The inactivation of Cryptosporidium parvum in
finished drinking water by medium-pressure UV light (200-300 nm) has
been investigated at both the bench scale, using a collimated beam
apparatus, and at the demonstration scale, using a Calgon Carbon
Corporation Sentinel™ system at the Mannheim Water Treatment
Plant, Kitchener, ON, Canada. The viability of the oocysts was
assessed using both in vitro (fluorogenic vital dyes (DAPI/PI) and
maximized in vitro excystation) and in vivo (neonatal mouse
infectivity) assays. In the bench-scale studies, a high degree of
inactivation (>4 logs) was found at UV doses as low as 41 mJ cm-2, as
assayed by neonatal mouse infectivity; whereas the in vitro surrogate
assays showed little or no inactivation at this and higher doses. This
indicates that the in vitro assays are unreliable and grossly
overestimate the UV doses required to prevent infection by the oocysts
in susceptible hosts. The demonstration studies, which were carried
out under the NSF/EPA ETV Program, provided results that agreed very
well with the bench-scale results and furthermore showed that a UV
dose as low as 19 mJ cm-2 provided 3.9 logs inactivation of the
Cryptosporidium oocysts.
Authors: James R. Bolton and Bertrand Dussert,
Calgon Carbon Corporation, Markham, ON, Canada; Zia Bukhari, Thomas
Hargy and Jennifer L. Clancy Clancy Environmental Consultants, Inc.,
St. Albans, VT .
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