The sewage treatment plant studied, located in a rural area, is designed to treat the wastewater for a population of 650. The station functions in accordance with the principle of natural lagoons via artificial wetlands combining macrophytes and microphytes lagoons arranged in series. The overall surface area including the primary lagoon gives rise to a specific load of 6 m2/inhabitant.
Both the primary and secondary treatments produce a very good water quality in accordance with the conventional parameters (SS, Suspended Solids; BOD5, the Biological Oxygen Demand over a 5 day period; COD, the Chemical Oxygen Demand). The tertiary purification of the nitrogen and phosphorus does not give as good results as expected, respectively 42% and 35% removal; very little better than those of a conventional installation. The tertiary quality standard appears not to be attainable since the successive biological mechanisms carrying out the elimination process are followed by a release of the pollutants and an insufficient elimination (plant exportation) by the macrophytes. The design and management of the macrophytes basins is relatively tricky, particularly with respect to the removal of weeds and the regulation of the water level in the macrophytes basins.