| Focus 1/3 | Sewage sludge: a boon for agricultural land?

Liming and thermal treatment of sewage sludge

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Figure 1. Liming of sewage sludge [Photo source: Pixabay]
The addition of quicklime (Figure 1) to sludge makes it possible to:

  • increase dryness to a value of 30% dry matter content.
  • increase the pH above 12 to slow down pathogenic activity.
  • reduce or even eliminate bacteria thanks to the exothermic reaction (temperature of around 60°C) produced by the contact between sludge and quicklime.
  • slow down anaerobic fermentation, which generates unpleasant odours

Thermal sludge is sludge that has been treated with heat (heated at a minimum of 190°C for 45 minutes at 20 bar pressure) and dehydrated either by filter press or mobile centrifuges.

In both cases, the sludge is said to be “sanitised”.