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]

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

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.