The effects of shear on the formation and break-up of flocs generated using aluminium sulphate (“alum”), polyaluminium chloride and a cationic polyelectrolyte have been investigated using conventional jar test procedure and by continuous optical monitoring. Using the experimentally determined optimum dosage, the breakage of flocs was followed at a high stirring speed, corresponding to average shear rate (G) of about 330-520 s-1. Most of the breakage occurred within a few seconds of increasing the shear rate. After each breakage the stirring rate was reduced to the original value to allow the flocs to re-grow. For alum and polyaluminium chloride, it was found that only limited re-growth of flocs occurred indicating a significant irreversibility of the floc break-up process. Residual turbidity increased after floc breakage and re-growth, indicating a reduction in sedimentation rate of the re-grown flocs, consistent with the continuous monitoring results. For the cationic polyelectrolyte, the re-growth of flocs occurred to a much greater extent and floc breakage was almost fully reversible.
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Research Article|
December 01 2002
Properties of flocs formed using different coagulants Available to Purchase
M.A. Yukselen;
M.A. Yukselen
*Marmara University, Department of Environmental Engineering, Kadikoy 81040, Istanbul, Turkey
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J. Gregory
J. Gregory
**Department of Civil and Environmental Engineering, University College London, Gower Street, London WC1E 6BT UK. Corresponding author
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Water Supply (2002) 2 (5-6): 95–101.
Citation
M.A. Yukselen, J. Gregory; Properties of flocs formed using different coagulants. Water Supply 1 December 2002; 2 (5-6): 95–101. doi: https://doi.org/10.2166/ws.2002.0156
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