Waste products from wastewater treatment

Waste products from wastewater treatment

The waste products from wastewater treatment add up to the following amounts per inhabitant and year:
  • 80 kg of sewage sludge per inhabitant and year

Sewage sludge is made of solid and liquid components as the result of various stages of wastewater treatment: after the mechanical or biological treatment stage (primary sludge or excess sludge).
Organic components are further decomposed in the process of aerobic and anaerobic stabilisation of the sewage sludge, which makes the sludge less reactive. Moreover, the content of water is reduced by mechanical or biological means, which makes it possible to reach, for example, a dry matter content of 35 per cent in excess sludge. The resulting sewage sludge is then composted, used in agriculture, or incinerated.
 

  • 7 kg of sand per inhabitant and year

The grit chamber is a sedimentation basin and part of the mechanical treatment stage. It is designed to remove larger separable, inorganic components out of the wastewater, e.g. sand, stones, or grit. These materials would lead to operational disruptions and breakdowns of the plant (wear and tear, blocking). The sand is ultimately disposed of.
 

  • 2 kg of screenings per inhabitant and year

Screenings are the result of the first mechanical treatment stage and primarily consist of foreign and interfering materials that should not be disposed of via the sewer system, e.g. hygiene products (cotton buds, wipes etc.). The screenings are incinerated.
 

  • 1 kg of fat per inhabitant and year

In line with the grit chamber, the wastewater treatment process filters out fats which would otherwise disrupt the microbiological decomposition. A fat separator works purely physically according to the principle of gravity, meaning that the specifically lighter fats and oils float on the surface of wastewater. These fats and oils are then used in biogas plants.