A centrifugation method for the assessment of low pressure compressibility of particulate suspensions
Dann Curvers¹, Hans Saveyn¹ Peter J. Scales², Paul Van der Meeren¹, Chemical Engineering Journal (2008) doi:10.1016/j.cej.2008.09.030
This work describes an easy methodology for assessing the compressibility of particulate suspensions
at relatively low pressures. The material used in this study was an anaerobically digested waste water
sludge. Using a centrifuge, the equilibrium sediment bed height was recorded as a function of rotational
speed during the centrifugation. This approach avoids errors due to expansion of the sediment bed after
the centrifugation is stopped, a phenomenon typically seen with waste water sludges. A straightforward
numerical method was used to solve a one-dimensional centrifugation model describing the equilibrium
sediment bed height as a function of rotational speed. It has been shown that this approach yields realistic
results. The one-dimensional model is able to describe the compressibility of the anaerobically digested
sludge. Besides yielding a close fit for the measured sediment bed heights, extrapolating these results
to a different initial solids volume fraction resulted in a good prediction of the bed height as well. Different
constitutive equations for the relation between solids pressure and solids volume fraction were
assessed. The typical power law functions [F. Tiller, W. Leu, Basic data fitting in filtration, Journal of the
Chinese Institute of Chemical Engineers 11 (1980) 61–70], often used in filtration modelling, were the
most adequate for describing the compressional behaviour of the sludge. A functional relation based on
the osmotic pressure within the solids network, suggested for describing the phenomenology of filtration
dewatering [K. Keiding, M. Rasmussen, Osmotic effects in sludge dewatering, Advances in Environmental
Research 7 (2003) 641–645], could not be used to adequately describe the behaviour of the sludge at the
low pressures generated during centrifugation.
Key words: Centrifugation • Modelling • Sludge • Dewatering • Filtration • Compressibility
¹ Particle and Interfacial Technology Group, Faculty of Bioscience Engineering, Ghent University, 9000 Ghent, Belgium; Particulate Fluids PRocessing Centre, University of Melbourne, Vicotria, Australia²Contact us
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