Wastewater treatment: a new experimental biostation

The Clos-de-Hilde biostation, the first instrumented experimental site dedicated to studying planted discharge areas (PDA), will be inaugurated in Bègles, in Gironde, on April 11 this year in the presence of Alain Juppé [1]. PDAs are facilities that aim to reduce pollutants that remain in water leaving wastewater treatment plants. These measures are in full development – there are currently over 500 facilities in France – yet their operation remains poorly understood. “Until now, PDAs were set up using available space, with no connection between their size and how effective they were supposed to be,” explains Irstea researcher Jean-Marc Choubert.

In this context, Irstea put nearly 10 years of expertise in the field to good use and launched the project [2] with Onema for an experimental site dedicated to studying PDAs. The aim was to improve the anti-pollution mechanisms involved on the surface and in the soil in order to evaluate their effectiveness. Set up in Bègles next to the wastewater treatment plant at Clos-de-Hilde, the experimental site has several advantages. Its chief advantage is its 6000 m² size, which makes it possible to compare several processes at once. Specifically, these include 3 types of PDAs and 2 types of water for clean up on a semi-industrial scale to ensure successful results.

Project profile

Project name: Biotrytis (2013-2018)
Research teams: Irstea Lyon (EPURE, LAMA),  Bordeaux (EPURE),  Antony (MP2) / University of Bordeaux – Membrane Biogenesis Laboratory (LBM), Laboratory of Physico- and Toxico-Chemistry of the Environment (LPTC)
Scientific Project Leader: Jean-Marc Choubert, Irstea Lyon-Villeurbanne
Funding: Onema (scientific project), Bordeaux Métropole and Adour-Garonne Water Agency (site construction)
Budget: 2 million euros
Contracting authority: Bordeaux Métropole
Project site: Biotrytis project

Panorama of the Clos-De-Hilde biostation © Irstea / J-M. Choubert

Original equipment

Regardless of type, planted discharge areas are always designed based on the interactions between 3 integral components: water, soil and plants. The Bègles experimental site is unique because it analyzes the contribution of each of these 3 components in transferring, reducing and retaining pollutants, which are one of two types:

  • key parameters, such as suspended matter and nutrients (nitrogen, phosphorous) that cause silting and eutrophication [3]
  • micropollutants or toxic chemical compounds at very low concentrations, such as certain metals, chemical products (pesticides, detergents, etc.) and drug residues. A total of 250 micropollutants will be investigated [4].
Good to know

Planted discharge areas are classified into 4 categories depending on the source of the material used (local soil or added matter) and the geometry of the area. These are:

  • meadows: local soil, relatively flat, no digging
  • basins: local soil, with digging and different levels
  • ditches: local soil, length significantly greater than width
  • other: soil recreated from added matter

The aim of the planted discharge areas is to recreate processes that occur naturally in the environment:

  • evaporation/evapotranspiration and infiltration into the soil to limit the amount of water released to the surroundings;
  • settling and filtering of suspended matter, adsorption and/or biodegradation of pollutants in the soil, photodegradation by sunlight, accumulation in some plants, processes that reduce the concentration of pollutants before releasing runoff to the surroundings.

Moreover, the study will make it possible to determine the effectiveness of 3 types of PDA – ditch, meadow, other – in eliminating these pollutants. It will also identify and prioritize the processes that influence how the pollutants behave. It will also look at whether a PDA can treat nitrogen (which causes eutrophication) by comparing the impact of water with nitrogen [5] and without.

To achieve these aims, 6 semi-industrial sized PDAs (2 meadows, 2 ditches and 2 other) have been designed and equipped by Irstea. The whole biostation is equipped with permanent sampling systems in the surface water and in the soil. Sensors will also measure the flow and quality of surface water and groundwater runoff. These readings will be complemented by regular sample collections and analysis of suspended matter deposits in the ground and plants [6].

Once it opens, the site will be monitored very closely for the next 3 years. During this period, we hope to discover exactly how PDAs work while taking into account their evolving nature (growth of plants and soil bacteria). The project will also look at how these facilities age and especially how to maintain their effectiveness once suspended matter accumulates, as this reduces transfers between surface and groundwater. From 2018, it will be possible to issue specific recommendations for public decision-makers and managers who are currently waiting for reliable answers before implementing optimized PDAs.


[1] President of Bordeaux Métropole, Mayor of Bordeaux and former Prime Minister

[2] The project is a continuation of the work carried out previously by the Evaluation of New Processes for Small and Medium Communities (EPNAC) group and of the Maximizing reduction of micropollutants in domestic wastewater processing plants (ARMISTIQ) project carried out between 2010 and 2014.

[3] Phenomenon linked to excessive quantities of nutrients (nitrogen and/or phosphorous) in water that can cause the proliferation of some aquatic plants, changing the environment.

[4] Analysis conducted by the Laboratory for Physicochemical Analyses of Aquatic Environments (LAMA) at the Irstea Lyon-Villeurbanne Center and the Laboratory of Physico- and Toxico-Chemistry of the Environment (EPOC-LPTC) at the University of Bordeaux

[5] Nitrification is one of the steps involved in processing waste water used to transform ammonium (NH4+) to nitrite (NO3-) using bacteria.

[6] Conducted primarily by the Membrane Biogenesis Laboratory at the University of Bordeaux

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