The biofilter functions on a biological basis. The filtration process at the Biofilter takes place in several steps. The Biofilter initially cleans rainwater through sedimentation. The inorganic particles in the rainwater settle thanks to the gentle feed operation. In addition to sedimentation, this quiet supply also provides an enrichment of the water with oxygen. This strengthens the biological cleaning. The specially designed filter housing creates a biological balance with a strong cleaning effect. In the Biofilter, a sedimentation layer forms that supports and strengthens biological processing. Organic particles are broken down and mineralized. Components have been built into the Biofilter to ensure optimal operation of biological cleaning with oxygen. The Biofilter copies, as it were, the natural cleansing of water as it happens in nature.