Filtration is one of the oldest known water treatment processes. It is a very effective and inexpensive process, characterized by great robustness and flexibility. There is a wide range of possible applications.
Filtration is a mechanical process for the separation of solids. Various materials are used as filtration media, primarily debris made of sand, gravel or other granular materials such as hydro-anthracite and pumice. The multi-layer filters are used as pressure filters from top to bottom. A distinction is made between different process steps in the course of a filtration cycle. During filtration, the water to be cleaned flows through the filter support layer at a specific velocity. During filtration, the filter filling fills up with solids and a differential pressure increase occurs across the filter medium due to "clogging". This causes dirt particles to accumulate in the cavities of the filter medium. By backwashing the filter, the cavities can be cleared of the dirt particles.
Multi-layer filters can be used in almost all areas to retain undissolved solids. They are used, for example, in chemical-physical wastewater and recycled water treatment for fine filtration prior to the final inspection, for the treatment of surface water and groundwater, and in cooling water treatment. In ReUse applications, multilayer filters are often used as the first stage followed by further treatment by ultrafiltration and reverse osmosis.