As membrane technologies are more widely employed in the drinking water
industry, membrane integrity becomes an increasingly important issue. Current and
proposed regulations require some form of integrity testing to demonstrate continued
successful performance of a membrane system. For example, a US Environmental Protection Agency (USEPA) report on low-
pressure membrane filtration as means for compliance with the Long-Term 2 Enhanced
Surface Water Treatment Rule (LT2 ESWTR) states that microbial removal credit can
only be awarded to the level at which the sensitivity of integrity testing can be guaranteed
(USEPA, 2001).
Besides sensitivity, reliability, the
frequency of testing, identifiability (i.e., the ability to locate/identify the failed filter
elements), and practicality of an integrity-testing method are all important issues. The questions addressed by each term include:
sensitivity - can a defect be detected with a given integrity testing procedure;
reliability - how reliable is the result of an integrity testing procedure; what is the
probability of a false positive or a false negative;
frequency of testing - how often can system integrity be monitored;
identifiability - is the integrity testing procedure able not only to detect, but also to
locate the defect,and if so, how soon; and,
practicality - are the additional costs associated with integrity testing, capital and
O&M, reasonable and affordable for the end-users, and is the implementation
of the method practical and user-friendly?
The integrity testing methods for low-pressure membrane systems (i.e.,
microfiltration and ultrafiltration) can be roughly classified into four categories:
pressure-driven methods such as pressure-hold and water
replacement flow (this type of method is usually identified as a direct test method);
methods based on measuring effluent quality such as turbidity
monitoring, particle counting, and particle monitoring;
methods based on challenge tests such as the spiked integrity method
(van Hoof et al., 2001); and,
methods based on measuring other physical characteristics such as
measuring acoustic signals (Glucina et al., 2001).
Once the criteria are quantified, various integrity-testing methods for low-pressure
membrane systems can be evaluated in more definitive terms. Moreover, the quantified
criteria provide a useful tool for evaluating newly developed integrity-testing methods.
This paper defines and quantifies at what level those criteria should be met, and
discusses how those criteria can be fulfilled with the integrity testing methods currently
in use. The purpose of this paper is to provide a systematic approach for evaluating
methods for testing membrane integrity.
Includes 8 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 330 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 14 |
| Published : | 11/01/2002 |
