Physicochemical aspects of Cryptosporidium surrogate removal in carbon block filtration

As the final barrier before consumption, properly designed and operated point-of-use water treatment systems like carbon block filters are useful in protecting public health. This article evaluates the relative importance of adsorptive filtration, straining filtration, and cake filtration in the removal of nominal test dust (NTD) and latex microspheres, the latter being a Cryptosporidium oocyst surrogate, by carbon block filtration. Three different carbon blocks were tested, and only one of these was able to pass a National Sanitation Foundation (NSF) certification test. Surface charge characteristics can explain why two carbon blocks failed the test; however, they cannot explain why one carbon block passed the test. Scanning electron microscopy and energy dispersive X-ray spectroscopy results together with the use of particle size distributions confirmed a lack of NTD penetration into the successful carbon block and suggest that cake filtration was the dominant NTD removal mechanism in this carbon block. Particle size analysis revealed that D-15 appears to be one of the determining factors in the passing the NSF certification test.