Indirect integrity testing on a pilot-scale UF membrane

As the use of membranes as the main unit operation within potable water treatment plants increases, methodologies to monitor membrane integrity has become a vital issue for the drinking water industry. This study evaluated the two most commonly used indirect integrity test procedures, namely particle counting and turbidity measurements, on permeate. A pilot-scale UF membrane module was intentionally operated under challenge conditions, defined as operation of the pilot-scale module for extended periods past the manufacturer's recommended run time. Indirect integrity test methodologies were evaluated on the intentionally compromised system to determine the capabilities of these monitoring procedures in detecting individual fibre pinholes. Both indirect test procedures failed to detect the intentional breach within the membrane operating system that occurred as a result of the challenge operating conditions. Dissolved organic carbon (DOC) and colour measurements were evaluated to determine their capability as potential alternative indirect integrity test procedures, and showed promising results in their ability to identify a significant increase in the concentration of dissolved contaminants within the permeate stream. In particular, there was a 150% increase, from 3.2±0.4 mg l⁻¹ to 7.9±1.8 mg l⁻¹ in DOC during the challenge trial when 1% of the membrane fibres were compromised, while turbidity measurements were constant at 0.20±0.04 NTU. This study demonstrates the need for robust on-line or rapid indirect test methodologies for monitoring membrane integrity in the drinking water industry.