Changes

[[File:Anaerobiclagoons.png|thumb|right|200px|Diagram of anaerobic lagoons]]

Anaerobic lagoons are not aerated, heated, or mixed. The typical depth of an aerated lagoon is greater than eight feet, with greater depths preferred. Such depths minimize the effects of oxygen diffusion from the surface, allowing anaerobic conditions to prevail. In this respect, anaerobic lagoons are different from shallower aerobic or facultative lagoons, making the process analogous to that experienced with a single stage unheated anaerobic digester, except that anaerobic lagoons are in an open earthen basin. Moreover, conventional digesters are typically used for sludge stabilization in a treatment process, whereas lagoons typically are used to pretreat raw wastewater. Pretreatment includes separation of settleable solids, digestion of solids, and treatment of the liquid portion.