Full Description

Many drinking water utilities replace free chlorine with chloramines (primarilymonochloramine) for secondary disinfection in order to reduce the formation ofchlorinated disinfection byproducts (DBPs) within the distribution system. Becausemonochloramine is a weaker oxidant than free chlorine, many water utilities that employchloramination temporarily switch to free chlorine in an attempt to control bacterialregrowth and, in particular, nitrification in distribution systems. The objective of thisresearch was to assess the water quality impacts of temporary switches to free chlorinefor one month periods within the distribution systems of two water utilities. Results todate have indicated several important effects: a traveling front of the breakpointchlorine chemistry with very low total chlorine residual occurs within the distributionsystem following the switch from chloramines to free chlorine and again when freechlorine replaced chloramines; DBPs increase within the distribution system duringthe free chlorination periods although the extent varies both spatially and temporally;bacteria continue to remain attached to pipe surfaces after periods of free chlorination;bacteria on pipe walls as measured by heterotrophic plate counts (HPC) is notreduced during exposure to free chlorine; and, nitrifying bacteria have been identified onpipe surfaces even though there was very little evidence of nitrification as measured byan increase in nitrate concentration the bulk water of the system. Includes 31 references, table, figures.

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Edition: Vol. - No. Published: 06/17/2005 Number of Pages: 17File Size: 1 file , 1.4 MB