Recycling sewage sludge

Increased costs of disposal and transport show environmental and economic opportunities to reduce the mass of sewage sludge to a minimum.

Valorising sewage sludge?

Here are some reasons to valorise sewage sludge.
- Bad smells are reduced or removed.
- The mass of sludge to be stored and disposed of is reduced.
- Sludge physical characteristics are improved (stabilisation, look, LHV).
- Pathogenic micro-organisms are eliminated.

Measuring sewage sludge moisture?

Measurement of the water content in sewage sludge contributes to characterize and monitor sludge and it’s essential to define its final destination and avoid dust creation. Indeed, the targeted water content depends on installations of valorisation –agricultural valorisation, storage, co-incineration and incineration–. On the other hand, if the sludge is too dry, it gets dusty which is unhealthy for the operators and harmful for environment.

Sewage sludge drying

At the end of wastewater treatment, sewage sludge water content is about 99% of the raw matter. By evaporation, sewage sludge loses all or part of its water and becomes solid.

Sludge drying beds for part drying

The technique of drying beds is done outdoors on liquid sludge and combines natural evaporation and free water drainage through a filter layer of sand and gravel. This extensive system, depending on weather conditions, gets the solid sludge to 35-40% of dry content.

Thermal drying or total drying

Thermal drying allows virtual elimination of water (dry content around 95%). The resulting sludge is either powder or granules/pellets. Thermal drying should develop in the coming years because other systems for sludge treatment, including incineration, are more expensive as a result of new regulatory and economic conditions.