Activated sludge dewatering in a filtration compression cell: deviations in comparison to the classical theory
Résumé
Wastewater treatment plants produce a residue that must be usually dewatered to reduce volume before handling and disposal, but operating parameters may impact activated sludge dewatering. On the one hand, the results obtained from tests conducted in the filtrationcompression cell (FCC) show an impact of the initial slurry concentration and its amount on filtration kinetic. However, a scaling with respect to the initial amount enables an interesting representation of these data. On the other hand, the working pressure does not modify filtration kinetics, but it has a significant effect on the expression stage. Larger amount of filtrate is extracted when a higher pressure is applied for the expression stage. Moreover, the squeezing ability of the filter cake greatly depends on the time when the pressure step is applied. All these results are not fully modelled by the current theories, and Ruth's equation, which is commonly used, has its limitations in being able to properly describe activated sludge filtration. Because the visco-elastic behaviour of filter cake is generally not considered by classical dewatering models, further work is needed to take into account this phenomenon.