A method, system and application for reducing reverse osmosis concentrate discharge

Abstract

The present application relates to the technical field of water treatment, in particular to a method, system and application for reducing reverse osmosis concentrated water discharge, the method for reducing reverse osmosis concentrated water discharge adopts a periodic closed loop operation method, including initial parameter design: presetting reverse osmosis water inlet concentration threshold according to raw water quality and reverse osmosis initial recovery rate; full reflux concentration stage: reverse osmosis concentrated water is fully refluxed and mixed with raw water, water production is continuously discharged, and water inlet concentration is gradually increased to the set threshold; concentrated water discharge stage and raw water replacement stage: after reaching the threshold, the reflux is cut off, the concentrated water is discharged, and the raw water feeding and water production discharge are maintained; after the concentrated water is discharged to a concentration that is reduced to the concentrated water concentration corresponding to the initial recovery rate, the discharge of concentrated water is stopped, the replacement is completed, the full reflux mode is restarted, and the periodic operation is repeated; the method breaks the limitation of the existing concentrated water reflux process, constructs a new closed loop operation mode of "concentration-discharge-replacement", and provides a new technical path for reverse osmosis high recovery rate and low discharge operation.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a method, system, and application for reducing reverse osmosis concentrate discharge. Background Technology

[0002] Reverse osmosis technology uses a semi-permeable membrane as its core carrier. A high-pressure pump applies external force, forcing water molecules to pass through the membrane, which has a pore size of only about 0.1 nanometers, against its concentration gradient. Meanwhile, dissolved salts, colloids, large organic molecules, microorganisms, and heavy metal ions are efficiently retained, achieving deep separation of water and pollutants. Reverse osmosis is widely used in ultrapure water preparation systems in photovoltaics, LCD panels, and electronic semiconductors, as well as in the recycling of reclaimed water.

[0003] Because reverse osmosis concentrate contains high concentrations of salts, organic matter, and other impurities, the design of a reverse osmosis system must consider the salt content and contaminant concentration of the feed water. A suitable recovery rate (the ratio of permeate to feed water) must be set, and specific chemical agents must be added to prevent these dissolved salts from forming insoluble substances on the membrane surface after concentration, thus avoiding blockage of the membrane pores and flow channels. Once contaminants deposit on the membrane surface, it leads to a decrease in reverse osmosis permeate flow, an increase in concentrate flow, and a decline in water resource utilization. Therefore, a reasonable design is crucial for the stable operation of a reverse osmosis unit.

[0004] The conductivity of municipal tap water typically ranges from 200 to 600 μS / cm, varying considerably across different regions. Ultrapure water systems generally employ a combined process of pretreatment, reverse osmosis, and fine treatment. Reverse osmosis plays a crucial role in desalination, followed by electrodeionization (EDI) and ion exchange units for further purification. The recovery rate of a typical first-stage reverse osmosis system is set at 70%–75%, with a concentrate discharge of 25%–30%. To improve utilization, the industry often adds a recovery reverse osmosis unit. This unit collects the concentrate from the first-stage reverse osmosis and pressurizes it via a high-pressure pump for further desalination. The permeate is then returned to the system for reuse, while the concentrate with higher salt content is discharged. The recovery rate of this recovery reverse osmosis unit is typically set at 50%–60%. Even with a recovery reverse osmosis unit, the final wastewater discharge still reaches 12%–15%.

[0005] The existing technology has the following objective defects: (1) Adding a concentrated water recovery reverse osmosis device requires additional equipment such as water tank, pump, filter, reverse osmosis membrane, and chemical dosing, which involves high investment and large footprint; (2) Some small factories are unable to install concentrated wastewater recovery systems due to cost and land constraints, resulting in high levels of concentrated wastewater discharge. (3) Existing systems are constrained by space and power, making them difficult to upgrade; (4) The conventional continuous concentration discharge mode has a low recovery rate limit and cannot achieve high recovery rate operation on a single RO unit. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method, system and application for reducing reverse osmosis concentrate discharge, to solve the problems of the upper limit of reverse osmosis recovery rate of only 75% and large amount of concentrate discharge in the prior art, as well as the problems that the prior art requires the addition of an independent concentrate recovery reverse osmosis system to improve the recovery rate, which is complex, has high investment and land costs, and the existing reverse osmosis system cannot achieve a significant improvement in recovery rate and reduction of concentrate discharge without adding new main equipment.

[0007] To achieve the above and other related objectives, this invention provides a method for reducing reverse osmosis concentrate discharge, employing a periodic closed-loop operation method, specifically including the following steps: (1) Initial parameter design: The reverse osmosis feed water concentration threshold is preset according to the raw water quality and the initial reverse osmosis recovery rate. The reverse osmosis feed water concentration threshold is 6 to 15 times the raw water concentration. (2) Full reflux concentration stage: The concentrated water produced by reverse osmosis is all refluxed. The refluxed concentrated water is mixed with the raw water to form reverse osmosis feed water to continue reverse osmosis. The raw water is continuously fed, the concentrated water is continuously refluxed, and the reverse osmosis permeate is continuously discharged, so that the concentration of reverse osmosis feed water accumulates from the initial concentration of raw water until the concentration of reverse osmosis feed water reaches the reverse osmosis feed water concentration threshold. (3) Concentrate discharge and raw water replacement stage: When the concentration of reverse osmosis feed water reaches the threshold of reverse osmosis feed water concentration, stop the concentrate reflux and discharge the concentrate, while maintaining the continuous feed of raw water and the continuous discharge of reverse osmosis permeate; continue to discharge the concentrate until its concentration drops to the concentrate concentration corresponding to the initial recovery rate, stop the concentrate discharge, and one closed-loop operation cycle is completed. Restart the concentrate full reflux mode and repeat steps (2) and (3).

[0008] The present invention also provides a system for reducing reverse osmosis concentrate discharge. The system includes a raw water tank, a filter and a reverse osmosis membrane module connected in sequence. The concentrate outlet of the reverse osmosis membrane module is connected to a concentrate control unit, and the product water outlet of the reverse osmosis membrane module is connected to a product water collection unit. The concentrate control unit includes a concentrate output pipeline, a concentrate return pipeline and a concentrate discharge pipeline respectively connected to the concentrate output pipeline. The concentrate output pipeline is equipped with a concentrate conductivity meter and a concentrate flow regulating valve. The output end of the concentrate return pipeline is connected to the inlet of the reverse osmosis membrane module. The concentrate return pipeline is also equipped with a concentrate return automatic valve. The concentrate discharge pipeline is equipped with a concentrate discharge automatic valve and a concentrate discharge flow meter. A reverse osmosis feed water conductivity meter is installed on the pipeline before the inlet of the reverse osmosis membrane module; The system also includes a PLC control unit, which is connected to a concentrate conductivity meter, a concentrate flow regulating valve, a concentrate reflux automatic valve, a concentrate discharge automatic valve, a concentrate discharge flow meter, and a reverse osmosis feed water conductivity meter, respectively.

[0009] The present invention also provides an application of the method for reducing reverse osmosis concentrate discharge as described above, which is used in the front-end reverse osmosis process for ultrapure water preparation in the photovoltaic, electronic semiconductor, and display panel industries, as well as in the reverse osmosis reuse process for recycled water.

[0010] As described above, the method, system, and application for reducing reverse osmosis concentrate discharge of the present invention have the following beneficial effects: The method for reducing reverse osmosis concentrate discharge of the present invention adopts a 100% full reflux concentration mode, and only discharges a small amount of high-concentration concentrate after the concentration reaches the standard. Compared with the conventional partial reflux and continuous concentrate discharge process, it can bring the water production rate of the reverse osmosis system close to the limit value, and solves the core pain points of low water production rate and insufficient water resource utilization in the prior art.

[0011] The present invention reduces reverse osmosis concentrate discharge through the linkage of a concentration detection unit and a control unit, which monitors the feed water concentration in real time and precisely controls the switching timing of each operating stage. This achieves efficient accumulation and concentration of solute, and resets the concentration in the system to a stable range through the raw water replacement stage. This avoids membrane scaling and fouling caused by long-term high-concentration circulation of concentrate, extends the service life of reverse osmosis membrane modules, and reduces the frequency of system maintenance.

[0012] The system of this invention boasts strong operational stability and ease of operation. The entire operation process achieves automated closed-loop control, eliminating the need for frequent manual intervention in concentration monitoring and stage switching. The precise application of the dynamic material balance equation clarifies the quantitative relationship between the concentration rise rate and time, facilitating system parameter debugging and large-scale replication, and adapting to reverse osmosis water treatment scenarios of different scales. Furthermore, the product water flow rate remains stable regardless of whether it is in the full reflux concentration stage or the concentrate discharge stage, solving the problem of reduced water production caused by membrane element fouling under conventional fixed flow mode.

[0013] The system of this invention adopts automated closed-loop control to reduce manual operation costs and the workload of manual monitoring and debugging; it reduces the risk of membrane fouling, thereby reducing the frequency of reverse osmosis membrane replacement and the consumption of consumables such as antiscalants and cleaning agents, while also reducing system downtime for maintenance, increasing the effective operating time of the equipment, and indirectly reducing production costs. Furthermore, the system has a simple structure and can be implemented by modifying existing reverse osmosis equipment without the need for adding a large number of complex devices, making the modification difficult and cost controllable. Compared with existing high-recovery-rate reverse osmosis systems, the process of this invention is simple, the parameters are easy to control, the operating energy consumption is lower, and long-term operation can significantly improve the return on investment of the equipment. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the system for reducing reverse osmosis concentrate discharge according to the present invention.

[0015] Figure 2 This is a graph showing the relationship between water quality and time for a tap water sample in Example 2 of the present invention during a discharge cycle.

[0016] Explanation of icon numbers 21. Raw water tank; 22. Raw water pump; 23. Filter; 24. High-pressure pump; 25. Reverse osmosis membrane module; 26. Product water tank; 31. Raw water flow meter; 32. Reverse osmosis feed water conductivity meter; 33. Reverse osmosis feed water pressure sensor; 34. Reverse osmosis product water flow meter; 35. Reverse osmosis product water conductivity meter; 36. Concentrate conductivity meter; 37. Concentrate flow regulating valve; 38. Concentrate reflux automatic valve; 39. Concentrate discharge automatic valve; 40. Concentrate discharge flow meter; 41. Antiscalant dosing tank; 42. Antiscalant dosing pump; 50. PLC control unit; 51. Raw water tank level transmitter; 52. Product water tank level transmitter; 10. Concentrate output pipeline; 11. Concentrate reflux pipeline; 12. Concentrate discharge pipeline. Detailed Implementation

[0017] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0018] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a communication connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0019] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0020] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0021] The first aspect of this invention provides a method for reducing reverse osmosis concentrate discharge, employing a periodic closed-loop operation method, specifically including the following steps: (1) Initial parameter design: Based on the raw water quality and the initial recovery rate of reverse osmosis, the reverse osmosis feed water concentration threshold is preset, which is 6 to 15 times the raw water concentration; for example, 6.1 times, 6.3 times, 6.5 times, 6.7 times, 6.9 times, 7 times, 7.5 times, 8 times, 8.5 times, 9 times, 9.5 times, 10 times, 10.5 times, 11 times, 11.5 times, 12 times, 12.5 times, 13 times, 13.5 times, 14 times, 14.5 times, 15 times, etc. (2) Full reflux concentration stage: The concentrated water produced by reverse osmosis is all refluxed. The refluxed concentrated water is mixed with the raw water to form reverse osmosis feed water to continue reverse osmosis. The raw water is continuously fed, the concentrated water is continuously refluxed, and the reverse osmosis permeate is continuously discharged, so that the concentration of reverse osmosis feed water accumulates from the initial concentration of raw water until the concentration of reverse osmosis feed water reaches the reverse osmosis feed water concentration threshold. (3) Concentrate discharge and raw water replacement stage: When the concentration of reverse osmosis feed water reaches the threshold of reverse osmosis feed water concentration, stop the concentrate reflux and discharge the concentrate, while maintaining the continuous feed of raw water and the continuous discharge of reverse osmosis permeate; continue to discharge the concentrate until its concentration drops to the concentrate concentration corresponding to the initial recovery rate, stop the concentrate discharge, and one closed-loop operation cycle is completed. Restart the concentrate full reflux mode and repeat steps (2) and (3).

[0022] In some embodiments of the present invention, the recovery rate of the first-stage reverse osmosis is typically designed to be 75%.

[0023] In some embodiments of the present invention, during the total reflux concentration stage in step (1), the concentration rise rate of the reverse osmosis feed water satisfies the dynamic material balance equation: V·dC / dt = Q f ·C f ; Where V is the total system volume; C is the real-time concentration of the reverse osmosis feed water after mixing raw water and concentrate; t is time; Q f C is the raw water feed flow rate; f This represents the concentration of the raw water.

[0024] A second aspect of the present invention provides a system for reducing reverse osmosis concentrate discharge, the system comprising a raw water tank 21, a filter 23 and a reverse osmosis membrane module 25 connected in sequence, the concentrate outlet of the reverse osmosis membrane module 25 being connected to a concentrate control unit, and the product water outlet of the reverse osmosis membrane module 25 being connected to a product water collection unit. The concentrate control unit includes a concentrate output pipeline 10, and a concentrate return pipeline 11 and a concentrate discharge pipeline 12 respectively connected to the concentrate output pipeline 10. The concentrate output pipeline 10 is equipped with a concentrate conductivity meter 36 and a concentrate flow regulating valve 37. The output end of the concentrate return pipeline 11 is connected to the inlet of the reverse osmosis membrane module 25. The concentrate return pipeline 11 is also equipped with a concentrate return automatic valve 38. The concentrate discharge pipeline 12 is equipped with a concentrate discharge automatic valve 39 and a concentrate discharge flow meter 40. A reverse osmosis feed water conductivity meter 32 is installed on the pipeline before the inlet of the reverse osmosis membrane module 25; The system also includes a PLC control unit 50, which is connected to a concentrate conductivity meter 36, a concentrate flow regulating valve 37, a concentrate reflux automatic valve 38, a concentrate discharge automatic valve 39, a concentrate discharge flow meter 40, and a reverse osmosis feed water conductivity meter 32, respectively.

[0025] In some embodiments of the present invention, the raw water tank 21 is connected to a raw water tank level transmitter 51, and the raw water tank level transmitter 51 is connected to a PLC control unit 50.

[0026] In some embodiments of the present invention, a raw water pump 22 is provided between the raw water tank 21 and the filter 23, and a scale inhibitor dosing tank 41 is connected to the pipeline between the raw water pump 22 and the filter 23. The scale inhibitor dosing tank 41 is controlled by the scale inhibitor dosing pump 42.

[0027] In some embodiments of the present invention, a raw water flow meter 31 is provided at the inlet of the filter 23, and the raw water flow meter 31 is connected to the PLC control unit 50.

[0028] In some embodiments of the present invention, a high-pressure pump 24 is further provided between the filter 23 and the reverse osmosis membrane assembly 25, the reverse osmosis feed water conductivity meter 32 is located at the inlet of the high-pressure pump 24, the output end of the concentrate return pipeline 11 is connected to the inlet of the reverse osmosis membrane assembly 25 through the high-pressure pump 24, and a reverse osmosis feed water pressure sensor 33 is provided at the inlet of the reverse osmosis membrane assembly 25, the reverse osmosis feed water pressure sensor 33 is connected to the PLC control unit 50.

[0029] In a preferred embodiment of the present invention, the high-pressure pump 24 is equipped with a frequency converter, and its operating frequency is controlled by data from the reverse osmosis feed water pressure sensor 33 and the reverse osmosis permeate flow meter 34.

[0030] In some embodiments of the present invention, the filter 23 is a security filter. In a preferred embodiment of the present invention, the security filter has a filtration accuracy of 5 μm. It serves as a protective device for the reverse osmosis feed water, preventing impurities larger than 5 μm from clogging the reverse osmosis membrane.

[0031] In some embodiments of the present invention, the permeate pipeline of the reverse osmosis membrane module 25 is further provided with a reverse osmosis permeate flow meter 34 and a reverse osmosis permeate conductivity meter 35, both of which are connected to the PLC control unit 50.

[0032] In some embodiments of the present invention, the permeate collection unit includes a permeate tank 26 and a permeate tank level transmitter 52 connected thereto, the permeate outlet of the reverse osmosis membrane assembly 25 is connected to the permeate tank 26, and the permeate tank level transmitter 52 is connected to a PLC control unit 50.

[0033] In this invention, the raw water tank 21 is used to collect and store raw water, and the raw water pump 22 is used to transport the raw water. The raw water first passes through the filter 23 to remove large particulate impurities, and then is pressurized by the high-pressure pump 24 before entering the reverse osmosis membrane module 25.

[0034] The third aspect of the present invention provides an application of the method for reducing reverse osmosis concentrate discharge as described above, for use in the front-end reverse osmosis process for ultrapure water preparation in the photovoltaic, electronic semiconductor, and display panel industries, as well as in the reverse osmosis reuse process for recycled water.

[0035] The present invention will be further described in detail below with reference to specific embodiments and comparative examples. The described embodiments are only for explaining the present invention and are not intended to limit the scope of protection of the present invention. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional experimental conditions in the art.

[0036] Example 1 Theoretical calculation explanation: Taking a reverse osmosis system with a production capacity of 100 m³ / h as an example, using tap water as the raw water source: the reverse osmosis product water flow rate is 100 m³ / h, designed with an initial recovery rate of 75%, the feed water flow rate is 100 m³ / h ÷ 75% = 133 m³ / h. 3 / h. The initial raw water concentration is 300 mg / L, the preset reverse osmosis feed water concentration threshold is 2000 mg / L, and the total system volume is 3 m³ / h. 3 .

[0037] Total reflux concentration stage: Raw water feed flow rate is 100 m³ / h 3 / h, concentrate recirculation flow rate is 33m³ / h 3 / h, the total reverse osmosis feed water flow rate is 133m³ / h. 3 / h, with a production water flow rate of 100m³ / h. 3 / h.

[0038] According to the dynamic material balance equation: V·dC / dt = Q f ·C f V is the total system volume; C is the real-time concentration of the reverse osmosis feed water after mixing raw water and concentrate; t is time; Q f C is the raw water feed flow rate; f This refers to the concentration of the raw water. dC / dt = 100 × 300 / 3 = 10000 mg / L / h, (2000 mg / L - 300 mg / L) / 10000 mg / L / h = 0.17 hr (i.e., 10.2 minutes), meaning the time for the initial raw water concentration to rise to the preset reverse osmosis feed water concentration threshold during the total reflux concentration stage is 10.2 minutes; during the concentrate total reflux stage, the permeate flow rate is 100 m³ / h. 3 / h, a total of 17m³ of water was produced within 10.2 minutes. 3 Since there is no concentrated water discharge, the total influent equals the total produced water.

[0039] During the concentrate discharge stage, the feed water is continuously supplied while the product water is continuously discharged. The high-concentration concentrate remaining in the system is replaced by low-concentration feed water until the concentration of the discharged concentrate drops to four times the concentration of the feed water (i.e., 1200 mg / L). At this point, discharge is stopped and full reflux concentration is resumed. The required time is based on a total system volume of 3m³. 3 ÷Concentrate flow rate 33m 3 / h=0.09hr=5.4 minutes.

[0040] During the concentrate discharge phase: water production 100m³ 3 / h, a total of 9m³ of water was produced within 5.4 minutes. 3 Concentrate flow rate 33m 3 / h, total concentrated wastewater discharge 2.97m³ 3 Raw water volume: 133m³ 3 / h, total raw water inflow 11.97m³ 3 .

[0041] In one cycle, the system water production rate = system water production / system water inflow = (17 + 9) ÷ (17 + 11.97) = 90%.

[0042] Example 2 Using tap water from a certain area in Jiangsu as a sample I. (1) The raw water quality indicators are shown in Table 1 below: Table 1

[0043] TDS (Total Dissolved Solids) refers to the total amount of dissolved inorganic salts, organic matter, and other soluble substances in water, excluding silt and suspended solids. Units: mg / L or ppm (1 mg / L = 1 ppm).

[0044] (2) The RO (reverse osmosis) unit is designed to produce 100m³ of water. 3 / h, designed recovery rate 75%, recovery rate = product water flow rate ÷ (raw water flow rate + concentrate return flow rate), RO unit volume is 3m³ / h. 3 The RO membrane is a fouling-resistant membrane with a 34mil wide flow channel.

[0045] (3) Theoretical calculation of the time required for the full concentration stage During the full concentration stage, all concentrate is returned to the feed water end, so the feed water flow rate equals the product water flow rate. Since the substance content in the product water is very low, its concentration is negligible. Therefore, the rate of increase in the reverse osmosis feed water concentration is determined by the total system volume, the feed water flow rate, and the feed water concentration, specifically satisfying the dynamic material balance equation: V·dC / dt = Q f ·C f Where V is the total system volume, C is the real-time concentration of the reverse osmosis feed water (the mixture of raw water and concentrate), t is time, and Q is... f C represents the raw water feed flow rate. f This represents the concentration of the raw water.

[0046] Using a TDS concentration of 255 mg / L as C f Qf 100m 3 / h, V=3m 3 Substituting into the dynamic material balance equation, 3 × dC / dt = 100 × 255, we get dC / dt = 8500 mg / L / h, meaning the concentration rises at a rate of 8500 mg / L per hour. Based on theoretical calculations, the concentration of the influent substance, C, increases every minute. t =C f +8500×t, after calculation, the value of the reverse osmosis feed water concentration changing with time can be obtained, as shown in Table 2 below: Table 2

[0047] (4) Using reverse osmosis calculation software (DuPont's Wave software), the above water quality can be input to simulate and calculate the RO operating pressure, permeate and concentrate water quality. The simulation results are shown in Table 3 below: Table 3

[0048] Note: For brackish water with a concentrate salinity (TDS) ≤ 10000 mg / L, the Langerile Index (LSI) is used as an indicator of the likelihood of CaCO3 scaling. When LSI ≥ 0, CaCO3 scaling will occur. Another scaling indicator is silica; if the raw water has a high silica content, it will also cause silica scaling. Therefore, the system needs to add a scale inhibitor. Based on the performance of the scale inhibitor LA 903, the maximum allowable value for the concentrate LSI is 2.5, and the maximum allowable concentration of SiO2 on the concentrate side is 300 mg / L. With the addition of the scale inhibitor, the concentration of SiO2 in the concentrate is close to 300 mg / L after 12 minutes of total concentrate reflux. Therefore, the influent conductivity value at 12 minutes is used as the threshold for the end of the total concentrate reflux stage.

[0049] (5) Calculate the concentrated wastewater discharge time When concentrated wastewater is discharged, the system is still producing water normally. At this time, the raw water inflow needs to be increased to 133m³. 3 To maintain a 75% RO design recovery rate, the concentrate discharge rate is 33m³ / h. 3 / h, total volume of reverse osmosis unit 3m³ 3 The time it takes to completely expel it is 3 ÷ 33 = 0.09 h = 5.4 min.

[0050] (6) Calculate the system recovery rate Concentrate recirculation stage: Raw water volume 100m³ 3 / h, water production 100m³ 3 / h, time 12min.

[0051] Concentrate discharge stage: Raw water volume 133m³3 / h, water production 100m³ 3 / h, time 5.4min.

[0052] Water production over the entire 17.4 minutes: 100 × (12 + 5.4) ÷ 60 = 29 m³ 3 .

[0053] The total raw water volume over the entire 17.4 minutes is: (100 × 12 + 133 × 5.4) ÷ 60 = 32 m³ 3 .

[0054] System recovery rate: 29 ÷ 32 = 91%.

[0055] (7) The relationship between water quality and time within a cycle, as shown in the attached figure. Figure 2 As shown.

[0056] II. Threshold Setting The three common types of fouling in reverse osmosis are key factors affecting the stability of reverse osmosis operation: <1> Microbial contamination: This is the most common cause, often resulting from inadequate sterilization and the easy formation of biofilms.

[0057] <2> Organic matter / colloidal contamination: Inadequate pretreatment and high SDI value.

[0058] <3> Scaling: CaCO3, CaSO4, SiO2, etc., precipitate out to form precipitates.

[0059] This invention has a good effect on controlling microbial contamination. Because the operating mode is constantly switching, the concentration and pressure inside the device are constantly changing, which is not conducive to the growth and reproduction of bacteria.

[0060] In this invention, the raw water needs to undergo ultrafiltration treatment before reverse osmosis to remove particulate matter from the raw water, so that the SDI is less than 3 when the raw water is used as reverse osmosis feed water.

[0061] For reverse osmosis systems using natural water as raw material, scale prevention is necessary. This requires a raw water testing report to analyze various ions and compounds in the raw water (including but not limited to conductivity, pH, hardness, alkalinity, SiO2, and ions such as Na, Cl, and SO4). Based on LSI, SiO2, and the upper limit of scale inhibitor tolerance, concentration thresholds are determined to prevent scale formation.

[0062] III. The specific operational methods for reducing reverse osmosis concentrate discharge include the following steps: like Figure 1The raw tap water is stored in a raw water tank 21, which is connected to a raw water pump 22 via a pipeline. The raw water pump 22 delivers the raw water to a security filter (filter 23), which has a filtration accuracy of 5µm. The permeate from the security filter enters a high-pressure pump 24, and the pressurized raw water is then sent to the reverse osmosis membrane module 25. A reverse osmosis unit consists of multiple membrane elements connected in series and parallel within a single device. The permeate from the reverse osmosis system is collected in a permeate tank 26 and then enters the downstream treatment unit. The reverse osmosis concentrate is output in two paths: one is a concentrate return pipeline 11, which connects to the inlet pipeline before the high-pressure pump 24; the other is a concentrate discharge pipeline 12, which connects to a drain or collection tank. A scale inhibitor dosing tank 41 is used to store scale inhibitors, and a scale inhibitor dosing pump 42 injects the scale inhibitor into the raw water via a pipeline connected to the inlet pipeline of the security filter.

[0063] Before the equipment can be put into automated operation, the entire system needs to be manually debugged in order to set various parameters.

[0064] Step 1: Before starting the equipment, check the valve status. The automatic concentrated water return valve 38 should be closed, the automatic concentrated water discharge valve 39 should be open, and the concentrated water flow regulating valve 37 should be fully open.

[0065] Step 2: After confirming that the above valve status is correct, start the raw water pump 22 and adjust the frequency of the raw water pump 22 so that the raw water pump outlet flow rate reaches 133 m³ / h. 3 At this time, the high-pressure pump is not started, and the raw water flows through the reverse osmosis unit at a low flow rate. Most of the water is discharged from the concentrate discharge pipe. Both the raw water flow meter 31 and the concentrate conductivity meter 36 show 133m³ / h. 3 / h.

[0066] Step 3: Turn on the high-pressure pump 24 and adjust its frequency. Simultaneously, gradually decrease the opening of the concentrate flow regulating valve 37. The concentrate flow rate will gradually decrease, while the permeate flow rate will gradually increase. When the reverse osmosis permeate flow meter 34 reaches 100 m³ / s... 3 / h, the concentrate conductivity meter reached 33m36. 3 / h, maintain the opening degree of the concentrate flow regulating valve 37 and the frequency of the high-pressure pump 24 at this time.

[0067] Step 4: Open the concentrate return automatic valve 38 and close the concentrate discharge automatic valve 39. At this time, manually reduce the frequency of the raw water pump 22, and reduce the flow rate of the raw water flow meter 31 to 100m³. 3 / h. At this point, the concentrate full recirculation mode has been entered. As time increases, the value of the reverse osmosis feed water conductivity meter will increase from the initial 420us / cm to the set threshold of 2880us / cm. At the same time, the value of the reverse osmosis feed water pressure sensor 33 will increase from 10.5bar to 12.5bar.

[0068] Step 5: When the influent conductivity reaches the design threshold, open the concentrate discharge automatic valve 39 and close the concentrate return automatic valve 38. The raw water pump frequency increases, and the raw water pump flow rate increases from the original 100m³ / h. 3 / h rose to 133m 3 / h. At this point, the permeate flow rate remains basically unchanged, and the high-salt water accumulated in the reverse osmosis unit is discharged. At this time, observe the conductivity of the reverse osmosis concentrate. When its value drops below 1600 μS / cm, the concentrate discharge can be stopped, and the full reflux stage can be entered again.

[0069] Step 6: Enable automatic operation mode. The control logic is shown in Table 4 below: Table 4

[0070] Note: L level is the position of the water tank outlet; H level is the position of the water tank overflow outlet.

[0071] In summary, the method for reducing reverse osmosis concentrate discharge of the present invention can be widely applied to various reverse osmosis water treatment scenarios such as industrial wastewater treatment, municipal water supply, and seawater desalination. It is particularly suitable for water-scarce areas and water-intensive industries, saving a significant amount of raw water consumption and reducing raw water intake and pretreatment costs. Simultaneously, it reduces concentrate treatment costs, avoiding the economic burden of additional treatment required for large amounts of concentrate discharge in conventional processes. This effectively improves water resource recycling efficiency, increases the total amount of available water resources, and contributes to the stability of social water supply. Furthermore, it breaks through the limitations of existing concentrate recirculation processes, constructing a new closed-loop operation mode of "concentration-discharge-replacement," providing a new technical path for high recovery rate and low emission operation of reverse osmosis, promoting technological progress in the water treatment industry, and contributing to the construction of a green and low-carbon society.

[0072] Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0073] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for reducing reverse osmosis concentrate discharge, characterized in that, The periodic closed-loop operation method includes the following steps: (1) Initial parameter design: The reverse osmosis feed water concentration threshold is preset according to the raw water quality and the initial reverse osmosis recovery rate. The reverse osmosis feed water concentration threshold is 6 to 15 times the raw water concentration. (2) Full reflux concentration stage: The concentrated water produced by reverse osmosis is all refluxed. The refluxed concentrated water is mixed with the raw water to form reverse osmosis feed water to continue reverse osmosis. The raw water is continuously fed, the concentrated water is continuously refluxed, and the reverse osmosis permeate is continuously discharged, so that the concentration of reverse osmosis feed water accumulates from the initial concentration of raw water until the concentration of reverse osmosis feed water reaches the reverse osmosis feed water concentration threshold. (3) Concentrate discharge and raw water replacement stage: When the concentration of reverse osmosis feed water reaches the threshold of reverse osmosis feed water concentration, stop the concentrate reflux and discharge the concentrate. At the same time, keep the raw water continuously fed and the reverse osmosis permeate continuously discharged. Continue to discharge the concentrate until its concentration drops to the concentrate concentration corresponding to the initial recovery rate. Stop the concentrate discharge. One closed-loop operation cycle is completed. Restart the concentrate full reflux mode and repeat steps (2) and (3).

2. The method for reducing reverse osmosis concentrate discharge according to claim 1, characterized in that, In the full reflux concentration stage described in step (2), the rate of increase in the concentration of the reverse osmosis feed water satisfies the dynamic material balance equation: V·dC / dt = Q f ·C f ; Where V is the total system volume; C is the real-time concentration of the reverse osmosis feed water after mixing raw water and concentrate; t is time; Q f C is the raw water feed flow rate; f This represents the concentration of the raw water.

3. A system for reducing reverse osmosis concentrate discharge, characterized in that, The system includes a raw water tank (21), a filter (23), and a reverse osmosis membrane module (25) connected in sequence. The concentrate outlet of the reverse osmosis membrane module (25) is connected to a concentrate control unit, and the product water outlet of the reverse osmosis membrane module (25) is connected to a product water collection unit. The concentrate control unit includes a concentrate output pipeline (10), a concentrate return pipeline (11) and a concentrate discharge pipeline (12) respectively connected to the concentrate output pipeline (10). The concentrate output pipeline (10) is equipped with a concentrate conductivity meter (36) and a concentrate flow regulating valve (37). The output end of the concentrate return pipeline (11) is connected to the inlet of the reverse osmosis membrane module (25). The concentrate return pipeline (11) is also equipped with a concentrate return automatic valve (38). The concentrate discharge pipeline (12) is equipped with a concentrate discharge automatic valve (39) and a concentrate discharge flow meter (40). A reverse osmosis feed water conductivity meter (32) is installed on the pipeline before the inlet of the reverse osmosis membrane module (25). The system also includes a PLC control unit (50), which is connected to a concentrate conductivity meter (36), a concentrate flow regulating valve (37), a concentrate return automatic valve (38), a concentrate discharge automatic valve (39), a concentrate discharge flow meter (40), and a reverse osmosis feed water conductivity meter (32), respectively.

4. The system for reducing reverse osmosis concentrate discharge according to claim 3, characterized in that, The raw water tank (21) is connected to a raw water tank level transmitter (51), and the raw water tank level transmitter (51) is connected to a PLC control unit (50).

5. The system for reducing reverse osmosis concentrate discharge according to claim 3, characterized in that, A raw water pump (22) is also provided between the raw water tank (21) and the filter (23). A scale inhibitor dosing tank (41) is also connected to the pipeline between the raw water pump (22) and the filter (23). The scale inhibitor dosing tank (41) is controlled by the scale inhibitor dosing pump (42).

6. The system for reducing reverse osmosis concentrate discharge according to claim 3, characterized in that, The filter (23) is equipped with a raw water flow meter (31) at its inlet, and the raw water flow meter (31) is connected to the PLC control unit (50).

7. The system for reducing reverse osmosis concentrate discharge according to claim 3, characterized in that, A high-pressure pump (24) is also provided between the filter (23) and the reverse osmosis membrane module (25). The reverse osmosis feed water conductivity meter (32) is located at the inlet of the high-pressure pump (24). The output end of the concentrate return pipeline (11) is connected to the inlet of the reverse osmosis membrane module (25) through the high-pressure pump (24). A reverse osmosis feed water pressure sensor (33) is provided at the inlet of the reverse osmosis membrane module (25). The reverse osmosis feed water pressure sensor (33) is connected to the PLC control unit (50).

8. The system for reducing reverse osmosis concentrate discharge according to claim 3, characterized in that, The reverse osmosis membrane module (25) is also equipped with a reverse osmosis permeate flow meter (34) and a reverse osmosis permeate conductivity meter (35) on the permeate pipeline. Both the reverse osmosis permeate flow meter (34) and the reverse osmosis permeate conductivity meter (35) are connected to the PLC control unit (50).

9. The system for reducing reverse osmosis concentrate discharge according to claim 3, characterized in that, The product water collection unit includes a product water tank (26) and a product water tank level transmitter (52) connected thereto. The product water outlet of the reverse osmosis membrane module (25) is connected to the product water tank (26), and the product water tank level transmitter (52) is connected to the PLC control unit (50).

10. An application of the method for reducing reverse osmosis concentrate discharge according to any one of claims 1 to 2, characterized in that, It is used in the front-end reverse osmosis process for ultrapure water preparation in the photovoltaic, electronic semiconductor, and display panel industries, as well as in the reverse osmosis reuse process for recycled water.

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