activated sludge

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ac·ti·vat·ed sludge meth·od

a method of sewage disposal in which sewage is treated with 15% bacterially active liquid sludge, which is produced by repeated vigorous aeration of fresh sewage to form floccules or sediment; when this flocculation process is complete, the resulting activated sludge contains large numbers of bacteria, together with yeasts, molds, and protozoa, which actively effect the oxidation of organic compounds; this mixture is piped to a sedimentation tank, the effluent from which is completely treated sewage.

activated sludge

any living material used in sewage treatment, consisting mainly of bacteria and protozoans, that breaks down organic matter in the sewage and increases by multiplication during the process. Part of the new sludge is used in the continuing treatment of the sewage.


a state of being more than usually active. In biological systems this is usually brought about by chemical or electrical means. Commonly said of pharmaceutical and chemical products.

activated clotting time (ACT)
a simplified version of the activated partial thromboplastin time which measures the intrinsic clotting activity of the whole blood. See also activated coagulation time, clotting time.
activated partial thromboplastin time (APTT)
a test of intrinsic clotting activity of whole blood. Partial prothrombin, usually rabbit or human brain prothrombins, is added to plasma activated with kaolin or ellagic acid. The time required for the test is short and the results are dependable.
activated sludge
a method of dealing with sewage and abattoir effluent. Consists of an aeration tank in which biologically active, previously sedimented sludge is mixed with incoming effluent and agitated in the presence of an ample supply of air.


a suspension of solid or semisolid particles in a fluid.

activated sludge
a means of encouraging biodegradation. See also activated sludge.
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