Lagooning is a treatment process of sewage water based on the biological balance of a set of artificial basins.

The sewage water (wastewater) is passed by gravity from one pond / basin to another where it remains approximately two weeks. Seaweed photosynthetic activity at pool surface produces available oxygen to endogenic anaerobic bacteria which decompose the organic matter in the sewage water. Carbon dioxide and nutriments from bacteria promote seaweed growth. Due to the absence of photosynthesis at the bottom of the basin, the sediment is decomposed by anaerobic bacteria (carbon dioxide gas and methane production).

This treatment process works only with organic matter and light energy inputs. This kind of purification is based on the balanced presence of producers (seaweed), primary consumers (bacteria), herbivores/carnivores (zooplankton and animal) and scavengers (fungi and bacteria).

The organic matter is degraded thanks to the specific functionalities of an ordered succession of the basins which ultimately enable the treated water to return to the environment.

• Anaerobic pool (2,5-5 m deep): anaerobic degradation of the settled organic matter;
• Optional pool (1,2-2,4 m): aerobic and anaerobic degradation (diminution of the phosphoric and the nitrogenous water content);
• Maturation or aerobic pool (<1,5 m): eliminates pathogens, accelerates the decomposition (high biological activity of the seaweed and the aerobic bacteria) and controls the seaweed populations;
• High-yield pool (optional) (0,3-0,6 m): mechanical production of oxygen which causes a high degrading biological activity.

Depends on the needs, some elements can be added upstream and downstream of the installation (aerobic or aquaculture basins, etc.). The aerobic pool biomass (reeds, hyacinths, duckweed, etc.) can be used as animal feed. Applied to agroecology, lagooning is an ecological treatment (low-power consumption, boosts biodiversity) of livestock manure based on ecosystemic services.