A tunnel wastewater treatment device based on multi-stage cross-flow filtration concentration

Abstract

The utility model relates to a kind of tunnel wastewater treatment device based on multistage crossflow filtration concentration, comprising: sludge-water separation unit;At least two or more crossflow filtration units;Concentrated water collection box;Variable frequency pump;Online turbidity monitoring unit;Automatic valve;PLC control unit;Backwashing unit;Positive washing unit, multistage crossflow filtration mode can effectively remove various types of particulate impurities and suspended solids in wastewater, effluent turbidity is stabilized at 10NTU or less, the removal rate of turbidity and suspended solids can reach more than 99%, slow down membrane pollution;Membrane pressure and effluent flow are automatically regulated by turbidity feedback, reducing the frequency of manual intervention;Automatic backwashing and positive washing function are set, to prolong the life of membrane module.

Description

Technical Field

[0001] This utility model relates to the field of rapid wastewater treatment technology, specifically a tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration. Background Technology

[0002] With the rapid development of transportation infrastructure construction, its impact on the ecological environment is receiving increasing attention. Tunnel engineering, a common and crucial construction method in railway construction, is widely used in mountainous and hilly areas. The large amounts of wastewater generated during tunnel excavation have become a major source of water pollution. Railway tunnel construction wastewater typically floods the natural environment in large quantities within a short period, severely impacting the regional aquatic ecosystem and disrupting its balance and stability. Simultaneously, this wastewater may also seep into the soil, polluting it and altering its physical and chemical properties.

[0003] The main sources of wastewater from railway tunnel construction include groundwater inflow, bedrock fissure water, water used for tunnel drilling, dust suppression water inflow, and wastewater generated from shotcrete and grouting. The main pollutant is suspended solids, with a content as high as 37–6530 mg / L. The particles are very small, mostly between 1 and 100 μm. At the same time, due to the unstable water volume, the conventional sedimentation combined with filtration method leads to excessive load on the sedimentation tank, and silt easily accumulates rapidly. Insufficient cleaning and maintenance result in too short a hydraulic stop time, which prevents the suspended solids in the wastewater from settling sufficiently, affecting the treatment effect and failing to meet discharge requirements.

[0004] Therefore, there is an urgent need for a wastewater treatment technology for railway tunnel construction with high suspended solids content. Utility Model Content

[0005] To overcome the shortcomings of the existing technology, the purpose of this utility model is to provide a tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration. The device has the functions of multi-stage concentration of concentrated water, dynamic adjustment of membrane pressure and automatic feedback control, which extends the service life of ceramic membrane, realizes efficient purification and resource utilization of wastewater, and solves the problems mentioned in the background technology.

[0006] This utility model discloses a tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration, suitable for the rapid treatment of wastewater from railway tunnel construction, effectively removing high suspended solids from the wastewater. Through a circulating treatment method, this wastewater treatment device significantly improves its adaptability to wastewater shock loads, enabling stable operation and meeting treatment needs under different water quality conditions. Simultaneously, while removing pollutants, the device effectively reduces wastewater discharge during the treatment process, even achieving a zero-discharge target.

[0007] To achieve the above objectives, this utility model provides a tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration. The wastewater treatment device includes: a mud-water separation unit; at least two stages of cross-flow filtration units, each stage of which is equipped with two or more stages of cross-flow filtration devices, with the concentrate outlet of each stage of the cross-flow filtration module connected to the inlet of the next stage of the filtration module to achieve progressive concentration of concentrate; a concentrate collection tank located between each filtration unit for concentrate buffering and regulation; and a variable frequency pump for transporting raw water and regulating the flow rate. After pretreatment, the raw water for each unit is delivered to the first-stage filtration unit via a variable frequency pump. An online turbidity monitoring unit monitors the turbidity of the water before the membrane module in the system. Automatic valves regulate membrane pressure and concentrate output. A PLC control unit, in conjunction with the online turbidity monitoring unit, controls the variable frequency pump speed and the opening of the automatic valves. A backwashing unit includes a backwashing pump and an air-washing interface located near the filtered water outlet to achieve combined air-water backwashing. A forward flushing unit is connected to a clean water source and equipped with an electrically controlled valve to perform a gravity-flow forward flushing operation when the system requires it.

[0008] The wastewater treatment unit employs a cross-flow filtration method for staged concentration. Turbidity feedback controls membrane pressure and effluent flow rate, automatically adjusting the variable frequency pump speed and automatic valve opening. The sludge-water separation unit separates the concentrated filtrate from the sediment in the concentrate tank, utilizing the sludge cake as a resource, and returning the supernatant to the beginning of the system to re-enter the multi-stage cross-flow filtration and concentration system.

[0009] Online turbidity monitoring units are installed before each stage of the variable frequency pump to detect changes in turbidity of the water before the membrane in real time and transmit the data to the PLC control unit in real time.

[0010] Furthermore, each cross-flow filtration unit uses a tubular ceramic membrane with a filtration accuracy of 0.1–0.2 μm, and is equipped with a multi-core membrane housing assembly with a membrane housing pressure resistance of 0.6 MPa or higher.

[0011] Furthermore, the concentrate collection tank is used to coordinate the influent flow rate of the next stage. It adopts a conical bottom structure with an included angle of 60° to 75° and is equipped with a sludge discharge port at the bottom. The sludge discharge system is automatically activated by controlling the sludge level gauge.

[0012] Furthermore, the online turbidity monitoring unit is installed before each stage of the variable frequency pump, at a 45° angle above the bottom of the pipeline. This avoids interference from sediment or air bubbles affecting the readings. It detects changes in turbidity of the water before the membrane in real time and transmits the data to the PLC control unit.

[0013] The concentrate from each stage of filtration is temporarily stored in the concentrate tank to regulate the concentrate flow rate and system rhythm. An automatic sludge removal system is installed at the bottom of the concentrate tank, periodically pumping settled sludge into the sludge-water separation unit for treatment via a sludge level gauge or timed control program. This structure effectively prevents sludge accumulation and blockage in the concentrate tank, while ensuring continuous operation and efficient concentration of the device. An optional stirring device can be added to improve the settling conditions for fine particles.

[0014] The variable frequency pump and automatic valve are controlled in a closed loop via a PLC control unit, enabling automatic adjustment of membrane pressure and flow rate. Specifically, the automatic valve and variable frequency pump are linked, and the valve opening is automatically adjusted based on membrane pressure and concentrate return flow rate.

[0015] Furthermore, the PLC control unit includes a comprehensive processing module for signals from level, flow, pressure, and sludge level sensors. This module performs coordinated control of pump speed, valve opening, membrane pressure at each stage, and sludge flow, enabling adaptive system operation. In other words, the PLC control unit integrates data from level gauges, flow meters, pressure sensors, turbidity meters, and sludge level gauges to perform coordinated control of pump speed, valve opening, membrane pressure at each stage, and sludge flow, achieving adaptive system operation.

[0016] Furthermore, the forward flushing water in the forward flushing unit enters the membrane module by gravity flow. Forward flushing is initiated once every 3 hours of operation, lasting 2-3 minutes, with the valves opened and closed by the PLC control unit. The air-water ratio and frequency of the backflushing unit are set and automatically adjusted by the PLC control unit. The backflushing unit uses a combined air-water method for self-cleaning of the membrane module, with a backflushing cycle of 30-60 minutes. Compressed air and cleaning water are mixed at a volume ratio of 1:2 to 1:3 and then injected into the membrane tube.

[0017] Furthermore, the air-water ratio and frequency of the backwashing unit are set and automatically adjusted by the PLC control unit; the backwashing unit uses a combined air-water method to self-clean the membrane module, with a backwashing cycle of 30 to 60 minutes. Compressed air and cleaning water are mixed at a volume ratio of 1:2 to 1:3 and then injected into the membrane tube. The air bubbles generate strong disturbance and shear force in the membrane cavity, effectively peeling off the fouling layer on the membrane surface, improving the backwashing effect and reducing water consumption.

[0018] Furthermore, each cross-flow filtration unit is equipped with an independent membrane pressure control unit and a concentrate outlet. The membrane pressure control unit automatically adjusts the operating pressure according to the raw water turbidity. When the turbidity level is <150 NTU, the membrane pressure difference is 0.15–0.2 MPa, ensuring stable operation and periodic backwashing. When the turbidity level is 150 NTU < 500 NTU, the membrane pressure difference is 0.20–0.25 MPa, increasing the shear force and appropriately increasing the pressure, with short-cycle backwashing. When the turbidity level is >500 NTU, the membrane pressure difference is 0.25–0.3 MPa, with high shear to prevent scaling, using pulsed cross-flow combined with high-frequency backwashing. During operation, the tubular ceramic membrane is dynamically adjusted by the PLC control unit based on turbidity feedback to maintain a stable cross-flow velocity and transmembrane pressure difference, improving membrane flux stability and anti-fouling capability.

[0019] Compared with the prior art, the beneficial effects of this utility model are:

[0020] 1. Multi-stage utilization of concentrated wastewater significantly improves water resource utilization efficiency and can achieve the goal of zero discharge;

[0021] 2. The multi-stage cross-flow filtration method can effectively remove various particulate impurities and suspended solids in wastewater, and the turbidity of the effluent is stable below 10 NTU. The removal rate of turbidity and suspended solids can reach more than 99%, thus reducing membrane fouling.

[0022] 3. Turbidity feedback enables automatic adjustment of membrane pressure and effluent flow rate, reducing the frequency of manual intervention;

[0023] 4. Automatic backwashing and forward washing functions are provided to extend the membrane module life;

[0024] 5. It features high resistance to impact loads, high integration, and stable operation, making it suitable for tunnel construction scenarios under various geological and water quality conditions.

[0025] 6. The sludge can be reused after dewatering, which is environmentally friendly and meets the requirements of green construction in railway tunnel construction. This utility model can be widely applied to the field of wastewater from railway tunnel construction, and has good application prospects and economic value. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of a tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration proposed in this utility model.

[0027] In the attached image:

[0028] 1. Filter inlet; 2. Filtered water outlet; 3. Gas backflush inlet; 4. Filtered water outlet; 5. Concentrate outlet; 6. Sludge outlet; 7. First-stage concentrate collection tank; 8. Second-stage concentrate collection tank; 9. Clear water tank; 11. First-stage pressure gauge; 12. First-stage flow meter; 13. First-stage online turbidity monitor; 14. Second-stage pressure gauge; 15. Second-stage flow meter; 16. Second-stage online turbidity monitor; 17. Third-stage pressure gauge; 18. Third-stage flow meter; 19. Third-stage online turbidity monitor; 21. First-stage variable frequency pump; 22. Second-stage variable frequency pump; 23. Third-stage variable frequency pump; 24. Backwash water pump; 25. First-stage ceramic membrane filtration unit; 26. Second-stage ceramic membrane filtration unit; 27. Third-stage ceramic membrane filtration unit; 28. Sludge-water separation unit; 31 32. First-stage concentrate tank sludge level gauge; 33. Second-stage concentrate tank sludge level gauge; 44. Backwash water pump pressure gauge; 45. Concentrate outlet pipe; 46. Clear water outlet pipe and backwash steam-water pipe; 47. Forward flush pipe; 48. Concentrate tank sludge discharge pipe; 49. Sludge discharge pipe; 50. Supernatant return pipe; 51. First-stage automatic pressure valve; 52. Second-stage automatic pressure valve; 53. Third-stage automatic pressure valve; 54. First-stage concentrate outlet automatic valve; 55. Second-stage concentrate outlet automatic valve; 56. Clear water outlet automatic valve; 57. Concentrate main outlet automatic valve; 58. Circulating flushing automatic valve; 59. Gas backflush inlet valve; 60. Backwash water pump downstream valve; 61. Clear water tank gravity flow valve; 62. First-stage concentrate collection tank sludge discharge valve; 63. Second-stage concentrate collection tank sludge discharge valve. Detailed Implementation

[0029] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. In the description of the present utility model, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and do not specifically refer to any order or sequence, nor are they intended to limit the present utility model. They are merely used to distinguish components or operations described with the same technical terms, and should not be construed as indicating or implying their relative importance or implicitly specifying the number of indicated technical features. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. The term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of the present utility model are intended to cover non-exclusive inclusion.

[0030] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to fixed connections or detachable connections; mechanical connections or electrical connections; direct connections or indirect connections through an intermediate medium; and internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances. Furthermore, in the description of this utility model, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model.

[0031] Example

[0032] This embodiment provides a tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration. The wastewater treatment device includes: a mud-water separation unit 28; a first-stage ceramic membrane filtration unit 25, a second-stage ceramic membrane filtration unit 26, and a third-stage ceramic membrane filtration unit 27, with each filtration unit connected in parallel with a cross-flow membrane tube assembly according to the water volume, and the concentrate outlet 5 of each cross-flow filtration unit connected to the inlet of the next-stage filtration unit; a first-stage concentrate collection tank 7 and a second-stage concentrate collection tank 8, located between each filtration unit; a first-stage variable frequency pump 21, a second-stage variable frequency pump 22, and a third-stage ceramic membrane filtration unit 27. The three-stage variable frequency pump 23 is used to transport raw water and regulate flow rate; the first-stage online turbidity monitor 13, the second-stage online turbidity monitor 14, and the third-stage online turbidity monitor 15 are used to monitor the turbidity of the water before the membrane module in the system, and simultaneously control the speed of the variable frequency pump and the opening of the automatic valve to control the membrane pressure difference and the flow rate through the membrane; the first-stage automatic valve 51, the second-stage automatic valve 52, and the third-stage automatic valve 53 regulate the membrane pressure and the concentrate output; the system also includes a backwash steam-water pipe 42 and a forward flush pipe 43 for cleaning the membrane module.

[0033] With a raw water turbidity of 100 NTU, the designed daily treatment capacity is 200 m³. 3 For example, if it runs continuously for 20 hours a day.

[0034] After pretreatment, the raw water flows into the filter inlet 1 by gravity and is then transported to the first-stage ceramic membrane filter unit 25 by the first-stage variable frequency pump 21. The operating frequency of the first-stage variable frequency pump 21 and the opening degree of the first-stage automatic valve 51 are controlled by the first-stage online turbidity monitor 13 to achieve the purpose of controlling the membrane pressure difference and the flow rate through the membrane.

[0035] The first-stage ceramic membrane filtration unit 25 is designed with a membrane area of ​​16m². 2 The designed inlet water volume is 10.0 m³. 3 / h, designed filtration capacity is 6.6m³ / h. 3 / h, designed concentrate flow rate is 3.4m³ / h. 3 The concentration of concentrate is controlled at 30% per hour; the operating pressure is set at 0.15 MPa; a 0.1 μm tubular ceramic membrane cross-flow filtration system is used; and the membrane design flux is 430 L / m³. 2 •h, the effluent turbidity is ≤10NTU, and the water quality information is monitored in real time by the first-stage pressure gauge 11, the first-stage flow meter 12 and the first-stage online turbidity monitor 13 and fed back to the PLC control unit.

[0036] The concentrated water from the first-stage ceramic membrane filtration unit 25 is then transported to the second-stage ceramic membrane filtration unit 26 by the second-stage variable frequency pump 22. The operating frequency of the second-stage variable frequency pump 22 and the opening degree of the second-stage automatic valve 52 are controlled by the second-stage online turbidity monitor 16 to control the membrane pressure difference and the flow rate through the membrane. The filtered water from the first-stage ceramic membrane filtration unit 25 flows out from the filtered water outlet 4, through the clear water outlet pipe and the backwash steam water pipe 42 to the filtered water main outlet 2, and then flows into the clear water tank 9. The concentrated water enters the first-stage concentrated water tank 7 through the concentrated water outlet 5.

[0037] The second-stage ceramic membrane filter unit 26 has a designed area of ​​6m². 2 The designed inlet water volume is 3.4m³. 3 / h, designed filtration capacity is 2.3m³ / h. 3 / h, designed concentrate flow rate is 1.1m³ / h. 3 The concentration of concentrate is controlled at 30% per hour; the operating pressure is set at 0.20 MPa; a 0.1 μm tubular ceramic membrane cross-flow filtration system is used; and the membrane design flux is 410 L / m³. 2 The system monitors water quality information in real time via the second-stage pressure gauge 14, the second-stage flow meter 15, and the second-stage online turbidity monitor 16, and feeds the information back to the PLC control unit.

[0038] The concentrated water from the second-stage ceramic membrane filtration unit 26 is then transported to the third-stage ceramic membrane filtration unit 27 by the third-stage variable frequency pump 23. The operating frequency of the third-stage variable frequency pump 23 and the opening degree of the third-stage automatic valve 53 are controlled by the third-stage online turbidity monitor 19 to control the membrane pressure difference and the flow rate through the membrane. The filtered water from the second-stage ceramic membrane filtration unit 26 flows out from the filtered water outlet 4, through the clear water outlet pipe and the backwash steam water pipe 42 to the filtered water main outlet 2, and then flows into the clear water tank 9. The concentrated water enters the second-stage concentrated water tank 8 through the concentrated water outlet 5.

[0039] The third-stage ceramic membrane filter unit 27 has a designed area of ​​3m². 2 The designed inlet water volume is 1.1m³.3 / h, designed filtration capacity is 0.55m³ / h. 3 / h, designed concentrate flow rate is 0.55m³ / h. 3 The concentration ratio is controlled at 50%; the operating pressure is set at 0.25 MPa; a 0.1 μm tubular ceramic membrane cross-flow filtration system is used; and the membrane design flux is 210 L / m³. 2 •h is the real-time monitoring of water quality information, which is fed back to the PLC control unit through the third-stage pressure gauge 17, the third-stage flow meter 18, and the third-stage online turbidity monitor 19.

[0040] The filtered water from the third-stage ceramic membrane filtration unit 27 flows out from the filtered water outlet 4, through the clear water outlet pipe and the backwash steam water pipe 42 to the filtered water main outlet 2, and then flows into the clear water tank 9; the concentrated water is sent to the mud-water separation unit 28 through the concentrated water outlet pipe 41 for mud-water separation, and the supernatant returns to the beginning of the device through the supernatant return pipe 46 as recycled water and enters the mud-water separation unit 28 through the filter inlet 1 to form a closed loop.

[0041] The first-stage concentrate tank 7 and the second-stage concentrate tank 8 are used to coordinate the inlet flow rate of the next stage. They adopt a conical bottom structure with an included angle of 65° and a sludge discharge port at the bottom. The sludge discharge system is automatically activated by the sludge level gauges 31 and 32 of the first-stage concentrate tank. The bottom has an automatic sludge discharge port, which is connected to the sludge-water separation unit 28 through the concentrate tank sludge discharge pipe 44 for sludge-water separation. The supernatant returns to the beginning of the system through the supernatant return pipe 46 and is used as recycled water. It enters the separation device through the filter inlet 1 to form a closed loop. The sludge cake is transported to the sludge discharge outlet 6 through the sludge discharge pipe 45 for resource utilization.

[0042] The first-stage concentrate tank sludge level gauge 31 and the second-stage concentrate tank sludge level gauge 32 adopt a linkage mode with the PLC control unit: the high liquid level is set to 70cm and the low liquid level to 40cm. After the sludge level reaches the upper limit, the PLC triggers the opening of the first-stage concentrate collection tank sludge discharge valve 62 and the second-stage concentrate collection tank sludge discharge valve 63. The sludge discharge pump runs to the lower liquid level limit and closes the first-stage concentrate collection tank sludge discharge valve 62 and the second-stage concentrate collection tank sludge discharge valve 63.

[0043] After each filtration cycle, the PLC system automatically closes the first-stage concentrate outlet valve 54, the second-stage concentrate outlet valve 55, and the total concentrate outlet valve 57, and opens the clear water tank gravity flow valve 61 and the circulation flushing valve 58. The opening of the first-stage automatic valve 51, the second-stage automatic valve 52, and the third-stage automatic valve 53 is increased to 100%. The filtered water generated in the clear water tank 9 flows by gravity to the first-stage variable frequency pump 21. The first-stage variable frequency pump 21 is turned on to perform system circulation cleaning. Forward flushing is performed 6 to 8 times a day, with a time of 90 seconds per flush, to ensure that fine particles do not adhere to the surface of the membrane module for a long time.

[0044] The clear water tank 9 is equipped with a backwashing device, which uses a combined air and water method for membrane module self-cleaning. During rinsing, the PLC system automatically controls and closes the clear water outlet valve 56, opens the gas backflush inlet valve 59 and the backwash water pump outlet valve 60, and uses the backwash water pump 24 and backwash water pump pressure gauge 33 to extract part of the water source in the clear water tank and control the backwash pressure. Compressed air is introduced from the gas backflush inlet 3 using an air compressor. The compressed air and cleaning water are mixed at a volume ratio of 1:2 and then injected into the membrane tube. The backwash cycle is 180 minutes, the backwash pressure is about 0.4 MPa, and the time is controlled within 60 seconds. The recovery rate can reach 70% of the highest water volume of the previous backwash. The bubbles generate strong disturbance and shear force in the membrane cavity, effectively peeling off the fouling layer on the membrane surface, improving the backwash effect and reducing water consumption, effectively reducing the risk of membrane fouling and extending the service life of the membrane module.

[0045] Meanwhile, ensure daily chemical flushing by preparing a mixed solution of 1% sodium hydroxide and 1.5% sodium hypochlorite and circulating it for 50 minutes in the same manner as the forward flushing. This can restore the membrane flux to 95% of the membrane's maximum flux.

[0046] This invention employs a multi-stage cross-flow filtration method to effectively remove various particulate impurities and suspended solids from wastewater, with effluent turbidity consistently below 10 NTU. The removal rate of turbidity and suspended solids can reach over 99%, mitigating membrane fouling. Turbidity feedback enables automatic adjustment of membrane pressure and effluent flow rate, reducing the frequency of manual intervention. Automatic backwashing and forward washing functions are included to extend the lifespan of the membrane module.

[0047] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration, characterized in that, include: The system includes: a mud-water separation unit; at least two stages of cross-flow filtration units, each stage connected in parallel with cross-flow membrane tubes according to water volume, with the concentrate outlet of each stage connected to the inlet of the next stage; a concentrate collection tank located between the filtration units; a variable frequency pump for delivering raw water and regulating flow rate; an online turbidity monitoring unit for monitoring the turbidity of the water before the membrane modules; automatic valves for regulating membrane pressure and concentrate output; a PLC control unit that works in conjunction with the online turbidity monitoring unit to control the variable frequency pump speed and automatic valve opening; a backwashing unit, including a backwash water pump and air-wash interface located near the filtered water outlet for combined air-water backwashing; and a forward flushing unit connected to a clean water source and equipped with electrically controlled valves.

2. The tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration according to claim 1, characterized in that, Each cross-flow filtration unit uses a tubular ceramic membrane with a filtration accuracy of 0.1–0.2 μm and is equipped with a multi-core membrane housing assembly with a membrane housing pressure resistance of 0.6 MPa or higher.

3. The tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration according to claim 1, characterized in that, The concentrate collection tank is used to coordinate the influent flow rate of the next stage. It adopts a conical bottom structure with an included angle of 60° to 75° and is equipped with a sludge discharge port at the bottom. The sludge discharge system is automatically activated by the sludge level gauge.

4. The tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration according to claim 1, characterized in that, The online turbidity monitoring unit is installed before each stage of the variable frequency pump, at a 45° angle above the bottom of the pipeline.

5. The tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration according to claim 1, characterized in that, The PLC control unit includes a comprehensive processing module for signals from liquid level, flow rate, pressure, and sludge level sensors. It performs linkage control on pump speed, valve opening, membrane pressure at each stage, and sludge-water mixture to achieve adaptive operation of the system.

6. The tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration according to claim 1, characterized in that, The forward flushing water in the forward flushing unit enters the membrane module by gravity flow; the forward flushing is initiated once every 3 hours of operation, lasting for 2 to 3 minutes, and the valve is opened and closed by the PLC control unit; the air-water ratio and frequency of the backflushing unit are set and automatically adjusted by the PLC control unit; the backflushing unit uses a combined air and water method to self-clean the membrane module, and the backflushing cycle is 30 to 60 minutes. Compressed air and cleaning water are mixed at a volume ratio of 1:2 to 1:3 and then injected into the membrane tube.

7. The tunnel wastewater treatment device based on multi-stage cross-flow filtration and concentration according to claim 2, characterized in that, Each cross-flow filtration unit is equipped with an independent membrane pressure control unit and a concentrate outlet. The membrane pressure control unit automatically adjusts the operating pressure according to the turbidity of the raw water. When the turbidity level is <150 NTU, the membrane pressure difference is 0.15–0.2 MPa; When 150 NTU < turbidity grade < 500 NTU, the membrane pressure difference is 0.20–0.25 MPa; When the turbidity level is >500 NTU, the membrane pressure difference is 0.25–0.3 MPa; During operation, the tubular ceramic membrane is dynamically adjusted by the PLC control unit based on turbidity feedback, which controls the frequency of the variable frequency pump and the valve opening.

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