Tiefenfilter

Tiefenfilter, or depth filter, is a filtration method in which filtration occurs throughout the thickness of a porous medium rather than mainly at its surface. The filter bed has a layered or fibrous structure with decreasing porosity, so incoming liquid passes through many small pores and particles are captured within the depth of the medium. This produces a gradual reduction of suspended solids and a high overall dirt-holding capacity.

The filtration mechanism combines several processes. Particles are intercepted or wedged in the pore network, while diffusion and adsorption draw smaller particles into the internal structure. As solids accumulate, a porous filter cake forms within the bed, which further increases removal efficiency. Depth filters are typically designed to handle varying load without a rapid rise in pressure, making them relatively tolerant of fluctuating turbidity.

Materials and configurations vary. Common media include nonwoven cellulose or glass fibers, polypropylene, and layered media mixed with mineral granules such as sand or anthracite. Depth filtration cartridges and multilayer filter packs are widely used in water treatment, beverage production, pharmaceuticals, and industrial process streams. In many installations, depth filters serve as prefilters to remove bulk solids before finer filtration steps or membrane processes.

Operation and maintenance involve periodic cleaning to restore flow. Backwashing or reverse-flow operations remove accumulated solids and restore porosity. The service life depends on influent quality, flow rate, media type, and cleaning effectiveness.

Advantages of Tiefenfiltering include high dirt-holding capacity, robustness to shock loads, and good performance with turbid or colloidal suspensions. Limitations include lower precision in particle sizecutting and the need for periodic replacement or regeneration of filter media. See also filtration, surface filtration, and membrane pretreatment.