1. The mechanical stage: a mechanical purification stage is required before the biological treatment. This stage can be carried out using a multi-chamber-pit, a pre-treatment tank or a self-cleaning drum filter. Each system is designed for recirculation of water from the biological stage, thus allowing for activation denitrification during the mechanical stage.
2. The biological stage: the biological purification of the sewage water is effected by rotating immersion discs (fix film reactors) mounted vertically on a horizontal rotating stainless steel shaft. By its rotation the disk package is exposed alternately to the wastewater and the atmospheric air. The fixed film of micro-organisms, which perform the biological treatment by decomposing soluble and suspended organic material, is attached to the surface of these disks. This biomass grows naturally by itself on the disks, while clogging is prevented by using especially designed plain disk units. When the wastewater flow to the system is high or low, a flow control unit before the disks keeps the hydraulic pressure at a constant level.
3. The clarification stage: after the biological purification process, the water is led to a Lamella-separator, where excess sludge is removed periodically from the clean water into the sludge pit. The Lamella separator is specially designed for a final clarification, using the physical effect of gravity in a highly efficient sedimentation process.