Calculating particle log reduction values based on pressure decay tests on Multibore® hollow fibre membranes

The Multibore (R) hollow fibre membrane has a distinct advantage in comparison to other hollow fibre membranes due to its extreme durability, which prevents fibre breaks to a very high degree. The integrity of a system nevertheless will need to be checked in order to make sure no membrane damage has occurred. The integrity of the membrane system is normally tested by means of a pressure decay test (PDT). The results of this test have to be interpreted so that a plant operator knows the actual log reduction value (LRV) of the plant. This paper deals with this interpretation and a formula is derived from which the LRV can be calculated. The method is partially based on the ASTM D6908-6906 method in which case, the air flow in an integrity test is compared to the air flow through a complete membrane breakage. It is shown that the PDT is sensitive enough to be able to detect a single broken membrane in even the largest membrane racks and that a 4-LRV can be guaranteed as long as the pressure decay rate is within the specified range.