AWWA WQTC56936

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.

Product Details

Edition:

Vol. - No.

Published:

11/01/2002

Number of Pages:

14

File Size:

1 file , 330 KB