlet pipe 10, and a grid filter 27 is provided inside the wastewater inlet pipe 10 for filtering out large particles of impurities in the wastewater. After filtration, the wastewater enters the demulsification reaction tank 2, and the top of the demulsification reaction tank 2 is connected to a dosing tank (not shown in the drawing) for adding a demulsifier to the demulsification reaction tank 2 to destroy the emulsion in the wastewater for subsequent membrane separation treatment. After being treated inside the demulsification reaction tank 2, the wastewater enters the ultrafiltration membrane assembly 4 through the first liquid pipe 3 for separation treatment. The first permeate output pipe 6 of the ultrafiltration membrane assembly 4 is connected to the external clean water collection box, and the concentrate output pipe is connected to the nanofiltration membrane assembly 7. The permeate outlet of the nanofiltration membrane assembly 7 is connected to the second permeate output pipe 8, which is connected to the middle part of the first liquid pipe 3, and a one-way valve is installed inside the second permeate output pipe 8. The one-way valve allows the permeate in the nanofiltration membrane assembly 7 to enter the first liquid pipe 3, and the concentrate outlet of the nanofiltration membrane assembly 7 is connected to the external concentrate collection box.

[0032] First of all, it should be noted that the ultrafiltration membrane assembly 4 and the nanofiltration membrane assembly 7 in this embodiment adopt currently mature technologies. The ultrafiltration membrane assembly 4 adopts a hollow fiber ultrafiltration membrane with a membrane pore size of 0.05 μm. A first pressure sensor and a first flow sensor are provided on its water inlet pipe. The nanofiltration membrane assembly 7 adopts a rolled nanofiltration membrane with a molecular weight cutoff of 500 Da. A second pressure sensor and a second flow sensor are provided on its water inlet pipe. A circulation pump 5 is provided between the concentrate outlet pipe of the ultrafiltration membrane assembly 4 and the nanofiltration membrane assembly 7. The circulation pump 5 is used to increase the water inlet pressure of the nanofiltration membrane assembly 7.

[0033] When the demulsifier inside the demulsification reaction tank 2 is mixed with the organic wastewater for reaction, in order to improve the demulsification efficiency, the present embodiment further provides a stirring structure inside the demulsification reaction tank 2. Specifically, the stirring structure includes a motor 9 fixed to the top of the outer side of the demulsification reaction tank 2, and a first stirring shaft 12 is fixedly connected to the motor shaft of the motor 9. The first stirring shaft 12 extends downward to the inside of the demulsification reaction tank 2 and is sleeved with a second stirring shaft 14. An array of first stirring paddles 15 are distributed on the circumferential surface of the second stirring shaft 14. It should be noted that at least two ribs are provided along the axial direction of the outer circumferential surface of the first stirring shaft 12, and a rib groove 23 adapted thereto is formed correspondingly on the interior of the second stirring shaft 14. The first stirring shaft 12 and the second stirring shaft 14 are provided with a plurality of stirring paddles 15. The shaft 14 is fitted with ribs and rib grooves 23, so that the two can only slide relative to each other in the axial direction, and they rotate synchronously in the circumferential direction. In addition, a connecting plate 13 is rotatably sleeved on the outer circumferential surface of the top of the second stirring shaft 14. The connecting plate 13 is distributed in the horizontal direction, and its end is fixedly connected to the piston end of the cylinder 11 fixed to the outside of the demulsification reaction tank 2. The first stirring shaft 12 and the second stirring shaft 14 are driven by the motor 9 to rotate synchronously, thereby mixing and stirring the demulsifier and organic wastewater inside the demulsification reaction tank 2, and the cylinder 11 drives the second stirring shaft 14 to move axially relative to the first stirring shaft 12, thereby stirring the systems at different heights inside the demulsification reaction tank 2, thereby increasing the stirring and mixing efficiency.

[0034] Since organic wastewater containing large-diameter particulate impurities is continuously injected into the demulsification reaction tank 2 from the wastewater inlet pipe 10, the grid filter 27 is usually distributed at the bottom of the wastewater inlet pipe 10. With this design, even if the grid filter 27 is blocked, the organic wastewater will not be immediately spilled outside the wastewater inlet pipe 10. The space from the grid filter 27 to the top of the wastewater inlet pipe 10 can be used as a buffer. When personnel find that the organic wastewater inside the wastewater inlet pipe 10 is constantly rising, it can be determined that the grid filter 27 is blocked. Although this design can prevent wastewater from spilling, another problem also arises. When the grid filter 27 is blocked, personnel need to take it out from the wastewater inlet pipe 10 for cleaning, and there may be some large particles of impurities inside the wastewater inlet pipe 10, which requires personnel to clean the inside of the wastewater inlet pipe 10. In order to facilitate personnel to clean the grid filter 27, this embodiment has a support rod 18 fixedly connected to the center of the bottom of the grid filter 27 in the vertical direction, and a fixing ring 19 is fixed at the connection point between the wastewater inlet pipe 10 and the demulsification reaction tank 2 through several support rods. The support rod 18 passes through the fixing ring 19 and is slidably connected thereto. The fixing ring 19 is mainly for the support rod The movement of 18 plays a limiting and guiding role. The outside of the second stirring shaft 14 is fixedly connected to the limiting ring 16 through several connecting rods 26. The inside of the limiting ring 16 is provided with a 360° annular guide groove 24 along its circumference. The top of the guide groove 24 is open and connected to the outside of the limiting ring 16. The bottom end of the support rod 18 is rotatably installed with a pulley 28, which is embedded in the guide groove 24 and slidably connected thereto. It should be noted that the width of the guide groove 24 at the opening is smaller than the width of the inside of the groove body, and the width of the inside of the groove body is just matched with the diameter of the pulley 28, so that the pulley 28 can be stuck in the guide groove 24, so that the support rod 18 and the limiting ring 16 can move synchronously in the vertical direction.

[0035] When the organic wastewater is injected into the demulsification reaction tank 2, the motor 9 is started to drive the first stirring shaft 12 and the second stirring shaft 14 to rotate synchronously. At the same time, the cylinder 11 drives the second stirring shaft 14 to move slowly upward in the vertical direction relative to the first stirring shaft 12. The first stirring paddle 15 stirs the liquid at different positions inside the demulsification reaction tank 2. When the second stirring shaft 14 is moving, the grid filter 27 moves upward inside the wastewater inlet pipe 10 under the action of the support rod 18. When the second stirring shaft 14 moves upward to the extreme When the screen 27 is in the limit position, the screen 27 will be exposed upward outside the wastewater inlet pipe 10. When the screen 27 moves upward inside the wastewater inlet pipe 10, it will remove the large-diameter particles accumulated inside the wastewater inlet pipe 10, and finally be exposed outside the wastewater inlet pipe 10. At this time, the cylinder 11 can be temporarily suspended, and the personnel can directly clean the screen 27 quickly. After the screen 27 is cleaned, the cylinder 11 restarts to drive the second stirring shaft 14 downward to reset the screen 27.

[0036] Furthermore, in order to facilitate the cleaning of impurities inside the wastewater inlet pipe 10 and on the grid filter 27, the present embodiment further has a first sprocket 20 fixedly sleeved on the outside of the support rod 18, and a second sprocket 21 fixedly sleeved on the outside of the second stirring shaft 14, and a chain 22 is sleeved between the second sprocket 21 and the first sprocket 20. Since the first and second stirring shafts 12 and 14 rotate rapidly inside the demulsification reaction tank 2, and the rotation of the grid filter 27 does not require such a fast rotation speed, the diameter of the first sprocket 20 can be set to be larger than the second sprocket 21, so that the rotation speed of the grid filter 27 can be reduced. The grid filter 27 is in a rotating state inside the wastewater inlet pipe 10 and is raised and lowered, which is conducive to scraping off impurities on the inner wall of the wastewater inlet pipe 10. Moreover, when the grid filter 27 is exposed outside the wastewater inlet pipe 10, when personnel clean the grid filter 27, the cleaned impurities will quickly separate from the grid filter 27 under the action of centrifugal force.

[0037] In addition, since a guide groove 24 is provided inside the limiting ring 16, in order to prevent organic wastewater from being retained inside the guide groove 24, the present embodiment further provides a plurality of arc-shaped liquid leakage grooves 25 at the bottom of the guide groove 24. The wastewater flowing into the guide groove 24 is directly sprinkled into the demulsification reaction tank 2 through the plurality of arc-shaped liquid leakage grooves 25. At the same time, although the limiting ring 16 can rotate synchronously with the second stirring shaft 14, it cannot stir the liquid inside the demulsification reaction tank 2. In view of this, the present embodiment further has a plurality of small blades 17 evenly distributed on the outer circumference of the limiting ring 16. While the limiting ring 16 rotates, it can also drive all the small blades 17 to stir the liquid inside the demulsification reaction tank 2, thereby improving the stirring efficiency of the entire system.

[0038] The operating principle of this embodiment is as follows: organic wastewater first enters the wastewater inlet pipe 10, passes through the grid filter 27 to remove large particles of impurities, and then enters the demulsification reactor 2. The dosing device adds a demulsifier (polyaluminum chloride demulsifiers used in the prior art can be selected) in proportion. The stirring mechanism inside the demulsification reactor 2 thoroughly stirs and mixes the wastewater and demulsifier, causing the wastewater to demulsify. After demulsification, the wastewater enters the ultrafiltration membrane module 4. A first pressure sensor and a first flow sensor monitor the inlet pressure and flow in real time and feed back to the PLC controller, which stabilizes the pressure at 0.1-0.15 MPa. The permeate from the ultrafiltration membrane module 4 enters the clean water collection tank, and the concentrate (containing large organic molecules) enters the nanofiltration membrane module 7.

[0039] The circulation pump 5 pumps the ultrafiltration concentrate into the nanofiltration membrane assembly 7. The second pressure sensor and the second flow sensor monitor the water inlet pressure (controlled at 0.5-0.6 MPa) and flow rate. The permeate of the nanofiltration membrane assembly 7 (containing some small molecular organic matter and water) flows back to the ultrafiltration membrane assembly 4 for reprocessing, and the concentrate (high concentration of organic matter) enters the concentrate collection tank.

[0040] In the description of the present invention, the terms "first," "second," "another," and "yet another" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more features. In the description of the embodiments of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0041] In the description of the present invention, it should be noted that, unless otherwise specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, it can mean a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood in specific circumstances. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0042] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A separation and concentration device suitable for treating organic wastewater, comprising a demulsification reaction tank (2), an ultrafiltration membrane assembly (4) and a nanofiltration membrane assembly (7) fixed on a base (1), characterized in that: The top of the base (1) is connected to a wastewater inlet pipe (10), a grid filter (27) is provided inside the wastewater inlet pipe (10), a stirring structure is provided inside the demulsification reaction tank (2), and the stirring structure reciprocates along its axial direction inside the demulsification reaction tank (2), the grid filter (27) slides inside the wastewater inlet pipe (10) following the stirring structure, and when the stirring structure moves upward to the highest position inside the demulsification reaction tank (2), the grid filter (27) moves outside the wastewater inlet pipe (10).

2. A separation and concentration device suitable for treating organic wastewater according to claim 1, characterized in that: The stirring structure comprises a motor (9) fixed on the top of the outer side of the demulsification reaction tank (2); a first stirring shaft (12) is fixedly connected to the motor shaft of the motor (9); the first stirring shaft (12) extends downward to the interior of the demulsification reaction tank (2) and is then sleeved with a second stirring shaft (14); and an array of first stirring paddles (15) are distributed on the circumferential surface of the second stirring shaft (14); At least two ribs are provided on the outer circumferential surface of the first stirring shaft (12) along its axial direction, and a rib groove (23) adapted thereto is correspondingly formed inside the second stirring shaft (14). The first stirring shaft (12) and the second stirring shaft (14) can only slide relative to each other in the axial direction through the cooperation of the ribs and the rib groove (23), and can rotate synchronously in the circumferential direction.

3. A separation and concentration device suitable for treating organic wastewater according to claim 2, characterized in that: A connecting plate (13) is rotatably sleeved on the outer circumferential surface of the top of the second stirring shaft (14). The connecting plate (13) is distributed in the horizontal direction, and its end is fixedly connected to the piston end of the cylinder (11) fixed outside the demulsification reaction tank (2).

4. A separation and concentration device suitable for treating organic wastewater according to claim 3, characterized in that: A support rod (18) is fixedly connected to the center of the bottom of the grid filter (27) in the vertical direction. A fixed collar (19) is fixed to the connection point between the wastewater inlet pipe (10) and the demulsification reaction tank (2) through several support rods. The support rod (18) passes through the fixed collar (19) and is slidably connected thereto.

5. A separation and concentration device suitable for treating organic wastewater according to claim 4, characterized in that: The outside of the second stirring shaft (14) is fixedly connected to the limiting ring (16) through several connecting rods (26). The inside of the limiting ring (16) is provided with a 360° annular guide groove (24) along its circumference. The top of the guide groove (24) is open and communicates with the outside of the limiting ring (16). The bottom end of the support rod (18) is rotatably mounted with a pulley (28), which is embedded in the guide groove (24) and slidably connected thereto.

6. The separation and concentration device for treating organic wastewater according to claim 5, characterized in that: The width of the opening of the guide groove (24) is smaller than the width of the interior of the groove body, and the width of the interior of the groove body is adapted to the diameter of the pulley (28).

7. The separation and concentration device for treating organic wastewater according to claim 5, characterized in that: The bottom of the guide groove (24) is provided with a plurality of arc-shaped liquid leakage grooves (25).

8. The separation and concentration device for treating organic wastewater according to claim 7, characterized in that: A plurality of small blades (17) are evenly distributed on the outer circumference of the limiting ring (16).

9. A separation and concentration device suitable for treating organic wastewater according to any one of claims 4 to 8, characterized in that: The outside of the support rod (18) is fixedly sleeved with a first sprocket (20), the outside of the second stirring shaft (14) is fixedly sleeved with a second sprocket (21), and a chain (22) is sleeved between the second sprocket (21) and the first sprocket (20).

10. The separation and concentration device for treating organic wastewater according to claim 1, characterized in that: The bottom of the demulsification reaction tank (2) is connected to the interior of the ultrafiltration membrane assembly (4) through the first liquid pipe (3), the first permeate output pipe (6) of the ultrafiltration membrane assembly (4) is connected to the external clean water collection box, the concentrated liquid output pipe is connected to the nanofiltration membrane assembly (7), the permeate outlet of the nanofiltration membrane assembly (7) is connected to the second permeate output pipe (8), the second permeate output pipe (8) is connected to the middle of the first liquid pipe (3), and the concentrated liquid outlet of the nanofiltration membrane assembly (7) is connected to the external concentrated liquid collection box.

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