Aerobic lagoons use aerobic bacteria and/or algae to treat wastewater in oxygen-adequate condition which is accomplished by either constructing the lagoons shallow so that air and sunlight can transfer into the system or relying on proper aeration. Facultative ones are between aerobic and anaerobic lagoons and the treatment occurs with the aid of facultative microorganisms. Anaerobic lagoons are oxygen free system in which anaerobic microorganisms play significant role in the treatment process.