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Invented in the 1930s, polyurethanes (PU) are a special group of polymeric materials. In France, only 3 kt of PU are recycled annually out of a production of 250 kt. The potential of recovery of this waste is therefore questioned and the agronomic way for the construction of fertile soils is considered. A study was conducted to evaluate the relevance of adding PU foam in a growing media (GM) for plantation, and to know if they can confer interesting characteristics for plant growth without any risk for the environment.The tested GMs were mixtures of compost (Material of Agronomic Interest from Water Treatment, NF U44-095), foams and arable topsoil. The foams used were derived from the core of PU mats. Four volume ratios of compost/foam mixtures were achieved. Topsoil was added at different volume ratios to constitute the final GMs (16 final GM).Ecotoxicological analyses show the safety of the tested GMs. Greenhouse trials over 54 days allowed to follow the development of ryegrass in GMs.Planting media with suitable agronomic potential for green roofs have been identified, based on the experimental results of the study, and will be tested on a larger scale., Inventé dans les années 1930, les polyuréthanes (PU) sont un groupe spécial de matériaux polymères. En France, seulement 3 kt de PU sont recyclés annuellement sur une production de 250 kt. Le potentiel de valorisation de ce déchet est donc questionné et la voie agronomique pour la construction de supports de cultures non alimentaire pourrait être envisagée. Une étude a été menée pour évaluer la pertinence d'apport de mousses PU dans un substrat de plantation, afin de savoir si elles peuvent lui conférer des caractéristiques physico-chimiques intéressantes pour la croissance végétale sans risque pour l'environnement. Les substrats testés sont des mélanges de compost (Matière d'Intérêt Agronomique issue du Traitement des Eaux, NF U44-095), de mousses PU et de terre végétale. Les mousses utilisées sont issues de l'âme de matelas en PU. Quatre ratios volumiques de mélanges compost/mousse ont été réalisés. De la terre végétale a été ajoutée à différents ratios volumiques pour constituer les substrats finaux (16 substrats finaux). Les analyses écotoxicologiques montrent l'innocuité environnementale des substrats testés. Des essais sous serre pendant 54 jours ont permis de suivre le développement du ray-grass dans les substrats. Des supports de plantation avec un potentiel agronomique adapté pour les toitures végétalisées ont été identifiés et seront testés à plus grande échelle.

International audience; There is today a growing demand to develop green spaces in city, as they provide a support for biodiversity and can contribute to ecological connectivity with surroundings. Greening urban areas requires large amounts of arable soil that is a non-renewable resource. The purpose of our study is todetermine whether river dam sediments can be used as alternative materials to preserve soil resource in urban greening. Indeed, sediments are natural materials coming mainly from soils erosion available in large volumes. Sediments are composed of elementary mineral and organic particles. Each year in France, several hundred thousand cubic meters of sediments are dredged from EDF hydraulic power installations to ensure their correct operation, and returned to the river to respect the sedimentary continuity. In some cases, sediments may not be returned to water. Then, ways of valorization are sought. Most often they do not contain anthropic contaminants, in relation with their origin, far fromhuman activities (Brochier et al., 2016), but in some cases, they could contain traces of heavy metalscoming from the natural geochemical backgrounds.

International audience; The greening of urban and suburban areas requires large amounts of arable earth that is a non-renewable resource. However, concentration of population in cities leads to the production of high amounts of wastes and by-products that are nowadays partly recycled as a resource and quite systematically exported out of urban areas. To preserve natural soil resources, a strategy of waste recycling as fertile substitutes is proposed. Eleven wastes are selected for their environmental harmlessness and their contrasted physico-chemical properties for their potential use in pedological engineering. The aim is (i) to demonstrate the feasibility of the formulation of fertile substrates exclusively with wastes and (ii) to model their physico-chemical properties following various types, number and proportions of constitutive wastes. Twenty-five binary and ternary combinations are tested at different ratios for total carbon, Olsen available phosphorus, cation exchange capacity, water pH, water retention capacity and bulk density. Dose-response curves describe the variation of physico-chemical properties of mixtures depending on the type and ratio of selected wastes. If these mixtures mainly mimic natural soils, some of them present more extreme urban soil features, especially for pH and P Olsen. The fertility of the new substrates is modelled by multilinear regressions for the main soil properties.