International audience | We assessed the temporal variability of nutrients, phytoplankton and bacterioplankton at two sites of different trophic status in New Caledonia's South-West lagoon, a tropical coastal ecosystem. During stable meteorological conditions, Chl.a, bacterial production and nutrient concentrations experience weak but consistent daily variation. Short-term (1–2 week interval) fluctuations of planktonic variables are in the same range as annual variations at both sites. A part of these short term variations is linked to local meteorological events (wind in the main channel, precipitation at the coastal station). Although annual variations are weak compared to short term variations, phytoplankton and bacterioplankton production show consistent temporal patterns, with maxima in December–January and April–May and minima in August. Annual bacterial production represents 21% and 34% of particulate primary production at the oligotrophic and mesotrophic sites, respectively. Mineral nutrient availability indicates that nitrogen is probably the primary limiting factor of phytoplankton throughout the year.

The MAPPE GIS based multimedia model is used to produce a quantitative description of the behaviour of γ-hexachlorocyclohexane (γ-HCH) in Europe, with emphasis on continental surface waters. The model is found to reasonably reproduce γ-HCH distributions and variations along the years in atmosphere and soil; for continental surface waters, concentrations were reasonably well predicted for year 1995, when lindane was still used in agriculture, while for 2005, assuming severe restrictions in use, yields to substantial underestimation. Much better results were yielded when same mode of release as in 1995 was considered, supporting the conjecture that for γ-HCH, emission data rather that model structure and parameterization can be responsible for wrong estimation of concentrations. Future research should be directed to improve the quality of emission data. Joint interpretation of monitoring and modelling results, highlights that lindane emissions in Europe, despite the marked decreasing trend, persist beyond the provisions of existing legislation. An spatially-explicit multimedia modelling strategy was applied to describe the historical distribution of γ-HCH in European soils and surface waters.

[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.

[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.

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[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.

[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 | Subsurface horizontal flow constructed wetlands (HFCW) and vertical flow constructed wetlands (VFCW) have been compared regarding their efficiencies on microbiological indicators removal. Seven types of HFCWs and two types of VFCWs have been monitored for several years. Fecal coliforms, E. coli, somatic coliphages and F-specific bacteriophages were analyzed in the influent and effluents of each system. All constructed wetlands monitored were planted with Phragmites australis but have different design characteristics and operation variables. All data were statistically treated (SPSS v17) in order to analyse the effect of design and operation variables on each microbiological indicator. VFCWs were more efficient than HFCWs systems when considering removal rates per surface for all the microbiological indicators (cfu or pfu removed/m2.d). Nevertheless, considering mean removal efficiencies (in log units), results did not show statistically significant differences. The hydraulic retention time was the key parameter regarding filter disinfection capacity in both types of filters. Bacterial indicators were removed at a higher rate than viral indicators.

[Departement_IRSTEA]Ecotechnologies [TR1_IRSTEA]TED [Axe_IRSTEA]TED-EPURE | International audience | We develop an original solid respirometric method to measure the biodegradation rates of COD and ammonium at different depths of a Vertical Flow Constructed Wetland (VFCW). The method is developed for a matrix operated under unsaturated conditions. The oxygen demand is measured versus time in a gas passing through a reactor containing a mixture of an organic matrix mixed with a bulking agent (wood). For the measurement of the nitrification rate, a solution of ammonia and hydrogenocarbonates is spread on the sample. We ran 15 experiments on different matrices with variable organic matter contents (sludge, VFCW gravels and sand). Within this paper we present the overall methodology, the factors that allow improving the accuracy (number of duplicates, blank, sample volume, bulking agent volume, gas flow, etc.) and the nitrification rates that were obtained.