A Case of Penetration of 0.2-µm Rated Membrane Filters by Bacteria

While conducting long term bacteria challenge tests of 0.2-µ.m rated sterilizing grade filters which retained 100% of the standard challenge organism P. diminuta, it was discovered that several species of indigenous water bacteria were not completely retained by these filters. This finding has been confirmed for a variety of commercially available Q.2-µm rated disc and cartridge filters. Filters were challenged with wellwater which contained naturally occurring bacterial species. The challenge system included a prefilter to remove debris and large microorganisms, the test filter, and an analysis membrane filter to monitor the total effluent. Influent bacteria levels were also