Filtration of clayey sludge by the use of geotextiles: experimental study

The filtration of granular soils in suspension in water has been widely studied and is used since many years in different applications. Nevertheless, the geotextile filtration of fine particles in suspension in water, or of clayey sludge, is more complex; in practice when geotextiles are used in such application, additives, like flocculants, are generally considered necessary to postpone (or avoid) the apparition of the “filter cake”. The original present study aims to precise more systematically the influence of the geotextile characteristics on the formation of the filter cake, without flocculants. The influence of the key parameters is analysed and discussed in detail. They include the type of soil, the concentration of fines, the type of water flow and the type of geotextile, by a specifically developed testing device with one horizontal cell ended by the tested geotextile placed vertically. The performance of the different systems is compared based on the analysis of the retained and passing soils, the time for clogging, and the global characteristic of the “filter cake”. As the permeability of the system will change with the creation of this “cake”, the initial permeability of the geotextile is less important than the influence of the geotextile on the creation process of the filter cake. Some criteria to optimize the selection of the geotextile for filtration of fine particles in suspension are proposed. This study allows showing the interest of geotextiles of low opening size and between these different geotextiles with O90 ≤ 60 micrometers, the thermally bonded nonwoven structure seems to offer the best compromise between the opening size and the support for a filter cake suitable for the long-term permeability of the system.