To minimize disinfection byproduct (DBP) formation, three general optimization
options are available to conventional treatment plants that chlorinate prior to or at the rapid
mix: lower the level of chlorine dosed at the rapid mix and re-chlorinate; move the point
of chlorination downstream of the rapid mix; or, switch to a different pre-disinfectant/
oxidant. Bench-scale results indicated that lowering the pre-chlorination dose and rechlorinating
after the sedimentation basin such that a target distribution system residual (1
mg/L at 24 hours) is maintained, yielded lower chlorine consumed and lower total
trihalomethanes (TTHMs) and haloacetic acids (HAA5) formed after 24 hours (up to 23% and
33%, respectively, after 5 days). This observed behavior could be explained by the
availability of natural organic matter (NOM) to react with chorine to form halogenated byproducts.
The first objective of this study was to assess and evaluate the conditions under which
optimizing preoxidation is effective in controlling DBPs. Chlorine dose, point of chlorine
application and the use of other preoxidants (chlorine dioxide, potassium permanganate and
mixed oxidant) were evaluated. Chlorine dose levels were varied to achieve three water
treatment goals: inorganic oxidation, bio-growth control and CT. Moving the point of chlorine
application from the rapid mix to mid-flocculation to post sedimentation was evaluated. The
alternative preoxidants were dosed to achieve inorganic oxidation and biogrowth control and
re-chlorinated (post sedimentation) to yield CT and a target distribution system residual.
The second objective was to understand the interactions of chlorine with NOM during
coagulation, flocculation and sedimentation (CFS), particularly the solid / liquid phase
formation of halogenated DBPs. Relating these results to those obtained from the first
objective enables the integration of fundamentals into applicable engineering, thereby
obtaining the full spectrum of understanding. Includes 3 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 340 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 06/15/2003 |
