Heat from sewage

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Short description

Different shape of the pipe for more efficient heat recovery


Reducing the cross-section makes the pipe more efficient as heat exchanger. Sewage is always there, in every city, it flows and it’s hot. A Swiss engineer invented a system to recover heat from sewage. The base is a heat exchanger which consists of a concrete gutter with pipes. It reduces the cross-section of the gutter at the bottom of a sewer pipe. This causes the sewage always fast enough, even at low water. It took to the engineer more than a decade to design concrete elements that are robust enough for fifty years (which is actually the life of a sewer). Worldwide there are now about fifty “Riothermie” (this is the name of the system) systems in the sewers; The Netherlands will have the first two systems next year. The average temperature at which water flows into the sewer, is 23 degrees Celsius, while the sewer itself on a winter day is about six degrees. The heat exchanger can be used thanks to this temperature difference in order to save energy. With this heat the device will be useful to heat houses and domestic hot water needs. The energy can also be used to cool buildings and it can be stored in a thermal storage system.








Material flows

  • Inputs

  • ->
  • ->
    mechanical device
  • Outputs

  • heat for households

Qualitative Analysis

Description of the Process

In the Netherlands, Eneco is building now the first Riothermie system in the Harnaschpolder near Delft. The heat will be used for heating homes and other buildings in the new district Harnaschpolder. The municipality of Enschede during the next year will equipped with a Riothermie system the pipe between the city sewer and sewage treatment. This is a pipe with a diameter of 2.2 m (the thickest of the Netherlands). The sewer, will provide heat to the citizens of Enschede, for their shower and toilet discharge, in an apartment complex of 220 dwellings.

Details of the processes in the project

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