The Stafford Springs Water Treatment Plant (SSWTP) is a 1.0-MGD facility owned and
operated by the Connecticut Water Company (CWC). The plant utilizes Pulsator clarification
and filtration through four feet of mono-media granular activated carbon (GAC). The GAC filter
media is changed out every three years for taste and odor control.
A previous study done by Metcalf & Eddy (M&E) noted that prechlorination was forming
significant levels of disinfection byproducts (DBPs) within the plant and recommended the use
of chlorine dioxide in lieu of chlorine for preoxidation, predisinfection, and DBP control.
Subsequently, M&E and CWC conducted a two-season, full-scale trial at the SSWTP in which
chlorine dioxide was utilized as a substitute for prechlorination.
During the full scale trial, the effectiveness of chlorine dioxide for preoxidation was evaluated at
doses from 0.8 to 3.0 mg/L, and the distance that a free residual could be sustained through the
plant was determined. Distribution system DBP levels and chlorite levels were also examined.
It was possible to carry a chlorine dioxide residual through the clarifier, thereby providing a
significant disinfection barrier; however, a relatively high dose of chlorine dioxide was needed.
Disinfection byproduct levels in the distribution system declined significantly as a result of the
substitution of chlorine dioxide for pre-chlorine.
This study was unique in that the chlorite removal ability of both newer and spent GAC filter
media was evaluated side by side in a full-scale application. In order to examine the influence
of GAC age and natural organic matter (NOM) saturation on chlorite removal, the media in
two of their three GAC filters was replaced before the start of the full-scale trial. The 3-year old
media in the third filter was not replaced, thereby providing an opportunity to evaluate chlorite
removal through new GAC filter media with filter media close to NOM saturation. The filter
containing the newer GAC media removed the majority of chlorite, while the filter containing 3
year old spent media exhibited a limited capacity for chlorite removal which continued to
decline throughout the study.
The study concluded that chlorine dioxide could be a viable alternative to prechlorination;
however, it was not considered favorable to carry a chlorine dioxide residual through the plant
due to the high doses required. The GAC filters were expected to control chlorite levels and
compliance with the 1.0 mg/L chlorite maximum contaminant level (MCL) in finished water;
however, modification of the GAC filter media replacement schedule was recommended. Includes 7 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 20 |
| Published : | 11/15/2004 |
