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Fecal sludge collected from pit latrines near Durban, South Africa, awaiting further treatment by drying

Sludge is a semi-solid slurry that can be produced from a range of industrial processes, from water treatment, wastewater treatment or on-site sanitation systems. It can be produced as a settled suspension obtained from conventional drinking water treatment,[1] as sewage sludge from wastewater treatment processes[2]: 23–25  or as fecal sludge from pit latrines and septic tanks. The term is also sometimes used as a generic term for solids separated from suspension in a liquid; this soupy material usually contains significant quantities of interstitial water (between the solid particles). Sludge can consist of a variety of particles, such as animal manure.[3][not specific enough to verify]

Industrial wastewater treatment plants produce solids that are also referred to as sludge. This can be generated from biological or physical-chemical processes.

In the activated sludge process for wastewater treatment, the terms "waste activated sludge" and "return activated sludge" are used.

In food processing and beverage-making industries, sludge can have a high protein content and can contain other nutrients that can be used for beneficial purposes such as processing for animal feed; this avoids having to dispose of the sludge at a landfill.


  1. ^ Edzwald, James K., ed. (2011). Water Quality and Treatment (6th ed.). McGraw-Hill. ISBN 978-0-07-163011-5.
  2. ^ Tchobanoglous, George; Burton, Franklin Louis; Stensel, H. David; Metcalf & Eddy (2003). Wastewater Engineering: Treatment and Reuse (4th ed.). McGraw Hill. ISBN 9780071122504.
  3. ^ Byfield, Mike (July 7, 1997). "Farmers line up for their slug of pulp sludge". Alberta Newsprint Co.