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. For example, it can be produced as a settled suspension obtained from conventional drinking water treatment, as sewage sludge from wastewater treatment processes: 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.
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 high protein content and other nutrients that can be used for beneficial purposes such as animal feed, thereby avoiding disposal at a landfill.
- Edzwald, James K., ed. (2011). Water Quality and Treatment (6th ed.). McGraw-Hill. ISBN 978-0-07-163011-5.
- Tchobanoglous, George; Burton, Franklin Louis; Stensel, H. David; Metcalf & Eddy (2003). Wastewater Engineering: Treatment and Reuse (4th ed.). McGraw Hill. ISBN 9780071122504.
- Byfield, Mike (July 7, 1997). "Farmers line up for their slug of pulp sludge". Alberta Newsprint Co.
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