Buying and selling of treated water, as a commodity, is commonplace in the water
industry. This practice dynamic is characterized by a wholesaler (WS) of the treated water and a
purchaser of the treated water, often referred to as a consecutive system (CS). This wholesaler
purchaser dynamic is responsible for serving approximately one-third of US water customers.
The primary goal of this study was to develop disinfection byproduct (DBP) control strategies for CSs, which will
facilitate their compliance with the LRAAs in the Stage 2 DBPR. The objective was to
characterize factors affecting DBP formation and control in CSs by developing a relationship
between the chlorine residuals and DBP concentrations in a distribution system (DS) and those in
a bench-scale "hold study" (HS). This relationship may be used to aid the CS in evaluating DBP
control strategies. DS samples were taken at the WS plant effluent, the CS entry point and at
three points in the CS focusing on the maximum DBP formation. Relationships in both DS and
HS were developed between the chlorine demand and DBPs (TTHM and HAA5). By comparing
HS data to the DS data, relationships were then developed for chlorine residuals, chlorine
demands, TTHM and HAA5 formation. A strong relationship between the chlorine demand and
TTHM formation was found in both the DS and HS samples. In some quarters, HAA5's were
found to degrade in the DS samples, but not in the HS samples. These relationships were then
used to assess two DBP control options: the impact of water age on distribution system DBP
occurrence; and, distribution system maintenance. Results of the eight utilities and over 500
DBP analyses have shown the following: Water Age - about 50% and 60% of the TTHMs and
HAA5s were formed in the WTP and about 65% and 75% were formed before the CS entry
point, thus water age management in the CS was not a strong option; Distribution System
Maintenance - comparison of the nine HS DS in this study has indicated that
the uncertainty involved with estimating the water age makes the use of the HS approach to
estimate excess chlorine demand difficult, at a minimum. However, changes in distribution
system management that yield lower chlorine demand will likely yield lower DBPs, especially Total Trihalomethanes
(TTHMs) as they form more slowly, relative to Haloacetic Acids (HAAs). Includes reference, tables, figures.
| Edition : | Vol. - No. |
| Number of Pages : | 16 |
| Published : | 06/01/2007 |
