V_Foussard_et_A_Hubert_2.mp4

Recording of presentations at the Suricates project closing conference

Title : Composting’s potentiality for the recovery of green wastes and sediments in nursery sector as growing media

Authors : Valérie FOUSSARD*1, Auxane HUBERT1 1 Etablissement Public Territorial de Bassin Rance, Frémur, Baie de Beaussais, Rue Gambetta, 22100 Dinan (France) * Corresponding author e-mail: sediments@eptb-rance.fr

Summary :

Historically, the sediments extracted from the Rance estuary are stored on shore in the La Hisse treatment facility and reused as soil improver for agricultural lands. This method allows to manage large volume of sediments (maximum of 100 000 m3 in 3 years). Agricultural reuse of sediments is regulated by a prefectural decree (2017-07-31). Spreading sediments is considered supplement of soil. The calculation of contaminant flows (e.g. salinity) is based on the soil/sediment mixture and not on the input of sediment alone. The volume of sediment spread is limited to 500 m3 per hectare because of the quantity of nickel, which is naturally high in local soils, and of the quantity of chloride. Chloride concentration in the soil/sediment mixture must be less than 1,000 mg/kg. This implies a storage on land for 2 to 3 years before spreading in the fields.

To ensure the long-term management of these marine sediments, the EPTB is exploring various ways of reuse, which would make it possible to manage large volumes of sediments, meet the territorial needs and develop a circular economy. Various reuse options were tested as part of the Interreg NWE Suricates project, including optimizing agricultural reuse, restoration of dry-stone wall (concrete application) and creation of dikes. During the project, 54 900 tons of dried sediments have been reused, mostly as supply of material to farmers for soil reconstruction (spreading of wet sediments and direct spreading of dry sediments).

Direct sediments spreading tests with a conventional spreader were carried out with 100 tons of sandy sediments and 100 tons of muddy sediments. Sediments used for the test have been taken from the top 50 centimetres of the lagoons of the La Hisse treatment facility. The roots of the plants that have grown on the lagoons helped the fragmentation of muddy sediments during their storage in la Hisse, into blocks of 1 to 10 millimeters suitable for direct spreading. Spreading of dry sediments with a conventional spreader used in agriculture is possible if the sediments are sufficiently dehydrated. Soil samples have been carried out before the spreading of sediments and eight months later on two plots of respectively 2.7 and 6.8 hectares that have received 500 m3 of sediment per hectare. These samples have been analysed by the University of Strathclyde, partners in the SURICATES project, to evaluate the environmental benefits of sediments supply (see abstract Lord et al.).

Acknowledgements: The SURICATES project is funded by the European Regional Development Fund (ERDF) as part of the Interreg NWE programme 2014-2020 and by the funders of the Rance estuary sediment management plan: French State, Brittany Region, Dinan Agglomération, Saint-Malo Agglomération, Communauté de communes Cotes d’Emeraude and Electricity of France