AWWA ACE60072

Databases on Cryptosporidium occurrence in filtered surface water supplies can be used toestimate the benefit of providing ultraviolet (UV) disinfection and the consequences of an interruption of theUV disinfection system operation. Calculations show that a conventional treatment plant couldoperate without UV disinfection for 7 days per year (or an average of 14 hours per month) beforeexceeding the 1/10,000 annual risk of Cryptosporidium infection. However, the down timewould be limited to only 3.67 hours per month during the spring months, when Cryptosporidiumlevels are the highest. The results demonstrate that UV disinfection systems can be brought backon-line within a practical time frame (i.e., several hours) after a power outage or equipmentmalfunction and that brief interruptions of a UV disinfection system would not create anunacceptable risk assuming continued operation of an upstream conventional treatment process.A similar approach was used to estimate the limits of operation when a UV system wasperforming outside of its validated operating criteria, and for unfiltered water systems. Althoughdata are limited, and additional data are needed to refine the analysis, the study concludes thatcontinuous operation of UV systems is not needed to achieve acceptable risk goals and thatextraordinary measures to increase UV disinfection system reliability (e.g., provision of UPS)provide marginal benefits provided a backup power source is available. Includes 28 references, tables, figure.

Product Details

Edition:

Vol. - No.

Published:

06/17/2004

Number of Pages:

10

File Size:

1 file , 330 KB