Facultative lagoons cause less odor, but may have problems functioning during cold periods when ice forms on the surface. Aerated lagoons and stabilization ponds are both aerobic systems. Stabilization ponds are the shallowest of all the systems, usually just 2 feet deep. They rely on surface diffusion of oxygen and algae growth to oxygenate the wastewater. Stabilization ponds require a large area of land, typically about 1 acre for every two hundred people, and are usually located in areas where the climate permits year round algae growth.
Aerated lagoons create aerobic conditions through mechanical means.
Limitations of surface space or cold winter temperatures are two reasons for mechanical aeration. It is recommended that lagoons be preceded by a holding tank so solids can settle out. Effluent from lagoons can be discharged to a drainfield, if water quality standards allow, or if necessary they can be followed by sand filters and disinfection before being directly discharged. These systems tend not to need a great deal of operation or repairs, so maintenance costs can be minimized. Yet construction of the lagoons can be costly and they do require more land than most other alternative systems.