Recent investigations of operational effects on Cryptosporidium passage through granular
media filters have demonstrated that, relative to optimized operating conditions, end-of-
run filtration is a particularly vulnerable period of operation during which increased
Cryptosporidium passage through filters may be expected. In the context of filter
operation, system failure can be considered the passage of pathogens through a filter or
multiple filters at levels that exceed a specified level or regulatory criterion. Information
regarding the risk of system failure and how this risk changes with respect to time is
critical to facilitating decision making and cost/benefit analyses for optimizing
operational strategies. Using previously reported pilot-scale Cryptosporidium removal
data obtained at the City of Ottawa pilot plant, the risk of an infectious dose of
Cryptosporidium oocysts being released into a filter effluent and the subsequent
distribution system was modeled. The model results demonstrated a considerable
increase in risk when a filter is operated beyond 0.3NTU compared to operating the filter
until 0.3NTU or to only 0.1NTU of filter effluent turbidity. The model also demonstrated
that operating multiple filters that are equally offset from one another is an alternative
method to reducing the risk of Cryptosporidium passage through the filtration step of the
treatment process.
Includes 12 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 310 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 10 |
| Published : | 11/01/2002 |
