Using one filter stage of unsaturated/saturated optimised vertical flow filters to reduce the footprint of constructed wetlands. | Utilisation d'un filtre planté non saturé/saturé optimisé pour réduire l'emprise au sol des filtres plantés

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED

International audience

anglais. French vertical flow constructed wetlands (VFCW) treating raw wastewater have been developed successfully over the last 30 years. The highly aerobic treatment observed on these two-stages of filter allows an almost complete nitrification and accepts high hydraulic loads with seasonal variations. Nevertheless, the French two-stage VFCWs need a total filtration area of 2-2.5 m2/PE and the use of sand on the second stage. Furthermore, it is not always economically competitive and their high removal efficiencies are not systematically needed. In this context, implementing a one-stage system allowing reaching standard requirements is of interest. One of the solutions developed in France is to use a vertical flow system with an unsaturated layer at the top and a saturated layer at the bottom. It is proposed by Epur Nature as Biho-Filter®. The aim of this study was to assess the potential of this new configuration, in order to optimize the design and operating conditions (bottom saturation layer depth, recirculation rate, etc.). The study consisted in hydraulic and removal assessment of 3 different Biho-Filter® plants. It presents the results regarding outflow concentrations that can be achieved (15 mg.L -1 in TSS, 70 mg.L -1 in COD, 15 mg.L -1 in BOD5, 25 mg.L -1 in TKN and 70% in TN removal) as well as the impact of the operation conditions on treatment performances and the limits of the systems.