AWWA ACE95255

AWWA ACE95255 Enhanced Coagulation With and Without Pre-Ozonation for Turbidity, NPOC and Color Control
Conference Proceeding by American Water Works Association, 01/01/1995

Anderson, W.B.; Douglas, I.P.; Van Den Oever, J.; Hunsinger, R.B. ; Huck, P.M.

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The Britannia Water Purification Plan in Ottawa, Canada, which treats a low alkalinity, colored water, currently practices prechlorination and low pH coagulation (pH 5.8) at full scale. However, with a view to overall process optimization the utility is examining a number of treatment alternatives. This paper reports on a pilot scale comparison of enhanced alum coagulation, as currently practiced, to acid enhanced alum coagulation with and without pre-sedimentation ozone. Because of sludge handling considerations, reduced alum dosages were investigated in the experiments involving pre-sedimentation ozonation. Process performance was assessed on the basis of nonpurgeable organic carbon (NPOC), UV absorbance, turbidity and color reduction. During this study it was observed that a minimum alum dose of 30 to 35 mg/L had to be applied (regardless of coagulation pH) before floc formation occurred. This was attributed to the elevated humic fraction of the raw water.