Extended aeration

Extended aeration is a method of sewage treatment using modified activated sludge procedures. It is preferred for relatively small waste loads, where lower operating efficiency is offset by mechanical simplicity.

Conventional sewage treatment

Mechanized sewage treatment typically includes settling in a primary clarifier, 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.

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 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.

Notes

References

Hammer, Mark J. (1975). Water and Waste-Water Technology. John Wiley & Sons. ISBN 0-471-34726-4.
Metcalf & Eddy, Inc. (1972). Wastewater Engineering. McGraw-Hill Book Company. ISBN 0-07-041675-3.
Steel, E.W. and McGhee, Terrence J. (1979). Water Supply and Sewerage, 5th Edition. McGraw-Hill Book Company. ISBN 0-07-060929-2.

Wastewater

Sources of wastewater	Acid mine drainage Ballast water Blackwater (coal) Blackwater (waste) Boiler blowdown Brine Combined sewer Cooling tower Cooling water Greywater Infiltration/Inflow Industrial effluent Ion exchange Leachate Manure Papermaking Produced water Return flow Reverse osmosis Sanitary sewer Sewage Sewage sludge Storm drain Urban runoff

Wastewater quality indicators	Biochemical oxygen demand Chemical oxygen demand Coliform index Dissolved oxygen Heavy metals pH Salinity Temperature Total dissolved solids Total suspended solids Turbidity

Wastewater treatment options	Activated sludge Aerated lagoon Agricultural wastewater treatment API oil-water separator Carbon filtration Chlorination Clarifier Constructed wetland Extended aeration Facultative lagoon Filtration Imhoff tank Industrial wastewater treatment Ion exchange Membrane bioreactor Reverse osmosis Rotating biological contactor Secondary treatment Sedimentation Septic tank Settling basin Sewage sludge treatment Sewage treatment Stabilization pond Trickling filter Ultraviolet germicidal irradiation UASB Wastewater treatment plant

Wastewater disposal options	Combined sewer Evaporation pond Groundwater recharge Infiltration basin Injection well Irrigation Marine dumping Marine outfall Sanitary sewer Septic drain field Sewerage Stabilization pond Storm drain Surface runoff Water reclamation

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