Purification by a natural waste stabilization pond: influence of weather and ageing on treatment quality and sediment thickness

The natural waste stabilization pond of Vauciennes, located in the north of France, underwent regular monitoring from October 1981 to July 1991, within the framework of a programme studying the evolution of operation parameters related to the ageing of plants. This study enabled us to assess the variations in the quality of the discharge depending on the season, in particular concerning the nitrogen and phosphorus parameters. The input/output reports made it possible to make specifications concerning the variations of the loads to be treated and the overloads caused by rainy episodes, and the real performances of the plants in relation to rainfall, evaporation, hydraulic exchanges with the soil and interannual seasonal variations. The evolution of the treatment, characterised by the parameters of the treated effluent, was observed, on the basis of equivalent climate conditions. Lastly, the growth of the deposits and their location in the first pond observed based on the systematic establishment of a cartography of the bottom of the pond.