All clear!

Cotton swabs, leftover food, faeces, packaging disposed of in the toilet: sewers are a kind of collecting basin for our civilisation. And the water is expected to go back into our lakes and rivers? Of course. Continue reading

For decades, sewage treatment plants have ensured that wastewater is free of impurities and harmful bacteria. And not only that: the sewage sludge, which consists of water as well as organic and mineral substances, is often used as fertilizer in agriculture. Also with the help of Kuhn Special Steel.

What does the sewage treatment process look like?

Today, almost 100 % of the wastewater produced is treated in sewage treatment plants with four purification stages:

  • mechanical stage for filtering and sorting out the coarse objects
  • two biological stages, during which bacteria break down organic material in wastewater and nitrogen compounds
  • chemical stage in which various substances such as phosphates are removed.

In the process, solids settle as sludge on the bottoms of the pre-treatment and flocculation tanks. This sludge is disposed of – either by being incinerated or used as fertilizer.

Better sludge

Different types of sludge are produced during the individual stages in wastewater treatment. In order to keep soils and waters clean, the sludge produced must be efficiently separated. The preferred technology: industrial centrifuges with decanters.

Two objectives are important in the separation process:

  • stabilised sludge: this means that the carbon contained in the sludge is broken down as much as possible.
  • reduced sludge volume: every tenth of a percent more dry matter in the sludge reduces the costs of sludge disposal and thus also the costs of our drinking water.

Modern dewatering decanters achieve a high dry matter content. During the thickening process, conveyor bodies ensure that as many solids as possible are separated. The decanters concentrate the dry matter content of the sewage sludge down to a few percent. This reduces transport and landfill costs. They also break down polymers so that the sludge can be used as fertilizer.

Resistant to wear

For the decanters, the centrifuge constructors rely on decanter drums and conveyor bodies from Kuhn Special Steel. The components produced by centrifugal casting are particularly resistant to abrasive wear and corrosion. They require less maintenance or need to be replaced less frequently. This also ensures lower costs for wastewater treatment. Clean and cheap water – that is what our components help to achieve.

Photo: © Pedro B.Cali –


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