General Sewage Technology

High-quality light-weight aggregate concrete from wastewater sludge for the construction industry

The method presented for utilising wastewater sludge is based on the PORDOUR process. It provides the opportunity to produce high-quality light-weight aggregate concrete from wastewater sludge and to thereby make us of its material and energetic properties.


During wastewater treatment, sludge accumulates which needs to be recycled or removed. Agricultural recycling poses a problem, and landfilling has not been possible anymore since the year 2005. Also, sludge incineration is  not suitable due to high ash accumulation.
Therefore this project introduces an alternative method to recycle wastewater sludge, whereby material and energetic properties are both utilised. The so-called PORDOUR method produces light-weight aggregate concrete for the construction industry. In this method, pellets are formed from the raw material, and subsequently undergo a thermal treatment. During combustion, the organic substances are oxidised and combustion gases blow up the pellets. The resulting construction materials are neither flammable nor degradable, and must not be treated with flame-resistant materials, fungicides or insecticides.


  • Longer pre-heating time, higher pre-heating temperatures, or (partial) addition of air result in an increased overflow of combustible substances.
  • The organic reduction should take place in such a way that the pellets do not stick together later. However, a reduction too large in degree lowers the pellet volume too extensively.
  • Environmental research shows that toxic organic materials are almost completely destroyed and heavy metals become stably fused. This holds true irrespective of the sludge used and the furnace atmosphere. The relevant regulations of  the DIBt-info sheet have been fulfilled.
  • The light-weight aggregate concrete produced from sludge does not show any disadvantages compared to the conventional products. This product can be used without any risks.
  • The PORDOUR method with 100% sludge usage delivers the best result as compared to various other methods, and compete with high quality swelling clay products.

More Project Information

Project title: Laboruntersuchungen zur Herstellung qualitativ hochwertiger Leichtzuschlagstoffe aus Klärschlamm für die Bauindustrie

Project number: 02WS0185

Project period: 2002 - 2005

Project region: Germany (Baden-Württemberg)

Project contact:

Herr em. Prof. Dr.-Ing. E.h. Ph.D. Hahn

+49 (0)721 / 608-42457
+49 (0)721 / 608-44151

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Source: German National Library of Science and Technology Hannover (TIB)