1. STERU sludge and associated risks

Urban sewage sludge is a by-product of the treatment of urban wastewater. Other materials of various kinds are irregularly added to domestic wastewater, and are also treated in STERUs: this may be runoff water if there is a combined collection system or part of one, or materials extracted from septic tanks if the plant is authorized to receive them, or sludge from small STERUs that is added to the sludge treatment process for larger STERUs, etc. This by-product is a by-product of the STERU treatment process.

The sludge generated by STERU plants consists mainly of solid particles that have not been captured/treated by :

• water pre-treatment upstream of the plant;

• STERU processes.

Sludge is made up of undecomposed organic matter, minerals, micro-organisms...