CN114772814A - Sewage treatment method and system combining composite pretreatment and ultrafiltration reverse osmosis - Google Patents

Abstract

A sewage treatment method and a system combining composite pretreatment and ultrafiltration reverse osmosis, wherein the method comprises the following steps: (1) adding sodium hypochlorite into raw sewage to be treated, mixing, and carrying out primary pretreatment; (2) irradiating the raw water subjected to the first pretreatment by ultraviolet light, and performing second pretreatment; (3) adding the powdered activated carbon mixed solution into the raw water subjected to the second pretreatment, mixing and stirring, and performing third pretreatment; (4) pressurizing the raw water pretreated for the third time, and filtering the raw water by using an ultrafiltration membrane; (5) and performing reverse osmosis filtration on the raw water filtered by the ultrafiltration membrane. The method fully utilizes the combination mode of sodium hypochlorite, ultraviolet light and active carbon as the pretreatment of the ultrafiltration and reverse osmosis membranes, effectively relieves membrane pollution caused by organic pollutants, does not introduce an oxidant into the components of the ultrafiltration and reverse osmosis membranes, reduces the risk of aging and damage to the membrane components, saves the cost of the membrane materials, and simultaneously more stably ensures the quality of effluent water.

Description

Sewage treatment method and system with composite pretreatment combined with ultrafiltration and reverse osmosis

technical field

The invention relates to a method and a device for treating sewage by a membrane method, and belongs to the technical field of sewage treatment.

Background technique

In recent years, with the increasing shortage of water resources and the increasing demand for reclaimed water, the recycling technology of sewage with ultrafiltration/reverse osmosis as the core has become one of the hot spots in the field of reclaimed water reuse. Ultrafiltration/reverse osmosis has the advantages of excellent desalination rate, high effluent quality and small footprint. Therefore, it has become a trend to develop a new type of new wastewater resource utilization technology with ultrafiltration/reverse osmosis as the core.

The choice of pre-membrane pretreatment technology in the process of wastewater recycling is directly related to "how to maximize the removal efficiency of membrane units and reduce membrane pollution most effectively". Among many pretreatment measures before membranes, oxidation, as a common and efficient water quality pretreatment technology, can decompose and transform pollutants in water, change the properties of organic matter in influent water, and thus change its mechanism of action in the membrane filtration process. Among them, the oxidation method with UV as the core has received extensive attention as an emerging green and safe pre-oxidation technology. A large number of studies have proved that UV catalytic oxidation can effectively remove pollutants from influent water and slow down membrane fouling.

The existing ultrafiltration/reverse osmosis treatment technologies in the recycling and treatment of wastewater all have the problem of membrane fouling.

CN1807268 discloses a double-membrane water treatment system and water treatment method, comprising a pretreatment unit and a desalination unit, a pressure liquid storage tank is arranged after the pretreatment unit and before the desalination unit, and the pretreatment unit provides liquid feed to the pressure liquid storage tank , the pressure liquid storage tank provides feed liquid to the desalination unit, and the pressure liquid storage tank also provides backflush liquid to the pretreatment unit. The method utilizes the storage pressure of the pressure liquid storage tank and the pressure difference generated by the pressure drop caused by the opening of the blowdown valve in the pretreatment device of the closed liquid inlet valve branch to implement instantaneous pulsating backwashing. CN102942265A discloses an integrated device for all-membrane water treatment, wherein a raw water pump, an ultrafiltration security filter, an ultrafiltration membrane assembly composed of an ultrafiltration device, an ultrafiltration water tank, a primary reverse osmosis high-pressure pump, and a reverse osmosis membrane are sequentially connected through pipelines Module, secondary reverse osmosis high pressure pump, secondary reverse osmosis membrane module, fresh water tank, EDI feed pump, EDI device to demineralized water effluent; there is an ultrafiltration backwash pump connected to the ultrafiltration membrane module for backwashing, and an acid dosing device , the alkali dosing device and the bactericide device are all connected to the ultrafiltration device.

The above-mentioned method focuses on the backwashing of the ultrafiltration device and the reverse osmosis membrane module, and cannot effectively solve the problem of membrane fouling.

SUMMARY OF THE INVENTION

Aiming at the problem of membrane pollution existing in the ultrafiltration and reverse osmosis treatment technologies in the existing sewage resource utilization and treatment, the invention provides a sewage treatment method through ultraviolet, sodium hypochlorite, activated carbon composite pretreatment combined with ultrafiltration and reverse osmosis, and simultaneously A system for implementing the method is provided.

The composite pretreatment combined ultrafiltration and reverse osmosis sewage treatment method of the present invention comprises the following steps:

(1) The raw water of sewage to be treated is mixed with sodium hypochlorite, and pretreatment is carried out for the first time;

The uniform mixing of sodium hypochlorite and raw water facilitates the removal of pollutants in raw water through advanced oxidation by ultraviolet light catalyzed sodium hypochlorite in the subsequent photochemical reaction pool.

(2) irradiating the raw water of the first pretreatment with ultraviolet light to carry out the second pretreatment;

The ultraviolet light irradiates the raw water evenly, fully catalyzes the sodium hypochlorite to produce active species with high oxidative ability, and oxidizes and decomposes the macromolecular pollutants in the raw water into small molecules.

(3) The raw water of the second pretreatment is added to the powdered activated carbon mixed solution, mixed and stirred, and the third pretreatment is carried out;

Powdered carbon can fully remove small molecule pollutants in raw water by adsorption.

(4) The raw water of the three pretreatments is pressurized into the ultrafiltration membrane for filtration;

(5) The raw water filtered by the ultrafiltration membrane is subjected to reverse osmosis filtration.

In the step (1), the dosage of sodium hypochlorite in the raw water is 20-70 mg/L.

In the step (2), the ultraviolet radiation intensity is 4.21 mW/cm ² , and the ultraviolet dose is 450 mJ/cm ² .

In the step (3), the concentration of activated carbon in the powdered activated carbon mixed solution is 0.5-2 g/L.

The stirring speed in the step (3) is 40-80 r/min.

In the step (4), the membrane pore size of the ultrafiltration membrane module is 0.01-0.1 μm, and the membrane flux is 40-80 L/m ² h.

In the step (4), the inlet pressure of the ultrafiltration membrane filtration is 20-100KPa.

The filtration of the ultrafiltration membrane in the step (4) runs for 0.5 to 1 hour.

The membrane flux of the reverse osmosis in the step (5) is 15-25 L/m ² h.

To realize the above-mentioned composite pretreatment combined ultrafiltration and reverse osmosis sewage treatment system, the following technical solutions are adopted:

The system includes an inlet pump, a sodium hypochlorite dosing tank, a sodium hypochlorite coagulator, a photochemical reaction pool, an activated carbon dosing pool, an activated carbon adsorption reaction pool, an ultrafiltration membrane module and a reverse osmosis membrane module; an inlet pump, a sodium hypochlorite coagulator, a photochemical The reaction pool, the activated carbon adsorption reaction pool, the ultrafiltration membrane module and the reverse osmosis membrane module are connected by pipelines in turn; the sodium hypochlorite dosing pool is connected with the connecting pipeline between the inlet pump and the sodium hypochlorite coagulator, and the activated carbon dosing pool is connected with the photochemical reaction pool and The connecting pipes between the activated carbon adsorption reaction tanks are connected; the photochemical reaction tank is provided with an ultraviolet lamp; a pressurized pump is provided between the activated carbon adsorption reaction tank and the ultrafiltration membrane module, and a high pressure pump is arranged between the ultrafiltration membrane module and the reverse osmosis membrane module .

A stirring device is provided in the activated carbon dosing pool and the activated carbon adsorption reaction pool; the bottom mud discharge port of the activated carbon adsorption reaction pool is provided with an adsorption pool mud discharge valve.

The irradiation intensity of the ultraviolet lamp is 4.21 mW/cm ² so as to be able to obtain ultraviolet light of 254 nm.

The ultrafiltration membrane module is a hollow fiber membrane module. The ultrafiltration membrane assembly is made of polyethersulfone. The membrane pore size of the ultrafiltration membrane module is 0.01-0.1 μm, and the membrane flux is 40-80 L/m ² h.

The raw water of the sewage is transported into the sodium hypochlorite coagulator through the inlet pump, and at the same time, the sodium hypochlorite in the sodium hypochlorite dosing tank is added to the sodium hypochlorite coagulator, and the raw water and the sodium hypochlorite are evenly mixed for the first pretreatment; the first pretreated raw water enters the photochemical The reaction tank is irradiated by the ultraviolet light of the ultraviolet lamp for the second pretreatment; then it enters the activated carbon adsorption reaction tank, and the powdered activated carbon mixture is injected into the activated carbon dosing tank for the third pretreatment; the raw water after the third pretreatment is added The pressure pump enters the ultrafiltration membrane module for filtration, and then enters the reverse osmosis membrane module for filtration.

The method of the invention combines the oxidative adsorption pretreatment with the ultrafiltration/reverse osmosis process to form a set of short-flow sewage recycling and utilization process. It occupies a small area and the quality of the effluent is stable. The turbidity, chloride and sulfate of the effluent after passing through the reverse osmosis membrane can meet the requirements of "Urban Sewage Regeneration and Application of Urban Miscellaneous Water Quality GB/T 18920-2020".

In the present invention, ultraviolet light and sodium hypochlorite play an advanced oxidation role, which is then adsorbed by an adsorbent. Under the irradiation condition of ultraviolet light, sodium hypochlorite can be better catalyzed to generate active species with higher oxidizing ability, thereby effectively removing conventional processes. Refractory organics with poor treatment effect. The activated carbon adsorption reaction tank is then connected, which shortens the hydraulic retention time and saves the space of the activated carbon adsorption reaction tank, thereby reducing the capital construction cost in engineering applications and strengthening the removal effect of pollutants. The removal rate of dissolved organic carbon can reach 40%, and the removal rate of macromolecular (>100kDa) and small molecule (<1kDa) organic matter can reach 90% and 40%, respectively.

In the present invention, ultrafiltration and reverse osmosis are used as the core units of the combined process, which can further intercept and remove microorganisms such as organic pollutants and bacteria in the raw water, thereby better ensuring the biological safety of the regenerated water. At the same time, the ultraviolet lamp in the photochemical reaction tank can inactivate some microorganisms while cooperating with sodium hypochlorite to remove pollutants, which improves the guarantee ability of water quality safety.

The invention makes full use of the combination of sodium hypochlorite, ultraviolet light and activated carbon as the pretreatment of ultrafiltration and reverse osmosis membranes, which effectively alleviates membrane pollution caused by organic pollutants, and the irradiation of ultraviolet lamps and activated carbon adsorption can reduce the introduction of oxidants In ultrafiltration and reverse osmosis membrane modules, this reduces the risk of aging damage to the membrane modules, saves the cost of membrane materials, and saves the cost of dosing chemicals.

The process of the invention is simple in operation, convenient in management, high in automation and small in floor space, suitable for engineering promotion, and can be used as a construction and renovation plan for a reclaimed water plant or a small rural water plant.

Description of drawings

FIG. 1 is a schematic diagram of the structure and principle of the sewage treatment system of the present invention with composite pretreatment combined with ultrafiltration and reverse osmosis.

In the picture: 1. Inlet water pump, 2. Sodium hypochlorite dosing pool, 3. Sodium hypochlorite coagulator, 4. Photochemical reaction pool, 5. Ultraviolet lamp, 6. Activated carbon dosing pool, 7. Activated carbon adsorption reaction pool, 8. Addition Pressure pump, 9. Ultrafiltration membrane module, 10. High pressure pump, 11. Reverse osmosis membrane module, 12. Sewage valve, 13. Sludge valve.

Detailed ways

The technical solutions of the present invention are not limited to the specific embodiments listed below, but also include any combination of specific embodiments. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

As shown in Figure 1, the sewage treatment system of this embodiment includes an inlet pump 1, a sodium hypochlorite dosing pool 2, a sodium hypochlorite coagulator 3, a photochemical reaction pool 4, an activated carbon dosing pool 6, an activated carbon adsorption reaction pool 7, and a pressurized pump 8. Ultrafiltration membrane module 9, high pressure pump 10 and reverse osmosis membrane module 11. The inlet water pump 1, the sodium hypochlorite coagulator 3, the photochemical reaction tank 4, the activated carbon adsorption reaction tank 7, the pressurizing pump 8, the ultrafiltration membrane module 9, the high pressure pump 10 and the reverse osmosis membrane module 11 are sequentially connected by pipelines. The sodium hypochlorite dosing tank 2 is arranged between the inlet water pump 1 and the sodium hypochlorite coagulator 3 . The activated carbon dosing pool 6 is arranged between the photochemical reaction pool 4 and the activated carbon adsorption reaction pool 7 .

The inlet pump 1 is communicated with the water inlet of the sodium hypochlorite condenser 3 through a pipeline. The sodium hypochlorite dosing pool 2 is communicated with the connecting pipeline between the inlet pump 1 and the sodium hypochlorite condenser 3 . The water outlet of the sodium hypochlorite coagulator 3 is connected with the water inlet of the photochemical reaction tank 4 through a pipeline, and the water outlet of the photochemical reaction tank 4 is connected with the middle water inlet of the activated carbon adsorption reaction tank 7 through a pipeline. The activated carbon dosing pool 6 communicates with the pipeline between the photochemical reaction pool 4 and the activated carbon adsorption reaction pool 7 . The middle water outlet of the activated carbon adsorption reaction tank 7 is communicated with the water inlet of the ultrafiltration membrane module 9 through the pressurizing pump 8 . The water outlet of the ultrafiltration membrane module 9 is communicated with the water inlet of the reverse osmosis membrane module 11 through the high pressure pump 10 .

The sodium hypochlorite dosing pool 2 is filled with sodium hypochlorite.

The sodium hypochlorite coagulator 3 is used for mixing raw water and sodium hypochlorite for pretreatment.

An ultraviolet lamp 5 is arranged inside the photochemical reaction tank 4 , and a sewage valve 12 is arranged at the sludge discharge port at the bottom of the photochemical reaction tank 4 . The ultraviolet lamp 5 is vertically arranged inside the photochemical reaction cell 4 . The ultraviolet lamp 5 is a low-pressure mercury lamp with an intensity of 4.21 mW/cm ² . A low-pressure mercury lamp with an intensity of 4.21 mW/cm ² can obtain ultraviolet light at 254 nm. The ultraviolet lamp 5 is immersed below the liquid surface.

A stirring device is arranged in the activated carbon dosing pool 6, and a powdered activated carbon mixture is prepared in the activated carbon dosing pool 6, which is formed by stirring the powdered activated carbon and water. The concentration of the activated carbon in the powdered activated carbon mixture is 0.5-2 g/L. Powdered activated carbon has a larger specific surface area than other forms of activated carbon such as granular activated carbon, and has a stronger adsorption and removal ability for small molecular pollutants.

The activated carbon adsorption pool 7 is provided with a stirring device, a mud discharge port is provided at the bottom, and a mud discharge valve 13 is connected to the mud discharge port.

The ultrafiltration membrane module 9 is a hollow fiber membrane module made of polyethersulfone, the membrane pore size is 0.01-0.1 μm, and the membrane flux is 40-80 L/m ² h. Reasonable choice of flux can avoid excessive membrane fouling (too high) or waste of membrane modules (too low). The water inlet pressure of the ultrafiltration membrane module 9 is 20-100KPa. Such inlet water pressure can ensure the stable water outlet of the membrane module and make the membrane fouling within a controllable range.

The reverse osmosis membrane module 11 is in the prior art, using a roll membrane, and the membrane material is polyamide, polysulfone or polyester.

The operation process of the above system is as follows.

1. The first preprocessing

The raw water of the sewage to be treated is transported into the sodium hypochlorite coagulator 3 through the inlet pump 1, and at the same time, the sodium hypochlorite in the sodium hypochlorite dosing pool 2 is added into the sodium hypochlorite coagulator 3, and the dosage of the sodium hypochlorite in the raw water is 20-70mg/L. Raw water is mixed with sodium hypochlorite for uniform coagulation pretreatment.

2. Second preprocessing

The raw water pretreated by sodium hypochlorite for the first time enters the photochemical reaction tank 4 . The ultraviolet lamp 5 in the photochemical reaction tank 4 is turned on, the ultraviolet lamp 5 is immersed below the liquid level, and the raw water pretreated by sodium hypochlorite in the photochemical reaction tank 4 is subjected to ultraviolet light irradiation, and the gear position of the ultraviolet lamp 5 is adjusted to make the ultraviolet irradiation intensity. is 4.21 mW/cm ² , and the UV dose is 450 mJ/cm ² .

3. The third preprocessing

The raw water pretreated for the second time enters the activated carbon adsorption reaction tank 7 . The powdered activated carbon mixture in the activated carbon dosing pool 6 is injected into the activated carbon adsorption reaction pool 7 . The stirring device in the activated carbon adsorption reaction tank 7 is turned on, and the raw water pretreated by sodium hypochlorite and ultraviolet light is mixed and stirred with the activated carbon, and the stirring speed is 40-80 r/min.

At this time, the raw water has undergone multiple pretreatments with sodium hypochlorite, ultraviolet light and activated carbon.

4. Ultrafiltration membrane filtration

The raw water pretreated by sodium hypochlorite, ultraviolet light and activated carbon enters the ultrafiltration membrane module 9 for filtration through the pressurized pump 8, and the membrane flux is controlled at 40-80L/m ² h, and the inlet water pressure is 20-100KPa.

After the ultrafiltration membrane module 9 is filtered and operated for 0.5 to 1 hour, backwashing is performed, and the backwashing wastewater is discharged through the drainage outlet at the bottom of the ultrafiltration membrane module 9 .

5. Reverse osmosis membrane filtration

The raw water filtered by the ultrafiltration membrane module 9 enters the reverse osmosis membrane module 11 through the high pressure pump 10 for filtration, and the flux of the reverse osmosis membrane is controlled at 15-25 L/m ² h.

The treated raw water is discharged from the reverse osmosis membrane module 11 to complete one operation cycle.

6. Refill the activated carbon adsorption reaction tank 7 with the reacted raw water formed in step 2 to prepare for the next operation cycle.

The bottom sludge in the photochemical reaction tank 4 can be discharged by the blowdown valve 12 . The bottom sludge in the activated carbon adsorption reaction tank 7 can be discharged by the sludge discharge valve 13 .

Specific examples are given below.

Taking the actual municipal sewage treatment plant effluent as the target water body, the relevant parameters are as follows:

The dosage of sodium hypochlorite in raw water is 45mg/L.

The irradiation intensity of the UV lamp 5 is 4.21 mW/cm ² ; the UV dose is 450 mJ/cm ² .

The concentration of activated carbon in the powdered activated carbon mixture was 1.2 g/L.

The stirring speed in the activated carbon adsorption reaction tank 7 was 60 r/min.

The membrane pore size of the ultrafiltration membrane module 9 is 0.06 μm, and the membrane flux is 60 L/m ² h;

The water inlet pressure of the ultrafiltration membrane module 9 is 60KPa; the filtration operation time of the ultrafiltration membrane module 9 is 0.7 hours;

The controlled reverse osmosis membrane flux of the reverse osmosis membrane module 11 is 20 L/m ² h.

process result:

The membrane fouling caused by the effluent of the sewage treatment plant is significantly alleviated, the stable operation time of the membrane is increased, and the decline rate of the membrane flux is delayed. Reached 90%, the removal rate of small molecules (<1kDa) organics reached 40%, and the removal rate of hydrophilic organics reached 40%.

In this example, UV/sodium hypochlorite/powder carbon pretreatment can decompose macromolecular organic matter into small molecular organic matter by oxidation, and remove small molecular organic matter by adsorption. In the range of >100kDa and <1kDa, the DOC removal rate is 96.02% And 45.14%; the removal rate of hydrophilic components is 45.2%, which is better than UV, sodium hypochlorite pretreatment and powder carbon pretreatment, effectively reducing the pollution load of organic matter in raw water to membrane units.

In addition, sodium hypochlorite/UV/powder carbon pretreatment has a mitigating effect on membrane fouling. When the raw water directly enters the membrane unit without pretreatment, the fouling resistance of the ultrafiltration membrane rises rapidly. The fouling of the ultrafiltration membrane is mainly reversible fouling, accounting for 69.84% of the total fouling membrane resistance, and the specific flux of the ultrafiltration membrane decreases rapidly. After adding UV/sodium hypochlorite pretreatment, the specific flux of ultrafiltration membrane filtration slows down, and the specific flux of ultrafiltration membrane can be increased by 10% compared with the direct filtration of raw water; at the same time, the accumulation of pollutants on the ultrafiltration membrane surface is reduced, and the pollution layer changes. The total fouling membrane resistance, reversible fouling membrane resistance and irreversible fouling membrane resistance were reduced by 50.40%, 69.31% and 6.58% respectively compared with the untreated raw water; but the reverse osmosis membrane water production rate and membrane surface fouling The accumulation did not change significantly.

After adding UV/sodium hypochlorite/powder carbon pretreatment, the fouling resistance of the ultrafiltration membrane was significantly reduced, the fouling layer on the ultrafiltration membrane surface became loose, and the total fouling membrane resistance, reversible fouling membrane resistance and irreversible membrane resistance were respectively lower than those of the untreated raw water. 65.48%, 88.64% and 18.20%; the decline rate of reverse osmosis membrane water production rate was effectively slowed down, and the effect was better than UV/sodium hypochlorite pretreatment or powder carbon pretreatment.

Claims (10)

1. a sewage treatment method of composite pretreatment combined ultrafiltration and reverse osmosis, is characterized in that, may further comprise the steps: (1) The raw water of sewage to be treated is mixed with sodium hypochlorite, and pretreatment is carried out for the first time; (2) irradiating the raw water of the first pretreatment with ultraviolet light to carry out the second pretreatment; (3) The raw water of the second pretreatment is added to the powdered activated carbon mixed solution, mixed and stirred, and the third pretreatment is carried out; (4) The raw water of the three pretreatments is pressurized into the ultrafiltration membrane for filtration; (5) The raw water filtered by the ultrafiltration membrane is subjected to reverse osmosis filtration. 2. The sewage treatment method of composite pretreatment combined with ultrafiltration and reverse osmosis according to claim 1, is characterized in that: in the described step (1), the dosage of sodium hypochlorite in raw water is 20-70mg/L. 3. the sewage treatment method of composite pretreatment combined with ultrafiltration and reverse osmosis according to claim 1, is characterized in that: in described step (2), ultraviolet light irradiation intensity is 4.21mW/cm ² ; UV dose is 450mJ/ cm ² . 4. The sewage treatment method of composite pretreatment combined with ultrafiltration and reverse osmosis according to claim 1, characterized in that: in the step (3), the concentration of activated carbon in the powdered activated carbon mixed solution is 0.5-2 g/L. 5. The sewage treatment method of composite pretreatment combined with ultrafiltration and reverse osmosis according to claim 1, wherein the stirring speed in the step (3) is 40-80 r/min. 6. The sewage treatment method of composite pretreatment combined with ultrafiltration and reverse osmosis according to claim 1, characterized in that: in the step (4), the membrane aperture of the ultrafiltration membrane module is 0.01-0.1 μm, and the ultrafiltration membrane The membrane flux is 40～80L/m ² h. 7. The sewage treatment method of composite pretreatment combined with ultrafiltration and reverse osmosis according to claim 1, characterized in that: in the step (4), the water inlet pressure filtered by the ultrafiltration membrane is 20-100KPa. 8 . The sewage treatment method of composite pretreatment combined with ultrafiltration and reverse osmosis according to claim 1 , wherein the operation of ultrafiltration membrane filtration in the step (4) is 0.5 to 1 hour. 9 . 9 . The wastewater treatment method of composite pretreatment combined with ultrafiltration and reverse osmosis according to claim 1 , wherein the membrane flux of the reverse osmosis in the step (5) is 15-25 L/m ² h. 10 . 10. A sewage treatment system of composite pretreatment combined with ultrafiltration and reverse osmosis, characterized in that it comprises an inlet pump, a sodium hypochlorite dosing pool, a sodium hypochlorite coagulator, a photochemical reaction pool, an activated carbon dosing pool, an activated carbon adsorption reaction pool, a The filter membrane module and the reverse osmosis membrane module; the inlet water pump, the sodium hypochlorite coagulator, the photochemical reaction tank, the activated carbon adsorption reaction tank, the ultrafiltration membrane module and the reverse osmosis membrane module are connected by pipelines in turn; the sodium hypochlorite dosing tank is mixed with the inlet water pump and sodium hypochlorite. The connecting pipes between the condensers are connected, and the activated carbon dosing tank is connected with the connecting pipes between the photochemical reaction tank and the activated carbon adsorption reaction tank; the photochemical reaction tank is provided with an ultraviolet lamp; the activated carbon adsorption reaction tank and the ultrafiltration membrane component are provided with a heater. A high-pressure pump is arranged between the ultrafiltration membrane module and the reverse osmosis membrane module.

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