Sludge from wastewater treatment plants coming from fermentation tanks and other equpment used for treatment municipal sewage. Sewage sludge is the product of sewage treatment and is formed through a series of physical, physico-chemical and biological processes occuring in wastewater treatment and pre-treatment plants.

In facilities for wastewater treatment, the following types of hydrated sewage sludge are generated:

• sludge pumped from putrid settling tanks,
• sludge removed from Imhoff's tanks,
• excessive sludge removed from activated sludge devices and rinsed from biofilters,
• polluted sand filers, so called fen soils.