Water pollution control - Energy recovery from sludge

Wastewater treatment plant sludge is the residue of industrial and domestic wastewater treatment. Disposal of sludge by agricultural spreading is the main recovery method in France.

When sludge cannot be recycled in agriculture, it becomes a wet waste that is difficult to burn and recover thermally. Energy recovery encompasses various technologies for converting the organic fraction of sludge into energy. Energy recovery can be a complementary or alternative disposal method to material recovery in agriculture.

Technologies for energy recovery from sewage sludge make it possible to take advantage of the need to dispose of and destroy sludge. On-site sludge recovery improves the environmental balance sheet by reducing sludge transport and producing energy (heat, electricity) that is directly consumed at the plant.

Some of these technologies are relatively new, and only benefit from occasional feedback. They are, however, serious alternatives to conventional incineration, often presented as the only possible thermal option.

The primary selection criteria are the quantity of sludge available and the technical impossibility of using the sludge for agricultural purposes (quality). To consider energy recovery, the sludge deposit must be significant, at least for treatment plants with more than 50,000 population equivalents, i.e. around 750 tonnes of dry matter.