Floc Size Distributions in Dissolved Air Flotation of Winnipeg Tap Water

Author: Gorczyca B.   Zhang G.  

Publisher: Taylor & Francis Ltd

ISSN: 0959-3330

Source: Environmental Technology, Vol.28, Iss.3, 2007-03, pp. : 243-254

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Abstract

A bench-scale continuous flow dissolved air flotation (DAF) system was operated using Winnipeg tap water. Three different dosages of alum were applied: 41.7 mg l−1, 25.5 mg l−1 and 15.5 mg l−1. Floc size distributions formed at different coagulant dosages were analyzed to identify characteristics of floc size distribution optimal for flotation. Alum dose of 25.5 mg l−1 was found to be optimal for the bench scale DAF unit in this study. At this dosage, the DAF effluent achieved a turbidity of 0.25 NTU and color of 3.8 TCU, significantly lower than that for the tap water. The optimum floc size distribution at the dose of 25 mg l−1 had the logarithmic mean size of 27 m which was close to the size of air bubbles produced by the saturator in this study (30 m). The results of this study suggest that the DAF treatment process is optimized when the logarithmic mean floc size and bubble size are equal.