Monday, March 5, 2012

"Absolute" retention - A necessary debate ?

Unfortunately the 80s are still with us and there are still believers of "absolute" retention, in instances even for prefilters. There are statements of such and such filter with "absolute" retention, retention rating or the "absolute" retention is justified by the mythical beta-value (not so mythical and extra ordinary in process engineering calculations of sieves and porous loads). Moreover, not that such statements are pretty unscientific, but there are some who argue the case of "absolute" retention or retention rating.
Well is that debate necessary ? No, absolutely not.
In reliable filtration, whether depth-, pre- or membrane filtration one has to determine the performance of the filter within the particular application; under the process conditions the specified contaminants requires to be separated to pre-defined levels. So no matter what "absolute" rating is given, it is unimportant as the performance needs to be tested under the process conditions of the particular application. Only then the real retentivity is determined, only then one can reliably say that the filter's retention rating holds what it promises. Retention rating labels are useful guidances to chose certain filter types, but ones chosen the retention performance needs to be verified, as filters can act differently under different process conditions, fluid streams and contaminants. The separation mechanisms of sieve and absorptive retention need to be checked for their effectiveness, are these still act in a sufficient way under the particular process conditions, fluid streams and contamination types. Process validation of filters is the most necessary action to gain a reliable filtration process.
"Absolute" filtration is obsolete, therefore an unnecessary debate or better expressed by Dr. Cooney "It should solely be used for vodka". I agree.