Abstract :
[en] In hot countries temperature conditions allow the use of various WSP technologies, including floating macrophytes. We studied duckweeds and they have been used for industrial or domestic waste water treatment. However, the vegetable carpet formed on the water surface must be managed in order to maintain a good efficiency. The duckweeds must be harvested regularly. Otherwise when the biomass is getting too large there is some overlap, mortality increases, and dead cells sink and degrade at the bottom creating a new pollution. In addition, a hazardous harvest of the lenses can involve the reduction in the capacity of purification and also support the development of algae. We tried to monitor the biomass and the environmental parameters of the system (luminosity, temperature, pH, nitrogen, phosphorus, alkalinity, COD…) as well.
Indeed, the duckweed biomass measurements were carried out by many researchers (Köner and Vermaat, 1998; Caicédo et al., 2000; Rhamani and Sternberg, 1999; Edwards et al., 1992;…) according mainly to two methods, : the measurement of fresh or dry weight. It appears that these two methods present disadvantages especially for rather long experiments. If the last one is more reliable but destructive, the first on the other hand is less destructive but less accurate and not very reproducible. In the present work, we considered numerical image processing by adapted soft wares, namely: ACDsee® and Image Pro-Plus®. The purpose of this study is thus to establish the surface-biomass relationship for a possible comparison of the resulting biomasses by image and weighing