Recognizing that pathogen removal is a primary end-user concern, various methods,
direct and indirect, have been developed for monitoring the integrity of membrane
systems. Indirect methods include turbidity and particle counting; they are on-line and
continuous, but suffer from low resolution and sensitivity.
Direct methods include many versions of air-based tests. Measuring membrane
integrity with an air test involves starting with membrane pores filled with water and
exposing one side or both sides of the membrane to air. Differential pressure is applied
across the membrane to force air through leaks. An air-based test allows quantification
and location of leaks, but requires that a unit be taken off-production for a period of 10-
15 minutes. As such, they are typically performed once per day.
Many regulators have accepted an air-based test as a primary membrane integrity
monitoring technique. Typically, test conditions must be selected to provide information
on defects larger than 3 m in order to ensure the removal of Cryptosporidium oocysts
(size ranging between 4 and 7 m). In addition, results are often converted to a log
removal value (LRV) using a method discussed in this paper (ASTM, 2003). This paper presents data comparing air-to-water and air-to-air integrity tests and
data validating the estimation of log removal values from air-based membrane integrity
tests. The paper also presents data comparing air-to-water and air-to-air integrity tests, data
validating the application of the Hagen-Poiseuille laminar flow model for estimating the
air-liquid conversion ratio and challenge test data validating the estimation of log
removal values from air-based integrity tests. Includes reference, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 180 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 10 |
| Published : | 11/01/2005 |
