Methods for determining the settling velocity profiles of solids in storm sewage

Author:

Aiguier Emmanuelle1,Chebbo Ghassan2,Bertrand-Krajewski Jean-Luc3,Hedges Peter4,Tyack Naomi5

Affiliation:

1. CERGRENE (ENPC), La Courtine, 93167 Noisy Le Grand Cédex, France and SAINT-DIZIER, 8, rue de Sèvres, 92100 Boulogne, France

2. CERGRENE (ENPC), La Courtine, 93167 Noisy Le Grand Cédex, France

3. CIRSEE, 38, rue du Président Wilson, 78230 Le Pecq, France

4. Department of Civil Engineering, Aston University, Aston triangle, Birmingham B4 7ET, UK

5. Division of Civil Engineering, University of Hertfordshire, Hatfield AL10 9AB, UK

Abstract

Recently, research has shown that a settling process is an efficient treatment for the removal of suspended solids from storm sewage. In order to design settling tanks, there is a need to determine the settling velocity characteristics of these solids. Devices and test methods for measuring settling velocities of solids in storm sewage have been developed by researchers. A literature review has revealed that the settling velocity profiles obtained with some methods (Chebbo, 1992), (Michelbach and Wohrle, 1993) and (Tyack et al., 1993) are very different. In order to explain why the results are different and to quantify the influence of the experimental procedure on the settling velocity grading curves, we have compared the selected methods when tested with the same sample and we have studied the effects of the conservation of the sample before the test, of the concentration of solids in the device and of the nature of the water on the settling velocity profiles. The results of the comparative tests indicate that the settling velocities are significantly lower with both the Cergrene and Aston methods than with the UFT test procedure. Moreover, the study has shown that the settling characteristics of solids change with time, that the use of sewage liquor rather than demineralised water or drinking water can change the results of the measurement and that the higher the concentration of solids, the greater the velocity of settled particles.

Publisher

IWA Publishing

Subject

Water Science and Technology,Environmental Engineering

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