As the final barrier
before consumption, properly designed and operated point-of-use (POU) water treatment systems are emerging
as a useful way of protecting the public health.
The National Sanitation Foundation (NSF) tests carbon block filters for cyst removal
capability by using either live Cryptosporidium oocysts or surrogate particles such as polystyrene
microspheres or test dusts. Nominal test dust (NTD) [Powder Technology Inc., Burnsville, MN]
may be used as a surrogate for Cryptosporidium oocysts in challenge tests as prescribed by NSF
Standard 53 (NSF, 2001b). NSF discontinued the use of fine test dust (FTD) [Powder
Technology Inc., Burnsville, MN] as a surrogate for Cryptosporidium oocysts in 1993. If a filter
removes a sufficient number of test dust particles, or a sufficient number of oocysts or
microspheres prior to and after being clogged with test dust, then NSF will certify that the
product is effective for oocyst removal.
The objective of this paper was to compare the effects of NTD and FTD on carbon
block's ability to pass the NSF challenge test. Electrophoretic mobility and particle sizing were
used to characterize the underlying physical and chemical processes of carbon block filtration.
Two test dusts, three different carbon blocks, and the raw materials for carbon block
manufacturing were tested. Under the challenge of NTD, only one of the three carbon blocks
passed the NSF certification test. When FTD was used as a surrogate, all three carbon blocks
qualified for certification. Carbon block materials and test dusts were negatively charged at pH >
5 and, therefore, the surface charge characteristics can explain why two carbon blocks failed the
NSF certification test. However, these characteristics cannot explain those carbon blocks that
passed the NSF certification test. Particle size analysis revealed that D15 appears to be one of the
determining factors in passing the NSF certification test.
Includes 24 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 320 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 15 |
| Published : | 11/01/2002 |
