A membrane method for upgrading and reconstructing a tap water system and a control method

Abstract

The present invention discloses a membrane method for upgrading and reconstructing a tap water system and a control method. The system includes a water intake device, a mechanical mixing and folded plate reaction horizontal flow sedimentation device, an ultrafiltration system, a nanofiltration system and a PLC control system connected in sequence; the PLC control system includes a host computer, a PLC main station and 4 PLC sub-stations. The host computer is connected to the PLC main station, and the PLC main station is connected to any one of the PLC sub-stations through a bus; the first PLC sub-station is connected to the water intake device for controlling water intake, filtration and drainage; the second PLC sub-station is connected to the mechanical mixing and folded plate reaction horizontal flow sedimentation device for coagulation sedimentation and automatic sludge discharge; the third PLC sub-station is connected to the ultrafiltration system for controlling the constant throughput water production of the ultrafiltration system; the fourth PLC sub-station is connected to the nanofiltration system for controlling the constant throughput water production of the nanofiltration system. The present invention applies the automatic control technology of the membrane combination of ultrafiltration + nanofiltration to the tap water process, further improving the quality of the tap water effluent and reducing the operating cost.

Description

Technical Field

[0001] The present invention relates to the field of tap water, and particularly to a membrane method for upgrading and reconstructing a tap water system and a control method. Background Art

[0002] Traditional tap water treatment methods mainly include several steps such as reaction, sedimentation, filtration, and sterilization. Generally, the raw water after these steps can meet the drinking water standards. However, with the development of the economy, a large number of pathogenic protozoa such as Giardia lamblia and Cryptosporidium parvum and algae have been found in the raw water. Traditional water purification technologies cannot completely treat the algae and protozoa in the water, and the resulting algal toxins and odors have become major microbial safety hazards in tap water production.

[0003] With the popularization and application of ultrafiltration membrane technology, on the basis of retaining traditional water treatment processes, replacing traditional filter pools with ultrafiltration membranes and removing most suspended solids, bacteria and other microorganisms in water through high-precision ultrafiltration membrane separation is the primary choice for existing tap water production enterprises. However, due to the low removal rate of small-molecular-weight organic matter, ammonia nitrogen, hardness (Ca 2+ , Mg 2+ ions) and other small-molecular pollutants in water, in order to ensure that the indicators such as organic matter, ammonia nitrogen, and hardness in tap water are qualified, generally, an ozone-activated carbon adsorption process needs to be added at the front end of the ultrafiltration membrane to remove small-molecular COD, ammonia nitrogen and other pollutants in water. This leads to disadvantages such as a long process flow, a large floor area, high operation difficulty, and high personnel costs for this water treatment process.

[0004] In addition, since the development of tap water purification technology in China since the early 20th century, the vast majority of tap water plants still adopt the first and second generation purification processes, namely the coagulation sedimentation filtration process and the ozone-activated carbon advanced treatment process. The third generation purification process technology represented by ultrafiltration membranes is suitable for newly built urban tap water plants and is not suitable for the upgrading and reconstruction of the first and second generation tap water plants with tight land use. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides a membrane method for upgrading and reconstructing a tap water system and a control method with a short process flow, a small floor area, simple operation, and low production cost. This system and method are particularly suitable for the upgrading and reconstruction of the first and second generation tap water plants with tight land use.

[0006] The technical solution adopted by the present invention is:

[0007] A membrane method for upgrading and reconstructing a tap water system, comprising a water intake device, a mechanical mixing and folded plate reaction horizontal flow sedimentation device, an ultrafiltration system, a nanofiltration system and a PLC control system connected in sequence; the PLC control system includes a host computer, a PLC master station and 4 PLC slave stations, the host computer is connected to the PLC master station, and the PLC master station is connected to each PLC slave station through a bus;

[0008] The first PLC slave station is connected to the water intake device and is used to control the water intake, filtration and drainage of the water intake device;

[0009] The second PLC slave station is connected to the mechanical mixing and folded plate reaction horizontal flow sedimentation device and is used to control the coagulation sedimentation and automatic sludge discharge of the mechanical mixing and folded plate reaction horizontal flow sedimentation device;

[0010] The ultrafiltration system includes a submerged ultrafiltration membrane device, a product water pump and an ultrafiltration cleaning device. The unqualified water separated by the submerged ultrafiltration membrane device returns to the mechanical mixing and folded plate reaction horizontal flow sedimentation device through the ultrafiltration return pipe for cyclic treatment, and the separated purified liquid is input into the nanofiltration system through the product water pump; an ultrafiltration membrane flux monitoring device and an ultrafiltration transmembrane pressure difference monitoring device are provided in the submerged ultrafiltration membrane device; the ultrafiltration membrane flux monitoring device includes an ultrafiltration influent flowmeter arranged on the influent pipeline, an ultrafiltration cleaning water flowmeter arranged on the outlet pipeline of the ultrafiltration cleaning device and an ultrafiltration unqualified water flowmeter arranged on the ultrafiltration return pipe; the transmembrane pressure difference monitoring device includes an ultrafiltration liquid level gauge arranged in the ultrafiltration membrane tank and an ultrafiltration pressure transmitter arranged at the product water outlet of the ultrafiltration membrane module; the ultrafiltration membrane effluent water quality monitoring device, the ultrafiltration membrane flux monitoring device, the ultrafiltration transmembrane pressure difference monitoring device, and the product water pump are all connected to the third PLC slave station, and the third PLC slave station is used to control the constant flux water production of the ultrafiltration system;

[0011] The nanofiltration system includes a booster pump, a nanofiltration membrane device and a nanofiltration cleaning device. The unqualified water separated by the nanofiltration membrane device returns to the ultrafiltration system through the nanofiltration return pipe for cyclic treatment, and the separated purified liquid is used as drinking water; a nanofiltration membrane flux monitoring device and a nanofiltration transmembrane pressure difference monitoring device are provided on the nanofiltration membrane device. The nanofiltration membrane flux monitoring device includes a nanofiltration influent flowmeter arranged on the influent pipeline of the nanofiltration membrane module, a nanofiltration cleaning water flowmeter arranged on the outlet pipeline of the nanofiltration cleaning device, a nanofiltration unqualified water flowmeter arranged on the nanofiltration return pipe and a nanofiltration concentrated water flowmeter arranged on the total concentrated water pipeline of the nanofiltration membrane device; the nanofiltration transmembrane pressure difference monitoring device includes a nanofiltration influent pressure transmitter arranged on the influent pipeline of the nanofiltration membrane device, a nanofiltration inter-stage influent pressure transmitter arranged on the influent pipeline between the first-stage nanofiltration membrane module and the second-stage nanofiltration membrane module, and a concentrated water pressure transmitter arranged on the total concentrated water pipeline of the nanofiltration membrane device; the booster pump, the nanofiltration membrane flux monitoring device and the nanofiltration transmembrane pressure difference monitoring device are all connected to the fourth PLC slave station, and the fourth PLC slave station is used to control the constant flux water production of the nanofiltration system.

[0012] Further, the water intake device includes a water intake pool, a mechanical grille, and a water intake pump. The mechanical grille is arranged at the front end of the water intake pool to filter mechanical impurities with a particle size greater than 3 mm, and the residence time of the water intake pool is 0.5 - 1 h.

[0013] Further, the mechanical mixing and folded plate reaction horizontal flow sedimentation device includes a coagulant dosing device and a horizontal flow sedimentation tank. In the horizontal flow sedimentation tank, a mechanical mixing unit, a flocculation unit, and a horizontal flow sedimentation unit are successively arranged from the water inlet to the water outlet direction. The mixed liquid undergoes a flocculation reaction in the flocculation unit. After the flocculation reaction is completed, it enters the horizontal flow sedimentation unit for sedimentation separation. The separated sludge is discharged from the system by a sludge discharge pump, and the separated supernatant enters the ultrafiltration system. The coagulant dosing device is used to add a flocculant to the mechanical mixing unit.

[0014] Further, in the flocculation unit, a first group of folded plates, a second group of folded plates, and a third group of folded plates are successively arranged from the water inlet to the water outlet direction. The first group of folded plates are opposite folded plates, the second group of folded plates are parallel folded plates, and the third group of folded plates are parallel straight plates.

[0015] Further, the submerged ultrafiltration membrane is made of a modified PVDF material, with an average membrane pore size ≤ 0.03 μm, a transmembrane pressure difference ≤ 80 kPa, a produced water turbidity ≤ 0.2 NTU, and a membrane flux of 30 - 80 L / (m 2 ·h).

[0016] Further, the nanofiltration membrane module is made of a spiral wound nanofiltration membrane, and the spiral wound nanofiltration membrane is made of a polyamide material, with a membrane flux of 20 - 40 L / (m 2 ·h), a desalination rate of 95 - 98%, and an operating pressure of 4.8 - 6.0 bar.

[0017] An ultrafiltration system constant throughput water production control method for the above-mentioned membrane method quality improvement and transformation of the tap water system includes the following steps:

[0018] Step 1: The ultrafiltration membrane flux monitoring device transmits the collected influent flow rate, produced water time, unqualified water flow rate, and cleaning water flow rate of the ultrafiltration system to the submerged ultrafiltration PLC sub-station, and calculates the ultrafiltration membrane flux;

[0019]

[0020] Wherein:

[0021] CMTL1 is the calculated ultrafiltration membrane flux, L / (m 2 ·h);

[0022] CQ is the daily influent volume of the ultrafiltration system collected by the ultrafiltration influent flow meter, m 3 / d;

[0023] CT is the daily operating time of the ultrafiltration system, h;

[0024] CS is the working membrane area of the ultrafiltration system, m 2 ;

[0025] CQ1 is the sum of the daily unqualified water volume of the system collected by the ultrafiltration unqualified water flowmeter and the cleaning water consumption collected by the ultrafiltration cleaning water flowmeter, m 3 / d;

[0026] Step 2: The ultrafiltration PLC sub-station adjusts the working frequency of the water production pump in real time according to the control deviation of the membrane flux. When the deviation is negative, the working frequency of the water production pump is increased according to formula (1); when the deviation is positive, the working frequency of the water production pump is decreased according to formula (1) to keep the system producing water with a constant flux;

[0027]

[0028] Where:

[0029] Cf t is the frequency of the water production pump at time t, Hz;

[0030] Cf0 is the frequency of the water production pump at time 0, Hz;

[0031] K p is the proportional coefficient of the frequency;

[0032] K i is the integral coefficient of the frequency;

[0033] Cδ is the control deviation of the ultrafiltration membrane flux,

[0034] Δ CMTL is the ultrafiltration membrane flux deviation, Δ CMTL =CMTL - CMTL1;

[0035] CMTL is the designed membrane flux, L / (m 2 ·h);

[0036] Cf is the working frequency of the water production pump, Hz;

[0037] L CMTL is the ultrafiltration membrane flux compensation value, L / (m 2 ·h);

[0038] t is the integral period.

[0039] Furthermore, the constant flux water production control method of the ultrafiltration system further includes the following steps;

[0040] Step 3: The ultrafiltration transmembrane pressure difference monitoring device transmits the collected ultrafiltration membrane tank liquid level and the pressure at the measuring point of the submerged ultrafiltration membrane water production pipe to the submerged ultrafiltration PLC sub-station, and calculates the ultrafiltration transmembrane pressure difference;

[0041] CTMP1 = (CLT - A) × C - (CPT + B) × C;

[0042] Where:

[0043] CTMP1 is the calculated transmembrane pressure difference of the submerged ultrafiltration membrane, kPa;

[0044] CLT is the liquid level of the ultrafiltration membrane tank collected by the ultrafiltration liquid level gauge, m;

[0045] CPT is the pressure at the measuring point of the water production pipe of the submerged ultrafiltration membrane collected by the ultrafiltration pressure transmitter, kPa;

[0046] A is the elevation of the top surface of the submerged ultrafiltration membrane - the elevation of the bottom surface of the ultrafiltration membrane tank, m;

[0047] B is the elevation of the top surface of the submerged ultrafiltration membrane - the installation elevation of the ultrafiltration pressure transmitter CS2, m;

[0048] C is a constant, C = 9.80 kPa / m;

[0049] Step 4: The ultrafiltration PLC sub - station sets the priority according to the working frequency Cf of the water production pump, the transmembrane pressure difference CTMP1 obtained in Step 3, and the membrane flux CMTL1 obtained in Step 2, and determines the operation mode of the submerged ultrafiltration system as operation or cleaning. When two of the working frequency Cf, transmembrane pressure difference CTMP1, or membrane flux CMTL1 exceed their set values, the PLC automatically switches the operation mode of the ultrafiltration system from the operation state to the cleaning state, and automatically resumes to the operation state after the cleaning ends, alternately executing the operation mode and the cleaning mode; the priority order is Cf, CTMP1, CMTL1.

[0050] An ultrafiltration system constant - production water control method for any of the above - mentioned membrane - method quality - improved tap water systems, comprising the following steps:

[0051] Step 1: The nanofiltration transmembrane pressure monitoring device transmits the collected inlet pressure, inter - stage pressure, and concentrated water pressure of the nanofiltration system to the nanofiltration PLC control sub - station, and calculates the operating pressure drop of the nanofiltration system;

[0052]

[0053] Where:

[0054] ΔP is the operating pressure drop of the nanofiltration system, bar;

[0055] PT is the nanofiltration membrane inlet pressure value collected by the nanofiltration inlet pressure transmitter, bar;

[0056] PT1 is the nanofiltration membrane inter - stage pressure value collected by the nanofiltration inter - stage inlet pressure transmitter, bar;

[0057] PT2 is the pressure value of the concentrated water of the nanofiltration membrane collected by the concentrated water pressure transmitter, bar;

[0058] Step 2: The nanofiltration PLC sub-station adjusts the operating frequency of the booster pump according to the operating pressure drop ΔP. When the pressure drop increases, the operating frequency of the booster pump is increased according to Equation (2); when the pressure drop decreases, the operating frequency of the booster pump is decreased according to Equation (2) to maintain the constant flux operation of the nanofiltration system;

[0059]

[0060] Where:

[0061] Nf t is the operating frequency of the booster pump at time t, Hz;

[0062] Nf0 is the operating frequency of the booster pump at time 0, Hz;

[0063] K p is the proportional coefficient of the frequency;

[0064] K i is the integral coefficient of the frequency;

[0065] Nδ is the control difference of the operating pressure drop, Hz;

[0066] L ΔP is the compensation value of the pressure drop, bar;

[0067] Nf is the operating frequency of the booster pump, Hz;

[0068] ΔP0 is the initial operating pressure drop, bar;

[0069] t is the integration period.

[0070] Furthermore, the constant flux water production control method of the ultrafiltration system further includes the following steps:

[0071] Step 3: The nanofiltration membrane flux monitoring device transmits the collected inlet water flow, water production time, unqualified water, concentrated water flow and cleaning water flow of the nanofiltration system to the nanofiltration PLC sub-station, and calculates the nanofiltration membrane flux;

[0072]

[0073] Where:

[0074] NMTL is the calculated nanofiltration membrane flux, L / (m 2 ·h);

[0075] NQ is the inlet water volume per hour of the nanofiltration system collected by the nanofiltration inlet water flowmeter, m 3 / h;

[0076] NS is the working membrane area of the nanofiltration system, m 2 ;

[0077] NQ1 is the sum of the nanofiltration flushing water volume collected by the nanofiltration cleaning water flowmeter, the nanofiltration unqualified water volume collected by the nanofiltration unqualified water flowmeter, and the nanofiltration system concentrated water volume collected by the nanofiltration concentrated water flowmeter, m 3 / h;

[0078] Step 4: The nanofiltration PLC substation sets the priority according to the working frequency Nf of the booster pump, the operating pressure drop ΔP obtained in Step 1, and the nanofiltration membrane flux NMTL1 obtained in Step 3, and determines the operating mode of the nanofiltration system as operation or cleaning. When two of the working frequency Nf, operating pressure drop ΔP, or nanofiltration membrane flux NMTL1 exceed their set values, the PLC automatically switches the operating mode of the nanofiltration system from the operating state to the cleaning state, and automatically resumes to the operating state after the cleaning ends, alternately executing the operating mode and the cleaning mode; the priority order is Nf, ΔP, NMTL1.

[0079] Advantages of the present invention:

[0080] 1. The present invention replaces the ozone-activated carbon process in the traditional membrane method tap water process with the nanofiltration membrane technology with ultra-low pressure drop and high recovery rate, improves the water quality index of the effluent, and reduces the activated carbon replacement cost of the traditional membrane method tap water process;

[0081] 2. The present invention shortens the process flow and reduces the floor area, providing technical feasibility for the water quality improvement transformation of traditional first- and second-generation old tap water plants;

[0082] 3. The present invention sets up a PLC control system, which consists of a water intake PLC substation, a mechanical mixing and folded plate reaction horizontal sedimentation PLC substation, a submerged ultrafiltration membrane PLC substation, and a nanofiltration membrane PLC substation. Each substation is automatically controlled through corresponding parameters, especially the automatic control logic of the ultrafiltration and nanofiltration membrane systems, greatly improving the degree of automation operation and reducing the labor cost. Description of the Drawings

[0083] Figure 1 is a schematic structural diagram of the membrane method water quality improvement and transformation tap water system of the present invention.

[0084] Description of the reference numerals:

[0085] 1. Mechanical grille; 2. Intake pool; 3. Intake pump; 4. Coagulant dosing device; 5. Mechanical mixing unit; 6. Flocculation unit; 7. Sedimentation unit; 8. Submerged ultrafiltration membrane device; 9. Ultrafiltration cleaning device; 10. Ultrafiltration membrane flux monitoring device; 11. Ultrafiltration transmembrane pressure difference monitoring device; 12. Ultrafiltration membrane effluent monitoring device; 13. Ultrafiltration return pipe; 14. Nanofiltration influent monitoring device; 15. Nanofiltration membrane device; 16. Nanofiltration membrane cleaning device; 17. Nanofiltration transmembrane pressure difference monitoring device; 18. Nanofiltration membrane flux monitoring device; 19. Nanofiltration effluent monitoring device; 20. Nanofiltration return pipe; 21. Booster pump; 22. Product water pump. Detailed implementation mode

[0086] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with embodiments, but the content of the present invention is not limited to the following embodiments.

[0087] Embodiment 1

[0088] Refer to Figure 1 , this embodiment provides a membrane method for upgrading and transforming a tap water system, including a water intake device, a mechanical mixing and folded plate reaction horizontal flow sedimentation device, an ultrafiltration system, and a nanofiltration system connected in sequence; and a PLC control system.

[0089] The PLC control system includes a host computer, a PLC master station, and 4 PLC slave stations. The host computer is connected to the PLC master station. The PLC master station is connected to any one of the PLC slave stations through a bus. The 4 PLC slave stations are respectively connected to the water intake device, the mechanical mixing and folded plate reaction horizontal flow sedimentation device, the ultrafiltration system, and the nanofiltration system. Each PLC slave station is an independent module and can operate independently. The data of each slave station is uploaded to the host computer through the master station.

[0090] The water intake device includes an intake pool 2, a mechanical grille 1, and an intake pump 3. The mechanical grille 1 is arranged at the front end of the intake pool 2. Preferably, the filtration accuracy of the mechanical grille is 3 - 5 mm. After the raw water is filtered by the mechanical grille 1, it enters the intake pool 2. Preferably, the residence time of the intake pool 2 is 0.5 - 1 h. The intake pump 3 is arranged at the bottom inside the intake pool 2. Preferably, the intake pump is a submersible pump, and the pump outlet is connected to the next device through a pipeline. The mechanical grille 1 and the intake pump 3 are connected to the first PLC slave station. The first PLC slave station controls the automatic start and stop of the intake pump and the automatic operation of the mechanical grille. This control method uses existing technology.

[0091] The mechanical mixing folded plate reaction horizontal flow sedimentation device includes a coagulant dosing device 4 and a horizontal flow sedimentation tank. In the horizontal flow sedimentation tank, a mechanical mixing unit 5, a flocculation unit 6, and a horizontal flow sedimentation unit 7 are sequentially arranged from the water inlet to the water outlet direction. The coagulant dosing device 4 is used to add flocculant to the mechanical mixing unit 5. The coagulant dosing device 4 can be arranged between the intake well 2 and the horizontal flow sedimentation tank, or can be arranged on the upper part of the horizontal flow sedimentation tank. A stirrer is provided in the mechanical mixing unit 5, and the stirrer is used to fully mix the raw water and the coagulant. Preferably, the stirring intensity of the stirrer is 60 - 90 r / min, and the stirring time is 1.5 - 2 min. In the flocculation unit 6, a first group of folded plates, a second group of folded plates, and a third group of folded plates are sequentially arranged from the water inlet to the water outlet direction. The first group uses relative folded plates, the second group uses parallel folded plates, and the third group uses parallel straight plates. The three - stage folded plate form is adopted to control the velocity gradient in stages, shorten the reaction time, and reduce the volume of the reaction tank. The mixed liquid undergoes a flocculation reaction in the flocculation unit 6. Preferably, the reaction time is 12 - 15 min. After the flocculation reaction is completed, it enters the horizontal flow sedimentation unit 7 for sedimentation separation. The separated sludge is discharged by a sludge pump, and the separated supernatant enters the ultrafiltration system. The coagulant dosing device 4, the stirrer, and the sludge pump are connected to the second PLC sub - station. The second PLC sub - station controls the automatic start - stop of the stirrer, the automatic dosing device of the coagulant, and the automatic sludge discharge of the sludge pump. This control method uses the existing technology.

[0092] The ultrafiltration system includes a submerged ultrafiltration membrane device 8 and an ultrafiltration cleaning device 9. The submerged ultrafiltration membrane device 8 includes an ultrafiltration membrane tank, submerged ultrafiltration membrane modules arranged in the ultrafiltration membrane tank, and a water production pump 22 arranged outside the ultrafiltration membrane tank. The submerged ultrafiltration membrane is made of modified PVDF material. The main performance parameters are: the average pore diameter of the membrane ≤ 0.03 μm, the transmembrane pressure difference (TMP) ≤ 80 kpa, the turbidity of the produced water ≤ 0.2 NTU, and the membrane flux is 30 - 80 L / (m 2 ·h). The membrane cleaning device 9 automatically cleans the membrane modules according to the operating parameters to promptly restore the performance and flux of the submerged ultrafiltration membrane. The unqualified water separated by the submerged ultrafiltration membrane modules returns to the mechanical mixing unit 5 through the ultrafiltration return pipe 13 for cyclic treatment, and the separated purified liquid is input into the nanofiltration system through the water production pump 22.

[0093] An ultrafiltration membrane effluent water quality monitoring device 12 is provided on the water production pipeline of the submerged ultrafiltration membrane module. The ultrafiltration membrane effluent water quality monitoring device 12 includes a turbidimeter and a particle counter.

[0094] The submerged ultrafiltration membrane device 8 is provided with an ultrafiltration membrane flux monitoring device 10 and an ultrafiltration transmembrane pressure difference monitoring device 11. The ultrafiltration membrane flux monitoring device 10 includes an ultrafiltration influent water flowmeter CF1 arranged on the influent pipeline, an ultrafiltration cleaning water flowmeter CF2 arranged on the effluent pipeline of the ultrafiltration cleaning device 9, and an ultrafiltration unqualified water flowmeter CF3 arranged on the ultrafiltration return pipe 13. The transmembrane pressure difference monitoring device 11 includes an ultrafiltration liquid level gauge CW1 arranged in the ultrafiltration membrane tank and an ultrafiltration pressure transmitter CS2 arranged at the water production port of the ultrafiltration membrane module.

[0095] The ultrafiltration membrane effluent water quality monitoring device 12, the ultrafiltration membrane flux monitoring device 10, the ultrafiltration transmembrane pressure difference monitoring device 11, and the water production pump are all connected to the ultrafiltration PLC sub-station, that is, the third PLC sub-station, and the monitoring data is fed back to the PLC control system to adjust the operating state of the ultrafiltration membrane and ensure the stability of the ultrafiltration membrane effluent.

[0096] The nanofiltration system includes a booster pump 21, a nanofiltration membrane device 15, and a nanofiltration cleaning device 16. The nanofiltration membrane device 15 is provided with a spiral wound nanofiltration membrane module. Preferably, the spiral wound nanofiltration membrane is made of polyamide materials, with a membrane flux of 20 - 40 L / (m 2 ·h), a salt rejection rate of 95 - 98%, and an operating pressure of 4.8 - 6.0 bar. The nanofiltration cleaning device 16 automatically cleans the nanofiltration membrane device 15 according to the operating parameters to promptly restore the performance and flux of the nanofiltration membrane. The unqualified water separated by the nanofiltration membrane device 15 is refluxed through the nanofiltration return pipe 20 to the submerged ultrafiltration membrane device 8 for cyclic treatment, and the separated purified liquid is used as drinking water.

[0097] A nanofiltration influent water quality monitoring device 14 is arranged on the influent pipeline of the nanofiltration membrane device 15. The nanofiltration influent water quality monitoring device 14 includes an influent conductivity meter, a residual chlorine meter, and an influent ORP meter. A nanofiltration effluent water quality monitoring device 19 is arranged on the effluent pipeline of the nanofiltration membrane. The nanofiltration effluent water quality monitoring device 19 includes an effluent conductivity meter and a TOC meter.

[0098] A nanofiltration membrane flux monitoring device 18 and a nanofiltration transmembrane pressure difference monitoring device 17 are arranged on the nanofiltration membrane device 15. The nanofiltration membrane flux monitoring device 18 includes a nanofiltration influent water flowmeter NF1 arranged on the influent pipeline of the nanofiltration membrane module, a nanofiltration cleaning water flowmeter NF2 arranged on the effluent pipeline of the nanofiltration cleaning device 16, a nanofiltration unqualified water flowmeter NF3 arranged on the nanofiltration return pipe 20, and a nanofiltration concentrated water flowmeter NF4 arranged on the total concentrated water pipeline of the nanofiltration membrane device 15. The nanofiltration transmembrane pressure difference monitoring device 17 includes a nanofiltration influent pressure transmitter NS1 arranged on the influent pipeline of the nanofiltration membrane device 15, a nanofiltration inter-stage influent pressure transmitter NS2 arranged on the influent pipeline between the first-stage nanofiltration membrane module and the second-stage nanofiltration membrane module, and a concentrated water pressure transmitter NS3 arranged on the total concentrated water pipeline of the nanofiltration membrane device 15.

[0099] The nanofiltration influent water quality monitoring device 14, the nanofiltration effluent water quality monitoring device 19, the nanofiltration membrane flux monitoring device 18, and the nanofiltration transmembrane pressure difference monitoring device 17 are all connected to the nanofiltration PLC sub-station, i.e., the fourth PLC sub-station, and feedback the monitoring data to the PLC system to adjust the operating state of the nanofiltration membrane and ensure the drinking safety of the nanofiltration membrane effluent.

[0100] Embodiment 2

[0101] A method for controlling the constant throughput production of an ultrafiltration system in a membrane method upgraded tap water system as described in Embodiment 1 includes the following steps:

[0102] Step 1: The ultrafiltration membrane flux monitoring device 10 transmits the collected influent flow rate, product water time, unqualified water flow rate, and cleaning water flow rate of the ultrafiltration system to the submerged third PLC sub-station, and calculates the ultrafiltration membrane flux CMTL1:

[0103]

[0104] Where:

[0105] CMTL1 is the calculated ultrafiltration membrane flux, L / (m 2 ·h);

[0106] CQ is the daily influent water volume of the ultrafiltration system collected by the ultrafiltration influent water flow meter CF1, m 3 / d;

[0107] CT is the daily operating time of the ultrafiltration system, h;

[0108] CS is the working membrane area of the ultrafiltration system, m 2 ;

[0109] CQ1 is the sum of the daily unqualified water volume of the system collected by the ultrafiltration unqualified water flow meter CF3 and the cleaning water consumption collected by the ultrafiltration cleaning water flow meter CF2, m 3 / d;

[0110] Step 2: The third PLC sub-station adjusts the working frequency Cf of the product water pump in real time according to the membrane flux deviation. When the deviation is negative, the working frequency Cf of the product water pump is increased according to formula (1); when the deviation is positive, the working frequency Cf of the product water pump is decreased according to formula (1) to maintain the constant throughput production of the system.

[0111]

[0112] Where:

[0113] Cf t is the frequency of the product water pump at time t, HZ;

[0114] Cf0 is the frequency of the product water pump at time 0, HZ;

[0115] K p is the proportional coefficient of frequency, and its value is 0 to 1.23;

[0116] K i is the integral coefficient of frequency, and its value is 0 to 1 min -1 ;

[0117] Cδ is the control deviation of the ultrafiltration membrane flux,

[0118] Δ CMTL is the membrane flux deviation, Δ CMTL = CMTL - CMTL1;

[0119] CMTL is the designed membrane flux;

[0120] CMTL1 is the membrane flux calculated at time 0;

[0121] Cf is the operating frequency of the water production pump, HZ;

[0122] L CMTL is the membrane flux compensation value, L / (m 2 ·h);

[0123] t is the integral period, and its value is 1.0 min.

[0124] Step 3: The ultrafiltration transmembrane pressure difference monitoring device 11 transmits the collected ultrafiltration membrane tank liquid level and the pressure at the measuring point of the submerged ultrafiltration membrane water production pipe to the submerged ultrafiltration PLC sub-station, and calculates the ultrafiltration transmembrane pressure difference CTMP1.

[0125] CTMP1 = (CLT - A) × C - (CPT + B) × C

[0126] Where:

[0127] CTMP1 is the calculated submerged ultrafiltration membrane transmembrane pressure difference, kpa;

[0128] CLT is the ultrafiltration membrane tank liquid level collected by the ultrafiltration liquid level gauge CW1, m;

[0129] CPT is the pressure at the measuring point of the submerged ultrafiltration membrane water production pipe collected by the ultrafiltration pressure transmitter CS2, kpa;

[0130] A is the elevation of the top surface of the submerged ultrafiltration membrane - the elevation of the bottom surface of the ultrafiltration membrane tank, m;

[0131] B is the elevation of the top surface of the submerged ultrafiltration membrane - the installation elevation of the ultrafiltration pressure transmitter CS2, m;

[0132] C is a constant, C = 9.80 kpa / m.

[0133] Step 4: The third PLC sub-station sets the priority according to the working frequency Cf of the water production pump, the transmembrane pressure difference CTMP1 obtained in Step 3, and the membrane flux CMTL1 obtained in Step 2, and determines the operation mode of the submerged ultrafiltration system as operation or cleaning. When two of the working frequency Cf, the transmembrane pressure difference CTMP1, or the membrane flux CMTL1 exceed their set values, the PLC automatically switches the operation mode of the ultrafiltration system from the operation state to the cleaning state to restore the performance of the ultrafiltration membrane. After the cleaning is completed, it automatically returns to the operation state, and the operation mode and the cleaning mode are alternately executed to ensure the constant-flux water production of the ultrafiltration system.

[0134] The priority order is Cf, CTMP1, CMTL1.

[0135] Embodiment 3

[0136] A method for controlling the constant-flux water production of a nanofiltration system in a membrane method for upgrading tap water system as described in Embodiment 1 includes the following steps:

[0137] Step 1: The nanofiltration transmembrane pressure difference monitoring device 17 transmits the collected nanofiltration membrane inlet pressure, nanofiltration inter-stage pressure, and nanofiltration concentrated water pressure to the fourth PLC control sub-station, and calculates the operation pressure drop ΔP of the nanofiltration system.

[0138]

[0139] Where:

[0140] PT is the nanofiltration membrane inlet pressure value collected by the nanofiltration inlet pressure transmitter NS1, bar;

[0141] PT1 is the nanofiltration membrane inter-stage pressure value collected by the nanofiltration inter-stage inlet pressure transmitter NS2, bar;

[0142] PT2 is the nanofiltration membrane concentrated water pressure value collected by the concentrated water pressure transmitter NS3, bar;

[0143] Step 2: The nanofiltration PLC sub-station adjusts the working frequency Nf of the booster pump according to the operation pressure drop ΔP. When the pressure drop increases, the working frequency Nf of the booster pump is increased according to Equation (2); when the pressure drop decreases, the working frequency Nf of the booster pump is decreased according to Equation (2) to maintain the constant-flux operation of the nanofiltration system.

[0144]

[0145] Where:

[0146] Nf t is the booster pump frequency at time t, Hz;

[0147] Nf0 is the booster pump frequency at time 0, Hz;

[0148] Kp K is the proportionality coefficient of frequency, and its value is 0.3 to 1.0;

[0149] K i is the integral coefficient of frequency, and its value is 0 to 1 min -1 ;

[0150] Nδ is the control difference of the operating pressure drop, Hz;

[0151] L ΔP is the compensation value of the pressure drop, bar;

[0152] Nf is the operating frequency of the increased pump, Hz;

[0153] ΔP0 is the initial operating pressure drop, bar;

[0154] t is the integral period, and its value is 1.0 min.

[0155] Step 3: The nanofiltration membrane flux monitoring device 18 transmits the collected influent flow rate, product water time, unqualified water flow rate, concentrated water flow rate, and cleaning water flow rate of the nanofiltration system to the fourth PLC sub-station, and calculates the nanofiltration membrane flux NMTL1:

[0156]

[0157] Where:

[0158] NMTL is the calculated nanofiltration membrane flux, L / (m 2 ·h);

[0159] NQ is the influent water volume of the nanofiltration system collected by the nanofiltration influent flow meter NF1, m 3 / h;

[0160] NS is the working membrane area of the nanofiltration system, m 2 ;

[0161] NQ1 is the sum of the nanofiltration flushing water volume collected by the nanofiltration cleaning water flow meter NF2, the nanofiltration unqualified water volume collected by the nanofiltration unqualified water flow meter NF3, and the nanofiltration system concentrated water volume collected by the nanofiltration concentrated water flow meter NF4, m 3 / h.

[0162] Step 4: The fourth PLC sub-station sets the priority according to the operating frequency Nf of the booster pump, the operating pressure drop ΔP obtained in Step 1, and the nanofiltration membrane flux NMTL1 obtained in Step 3, and determines the operating mode of the nanofiltration system as operation or cleaning. When two of the operating frequency Nf, the operating pressure drop ΔP, or the nanofiltration membrane flux NMTL1 exceed their set values, the PLC automatically switches the operating mode of the nanofiltration system from the operating state to the cleaning state to restore the performance of the nanofiltration membrane. After the cleaning is completed, it automatically returns to the operating state, and the operation mode and the cleaning mode are alternately executed to ensure the constant-throughput water production of the nanofiltration system.

[0163] The priority order is Nf, ΔP, NMTL1.

[0164] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A control method for upgrading a tap water system by membrane method, characterized in that The tap water system upgraded by membrane method includes a water intake device, a mechanical mixing and folded plate reaction horizontal flow sedimentation device, an ultrafiltration system, a nanofiltration system and a PLC control system connected in sequence; the PLC control system includes a host computer, a PLC main station and 4 PLC sub-stations. The host computer is connected to the PLC main station, and the PLC main station is connected to each PLC sub-station through a bus; The first PLC sub-station is connected to the water intake device for controlling the water intake, filtration and drainage of the water intake device; The second PLC sub-station is connected to the mechanical mixing and folded plate reaction horizontal flow sedimentation device for controlling the coagulation sedimentation and automatic sludge discharge of the mechanical mixing and folded plate reaction horizontal flow sedimentation device; The ultrafiltration system includes an immersed ultrafiltration membrane device, a product water pump and an ultrafiltration cleaning device. The unqualified water separated by the immersed ultrafiltration membrane device is returned to the mechanical mixing and folded plate reaction horizontal flow sedimentation device for circular treatment through the ultrafiltration return pipe, and the separated purified liquid is input into the nanofiltration system through the product water pump; an ultrafiltration membrane flux monitoring device and an ultrafiltration transmembrane pressure difference monitoring device are provided in the immersed ultrafiltration membrane device; the ultrafiltration membrane flux monitoring device includes an ultrafiltration influent flowmeter arranged on the influent pipeline, an ultrafiltration cleaning water flowmeter arranged on the outlet pipeline of the ultrafiltration cleaning device and an ultrafiltration unqualified water flowmeter arranged on the ultrafiltration return pipe; the transmembrane pressure difference monitoring device includes an ultrafiltration liquid level gauge arranged in the ultrafiltration membrane tank and an ultrafiltration pressure transmitter arranged at the product water outlet of the ultrafiltration membrane module; the ultrafiltration membrane effluent water quality monitoring device, the ultrafiltration membrane flux monitoring device, the ultrafiltration transmembrane pressure difference monitoring device and the product water pump are all connected to the third PLC sub-station, and the third PLC sub-station is used to control the constant flux production water of the ultrafiltration system; The nanofiltration system includes a booster pump, a nanofiltration membrane device and a nanofiltration cleaning device. The unqualified water separated by the nanofiltration membrane device is returned to the ultrafiltration system for circular treatment through the nanofiltration return pipe, and the separated purified liquid is used as drinking water; a nanofiltration membrane flux monitoring device and a nanofiltration transmembrane pressure difference monitoring device are provided on the nanofiltration membrane device. The nanofiltration membrane flux monitoring device includes a nanofiltration influent flowmeter arranged on the influent pipeline of the nanofiltration membrane module, a nanofiltration cleaning water flowmeter arranged on the outlet pipeline of the nanofiltration cleaning device, a nanofiltration unqualified water flowmeter arranged on the nanofiltration return pipe and a nanofiltration concentrated water flowmeter arranged on the total concentrated water pipeline of the nanofiltration membrane device; the nanofiltration transmembrane pressure difference monitoring device includes a nanofiltration influent pressure transmitter arranged on the influent pipeline of the nanofiltration membrane device, a nanofiltration inter-stage influent pressure transmitter arranged on the influent pipeline between the first-stage nanofiltration membrane module and the second-stage nanofiltration membrane module and a concentrated water pressure transmitter arranged on the total concentrated water pipeline of the nanofiltration membrane device; the booster pump, the nanofiltration membrane flux monitoring device and the nanofiltration transmembrane pressure difference monitoring device are all connected to the fourth PLC sub-station, and the fourth PLC sub-station is used to control the constant flux production water of the nanofiltration system; The control method for the constant flux production water of the ultrafiltration system includes the following steps: Step 1: The ultrafiltration membrane flux monitoring device transmits the collected influent flow rate, product water time, unqualified water flow rate and cleaning water flow rate of the ultrafiltration system to the immersed ultrafiltration PLC sub-station, and calculates the ultrafiltration membrane flux; Wherein: CMTL1 is the calculated ultrafiltration membrane flux, L / (m 2 ·h); CQ is the daily water intake of the ultrafiltration system collected by the ultrafiltration influent flowmeter, m 3 / d; CT is the daily operation time of the ultrafiltration system, h; CS is the working membrane area of the ultrafiltration system, m 2 ; CQ1 is the sum of the daily unqualified water volume of the system collected by the ultrafiltration unqualified water flowmeter and the cleaning water consumption collected by the ultrafiltration cleaning water flowmeter, m 3 / d; Step 2: The ultrafiltration PLC sub-station adjusts the operating frequency of the water production pump in real time according to the control deviation of the membrane flux. When the deviation is negative, the operating frequency of the water production pump is increased according to Equation (1); when the deviation is positive, the operating frequency of the water production pump is decreased according to Equation (1) to maintain constant flux water production in the system; Where: Cf t is the frequency of the water production pump at time t, HZ; Cf0 is the frequency of the water production pump at time 0, HZ; K p is the proportionality coefficient of the frequency; K i is the integral coefficient of the frequency; Cδ is the control deviation of the ultrafiltration membrane flux, Δ CMTL is the ultrafiltration membrane flux deviation, Δ CMTL = CMTL - CMTL1; CMTL is the designed membrane flux, L / (m 2 ·h); Cf is the operating frequency of the water production pump, HZ; L CMTL is the ultrafiltration membrane flux compensation value, L / (m 2 ·h); t is the integration period; Step 3: The ultrafiltration transmembrane pressure difference monitoring device transmits the collected ultrafiltration membrane tank liquid level and the pressure at the measuring point of the immersed ultrafiltration membrane water production pipe to the immersed ultrafiltration PLC sub-station, and calculates the ultrafiltration transmembrane pressure difference; CTMP1 = (CLT - A) × C - (CPT + B) × C; Where: CTMP1 is the calculated transmembrane pressure difference of the immersed ultrafiltration membrane, kpa; CLT is the ultrafiltration membrane tank liquid level collected by the ultrafiltration liquid level gauge, m; CPT is the pressure at the measuring point of the immersed ultrafiltration membrane water production pipe collected by the ultrafiltration pressure transmitter, kpa; A = elevation of the top surface of the immersed ultrafiltration membrane - elevation of the bottom surface of the ultrafiltration membrane tank, m; B = elevation of the top surface of the immersed ultrafiltration membrane - elevation of the installation elevation of the ultrafiltration pressure transmitter CS2, m; C is a constant; Step 4: The ultrafiltration PLC sub-station sets priorities according to the operating frequency Cf of the water production pump, the transmembrane pressure difference CTMP1 obtained in Step 3, and the membrane flux CMTL1 obtained in Step 2, and determines the operating mode of the immersed ultrafiltration system as operation or cleaning. When two of the operating frequency Cf, transmembrane pressure difference CTMP1, or membrane flux CMTL1 exceed their set values, the PLC automatically switches the operating mode of the ultrafiltration system from the operating state to the cleaning state, and automatically resumes to the operating state after the cleaning is completed, alternately executing the operating mode and the cleaning mode; the priority order is Cf, CTMP1, CMTL1.

2. A control method for a membrane method quality improvement and transformation of a tap water system, characterized in that The membrane method quality improvement and transformation of the tap water system includes a water intake device, a mechanical mixing and folded plate reaction horizontal flow sedimentation device, an ultrafiltration system, a nanofiltration system, and a PLC control system connected in sequence; the PLC control system includes a host computer, a PLC main station, and 4 PLC sub-stations. The host computer is connected to the PLC main station, and the PLC main station is connected to each PLC sub-station through a bus; The first PLC sub-station is connected to the water intake device and is used to control the water intake, filtration, and drainage of the water intake device; The second PLC sub-station is connected to the mechanical mixing and folded plate reaction horizontal flow sedimentation device and is used to control the coagulation sedimentation and automatic sludge discharge of the mechanical mixing and folded plate reaction horizontal flow sedimentation device; The ultrafiltration system includes an immersed ultrafiltration membrane device, a product water pump, and an ultrafiltration cleaning device. The unqualified water separated by the immersed ultrafiltration membrane device is returned to the mechanical mixing folded plate reaction horizontal flow sedimentation device through the ultrafiltration return pipe for cyclic treatment, and the separated purified liquid is input into the nanofiltration system through the product water pump; an ultrafiltration membrane flux monitoring device and an ultrafiltration transmembrane pressure difference monitoring device are provided in the immersed ultrafiltration membrane device; the ultrafiltration membrane flux monitoring device includes an ultrafiltration influent flowmeter arranged on the influent pipeline, an ultrafiltration cleaning water flowmeter arranged on the outlet pipeline of the ultrafiltration cleaning device, and an ultrafiltration unqualified water flowmeter arranged on the ultrafiltration return pipe; the transmembrane pressure difference monitoring device includes an ultrafiltration liquid level gauge arranged in the ultrafiltration membrane tank and an ultrafiltration pressure transmitter arranged at the product water outlet of the ultrafiltration membrane module; the ultrafiltration membrane effluent water quality monitoring device, the ultrafiltration membrane flux monitoring device, the ultrafiltration transmembrane pressure difference monitoring device, and the product water pump are all connected to the third PLC sub-station, and the third PLC sub-station is used to control the constant flux water production of the ultrafiltration system; The nanofiltration system includes a booster pump, a nanofiltration membrane device, and a nanofiltration cleaning device. The unqualified water separated by the nanofiltration membrane device is returned to the ultrafiltration system through the nanofiltration return pipe for cyclic treatment, and the separated purified liquid is used as drinking water; a nanofiltration membrane flux monitoring device and a nanofiltration transmembrane pressure difference monitoring device are provided on the nanofiltration membrane device. The nanofiltration membrane flux monitoring device includes a nanofiltration influent flowmeter arranged on the influent pipeline of the nanofiltration membrane module, a nanofiltration cleaning water flowmeter arranged on the outlet pipeline of the nanofiltration cleaning device, a nanofiltration unqualified water flowmeter arranged on the nanofiltration return pipe, and a nanofiltration concentrated water flowmeter arranged on the total concentrated water pipeline of the nanofiltration membrane device; the nanofiltration transmembrane pressure difference monitoring device includes a nanofiltration influent pressure transmitter arranged on the influent pipeline of the nanofiltration membrane device, a nanofiltration inter-stage influent pressure transmitter arranged on the influent pipeline between the first-stage nanofiltration membrane module and the second-stage nanofiltration membrane module, and a concentrated water pressure transmitter arranged on the total concentrated water pipeline of the nanofiltration membrane device; the booster pump, the nanofiltration membrane flux monitoring device, and the nanofiltration transmembrane pressure difference monitoring device are all connected to the fourth PLC sub-station, and the fourth PLC sub-station is used to control the constant flux water production of the nanofiltration system; The method for controlling the constant flux water production of the ultrafiltration system includes the following steps: Step 1: The nanofiltration transmembrane pressure difference monitoring device transmits the collected inlet pressure, inter-stage pressure, and concentrated water pressure of the nanofiltration system to the nanofiltration PLC control sub-station, and calculates the operating pressure drop of the nanofiltration system; Wherein: ΔP is the operating pressure drop of the nanofiltration system, bar; PT is the nanofiltration membrane inlet pressure value collected by the nanofiltration influent pressure transmitter, bar; PT1 is the nanofiltration membrane inter-stage pressure value collected by the nanofiltration inter-stage influent pressure transmitter, bar; PT2 is the nanofiltration membrane concentrated water pressure value collected by the concentrated water pressure transmitter, bar; Step 2: The nanofiltration PLC sub-station adjusts the operating frequency of the booster pump according to the operating pressure drop ΔP. When the pressure drop increases, the operating frequency of the booster pump is increased according to formula (2); when the pressure drop decreases, the operating frequency of the booster pump is decreased according to formula (2) to maintain the constant flux operation of the nanofiltration system; Wherein: Nf t is the increased pump operating frequency at time t, Hz; Nf0 is the operating frequency of the booster pump at time 0, HZ; K p is the proportionality coefficient of the frequency; K i is the integral coefficient of the frequency; Nδ is the control difference of the running pressure drop, HZ; L ΔP is the compensation value for the pressure drop, bar; Nf is the operating frequency of the booster pump, HZ; ΔP0 is the initial operating pressure drop, bar; t is the integration period; Step 3: The nanofiltration membrane flux monitoring device transmits the influent flow rate, product water time, unqualified water, concentrate flow rate, and cleaning water flow rate of the nanofiltration system collected to the nanofiltration PLC sub-station, and calculates the nanofiltration membrane flux; Wherein: NMTL is the calculated nanofiltration membrane flux, L / (m 2 ·h); $N_Q$ is the inlet water flow rate of the nanofiltration system collected by the nanofiltration inlet water flowmeter, $m^3$ / h; 3 / h; NS is the working membrane area of the nanofiltration system, m 2 ; NQ1 is the sum of the nanofiltration flushing water volume collected by the nanofiltration cleaning water flowmeter, the nanofiltration unqualified water volume collected by the nanofiltration unqualified water flowmeter, and the nanofiltration system concentrated water volume collected by the nanofiltration concentrated water flowmeter, m 3 / h; Step 4: The nanofiltration PLC sub-station sets the priority according to the operating frequency Nf of the booster pump, the operating pressure drop ΔP obtained in Step 1, and the nanofiltration membrane flux NMTL1 obtained in Step 3, and determines the operating mode of the nanofiltration system as operation or cleaning. When two of the operating frequency Nf, operating pressure drop ΔP, or nanofiltration membrane flux NMTL1 exceed their set values, the PLC automatically switches the operating mode of the nanofiltration system from the operating state to the cleaning state. After the cleaning is completed, it automatically returns to the operating state, and the operating mode and cleaning mode are alternately executed; the priority order is Nf, ΔP, NMTL1.

3. The control method for upgrading and reconstructing a tap water system by membrane method according to claim 1 or 2, characterized in that, characterized in that, The water intake device includes a water intake pool, a mechanical grille, and a water intake pump. The mechanical grille is arranged at the front end of the water intake pool to filter mechanical impurities with a particle size greater than 3 mm. The residence time of the water intake pool is 0.5 - 1 h.

4. The control method for upgrading a tap water system by membrane method according to claim 1 or 2, characterized in that, The mechanical mixing folded plate reaction horizontal flow sedimentation device includes a coagulant dosing device and a horizontal flow sedimentation tank. In the horizontal flow sedimentation tank, a mechanical mixing unit, a flocculation unit, and a horizontal flow sedimentation unit are sequentially arranged from the influent to the effluent direction. The mixed liquid undergoes a flocculation reaction in the flocculation unit. After the flocculation reaction is completed, it enters the horizontal flow sedimentation unit for sedimentation separation. The separated sludge is discharged from the system by a sludge discharge pump, and the separated supernatant enters the ultrafiltration system; the coagulant dosing device is used to add a flocculant to the mechanical mixing unit.

5. The control method for upgrading a tap water system by membrane method according to claim 1 or 2, characterized in that, In the flocculation unit, a first group of folded plates, a second group of folded plates, and a third group of folded plates are sequentially arranged from the influent to the effluent direction; the first group of folded plates are opposite folded plates, the second group of folded plates are parallel folded plates, and the third group of folded plates are parallel straight plates.

6. The constant-throughput water production control method for the ultrafiltration system according to claim 1 or 2, wherein the submerged ultrafiltration membrane is made of a modified PVDF material, the membrane pore size ≤ 0.03 μm, the transmembrane pressure difference ≤ 80 kPa, the product water turbidity ≤ 0.2 NTU, and the membrane flux is 30 - 80 L / (m2·h).

7. The control method for upgrading the tap water system by membrane method according to claim 1 or 2, characterized in that, The nanofiltration membrane module is made of a spiral wound nanofiltration membrane, and the spiral wound nanofiltration membrane is made of a polyamide material, with a membrane flux of 20 - 40 L / (m2·h), a salt rejection rate of 95 - 98%, and an operating pressure of 4.8 - 6.0 bar.

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