Assessment of pressure decay test for RO protozoa removal validation in remote operations

© 2016 Elsevier B.V.. Essential requirements for remote potable water reuse in small communities include highly automated processes, remote monitoring and control, and high pathogen removal values that can be easily validated. A plant for advanced tertiary water treatment for remote operations using six pathogen barriers has been tested. It can achieve a credible Log Removal Value (LRV) for virus and bacteria well above target values recommended by current guidelines, but not for protozoa since this pathogen type is commonly resistant to most chemical disinfectants. As a result, the required LRV credit requirement for protozoa for the reverse osmosis (RO) barrier of the plant was at least 2 to reach the desired outcome. Furthermore, the maximum certified LRV for protozoa in Australia for RO in recycled water is no greater than 2 due to the lack of recognized integrity testing techniques to validate the process during operation. In this study, a pressure decay test (PDT) for RO systems is presented and verified by particle challenge testing. It is demonstrated with both laboratory scale and single element pilot scale tests that the PDT is more conservative than the particle challenge test. It is also demonstrated that frequent PDTs will not cause physical damage to membranes, based on a sample of 304 PDTs, as well as a visual check of the RO element structure and salt rejection.