[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED [Axe_IRSTEA]TED-EPURE | International audience | Phosphorus (P) removal in constructed wetlands (CWs) has received particular attention during the last decades by using specific materials which promote P adsorption/precipitation phenomena. Recent studies have shown an interest in using apatite materials to promote P precipitation onto their surface. About ten years of experiments at different scales (laboratory, pilot, full scale) have passed. The process is now open in France. This paper presents the first design recommendations according to the apatite mineral quality and treatment outlet requirements. Kinetics and their evolution with the material saturation degree are presented based on the k-C* model. The process can achieve 1 mgP.l-1 for long term while using surface P removal filter area of 0.5 m².p.e.-1. With a low land footprint and high P removal efficiency, the interest of the process also result in the orthophosphates accumulation on a phosphate mineral which makes easier to reuse phosphorus from wastewater once saturated.

International audience

This study examines the common ground between current scientific knowledge and stakeholders’ perception of ecosystem services in mixed forests versus monocultures. An enquiry was performed within the frame of the project FORBIO aiming at the ‘Assessment of the effects of tree species BIOdiversity on FORest ecosystem functioning’ (http://forbio.biodiversity.be). The objective of this enquiry was to confront the perception of the influence of mixed species stands on ecosystem services in Belgium with actual scientific knowledge. The target groups were forest managers, users and scientists. As a general frame for the questionnaire, the ‘Millenium Ecosystem Assessment’, assessing the consequences of ecosystem change for human well-being, was selected. Respondents were asked to express their degree of agreement with statements related to the provisioning (production/quality, financial return), supporting (biodiversity, nutrient cycling, resistance), regulating (climate, air, soil, water) and cultural (aesthetics, recreation) ecosystem services, comparing mixed species to pure stands. Other questions addressed management objectives and the general profile of participants. The web-based questionnaires (SurveyMonkey) were established in Flemish and in French and invitations to respond were distributed by e-mail among key contact persons of forestry/nature associations, forest managers and scientists. After one month, a total of 142 and 228 responses were collected for the questionnaire in Flemish and in French, respectively. In this paper, we summarize main results by analyzing the profile of respondents and describing their perception of forest ecosystem services. Through the confrontation of this perception with the current scientific knowledge and through the identification of established scientific facts unknown to the general public, we identify gaps in scientific knowledge and ways of improving communication between scientists and managers. | FORBIO: Assessment of the effects of tree species BIOdiversity on FORest ecosystem functioning’

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED [Axe_IRSTEA]TED-EPURE | International audience | This paper presents the key elements that emerged from a 3-year study on 4 campsites. Each of them has its own Vertical-Flow Constructed Wetlands (VFCW) for on-site wastewater treatment. Each year, the pollution discharge peaked in the 5 to 6-week summer period but was zero for a 6-month period. The natural-concentrate wastewater is collected into a short sewer network. Hydraulic load and campground occupancy rate were tightly correlated. The effluent has a characteristically high nitrogen concentration due to the lower greywater-producing activity. These quantitative and qualitative elements were used to define the camper equivalent' as a daily pollutant load of about 100 L water, 90 gCOD, 35 gBOD5, 40 gSS, 11 gKN and 1.4 gPt. During the 5-6 weeks of peak visitor traffic, the full first stage receives an organic load of 200 gCOD.m-2.d-1 and 25 gKN.m-2.d-1, which is 2 to 3.5-fold higher than the loads conventionally applied in VFCW systems in France. Despite these heavy loads, COD removal remains constant (at 91%) over the season. During the summer peak, nitrification drops sharply but KN removal rate holds steady near 60%. This study demonstrates that VFCWs can robustly handle massive load increases. The paper concludes that total system size can be downscaled to 0.75 m²/camper. This design allows to reach minimum yields of 75% KN, provided that the system is built and run to state-of-the-art rules. | Cet article présente les éléments clés issus d'une étude de 3 ans sur 4 campings qui traitent leurs eaux usées de manière individuelle par des Filtres Plantés de Roseaux à écoulement vertical (FPRV) aux dimensionnements différents. La charge hydraulique et le taux d'occupation du camping sont étroitement corrélés. L'émission est nulle 6 mois par an et la pointe estivale dure 5 à 6 semaines. Les eaux usées, collectées par un réseau court sont naturellement concentrées. L'effluent présente notamment une très forte concentration en azote du fait d'une activité ménagère réduite. Ces éléments qualitatifs et quantitatifs permettent de définir l' « équivalent campeur » par une charge de pollution journalière d'environ 100 L d'eau, 90 g de DCO, 35 g de DBO5, 40 g de MES, 11 g de NK et 1,4 g de Pt. Au cours des 5-6 semaines de fréquentation maximale, la totalité du 1er étage reçoit une charge organique d'environ 200 gDCO.m-².j-1 et 25 gNK.m-².j-1, soit 2 à 3,5 fois plus que les charges classiques appliquées en FPRV en France. En dépit de ces fortes charges, l'élimination de la DCO reste constante (91 %) au cours de la saison. Lors du pic de fréquentation estival, la nitrification décroît fortement mais le rendement global se maintient à environ 60 %. La robustesse des FPRV face à une augmentation massive des charges appliquées est démontrée. L'article conclut par un dimensionnement réduit de 0.75 m2/campeur au total. Ce dimensionnement permet d'atteindre un rendement minimum de 75 % du NK, correspondant à la nitrification, sous réserve que les règles de l'art de construction et d'exploitation soient strictement respectées.

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED [Axe_IRSTEA]TED-EPURE | International audience | On the 2006 IWA International Wetlands Conference in Portugal, two wetland pilot plants in the small tropical island of Mayotte, in the Indian Ocean, were presented. The first pilot plant being a vertical flow filter with recirculation, fed with raw sewage, and the second one a horizontal flow filter after an Imhoff tank. These plants where put into operation the end of 2005 and early 2006, respectively, by SIEAM, which is a syndicate created by the islands authorities who will have the task to operate all water and sewage equipment on the island. The plants have been monitored by SIEAM ever since they went into operation and first results were presented at the 2006 Wetlands conference. In this paper, we present the operation conditions, treatment results and problems encountered during the last 4 years of operation and monitoring of these pilot plants, which will be of particular interest in the aim of finding sustainable treatment solutions for small communities in the tropics, even though the amount of date gathered during this four year period is not as important as we had hoped.

International audience

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[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED [Axe_IRSTEA]TED-EPURE | International audience | French vertical flow constructed wetlands treating raw wastewater have been developed successfully over the last 30 years. During the last years, SINT and Epur Nature developed the approach further by introducing a deep single-stage vertical flow bed that comprises both stages into one in the aim to reduce the footprint. This process, patented by Epur Nature as Bi-filtre®, consists in two vertical stages piled-up. While classical systems in France are designed with 2m².PE-1 (1.2m² and 0.8m² on the first and second stage respectively), the Bi-filtre® has a larger total filtration area with 2.5 m²/PE (1.5m² and 1 m² on the first upper and second lower stage respectively) but a foot print reduced to 1.5 m².PE-1. To favour aeration of the system, an intermediate natural aeration system is introduced at the interface between the first and second stage. The paper will present a study on a fullscale plant (Saint Michel l'Observatoire, 175 PE, France) running at full load in which different materials (sand, pozzolana of different particle size) were tested at the second stage. The aim was to identify the best materials to use to guarantee performance and avoid clogging on this unplanted and buried stage. The study consisted in measuring hydraulic conditions (inlet/outlet flows, infiltration rates, tracer experiments) correlated with 24h composite samples assessments. The results shows that such systems, if well designed, can guarantee an outlet quality of 35 mg.L-1 in SS, 125 mg.L-1 in COD, 25 mg.L-1 in BOD and 20 mg/L in KN with a total foot print of 1.5 m².PE-1. The paper will present the design recommendations and the limits of the systems taking into account a larger experience gathered on different existing plants (e.g. Chorges Bifilter®, 2 150 P.E, France).

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED [Axe_IRSTEA]TED-EPURE | International audience | Oxygen renewal, as a prominent phenomenon for aerobic bacteria activity, deeply impacts VFCW treatment efficiency. We introduce MIGRA, a new model able to simulate oxygen transfer in VFCW. It is based on a realistic two-phase flow module, that allows us to describe various loading sequences, and a transport module. The multi-component transport module is able to deal with convection/diffusion phenomena, inter-phase (air-water) mass exchange, and first-order kinetics. It is validated with analytical solutions and data from an experimental VFCW (column). We show the benefits of a two-phase flow modeling using a comparison with HYDRUS.