Full Description

This paper describes the use of the risk assessment methodology to establish treatment levels for conventional treatment plants to reduce the risk of Cryptosporidiosis outbreaks. The finished water quality goal for Lake Michigan was determined to be approximately 5.0 x 10-6 oocyst per liter as an annual average, based on an acceptable risk level of one infection in ten thousand individuals per year. Using the available Cryptosporidium data for the west shore of Lake Michigan, it was established that, based on 10,000 Monte Carlo trials there is a 1% probability that the raw water oocyst levels will be 8 per liter or greater. It was also shown that there is a 0.1% probability that the oocysts level would be 40 per liter or greater. Based on these results, it was determined that a minimum of 4.3 log removal of Cryptosporidium was required to achieve the acceptable risk, assuming a standard deviation of less than 0.2 logs. The process analysis showed that if sedimentation provides a mean of 0.7 log removal and the filtration process achieves a mean of 3.7 log removal, then a removal of only 0.2 log units in the backwash water treatment process (40% removal) would be sufficient to produce, on average, a product water of acceptable quality.

Product Details

Published: 01/01/1999 ISBN(s): 1583210016 Number of Pages: 14File Size: 1 file , 230 KB