CN215947010U - Novel low-pressure high-recovery-rate nanofiltration system - Google Patents
Novel low-pressure high-recovery-rate nanofiltration system Download PDFInfo
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- 238000001728 nano-filtration Methods 0.000 title claims abstract description 103
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- 238000004140 cleaning Methods 0.000 claims abstract description 72
- 239000012528 membrane Substances 0.000 claims abstract description 72
- 239000007788 liquid Substances 0.000 claims abstract description 46
- 238000004659 sterilization and disinfection Methods 0.000 claims abstract description 41
- 238000004065 wastewater treatment Methods 0.000 claims abstract description 28
- 239000002351 wastewater Substances 0.000 claims abstract description 25
- 238000011084 recovery Methods 0.000 claims abstract description 23
- 238000004519 manufacturing process Methods 0.000 claims abstract description 10
- 239000000126 substance Substances 0.000 claims description 38
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- 238000004062 sedimentation Methods 0.000 claims description 5
- 238000009292 forward osmosis Methods 0.000 claims description 4
- 238000005374 membrane filtration Methods 0.000 claims description 3
- 239000010802 sludge Substances 0.000 claims description 3
- 239000003651 drinking water Substances 0.000 description 13
- 235000020188 drinking water Nutrition 0.000 description 13
- 238000000034 method Methods 0.000 description 13
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- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 3
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- 244000005700 microbiome Species 0.000 description 3
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Abstract
The utility model discloses a novel low-pressure high-recovery nanofiltration system, which comprises a water inlet pool (1), a pretreatment system (2), a low-pressure nanofiltration membrane system (3), a concentrated/wastewater treatment system (4) and a total wastewater pipe which are communicated in sequence; the pretreatment system (2) and the low-pressure nanofiltration membrane system (3) are both communicated with a physicochemical cleaning device (5); the pretreatment system (2) is communicated with the low-pressure nanofiltration membrane system (3) through an intermediate lift pump (10), the intermediate lift pump (10) is communicated with a dosing system (9), and the dosing system (9) is communicated with an ultraviolet disinfection unit (6) and a gas-liquid disinfection unit (7); the pretreatment system (2) and the low-pressure nanofiltration membrane system (3) are both communicated with a concentrated/wastewater treatment system (4); the low-pressure nanofiltration membrane system (3) and the concentrated/wastewater treatment system (4) are both communicated with a water production tank (8).
Description
Technical Field
The utility model relates to the field of advanced treatment of nanofiltration drinking water, and in particular relates to a low-pressure and high-recovery nanofiltration system for advanced treatment of the drinking water of a nanofiltration system specially aiming at surface water of micro organic pollutants.
Background
The problem of water quality safety of drinking water is directly related to the health of the masses, and along with the continuous improvement of living matter level, the masses also put forward higher requirements on drinking water. The membrane separation technology has better effect on water pollution than the traditional coagulation-precipitation-filtration-disinfection and ozone activity process. Wherein the Nanofiltration (NF) membrane has a smaller pore size than the Microfiltration (MF) membrane; compared with an Ultrafiltration (UF) membrane, the technology has stronger selective separability, and can effectively remove organic pollutants and multivalent ions; compared with Reverse Osmosis (RO) membrane, the operation pressure is lower, and some minerals needed by human body can be effectively retained. However, the NF separation solute is mainly subjected to charge action and sieving action, and pollutants (such as organic matters, colloid, inorganic salt and bacteria) are easy to be intercepted and blocked on the surface of the membrane to cause pollution, so that the operating pressure of the NF membrane is increased, the flux is reduced, the chemical cleaning frequency is high, the service life is shortened, and the operating energy consumption/drug consumption is increased, but the pollutants are difficult to remove by the conventional treatment process of a water plant. For example, in the department of overseas city and water supply and drainage companies which take nanofiltration membrane technology first in China, the chemical cleaning cycle of the nanofiltration drinking water advanced treatment system is 1 time per 3 months, and the high-frequency chemical cleaning is easy to damage the structure of the NF membrane, affect the service life of the NF membrane, and increase the costs of operating chemical consumption, power consumption and the like.
At present, measures for relieving NF membrane pollution in engineering are effective pretreatment and maintainable cleaning. The conventional NF pretreatment measures in the prior art are ultrafiltration and a cartridge filter, the ultrafiltration pore diameter is 20-100 nm, but the common pore diameter of a cartridge filter element is 5 mu m, and after the ultrafiltration pretreatment with a small pore diameter, the subsequent large-pore-diameter cartridge filter only plays a psychological comfort 'security' role, is unnecessary and is wasted; in addition, the security filter NF system is a disposable consumable in actual operation and needs to be replaced once every 6 months, so that the construction and operation costs of the NF system are greatly improved. The water plant treatment process inherits the principle of short process and good effect, and particularly, the flow of the ultrafiltration and the security filter for the pretreatment of the drinking water of the nanofiltration membrane is longer in the southern surface water system, so that the operation and subsequent maintenance cost of the whole NF system is increased. In addition, the nanofiltration membrane can generate concentrated waste water and chemical cleaning waste water with highly concentrated organic matters and inorganic salts in the operation process, and the untreated direct discharge can cause environmental pollution. Therefore, there is a need for a functionally enhanced nanofiltration system for advanced treatment of drinking water.
SUMMERY OF THE UTILITY MODEL
In order to overcome the defects in the prior art, the utility model aims to provide a novel low-pressure high-recovery nanofiltration system, which can realize the remarkable advantages of shortened process flow, high pretreatment efficiency, low-pressure characteristic of nanofiltration membrane, high recovery rate, low drug consumption, secondary utilization of concentrated/waste water and the like, and simultaneously has the functions of reducing the running cost and energy consumption of the nanofiltration system, reducing pollution and improving the water quality safety and health of drinking water.
In order to achieve the purpose, the utility model provides a novel low-pressure high-recovery nanofiltration system, which comprises a water inlet pool, a pretreatment system, a low-pressure nanofiltration membrane system, a concentration/wastewater treatment system and a total wastewater pipe which are sequentially communicated; the pretreatment system and the low-pressure nanofiltration membrane system are both communicated with a physicochemical cleaning device; the pretreatment system is communicated with the low-pressure nanofiltration membrane system through an intermediate lift pump, the intermediate lift pump is communicated with a dosing system, and the dosing system is communicated with an ultraviolet disinfection unit and a gas-liquid disinfection unit; the pretreatment system and the low-pressure nanofiltration membrane system are both communicated with a concentrated/wastewater treatment system; the low-pressure nanofiltration membrane system and the concentrated/wastewater treatment system are both communicated with a water production tank.
The water coming from the water inlet tank is one of raw water of surface water polluted by micro organic matters, effluent of a flocculation tank of a water plant, effluent of a sedimentation tank of the water plant and effluent of a sand filter tank of the water plant.
The pretreatment system adopts one or more of a ceramic membrane, a disc filter, a pressure sand filter tank and a backwashing filter element to obtain the sludge density index SDI of pretreated effluent15＜3。
The concentrated/waste water treatment system is one of a disc tube type reverse osmosis membrane/nanofiltration membrane, low-pressure reverse osmosis, compact nanofiltration and forward osmosis.
The physical and chemical cleaning device carries out physical backwashing on the pretreatment system through water-gas combined backwashing, and the cleaning frequency is that the continuous operation of the pretreatment system reaches 10-15 days or the transmembrane pressure difference is increased to 0.06 MPa; the physical chemical cleaning device carries out chemical cleaning on the pretreatment system through sterilization and alkaline cleaning, and the cleaning frequency is that the continuous operation of the pretreatment system reaches 30-50 days or the transmembrane pressure difference is increased to 0.1-0.12 MPa; the physical chemical cleaning device is used for chemically cleaning the low-pressure nanofiltration membrane system through sterilization, alkali cleaning and acid cleaning, and the cleaning frequency is that the low-pressure nanofiltration membrane system continuously operates for 3-5 months.
The ultraviolet disinfection unit is used for ultraviolet intermittent disinfection, one of independent ultraviolet, ultraviolet and bactericide coupling is adopted, and the disinfection frequency is 5-15 days/time; the gas-liquid disinfection unit is used for gas-liquid intermittent positive flushing disinfection at 85 ℃, one or two of gas-liquid, gas-liquid and alkali liquor coupling is adopted, the disinfection frequency is 5-15 days/time, the gas-liquid mixing ratio in the gas-liquid, gas-liquid and alkali liquor coupling is 1/14-1/7, and the alkali liquor concentration is 0.2-2.0%.
Compared with the prior art, the utility model has the following advantages:
(1) the low-pressure nanofiltration membrane is arranged, so that the removal rate of sulfate radicals in inlet water is 40-60%, the removal rate of TOC in inlet water is 30-50%, the removal rate of ammonia nitrogen in inlet water is 15-30%, and the removal rate of calcium, magnesium and total hardness is less than 10% under the low-pressure operation of 0.4-0.6 MPa;
(2) by arranging the concentration/wastewater treatment system, high recovery rate of drinking water advanced treatment can be realized, the overall recovery rate is improved by 1-5%, and the produced water can meet the requirements of 'domestic drinking water quality standard' (DB31/T1091-2018) in Shanghai city; organic matters, inorganic salt highly-concentrated/waste water and chemical waste water generated in the operation process of the nanofiltration membrane can be fully and effectively treated, the environmental pollution caused by direct discharge without treatment is avoided, and the requirements of the Integrated wastewater discharge Standard (DB 31/199-;
(3) a security filter system is cancelled, so that the high-efficiency pretreatment of raw water is realized, and the operation cost is reduced;
(4) by arranging the cleaning device and the disinfection device, the pollution of organic matters and microorganisms to the nanofiltration membrane can be effectively relieved, the service life of the nanofiltration membrane is prolonged, a chemical cleaning scheme is further improved, and the medicine consumption is reduced;
(5) the method can realize the secondary utilization of the concentrated/waste water, combine the cleaning waste liquid with the nanofiltration concentrated/waste water, directly enter a concentrated/waste water treatment system for treatment without adding corresponding acid liquid and alkali liquid additionally, simplify the process flow and improve the operation efficiency.
Drawings
Fig. 1 is a schematic structural diagram of a novel low-pressure high-recovery nanofiltration system of the utility model.
In the figure: 1. a water inlet pool; 2. a pre-treatment system; 3. a low pressure nanofiltration membrane; 4. a concentrate/wastewater treatment system; 5. a physical chemical cleaning device; 6. an ultraviolet disinfection unit; 7. a gas-liquid disinfection unit; 8. a water producing pool; 9. a dosing system; 10. an intermediate lift pump.
Detailed Description
Other advantages and capabilities of the present invention will be readily apparent to those skilled in the art from the present disclosure by describing the embodiments of the present invention with specific embodiments thereof in conjunction with the accompanying drawings. The utility model is capable of other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention.
Fig. 1 is a schematic diagram of a novel low-pressure high-recovery nanofiltration system of the utility model. As shown in fig. 1, the device comprises a water inlet pool 1, a pretreatment system 2, a low-pressure nanofiltration membrane system 3, a concentrated/wastewater treatment system 4 and a total wastewater pipe which are communicated in sequence; the pretreatment system 2 and the low-pressure nanofiltration membrane system 3 are both communicated with a physicochemical cleaning device 5; the pretreatment system 2 is communicated with the low-pressure nanofiltration membrane system 3 through an intermediate lift pump 10, the intermediate lift pump 10 is communicated with a dosing system 9, and the dosing system 9 is communicated with an ultraviolet disinfection unit 6 and a gas-liquid disinfection unit 7; the pretreatment system 2 and the low-pressure nanofiltration membrane system 3 are both communicated with a concentrated/wastewater treatment system 4; the low-pressure nanofiltration membrane system 3 and the concentrated/wastewater treatment system 4 are both communicated with a water production pool 8.
Preferably, the water coming from the water inlet tank 1 is one of raw water of surface water polluted by micro-organic matters, effluent of a flocculation tank of a water plant, effluent of a sedimentation tank of the water plant and effluent of a sand filter of the water plant.
Preferably, the pretreatment system 2 adopts one or more of ceramic membrane, disc filter, pressure sand filter tank and back-washable filter element to obtain the sludge density index SDI of the pretreated effluent15＜3。
Preferably, the concentration/wastewater treatment system 4 is one of a disc-tube reverse osmosis/nanofiltration membrane (DTRO/NF), Low Pressure Reverse Osmosis (LPRO), Dense Nanofiltration (DNF), and Forward Osmosis (FO).
Preferably, the physical and chemical cleaning device 5 carries out physical backwashing on the pretreatment system 2 through water-gas combined backwashing, and the cleaning frequency is that the continuous operation of the pretreatment system 2 reaches 10-15 days or the transmembrane pressure difference is increased to 0.06 MPa; the physical chemical cleaning device 5 is used for chemically cleaning the pretreatment system 2 through sterilization and alkaline cleaning, and the cleaning frequency is that the continuous operation of the pretreatment system 2 reaches 30-50 days or the transmembrane pressure difference is increased to 0.1-0.12 MPa; the physical and chemical cleaning device 5 carries out chemical cleaning on the low-pressure nanofiltration membrane system 3 through sterilization, alkali cleaning and acid cleaning, and the cleaning frequency is that the low-pressure nanofiltration membrane system 3 continuously operates for 3-5 months.
Preferably, the ultraviolet disinfection unit 6 is used for ultraviolet intermittent disinfection, and adopts one of independent ultraviolet, ultraviolet and bactericide coupling, and the disinfection frequency is 5-15 days/time; the gas-liquid disinfection unit 7 is used for gas-liquid intermittent positive flushing disinfection at 85 ℃, one or two of gas-liquid, gas-liquid and alkali liquor coupling is adopted, the disinfection frequency is 5-15 days/time, the gas-liquid mixing ratio in the gas-liquid, gas-liquid and alkali liquor coupling is 1/14-1/7, and the alkali liquor concentration is 0.2-2.0%.
The water production principle and the concentrated/waste water treatment principle of the novel low-pressure high-recovery nanofiltration system are as follows:
inputting incoming water into the water inlet tank 1, wherein the incoming water can be one of raw water of surface water polluted by micro organic matters, effluent of a flocculation tank of a water plant, effluent of a sedimentation tank of the water plant and effluent of a sand filter tank of the water plant; wherein the potassium permanganate index COD of the micro-organic polluted surface waterMnThe total organic carbon TOC is 1.8-3.9 mg/L, the effluent temperature of the flocculation tank effluent of the water plant, the effluent temperature of the sedimentation tank effluent of the water plant and the effluent temperature of the sand filter of the water plant are generally between 4 ℃ and 35 ℃, the effluent turbidity is generally less than or equal to 0.1-27 NTU, and the free chlorine/ozone content of the effluent is generally less than 0.1 mg/L.
The incoming water flows into a pretreatment system 2 for pretreatment, and the pretreatment mode can select one or more of a ceramic membrane, a disc filter, a pressure sand filter tank and a backwashing filter core to obtain the SDI15Less than 3 of pretreated water; wherein the aperture of the ceramic membrane is 0.1-3 μm, the absolute filtering precision of the disc filter is 3-5 μm, the sand filtering particle size of the pressure sand filtering tank is 30-50% of the conventional sand filtering particle size of a water plant, and the filtering precision of the backwashing filter element is 1-3 μm;
the pretreated water flows through an intermediate lifting pump 10, organic matter pollution and microorganism pollution are removed through a chemical adding system 9, the water is pumped into a low-pressure nanofiltration membrane system 3 through the intermediate lifting pump 10 to be treated, the operating pressure of a low-pressure nanofiltration membrane 3 in the low-pressure nanofiltration membrane system 3 is 0.4-0.6 MPa, the removal rate of sulfate radicals in inlet water is 40-60%, the removal rate of TOC in the inlet water is 30-50%, the removal rate of ammonia nitrogen in the inlet water is 15-30%, the removal rate of calcium, magnesium and total hardness is less than 10%, and the recovery rate of the low-pressure nanofiltration system is not less than 85%, so that nanofiltration produced water and nanofiltration concentrated/waste water are obtained;
when the low-pressure nanofiltration membrane system 3 continuously operates for 5-15 days, the low-pressure nanofiltration membrane system passes through the ultraviolet disinfection unit 6 and the gasThe liquid sterilizing unit 7 performs sterilization; wherein, the ultraviolet disinfection unit 6 adopts one of ultraviolet, ultraviolet and bactericide coupling for ultraviolet intermittent disinfection; the gas-liquid disinfection unit 7 adopts 85 ℃ gas-liquid intermittent positive flushing and adopts one or two of gas-liquid, gas-liquid and alkali liquor coupling; the ultraviolet intensity in the single ultraviolet, ultraviolet and bactericide coupling intermittent disinfection process is 40-80 mj/cm22-6 ultraviolet irradiation channels are arranged, the length of the channels in front of and behind the lamp tube is 1-6 m, water flow of the irradiation channels is uniformly distributed, and the water depth of the irradiation channels meets the submergence requirement of the ultraviolet lamp tube; the gas-liquid mixing ratio in the coupling of gas-liquid, gas-liquid and alkali liquor is 1/14-1/7, and the concentration of the alkali liquor is 0.2-2.0%.
Inputting the nanofiltration concentrate/wastewater into a concentrate/wastewater treatment system 4 to obtain concentrate/wastewater produced water and secondary concentrate/wastewater; the concentrated/wastewater treatment system 4 is one of a reverse osmosis membrane/nanofiltration membrane (DTRO/NF), a low-pressure reverse osmosis (LPRO), a Dense Nanofiltration (DNF) and a Forward Osmosis (FO), so that the overall recovery rate of the nanofiltration system is improved by 1-5%;
and inputting the nanofiltration water production and the concentrated/waste water production into a water production pool 8 for mixing to obtain final water production, wherein the final water production can meet the requirements of the domestic drinking water quality standard (DB31/T1091-2018) of Shanghai city.
The cleaning principle and the cleaning waste liquid treatment principle of the novel low-pressure high-recovery nanofiltration system are as follows:
when the continuous operation of the pretreatment system 2 reaches 10-15 days or the transmembrane pressure difference is increased to 0.06MPa, the physical and chemical cleaning device 5 carries out physical backwashing on the pretreatment system 2 through water-gas combined backwashing, is started during dosing, circulation and flushing, and carries out backwashing for 2-5 min each time to obtain physical backwashing waste liquid, and the physical backwashing liquid is input into the concentrated/wastewater treatment system 4 for treatment;
when the continuous operation of the pretreatment system 2 reaches 30-50 days or the transmembrane pressure difference is increased to 0.1-0.12 MPa, the physical and chemical cleaning device 5 carries out chemical cleaning on the pretreatment system 2 through sterilization and alkali cleaning to obtain a pretreatment system cleaning waste liquid, and the pretreatment system cleaning waste liquid is input into a concentrated/wastewater treatment system 4 for treatment;
further, the chemical cleaning agent is a non-oxidizing bactericide and alkali liquor, the concentration of the non-oxidizing bactericide is 0.01-0.09%, and the concentration of the alkali liquor is 5000-7500 mg/L.
Further, the chemical cleaning sequence is as follows: and adding the non-oxidizing bactericide, circulating for 10-30 min, adding the alkali liquor, circulating for 10-30 min, soaking for 0-90 min, circulating for 10-30 min, and washing for 15-30 min.
When the low-pressure nanofiltration membrane system 3 continuously operates for 3-5 months, the physical and chemical cleaning device 5 performs chemical cleaning on the low-pressure nanofiltration membrane system 3 by a chemical cleaning optimization scheme to obtain nanofiltration chemical cleaning waste liquid, and the nanofiltration chemical cleaning waste liquid is input into a concentrated/wastewater treatment system 4 for treatment;
further, the chemical cleaning optimization scheme is divided into two steps:
firstly, sterilizing and carrying out alkaline washing chemical cleaning;
specifically, the preparation method comprises the steps of flushing by gas-liquid and alkali liquor at 85 ℃, replenishing water, dispensing, sequentially performing first-stage circulation, second-stage circulation and first-stage circulation on a non-oxidizing bactericide with the concentration of 0.03-0.9%, dispensing again, sequentially performing second-stage circulation and first-stage circulation on an alkaline bactericide with the concentration of 1.5-3.0%, soaking, and sequentially flushing the second stage and the first stage.
Secondly, carrying out acid-washing chemical cleaning;
specifically, water replenishing and dispensing are sequentially carried out, the medicament is an acidic medicament with the concentration of 0.5-2.5%, and two-stage circulation, one-stage flushing and two-stage flushing are sequentially carried out.
All the above-mentioned step sequence valves are operated unchanged, and only the step sequence is regulated.
Wherein the total "cycle" step time is 30 minutes, the "flush" time is 30 minutes, and the "soak" time is at least 2 hours.
And discharging the secondary concentrated/wastewater and (or) the physical backwashing waste liquid treated by the concentrated/wastewater treatment system 4, and (or) the pretreatment system waste liquid and (or) the nanofiltration chemical cleaning waste liquid into a total wastewater pipe according to a proportion of 1/14-1/7, so that the requirements of comprehensive wastewater discharge standard (DB31/199-2018) can be met.
Therefore, the novel low-pressure high-recovery nanofiltration system provided by the utility model has the advantages that the related parameters of raw water to be treated or effluent of a water plant can meet the water inlet requirement of a nanofiltration membrane through the efficient pretreatment system; low-pressure high-recovery water treatment is realized through a low-pressure nanofiltration membrane system; the recovery rate is improved and the produced water meets the water quality standard requirement through the treatment of a concentration/waste water treatment system; when the cleaning conditions are met, the physical and chemical cleaning device is used for cleaning the pretreatment system and the low-pressure nanofiltration membrane system, and parameter optimization is carried out on chemical cleaning; when the disinfection condition is met, the ultraviolet disinfection unit and the gas-liquid disinfection unit disinfect the low-pressure nanofiltration membrane system; and (4) obtaining final produced water in the water producing tank, and obtaining low-pollution concentrated/waste water and cleaning waste liquid in the total waste water pipe.
Compared with the prior art, the utility model has the following advantages:
(1) the low-pressure nanofiltration membrane is arranged, so that the removal rate of sulfate radicals in inlet water is 40-60%, the removal rate of TOC in inlet water is 30-50%, the removal rate of ammonia nitrogen in inlet water is 15-30%, and the removal rate of calcium, magnesium and total hardness is less than 10% under the low-pressure operation of 0.4-0.6 MPa;
(2) by arranging the concentration/wastewater treatment system, high recovery rate of drinking water advanced treatment can be realized, the overall recovery rate is improved by 1-5%, and the produced water can meet the requirements of 'domestic drinking water quality standard' (DB31/T1091-2018) in Shanghai city; organic matters, inorganic salt highly-concentrated/waste water and chemical waste water generated in the operation process of the nanofiltration membrane can be fully and effectively treated, the environmental pollution caused by direct discharge without treatment is avoided, and the requirements of the Integrated wastewater discharge Standard (DB 31/199-;
(3) a security filter system is cancelled, so that the high-efficiency pretreatment of raw water is realized, and the operation cost is reduced;
(4) by arranging the cleaning device and the disinfection device, the pollution of organic matters and microorganisms to the nanofiltration membrane can be effectively relieved, the service life of the nanofiltration membrane is prolonged, a chemical cleaning scheme is further improved, and the medicine consumption is reduced;
(5) the method can realize the secondary utilization of the concentrated/waste water, combine the cleaning waste liquid with the nanofiltration concentrated/waste water, directly enter a concentrated/waste water treatment system for treatment without adding corresponding acid liquid and alkali liquid additionally, simplify the process flow and improve the operation efficiency.
The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the utility model. Modifications and variations can be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the present invention. Therefore, the scope of the utility model should be determined from the following claims.
Claims (5)
1. A novel low-pressure high-recovery nanofiltration system is characterized in that: the device comprises a water inlet pool (1), a pretreatment system (2), a low-pressure nanofiltration membrane system (3), a concentrated/wastewater treatment system (4) and a total wastewater pipe which are communicated in sequence; the pretreatment system (2) and the low-pressure nanofiltration membrane system (3) are both communicated with a physicochemical cleaning device (5); the pretreatment system (2) is communicated with the low-pressure nanofiltration membrane system (3) through an intermediate lift pump (10), the intermediate lift pump (10) is communicated with a dosing system (9), and the dosing system (9) is communicated with an ultraviolet disinfection unit (6) and a gas-liquid disinfection unit (7); the pretreatment system (2) and the low-pressure nanofiltration membrane system (3) are both communicated with a concentrated/wastewater treatment system (4); the low-pressure nanofiltration membrane system (3) and the concentrated/wastewater treatment system (4) are both communicated with a water production tank (8).
2. The novel low pressure high recovery nanofiltration system of claim 1, wherein: the water coming from the water inlet tank (1) is one of raw water of surface water polluted by micro organic matters, effluent of a flocculation tank of a water plant, effluent of a sedimentation tank of the water plant and effluent of a sand filter tank of the water plant.
3. The novel low pressure high recovery nanofiltration system of claim 1, wherein: the pretreatment system (2) adopts one or more of a ceramic membrane, a disc filter, a pressure sand filter tank and a backwashing filter core to obtain the sludge density index SDI of pretreated effluent15＜3。
4. The novel low pressure high recovery nanofiltration system of claim 1, wherein: the concentrated/wastewater treatment system (4) is one of a disc tube type reverse osmosis membrane/nanofiltration membrane, low-pressure reverse osmosis, dense nanofiltration and forward osmosis.
5. The novel low pressure high recovery nanofiltration system of claim 1, wherein: the physical and chemical cleaning device (5) carries out physical backwashing on the pretreatment system (2) through water-gas combined backwashing, and the cleaning frequency is that the continuous operation of the pretreatment system (2) reaches 10-15 days or the transmembrane pressure difference is increased to 0.06 MPa; the physical chemical cleaning device (5) carries out chemical cleaning on the pretreatment system (2) through sterilization and alkali cleaning, and the cleaning frequency is that the continuous operation of the pretreatment system (2) reaches 30-50 days or the transmembrane pressure difference is increased to 0.1-0.12 MPa; the physical and chemical cleaning device (5) carries out chemical cleaning on the low-pressure nanofiltration membrane system (3) through sterilization, alkali cleaning and acid cleaning, and the cleaning frequency is that the low-pressure nanofiltration membrane system (3) continuously operates for 3-5 months.
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