JP2000079328A - Cleaning method for reverse osmosis membrane module - Google Patents

Abstract

(57) [Problem] To provide a method for efficiently cleaning a film at low cost. In a reverse osmosis membrane module for separating a solute and a solvent in a solution by supplying a solution to a reverse osmosis membrane under a pressure higher than the osmotic pressure, when the membrane is washed, no pressure is applied to less than the osmotic pressure. A method for cleaning a reverse osmosis membrane module, comprising continuously supplying a solution to the membrane module within the pressure range described above, adding a cleaning agent to the permeate, and removing contaminants on the membrane surface using a suck-back phenomenon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for cleaning a reverse osmosis membrane module. More specifically, the present invention belongs to a method of cleaning a reverse osmosis membrane module in which contaminants are deposited and deposited on the membrane surface in order to recover the separation performance of the membrane and / or reduce the pressure loss.

[0002]

2. Description of the Related Art Ultrafiltration membranes (UF membranes) and reverse osmosis membranes (RO membranes)
A liquid separation membrane module equipped with a reverse osmosis membrane such as a membrane) as a separation means is advantageous in energy because it does not require heat energy and, unlike the distillation method, does not involve a phase change, so that operation management is easy. It is used in various industrial fields as a separation method.

According to the reverse osmosis method, demineralized water can be produced by applying a pressure higher than the osmotic pressure to water containing salt, such as seawater or irrigation water, to permeate the reverse osmosis membrane module. Therefore, reverse osmosis is used to desalinate seawater or low-concentration saline water to provide industrial, agricultural, or domestic water. It is also used for the production of industrial ultrapure water.

When the liquid separation operation is performed over a long period of time using a membrane module, or when the liquid quality of the stock solution supplied to the membrane is poor, various organic substances, inorganic colloids, scale components, etc. are formed on the membrane surface on the supply side. Inorganic substances (hereinafter referred to as "contaminants") may be deposited and deposited to lower the separation performance of the membrane, increase the pressure loss, and ultimately damage the membrane module.

Therefore, it is necessary to clean a film contaminated with contaminants. Conventionally, as a cleaning method, a chemical method of flowing a specific cleaning agent from the supply side of a membrane to dissolve and remove contaminants from the membrane surface (Japanese Patent Application Laid-Open No. 61-11108), Physical methods are known for pushing water or air under pressure toward the feed side to release contaminants from the membrane.

[0006]

However, in the above-mentioned chemical method, although the cleaning agent flows on the surface of the contaminant layer deposited on the film surface, the cleaning agent sufficiently flows to the interface between the film surface and the contaminant layer. In some cases, the separation performance of the membrane could not be sufficiently recovered due to the infiltration of water. Further, the physical method requires installation of a device for press-fitting the cleaning fluid, which requires a great deal of cost. Therefore, an object of the present invention is to provide a method for efficiently and efficiently cleaning a membrane at low cost.

[0007]

In order to achieve the object, a cleaning method according to the present invention separates a solute and a solvent in a solution by supplying the solution to a reverse osmosis membrane under a pressure higher than the osmotic pressure. The reverse osmosis membrane module is characterized in that when washing the membrane, the solution is continuously supplied in the pressure range from no pressure to less than the osmotic pressure, and the detergent is added to the permeate to remove contaminants on the membrane surface. And

When the pressure of the solution supplied to the reverse osmosis membrane is lower than the osmotic pressure, a suck-back phenomenon occurs due to the osmotic pressure, and the solvent flows backward from the permeation side of the membrane to the supply side. In the present invention, since the cleaning agent is added to the permeate at this time, the solvent containing the cleaning agent permeates the membrane toward the supply side and penetrates into the interface between the membrane surface and the contaminant layer. Therefore, the contaminants are quickly separated and removed. Moreover, as long as the solution having a pressure lower than the osmotic pressure is continuously supplied to the supply side, the suck-back phenomenon does not stop. Further, the contaminants are more quickly separated and removed by the water flow from the undiluted solution side. By stopping the supply of the solution, after a while, the concentrations on the supply side and the permeate side of the membrane become the same, the osmotic pressure difference disappears, and the washing operation can be stopped. Therefore, the cleaning time can be adjusted.

By adding a cleaning agent to a supply solution that continuously causes a suck-back phenomenon, the cleaning agent reacts from both the surface side and the film surface side of the contaminant layer deposited on the film surface, resulting in a cleaning effect. Can be increased.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the cleaning method of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram illustrating a reverse osmosis membrane separation device that realizes the cleaning method of the embodiment.

In this reverse osmosis membrane separation apparatus, a stock solution to be processed is always supplied from a stock solution supply line 1, pH is adjusted and scale is removed by a pretreatment unit 2, and then temporarily stored in a stock solution tank 12. . Then, the undiluted solution is sent to the reverse osmosis membrane module 4 by the pressure pump 3, where the separation operation is performed, and the permeate is stored in the permeate tank 10 via the permeation line 6, while the concentrated solution is stored in the condensate line 5.
Is discharged through.

During this time, the stock solution tank valve 11 and the permeate solution tank valve 9 are open, and the stock solution input liquid valve 16, the permeate solution drain valve 13 and the detergent tank valve 7 are closed.
The stock solution input liquid valve 16 is provided in a line branched from the stock solution supply line 1 between the stock solution tank valve 11 and the pressure pump 3. Further, on the extension thereof, one branch is further branched, one is a clean water tank 15 via a clean water tank valve 14, and the other is a detergent second tank 17 via a detergent second tank valve 18.
And each is connected. During the separation operation, the valves for these tanks are also closed. In the valve in the figure, the white outline is open,
The fill indicates closure. The same applies to FIGS. 2 and 3 below.

When cleaning is started, the drive of the pump 3 is lowered to adjust the pressure of the stock solution supplied to the membrane module from a pressure lower than the osmotic pressure of the stock solution to a non-pressurized range, and as shown in FIG. With the liquid side drain valve 13 closed, the permeated liquid tank valve 9 is closed. Then, the cleaning agent second tank valve 1
8. Open the stock solution input liquid valve 16 and the cleaning agent tank valve 7.
Then, the cleaning agent from the cleaning agent second tank 17 flows into the supply line 1 and the cleaning agent from the cleaning agent tank 8 flows into the permeation line 6, and mixes with the undiluted solution and the permeate, respectively.

Then, the permeated liquid containing the cleaning agent flows backward to the supply side of the reverse osmosis membrane module 4 due to the suck-back phenomenon, and penetrates into the interface between the contaminants attached to the membrane surface and the membrane surface,
Contaminants are released from the membrane surface. During this time, a solution (stock solution) having a higher osmotic pressure than the permeate is continuously supplied,
The suck-back phenomenon occurs continuously, and the washing operation can be continued. In addition, since the detergent flows into the undiluted liquid from the detergent second tank valve 18, the surface of the contaminant is hit with a water stream containing the detergent, whereby the contaminant is quickly removed. The cleaning agent may be the same as or different from the cleaning agent used on the permeate side, and is appropriately selected depending on the properties of the contaminants. Similarly, the concentration is appropriately selected. The removed contaminants are discharged through the concentration line S.

Next, the driving of the pump 3 is stopped to stop the supply of the stock solution. After a while, the osmotic pressure difference on both sides of the membrane disappears and the backflow ends. Thereafter, the cleaning agent second tank valve 18 and the cleaning agent tank valve 7 are closed. Then, the clean water tank valve 14 is opened as shown in FIG.
1, and at the same time, the permeated liquid side drain valve 13 is opened. When the operation of the pump 3 is restarted, the supply-side liquid in which the contaminants are suspended is discharged through the concentration line 5 by the clean water supplied from the clean water tank 15 without pressurization, and the membrane surface is cleaned water. Rinse. Further, the permeated liquid containing the cleaning agent remaining in the permeation line 6 is discharged from the permeated liquid side drain valve 13. By stopping the driving of the pump 3, the rinsing process is completed.

Thus, the cleaning operation is completed. Subsequently, when performing the liquid separation operation, as shown in FIG. 1, the clean water tank valve 14, the stock solution input liquid valve 16 and the permeate liquid drain valve 1
At the same time as closing 3, the stock tank valve 11 and the permeate tank valve 9 are opened, and the pump 3 is driven.

When the contaminants on the film surface are inorganic substances such as metals, metal oxides, calcium carbonate and other salts, the cleaning agent is preferably an acid having a pH of 1 to 6. For example, hydrochloric acid,
It is an inorganic acid such as nitric acid or sulfuric acid, or an organic acid such as oxalic acid, citric acid or phosphoric acid. When the pH of the cleaning agent exceeds 6, it is difficult to impregnate the contaminants composed of inorganic substances, and the cleaning effect is reduced. A particularly preferred pH range is 2-5.

When the solute is an organic substance such as a microorganism or an oil, or a silica scale, the pH of the detergent is pH =
8-12 alkalis are preferred. For example, hydroxide of alkali metal (Li, Na, K) and ammonia. If the pH of the detergent is less than 8, it is difficult to impregnate microorganisms, organic substances such as oils, or contaminants composed of silica scale,
The cleaning action is reduced. A particularly preferred pH range is 9-11.
It is.

When the contaminant is an organic substance such as oil, a surfactant having a concentration of 1 to 10000 ppm is preferable as the cleaning agent. For example, an anionic surfactant such as sodium alkylbenzene sulfonate. When the concentration of the surfactant exceeds 10,000 ppm, the surfactant may deteriorate the performance of the permeable membrane. A particularly preferred concentration range is 1 to 5000 ppm.

When the contaminant is a microorganism or an organic substance, a reducing agent having a concentration of 1 to 10000 ppm is preferable as the cleaning agent. For example, hydrazine and hydrazine hydrate. If the concentration of the reducing agent exceeds 10,000 ppm, the reducing agent may reduce the performance of the permeable membrane. A particularly preferred concentration range is 1 to 5000 ppm.

When the contaminant is a microorganism or an organic substance, an oxidizing agent having a concentration of 1 to 10000 ppm is also preferable as the cleaning agent. For example, hydrogen peroxide, peroxide, hypochlorite, and iodine. Oxidant concentration is 10,000ppm
If it exceeds, the oxidizing agent may degrade the performance of the permeable membrane. A particularly preferred concentration range is 1 to 5000 ppm.

When the contaminant is, for example, both an inorganic substance and an organic substance, washing is performed in a plurality of times, for example, washing with an alkali, and then washing with an acid. It may be washed first with an acid and then with an alkali. The osmotic pressure of the solution supplied during the separation operation is 1 k higher than the osmotic pressure of the permeate.
It is preferably higher than gf / cm ² . Osmotic pressure difference is 1kg
If it is less than f / cm ² , the occurrence of the suck-back phenomenon is insufficient. Therefore, the osmotic pressure of the supplied solution is 1
kgf / cm ² or more is required.

[0023]

EXAMPLE In the reverse osmosis membrane separation apparatus shown in FIG. 1, a spiral type reverse osmosis membrane module (Nitto Denko Corporation aromatic polyamide composite membrane NTR-70) was used as the reverse osmosis membrane module 4.
Using SWC-S8), a 3.5% aqueous solution of NaCl having a pH of 6.8 is supplied as a stock solution under the conditions of a supply pressure of 56 kgf / cm ² and a flow rate of the concentrated water of 80 L / min. Was performed. Then, the initial pressure loss (ΔP) on the stock solution supply side was 0.18 kgf / cm ² , but increased to 0.60 kgf / cm ² as a result of the reverse osmosis membrane being contaminated by organic substances such as slime.

Again, while maintaining ΔP = 0.60 kgf / cm ² , the reverse osmosis membrane module 4 is supplied with 3.5% N at pH = 6.8.
Using an aCl aqueous solution (osmotic pressure: 35 kgf / cm ² ) as a stock solution, supply pressure 56 kgf / cm ² , and concentrated water flow rate 80 L /
min, and the operation was performed to separate the stock solution into concentrated water and permeate.

Next, the output of the pump 3 is reduced for cleaning the membrane, the pressure of the stock solution to be supplied is set to 1 kgf / cm ² lower than the osmotic pressure of the stock solution, and the valve is opened and closed as shown in FIG. An aqueous nitric acid solution having a pH of 2 from 8 was charged into the permeate, and was allowed to flow backward. At the same time, p
An aqueous solution of nitric acid with H = 2 was charged into the stock solution and applied to the contaminant layer on the membrane surface. After the start of the backflow, the stock solution was continuously supplied at the above pressure for 5 minutes. During the supply of the stock solution, the permeate continued to flow backward. Thereafter, the valve was opened and closed as shown in FIG. 3, pure water was introduced from the clean water tank 15, and contaminants on the membrane surface were discharged. As a result, the pressure loss of the reverse osmosis membrane module 4 is 0.20 kgf.
/ Cm ² .

For comparison, the membrane was washed under the same conditions as above except that the operation of the pump 3 was stopped immediately before the opening and closing of the valve was brought to the state shown in FIG. As a result, the pressure loss of the reverse osmosis membrane module 4 was reduced only to 0.25 kgf / cm ² . Similarly, for comparison, except that the operation of the pump 3 was stopped immediately before the opening and closing of the valve in the state shown in FIG. The membrane was washed under the same conditions. As a result, the pressure loss did not change ^remains 0.60kgf / cm2.

[0027]

According to the present invention, unlike the ordinary physical cleaning method, the cleaning agent is caused to flow backward by utilizing the suck-back phenomenon, so that a separate device or power source for flowing the cleaning agent is not required, and the cost is not so high. Further, unlike the ordinary chemical cleaning method, the cleaning agent can be made to penetrate into the interface between the contaminant layer and the film surface, so that the film performance can be almost completely restored.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a liquid separation step of a reverse osmosis membrane separation device that realizes a cleaning method according to an embodiment.

FIG. 2 is a configuration diagram showing a cleaning step of a reverse osmosis membrane separation device that realizes the cleaning method of the embodiment.

FIG. 3 is a configuration diagram showing a rinsing step of the reverse osmosis membrane separation device for realizing the cleaning method of the embodiment.

[Explanation of symbols]

 Reference Signs List 1 stock solution supply line 2 pretreatment unit 3 pressurizing pump 4 reverse osmosis membrane module 5 concentration line 6 permeation line 7 detergent tank valve 8 detergent tank 9 permeate tank valve 10 permeate tank 11 stock solution tank valve 12 stock solution tank 13 permeation Liquid side drain valve 14 Clean water tank valve 15 Clean water tank 16 Stock solution input liquid valve 17 Detergent second tank 18 Detergent second tank valve

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA03 HA61 KC04 KC16 KE06R KE22Q KE24Q KE28Q MA06 MC54X PA02 PB03 PB22 PB23 PB24

Claims (10)

[Claims] 1. A reverse osmosis membrane module for separating a solute and a solvent in a solution by supplying the solution to the reverse osmosis membrane under a pressure higher than the osmotic pressure. A method for cleaning a reverse osmosis membrane module, comprising continuously supplying a solution within a pressure range of less than 10% and adding a cleaning agent to a permeate to remove contaminants on the membrane surface. 2. The method according to claim 1, wherein the solution supplied when cleaning the membrane contains a cleaning agent. 3. The method of claim 1 wherein said contaminants are inorganic and said cleaning agent is an acid. 4. The method according to claim 1, wherein said contaminants are organic matter, microorganisms or silica scale, and said detergent is alkaline. 5. The method according to claim 1, wherein the contaminant is an organic substance, and the cleaning agent is a surfactant. 6. The contaminant is an organic substance or a microorganism,
The method according to claim 1, wherein the cleaning agent is a reducing agent. 7. The contaminant is an organic substance or a microorganism,
The method according to claim 1, wherein the cleaning agent is an oxidizing agent. 8. The osmotic pressure difference between the supplied solution and the permeate is 1 k.
The method according to claim 1, wherein the gf / cm ² or more. 9. The osmotic pressure of the solution to be supplied is 1 kgf / cm ²
The method of claim 1, wherein: 10. The method according to claim 1, wherein the solution to be supplied is seawater.