Improving membrane integrity monitoring indirect methods to reduce plant downtime and increase microbial removal credit

This work reports an ongoing AWWARF research project on integrity testing of low-pressure membrane processes. The project includes an evaluation of existing and improved methods through testing at full-scale plants representing different membrane systems. The assessment and advancement of integrity monitoring methods is being performed using five essential criteria: sensitivity, continuity, identifiability, reliability, and cost effectiveness. The project approach focuses on full-scale surveying, representation, testing, correlation, and validation of several existing and improved or newly developed integrity monitoring methods and concepts. The plant survey has been completed at testing and the full scale facilities is ongoing. The international plant survey results indicate that amongst direct methods, the pressure decay test (PDT) was the most frequently used method for integrity monitoring. Turbidity monitoring, routine microbial analysis, and particle counting were the most frequently used indirect methods. Particle counting, though sometimes considered to be relatively costly, was seen to be utilized by almost half of the plants surveyed. Particle monitoring is currently not employed by most plants. It appears that if improvements can be made to online indirect methods for monitoring membrane integrity, such as better sensitivity for traditional instruments (e.g. improvements to turbidimeter) or better economics for more advanced instruments (e.g. less costly particle counters), then the advantages of no plant downtime can be combined with advantages of online monitoring with required sensitivity and affordable cost.