Direct membrane integrity testing: Impact of parameter selection on log removal value calculations

The USEPA Long Term 2 Enhanced Surface Water Treatment rule has put in place specific requirements to monitor membrane integrity. The main tool used to monitor membrane pathogen rejection is the pressure decay test (PDT) and the EPA issued the Membrane Filtration Guidance Manual (MFGM) to provide stakeholders a framework for the application of the rule. This paper shares experiences, questions, and problems encountered while applying the guidance currently in place. A new way to account for diffusion is also presented in an attempt to simplify its use in the future. Questions raised during the establishment of the Quality Control Release Value (QCRV) are also shared with an analysis of their impact. The pressure decay test timing was also shown to have an impact on the calculated log removal value (LRV) that can be counterintuitive in certain circumstances.

Research Highlights
► Normalizing diffusion makes accounting for it easier in LRV calculations.
► Module selection for challenge testing should likely not rely on average quality.
► LRV conservatism not always guaranteed after membrane cleaning.
► Parameter selection (flow and transmembrane pressure) crucial in LRV calculations.