期刊
WATER RESEARCH
卷 90, 期 -, 页码 119-127出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.watres.2015.12.018
关键词
Ballasted flocculation; Floc density; Floc size; Floc shape; Optical microscopy; Settling velocity
资金
- Veolia Water Technologies Canada, Inc.
- City of Montreal
- City of Laval
- City of Repentigny
Ballasted flocculation is widely used in the water industry for drinking water, municipal wastewater, storm water and industrial water treatment. This gravity-based physicochemical separation process involves the injection of a ballasting agent, typically microsand, to increase the floc density and size. However, the physical characteristics of the final ballasted flocs are still ill-defined. A microscopic method was specifically developed to characterize floc 1) density, 2) size and 3) shape factor. Using this information, probability density functions (PDFs) of the floc settling velocity were calculated. The impacts of the mixing intensity, polymer dosage, microsand size and contact time during the floc maturation phase were assessed. No correlation was identified between the floc diameter, form and density PDFs. The floc equivalent diameter mainly controls the settling velocity (r = 0.94), with the floc density (r = 0.26) and shape factor (r = 0.25) having lower impacts. A velocity gradient of 165 s(-1) was optimal to maintain the microsand in suspension while simultaneously maximizing the floc diameter. An anionic high molecular weight polyacrylamide formed 1.5-fold larger aggregates compared with the starch based polymer tested, but both polymers produced flocs of similar density (relative density = 1.53 +/- 0.03). Generally, the floc mean settling velocity is a good predictor of the turbidity removal. An in-depth analysis of the floc characteristics indicates a correlation between the floc size and the largest microsand grain potentially embeddable in the floc structure. (C) 2015 Elsevier Ltd. All rights reserved.
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