Some dinoflagellates (Ceratium
) are sufficient component of saprobic waters, whereas many ciliates are compound of activated sludge in aeration tanks. The activated sludge process is a type of biological wastewater treatment
process for treating sewage
or industrial wastewaters
and a biological floc
composed of bacteria and protozoa
. It uses air (or oxygen
) and microorganisms
to biologically oxidize
organic pollutants, producing a waste sludge (or floc
) containing the oxidized material. The general arrangement of an activated sludge process for removing carbonaceous pollution includes the following items: An aeration tank where air (or oxygen) is injected in the mixed liquor. This is followed by a settling tank (usually referred to as “final clarifier” or “secondary 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, sequencing batch reactors
(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. A new development of the activated sludge process is the Nereda
process which produces a granular sludge that settles very well.