The activated sludge process is a type of biological wastewater treatment process for treating sewage or industrial wastewaters using aeration 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 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, 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. Purpose The activated sludge process is a biological process used to oxidise carbonaceous biological matter, oxidising nitrogenous matter (mainly ammonium and nitrogen) in biological matter, and removing nutrients (nitrogen and phosphorus). Process description The process takes advantage of aerobic micro-organisms that can digest organic matter in sewage, and clump together by flocculation entrapping fine particulate matter as they do so. It thereby produces a liquid that is relatively free from suspended solids and organic material, and flocculated particles that will readily settle out and can be removed. The general arrangement of an activated sludge process for removing carbonaceous pollution includes the following items: Aeration tank where air (or oxygen) is injected in the mixed liquor. 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. Treatment of nitrogenous matter or phosphate involves additional steps where the processes are managed to generate an anoxic zone so that phosphates can be solubilised in the reducing environment and oxides