Mechanical treatment

About 40 million m³ of wastewater flow from the cities and municipalities of the Steinhäule Treatment Plant Administrative Union to the treatment plant at the river Danube every year. Mechanical treatment processes clean the water by up to 15% before it moves on to the biological treatment part of the plant. During the mechanical treatment process, substances are removed as settleable solids or suspended solids based on their weight. The wastewater first flows through the grit chamber and grease trap, then into the fine screen system and finally into two primary clarifiers.


01 Aerated grit chamber

Illustration Sand- und Fettfang

The wastewater’s reduced flow rate allows heavy substances, such as sand, gravel and rocks, to sink to the grit chamber bottom. The sand is regularly pumped out, washed and used in thermal recycling. The water in the grit chamber is aerated to ensure that no organic settleable solids sink to the bottom. This improves the buoyancy of the suspended materials and fatty substances, which are separated from the water in a second chamber and subsequently thermally recycled.

02 Fine-screen system

Illustration Feinrechenanlage

The screen consists of parallel steel rods installed at a distance of 6 mm into the inflow channel. The screen captures coarse waste materials, such as toilet paper. These materials are thermally recycled in the incineration plant.

03 Primary Clarifier

Illustration Vorklärbecken

More settleable and sus­pended materials are removed in the primary clarifier. Materials that are heavier than water settle during lower flow rates. The scraper shield pushes the resulting sludge into the sludge hoppers, from where it is pumped to the sludge treatment. Substances that are lighter than water float on top, are removed from the water’s surface and are also thermally recycled.

Mechanical wastewater treatment is complete after these processes are finished. The wastewater still contains 85% of its overall contamination in a dissolved and finely dispersed state.