A low-pressure high-efficiency wastewater concentration system based on a reverse osmosis membrane group

Abstract

This invention proposes a low-pressure, high-efficiency wastewater concentration system based on reverse osmosis membrane modules, relating to the field of wastewater treatment technology. The system includes a first-stage reverse osmosis membrane module and multiple second-stage reverse osmosis membrane modules. The second concentrate outlet of any second-stage reverse osmosis membrane module is connected to the second inlet of its adjacent second-stage reverse osmosis membrane module. The second inlet of the first-end second-stage reverse osmosis membrane module is connected to the first concentrate outlet. A forward osmosis membrane module is installed at the second outlet of any second-stage reverse osmosis membrane module, and its third inlet is connected to both the second outlet and the second concentrate outlet. Each diluent outlet is connected to the first inlet. A differential pressure fluid is introduced between the third inlet and its corresponding second outlet. This invention ensures a stable osmotic pressure difference across the second-stage reverse osmosis membrane module under low external pressure, thereby achieving efficient wastewater concentration and recovery.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more specifically, to a low-pressure, high-efficiency wastewater concentration system based on reverse osmosis membrane modules. Background Technology

[0002] Reverse osmosis technology, as a highly efficient water treatment method, has been widely used in the deep concentration and zero-discharge processes of high-salinity wastewater. Its core principle is to force water molecules through a semi-permeable membrane by applying external pressure exceeding the osmotic pressure of the wastewater, thereby separating salt from water. However, as the reverse osmosis process proceeds, the total dissolved solids concentration on the concentration side of the membrane module continuously increases, leading to a sharp increase in its osmotic pressure. To overcome this rising osmotic pressure and maintain the permeate flux, the system must apply higher operating pressures, which directly results in a significant increase in energy consumption, constituting a major part of the operating costs in zero-discharge wastewater treatment.

[0003] To further improve system recovery rates and reduce the discharge of final concentrate, multi-stage reverse osmosis systems have emerged. These systems send the concentrate from primary reverse osmosis to subsequent, higher-pressure reverse osmosis membrane modules for further concentration. While this method improves the overall recovery rate, each stage must independently overcome the high osmotic pressure of its corresponding feed water, necessitating the use of high-pressure pumps between stages, significantly increasing system energy consumption and equipment complexity. This is especially true for the final stage of reverse osmosis, where the feed water is the extremely high-concentration concentrate from the preceding stages, with already very high osmotic pressure. This forces the final stage to operate under exceptionally high pressure, placing stringent demands on the mechanical strength and chemical stability of the membrane elements and severely limiting further improvements in system recovery rates and economic efficiency.

[0004] In existing technologies, a portion of the concentrate is recirculated back to the effluent side of the preceding reverse osmosis membrane to increase the solution concentration on that side, thereby reducing the osmotic pressure difference across the reverse osmosis membrane. This allows for the application of a lower external pressure to the high-concentration solution side of the reverse osmosis membrane, further concentrating the wastewater. However, in this process, the concentrate is directly recirculated to the effluent side of the reverse osmosis membrane, and the solution on that side flows to the next component. This makes it difficult to effectively control the solution concentration on the effluent side, leading to instability in the osmotic pressure difference across the reverse osmosis membrane. In extreme cases, the recirculated concentrate may even be directly fed into the next component, failing to achieve the goal of increasing the solution concentration on the effluent side. This can easily result in a decrease in wastewater concentration and recovery efficiency. Therefore, a concentration system is needed that can stably control the osmotic pressure difference across the reverse osmosis membrane, ensuring efficient wastewater concentration and recovery under low external pressure across multiple reverse osmosis membrane stages. Summary of the Invention

[0005] The purpose of this invention is to provide a low-pressure, high-efficiency wastewater concentration system based on a reverse osmosis membrane module, which can ensure the stability of the osmotic pressure difference across the second-stage reverse osmosis membrane module under low external pressure conditions, thereby enabling efficient concentration and recovery of wastewater.

[0006] The embodiments of the present invention are implemented as follows:

[0007] This application provides a wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules, including a primary reverse osmosis module and a secondary reverse osmosis module connected in series. The primary reverse osmosis module includes a first section of reverse osmosis membrane modules, which are provided with a first inlet, a first concentrate outlet and a first outlet.

[0008] The secondary reverse osmosis module includes multiple second-stage reverse osmosis membrane units connected in series. Each second-stage reverse osmosis membrane unit is provided with a second inlet, a second concentrate outlet, and a second outlet. The second concentrate outlet of any second-stage reverse osmosis membrane unit is connected to the second inlet of its adjacent second-stage reverse osmosis membrane unit. The second inlet of the first-end second-stage reverse osmosis membrane unit is connected to the first concentrate outlet.

[0009] A forward osmosis membrane group is provided at the second outlet of any of the second-stage reverse osmosis membrane groups. The forward osmosis membrane group is provided with a third inlet and a diluent outlet. The third inlet is connected to the second outlet of the corresponding second-stage reverse osmosis membrane group, and the diluent outlet is connected to the second concentrate outlet of the corresponding second-stage reverse osmosis membrane group. This is used to return a portion of the concentrate at the second concentrate outlet to the corresponding diluent outlet side. Each diluent outlet is connected to the first inlet.

[0010] A differential pressure liquid is introduced between the third inlet and its corresponding second outlet. The concentration of the differential pressure liquid is lower than the concentration of the concentrate at the corresponding second inlet side and higher than the concentration at the corresponding diluent outlet side.

[0011] In some embodiments of the present invention, a liquid conditioning chamber is connected in series between the third liquid inlet and its corresponding second water outlet, and the liquid conditioning chamber contains the differential pressure liquid.

[0012] In some embodiments of the present invention, the above-mentioned liquid preparation chamber is provided with a concentration adjustment component, which is used to adjust the concentration of the differential pressure liquid.

[0013] In some embodiments of the present invention, the concentration adjustment component includes an ionization device disposed in the liquid adjustment chamber. The ionization device includes a positive electrode and a negative electrode that can be electrically ionized from each other, and both the positive electrode and the negative electrode are disposed in the liquid adjustment chamber.

[0014] In some embodiments of the present invention, a first particle filter is provided between the liquid conditioning chamber and its corresponding third liquid inlet, and a second particle filter is provided between the liquid conditioning chamber and its corresponding second water outlet.

[0015] In some embodiments of the present invention, the first particle filter and the second particle filter are both filter plate structures, and the two filter plate structures are end caps at both ends of the liquid conditioning chamber.

[0016] In some embodiments of the present invention, a three-way proportional valve is provided between each second concentrate outlet and its corresponding second inlet. The three-way proportional valve includes an inlet end, a first outlet end and a second outlet end. The inlet end is connected to its corresponding second concentrate outlet, the first outlet end is connected to its corresponding second inlet end, and the second outlet end is connected to its corresponding diluent outlet of the forward osmosis membrane module.

[0017] In some embodiments of the present invention, the above-mentioned three-way proportional valve is an adjustable proportional valve.

[0018] In some embodiments of the present invention, an ultrafiltration component and a nanofiltration component are connected in series, and the first inlet is connected to the concentrate outlet of the nanofiltration component.

[0019] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects:

[0020] This invention provides a low-pressure, high-efficiency wastewater concentration system based on reverse osmosis membrane modules. After wastewater is introduced into the first inlet of a first-stage reverse osmosis membrane module, an external pressure is applied near the first inlet, causing a portion of the wastewater to be discharged through the first outlet. The pre-concentrated wastewater then enters the corresponding next second-stage reverse osmosis membrane module through the first concentrate outlet. External pressure is then applied to the second inlet of the second-stage reverse osmosis membrane module, causing wastewater to enter through the second inlet. A portion of the wastewater is discharged through the second outlet, while the further concentrated wastewater enters the second inlet of the next second-stage reverse osmosis membrane module. This process is repeated multiple times to obtain high-concentration wastewater. During this process, a portion of the concentrate discharged from the second concentrate outlet of any second-stage reverse osmosis membrane module is returned to the corresponding diluent outlet of that second-stage reverse osmosis membrane module. The concentrate flowing back from the diluent outlet increases the solution concentration on that side of the forward osmosis membrane module. Simultaneously, the water discharged from the corresponding second outlet dilutes and reduces the differential liquid concentration on the other side of the forward osmosis membrane module. This dynamically compensates for the differential liquid concentration, maintaining a dynamic equilibrium. Maintaining this dynamic equilibrium effectively ensures a stable osmotic pressure difference across the second-stage reverse osmosis membrane module under low-pressure external conditions, enabling efficient wastewater concentration and recovery. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the planar structure rotated 90° according to an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the installation structure of the ionization device in an embodiment of the present invention.

[0024] Icons: 1-First stage reverse osmosis membrane module; 2-Second stage reverse osmosis membrane module; 3-First inlet; 4-First concentrate outlet; 5-First outlet; 6-Second inlet; 7-Second concentrate outlet; 8-Second outlet; 9-Third inlet; 10-Dilution outlet; 11-Adjusting chamber; 12-Positive electrode; 13-Negative electrode; 14-End cap; 15-Three-way proportional valve; 16-Inlet end; 17-First outlet end; 18-Second outlet end; 19-Ultrafiltration module; 20-Nanofiltration module; 21-Forward osmosis membrane module; 22-Ionization device. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0027] Example

[0028] Please refer to Figure 1 and Figure 2 This embodiment provides a low-pressure, high-efficiency wastewater concentration system based on reverse osmosis membrane modules, including a primary reverse osmosis module and a secondary reverse osmosis module connected in series. The primary reverse osmosis module includes a first reverse osmosis membrane module 1, which is provided with a first inlet 3, a first concentrate outlet 4, and a first outlet 5. The secondary reverse osmosis module includes multiple second reverse osmosis membrane modules 2 connected in series. Each second reverse osmosis membrane module 2 is provided with a second inlet 6, a second concentrate outlet 7, and a second outlet 8. The second concentrate outlet 7 of any second reverse osmosis membrane module 2 is connected to the second inlet 6 of its adjacent second reverse osmosis membrane module 2. The second inlet 6 of the first second reverse osmosis membrane module 2 is connected to the first concentrate outlet 4. A forward osmosis membrane module 21 is installed at the second outlet of any second-stage reverse osmosis membrane module 2. The forward osmosis membrane module 21 has a third inlet 9 and a diluent outlet 10. The third inlet 9 is connected to the second outlet of the corresponding second-stage reverse osmosis membrane module 2, and the diluent outlet 10 is connected to the second concentrate outlet 7 of the corresponding second-stage reverse osmosis membrane module 2, used to return a portion of the concentrate from the second concentrate outlet 7 to the corresponding diluent outlet 10. Each diluent outlet 10 is connected to the first inlet 3. A differential pressure liquid is introduced between the third inlet 9 and its corresponding second outlet 8. The concentration of the differential pressure liquid is lower than the concentrate concentration at its corresponding second inlet 6 but higher than the concentration at its corresponding diluent outlet 10.

[0029] In actual operation, wastewater first enters through the first inlet 3 of the first-stage reverse osmosis membrane module 1. External primary pressure is applied to the first-stage reverse osmosis membrane module 1 located on the side of the first inlet 3, and some of the wastewater will be discharged through the first outlet for further treatment or recycling. The concentrated primary wastewater will flow out through the first concentrate outlet 4 and enter the second inlet 6 of the second-stage reverse osmosis membrane module 2 located at the beginning.

[0030] External pressure is applied to the second inlet 6 of the first reverse osmosis membrane module. Primary wastewater enters through the second inlet 6 of the second reverse osmosis membrane module 2. Part of the primary wastewater is discharged through the second outlet 8, while the further concentrated wastewater enters the second inlet 6 of the next second reverse osmosis membrane module 2. This process is repeated to concentrate the wastewater to obtain a high concentration. During this process, a portion of the concentrate discharged from the second concentrate outlet 7 of any second reverse osmosis membrane module 2 flows back to the corresponding diluent outlet 10. The concentrate flowing back to the diluent outlet 10 increases the solution concentration on that side of the forward osmosis membrane module 21. Simultaneously, the water discharged from the corresponding second outlet 8 dilutes and reduces the differential liquid concentration on the other side of the forward osmosis membrane module 21. Thus, by ensuring that the differential liquid concentration is lower than the concentrate concentration at its corresponding second inlet 6 and higher than the concentration at its corresponding diluent outlet 10, the differential liquid concentration can be relatively stable. Under the above conditions, the differential pressure concentration can be dynamically compensated through external means, bringing the differential pressure concentration towards dynamic equilibrium. Maintaining dynamic equilibrium of the differential pressure concentration effectively ensures the stability of the osmotic pressure difference across the second-stage reverse osmosis membrane module 2 under the influence of an external low-pressure environment, thereby enabling efficient concentration and recovery of wastewater.

[0031] In the above process, the mixture of the corresponding concentrated primary wastewater at each diluent outlet 10 is recycled to the first inlet 3 of the first-stage reverse osmosis membrane module 1, allowing the primary wastewater to be concentrated again. The entire system achieves efficient wastewater concentration treatment under low-pressure conditions through this combination of multi-stage reverse osmosis and forward osmosis. All permeate from the entire system is discharged through the first outlet of the first-stage reverse osmosis membrane module 1.

[0032] Please refer to Figure 1 and Figure 2 Specifically, a liquid conditioning chamber 11 is connected in series between the third inlet 9 and its corresponding second outlet 8. The liquid conditioning chamber 11 is equipped with a concentration detection device for real-time detection of the concentration of the differential pressure liquid within the chamber. When a change in the differential pressure liquid concentration is detected, dynamic adjustment can be made to compensate for the change.

[0033] Please refer to Figure 1 and Figure 2Furthermore, in order to dynamically compensate for the differential pressure fluid concentration through external action, the above-mentioned fluid adjustment chamber 11 is equipped with a concentration adjustment component, which is used to adjust the concentration of the differential pressure fluid.

[0034] Please refer to Figure 1 and Figure 2 Specifically, the concentration adjustment component includes an ionization device 22, which is disposed in the liquid adjustment chamber 11. The ionization device 22 includes a positive electrode 12 and a negative electrode 13 that can be electrically ionized from each other. Both the positive electrode 12 and the negative electrode 13 are disposed in the liquid adjustment chamber 11.

[0035] When it is necessary to adjust the concentration of the differential pressure liquid in the adjustment chamber 11, the positive electrode 12 and negative electrode 13 of the ionization device 22 can be energized. Under the action of the electric field, the ions in the differential pressure liquid will move in a directional manner, and some ions may form crystals that attach to the positive electrode 12 or negative electrode 13, thereby changing the concentration of ions in the differential pressure liquid and thus achieving the purpose of adjusting the concentration of the differential pressure liquid. For example, when the concentration of the differential pressure liquid is detected to be too high, some ions can be precipitated by controlling the ionization device 22 to reduce the concentration of the differential pressure liquid; when the concentration of the differential pressure liquid is detected to be too low, the ionization process can be appropriately adjusted to reduce the amount of ion precipitation or to increase the amount of ions that have been precipitated by reversing the current to allow the attached crystals to reform into ions, thereby increasing the concentration of the differential pressure liquid. In this way, the concentration of the differential pressure liquid can be restored to a suitable range to maintain the stable operation of the entire wastewater concentration system.

[0036] In other embodiments, the concentration adjustment component described above can also be other structures, such as a temperature adjustment component that uses temperature difference to adjust the saturation of differential pressure liquid, thereby adjusting the concentration of differential pressure liquid by adjusting the saturation of differential pressure liquid.

[0037] This embodiment uses sodium-containing wastewater as an example. Existing commercial reverse osmosis membranes (mainly polyamide composite membranes) have extremely high rejection rates for both monovalent sodium ions and divalent copper ions. This means that the second-stage reverse osmosis membrane module 2 can effectively "lock" sodium and copper ions on their respective sides, allowing only water molecules to pass through. In practice, the copper-containing solution is "locked" in the adjustment chamber 11 as a differential pressure solution, while preventing sodium ions from entering the adjustment chamber 11. Thus, the concentration of the differential pressure solution can be adjusted by regulating the content of copper ions in the differential pressure solution through ionization.

[0038] Please refer to Figure 2 In some application scenarios, a first particle filter is installed between the liquid conditioning chamber 11 and its corresponding third inlet 9, and a second particle filter is installed between the liquid conditioning chamber 11 and its corresponding second outlet 8. The first and second particle filters are used to prevent particles from approaching and entering the second reverse osmosis membrane module 2 or the forward osmosis membrane module 21 during ionization, thus avoiding damage to the second reverse osmosis membrane module 2 or the forward osmosis membrane module 21.

[0039] Specifically, both the first and second particulate filters mentioned above are filter plate structures, with the two filter plate structures serving as end caps 14 at both ends of the liquid mixing chamber 11. Each of these filter plate structures has multiple filter holes, the size of which is set according to actual needs, ensuring both the smooth passage of water molecules and effective interception of particulate matter. Furthermore, the filter plate structures are sealed to the end caps 14 of the liquid mixing chamber 11 to prevent leakage and further ensure the normal operation of the system.

[0040] Please refer to Figure 1 In some embodiments of this example, a three-way proportional valve 15 is provided between each second concentrate outlet 7 and its corresponding second inlet 6. The three-way proportional valve 15 includes an inlet end 16, a first outlet end 17, and a second outlet end 18. The inlet end 16 is connected to its corresponding second concentrate outlet 7, the first outlet end 17 is connected to its corresponding second inlet 6, and the second outlet end 18 is connected to the diluent outlet 10 of its corresponding forward osmosis membrane module 21. Specifically, the three-way proportional valve 15 is an adjustable proportional valve.

[0041] In practice, the aforementioned three-way proportional valve 15 allows for flexible adjustment of the liquid flow direction and flow rate according to actual needs. When the system is running, controlling the three-way proportional valve 15 precisely controls the amount of concentrate entering the second inlet 6 and the amount of concentrate flowing into the diluent outlet 10 of the forward osmosis membrane module 21. Thus, the amount of concentrate flowing into the diluent outlet 10 of the forward osmosis membrane module 21 can be adjusted according to actual requirements.

[0042] Please refer to Figure 1 In this embodiment, the wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules further includes an ultrafiltration module 19 and a nanofiltration module 20 connected in series. The first inlet 3 is connected to the concentrate outlet of the nanofiltration module 20. The ultrafiltration module 19 can effectively trap large molecules, colloids, particles, and bacteria in the water, performing preliminary purification treatment on the wastewater and reducing its turbidity and suspended solids content. The nanofiltration module 20 further filters the water after ultrafiltration, trapping substances with relatively small molecular weights, such as some divalent ions and organic matter, thereby further improving water quality and reducing the processing burden on the subsequent reverse osmosis membrane modules. The first inlet 3 is connected to the concentrate outlet of the nanofiltration module 20, allowing the concentrate produced after nanofiltration to smoothly enter the subsequent reverse osmosis membrane modules for further concentration treatment, forming a complete and efficient wastewater treatment process, improving the overall system's concentration efficiency and treatment effect.

[0043] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-pressure, high-efficiency wastewater concentration system based on reverse osmosis membrane modules, comprising a primary reverse osmosis module and a secondary reverse osmosis module connected in series, characterized in that, The primary reverse osmosis component includes a first reverse osmosis membrane module, which is provided with a first liquid inlet, a first concentrate outlet and a first water outlet. The secondary reverse osmosis module includes multiple second-stage reverse osmosis membrane units connected in series. Each second-stage reverse osmosis membrane unit is provided with a second inlet, a second concentrate outlet, and a second outlet. The second concentrate outlet of any second-stage reverse osmosis membrane unit is connected to the second inlet of its adjacent second-stage reverse osmosis membrane unit. The second inlet of the first-end second-stage reverse osmosis membrane unit is connected to the first concentrate outlet. A forward osmosis membrane group is provided at the second outlet of any of the second-stage reverse osmosis membrane groups. The forward osmosis membrane group is provided with a third inlet and a diluent outlet. The third inlet is connected to the second outlet of the corresponding second-stage reverse osmosis membrane group, and the diluent outlet is connected to the second concentrate outlet of the corresponding second-stage reverse osmosis membrane group. This is used to return a portion of the concentrate at the second concentrate outlet to the corresponding diluent outlet side. Each diluent outlet is connected to the first inlet. A differential pressure liquid is introduced between the third inlet and its corresponding second outlet. The concentration of the differential pressure liquid is lower than the concentration of the concentrate at the corresponding second inlet side and higher than the concentration at the corresponding diluent outlet side.

2. The wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules according to claim 1, characterized in that, A liquid conditioning chamber is connected in series between the third liquid inlet and its corresponding second water outlet, and the liquid conditioning chamber contains the differential pressure liquid.

3. The wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules according to claim 2, characterized in that, The mixing chamber is equipped with a concentration adjustment component, which is used to adjust the concentration of the differential pressure liquid.

4. The wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules according to claim 3, characterized in that, The concentration adjustment component includes an ionization device disposed in the liquid adjustment chamber. The ionization device includes a positive electrode and a negative electrode capable of ionization by electricity, both of which are disposed in the liquid adjustment chamber.

5. The wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules according to claim 4, characterized in that, A first particle filter is provided between the liquid conditioning chamber and its corresponding third liquid inlet, and a second particle filter is provided between the liquid conditioning chamber and its corresponding second water outlet.

6. The wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules according to claim 5, characterized in that, Both the first particle filter and the second particle filter are filter plate structures, and the two filter plate structures are end caps at both ends of the liquid conditioning chamber.

7. The wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules according to any one of claims 1-6, characterized in that, A three-way proportional valve is provided between each of the second concentrate outlets and its corresponding second inlet. The three-way proportional valve includes an inlet end, a first outlet end, and a second outlet end. The inlet end is connected to its corresponding second concentrate outlet, the first outlet end is connected to its corresponding second inlet end, and the second outlet end is connected to its corresponding diluent outlet of the forward osmosis membrane module.

8. The wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules according to claim 7, characterized in that, The three-way proportional valve is an adjustable proportional valve.

9. The wastewater low-pressure high-efficiency concentration system based on reverse osmosis membrane modules according to claim 1, characterized in that, It also includes an ultrafiltration unit and a nanofiltration unit connected in series, with the first inlet connected to the concentrate outlet of the nanofiltration unit.

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