Pre-Treatment Step

In the mechanical pre-treatment step, solids, sediment particles and floating particles such as fat are separated. Different technologies are used depending on the plant size.

For smaller units, a multi-chamber pit (following DIN 4261 Part 1), is recommended. The first chamber represents the main part of the total volume. In this chamber, the primary sludge, consisting mostly of feces, cellulose, food rests and secondary sludge is stored. The chambers are connected via diving walls so that no floating sludge can pass through. In 3-chamber-pits, a reduction of the organic load of about one third can be taken into account.

For bigger plants, conventional pre-treatment steps are used, such as the Emscher Tank. Additional reaction tanks in the pre-treatment area are required if an up flow denitrification (see also biological step) is foreseen. With these tanks a further reduction of the organic load can be achieved.


The retention time of the raw wastewater in the pre-treatment step should be less than 1.5 – 2.0 hours.

The pre-treatment step can be extended on demand by elements such as screening units, rotating drum sieves, grit chambers and grease traps.

For smaller units, System S&P® relies on traditional and economic multi-chamber pits in prefab construction. For bigger System S&P® wastewater treatment plants, additional rotating drum sieves are used. If plants are run on a mixed system, one inlet for storm water and wastewater and then a grit chamber are used. Already existing nonaerated wastewater ponds can be extended following the current state-of-the-art designs by System S&P® wastewater treatment plants.