A method for deep treatment of wastewater by gradient utilization of reverse osmosis concentrated water and energy recovery

Abstract

The present application relates to wastewater advanced treatment technical field, specifically disclose a kind of gradient utilization and energy recovery of reverse osmosis concentrated water wastewater advanced treatment method.The technical scheme of the present application is by the path distribution of concentrated water according to pressure threshold, control energy recovery device extracts pressure energy from concentrated water and is coupled to the water inlet end of reverse osmosis membrane module, while controlling concentrated water sequentially flows through multi-stage membrane concentration device to carry out gradient concentration and step-by-step fresh water output, according to the conductivity of fresh water feedback adjusts the operating pressure of each stage membrane concentration device, and controls the last stage concentrated water into evaporation crystallization unit, solve the single concentrated water disposal path in prior art, pressure energy waste, water resource recovery is insufficient, the problem of high processing cost and easy to cause secondary pollution, reduce overall operation energy consumption, improve water resource recovery rate and operation economy.

Description

Technical Field

[0001] This invention relates to the field of advanced wastewater treatment technology, and in particular to an advanced wastewater treatment method that utilizes reverse osmosis concentrate gradient and energy recovery. Background Technology

[0002] Reverse osmosis technology has been widely used in the field of advanced industrial wastewater treatment. It uses a high-pressure pump to drive wastewater through a membrane module for purification and separation. The resulting high-salinity concentrate is typically discharged directly or subjected to simple evaporation and crystallization. Current treatment methods do not effectively recover the usable water resources remaining in the concentrate, leading to water waste and increased treatment costs. Furthermore, the concentrate is discharged at high pressure, and existing systems lack an effective mechanism for recovering this pressure energy, resulting in high overall energy consumption. In addition, the concentrate contains high concentrations of salt and organic matter, and direct discharge can easily cause secondary pollution. Existing treatment processes fail to achieve synergistic optimization of the gradient utilization of valuable components in the concentrate and energy recovery. The concentrate treatment path is singular, and the water resource and energy recovery processes are disconnected, restricting the resource utilization efficiency and operational economy of advanced wastewater treatment systems and failing to meet current development needs for energy conservation, emission reduction, and resource recycling.

[0003] Therefore, there is an urgent need to provide a technical solution to address the above problems. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for advanced wastewater treatment that utilizes reverse osmosis concentrate gradient and recovers energy. The technical solution of this method is as follows: When the pressure at the concentrate outlet of the reverse osmosis membrane module is greater than a preset threshold, the concentrate is allocated to the first path; otherwise, it is allocated to the second path for direct discharge. In the first path, the energy recovery device is controlled to extract pressure energy from the concentrate and couple the pressure energy to the inlet of the reverse osmosis membrane module. At the same time, the concentrate after the energy recovery device is controlled to flow through at least two membrane concentration devices in sequence. Each membrane concentration device concentrates the concentrate and produces fresh water. The conductivity of the freshwater produced by each stage of the membrane concentration unit is detected. If the conductivity of the freshwater is less than the target conductivity, the operating pressure of the corresponding stage of the membrane concentration unit is reduced; otherwise, the operating pressure of the corresponding stage of the membrane concentration unit is increased. The conductivity of the concentrate discharged from the final stage membrane concentration unit is collected. When the conductivity of the concentrate is greater than the discharge threshold, the final stage concentrate is controlled to enter the evaporation and crystallization unit.

[0005] The technical solution of this invention allocates the path of concentrated water according to the pressure threshold, controls the energy recovery device to extract pressure energy from the concentrated water and couple it to the inlet of the reverse osmosis membrane module, and controls the concentrated water to flow through a multi-stage membrane concentration device for gradient concentration and step-by-step desalination. The operating pressure of each stage of the membrane concentration device is adjusted according to the conductivity of the desalination water, and the final stage of concentrated water is controlled to enter the evaporation and crystallization unit. This solves the problems of single concentrated water treatment path, waste of pressure energy, insufficient water resource recovery, high treatment cost and easy secondary pollution in the prior art, reduces the overall operating energy consumption, and improves the water resource recovery rate and operating economy.

[0006] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0007] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0008] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a schematic flowchart of an embodiment of a wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to the present invention. Detailed Implementation

[0009] Exemplary embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0010] Figure 1 This diagram illustrates a flow chart of an embodiment of a wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery provided by the present invention, executed by a control terminal. Figure 1 As shown, this wastewater deep treatment method utilizing reverse osmosis concentrate gradient and energy recovery includes the following steps: S1. When the pressure value of the concentrate outlet is greater than the preset threshold during the operation of the reverse osmosis membrane module, the concentrate is allocated to the first path; otherwise, it is allocated to the second path for direct discharge.

[0011] The reverse osmosis membrane module refers to the core separation unit used for advanced wastewater treatment. It forces water molecules through a semi-permeable membrane under high pressure, while retaining salts and organic matter, thus producing fresh water and concentrated water. For example, a chemical plant installed a reverse osmosis membrane module with a rated permeate flow rate of 50 m³ / h on May 1, 2026, with an inlet pressure of 1.6 MPa and an inlet conductivity of 3000 μS / cm. The concentrated water outlet refers to the interface on the reverse osmosis membrane module used to discharge the retained concentrated water. For example, during operation, the pressure measured at the concentrated water outlet of the aforementioned reverse osmosis membrane module was 1.2 MPa, and the concentrated water flow rate was 15 m³ / h.

[0012] The pressure value refers to the fluid pressure at the concentrate outlet; for example, after the reverse osmosis membrane module has been running continuously for 8 hours, the pressure at the concentrate outlet stabilizes between 1.15 MPa and 1.25 MPa. The preset threshold refers to a pre-set critical pressure value used to determine whether the concentrate needs pressure energy recovery and gradient utilization; for example, based on 50% of the reverse osmosis membrane module's feed water pressure of 1.6 MPa, the preset threshold is set to 0.8 MPa.

[0013] The first path refers to the flow channel through which the concentrate is allocated to energy recovery and cascade concentration treatment when the concentrate outlet pressure exceeds a preset threshold. For example, if the concentrate outlet pressure is 1.2 MPa, which is 0.8 MPa higher than the preset threshold, the control system switches the concentrate to the first path. The second path refers to the flow channel through which the concentrate is directly discharged without energy recovery and concentration treatment when the concentrate outlet pressure is less than or equal to the preset threshold. For example, if the concentrate outlet pressure drops to 0.7 MPa due to deterioration of the feed water quality, the control system allocates the concentrate to the second path for direct discharge.

[0014] S2. In the first path, the energy recovery device is controlled to extract pressure energy from the concentrate and couple the pressure energy to the inlet of the reverse osmosis membrane module. At the same time, the concentrate after passing through the energy recovery device is controlled to flow through at least two membrane concentration devices in sequence. Each membrane concentration device concentrates the concentrate and produces fresh water.

[0015] The energy recovery device refers to a device that extracts pressure energy from high-pressure concentrate and transfers it to the feed water end of the reverse osmosis membrane module. For example, a piston-type pressure exchanger is installed in the first path as an energy recovery device, which extracts pressure energy from concentrate with a pressure of 1.2 MPa. Pressure energy refers to the pressure potential energy of a high-pressure fluid that can be used to do work. For example, the pressure energy contained in the 1.2 MPa concentrate can increase the feed water pressure by 0.5 MPa after being converted by the energy recovery device. The feed water end refers to the raw water inlet location of the reverse osmosis membrane module. For example, the energy recovery device couples the recovered pressure energy to the feed water end of the reverse osmosis membrane module, increasing the feed water pressure from 1.6 MPa to 2.1 MPa.

[0016] The membrane concentration unit refers to a membrane separation device that further concentrates the concentrate. For example, in the first path, two membrane concentration units are connected in series, each using a reverse osmosis membrane module. Concentration treatment refers to the operation of increasing the concentration of salt and organic matter in the concentrate while simultaneously producing fresh water through membrane separation. For example, the first-stage membrane concentration unit concentrates the incoming concentrate from a conductivity of 40,000 μS / cm to 60,000 μS / cm, while simultaneously producing fresh water.

[0017] S3. Detect the conductivity of the freshwater produced by each stage of the membrane concentration unit. If the conductivity of the freshwater is less than the target conductivity, reduce the operating pressure of the corresponding stage of the membrane concentration unit; otherwise, increase the operating pressure of the corresponding stage of the membrane concentration unit.

[0018] Here, the freshwater conductivity refers to the electrical conductivity value of the freshwater produced by the membrane concentration unit, used to characterize the purity of the freshwater; for example, the conductivity of the freshwater produced by the first-stage membrane concentration unit is 150 μS / cm. The target conductivity refers to the upper limit of the conductivity expected to be achieved in the freshwater produced by the membrane concentration unit; for example, according to the recycled water standard, the target conductivity is set at 200 μS / cm.

[0019] Operating pressure refers to the pressure applied to the inlet side of the membrane module during operation of the membrane concentration unit; for example, the current operating pressure of the first-stage membrane concentration unit is 2.0 MPa.

[0020] S4. Collect the conductivity of the concentrate discharged from the final stage membrane concentration unit. When the conductivity of the concentrate is greater than the discharge threshold, control the final stage concentrate to enter the evaporation and crystallization unit.

[0021] The term "final stage membrane concentrator" refers to the last stage in at least two stages of membrane concentrators; for example, in a first path with two membrane concentrators connected in series, the second stage is the final stage membrane concentrator. The term "concentrate conductivity" refers to the conductivity value of the concentrate discharged from the final stage membrane concentrator; for example, the conductivity of the concentrate discharged from the final stage membrane concentrator reaches 90,000 μS / cm.

[0022] The discharge threshold refers to the critical conductivity value at which the final stage concentrate is allowed to be directly discharged or enter the evaporation crystallization unit; for example, the discharge threshold is set to 80,000 μS / cm. The evaporation crystallization unit refers to a treatment device that evaporates water from the concentrate and causes salt crystallization through heating; for example, when the conductivity of the final stage concentrate (90,000 μS / cm) exceeds the discharge threshold of 80,000 μS / cm, the final stage concentrate is controlled to enter the evaporation crystallization unit for solidification treatment.

[0023] The technical solution of this embodiment allocates the path of the concentrate according to the pressure threshold, controls the energy recovery device to extract pressure energy from the concentrate and couple it to the inlet of the reverse osmosis membrane module, and controls the concentrate to flow through a multi-stage membrane concentration device for gradient concentration and step-by-step desalination. The operating pressure of each stage of the membrane concentration device is adjusted according to the conductivity of the desalination, and the final stage concentrate is controlled to enter the evaporation and crystallization unit. This solves the problems of single concentrate treatment path, waste of pressure energy, insufficient water resource recovery, high treatment cost and easy secondary pollution in the prior art, reduces the overall operating energy consumption, and improves the water resource recovery rate and operating economy.

[0024] In one alternative approach, the preset threshold is obtained by dividing the product of the inlet water pressure and the inlet water conductivity of the reverse osmosis membrane module by the product of the reference pressure and the reference conductivity, and then multiplying the result by a reference threshold.

[0025] The feed water pressure refers to the pressure applied to the raw water entering the reverse osmosis membrane module; for example, the feed water pressure of the reverse osmosis membrane module is 1.6 MPa. The feed water conductivity refers to the conductivity of the raw water entering the reverse osmosis membrane module; for example, the feed water conductivity of the reverse osmosis membrane module is 3000 μS / cm.

[0026] The reference pressure value refers to the pressure value used as a standardization benchmark when calculating the preset threshold; for example, the reference pressure value is set to 1.0 MPa. The reference conductivity refers to the conductivity value used as a standardization benchmark when calculating the preset threshold; for example, the reference conductivity is set to 2000 μS / cm. The benchmark threshold refers to the critical pressure value used as the base value in the dynamic calculation formula of the preset threshold; for example, the benchmark threshold is set to 0.6 MPa.

[0027] In the above-mentioned optional methods, the pressure threshold can be dynamically adjusted according to the actual feed water pressure and feed water conductivity of the reverse osmosis membrane module, thereby improving the rationality and accuracy of concentrate path allocation.

[0028] In one alternative embodiment, the energy recovery device is a piston-type pressure exchanger, which couples the extracted pressure energy to the inlet of the reverse osmosis membrane module through alternating pressure exchange between concentrated water and low-pressure feed water in the piston cylinder.

[0029] Among them, the piston pressure exchanger refers to an energy recovery device that realizes direct pressure exchange between high-pressure concentrate and low-pressure feed water through the reciprocating motion of the piston in the cylinder; for example, the energy recovery device uses a piston pressure exchanger, which has two symmetrical piston cylinders.

[0030] In this context, "concentrated water in the piston cylinder" refers to the high-pressure concentrated water contained on one side of the piston-type pressure exchanger; for example, the left chamber of the piston cylinder is filled with concentrated water at a pressure of 1.2 MPa. "Low-pressure feed water" refers to unpressurized or low-pressure raw water diverted from the inlet of the reverse osmosis membrane module; for example, purified water at a pressure of 0.2 MPa diverted from the main inlet pipe enters the right chamber of the piston cylinder. Alternating pressure exchange refers to the process where high-pressure concentrated water and low-pressure feed water are alternately pressurized and pressure energy is transferred during the reciprocating motion of the piston; for example, when the piston moves to the right, the high-pressure concentrated water on the left pushes the piston, pressurizing the low-pressure feed water on the right; when the piston moves to the left, the high-pressure concentrated water on the right pressurizes the low-pressure feed water on the left, and so on, alternating to complete the pressure exchange.

[0031] In the above-mentioned optional methods, a piston-type pressure exchanger is further used to achieve direct pressure transmission between the concentrate and the low-pressure feed water, and the extracted pressure energy is coupled to the feed water end of the reverse osmosis membrane module to improve the stability of energy recovery.

[0032] In one optional embodiment, an intermediate booster pump is provided between adjacent stages in the at least two-stage membrane concentration unit. The speed adjustment step of the intermediate booster pump includes: obtaining the difference between the real-time pressure value of the concentrate outlet of the previous stage membrane concentration unit and the operating pressure set value of the next stage membrane concentration unit, and controlling the speed of the intermediate booster pump according to the proportional-integral adjustment signal of the difference.

[0033] The intermediate booster pump refers to a pump installed between two adjacent membrane concentration units to increase the pressure of the concentrate to meet the operating pressure requirements of the next stage; for example, an intermediate booster pump is installed between the first-stage membrane concentration unit and the second-stage membrane concentration unit.

[0034] The real-time pressure value at the concentrate outlet refers to the pressure measurement at the concentrate outlet of the previous stage membrane thickener at the current moment; for example, the real-time pressure value at the concentrate outlet of the first stage membrane thickener is 1.8 MPa. The operating pressure setpoint refers to the target operating pressure value preset for the next stage membrane thickener; for example, the operating pressure setpoint for the second stage membrane thickener is 2.3 MPa.

[0035] Among them, the proportional-integral control signal refers to the control signal generated based on the proportional and integral calculation results of the pressure difference to control the speed of the intermediate booster pump; for example, the controller calculates that the difference between the real-time pressure value of the concentrate outlet of 1.8 MPa and the operating pressure set value of 2.3 MPa is 0.5 MPa, and outputs a frequency adjustment signal after proportional-integral calculation to increase the speed of the intermediate booster pump.

[0036] In the above-mentioned optional methods, an intermediate booster pump is further installed between two adjacent membrane concentration units, and the speed is controlled according to the proportional-integral adjustment signal to ensure a smooth transition of pressure between stages and to ensure the continuous operation of the multi-stage concentration process.

[0037] In one alternative approach, the step of detecting the conductivity of the freshwater produced by each stage of the membrane concentration unit includes: An online conductivity sensor is installed on the freshwater output pipeline of each stage membrane concentration unit. The online conductivity sensor acquires real-time conductivity signals by continuous sampling and transmits the real-time conductivity signals to the controller.

[0038] Among them, an online conductivity sensor refers to a detection element installed on a pipeline that can measure the conductivity of a fluid in real time; for example, an online conductivity sensor is installed on the freshwater output pipeline of a first-stage membrane concentration unit.

[0039] Continuous sampling refers to a working mode that repeatedly acquires signals without interruption or at extremely high frequencies; for example, an online conductivity sensor acquires conductivity data 10 times per second. Real-time conductivity signal refers to the electrical signal corresponding to the instantaneous conductivity measurement value output by the sensor; for example, an online conductivity sensor outputs a current signal of 4 to 20 mA, where 15 mA corresponds to 150 μS / cm. A controller refers to an automated device that receives sensor signals and outputs control commands according to a preset algorithm; for example, a programmable logic controller (PLC) receives real-time conductivity signals from an online conductivity sensor.

[0040] In the above-mentioned optional methods, online conductivity sensors are further configured on the freshwater output pipelines of each stage of the membrane concentration unit to obtain real-time conductivity signals through continuous sampling, providing timely data support for operating pressure regulation.

[0041] In one alternative approach, the step of reducing or increasing the operating pressure of the corresponding stage membrane concentration unit includes: The operating pressure is changed by adjusting the speed of the variable frequency booster pump on the inlet pipe of the corresponding stage membrane concentration unit. The adjustment range of the operating pressure is linearly related to the deviation of the freshwater conductivity from the target conductivity, the cumulative integral value of the deviation value, and the rate of change of the deviation value.

[0042] Among them, the variable frequency booster pump refers to a booster pump that adjusts the output pressure and flow by changing the power supply frequency to regulate the motor speed; for example, a variable frequency booster pump is installed on the inlet pipe of each stage membrane concentration unit.

[0043] In the above-mentioned optional methods, the operating pressure is further changed by adjusting the speed of the variable frequency booster pump, and the adjustment range is linearly related to the conductivity deviation, the cumulative integral of the deviation, and the rate of change, so as to achieve precise adjustment of the operating pressure.

[0044] In one alternative approach, the target conductivity is set in segments based on the feed water quality level of the reverse osmosis membrane module, and the step of determining the feed water quality level includes: Obtain the total dissolved solids (TDS) and turbidity values ​​of the feed water to the reverse osmosis membrane module. Multiply the TDS by a first weighting coefficient and add it to the turbidity by a second weighting coefficient. Determine the corresponding feed water quality level based on the preset range into which the sum falls.

[0045] The total dissolved solids (TDS) value refers to the total content of dissolved solids in water, usually expressed indirectly as mg / L or μS / cm; for example, the TDS value of the feed water for a reverse osmosis membrane module is 1500 mg / L. Turbidity value refers to the degree of light scattering caused by suspended particulate matter in water, measured in NTU; for example, the turbidity value of the feed water for a reverse osmosis membrane module is 5 NTU.

[0046] The first weighting factor is the multiplier factor assigned to the total dissolved solids value when calculating the influent water quality grade; for example, the first weighting factor is 0.7. The second weighting factor is the multiplier factor assigned to the turbidity value when calculating the influent water quality grade; for example, the second weighting factor is 0.3.

[0047] The preset range refers to a pre-defined numerical range used to map the weighted calculation results to the corresponding water quality level. For example, a weighted calculation result of 0 to 50 corresponds to Grade I water quality, 51 to 100 corresponds to Grade II water quality, and above 101 corresponds to Grade III water quality. The influent water quality level refers to the degree of pollution of the raw water as comprehensively assessed based on the total dissolved solids (TDS) and turbidity values. For example, a TDS value of 1500 multiplied by 0.7 plus a turbidity value of 5 multiplied by 0.3 equals 1050.5, which falls within the range above 101, thus the influent water quality level is determined to be Grade III.

[0048] In the above-mentioned optional methods, the water quality grade of the influent is further determined by weighting the total dissolved solids value and turbidity value, and the target conductivity is set in segments accordingly, so that the freshwater quality control standard is adapted to the actual conditions of the influent.

[0049] In one alternative approach, the step of collecting the conductivity of the concentrate discharged from the final membrane concentrator includes: When the conductivity of the concentrate is greater than the discharge threshold and the concentrate outlet flow rate of the final stage membrane concentration device is greater than the preset lower flow rate limit, the final stage concentrate is controlled to enter the evaporation and crystallization unit; otherwise, the final stage concentrate is returned to the front end of the energy recovery device in the first path.

[0050] The preset flow rate lower limit refers to the minimum flow rate of concentrate required to allow the final stage concentrate to enter the evaporation and crystallization unit. For example, if the preset flow rate lower limit is set to 2 m³ / h, the final stage concentrate flow rate will be returned to the front end of the energy recovery device if it is lower than 2 m³ / h.

[0051] In the above-mentioned optional methods, the final stage concentrate conductivity and outlet flow rate are used to determine whether it enters the evaporation crystallization unit or is returned to the energy recovery front end, so as to avoid the idling loss of the evaporation crystallization equipment under low flow conditions.

[0052] In one alternative approach, during the step of reducing or increasing the operating pressure of the corresponding stage membrane concentrator, the operating pressure adjustment value of the nth stage membrane concentrator is calculated using the following formula. : ; in, This indicates the operating pressure adjustment amount for the nth stage membrane concentration unit. It is a dimensionless proportionality coefficient. The conductivity of the freshwater produced by the nth stage membrane concentration unit. For the target conductivity, It is a non-linear exponential factor. The operating pressure value of the (n-1)th stage membrane concentration unit and when hour Take the concentrated water pressure value at the outlet of the energy recovery device. The coupling coefficient is... The freshwater flow rate produced by the (n-1)th stage membrane concentration unit. The permeate flow rate of the reverse osmosis membrane module. The conductivity of the concentrate at the inlet of the (n-1)th stage membrane concentration unit. Let be the conductivity of the concentrate at the outlet of the (n-1)th stage membrane concentration unit.

[0053] It should be noted that the above formula is based on the relative deviation between the conductivity of the freshwater produced by the nth stage membrane concentration unit and the target conductivity, amplified by a nonlinear exponential factor. It is combined with the operating pressure value of the previous stage and the coupling term formed by multiplying the ratio of the freshwater flow rate of the previous stage membrane concentration unit to the permeate flow rate of the reverse osmosis membrane module by the ratio of the inlet and outlet conductivity of the previous stage membrane concentration unit. The above formula, by introducing nonlinear correction and inter-stage coupling information, makes the adjustment of the operating pressure more adaptable to the gradual change of concentrate quality and the dynamic characteristics of the system, avoiding over-adjustment or under-adjustment caused by traditional linear adjustment, thereby improving the freshwater production quality and operational stability of each stage of the membrane concentration unit.

[0054] In the above-mentioned optional methods, a dimensionless proportional coefficient, a nonlinear exponential factor, and a coupling coefficient are further introduced to calculate the operating pressure adjustment amount, so that the pressure regulation takes into account the operating status of both the current stage and the upstream membrane concentration unit.

[0055] In one alternative approach, during the step of controlling the energy recovery device to extract pressure energy from concentrated water, the instantaneous efficiency coefficient of the energy recovery device is... The following relationship must be satisfied: ; in, Let be the instantaneous efficiency coefficient of the energy recovery device at time t. For reference efficiency values, The conductivity influencing factor Let be the conductivity of the concentrated water at the inlet of the energy recovery device at time t. The maximum allowable concentrate conductivity for the energy recovery device. Let τ be the concentrated water pressure at the inlet of the energy recovery device. This is the rated pressure value. The length of the integration time window. Let τ be the concentrate flow rate at the inlet of the energy recovery device. This is the rated flow rate. This refers to the factors affecting traffic flow fluctuations.

[0056] It should be noted that the above formula is based on the reference efficiency value of the energy recovery device, and is multiplied by a conductivity effect term corrected by an exponential decay factor for the ratio of inlet concentrate conductivity to the maximum allowable conductivity, a pressure fluctuation penalty term consisting of the pressure fluctuation intensity, rated pressure, and time window, and a flow fluctuation penalty term consisting of the flow fluctuation variance, rated flow rate, and time window. The product of these three terms defines the instantaneous efficiency coefficient. The above formula provides a basis for dynamically adjusting the operating parameters of the energy recovery device or triggering maintenance warnings by evaluating the actual efficiency of the energy recovery device under the coupling of multiple factors such as increased conductivity, drastic pressure changes, and flow pulsation in real time. This ensures the high efficiency and long-term reliability of pressure energy recovery.

[0057] In the above-mentioned optional methods, the instantaneous efficiency coefficient of the energy recovery device is further corrected based on the real-time conductivity, pressure fluctuation integral, and flow fluctuation integral to ensure stable output of the energy recovery process under operating condition fluctuations.

[0058] In one alternative approach, the freshwater produced by each stage of the membrane concentration unit is collected and reused as industrial makeup water in the production process, and the crystallized salt produced by the evaporation and crystallization unit is sold as industrial raw material after purity testing, thereby achieving full-scale cascade recovery of water and salt resources in the concentrate.

[0059] Among the above-mentioned optional methods, the comprehensive utilization rate of resources in the wastewater treatment system is further improved. By collecting the fresh water produced by each level of membrane concentration unit and using it as industrial supplement water for production processes, and selling the crystallized salt produced by the evaporation and crystallization unit as industrial raw material after purity testing, the full-scale cascade recovery of water resources and salt resources in the concentrated water is realized, reducing the total amount of pollutants discharged and increasing additional economic benefits.

[0060] In one alternative approach, the instantaneous efficiency coefficient of the energy recovery device... When the efficiency falls below the preset minimum value (e.g., 0.65), the controller triggers an online cleaning command or switches to the backup energy recovery device to ensure the energy recovery efficiency of the system's continuous operation.

[0061] Among the above-mentioned optional methods, the long-term efficient and stable operation of the energy recovery device is further guaranteed. When the instantaneous efficiency coefficient of the energy recovery device is lower than the preset efficiency lower limit, the controller triggers an online cleaning command or switches to the backup energy recovery device, avoiding the energy recovery efficiency decay caused by device contamination or aging, and reducing the risk of overall system energy consumption fluctuation.

[0062] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for advanced wastewater treatment utilizing reverse osmosis concentrate gradient and energy recovery, characterized in that, include: When the pressure at the concentrate outlet of the reverse osmosis membrane module is greater than a preset threshold, the concentrate is allocated to the first path; otherwise, it is allocated to the second path for direct discharge. In the first path, the energy recovery device is controlled to extract pressure energy from the concentrate and couple the pressure energy to the inlet of the reverse osmosis membrane module. At the same time, the concentrate after the energy recovery device is controlled to flow through at least two membrane concentration devices in sequence. Each membrane concentration device concentrates the concentrate and produces fresh water. The conductivity of the freshwater produced by each stage of the membrane concentration unit is detected. If the conductivity of the freshwater is less than the target conductivity, the operating pressure of the corresponding stage of the membrane concentration unit is reduced; otherwise, the operating pressure of the corresponding stage of the membrane concentration unit is increased. The conductivity of the concentrate discharged from the final stage membrane concentration unit is collected. When the conductivity of the concentrate is greater than the discharge threshold, the final stage concentrate is controlled to enter the evaporation and crystallization unit.

2. The wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to claim 1, characterized in that, The preset threshold is obtained by dividing the product of the inlet water pressure and the inlet water conductivity of the reverse osmosis membrane module by the product of the reference pressure and the reference conductivity, and then multiplying the result by the benchmark threshold.

3. The wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to claim 2, characterized in that, The energy recovery device is a piston-type pressure exchanger, which couples the extracted pressure energy to the inlet of the reverse osmosis membrane module through the alternating pressure exchange between concentrated water and low-pressure feed water in the piston cylinder.

4. The wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to claim 3, characterized in that, An intermediate booster pump is provided between adjacent two stages in the at least two-stage membrane concentration unit. The speed adjustment steps of the intermediate booster pump include: obtaining the difference between the real-time pressure value of the concentrate outlet of the previous stage membrane concentration unit and the operating pressure set value of the next stage membrane concentration unit, and controlling the speed of the intermediate booster pump according to the proportional-integral adjustment signal of the difference.

5. The wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to claim 4, characterized in that, The steps for testing the conductivity of the freshwater produced by each stage of the membrane concentration unit include: An online conductivity sensor is installed on the freshwater output pipeline of each stage membrane concentration unit. The online conductivity sensor acquires real-time conductivity signals by continuous sampling and transmits the real-time conductivity signals to the controller.

6. The wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to claim 5, characterized in that, The steps for reducing or increasing the operating pressure of the corresponding stage membrane concentration unit include: The operating pressure is changed by adjusting the speed of the variable frequency booster pump on the inlet pipe of the corresponding stage membrane concentration unit. The adjustment range of the operating pressure is linearly related to the deviation of the freshwater conductivity from the target conductivity, the cumulative integral value of the deviation value, and the rate of change of the deviation value.

7. The wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to claim 6, characterized in that, The target conductivity is set in stages according to the feed water quality level of the reverse osmosis membrane module. The steps for determining the feed water quality level include: Obtain the total dissolved solids (TDS) and turbidity values ​​of the feed water to the reverse osmosis membrane module. Multiply the TDS by a first weighting coefficient and add it to the turbidity by a second weighting coefficient. Determine the corresponding feed water quality level based on the preset range into which the sum falls.

8. The wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to claim 1, characterized in that, The steps for collecting the conductivity of the concentrate discharged from the final membrane concentration unit include: When the conductivity of the concentrate is greater than the discharge threshold and the concentrate outlet flow rate of the final stage membrane concentration device is greater than the preset lower flow rate limit, the final stage concentrate is controlled to enter the evaporation and crystallization unit; otherwise, the final stage concentrate is returned to the front end of the energy recovery device in the first path.

9. The wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to claim 7, characterized in that, In the step of reducing or increasing the operating pressure of the corresponding stage membrane concentrator, the operating pressure adjustment value of the nth stage membrane concentrator is calculated using the following formula. : ； in, This indicates the operating pressure adjustment amount for the nth stage membrane concentration unit. It is a dimensionless proportionality coefficient. The conductivity of the freshwater produced by the nth stage membrane concentration unit. For the target conductivity, It is a non-linear exponential factor. The operating pressure value of the (n-1)th stage membrane concentration unit and when hour Take the concentrated water pressure value at the outlet of the energy recovery device. The coupling coefficient is... The freshwater flow rate produced by the (n-1)th stage membrane concentration unit. The permeate flow rate of the reverse osmosis membrane module. The conductivity of the concentrate at the inlet of the (n-1)th stage membrane concentration unit. Let be the conductivity of the concentrate at the outlet of the (n-1)th stage membrane concentration unit.

10. The wastewater deep treatment method based on reverse osmosis concentrate gradient utilization and energy recovery according to claim 8, characterized in that, In the step of controlling the energy recovery device to extract pressure energy from concentrated water, the instantaneous efficiency coefficient of the energy recovery device is... The following relationship must be satisfied: ； in, Let be the instantaneous efficiency coefficient of the energy recovery device at time t. For reference efficiency values, The conductivity influencing factor Let be the conductivity of the concentrated water at the inlet of the energy recovery device at time t. The maximum allowable concentrate conductivity for the energy recovery device. Let τ be the concentrated water pressure at the inlet of the energy recovery device. This is the rated pressure value. The length of the integration time window. Let τ be the concentrate flow rate at the inlet of the energy recovery device. This is the rated flow rate. This refers to the factors affecting traffic flow fluctuations.

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