Eichhornia crassipes: Production in repeated harvest systems on waste water in the Languedoc Region (France)

Abstract

This study was carried out with a view to setting up Eichhornia crassipes systems, bringing together biomass production and water purification. The original method attempted allows the study of E. crassipes production (in terms of real harvest values) and the purification results (in terms of biomass removed) on a seasonal and annual basis, using five systems operating in parallel on waste water. These systems have different on-site biomass values, maintained by regular harvests; the harvest is adjusted each time according to system production. Production, conditioned by maximum temperatures greater than 15°C, went on for 6 months, 4/5 (production greater than 20 g m −2 day −1) being concentrated in the three summer months. In integrated harvest systems the mean varies between 40·5 to 47 t ha −1 year −1 DW (30·6–35·2 g DW m −2 day −1 for the whole of the production period). Purification thus corresponds to the removal of 1500–1900 g m −2 of C, 180–220 g m −2 of N and 35–43 g m −2 of P 2O 5. The best system (annual production of 69·5 t ha −1 year −1) in this cultivation mode had an on-site biomass of 13 kg WW m −2 at the beginning of the summer and 33 kg WW m −2 at the end of the summer (the production peak varied somewhat, due to the age and structure of the population, parameters which depend on the season and the harvesting methods). Production and purification of systems limited to a single harvest (at the end of the summer) were inferior by a factor of 3. The discussion concerns production analysis, with regard to different ecological parameters and bibliographical data, and comparison of Eichhornia systems with the other macrophyte systems tested on waste water in the region.