Sludge is a semi-solid slurry that can be produced from industrial processes, from water treatment, wastewater treatment or on-site sanitation systems.
Sludge can be produced as a settled suspension obtained from conventional drinking water treatment, as sewage sludge from wastewater treatment processes or as fecal sludge from pit latrines and septic tanks.
The sludge term is sometimes used as a generic term for solids separated from suspension in a liquid soupy material, containing significant quantities of water between the solid particles.
Sludge can consist of a variety of particles, such as animal manure.
In the food processing and beverage-making industries, sludge can have high protein content and other nutrients that can be used for beneficial purposes such as animal feed, thereby avoiding disposal at a landfill.