KR20100124408A - Method for cleaning the membrane filter - Google Patents

Abstract

PURPOSE: A method for cleaning a membrane filter is provided to shortly and effectively clean a bio-fouling contaminant by supercritical fluid. CONSTITUTION: A supercritical fluid providing unit(10) provides supercritical fluid to a cleaning chamber(37). The cleaning chamber of a membrane filter cleaning unit(30) receives the supercritical fluid. The cleaning chamber cleans a membrane filter contaminated by bio-fouling. A contaminant collecting chamber(49) receives a contaminant and the supercritical fluid. The contaminant collecting chamber receives the contaminant. The contaminant collecting chamber converts the supercritical fluid into a gas state.

Description

Method for cleaning the membrane filter

The present invention relates to a membrane filter cleaning method, and more particularly, to remove bio-fouling generated in a membrane filter applied to a filtration process and to sterilize microorganisms by using inherent properties and microbial sterilizing power possessed by a supercritical fluid. It relates to a membrane filter cleaning method.

There is an increasing demand for membrane filtration technology to purify contaminated water or to use seawater as fresh water. In particular, desalination of seawater is performed by a filtration process using a reverse osmosis membrane filter. The membrane filter used at this time causes a problem of contamination when used for a certain period of time. Contamination of reverse osmosis membrane filters is largely due to crystalline fouling formed by minerals, organic fouling by organic acids, etc., particles and colloidal fouling by insoluble particles such as clay, and There is microbiological fouling. Contamination of the membrane filter is not caused by any one type of contamination, but is formed by a combination of various types of contamination. In general, crystallization, organic, particle, and colloidal membrane contamination can be controlled to some degree through a high degree of pretreatment and control efficiency is high. On the other hand, contamination by microorganisms, that is, contamination of bio-fouling by biofilm formation, has been known to limit the effective removal according to previous studies. Here, bio-fouling, which is a contaminant, includes a form in which microorganisms are simply aggregated on the membrane surface, and is complex and tightly bound by extracellular secretions such as polysaccharides and proteins secondary to microbial secretion. A dimensional structure. Such bio-fouling is not only very resistant to chemical cleaners, but also very resistant to physical action. In addition, the extracellular secretion derived from the biofilm has a great effect on the permeation performance of the reverse osmosis membrane filter.

Therefore, in the filtration process using the membrane filter, the membrane filter is regenerated, and the required and commercially used membrane filter cleaning methods include chemical methods such as chlorine, ozone, hydrogen peroxide, peracetic acid, and complex compounds, and water pressure, air pressure, and steam. And physical methods such as ultrasound. However, the use of oxidants and mechanical methods is difficult to completely remove the bio-fouling as well as damage the surface of the membrane filter has a problem that there are many restrictions on the use. In addition, the use of chemical cleaners for the cleaning of the membrane filter secondaryly generates a large amount of contaminants to burden the environment and costly for the additional treatment of secondary contaminants.

Carbon dioxide above the critical temperature and pressure turns into supercritical fluid and has very different properties from gas and liquid carbon dioxide. It has fast diffusivity like gas and high dissolving power like liquid, so it is easy to penetrate into small particle structure and has high microbial sterilization power. In addition, supercritical carbon dioxide has been widely used as an environmentally friendly cleaning solvent for the removal of organic contaminants, and is also used for dry cleaning and semiconductor cleaning. Supercritical carbon dioxide cleaning technology can be reused through fluid recovery after cleaning and does not require additional secondary cleaning as it is not persistent.

In the conventional cleaning technology using supercritical carbon dioxide, the removal of organic pollutants dissolved in most supercritical carbon dioxide was the core of the technology, and the organic pollutants were used for the purpose of removing or recovering the organic pollutants from the contaminated surface. Recently, a technique for removing metal or inorganic material using supercritical carbon dioxide has been developed, in which case an appropriate surfactant or chelating compound is used. It is well known that supercritical carbon dioxide is very effective for the sterilization of food and medical equipment, and sterilization technology using such carbon dioxide has been developed.

However, the conventional technique for sterilizing microorganisms using supercritical carbon dioxide is mostly about sterilizing ability between planktonic cells and supercritical fluids, and cells that are secreted through quorum sensing mechanism by attaching microorganisms to the surface. Techniques for removing bio-fouling formed by extraneous substances (polysaccharides and proteins) are unknown.

It is an object of the present invention to provide a membrane filter cleaning method that is environmentally friendly and can effectively remove bio-fouling generated in a membrane filter without generating secondary pollutants and damaging the membrane filter.

The cleaning of the membrane filter according to an embodiment for achieving the above object of the present invention is by placing a membrane filter with bio-fouling generated in the cleaning chamber and then continuously flowing / passing the supercritical fluid in the cleaning chamber. Can be done. Accordingly, the bio-fouling and microorganisms generated on the surface of the membrane filter subjected to the cleaning process can be significantly reduced.

According to one embodiment, the cleaning method described above is complicated by extracellular secretory substances (polysaccharides and proteins), which include a form in which microorganisms are simply aggregated on the surface, and at which microorganisms are secreted through quorum sensing mechanisms. It can be performed to reduce and eliminate bio-fouling, a three-dimensional structure that is tightly coupled.

According to one embodiment, the supercritical fluid during the membrane filter cleaning may be continuously introduced into the cleaning chamber at a flow rate of 8 to 20 ml / min.

According to one embodiment, during the cleaning process, 1 to 3% by volume of water of the supercritical fluid is continuously introduced into the cleaning chamber while the supercritical fluid is introduced, thereby greatly improving the bio-fouling removal effect. have.

According to one embodiment, the bio-fouling removal may be performed at a pressure of 95 to 210 bar and a temperature of 31 to 40 ℃.

According to the cleaning method of the membrane filter of the present invention described above, bio-fouling contaminants that are difficult to clean without generating secondary pollutants compared to conventional chemical and physical cleaning methods can be cleaned and removed very effectively in a short time. . In addition, since the membrane filter uses a supercritical fluid, permeability is higher than gas and liquid states, and there is no toxicity and residual property, and thus, bio-fouling can be removed without damaging the membrane filter. Furthermore, the co-solvent water is provided together with the supercritical fluid in the cleaning of the bio-fouling to significantly improve the cleaning ability of the bio-fouling.

Hereinafter, a method for cleaning a membrane filter using a supercritical fluid according to preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

As the inventive concept allows for various changes and numerous modifications, the embodiments will be described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. Like reference numerals are used for like elements in describing each drawing. The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprise" or "consist of" are intended to indicate that there is a feature, number, step, operation, component, part, or combination thereof described on the specification, but one or more other features. It is to be understood that the present invention does not exclude the possibility of the presence or the addition of numbers, steps, operations, components, parts, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

Membrane filter cleaning device

1 is a block diagram showing a membrane filter cleaning device applied to remove the bio-fouling generated in the membrane filter according to an embodiment of the present invention.

Referring to FIG. 1, the membrane filter cleaning device 100 includes a supercritical fluid providing unit 10, a membrane filter cleaning unit 30, and a contaminant recovery unit 40. As an example, the cleaning apparatus may further include a co-solvent providing unit 20.

The supercritical fluid providing unit 10 includes a fluid storage tank 11, a cooler 12, and a first pump 13. The fluid storage tank 11 contains a fluid that can be converted into a supercritical fluid used in the cleaning process of the membrane filter. As an example, the fluid storage tank receives liquid carbon dioxide. The cooler 12 is connected to the fluid storage tank 11 and cools the fluid supplied from the fluid storage tank 11 to supercool. The first pump 13 is connected to the cooler 12 and converts the supercooled fluid passed through the cooler 12 into a fluid (liquid) in a high pressure state above the threshold pressure. In addition, the first pump 13 may perform a function of adjusting the pressure in the cleaning chamber 32 to have a pressure of about 95 to 210 bar. As an example, the supercritical fluid providing unit 10 may introduce the supercritical fluid into the cleaning chamber 37 at a flow rate of about 8 to 20 mg / min.

The membrane filter cleaner 30 includes a heater 36 and a cleaning chamber for heating the high pressure fluid. The heater 36 serves to maintain the high pressure fluid continuously provided into the cleaning chamber 37 above the critical temperature and pressure. That is, the internal temperature of the cleaning chamber in which the cleaning process of the membrane filter is performed may be maintained at about 31 to 40 ° C. The cleaning chamber 37 has a space for receiving the reverse osmosis membrane filter contaminated with bio-fouling, and receives the supercritical fluid to clean the membrane filter M contaminated with the bio-fouling. The constant temperature chamber 38 accommodates the cleaning chamber 37 and keeps the temperature of the cleaning chamber 37 constant at a temperature necessary for a supercritical state.

The cosolvent providing unit 20 is provided to further improve the cleaning efficiency of the membrane filter and has a configuration including a water tank 25 and a second pump 24. Specifically, the co-solvent provider 20 supplies the water of the water tank 25 to the cleaning chamber 37 through the second pump 24 together with the supercritical fluid while the supercritical fluid is supplied to the cleaning chamber 37. Allow inflow. The co-solvent providing unit 20 introduces 1 to 3% by volume of water of the supercritical carbon dioxide into the cleaning chamber 37 to allow the membrane filter to be cleaned more effectively.

The contaminant recovery unit 40 includes a discharge valve 48 provided in the discharge line and a contaminant recovery chamber 49 connected to the discharge line. The discharge valve 48 controls the supercritical fluid entering the contaminant recovery chamber and the amount of contaminant (bio-fouling) contained therein. The contaminant recovery chamber 49 receives the contaminant and the supercritical fluid to receive the contaminant in its inner space and converts the fluid into a gaseous state and discharges it to the outside.

Hereinafter, a method of cleaning a membrane filter according to an embodiment of the present invention will be described with reference to the cleaning device shown in FIG. 1.

In order to clean the membrane filter, first, the membrane filter M in which the bio-fouling is produced is placed in the high-pressure cleaning chamber 37. As an example, the membrane filter may include a reverse osmosis membrane filter. The bio-fouling includes a form in which microorganisms are simply aggregated on the surface, and at the same time, the microorganisms are complex and tightly bound by extracellular secretory substances (polysaccharides and proteins) secreted by quorum sensing mechanisms. As a three-dimensional structure, it has a very high resistance to chlorine, hydrogen peroxide or ozone and is difficult to remove by chemical and physical cleaning processes. In addition, bio-fouling is Pseudomonas Ke Rouge labor (Pseudomonas aeruginosa), Vibrio habe children (Vibrio harveyi), Agrobacterium Tome Pacific Enschede (Agrobacterium tumefaciens), gram, such as E. coli (Escherichia coli) bacteria and Candida albicans (Candidad albicans ), such as fungal biofilms may be further included.

Subsequently, after placing the membrane filter in which the bio-fouling is generated in the cleaning chamber 37, a high pressure or supercritical fluid is introduced into the cleaning chamber 37 through the supercritical fluid providing unit 10. The cleaning chamber 37 is maintained at a constant temperature by the thermostat 38 maintained above the critical temperature of the fluid to be supplied, and the incoming fluid has a supercritical state by having a temperature and pressure exceeding the critical temperature and the critical pressure. Can have Examples of the supercritical fluid include supercritical carbon dioxide, supercritical dinitrogen monoxide, or mixed fluids thereof.

As an example, in the case of using supercritical carbon dioxide as the supercritical fluid, the temperature and pressure of the cleaning chamber 37 exceed the critical temperature of carbon dioxide (T _C = 30.978 ° C.) and the critical pressure (P _C = 73.8 bar). By adjusting, the supercritical state can be maintained. For example, the cleaning chamber 37 may have a temperature of about 31 to 40 ° C. In addition, the pressure of the autoclave is preferably about 74 to about 500 bar, more preferably 95 to 200 bar in consideration of the efficiency of the cleaning process.

In another embodiment, the cleaning of the membrane filter may be provided with a supercritical fluid and a predetermined amount of water may be provided into the cleaning chamber 37 by the co-solvent providing unit 20. It is preferable that water is provided separately during the cleaning process because only the supercritical carbon dioxide is used, it is not easy to remove the bio-fouling having hydrophilic properties when cleaning the membrane filter. In this case, the co-solvent water may be provided with 1 to 3% by volume of the amount of supercritical carbon dioxide in the membrane filter cleaning. If the amount of water provided is less than 1% by volume or more than 3% by volume, bio-fouling may cause a problem in that the efficiency of washing is reduced. Therefore, the co-solvent water is preferably provided in the range of 1 to 3% by volume. Cosolvents are also available, as well as ethanol, which can enhance hydrophilicity.

As an example, the providing time of the supercritical fluid, which is provided to the membrane filter M to remove bio-fouling, may vary slightly depending on the temperature and pressure of the supercritical fluid. Time can achieve a cleaning effect that sufficiently removes bio-fouling, a contaminant produced in the membrane filter.

Subsequently, after contact with the membrane filter, a supercritical fluid including contaminants is introduced into the contaminant recovery chamber. In this case, the supercritical fluid introduced into the contaminant recovery chamber 49 may be vaporized and converted into a gaseous state and discharged to the outside, and the contaminants dissolved in the supercritical fluid may be accommodated in the recovery chamber due to the vaporization supercritical fluid. .

Hereinafter, the present invention will be described in more detail through experimental examples. However, the following experimental example is intended to illustrate the present invention, the present invention is not limited by the following experimental example may be variously modified and changed.

Evaluation of the effect of the cleaning process on the membrane filter 1

The membrane filter before and after the cleaning treatment of the membrane filter using supercritical carbon dioxide was observed using an electron scanning microscope. The results are shown in the SEM photographs of FIGS. 2A and 2B. The membrane filter is a polyamide reverse osmosis membrane filter, and the cleaning process was performed by continuously supplying supercritical carbon dioxide to the membrane filter at a pressure of 100 bar and a temperature of 35 ° C. for 1 hour. .

2A is an electron scanning microscope photograph showing the membrane filter surface before the cleaning process using supercritical carbon dioxide, and FIG. 2B is an electron scanning microscope photograph showing the membrane filter surface after the cleaning process using the supercritical carbon dioxide.

As can be seen from the electron scanning micrographs of FIGS. 2A and 2B, the membrane filter before and after the supercritical carbon dioxide treatment did not have any special property change such as pinhole formation.

Evaluation of the Effect of Cleaning Process on Membrane Filter 2

The membrane filter before and after the cleaning treatment of the membrane filter using supercritical carbon dioxide was observed using ATR-FTIR, and the results are shown in FIG. 3.

3 is an ATR-FTIR graph showing chemical component changes before and after cleaning a membrane filter using supercritical carbon dioxide.

As can be seen in FIG. 3, almost no changes in chemical composition and chemical distribution were observed in the ART-FTIR results before and after cleaning the membrane filter using supercritical carbon dioxide. Accordingly, it was confirmed that the cleaning process using the supercritical fluid is suitable for the cleaning process of the membrane filter because it does not affect the physical and chemical effects.

Evaluation of cleaning capacity of bio-bowling

In order to evaluate the cleaning of the membrane filter generated bio-bowling through supercritical carbon dioxide treatment, the reverse osmosis membrane filter filtration system was operated for about 48 hours after injecting the strain with 10 ⁷ cfu / ml of Pseudomonas aurezinosa. To prepare a membrane filter in which bio-fouling was produced. This bio-fouling membrane filter is confirmed that the flow rate reduced by about 40% compared to the initial flux (flux) is shown in Figure 4 as a result. 4 is an electron scanning micrograph showing a membrane filter produced bio-fouling. As shown in the scanning electron micrograph of FIG. 4, it was confirmed that green live Pseudomonas aureusinosa and red inactivated Pseudomonas aurezino were present in the membrane filter.

Subsequently, in order to evaluate the cleaning ability of the bio-fouling, the membrane filter generated with the bio-fouling was placed in a supercritical carbon dioxide scrubber, and then supercritical carbon dioxide at a flow rate of 10 ml / min at 100 bar and 35 ° C. for 1 hour. Was injected to clean the membrane filter in which the bio-fouling was produced, and the results are shown in FIG. 5.

In addition, in order to evaluate the cleaning ability of the bio-mauling, the membrane filter generated with bio-fouling was placed in a supercritical carbon dioxide scrubber, and then supercritical carbon dioxide was discharged at a rate of 10 ml / min at 100 bar and 35 ° C for 1 hour. While injecting to clean the membrane filter with bio-fouling, 1% (v / v) of water was continuously injected with supercritical carbon dioxide to clean the membrane filter with bio-fouling. Shown in

FIG. 5 is an electron scanning microscope photograph showing a membrane filter cleaned using supercritical carbon dioxide, and FIG. 6 is an electron scanning microscope photograph showing a membrane filter cleaned using supercritical carbon dioxide and water.

5 and 6, it was confirmed that Pseudomonas aurezinosa inside most bio-foulings after the supercritical carbon dioxide cleaning treatment was red and inactive (removed) by the supercritical carbon dioxide treatment. In particular, it was confirmed that the result of washing with injection of 1% water was more bio-fouling was removed than the result of washing using only supercritical carbon dioxide.

The membrane filter cleaning method using the carbon dioxide of the present invention described above may be utilized as a technique for effectively cleaning the bio-fouling generated in the filter by supplementing the disadvantages of the conventional chemical cleaning and physical cleaning. In addition, the cleaning method is carbon dioxide itself is not toxic, easy to recover and do not require no additional cleaning procedure because there is no residual can be utilized as an environmentally friendly membrane cleaning technology. In addition, it is very economical because it does not need additional disinfection and disinfectant treatment using microbial sterilization power of supercritical carbon dioxide itself.

As described above with reference to the embodiments of the present invention, those skilled in the art may variously modify and change the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. I can understand that you can.

1 is a block diagram showing a membrane filter cleaning device applied to remove the bio-fouling generated in the membrane filter according to an embodiment of the present invention.

2A is an electron scanning micrograph showing the surface of the membrane filter before the cleaning process using supercritical carbon dioxide.

FIG. 2B is an electron scanning microscope photograph of the membrane filter surface after the cleaning process using supercritical carbon dioxide.

3 is an ATR-FTIR graph showing chemical component changes before and after cleaning a membrane filter using supercritical carbon dioxide.

4 is an electron scanning micrograph showing a membrane filter produced bio-fouling.

5 is an electron scanning micrograph showing a membrane filter cleaned using supercritical carbon dioxide.

6 is an electron scanning micrograph showing a membrane filter cleaned using supercritical carbon dioxide and water.

<Description of the symbols for the main parts of the drawings>

10: supercritical fluid providing unit 20: co-solvent providing unit

30 membrane filter cleaning unit 40 contaminant recovery unit

Claims (6)

Positioning the membrane filter in which the bio-fouling has been generated in the cleaning chamber; And Flowing a supercritical fluid into the cleaning chamber to remove bio-fouling and microorganisms generated in the membrane filter. The method of claim 1, wherein the bio-fouling includes a form in which microorganisms are simply aggregated on a surface, and is complicated by extracellular secretory substances (polysaccharides and proteins) secreted by quorum sensing mechanisms. And a three-dimensional structure that is tightly coupled. The method of claim 1, wherein the supercritical fluid flows into the cleaning chamber at a flow rate of 8 to 20 ml / min. The membrane filter cleaning method according to claim 1, wherein 1 to 3% by volume of supercritical fluid inflow is introduced into the cleaning chamber during cleaning of the membrane filter. The membrane filter cleaning method according to claim 1, wherein the cleaning of the membrane filter is performed at a pressure of 95 to 210 bar and a temperature of 31 to 40 ° C. The method of claim 1, wherein the supercritical fluid introduced into the cleaning chamber is continuously introduced into the contaminant recovery chamber after contacting the membrane filter.

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