Extended aeration is a method of sewage treatment using modified
activated sludge
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 ...
procedures. It is preferred for relatively small waste loads, where lower operating efficiency is offset by mechanical simplicity.
[Steel & McGhee (1979) p.501]
Conventional sewage treatment
Mechanized
sewage treatment
Sewage treatment is a type of wastewater treatment which aims to remove contaminants from sewage to produce an effluent that is suitable to discharge to the surrounding environment or an intended reuse application, thereby preventing water p ...
typically includes settling in a primary
clarifier
Clarifiers are settling tanks built with mechanical means for continuous removal of solids being deposited by Sedimentation (water treatment), sedimentation. A clarifier is generally used to remove solid particulates or suspended solids from li ...
, followed by biological treatment and a secondary clarifier. Both clarifiers produce waste
sludge requiring
sewage sludge treatment and disposal. Activated sludge agitates a portion of the secondary clarifier sludge in the primary clarifier effluent. Remaining secondary sludge and all primary sludge typically require digestion prior to disposal.
Process modification
Extended aeration agitates all incoming waste in the sludge from a single clarifier. The combined sludge starts with a higher concentration of inert solids than typical secondary sludge and the longer mixing time required for digestion of primary solids in addition to dissolved organics produces aged sludge requiring greater mixing energy input per unit of waste oxidized.
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Applications
Extended aeration is typically used in prefabricated "package plants" intended to minimize design costs for waste disposal from small communities, tourist facilities, or schools. In comparison to traditional activated sludge, longer mixing time with aged sludge offers a stable biological ecosystem better adapted for effectively treating waste load fluctuations from variable occupancy situations. Supplemental feeding with something like sugar is sometimes used to sustain sludge microbial
A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...
populations during periods of low occupancy; but population response to variable food characteristics is unpredictable, and supplemental feeding increases waste sludge volumes. Sludge may be periodically removed by septic tank pumping trucks as sludge volume approaches storage capacity.[Hammer (1975) pp.390 & 391]
See also
* List of waste-water treatment technologies
Notes
References
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{{Wastewater
Environmental engineering
Pollution control technologies
Sanitation
Sewerage
Sewerage infrastructure
Waste treatment technology
Water treatment