Editing Activated sludge (section)

{{short description|Wastewater treatment process using aeration and a biological floc}}
[[File:Beckton STP, Activated Sludge Tank - geograph.org.uk - 1481906.jpg|thumb|upright|Activated sludge tank at Beckton [[sewage treatment plant]], UK. The white bubbles are due to the diffused air aeration system.]]
The '''activated sludge''' '''process''' is a type of biological [[wastewater treatment]] process for treating [[sewage]] or [[Industrial wastewater treatment|industrial wastewaters]] using [[aeration]] and a biological [[floc (biofilm)|floc]] composed of bacteria and [[protozoa]]. It is one of several biological wastewater treatment alternatives in [[secondary treatment]], which deals with the removal of biodegradable organic matter and suspended solids. It uses air (or [[oxygen]]) and [[microorganism]]s to [[Biological oxidizer|biologically oxidize]] organic pollutants, producing a waste sludge (or [[Flocculation|floc]]) containing the oxidized material.

The activated sludge process for removing carbonaceous pollution begins with an aeration tank where air (or oxygen) is injected into the waste water. This is followed by a settling tank to allow the biological flocs (the sludge blanket) to settle, thus separating the biological sludge from the clear treated water. Part of the waste sludge is recycled to the aeration tank and the remaining waste sludge is removed for further treatment and ultimate disposal.

Plant types include package plants, oxidation ditch, deep shaft/vertical treatment, surface-aerated basins, and [[sequencing batch reactor]]s (SBRs). Aeration methods include diffused aeration, surface aerators (cones) or, rarely, pure oxygen aeration.

[[Sludge bulking]] can occur which makes activated sludge difficult to settle and frequently has an adverse impact on final effluent quality. Treating sludge bulking and managing the plant to avoid a recurrence requires skilled management and may require full-time staffing of a works to allow immediate intervention.<ref name=":0" /> A new development of the activated sludge process is the [[Nereda]] process which produces a granular sludge that settles very well.<ref name="thesourcemagazine.org" /><ref name=":2" />