WO2023040018A1 - Novel low-pressure high-recovery rate nanofiltration system and method - Google Patents

Abstract

Disclosed are a novel low-pressure high-recovery rate nanofiltration system and method. The system comprises a water intake tank (1), a pretreatment system (2), a low-pressure nanofiltration membrane system (3), a concentrated/waste water treatment system (4), and a total waste water pipe that sequentially communicate with one another; both the pretreatment system (2) and the low-pressure nanofiltration membrane system (3) communicate with a physical and chemical cleaning device (5); the pretreatment system (2) communicates with the low-pressure nanofiltration membrane system (3) by means of an intermediate lift pump (10), the intermediate lift pump (10) communicating with a dosing system (9), and the dosing system (9) communicating with an ultraviolet disinfection unit (6) and a gas-liquid disinfection unit (7); both the pretreatment system (2) and the low-pressure nanofiltration membrane system (3) communicating with the concentrated/waste water treatment system (4); and both the low-pressure nanofiltration membrane system (3) and the concentrated/waste water treatment system (4) communicate with a water production tank (8).

Description

A novel low-pressure high-recovery nanofiltration system and method technical field

The invention relates to the field of nanofiltration advanced treatment of drinking water and the like, in particular to a low-pressure, high-recovery nanofiltration system and method for advanced treatment of drinking water in a nanofiltration system for micro-organic pollutant surface water.

Background technique

The safety of drinking water quality is directly related to the health of the general public. With the continuous improvement of living standards, the public has also put forward higher requirements for drinking water. Membrane separation technology is better than traditional coagulation-sedimentation-filtration-disinfection and ozone-activated processes in dealing with water pollution. Among them, nanofiltration (NF) membrane has a smaller pore size than microfiltration (MF) membrane; compared with ultrafiltration (UF) membrane, the technology has stronger separation and can effectively remove organic pollutants and multivalent ions; Compared with reverse osmosis (RO) membrane, the operating pressure is lower, which can effectively retain some minerals needed by the human body. However, NF separation of solutes is mainly through the action of charge and sieving. Pollutants (such as organic matter, colloids, inorganic salts, bacteria) are easily trapped on the surface of the membrane to block the pores of the membrane and cause pollution, which will increase the operating pressure of the NF membrane, decrease the flux, and cause chemical cleaning. The frequency is high, the life is shortened, and the operating energy consumption/medicine consumption is increased, but it is difficult for the conventional treatment process of the water plant to remove such pollutants. For example, Shanghai City Investment (Water Affairs) Group and Zhangjiagang City Water Supply and Drainage Company, which are the first to adopt nanofiltration membrane technology in China, have a chemical cleaning cycle of their nanofiltration drinking water advanced treatment system once every 3 months, with high frequency Excessive chemical cleaning can easily damage the structure of the NF membrane, affect the service life of the NF membrane, and increase the cost of running chemicals and electricity.

technical problem

At present, the engineering measures to alleviate NF membrane fouling are effective pretreatment and maintenance cleaning. The existing NF conventional pretreatment measures are ultrafiltration + security filter. The pore size of ultrafiltration is 20-100nm, but the commonly used pore size of security filter element is 5μm. The filter only plays the role of "security" for psychological comfort, which is unnecessary and wasteful; in addition, the security filter NF system is a one-time consumable in actual operation and needs to be replaced every 6 months, which greatly improves the safety of the NF system. construction and operating costs. The water treatment process adheres to the principle of short process and good effect, especially in the southern surface water system. The process of ultrafiltration + security filter for drinking water pretreatment of nanofiltration membrane is relatively long, which increases the operation and subsequent maintenance costs of the entire NF system. . In addition, during the operation of nanofiltration membranes, organic matter and highly concentrated inorganic salt wastewater and chemical cleaning wastewater will be generated, and direct discharge without treatment may cause environmental pollution. Therefore, it is necessary to propose a functionally enhanced nanofiltration system for the advanced treatment of drinking water.

technical solution

In order to overcome the deficiencies in the above-mentioned prior art, the object of the present invention is to provide a novel low-pressure high-recovery nanofiltration system and method, which can realize shortened process flow, high-efficiency pretreatment, low-pressure characteristics of the nanofiltration membrane, high recovery rate, Notable advantages such as low chemical consumption, secondary utilization of concentrated/wastewater, etc., and at the same time, it has the functions of reducing the operating cost and energy consumption of the nanofiltration system, reducing pollution, and improving the safety and health of drinking water quality.

For reaching above-mentioned purpose, the present invention proposes a kind of novel low-pressure high-recovery rate nanofiltration system, comprising:

Inlet pool, pretreatment system, low-pressure nanofiltration membrane system, concentrated/wastewater treatment system and total waste water pipe connected in sequence; both the pretreatment system and the low-pressure nanofiltration membrane system are connected with physical and chemical cleaning devices; the pretreatment system It is communicated with the low-pressure nanofiltration membrane system through an intermediate lift pump, and the intermediate lift pump is communicated with the 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 It is connected with the concentrated/wastewater treatment system; both the low-pressure nanofiltration membrane system and the concentrated/wastewater treatment system are connected with the produced water tank.

The incoming water of the water inlet pool is one of the raw water of micro-organic polluted surface water, the effluent of the flocculation tank of the water plant, the effluent of the sedimentation tank of the water plant, and the effluent of the sand filter of the water plant.

The pretreatment system uses one or more of ceramic membranes, disc filters, pressure sand filter tanks, and backwashable filter elements to obtain the sludge density index SDI ₁₅ <3 of the pretreated effluent.

The concentrated/wastewater treatment system is one of disc-type reverse osmosis membrane/nanofiltration membrane, low-pressure reverse osmosis, dense nanofiltration, and forward osmosis.

The physical and chemical cleaning device performs physical backwashing of the pretreatment system through water-gas combined backwashing, and the cleaning frequency is that the pretreatment system runs continuously for 10 to 15 days or the transmembrane pressure difference rises to 0.06MPa; the physical and chemical The cleaning device performs chemical cleaning on the pretreatment system through sterilization and alkali cleaning, and the cleaning frequency is that the continuous operation of the pretreatment system reaches 30-50 days or the transmembrane pressure difference rises to 0.1-0.12MPa; the physical and chemical cleaning device The low-pressure nanofiltration membrane system is chemically cleaned by sterilization + alkali washing and pickling, and the cleaning frequency is that the continuous operation of the low-pressure nanofiltration membrane system reaches 3 to 5 months.

The ultraviolet disinfection unit is intermittent ultraviolet disinfection, which adopts one of the coupling of single ultraviolet and ultraviolet + bactericide, and the disinfection frequency is 5 to 15 days/time; the gas-liquid disinfection unit is 85°C gas-liquid intermittent forward flushing disinfection, One or both of gas-liquid, gas-liquid+alkali coupling are used, and the disinfection frequency is 5-15 days/time, and the gas-liquid mixing ratio in the gas-liquid, gas-liquid+alkali coupling is 1/14-1 /7, the concentration of lye is 0.2-2.0%.

For reaching above-mentioned object, the present invention also proposes a kind of novel low-pressure high-recovery nanofiltration method, comprises the steps:

Step S1, input the incoming water in the water inlet tank into the pretreatment system to obtain the pretreated water with the sludge density index SDI ₁₅ <3; pump the pretreated water into the low-pressure sodium Treat in the membrane filtration system to obtain nanofiltration product water and nanofiltration concentrated/wastewater; input the nanofiltration concentrated/wastewater to the concentrated/wastewater treatment system to obtain concentrated/wastewater produced water and secondary concentrated/wastewater; The nanofiltration product water and the concentrated/waste water product water are input to the product water tank and mixed to obtain the final product water;

Step S2, when the low-pressure nanofiltration membrane system has been continuously operated for 5 to 15 days, it is disinfected through the ultraviolet disinfection unit and the gas-liquid disinfection unit;

Step S3, when the continuous operation of the pretreatment system reaches 10 to 15 days or the transmembrane pressure difference rises to 0.06MPa, the physical and chemical cleaning device performs physical backwashing on the pretreatment system through water-air combined backwashing to obtain Physically backwash waste liquid and input it to the concentrated/wastewater treatment system for treatment; when the pretreatment system runs continuously for 30-50 days or the transmembrane pressure difference rises to 0.1-0.12MPa, the physical-chemical cleaning device will The pretreatment system is chemically cleaned by sterilization and alkali washing to obtain the cleaning waste liquid of the pretreatment system and input it to the concentrated/wastewater treatment system for treatment;

Step S4, when the low-pressure nanofiltration membrane system has been running continuously for 3 to 5 months, the physical and chemical cleaning device performs chemical cleaning on the low-pressure nanofiltration membrane system through a chemical cleaning optimization scheme to obtain nanofiltration chemical cleaning waste liquid and input it to the The concentrated/waste water treatment system is processed;

Step S5, the secondary concentrated/wastewater described in step S1,

And/or the physical backwash waste liquid treated in step S3 and/or the pretreatment system cleaning waste liquid after treatment,

And/or the nanofiltration chemical cleaning waste liquid treated in step S4 is discharged into the total waste water pipe in a ratio of 1/14 to 1/7.

In step S1, the incoming water in the water inlet pool is one of the raw water of surface water with micro-organic pollution, the effluent of the sedimentation tank of the water plant, and the effluent of the sand filter of the water plant; the pretreatment system adopts ceramic membrane and disc filter One or more of filter, pressure sand filter tank, and backwashable filter element to obtain the sludge density index SDI ₁₅ <3 of the pretreated effluent; the concentrated/wastewater treatment system is a disc tube reverse osmosis membrane/nano One of filter membrane, low-pressure reverse osmosis, dense nanofiltration, and forward osmosis.

In step S2, the ultraviolet disinfection unit is intermittent ultraviolet disinfection, which adopts one of the coupling of single ultraviolet and ultraviolet + bactericide; One or two of the liquid+alkali coupling, the gas-liquid mixing ratio in the gas-liquid and gas-liquid+alkali coupling is 1/14-1/7, and the alkali concentration is 0.2-2.0%.

In step S4, the chemical cleaning optimization scheme includes two steps of sterilization + alkali washing and pickling. The sterilization + alkali washing step is: washing with gas-liquid and alkali liquid at 85°C, followed by water replenishment, dispensing, and medicament It is a non-oxidizing fungicide with a concentration of 0.03-0.9%, which is followed by one-stage cycle, two-stage cycle, and one-stage cycle, and then dispensed again. Soaking, followed by two stages of rinsing and one stage of rinsing; the pickling steps are: sequentially replenish water and dispense medicines, and the medicament is an acidic agent with a concentration of 0.5-2.5%, followed by two stages of circulation, one stage of circulation, one stage of rinsing, and two stages of rinsing. part.

Compared with prior art, the present invention has following advantage:

(1) By setting the low-pressure nanofiltration membrane, it can be realized under the low-pressure operation of 0.4-0.6MPa, the removal rate of sulfate radical in the influent is 40-60%, and the removal rate of TOC in the influent is 30-50%. The removal rate of ammonia nitrogen in water is 15-30%, and the removal rate of calcium, magnesium and total hardness is less than 10%;

(2) By setting up the concentration/wastewater treatment system, the high recovery rate of advanced treatment of drinking water can be realized, the overall recovery rate can be increased by 1-5%, and the produced water can reach the Shanghai "Drinking Water Quality Standard" (DB31/T 1091-2018) requirements; and can fully and effectively treat the organic matter, highly concentrated inorganic salt concentrated/wastewater and chemical wastewater generated during the operation of the nanofiltration membrane, to avoid environmental pollution caused by direct discharge without treatment, and to achieve the "Sewage Comprehensive Emission Standard" (DB31/199-2018);

(3) Cancel the security filter system to achieve efficient pretreatment of raw water and reduce operating costs;

(4) By installing cleaning devices and disinfection devices, the pollution of nanofiltration membranes by organic matter and microorganisms can be effectively alleviated, the service life of nanofiltration membranes can be improved, and the chemical cleaning scheme can be further improved to reduce drug consumption;

(5) The secondary utilization of concentrated/wastewater can be realized, and the cleaning waste liquid and nanofiltration concentrated/wastewater can be combined without additional addition of corresponding acid and lye directly into the concentrated/wastewater treatment system for treatment, simplifying the process flow, Improve operational efficiency.

Description of drawings

Fig. 1 is the structural representation of a kind of novel low pressure high recovery rate nanofiltration system of the present invention;

Fig. 2 is a flow chart of steps of a novel low-pressure high-recovery nanofiltration method of the present invention.

In the figure: 1. Water inlet pool; 2. Pretreatment system; 3. Low-pressure nanofiltration membrane; 4. Concentrated/wastewater treatment system; 5. Physical and chemical cleaning device; 6. Ultraviolet disinfection unit; 7. Gas-liquid disinfection unit; 8 , Production pool; 9, dosing system; 10, intermediate lift pump.

Embodiments of the present invention

The implementation of the present invention is described below through specific examples and in conjunction with the accompanying drawings, and those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific examples, and various modifications and changes can be made to the details in this specification based on different viewpoints and applications without departing from the spirit of the present invention.

Fig. 1 is a schematic diagram of a novel low-pressure high-recovery nanofiltration system of the present invention. As shown in Fig. 1, comprise the water inlet pool 1, pretreatment system 2, low-pressure nanofiltration membrane system 3, concentrated/wastewater treatment system 4 and total waste water pipe that are connected successively; Described pretreatment system 2 and low-pressure nanofiltration membrane system 3 All communicate with physicochemical cleaning device 5; Described pretreatment system 2 communicates with low-pressure nanofiltration membrane system 3 through intermediate lift pump 10, and described intermediate lift pump 10 communicates with dosing system 9, and described dosing system 9 communicates with ultraviolet Disinfection unit 6 and gas-liquid disinfection unit 7 are communicated; Described pretreatment system 2 and low-pressure nanofiltration membrane system 3 are all communicated with concentrated/wastewater treatment system 4; Described low-pressure nanofiltration membrane system 3 and thick/wastewater treatment system 4 are all connected It is connected with the water production pool 8.

Preferably, the incoming water of the water inlet tank 1 is one of the raw water of slightly organically polluted surface water, the effluent of the flocculation tank of the water plant, the effluent of the sedimentation tank of the water plant, and the effluent of the sand filter of the water plant.

Preferably, the pretreatment system 2 uses one or more of ceramic membranes, disc filters, pressure sand filter tanks, and backwashable filter elements to obtain a sludge density index SDI ₁₅ <3 of the pretreated effluent.

Preferably, the concentrated/wastewater treatment system 4 is one of disk-type reverse osmosis membrane/nanofiltration membrane (DTRO/NF), low-pressure reverse osmosis (LPRO), dense nanofiltration (DNF), and forward osmosis (FO). kind.

Preferably, the physical and chemical cleaning device 5 performs physical backwashing of the pretreatment system 2 through water-air combined backwashing, and the cleaning frequency is that the pretreatment system 2 runs continuously for 10 to 15 days or the transmembrane pressure difference rises to 0.06 MPa; the physical and chemical cleaning device 5 chemically cleans the pretreatment system 2 through sterilization and alkali cleaning, and the cleaning frequency is that the pretreatment system 2 runs continuously for 30-50 days or the transmembrane pressure difference rises to 0.1- 0.12MPa; the physical and chemical cleaning device 5 performs chemical cleaning on the low-pressure nanofiltration membrane system 3 through sterilization + alkali cleaning and pickling, and the cleaning frequency is that the low-pressure nanofiltration membrane system 3 runs continuously for 3 to 5 months.

Preferably, the ultraviolet disinfection unit 6 is intermittent ultraviolet disinfection, which adopts one of the coupling of single ultraviolet and ultraviolet + bactericide, and the disinfection frequency is 5 to 15 days/time; the gas-liquid disinfection unit 7 is 85°C gas-liquid Intermittent forward flushing disinfection, using one or two of gas-liquid, gas-liquid + lye coupling, the disinfection frequency is 5 to 15 days/time, and the gas-liquid mixing ratio in the gas-liquid, gas-liquid + lye coupling is 1/14～1/7, the concentration of lye is 0.2～2.0%.

The water production principle and concentrated/wastewater treatment principle of a novel low-pressure high-recovery nanofiltration system of the present invention are as follows:

Incoming water is input in the water inlet pool 1, and the incoming water can be a kind of micro-organic polluted surface water raw water, water plant flocculation tank effluent, water plant sedimentation tank effluent, water plant sand filter effluent; wherein, the micro-organic pollution The potassium permanganate index COD _Mn of the surface water is 3.01-4.44mg/L, and the total organic carbon TOC is 1.8-3.9mg/L. The outlet water temperature is generally between 4°C and 35°C, the outlet water turbidity is generally ≦0.1~27NTU, and the free chlorine/ozone content in the outlet water is generally <0.1mg/L.

The incoming water flows into the pretreatment system 2 for pretreatment. The pretreatment method can be selected from one or more of ceramic membranes, disc filters, pressure sand filter tanks, and backwashable filter elements to obtain a pretreatment of SDI ₁₅ <3. Water treatment; wherein, the pore size of the ceramic membrane is 0.1-3 μm, the absolute filtration accuracy of the disc filter is 3-5 μm, and the sand filter particle size of the pressure sand filter tank is 30% of the conventional sand filter particle size of the water plant ~50%, the filtration precision of the backwashable filter element is 1~3μm;

The pretreated water flows through the intermediate lift pump 10 to remove organic pollution and microbial contamination through the dosing system 9, and the water is pumped into the low-pressure nanofiltration membrane system 3 by the intermediate lift pump 10 for processing. The operating pressure of the low-pressure nanofiltration membrane 3 is 0.4-0.6 MPa, the removal rate of sulfate radical in the influent is 40-60%, the removal rate of TOC in the influent is 30-50%, and the removal rate of ammonia nitrogen in the influent is 15% ~30%, the removal rate of calcium, magnesium and total hardness is less than 10%, the recovery rate of the low-pressure nanofiltration system is ≥85%, and the nanofiltration product water and nanofiltration concentrated/wastewater are obtained;

When the low-pressure nanofiltration membrane system 3 runs continuously for 5 to 15 days, it is sterilized by the ultraviolet disinfection unit 6 and the gas-liquid disinfection unit 7; wherein, the ultraviolet disinfection unit 6 is intermittent ultraviolet disinfection, which uses a single ultraviolet, ultraviolet + bactericide coupling The gas-liquid disinfection unit 7 is 85 ℃ gas-liquid intermittent forward flushing, using one or two of gas-liquid, gas-liquid + lye coupling; the separate ultraviolet, ultraviolet + bactericide coupling intermittent disinfection The intensity of ultraviolet light in the process is 40-80mj/cm ² , the number of ultraviolet irradiation channels is 2-6, the length of the channel before and after the lamp tube is 1-6m, the water flow of the irradiation channel is uniform, and the water depth of the irradiation channel meets the burial of the ultraviolet lamp tube Requirements: The gas-liquid mixing ratio in the gas-liquid, gas-liquid+lye coupling is 1/14-1/7, and the concentration of the lye is 0.2-2.0%.

The nanofiltration concentrated/wastewater is input to the concentrated/wastewater treatment system 4 to obtain concentrated/wastewater produced water and secondary concentrated/wastewater; wherein, the concentrated/wastewater treatment system 4 is a reverse osmosis membrane/nanofiltration membrane (DTRO /NF), low-pressure reverse osmosis (LPRO), dense nanofiltration (DNF), and forward osmosis (FO), which can increase the overall recovery rate of the nanofiltration system by 1 to 5%;

The nanofiltration produced water and the concentrated/wastewater produced water are input into the produced water tank 8 and mixed to obtain the final produced water, which can meet the Shanghai "Drinking Water Quality Standard" (DB31/T 1091-2018) Require.

The cleaning principle and cleaning waste liquid treatment principle of a novel low-pressure high-recovery nanofiltration system of the present invention are as follows:

When the pretreatment system 2 runs continuously for 10 to 15 days or the transmembrane pressure difference rises to 0.06 MPa, the physical and chemical cleaning device 5 performs physical backwashing on the pretreatment system 2 through combined water and air backwashing, and then Dosing, circulation and flushing are started, each time of backwashing is 2 to 5 minutes, and physical backwashing waste liquid is obtained, and the physical backwashing liquid is input into the concentrated/wastewater treatment system 4 for processing;

When the continuous operation of the pretreatment system 2 reaches 30-50 days or the transmembrane pressure difference rises to 0.1-0.12MPa, the physical and chemical cleaning device 5 chemically cleans the pretreatment system 2 through sterilization and alkali cleaning to obtain The pretreatment system cleaning waste liquid is input to the concentrated/wastewater treatment system 4 for processing;

Further, the chemical cleaning agent is a non-oxidizing bactericide and lye, the concentration of the non-oxidizing bactericide is 0.01-0.09%, and the concentration of the lye is 5000-7500 mg/L.

Further, the chemical cleaning sequence is: dosing of non-oxidizing bactericide, circulation for 10-30 minutes, dosing of lye, circulation for 10-30 minutes, soaking for 0-90 minutes, circulation for 10-30 minutes, and rinsing for 15-30 minutes.

When the continuous operation of the low-pressure nanofiltration membrane system 3 reaches 3 to 5 months, the physical and chemical cleaning device 5 performs chemical cleaning on the low-pressure nanofiltration membrane system 3 through a chemical cleaning optimization scheme to obtain nanofiltration chemical cleaning waste liquid, which is then The nanofiltration chemical cleaning waste liquid is input to the concentrated/wastewater treatment system 4 for processing;

Further, the chemical cleaning optimization scheme is divided into two steps:

The first step is to carry out sterilization + alkali cleaning chemical cleaning;

Specifically, flushing with gas-liquid and lye at 85°C, replenishing water, and dispensing. The agent is a non-oxidizing fungicide with a concentration of 0.03-0.9%. The first cycle, the second cycle, and the first cycle are performed in sequence, and the drug is dispensed again. The medicament is an alkaline medicament with a concentration of 1.5-3.0%. The two-stage cycle and the one-stage cycle are sequentially performed for soaking, followed by two stages of washing and one stage of washing in sequence.

The second step is to carry out pickling chemical cleaning;

Specifically, replenishing water and dispensing medicine in sequence, the medicine is an acidic medicine with a concentration of 0.5-2.5%, followed by two stages of circulation, one stage of circulation, one stage of flushing, and two stages of flushing.

All the valve operations of the above steps remain unchanged, only the sequence of steps is adjusted.

Wherein, all " cycle " step sequence time is 30 minutes, " flushing " time is 30 minutes, " soaking " time is at least 2 hours.

The physical backwash waste liquid and (or) pretreatment system waste liquid and (or) nanofiltration chemical cleaning waste liquid treated by the secondary concentrated/waste water and (or) the concentrated/waste water treatment system 4 are treated at a rate of 1/ 14~1/7 ratio is discharged into the total waste water pipe, which can meet the requirements of the "Comprehensive Wastewater Discharge Standard" (DB31/199-2018).

Fig. 2 is a flow chart of steps of a novel low-pressure high-recovery nanofiltration method of the present invention. As shown in Figure 2, a kind of novel low pressure high recovery rate nanofiltration method of the present invention comprises the steps:

Step S1, input the incoming water in the water inlet tank 1 into the pretreatment system 2 to obtain pretreated water with a sludge density index SDI ₁₅ <3; pass the pretreated water through the intermediate lift pump 10 and the dosing system 9 to pump into the low-pressure nanofiltration membrane system 3 for processing to obtain nanofiltration product water and nanofiltration concentrated/wastewater; the nanofiltration concentrated/wastewater is input to the concentrated/wastewater treatment system 4 to obtain concentrated/wastewater produced water and secondary concentrated /waste water; the nanofiltration product water and the concentrated/waste water product water are input to the product water tank 8 and mixed to obtain the final product water;

Preferably, the incoming water in the water inlet pool 1 is one of micro organically polluted surface water, effluent from a sedimentation tank in a water plant, and effluent from a sand filter in a water plant; the pretreatment system 2 uses ceramic membranes and disc filters One or more of filter, pressure sand filter tank, and backwashable filter element; the concentrated/wastewater treatment system 4 is a disc-type reverse osmosis membrane/nanofiltration membrane, low-pressure reverse osmosis, dense nanofiltration, and forward osmosis medium a kind of

Wherein, the potassium permanganate index COD _Mn of the micro-organic polluted surface water is 3.01-4.44mg/L, the total organic carbon TOC is 1.8-3.9mg/L, and the effluent of the flocculation tank of the water plant and the effluent of the sedimentation tank of the water plant . The outlet water temperature of the sand filter in the water plant is generally between 4°C and 35°C, the turbidity of the outlet water is generally ≦0.1~27NTU, and the free chlorine/ozone content of the outlet water is generally <0.1mg/L;

The pore size of the ceramic membrane is 0.1-3 μm, the absolute filtration accuracy of the disc filter is 3-5 μm, and the sand filter particle size of the pressure sand filter tank is 30-50% of the conventional sand filter particle size of the water plant. The filtration precision of the above-mentioned backwashable filter element is 1-3 μm;

The operating pressure of the low-pressure nanofiltration membrane 3 in the low-pressure nanofiltration membrane system 3 is 0.4-0.6 MPa, the removal rate of sulfate in the influent is 40-60%, and the removal rate of TOC in the influent is 30-50%. The removal rate of ammonia nitrogen in the influent 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 ≥85%, so as to obtain nanofiltration product water and nanofiltration concentrated/wastewater.

The produced water can meet the requirements of Shanghai's "Drinking Water Quality Standard" (DB31/T 1091-2018).

Step S2, when the low-pressure nanofiltration membrane system 3 has been continuously operated for 5 to 15 days, it is sterilized by the ultraviolet disinfection unit 6 and the gas-liquid disinfection unit 7;

Preferably, in step S2, the ultraviolet disinfection unit 6 is intermittent ultraviolet disinfection, which adopts one of the couplings of single ultraviolet and ultraviolet + bactericide; the gas-liquid disinfection unit 7 is intermittent positive flushing disinfection of gas-liquid at 85°C, Use one or both of gas-liquid, gas-liquid + lye coupling, disinfection frequency is 5-15 days/time, the gas-liquid at 85°C is gas-liquid, and the gas-liquid mixing ratio in gas-liquid + lye coupling is 1/14～1/7, the concentration of lye is 0.2～2.0%.

Wherein, the intensity of ultraviolet in the intermittent disinfection process of single ultraviolet, ultraviolet + bactericide coupling is 40-80mj/cm ² , the disinfection frequency is 5-15 days/time, the number of ultraviolet irradiation channels is 2-6, the front and rear of the lamp tube The length of the canal is 1-6m, the water flow in the irradiated canal is uniform, and the water depth of the irradiated canal meets the burying requirements of the ultraviolet lamp.

Step S3, when the pretreatment system 2 has been continuously operated for 10-15 days or the transmembrane pressure difference has risen to 0.06MPa, the physical and chemical cleaning device 5 performs physical backwashing on the pretreatment system 2 through combined water-air backwashing. Washing, the obtained physical backwash waste liquid is input to the concentrated/wastewater treatment system 4 for treatment; when the pretreatment system 2 runs continuously for 30-50 days or the transmembrane pressure difference rises to 0.1-0.12MPa, the The physical and chemical cleaning device 5 performs chemical cleaning on the pretreatment system 2 through sterilization and alkali cleaning, and the obtained pretreatment system cleaning waste liquid is input to the concentrated/wastewater treatment system 4 for processing;

Wherein, the physical backwashing is started during dosing, circulation and flushing, and the backwashing time is 2 to 5 minutes each time;

The chemicals for chemical cleaning are non-oxidative bactericide and lye, the concentration of the non-oxidative bactericide is 0.01-0.09%, and the concentration of the lye is 5000-7500 mg/L.

The chemical cleaning sequence is: dosing of non-oxidizing bactericide, circulation for 10-30 minutes, dosing of lye, circulation for 10-30 minutes, soaking for 0-90 minutes, circulation for 10-30 minutes, and washing for 15-30 minutes.

Step S4, when the low-pressure nanofiltration membrane system 3 has been continuously operated for 3 to 5 months, the physical and chemical cleaning device 5 performs chemical cleaning on the low-pressure nanofiltration membrane system 3 through a chemical cleaning optimization scheme, and the obtained nanofiltration chemical cleaning waste The liquid is input to the concentrated/wastewater treatment system 4 for processing;

Preferably, the chemical cleaning optimization scheme includes two steps of sterilization + alkali washing and pickling. The sterilization + alkali washing step is: washing with gas-liquid and alkali liquid at 85°C, followed by water replenishment and dispensing. 0.03-0.9% non-oxidizing fungicide, followed by one-stage cycle, two-stage cycle, one-stage cycle, and redispensing. The agent is an alkaline agent with a concentration of 1.5-3.0%, followed by two-stage cycle, one-stage cycle, and soaking , performing the second stage of washing and the first stage of washing in sequence; the pickling steps are: sequentially replenish water and dispense the medicine, the medicine is an acidic medicine with a concentration of 0.5-2.5%, and then perform the second stage of circulation, the first stage of circulation, the first stage of washing, and the second stage of washing.

All the valve operations of the above steps remain unchanged, only the sequence of steps is adjusted.

Among them, all the "circulation" step sequence time is 30 minutes, the "rinsing" time is 30 minutes, and the "soaking" time is at least 2 hours.

Step S5, the secondary concentrated/wastewater described in step S1,

And/or the physical backwash waste liquid treated in step S3 and/or the pretreatment system cleaning waste liquid,

And/or the nanofiltration chemical cleaning waste liquid treated in step S4 is discharged into the total waste water pipe in a ratio of 1/14 to 1/7.

The cleaning wastewater and secondary concentrated/wastewater can meet the requirements of the "Integrated Wastewater Discharge Standard" (DB31/199-2018).

It can be seen that a novel low-pressure high-recovery nanofiltration system and method of the present invention, through an efficient pretreatment system, make the relevant parameters of the raw water to be treated or the effluent of the water plant meet the requirements of nanofiltration membrane water intake; through the low-pressure nanofiltration membrane system Realize low-pressure and high-recovery water treatment; through concentrated/wastewater treatment system treatment, the recovery rate is improved and the produced water meets the water quality standard requirements; when the cleaning conditions are met, the pretreatment system and the low-pressure nanofiltration membrane system are cleaned by a physical and chemical cleaning device , and optimize the parameters of the chemical cleaning; when the disinfection conditions are met, the low-pressure nanofiltration membrane system is disinfected by the ultraviolet disinfection unit and the gas-liquid disinfection unit; the final produced water is obtained in the produced water tank, and the low-pollution water is obtained in the total waste water pipe Concentrated/waste water, cleaning waste liquid.

Compared with prior art, the present invention has following advantage:

(1) By setting the low-pressure nanofiltration membrane, it can be realized under the low-pressure operation of 0.4-0.6MPa, the removal rate of sulfate radical in the influent is 40-60%, and the removal rate of TOC in the influent is 30-50%. The removal rate of ammonia nitrogen in water is 15-30%, and the removal rate of calcium, magnesium and total hardness is less than 10%;

(2) By setting up the concentration/wastewater treatment system, the high recovery rate of advanced treatment of drinking water can be realized, the overall recovery rate can be increased by 1-5%, and the produced water can reach the Shanghai "Drinking Water Quality Standard" (DB31/T 1091-2018) requirements; and can fully and effectively treat the organic matter, highly concentrated inorganic salt concentrated/wastewater and chemical wastewater generated during the operation of the nanofiltration membrane, to avoid environmental pollution caused by direct discharge without treatment, and to achieve the "Sewage Comprehensive Emission Standard" (DB31/199-2018);

(3) Cancel the security filter system to achieve efficient pretreatment of raw water and reduce operating costs;

(4) By installing cleaning devices and disinfection devices, the pollution of nanofiltration membranes by organic matter and microorganisms can be effectively alleviated, the service life of nanofiltration membranes can be improved, and the chemical cleaning scheme can be further improved to reduce drug consumption;

(5) The secondary utilization of concentrated/wastewater can be realized, and the cleaning waste liquid and nanofiltration concentrated/wastewater can be combined without additional addition of corresponding acid and lye directly into the concentrated/wastewater treatment system for treatment, simplifying the process flow, Improve operational efficiency.

The above-mentioned embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Any person skilled in the art can modify and change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be listed in the claims.

Industrial Applicability

Those skilled in the art can easily know from the above description that the technical solution of the present invention is suitable for industrial manufacture and use in production and daily life, so the present invention has industrial applicability.

Claims (10)

1. A novel low-pressure high-recovery nanofiltration system is characterized in that it includes sequentially connected water inlet pools (1), a pretreatment system (2), a low-pressure nanofiltration membrane system (3), a concentrated/wastewater treatment system (4) and Total waste water pipe; described pretreatment system (2) and low pressure nanofiltration membrane system (3) are all communicated with physicochemical cleaning device (5); described pretreatment system (2) and low pressure nanofiltration membrane system (3) pass Middle lift pump (10) is communicated, and described middle lift pump (10) is communicated with dosing system (9), and described dosing system (9) is communicated with ultraviolet disinfection unit (6) and gas-liquid disinfection unit (7); The pretreatment system (2) and the low-pressure nanofiltration membrane system (3) are all connected with the thick/wastewater treatment system (4); the low-pressure nanofiltration membrane system (3) and the thick/wastewater treatment system (4) are connected with the production Pool (8) is connected.
2. A new type of low-pressure high-recovery nanofiltration system as claimed in claim 1, characterized in that: the incoming water of the water inlet tank (1) is the raw water of surface water with slight organic pollution, the effluent of the flocculation tank of the water plant, and the sedimentation tank of the water plant A kind of effluent, water plant sand filter effluent.
3. A new type of low-pressure high-recovery nanofiltration system as claimed in claim 1, characterized in that: said pretreatment system (2) adopts ceramic membranes, disc filters, pressure sand filter tanks, and backwashable filter elements. One or more to obtain the sludge density index SDI ₁₅ <3 of the pretreated effluent.
4. A new type of low-pressure high-recovery nanofiltration system as claimed in claim 1, characterized in that: the concentrated/wastewater treatment system (4) is a dish-type reverse osmosis membrane/nanofiltration membrane, low-pressure reverse osmosis, dense nanofiltration One of filtration and forward osmosis.
5. A new type of low-pressure high-recovery nanofiltration system according to claim 1, characterized in that: the physical and chemical cleaning device (5) performs physical backwashing of the pretreatment system (3) through water-gas combined backwashing , the cleaning frequency is that the pretreatment system (2) runs continuously for 10 to 15 days or the transmembrane pressure difference rises to 0.06MPa; Carry out chemical cleaning, and the cleaning frequency is that the continuous operation of the pretreatment system (2) reaches 30-50 days or the transmembrane pressure difference rises to 0.1-0.12MPa; 3) Chemical cleaning is carried out by sterilization+alkaline cleaning and pickling, and the cleaning frequency is such that the continuous operation of the low-pressure nanofiltration membrane system (3) reaches 3 to 5 months.
6. A new type of low-pressure high-recovery nanofiltration system as claimed in claim 1, characterized in that: the ultraviolet disinfection unit (6) is intermittent ultraviolet disinfection, using one of the couplings of independent ultraviolet and ultraviolet + bactericide to sterilize The frequency is 5 to 15 days/time; the gas-liquid disinfection unit (7) is 85 ° C gas-liquid intermittent forward flushing disinfection, using one or two of gas-liquid, gas-liquid + lye coupling, and the disinfection frequency is 5 ~15 days/time, the gas-liquid mixing ratio in the gas-liquid, gas-liquid+lye coupling is 1/14-1/7, and the concentration of lye is 0.2-2.0%.
7. A novel low-pressure high-recovery nanofiltration method comprising the steps of:

   Step S1, input the incoming water in the water inlet tank (1) into the pretreatment system (2) to obtain pretreated water with a sludge density index SDI ₁₅ <3; pass the pretreated water through an intermediate lift pump (10) and dosing system (9) into the low-pressure nanofiltration membrane system (3) for processing to obtain nanofiltration product water and nanofiltration concentrated/wastewater; the nanofiltration concentrated/wastewater is input to the concentrated/wastewater treatment system (4 ), to obtain concentrated/wastewater product water and secondary concentrated/wastewater; the nanofiltration product water and the concentrated/wastewater product water are input to the water production pool (8) to mix to obtain the final product water;

   Step S2, when the low-pressure nanofiltration membrane system (3) runs continuously for 5 to 15 days, it is sterilized by the ultraviolet disinfection unit (6) and the gas-liquid disinfection unit (7);

   Step S3, when the pretreatment system (2) runs continuously for 10 to 15 days or the transmembrane pressure rises to 0.06MPa, the physical and chemical cleaning device (5) passes water vapor to the pretreatment system (2) Perform physical backwashing in conjunction with backwashing to obtain physical backwashing waste liquid and input it to the concentrated/wastewater treatment system (4) for treatment; when the pretreatment system (2) runs continuously for 30 to 50 days or the transmembrane pressure The difference rises to 0.1-0.12MPa, and the physical and chemical cleaning device (5) chemically cleans the pretreatment system (2) through sterilization and alkali cleaning to obtain the cleaning waste liquid of the pretreatment system and input it into the concentrated/wastewater processing system (4) for processing;

   Step S4, when the low-pressure nanofiltration membrane system (3) has been continuously operated for 3 to 5 months, the physical and chemical cleaning device (5) performs chemical cleaning on the low-pressure nanofiltration membrane system (3) through a chemical cleaning optimization scheme to obtain Nanofiltration chemical cleaning waste liquid is also input to the concentrated/wastewater treatment system (4) for processing;

   Step S5, the secondary concentrated/wastewater described in step S1,

   And/or the physical backwash waste liquid treated in step S3 and/or the pretreatment system cleaning waste liquid after treatment,

   And/or the nanofiltration chemical cleaning waste liquid treated in step S4 is all discharged into the total waste water pipe in a ratio of 1/14～1/7.
8. A novel low-pressure high-recovery nanofiltration method as claimed in claim 7, characterized in that: in step S1, the incoming water in the inlet pool (1) is slightly organic polluted surface water raw water, water plant sedimentation tank One or more of the effluent water and the effluent water of the sand filter of the water plant; the pretreatment system (2) adopts one or more of ceramic membranes, disc filters, pressure sand filter tanks, and backwashable filter elements; the concentrated The waste water treatment system (4) is one of disc-type reverse osmosis membrane/nanofiltration membrane, low-pressure reverse osmosis, dense nanofiltration and forward osmosis.
9. A novel low-pressure high-recovery nanofiltration method as claimed in claim 7, characterized in that: in step S2, the ultraviolet disinfection unit (6) is intermittent ultraviolet disinfection, using a separate ultraviolet, ultraviolet + bactericide coupling A kind of; The gas-liquid disinfection unit (7) is 85 ℃ gas-liquid intermittent forward flushing disinfection, adopting one or both of gas-liquid, gas-liquid+alkali coupling; the gas-liquid, gas-liquid+alkali The gas-liquid mixing ratio in the liquid coupling is 1/14 to 1/7, and the concentration of the lye is 0.2 to 2.0%.
10. A novel low-pressure high-recovery nanofiltration method according to claim 7, characterized in that: in step S4, the chemical cleaning optimization scheme includes two steps of sterilization+alkali washing and pickling, and the sterilization+alkali The washing steps are: wash with gas-liquid and lye at 85°C, followed by water replenishment and dispensing. The medicament is an alkaline medicament with a concentration of 1.5-3.0%, which is followed by two-stage circulation and one-stage circulation, followed by soaking, followed by two stages of rinsing and one stage of rinsing; 0.5-2.5% acidic chemicals, followed by two stages of circulation, one stage of circulation, one stage of flushing, and two stages of flushing.

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