Characterizing flocculation under heterogeneous turbulence
- Department of Civil Engineering, North Carolina State University, 208 Mann Hall, Raleigh, NC 27695-7908, USA
- Received 5 November 2002
- Accepted 18 April 2003
- Available online 3 July 2003
Abstract
This study investigated the impact of turbulent heterogeneity in a flocculation reactor on particle aggregation and breakup. In particular, the influence of average characteristic velocity gradient (G), particle concentration, and coagulation mechanism (sweep floc vs charge neutralization) on the floc growth, steady-state size, and variance was analyzed. Experiments were performed in a bench-scale reactor with a low-shear axial-flow impeller using a photometric dispersion analyzer (PDA). Results indicated that as G increased, floc growth increased while the mean size and variance in the floc size distribution decreased. In addition, floc growth, mean size, and variance increased with increasing primary particle concentration and when the coagulation mechanism was switched from charge neutralization to sweep floc. Lastly, floc growth, mean size, and variance were found to vary spatially in the reactor at low G values with larger floc size and growth rate in the bulk region and a larger variance in the impeller discharge region.
Keywords
- Flocculation;
- Heterogeneous turbulence;
- Mixing;
- Water treatment
Figures and tables from this article:
- Fig. 1.
Schematic of experimental setup.
- Fig. 2.
Ratio distribution curve (a) with one steady-state region, (b) with a lower steady-state region following a maximum.
- Fig. 3.
Best-fit line approximation of linear growth region.
- Fig. 4.
Differences in floc structure and its association to variance.
- Fig. 5.
Slope vs G value. Comparison of floc growth at different experimental conditions. 50=50 mg/l; 100=100 mg/l; SF = sweep floc; CN= charge neutralization; I = impeller discharge region; B = bulk region.
- Fig. 6.
Ratio vs G value. Comparison of floc size at different experimental conditions. 50=50 mg/l; 100=100 mg/l; SF = sweep floc; CN = charge neutralization; I = impeller discharge region; B = bulk region.
