Membrane integrity testing

If the normalized salt rejection is low or the normalized permeate flow is high, the integrity of the membrane may be in question. The vacuum decay test is a direct test for the integrity of a spiral wound RO membrane module. The test is best used to identify leaks within the membrane modules rather than leaks due to chemical attack. The test requires the isolation of an individual membrane module or the entire pressure vessel. A vacuum is then pulled on the membrane(s) and the rate of decay in pressure is observed. A decay of greater than 100 millibar per minute is indicative of a leaky membrane. Refer to ASTM Standards D39235 and D69086 for a more detailed review of the technique. 

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Guo, H., Wyart, Y, Perot, J., Nauleau, R, and Moulin, P. 2010. Low-pressure membrane integrity tests for drinking water treatment A review. Water Res. 44 41-57. 

Compressed air supply system Rotary screw air compressors supply air at 9 bar g for air-assisted liquid backwash to remove particulates from the membrane surface. It also supplies air for the Membrane Integrity Test as well as various plant instruments and controls. 

Diversity of Membrane Eiements and Configurations Currently, all membrane manufacturers offer their own design, size, and configuration of membrane elements and systems. The membrane systems differ by the type of filtration driving force (pressure versus vacuum), the size of the individual membrane elements, the size of the membrane vessels, the configuration of the membrane modules, the type of membrane element backwash, and the type of membrane integrity testing method and other factors. 

Drinking Water Inspectorate (DWI) (2001). Membrane integrity testing Membrane company level. In Review of the Adequacy of Existing Proposals for Membrane Integrity Monitoring. Available http //www.dwi.gov.uk/regs/pdf/mim.pdf, accessed May 22, 2006. 

TABLE 10.6 Summary of Membrane Integrity Test Methods for Submerged Membranes... 

Filters for use in sterile gas filtration must conform to standards similar to those mandated for sterile hquid filtration. Nondestmctive integrity tests may be apphed. The tests are performed by wetting the filter with an appropriate solvent, commonly 60/40 isopropyl alcohol/water for hydrophobic membranes, and applying air or nitrogen gas at a preset pressure. 

Early ultrafiltration membranes had thin surface retentive layers with an open structure underneath, as shown in Fig. 20-62. These membranes were prone to defects and showed poor retention and consistency. In part, retention by these membranes would rely on large retained components in the feed that polarize or form a cake layer that plugs defects. Composite membranes have a thin retentive layer cast on top of a microfiltration membrane in one piece. These composites demonstrate consistently high retention and can be integrity-tested by using air diffusion in water. 

Step 4 Capsule Mechanical Stability. The mechanical stability of the membranes was assessed semi-quantitatively by applying a compressional force via a micrometer. While this method is not precise, it did permit us to assess if the capsules could withstand deformations and if they ruptured in a controlled or catastrophic manner. Another test which was selectively employed was to place capsules between microscope slides and measure the force required to compromise the integrity of the membrane. These tests measured the resistance of the weakest point of the membrane. For certain capsules a needle was used to probe the breaking strength of a local region of the membrane. 

The antioxidant activity afforded by NO is most important if it translates into a meaningful therapeutic event. To test the importance of this reaction pathway to cell survival, we compared viability of the cells exposed to in the presence or absence of NO, When cells are exposed to 20 pM there was appreciable loss of cell membrane integrity as measured by trypan blue dye exclusion (Kelley et al, 1999) the addition of NO deaeased cell membrane damage (Figure 6). 

Integrity testing of vent filter membranes associated with the sterilizer... 

The bubble point test is a popular single-point physical integrity test for disc filter membranes based on Eq. (21). A fdter medium is wetted with a liquid, and test gas pressure is slowly raised until a steady stream of bubbles appears from a tube or hose attached to the downstream side of the filter and immersed in water (Fig. 9). The pressure at which the bubbles first appear is recorded as the bubble point and is related to the largest pores in the fdter medium. A pore size can be calculated from Eq. (21) however, it must be realized that the bubble point test does not measure the actual pore size, but only allows correla-... 

Another integrity test referred to as the pressure hold test makes use of the fact that below the transition pressure no bulk flow of the test gas takes place. Therefore, in a pressure hold test, once a filter system is in place and the filter medium wetted, pressure is applied to the system and then shut off and sealed. If there are no leaks in the system or holes in the membrane larger than the corresponding test pressure used, the pressure should remain constant. If the pressure drops, there is a leak somewhere in the system that should be corrected. The pressure hold test is popular in testing filter assemblies and systems in... 

F. Hofmann, Integrity Testing of Microfiltration Membranes, J. Parenteral Sci. Tech-nol. 38, 148 (1984). 

Before implantation several in vitro tests were performed. For evaluation of a possible toxic reaction, we investigated the material and the whole devices in vitro with cell culture methods. Direct contact and extraction tests with a mouse fibroblasts cell line (L 929) and a neuroblastoma cell line (neuro-2-a) were performed according to the international standard ISO 10993 ( Biological Evaluation of Medical Devices ). The materials and devices showed no toxicity, i.e. no significant differences in membrane integrity of the cell membranes, mitochondrial activity and DNA synthesis rate. The neuro-2-a cell line is so sensitive that even small changes in process technology are detectable. The flexible polyimide structures proved to be non toxic. 

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