AWWA WQTC62501

AWWA WQTC62501 Factors Affecting Monochloramine Stability in Ozone-BAC Process
Conference Proceeding by American Water Works Association, 11/01/2005

Marda, Saurabh; Kim, Dooil; Pierpont, John; Kim, Myung J.; Craig, Marjorie; Perdue, Michael; Amirtharajah, Appiah; Kim, Jae-Hong

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The objective of this study was to gain an understanding of the factors affecting the stability ofmonochloramine in waters treated by ozone-biologically activated carbon (BAC) processes. The kinetics of monochloraminedecay 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 TreatmentFacility (DLTWTF) located at Tampa, Florida. The laboratory synthetic waters were prepared withstandard Suwannee River natural organic matter (NOM). Treating ozonated waters by BAC filters at the DLTWTF resulted in substantial loss ofmonochloramine 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 filterbackwashing. The kinetics of monochloramine decay were found to be related to the amount ofparticles generated by the BAC filters. Consequently, filtering the BAC effluents with 1.2 mand 0.4 m polycarbonate iso-pore filters resulted in dramatic increase in monochloraminestability.Similar phenomena have been reported in literature and some researchers have postulatedthat the increase in monochloramine demand in the BAC filter effluents might be caused byactivated carbon fines produced from extensive abrasion of GACs during backwashing.This hypothesis was proven invalid in this study. Controlled addition of fine particles of GACsup to 1 mg/L did not show any appreciable change in monochloramine decay kinetics in organic-freesynthetic waters. In contrast, addition of GAC fines to the ozone treated natural watersamples obtained from the DLTWTF resulted in a decrease of the chloramine demand. Furtherbatch kinetic experiments performed with commercial powdered activated carbon (PAC, WPLcarbons, Calgon Corp., Pittsburg, PA) suggested that monochloramine demand by PAC was alsonegligible up to a PAC concentration of 1 mg/L. Includes 10 references, table, figures.