The mechanical cleaning is divided into three stages. First, the wastewater flows into a basin in which a screen is installed. A rake is a grid of bars, which is intended to prevent coarser and finer impurities such as faeces, textiles, wood and stones from flowing through. These detained impurities are called screenings and are removed from the basin. Next, the water flows into a sand trap basin, where heavier substances such as sand sink to the ground and lighter substances such as fats and oils float on the water surface. In this way, the floating substances can be skimmed off. The water then flows into a primary clarifier, where the remaining sinkable substances sink to the bottom and separate from the water.

After the primary clarifier the biological cleaning starts. This is divided into two stages. First, the water enters an activated sludge tank. There, bacteria ensure that the suspended matter, which could not sink and can only be recognized as turbidity of the water, is decomposed or flocculated. So that the bacteria can work, the tank is aerated with oxygen. After the flocculation of the suspended particles, they can sink to the bottom in the secondary clarifier and also be removed from the water. The clean water is then discharged into the river. The sunk substances in the secondary clarifier are called sewage sludge. The sludge is partially returned to the activated sludge tank. The other part is led into a digestion tower. Gases are produced there which can be used to generate energy. The remaining sludge is used as fertilizer, for example.

• Mud
• Urin
• Toilet paper
• Sand
• Wood

Do not throw garbage into the toilet or drain that could block the sewer or damage the pumps. In addition, no substances should enter the sewer that could be toxic to the bacteria in the sewage treatment plant or later to the animals in the river.

• Food leftovers
• Hygiene articles such as diapers, tampons, bandages etc.
• Cigarettes
• Cat litter
• Paints, varnishes and wood preservatives
• Acids and alkalis
• Solvents of all kinds
• Engine oils and fats
• Special cleaner such as oven and grill cleaner
• Disinfectants
• WC Beckenstein
• Drain cleaner
• Plant protection products
• Pesticides and pesticides
• Drugs