Optimisation of floc-stability by mechanical pre- and post-stressing

J. A. Müller and S. K. Dentel


In the presented research work, the influence of mechanical shear stress on the structure and dewatering properties of flocculated sewage sludge is investigated. Shear forces are applied before, during and after floc formation. Linear and x-linked polymers are used for conditioning.



Best dewatering results are obtained only if polymer dose, mixing intensity and mixing time are matching. Sludge-stressing prior to conditioning will lead to more shear-sensitive flocs. Stronger flocs that can withstand extended shear stress in the subsequent dewatering process are formed by increased shear during conditioning. Using low shear forces during conditioning, a higher dosage of flocculants is necessary to achieve the same results in shear intensive dewatering processes. Shear resistant flocs can be obtained by application of x-linked polymers, but will require a higher polymer dosage. Filamentous flocs can be destroyed by shear forces while a better sedimentation is attained.


J. Müller und S. Dentel (2002). Optimisation of Floc-Stability by Mechanical Pre- and Post-Stressing,in: H. H. Hahn, E. Hoffmann und H. Odegaard (Eds.) "Chemical Water and Wastewater Treatment VII6quot;, Proceedings of the 10th Gothenburg Symposium, Gothenburg, Sweden, June 2002, 297 - 307, ISBN 1-84339-009-4

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