Abstract
The mechanical dewatering of biological materials, such as activated sludge, is troublesome due to their high compressibility. The dewatering can be improved drastically by the use of electro-osmosis, a technique in which a direct current electric field is applied to the filter cake, inducing an electro-kinetic displacement of the liquid phase. In this article, a model is presented which describes this process for a one-dimensional, one-sided filter press. The model starts from two existing models, each describing a part of the process [Iwata, M., Igami, H., Murase, T., 1991. Analysis of electroosmotic dewatering. Journal of Chemical Engineering of Japan 24(1), 45–50; Sørensen, P.B., Moldrup, P., Hansem, J.A., 1996. Filtration and expression of compressible cakes. Chemical Engineering Science 51(6), 967–979]. A robust solution scheme for the basic flux and continuity equations is used to describe filtration and expression. Regarding the electro-osmosis, an adapted form of the Darcy equation, expressing electro-osmotic induced flow as well as pressure induced flow, is integrated into the former solution scheme. This permits the simulation of the overall process using a single model. Validation of the model revealed that the experimental piston height during dewatering can be described accurately provided that temperature effects are taken into account.
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