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From waste to fertile Technosol - The circular approach of the french research SITERRE project.

Résumé

Today, 50 % of the world population is living in urban areas with an increasing evolution for the next decade. The modern city presents a “linear metabolism” that needs inputs (food, industrial products, raw materials) to develop all its activities with a lot of circulation and transformation of material resources. At the end of the metabolism chain, the city produces wastes that flow out of the urban system involving depletion of natural resources, pollution and toxic environments. Thus in the urban context, the balance, necessary for human physical and mental health, is a main issue that must be dealed with the environment and the nature. To preserve its viability, the urban system must evolve rapidly to a “circular metabolism” by decreasing input consumption and by limiting economic and ecological costs for the transportation, treatment and landfill of waste materials. For the well-being of inhabitants, it is thus necessary to reinvent the nature in town and the new relation between the people and the nature. This reconnection to the nature is very important for the new generations. It is a new ecological responsibility, a component of the public health, the source of emotion and delight and an element of social link. To understand the evolution of natural-human relationship in the urban context, we shall wonder about the best way to mimic natural ecosystems and favor circulation and reusing of resources in city. Cities develop greening and renaturation strategies whose success depends on the quality and functions of soils supporting vegetation. Therefore, large quantities of topsoil from agricultural or forestlands are used to implement urban green areas (in France, 3 million of m3 year -1). This practice for urban greening is currently controversial due to the decrease of arable surface area. Turning waste, produced by the city, into a resource of ‘secondary raw materials’ used to construct urban fertile soils could not only contribute to the reduction of threats on soil resources, but could also lead to an improved quality of urban green infrastructures. Organic and inorganic wastes could be used to construct new soils (Technosols) with fertile properties for ornamental greening. Such Technosols have to be able to support plant growth, tree development and light traffic. Thus, they must have adequate bearing capacity, agronomic properties, and drainage capacity. Moreover, they must comply with environmental restrictions to prevent pollutants release into the environment. The national research program (SITERRE, 2011-16) funded by the French Environmental Agency (ADEME) was dedicated to the construction of soils with urban wastes for city greening, as an alternative to the consumption of natural resources. The objectives of the program were to: (1) express the expected properties of soils that could fulfil optimally the main green area land-uses in terms of fertility, bearing capacity and environmental impacts, (2) define relevant indicators of the soil fertility and the expected quality for constructed soils, (3) propose constructed soil design profiles linked with land-uses, (4) identify and report the wastes that may be suitable for soil construction,(5) evaluate soil agronomic properties evolution under in situ conditions, and (6) check the safety of the mixtures for the environment and the health of the inhabitants. The evolution of the physico-chemical fertility of organic and mineral waste mixtures was described in the early stages following soil construction. The results confirmed that mixtures mimic natural soils with relevant physico-chemical properties while ensuring root development. The chemical fertility level is higher than agricultural soil references or standards, with available P contents ranging from 0.16 to 1 g kg-1 and nearly 3 to 20 times higher than the average concentrations of 0.05 g kg-1 of all French topsoils (Jolivet et al. 2006). The waste mixtures designed and tested during the SITERRE project are efficient to develop alternative fertile soils, providing the suitable soil functions for a sustainable urban landscape management, as well as ecosystem services for the cities: waste recycling, plant support, water filtering or climate regulation. To develop urban horticulture, it is essential to educate all the city makers (landscape architects, civil engineers, urban planners, municipal officials and urban farmers) about optimal soil specifications expected for urban soils and how to establish sustainable soil management. The results of the work, published in a book (Damas and Coulon, 2016) should now help to develop an efficient decision support system for urban landscape managers. But the use of alternative techniques for the construction of soil with waste requires the development of recycling facilities and a new sector of soil construction. The Technosols proposed by the SITERRE program are fertile provided they follow a precise protocol and call on expert appraisals. The strengths and weaknesses, the technical foundations, the economic model of this new sector have been developed within the framework of the SITERRE program and are presented in the last chapter of the book. This work has also included reflections on the regulatory provisions, the social acceptability of the sector and the associated communication challenges.
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Dates et versions

hal-02512100 , version 1 (19-03-2020)

Identifiants

  • HAL Id : hal-02512100 , version 1

Citer

Laure Vidal Beaudet, Patrice Cannavo, Christophe Schwartz, Geoffroy Séré, Béatrice Bechet, et al.. From waste to fertile Technosol - The circular approach of the french research SITERRE project.. International congress Sustainable Urban Agricultures: Vector for the Ecological Transition, Jun 2017, Toulouse, France. pp.Session 4. ⟨hal-02512100⟩
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