KR101590191B1 - Method for Testing Integrity of Membrane - Google Patents

Abstract

A membrane-specific integrity test method is disclosed that is capable of ensuring accurate integrity test results for membranes of any form or material based on actual data. The film integrity test method of the present invention comprises the steps of: preparing a plurality of damaged films having different degrees of damage; Measuring a pressure decay rate (PDR) of the plurality of damage films; Measuring a log removal value (LRV) of the plurality of damage films; And deriving a reference graph based on the measured pressure drop rates (PDRs) and log removal rates (LRV).

Membrane, filtration, integrity, test

Description

METHOD FOR Testing Integrity of Membrane}

The present invention relates to a membrane integrity test method, and more particularly, to a membrane integrity test method capable of ensuring improved accuracy based on actual measurement data.

One of the reasons for this is that the desired quality of water can be stably obtained depending on the pore size of the membrane, thereby increasing the reliability of the process. In addition, the membrane filtration process has an excellent ability to remove pathogenic microorganisms as compared with conventional water treatment processes, thereby reducing the amount of disinfectant used to remove microorganisms.

If the membrane is damaged during the water treatment, there is a risk that the pathogenic protozoa such as Giadia and Cryptosporidium will not be removed and supplied to the consumer. Therefore, in order to ensure the stability of the membrane filtration facility, an analysis of membrane microbial removal capability, that is, membrane integrity test, should be performed periodically.

Membrane integrity test methods can be largely classified into direct method and indirect method. According to the US EPA, which defines the membrane integrity evaluation method, a pressure decay test (PDT), which is a type of direct integrity test, is performed under specific conditions, Log removal value (LRV) is theoretically calculated. Calculating the logarithmic removal rate (LRV) for particles of 3 mu m is because the US EPA regulation regards the size (3 mu m) of the pathogenic protozoan Cryptosporidium as the minimum size of the particles to be removed. In order to ensure that more than 99.99% of the cryptosporidium is removed by the membrane, the US EPA requires that the membrane used for water treatment be maintained at a log removal rate (LRV) of 4 or greater.

However, the membrane integrity test method prescribed by the US EPA is not only uniformly applied to various types of membranes, but also has a limited accuracy because the log removal rate is theoretically calculated.

Accordingly, the present invention is directed to a membrane integrity test method that can avoid problems due to limitations and disadvantages of the related art.

One aspect of the present invention is to provide membrane-specific integrity test methods to ensure accurate integrity test results for membranes of any form or material.

Another aspect of the present invention is to provide a film integrity test method with improved accuracy based on actual measurement data.

Other features and advantages of the invention will be described hereinafter, and in part will be apparent from the description. Alternatively, other features and advantages of the invention may be learned through practice of the invention. Objects and advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims of the appended claims.

According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: preparing a plurality of damaged films having different degrees of damage; Measuring a pressure decay rate (PDR) of the plurality of damage films; Measuring a log removal value (LRV) of the plurality of damage films; And deriving a reference graph based on the measured pressure drop rates (PDRs) and log removal rates (LRV).

The log removal rate (LRV) can be measured using beads having a diameter of 3.0 +/- 0.2 mu m.

The membrane integrity testing method of the present invention may further comprise obtaining a Critical PDR corresponding to a log removal rate (LRV) of 4.0 from the reference graph. In this case, the test method of the present invention includes: preparing a target film; Measuring a pressure decrease rate (PDR) of the target membrane; And comparing the pressure decrease rate (PDR) of the target film with the critical pressure decrease rate (Critical PDR).

The film integrity test method of the present invention includes: preparing a target film; Measuring a pressure drop rate (PDR) of the target membrane; And deriving a log removal rate (LRV) of the target membrane based on the pressure decrease rate (PDR) of the target membrane and the reference graph.

The steps of preparing the plurality of damaged films can be performed by forming pinholes in the normal film.

The normal membrane may comprise a tubular braid and a coating layer applied on the outer surface of the tubular knitted fabric. In this case, the steps of preparing the plurality of damage films may be performed by partially peeling off the coating layer of the normal film.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed.

Since the membrane integrity test method of the present invention is a membrane-specific integrity test method based on actual data, it is possible to ensure accurate integrity test results for membranes of any shape or material.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention. Therefore, the present invention encompasses all changes and modifications that come within the scope of the invention as defined in the appended claims and equivalents thereof.

As used herein, the term " normal membrane " should be understood to include all membranes except those membranes that are intentionally damaged.

As used herein, the term " target membrane " refers to a membrane that is used in actual filtration operations and in which the possibility of continuous use must be periodically monitored.

Hereinafter, embodiments of a film integrity testing method according to the present invention will be described in detail with reference to the accompanying drawings. There is no limitation on the type of membrane to which the membrane integrity testing method of the present invention can be applied, but for convenience of explanation, the hollow fiber membrane will be described below as an example.

1. Derive a baseline graph

As an experimental sample to be used to derive the reference graph, prepare a number of damaged membranes with different degrees of damage with the normal membrane.

The normal membrane may be in the form of a composite membrane coated with a coating layer on the outer surface of a tubular braid or may be in the form of a single membrane.

A damaged membrane refers to a membrane that is intentionally damaged by a normal membrane. A pinhole can be formed in the normal membrane to intentionally damage the membrane. In this case, a plurality of damaged films having different degrees of damage have different numbers of pinholes. When the normal film is in the composite film form, the normal film may be damaged by partially peeling off the coating layer of the film.

Next, using the filtration system 100 shown in FIG. 1, the pressure decay rate (PDR) of the normal film and the plurality of damage films are measured in the following manner.

First, the first valve (V1) is opened to allow inflow water to flow into the water tub (110). A predetermined amount of influent water flows into the water tub 110 and then the first valve V1 is closed so that no more inflow water flows into the water tub 110. [

Then, the membrane module 120 including the normal membrane is immersed in the inflow water in the water tub 110. [ At this time, the second valve V2 and the permeate water for allowing the filtration operation to be transmitted to the membrane module from the negative pressure generated from the suction pump 130 to the water tub 110 And the third valve V3 for returning is in an open state. On the other hand, the fourth valve (V4) for sampling the filtered water and the fifth valve (V5) for injecting air into the membrane module (120) are closed.

The membrane module 120 is immersed in the influent and vented out of the membrane module 120 for 20 to 40 minutes. Subsequently, the suction pump 130 is turned on to circulate the filtered water for 20 to 40 minutes to sufficiently wet the membrane of the membrane module 120.

After the membrane is sufficiently wetted by the circulation of the filtered water, the second valve V2 is closed to stop the filtration operation. Then, the fifth valve (V5) is opened to inject air into the membrane module (120).

When the air pressure applied to the membrane module 120 becomes equal to a predetermined size, the fifth valve V5 is closed to block the air in the membrane module 120 and the pressure of the membrane Measure the pressure drop rate (PDR).

 After measuring the pressure drop rate (PDR) of the normal membrane, the pressure drop rate (PDR) is measured by performing the above-described experiment on a plurality of damaged membranes having different degrees of damage.

Next, the log removal value (LRV) of the normal film and the plurality of damage films is measured by the following method.

First, raw water containing beads having a predetermined particle size at a concentration of 10 ⁵ / L or more is prepared. Considering that US EPA regulations are based on the removal rate for the pathogenic protozoan Cryptosporidium, beads with a particle size of 3.0 ± 0.2 μm, such as Nihon Koken Kogyo Co., Ltd. ) Of Cryptracer-M ^? Can be used. A predetermined amount of raw water is sampled to measure the bead concentration of the raw water.

Subsequently, all water present in the water tank 1 is discharged through a discharge port (not shown), and then the first valve V1 is opened to allow the raw water to flow into the water tank 110. [ For example, 500 L of raw water flows into the water tub 110, and then the first valve V1 is closed to prevent further inflow water from flowing into the water tub 110. The blower 141 is operated to blow air from the aeration tube 142 so that the beads in the raw water are completely and evenly mixed during the test.

Subsequently, the membrane module 120 including the normal membrane is immersed in the raw water in the water tank 110. The suction pump 130 is operated and the second and third valves V2 and V3 are opened to transmit a negative pressure to the membrane module to perform the filtration operation and return the permeate water to the water tank 110 again Return. At this time, the fourth valve (V4) for sampling filtered water and the fifth valve (V5) for injecting air into the membrane module (120) are closed.

Sampling of the filtered water is performed by opening the fourth valve (V4) at regular intervals, for example, every 30 minutes, during the filtration work. The bead concentrations for these filtered and raw water samples are measured in the following manner, respectively.

* Bead concentration measurement of raw water

0.2 to 1.0 mL of raw water is dropped on a filtration membrane having a pore size of 0.8 mu m, and then the number of beads is counted using a direct fluorescent microscope. Such measurement is carried out five or more times to obtain the average value of the number of beads, and the bead concentration of the raw water is calculated using this average value.

* Measurement of bead concentration in filtered water

20 L of filtration water is filtered through a filtration membrane having a pore size of 0.8 mu m. The sample bottle containing the filtered water was washed with 500 mL of PBS with a solution containing 80 mL of Tween, and the rinsed solution was filtered through the filtration membrane. Subsequently, the sample bottle is again washed with 1 L of purified water, and the washed solution is filtered with the filtration membrane. Next, the number of beads present on the filtration film is directly counted by a fluorescence microscope, and the bead concentration of the filtered water is calculated using the value. The bead concentration is measured in the same manner for all of the filtered water sampled at the predetermined period.

The log removal rate (LRV) is obtained by substituting the bead concentration of the raw water and the filtered water samples obtained above into the following equation 1, and an average value of the log removal rate (LRV) of the filtered water samples is obtained.

Equation 1: log removal rate _{(LRV) = log (C s} ) - log (C f)

Where C _s is the bead concentration of the raw water and C _f is the bead concentration of the filtered water.

After measuring the log removal rate (LRV) of the normal membrane by the above method, the log removal rate (LRV) of each of the damaged membranes having different degrees of damage is measured in the same manner.

The reference graph is derived based on the pressure decrease rates (PDR) and log removal rates (LRV) of the normal film and the plurality of damage films thus obtained.

2 is an example of a reference graph derived according to an embodiment of the present invention. Kolon Co., Ltd. of ^Cleanfil? A normal film and first to third damage films having pinholes of 0, 1, 2, and 3, respectively, were used in the -S20H hollow fiber membrane, and the pressure loss rate (PDR) The initial pressure was 0.3 ± 0.01 Kgf / cm ² and the pressure decrease rate was measured for 5 minutes. For the log removal rate (LRV) measurement, Cryptracer-M ^? Of Nihon Koken Kogyo Co., Ltd. Was used as the bead, and the sampling of the filtered water was performed at 30 minutes, 60 minutes, and 90 minutes after the filtration operation, respectively. The pressure drop rate (PDR), bead concentration, and log removal rate (LRV) measured for the normal membrane and the three damaged membranes are shown in Tables 1 to 3 below.

[Table 1]: Pressure Reduction Rate (PDR)

Pressure (Kgf / cm ² ) PDR
[Kgf / (cm < ² > min)] The initial (initial) The final (final) Normal membrane 0.306 0.301 0.001 The first damaged membrane 0.306 0.280 0.005 Second Damage Membrane 0.308 0.259 0.010 Third Damage Membrane 0.310 0.239 0.014

[Table 2]: Bead concentration

Sample Bead concentration (Dog / L)
Normal membrane Source water 4.5 × 10 ⁷
filtrate 30 minutes 2.45 x 10 ² 60 minutes 0.8 × 10 ² 90 minutes 0.6 x 10 ²
The first damaged membrane Source water 1.9 × 10 ⁷
filtrate
30 minutes 4.0 x 10 ² 60 minutes 2.25 x 10 ² 90 minutes 1.45 x 10 ²
Second Damage Membrane Source water 3.4 × 10 ⁷
filtrate
30 minutes 0.6 x 10 ³ 60 minutes 2.4 × 10 ³ 90 minutes 1.85 x 10 ³
Third Damage Membrane Source water 2.4 × 10 ⁷
filtrate
30 minutes 7.0 x 10 ³ 60 minutes 1.95 × 10 ³ 90 minutes 3.75 x 10 ³

[Table 3]: Log removal rate (LRV)

LRV Average LRV
Normal membrane 30 minutes 5.264
5.630
60 minutes 5.750 90 minutes 5.875
The first damaged membrane 30 minutes 4.677
4.907
60 minutes 4.927 90 minutes 5.117
Second Damage Membrane 30 minutes 4.753
4.390
60 minutes 4.151 90 minutes 4.264
Third Damage Membrane 30 minutes 3.535
3.810
60 minutes 4.090 90 minutes 3.806

According to an embodiment of the present invention, a critical pressure reduction rate (Critical PDR) corresponding to a log removal rate (LRV) of 4.0 is obtained from the reference graph. For example, in the graph of FIG. 2, 0.013 Kgf / (cm ² .min) is the critical pressure reduction rate (critical PDR). The integrity of the membrane used in the actual filtration operation is periodically checked based on the critical pressure reduction rate (critical PDR). For example, after preparing a membrane (hereinafter referred to as a "target membrane") used in an actual filtration operation and measuring the pressure decrease rate (PDR) of the target membrane, the pressure decrease rate (PDR) Comparing the reduction rate (Critical PDR). If the pressure drop rate (PDR) of the target membrane is greater than the critical pressure decrease rate (Critical PDR), it means that the membrane is damaged to the extent that the LRV reference value of 4.0 is not satisfied.

According to another embodiment of the present invention, after the target film is prepared and the pressure decrease rate (PDR) of the target film is measured, the target removal rate (LRV) of the target film based on the pressure decrease rate . When the integrity test of the target membrane is periodically performed and the log removal rate (LRV) of the target membrane is lower than a predetermined reference value, for example, 4.0, the target membrane must be repaired or replaced.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

1 is a schematic view schematically illustrating an example of a filtration system for performing a membrane integrity test,

2 is an example of a reference graph derived according to an embodiment of the present invention.

<Brief Description of Reference Numerals>

100: Filtration system 110: Water tank

120: membrane module 130: suction pump

141: blower 142: diffuser

V1 to V5: first to fifth valves

Claims (7)

Preparing a plurality of damage films having different degrees of damage; Measuring a pressure decay rate (PDR) of the plurality of damage films; Measuring a log removal value (LRV) of the plurality of damage films; Deriving a reference graph based on the measured pressure drop rates (PDRs) and log removal rates (LRV); Preparing a target membrane; Measuring a pressure decrease rate (PDR) of the target membrane; And And evaluating the membrane integrity of the target membrane based on the pressure drop rate (PDR) of the target membrane and the reference graph. The method according to claim 1, Wherein the log removal rate (LRV) is measured using beads having a diameter of 3.0 +/- 0.2 mu m. delete The method according to claim 1, Wherein evaluating the membrane integrity of the target membrane comprises: Obtaining a critical pressure reduction rate (Critical PDR) corresponding to a log removal rate (LRV) of 4.0 from the reference graph; And And comparing the pressure decrease rate (PDR) of the target membrane with the critical pressure decrease rate (Critical PDR). The method according to claim 1, Wherein evaluating the membrane integrity of the target membrane comprises: And deriving a log removal rate (LRV) of the target membrane based on the pressure decrease rate (PDR) of the target membrane and the reference graph. The method according to claim 1, Wherein preparing the plurality of damaged films comprises forming pinholes or pinholes in the normal film. The method according to claim 1, Wherein preparing the plurality of damaging membranes comprises damaging the normal membrane comprising a tubular braid and a coating layer applied on the outer surface of the tubular knitted fabric, Wherein the step of damaging the normal film is performed by partially stripping the coating layer of the normal film.

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