The objective of this study was to gain an understanding of the factors affecting the stability of
monochloramine in waters treated by ozone-biologically activated carbon (BAC) processes. The kinetics of monochloramine
decay in both natural and synthetic waters were determined by bench-scale batch experiments.
Natural waters were sampled at various treatment stages in David L. Tippin Water Treatment
Facility (DLTWTF) located at Tampa, Florida. The laboratory synthetic waters were prepared with
standard Suwannee River natural organic matter (NOM). Treating ozonated waters by BAC filters at the DLTWTF resulted in substantial loss of
monochloramine stability in spite of total organic carbon (TOC) and turbidity decrease and pH increase.
Monochloramine was the least stable in the samples collected immediately after the filter
backwashing. The kinetics of monochloramine decay were found to be related to the amount of
particles generated by the BAC filters. Consequently, filtering the BAC effluents with 1.2 µm
and 0.4 µm polycarbonate iso-pore filters resulted in dramatic increase in monochloramine
stability.
Similar phenomena have been reported in literature and some researchers have postulated
that the increase in monochloramine demand in the BAC filter effluents might be caused by
activated carbon fines produced from extensive abrasion of GACs during backwashing.
This hypothesis was proven invalid in this study. Controlled addition of fine particles of GACs
up to 1 mg/L did not show any appreciable change in monochloramine decay kinetics in organic-free
synthetic waters. In contrast, addition of GAC fines to the ozone treated natural water
samples obtained from the DLTWTF resulted in a decrease of the chloramine demand. Further
batch kinetic experiments performed with commercial powdered activated carbon (PAC, WPL
carbons, Calgon Corp., Pittsburg, PA) suggested that monochloramine demand by PAC was also
negligible up to a PAC concentration of 1 mg/L. Includes 10 references, table, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 190 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 5 |
| Published : | 11/01/2005 |
