Description
The overall objective of this research was to characterize the impact of ClO<sub>2</sub>-only and combinedClO<sub>2</sub>/Cl<sub>2</sub> pre-oxidation processes on total trihalomethane (TTHM) and haloacetic acid (HAA-5) formation in simulated distributionsystems for a wide range of raw water quality. Specific objectives for the combined process wereto determine the impact of raw water TOC concentration on TTHM/HAA-5 formation, and to determine the optimum ClO<sub>2</sub>:Cl<sub>2</sub> mass ratio. Approximately 50 water utilities across the U.S. participated in this 3-year project, providing raw water samples and full-scale treatment information. The raw water TOC concentrations ranged from 3.09 to 7.80 mg/L. In general, an attempt was made to conduct each set of experiments under similar conditions, particularly during the simulated distribution system (SDS) phase. However, the full-scale operating conditions of each utility did play a role in determining the experimental approach in each study. For example, although a vast majority of the SDS post-chlorine doses were in the range of 2.5 – 3.5 mg/L, they were not all exactly thesame, given the wide range of settled water TOC levels. Likewise, although a majority of theSDS experiments were conducted at pH = 8.0, the overall range was 7.8 ± 0.4. Bench-scale SDSexperiments were conducted with each sample in order to determine the impact of various preoxidationscenarios on TTHM/HAA-5 formation. The pre-oxidation scenarios generally includeda minimum of: control (no pre-oxidant); ClO<sub>2</sub> only; ClO<sub>2</sub>/Cl<sub>2</sub> (dose 1); and, ClO<sub>2</sub>/Cl<sub>2</sub>(dose 2). The same coagulation/flocculation/sedimentation processes, based on full-scaleinformation, were then applied to all samples, followed by pH adjustment, chlorination, and a 5-day holding period, in the dark at 20ºC, before TTHM/HAA-5 samples were collected. Includes 6 references, figures.
Product Details
- Edition:
- Vol. – No.
- Published:
- 11/01/2009
- Number of Pages:
- 7
- File Size:
- 1 file , 750 KB
- Note:
- This product is unavailable in Ukraine, Russia, Belarus
