CN104192947B - A kind of method suppressing membrane component fouling during brackish water desalination - Google Patents

Abstract

The invention discloses a method for inhibiting fouling of membrane elements in the process of desalination of brackish water. The key points of the technical solution of the invention are: respectively monitoring the membrane shell at the end stage through an adaptive non-in-situ inorganic scale monitoring device and a scaling prediction device The critical fouling condition is reached on the membrane surface of the membrane element on the inner concentrated water side and inorganic scaling is predicted to occur on the membrane surface of the membrane element on the concentrated water side of the last stage, so as to realize the reversal of the influent fluid and destroy the concentration boundary layer formed on the surface of the membrane element. In turn, the fouling on the surface of the membrane element is inhibited, and the recovery rate of the product water is maximized.

Description

A method for inhibiting fouling of membrane elements during desalination of brackish water

technical field

The invention belongs to the technical field of desalination of brackish water, and in particular relates to a method for inhibiting fouling of membrane elements during the desalination of brackish water.

Background technique

The acquisition of fresh water resources is a major environmental and survival issue facing mankind, and all countries attach great importance to technology research and development and investment in this area. Groundwater brackish water accounts for more than half of groundwater resources in the global water balance, and this type of unconventional water resource is increasingly recognized as a potentially important and alternative source of drinking water in the near future. Common brackish water desalination processes include: reverse osmosis, nanofiltration, forward osmosis, and electrodialysis. These membrane separation processes use the operating pressure gradient as the driving force without a large amount of heat energy change. They are energy-saving, continuous operation, and easy to automate. characteristics, so it is more and more popular. At present, reverse osmosis desalination technology for brackish water is the most common in industrial applications.

Usually in the desalination process of reverse osmosis brackish water, the membrane elements are easily polluted by certain pollutants in the feed water, resulting in a decrease in separation performance and an increase in operating costs. The brackish water is mostly taken from deep underground wells. After filtering through multi-media (sand, clay and rocks, etc.), many particulate matter and some organic matter in the feed water are removed, and with the advancement of membrane pretreatment technology, colloid, Suspended solids and most microorganisms can be more effectively removed by the ultrafiltration membrane, and organic matter, especially macromolecular organic matter, can be mostly retained by the ultrafiltration membrane. In addition, the salt content of total dissolved solids in seawater is mainly composed of monovalent Na ⁺ and Cl ⁻ , while the salt content of total dissolved solids in brackish water is usually composed of divalent scaling ions Ca ²⁺ , CO ₃ ^{2 −} and SO ₄ ^{2 −} composition. In reverse osmosis brackish water desalination process, the concentration factor of dissolved inorganic salts is generally between 4-10. Therefore, the most likely problem encountered in the process of reverse osmosis brackish water desalination is the inorganic fouling on the membrane surface, and inorganic fouling is the most important factor affecting the recovery rate and desalination cost of membrane brackish water desalination. Therefore, it is of great significance to develop a new process to increase the recovery rate of produced water and inhibit inorganic scaling on the membrane surface in the process of desalination of brackish water, which is of great significance for greatly reducing the cost of produced water.

Publication No. US 5690829 discloses a countercurrent process for cleaning dust particles on the membrane surface. After the countercurrent operation is adopted, the outlet section of the final membrane module with the most serious accumulation of dust particles can be physically flushed by the raw water, and the conventional pretreatment device placed in front of the membrane separation module can be eliminated, thereby reducing the area occupied by the system process and water production costs. The disadvantage of this technology is that it does not take into account the complexity of the influent composition and the specific pollution causes of different pollutants on the membrane surface, and it also does not take into account the precise critical conditions for cleaning the dust particles on the membrane surface and starting the counterflow process. The patent with the publication number of CN 101053776A discloses a flow direction switching method for retarding fouling of reverse osmosis membranes in the presence of antiscalants. Several membrane shells are connected in series to form a reverse osmosis unit. During the operation of the reverse osmosis system, within a time interval shorter than the membrane fouling induction period, the flow direction of the raw water in the membrane unit is alternately changed to destroy the high-concentration boundary layer established on the membrane surface, prolong the fouling induction period, and thereby inhibit For reverse osmosis membrane fouling, the permeability coefficient of the last membrane shell is calculated by monitoring, and then the degree of retardation of membrane fouling is obtained. The disadvantage of this technology is that it does not take into account the absolute existence of the concentration polarization phenomenon during the operation of the reverse osmosis membrane element, ignores the difference in fouling tendency between the bulk solution at both ends of the membrane element and the membrane surface, and uses the membrane water flow rate or permeation The coefficient drop is used as a monitoring method to characterize the fouling of the reverse osmosis membrane, which confuses the concept of membrane fouling and inorganic fouling on the membrane surface, including inorganic pollution, organic pollution, microbial pollution and colloidal particle pollution, so that the calculation results lack rigorous science sex. In addition, the necessary step of adding antiscalant increases the cost of pretreatment process and environmental pollution.

Patents with publication numbers CN 102294174A, CN 102712512A, and CN 101754934A respectively disclose chemical cleaning methods for reverse osmosis membranes, which reduce membrane fouling to varying degrees; they are used to improve the permeability of membrane filtration systems, especially in water or wastewater treatment processes A method for controlling membrane fouling by means of a flux and a composition; a method for adjusting various process variables in a membrane bioreactor system for controlling fouling of a membrane filter. These methods all achieve the purpose of inhibiting inorganic fouling on the reverse osmosis membrane surface by changing operating parameters and increasing chemical cleaning.

Contents of the invention

The present invention provides a method for inhibiting fouling of membrane elements in the brackish water desalination process in order to solve the prominent problem of fouling on the reverse osmosis membrane surface when increasing the recovery rate of produced water in the existing membrane process for desalination of brackish water .

The technical solution of the present invention is: a method for inhibiting fouling of membrane elements in the process of desalination of brackish water, which is characterized in that it comprises the following steps:

(1) After the raw water of brackish water is pretreated by multi-media filtration or membrane method, it meets the requirements of SDI15≤3.0 and turbidity≤0.01NTU before entering the water inlet tank of the membrane desalination device;

(2) Connect 3-12 membrane shells in series to form a multi-stage reverse osmosis module. The inlet and outlet ends of each membrane shell are respectively equipped with anti-retraction rings to fix the membrane elements in the membrane shells. The membrane elements are reverse osmosis membranes or Nanofiltration membrane, multi-stage reverse osmosis modules are arranged in a conical shape, the concentrated water in the first and last sections of the multi-stage reverse osmosis module is connected to the reverse osmosis high-pressure pump, security filter, booster pump and membrane desalination device in turn through valves. box, and the concentrated water in the first and last membrane shells of the multi-stage reverse osmosis module respectively flows into the reverse osmosis concentrated water discharge channel through valves, and the reverse osmosis concentrated water discharge channel is respectively connected with self-adaptive non-in-situ inorganic scale through valves. Monitoring device and scaling prediction device, in which the self-adaptive non-in-situ inorganic scale monitoring device is composed of a plate-and-frame RO membrane pool with a size of 7.5cm×2.5cm×2.7mm;

(3) Connect the permeate pipes of each branch membrane shell in the multi-stage reverse osmosis module, merge into the water production channel of the membrane method brackish water desalination system, and finally enter the desalination water tank;

(4) Run the system, start the reverse osmosis high-pressure pump, the raw water flows in the forward direction in the multi-stage reverse osmosis module, that is, it flows in from the first membrane shell and flows out from the last membrane shell, and the permeate enters the desalination water tank, and the concentrated water is used Physical flushing of pretreatment devices;

(5) When the adaptive non-in-situ inorganic scale monitoring device and the scaling prediction device respectively monitor that the membrane surface of the membrane element on the concentrated water side in the last membrane shell reaches the critical scaling condition and predict that the membrane on the concentrated water side of the last stage will When inorganic fouling occurs on the membrane surface of the element, the influent fluid reversal process is started to change the flow direction of the raw water in the multi-stage reverse osmosis module and flow in the reverse direction, that is, the raw water flows in from the last membrane shell and flows out from the first membrane shell. The permeate enters the desalinated water tank, and the concentrated water is used for physical flushing of the pretreatment device. The realization process of the adaptive non-situ inorganic scale monitoring device and the scaling prediction device are as follows: every 5 minutes, using scanning electron microscopy-energy dispersive The spectrum analyzes the morphology, qualitative and quantitative analysis of the inorganic crystals on the membrane surface in the plate and frame RO membrane tank, and accurately judges whether there is scaling on the membrane surface. The type RO membrane tank realizes self-adaptive monitoring of the inorganic scaling on the membrane surface of the concentrated water side in the first membrane shell; every 2 minutes, the scale ion activity is calculated according to the influent composition of the plate and frame RO membrane tank, combined with Concentration polarization theory, predicting the presence or absence of scaling on the membrane surface of the concentrated water side, when the Langelier index LSI or the Steve & Davy stability index S&DSI at the membrane surface of the concentrated water side is greater than zero, or based on the Pitzer Electrolyte solution theory predicts that when the supersaturation index SI of refractory salts on the membrane surface of the concentrated water side is greater than 1, it indicates the occurrence of critical scaling conditions;

(6) When the influent fluid reverses the process and runs until the self-adaptive non-in-situ inorganic scale monitoring device and the scaling prediction device respectively monitor that the membrane surface of the concentrated water side membrane element in the first branch membrane shell reaches the critical scaling condition and predict When inorganic scaling occurs on the membrane surface of the membrane element on the concentrated water side in the last stage, the periodic feedwater fluid reversal process is started again to destroy the concentration boundary layer formed on the surface of the membrane element, thereby inhibiting the surface scaling of the membrane element and maximizing the production. Water recovery.

The reverse osmosis membrane or nanofiltration membrane described in the present invention is the membrane element of commercial diameter 8 inches, 4 inches or 2.5 inches, and the type of inorganic fouling is reverse osmosis membrane or nanofiltration membrane concentrated water side or membrane surface CaCO ₃ , Inorganic salt precipitation of CaSO ₄ , BaSO ₄ , SrSO ₄ , Ca ₃ (PO ₄ ) ₂ , metal oxides or silicon deposits.

The operating temperature of the multistage reverse osmosis module described in the present invention is 0-60°C.

Compared with the prior art, the present invention has the following obvious advantages: First, based on the inorganic fouling problem on the membrane surface that is most likely to be encountered in the membrane process of brackish water desalination, the self-adaptive non-situ inorganic scale monitoring and prediction The method and the deep coupling of the self-adaptive influent fluid reversal process have achieved a recovery rate of more than 85% of the system's water production without the risk of scaling, further reduced the cost of water production, and increased the recovery rate of the system's water production by more than 10% compared with traditional technologies The second is to periodically change the flow direction of the influent water in the multi-stage reverse osmosis module, so that the membrane element with the largest fouling potential is self-adaptively exposed to the influent water environment that is far from saturated, which may have formed in the last stage. The inorganic scale on the water side or the membrane surface is dissolved; the third is to consider the concentration polarization phenomenon during the operation of the roll-type reverse osmosis membrane element or nanofiltration membrane element and the resulting bulk solution and membrane surface on both sides of the boundary layer. The concentration difference at the place, so as to increase the scientificity of the scale prediction of the membrane surface; Fourth, the scaling phenomenon of the reverse osmosis membrane and the nanofiltration membrane is characterized by scanning electron microscopy and energy dispersive spectroscopy, which improves the inorganic structure of the membrane element membrane surface. The accuracy of scale monitoring; the fifth is to adopt the self-adaptive non-situ inorganic scale monitoring technology and the prediction method of inorganic scale on the concentrated water side and membrane surface of the membrane based on the high-concentration electrolyte theory to further expand the influent fluid reversal process cycle The critical condition for active start-up suppresses the potential of inorganic fouling on the membrane surface to the greatest extent.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

Drawing description: 1. Membrane desalination device inlet tank, 2. Booster pump, 3. Security filter, 4. Reverse osmosis high pressure pump, 5. Reverse osmosis inlet valve, 6. Multi-stage reverse osmosis components, 7. Reverse osmosis Osmosis product water valve, 8. Reverse osmosis concentrated water valve, 9. Inlet valve of final membrane element membrane surface scaling prediction device, 10. Fouling prediction device, 11. Final membrane element membrane surface self-adaptive non-situ Water intake valve for inorganic scale monitoring device, 12. Self-adaptive non-in-situ inorganic scale monitoring device, 13. Reverse osmosis concentrated water discharge valve, 14. Influent fluid reverse mode reverse osmosis intake valve, 15. Influent fluid reverse mode Reverse osmosis concentrated water valve.

detailed description

The above-mentioned contents of the present invention are described in further detail below through the embodiments, but this should not be interpreted as the scope of the above-mentioned themes of the present invention being limited to the following embodiments, and all technologies realized based on the above-mentioned contents of the present invention all belong to the scope of the present invention.

Combining with Figure 1, it can be seen that the device is mainly composed of membrane desalination device inlet tank 1, booster pump 2, security filter 3, reverse osmosis high pressure pump 4, reverse osmosis water inlet valve 5, multi-stage reverse osmosis module 6, reverse osmosis water production Valve 7, reverse osmosis concentrated water valve 8, final membrane element membrane surface scaling prediction device inlet valve 9, scaling prediction device 10, final membrane element self-adaptive non-in-situ inorganic scale detection device inlet valve 11, The self-adaptive non-in-situ inorganic scale monitoring device 12, the reverse osmosis concentrated water discharge valve 13, the reverse osmosis water inlet valve 14 in the feed fluid reversal mode and the reverse osmosis concentrated water valve 15 in the feed fluid reverse mode are connected. In the above process, the water outlet of the water inlet tank 1 of the membrane desalination device is connected to the water inlet of the booster pump 2, the water outlet of the booster pump 2 is connected to the water inlet of the security filter 3, and the water outlet of the security filter 3 is connected to the water inlet of the reverse The water inlet of the osmotic high-pressure pump 4 is connected, and the water outlet of the reverse osmosis high-pressure pump 4 is respectively connected with the water inlet of the reverse osmosis water inlet valve 5 and the water inlet fluid reverse mode reverse osmosis water inlet valve 14 through a three-way valve. The water outlet of valve 5 is connected to the water inlet of multi-stage reverse osmosis module 6, the permeate of multi-stage reverse osmosis module 6 is connected to the water inlet of reverse osmosis water production valve 7, the concentrated water of multi-stage reverse osmosis module 6 is connected to the reverse osmosis concentrated water valve 8 is connected to the water inlet, and the outlet of the reverse osmosis concentrated water valve 8 is respectively connected to the water inlet valve 9 of the membrane surface scaling prediction device of the final membrane element and the self-adaptive non-situ inorganic scale detection device of the final membrane element through the four-way valve. The water valve 11 is connected to the water inlet of the reverse osmosis concentrated water discharge valve 13, the water outlet of the water inlet valve 9 of the membrane surface scaling prediction device of the final membrane element is connected to the water inlet of the scaling prediction device 10, and the final membrane element is self-adaptive The water outlet of the water inlet valve 11 of the non-in-situ inorganic scale detection device is connected to the water inlet of the self-adaptive non-in-situ inorganic scale monitoring device 12, and the water inlet of the reverse osmosis concentrated water valve 15 in the reverse osmosis mode of the water inlet fluid is connected to the multi-stage reverse osmosis The water inlet of module 6 is connected, and the water outlet of the reverse osmosis concentrated water valve 15 in the reverse osmosis mode of the water inlet fluid is respectively connected to the water inlet valve 9 of the membrane surface scaling prediction device of the final membrane element and the adaptive non-adaptive valve of the final membrane element through the four-way valve. The water inlet valve 11 of the in-situ inorganic scale detection device is connected to the water inlet of the reverse osmosis concentrated water discharge valve 13 . When starting the normal feedwater fluid operation mode, open the reverse osmosis water inlet valve 5, the reverse osmosis water production valve 7, the reverse osmosis concentrated water valve 8, the final membrane element membrane surface scaling prediction device water inlet valve 9, the final membrane Component self-adaptive non-situ inorganic scale detection device inlet valve 11 and reverse osmosis concentrated water discharge valve 13, close the reverse osmosis water inlet valve 14 of the feed fluid reversal mode and the reverse osmosis concentrated water valve 15 of the feed fluid reversal mode, when When the influent fluid reversal operation mode is started, open the reverse osmosis inlet valve 14 in the influent fluid inversion mode, the reverse osmosis production water valve 7, the influent fluid inversion mode reverse osmosis concentrated water valve 15, and the scale prediction on the membrane surface of the final membrane element The water inlet valve 9 of the device, the water inlet valve 11 of the end-stage membrane element adaptive non-situ inorganic scale detection device and the reverse osmosis concentrated water discharge valve 13 are closed. The reverse osmosis water inlet valve 5 and the reverse osmosis concentrated water valve 8 are closed.

Example 1

The selected brackish water is underground brackish water with a salt content of 0.5-3.0g L ⁻¹ . The specific steps include: start the booster pump 2, and pump the raw water in the water tank 1 of the membrane desalination device into the security filter 3. The water produced by the security filter enters the reverse osmosis high-pressure pump 4, opens the reverse osmosis water inlet valve 5, and at the same time closes the reverse osmosis water inlet valve 14 of the influent fluid reverse mode, the water outlet of the reverse osmosis water inlet valve 5 and the multi-stage reverse osmosis component 6 connected to the water inlet, keep the reverse osmosis water inlet pressure at 4.5MPa, the reverse osmosis water inlet flow at 1000L·h ^-1 unchanged, the multi-stage reverse osmosis module 6 is effective for Ca ²⁺ , Mg ²⁺ , SO ₄ ² in brackish water The rejection rates of ⁻ , HCO ₃ ⁻ , TDS and total hardness are 99%, 99.2%, 99.4%, 95%, 99.2% and 99.4% respectively, and the pressure drop of the inner membrane element of the reverse osmosis single membrane shell is less than 0.1MPa. Open the reverse osmosis product water valve 7 to collect the product water from the multi-stage reverse osmosis module 6, the recovery rate of the system product water is ≥88%, and wait for post-processing. The reverse osmosis concentrated water in the previous stage enters the next stage of reverse osmosis components in turn, and the reverse osmosis concentrated water valve 8 and the reverse osmosis concentrated water discharge valve 13 are opened respectively. Water for flushing; at the same time, open the water inlet valve 9 of the membrane surface scaling prediction device of the last membrane element, the water inlet valve 11 of the self-adaptive non-in-situ inorganic scale detection device of the last membrane element, and a small amount of concentrated water in the last stage of the multi-stage reverse osmosis module Enter the scaling prediction device 10 and the adaptive non-situ inorganic scale monitoring monitoring device 12 respectively.

Whether the Langelier index or the Steve & Davy stability index at the membrane surface on the concentrated water side is greater than zero, or whether the supersaturation index of refractory salts at the membrane surface on the concentrated water side is greater than 1. When the fouling prediction device 10 of the final membrane element predicts inorganic fouling on the concentrated water side or on the membrane surface, or the inorganic crystals on the membrane surface in the plate-and-frame RO membrane pool are respectively formed according to the scanning electron microscope-energy dispersive spectrum Appearance, qualitative and quantitative analysis to accurately determine whether there is scaling on the membrane surface. When the adaptive non-in-situ inorganic scale monitoring device 12 detects inorganic scale on the membrane surface, it will start the influent fluid reversal process, and open the inlets one by one. Reverse osmosis water inlet valve 14 in water fluid reversal mode, reverse osmosis production water valve 7, reverse osmosis concentrated water valve 15 in feed fluid reversal mode, water inlet valve 9 of final membrane element membrane surface scaling prediction device, final membrane element automatic The water inlet valve 11 and the reverse osmosis concentrated water discharge valve 13 of the suitability non-situ inorganic scale detection device are closed, and the reverse osmosis water inlet valve 5 and the reverse osmosis concentrated water valve 8 are closed. The forward flow changes to the reverse flow, and when the fouling prediction device 10 of the final membrane element or the adaptive non-in-situ inorganic scale detection device 12 predicts or detects the occurrence of inorganic scale on the membrane surface again, the normal influent fluid is started again operating mode. In this way, the operation mode of alternately changing the flow direction of the inlet water in the membrane module is adopted to destroy the concentration polarization layer established on the concentrated water side or the membrane surface, and inhibit membrane scaling. Compared with the traditional influent fluid, non-adaptive non-situ inorganic scale prediction and non-monitoring process, the system water recovery rate of the process of the present invention is higher than the latter by more than 10%.

Example 2

Keep the reverse osmosis inlet water pressure at 5.0MPa, keep the reverse osmosis concentrated water flow rate at 800L·h ^-1 constant, the multi-stage reverse osmosis module 6 is good for Ca ²⁺ , Mg ²⁺ , SO ₄ ²⁻ , HCO ₃ in brackish water ⁻ , TDS and total hardness rejection rates are 98.8%, 99.1%, 99.3%, 94.7%, 99% and 99.3% respectively, the pressure drop of the membrane element in the reverse osmosis single membrane shell is less than 0.1Mpa, and the multi-stage reverse osmosis module 6 in Under the above experimental conditions, the system water recovery rate was 85%.

This example shows that when the tangential flow velocity of the membrane surface at the outlet end of the reverse osmosis is reduced, the concentration polarization of the main scaling ions Ca ²⁺ , Mg ²⁺ and SO ₄ ²⁻ increases under the condition that the raw water flow direction remains unchanged. When the system product water recovery rate was 85%, the concentration polarization factors of Ca ²⁺ , Mg ²⁺ and SO ₄ ²⁻ increased from 1.27, 1.96 and 1.87 in Example 1 to 1.48, 2.91 and 2.35, respectively. Scaling occurs on the membrane surface of the element in advance, but the fouling of the membrane element can still be significantly inhibited by changing the flow direction of the water in the multi-stage reverse osmosis module.

The above embodiments have described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What are described in the above embodiments and description are only to illustrate the principles of the present invention. Without departing from the scope of the principle of the present invention, there will be various changes and improvements in the present invention, and these changes and improvements all fall within the protection scope of the present invention.

Claims (3)

1. A method for inhibiting fouling of membrane elements in a brackish water desalination process, characterized in that it comprises the following steps: (1) After the raw brackish water with a salt content of 0.5-3.0g L ^{− 1} is pretreated by multi-media filtration or membrane method, it will enter the membrane desalination after meeting the requirements of SDI15≤3.0 and turbidity≤0.01NTU. The device enters the water tank; (2) Connect 3-12 membrane shells in series to form a multi-stage reverse osmosis module. The inlet and outlet ends of each membrane shell are respectively equipped with anti-retraction rings to fix the membrane elements in the membrane shells. The membrane elements are reverse osmosis membranes or Nanofiltration membrane, multi-stage reverse osmosis modules are arranged in a conical shape, the concentrated water in the first and last sections of the multi-stage reverse osmosis module is connected to the reverse osmosis high-pressure pump, security filter, booster pump and membrane desalination device in turn through valves. box, and the concentrated water in the first and last membrane shells of the multi-stage reverse osmosis module respectively flows into the reverse osmosis concentrated water discharge channel through valves, and the reverse osmosis concentrated water discharge channel is respectively connected with self-adaptive non-in-situ inorganic scale through valves. Monitoring device and scaling prediction device, in which the self-adaptive non-in-situ inorganic scale monitoring device is composed of a plate-and-frame RO membrane pool with a size of 7.5cm×2.5cm×2.7mm; (3) Connect the permeate pipes of each branch membrane shell in the multi-stage reverse osmosis module, merge into the water production channel of the membrane method brackish water desalination system, and finally enter the desalination water tank; (4) Run the system, start the reverse osmosis high-pressure pump, the raw water flows in the forward direction in the multi-stage reverse osmosis module, that is, it flows in from the first membrane shell and flows out from the last membrane shell, and the permeate enters the desalination water tank, and the concentrated water is used Physical flushing of pretreatment devices; (5) When the adaptive non-in-situ inorganic scale monitoring device and the scaling prediction device respectively monitor that the membrane surface of the membrane element on the concentrated water side in the last membrane shell reaches the critical scaling condition and predict that the membrane on the concentrated water side of the last stage will When inorganic fouling occurs on the membrane surface of the element, the influent fluid reversal process is started to change the flow direction of the raw water in the multi-stage reverse osmosis module and flow in the reverse direction, that is, the raw water flows in from the last membrane shell and flows out from the first membrane shell. The permeate enters the desalinated water tank, and the concentrated water is used for physical flushing of the pretreatment device. The realization process of the adaptive non-situ inorganic scale monitoring device and the scaling prediction device are as follows: every 5 minutes, using scanning electron microscopy-energy dispersive The spectrum analyzes the morphology, qualitative and quantitative analysis of the inorganic crystals on the membrane surface in the plate and frame RO membrane tank, and accurately judges whether there is scaling on the membrane surface. The type RO membrane tank realizes self-adaptive monitoring of the inorganic scaling on the membrane surface of the concentrated water side in the first membrane shell; every 2 minutes, the scale ion activity is calculated according to the influent composition of the plate and frame RO membrane tank, combined with Concentration polarization theory, to predict whether scaling occurs on the membrane surface on the concentrated water side, when the Langelier index LSI on the membrane surface on the concentrated water side is greater than zero, or based on the Pitzer electrolyte solution theory to predict the occurrence of scaling on the membrane surface on the concentrated water side When the insoluble salt supersaturation index SI at the place is greater than 1, it indicates that critical fouling conditions occur; (6) When the influent fluid reverses the process and runs until the self-adaptive non-in-situ inorganic scale monitoring device and the scaling prediction device respectively monitor that the membrane surface of the concentrated water side membrane element in the first branch membrane shell reaches the critical scaling condition and predict When inorganic scaling occurs on the membrane surface of the membrane element on the concentrated water side in the last stage, the periodic feedwater fluid reversal process is started again to destroy the concentration boundary layer formed on the surface of the membrane element, thereby inhibiting the surface scaling of the membrane element and maximizing the production. The recovery rate of water has achieved a system water recovery rate of ≥85% without the risk of scaling on the membrane surface. 2. The method for inhibiting fouling of membrane elements in the brackish water desalination process according to claim 1, characterized in that: said reverse osmosis membrane or nanofiltration membrane is a membrane with a commercial diameter of 8 inches, 4 inches or 2.5 inches Components, the type of inorganic scaling is reverse osmosis membrane or nanofiltration membrane concentrated water side or membrane surface CaCO ₃ , CaSO ₄ , BaSO ₄ , SrSO ₄ , Ca ₃ (PO ₄ ) ₂ , metal oxide or silicon deposit inorganic Salt precipitation. 3. The method for inhibiting fouling of membrane elements in the process of desalination of brackish water according to claim 1, characterized in that: the operating temperature of the multi-stage reverse osmosis module is 0-60°C.