Domestic Wastewater Treatment in Tanks Planted with Rooted Macrophytes: Case Study; Description of the System; Design Criteria; and Efficiency

Abstract

For several years, the CEMAGREF has been interested in the study of treatment plants adapted to rural areas. In this field, “macrophyte beds”, as a new procedure in water treatment, has been closely followed. This treatment plant is made up of a series of watertight tubes filled with gravel and rooted with aquatic plants. Since autumn of 1982, this plant has been treating the wastewater of a rehabilitation center which functions according to a scholastic calendar. Receiving loading of 28 population equivalents, the plant must be able to cope with loading variations reaching a factor of 6. The total planted surface is 63 m2, thus 2.5 m2 per population equivalent. The different series of measurements taken during an annual plant cycle show that:–the abatement of the organic loading (COD, BOD5) reaches 85% to 90%;–the elimination rate of total nitrogen is near 50%;–the phosphorus is mineralised but is not retained by the treatment. The samplings of effluent discharge, taken several times over a three year study period, showed that the once satisfactory discharge had degraded. The origin of this degradation should be looked into. The first results (as described above) will be completed by those obtained during a study which is being conducted on a larger scale (500 population equivalent). This plant was put into use in September 1985 and receives a loading of domestic wastewater from an urban neighborhood. The research project has as its aim to optimize both the economic and operational aspects of the treatment plant to answer the real needs of small rural communities.