Membrane filtration for cold regions – impact of cold water on membrane integrity monitoring tests

Abstract

Low-pressure water treatment membranes, microfiltration (MF) and ultrafiltration (UF) have enjoyed unprecedented growth during the past decade. These systems are particularly suited for cold region communities because of their operational simplicity, small footprint, and consistent performance despite the fluctuations in raw water characteristics. Effective operation of MF and UF membrane systems in cold regions, however, must account for the impact of low water temperatures on membrane operation. Of particular interest is the impact of cold water on direct membrane integrity monitoring tests. Most regulatory bodies require that regular integrity monitoring tests be performed for low-pressure membranes to ensure the integrity of the membrane systems. Currently, the most widely-used integrity monitoring test is the pressure decay test. Our studies, however, indicated that the pressure-based direct integrity monitoring tests are affected by variations in water temperature, especially in the range of 0 to 5 °C. The considerable drop in diffusive air flow rates and consequent decrease in pressure decay rate for an intact membrane as water temperatures approach 0 may mask the impact of a defect and should be accounted for. It is suggested that the criteria for membrane integrity tests in cold regions shift downward to account for the effect of temperature. This paper presents the results obtained from studies on the effect of water temperature on the pressure-based direct integrity monitoring tests. Key words: membrane integrity monitoring, pressure decay test, diffusive air flow test, low-pressure membranes, microfiltration, ultrafiltration, water treatment, pathogen removal.