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a Laboratoire de Biologie et Physiologie Végétales, Université de Reims, Champagne-Ardenne, UFR des Sciences Exactes et Naturelles, Bâtiment 18, Moulin de la Housse-BP 1039, 51687 REIMS Cedex 2, France
b UMR A408. Qualité et sécurité des aliments d'origine végétale, Université d'Avignon et Pays de Vaucluse, 33 rue Louis-Pasteur, F-84029 Avignon, France
c Laboratoire de Biotechnologies, Environnement-Santé, Université d'Auvergne, IUT d'Aubière, 100 rue de l'Egalité, F-15000 Aurillac, France
* Corresponding author (nathalie.vaillant{at}univ-reims.fr).
Received for publication April 15, 2002. The objectives in this work were to investigate a conceptual layout for an inexpensive and simple system that would treat primary municipal wastewater to discharge standards. A commercial hydroponic system was adapted for this study and the wastewater was used to irrigate wooly digitalis (Digitalis lanata Ehrh.) and foxglove (Digitalis purpurea L.). These plants are medicinal and produce cardenolide compounds. Influent and effluent samples were collected once a month for six months and analyzed to determine the various parameters relating to water quality. The legal discharge levels for total suspended solids (SS), biochemical oxygen demand (BOD5), and chemical oxygen demand (COD) were reached for the two tested plants after 48 h of wastewater treatment; the removal was 82, 93, and 79%, respectively, for wooly digitalis and 92, 92, and 84%, respectively, for foxglove. Similar results were obtained during a 6-mo period although the sewage composition varied widely. The system tended to be unable to remove N and P to concentrations below regulated levels. Compared with the nutrient solution composition, the wastewater was more concentrated in Na+ and Cl and less in N, K+, and Ca2+. These variations can lead to the decline of wooly digitalis plants. Foxglove developed a significant root system to increase mineral absorption wastewater being used as the unique nutritive source. After 10 wk all the wooly digitalis seedlings were dead. Despite this fact, however, the root system remained in place for a significant time (<4 mo), thus continuing to filter wastewater and to be used as a bacterial support thus making it possible to have a security period to replace the dead plants.
Abbreviations: BOD5, biochemical oxygen demand COD, chemical oxygen demand NFT, nutrient film technique SS, suspended solids
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