Aerated lagoon

[5] The objective of the lagoon is therefore to act as a biologically assisted flocculator which converts the soluble biodegradable organics in the influent to a biomass which is able to settle as a sludge.

The effluent can then be removed from the top with a low chemical oxygen demand, while the sludge accumulates on the floor and undergoes anaerobic stabilisation.

Typically, the floating high speed surface aerators are rated to deliver the amount of air equivalent to 1 to 1.2 kg [[O2]]/kWh.

[6] With low speed surface aerators SOTE (Standard Oxygen Transfer Efficiency) is higher thanks to better mixing capacity.

This is why low speed surface aerators are mostly used in sewage or industrial treatment as WWTP[clarification needed] are bigger and sparing energy becomes very interesting.