Diagnosis of Waste Treatments for Contaminant Fates in the Environment – DIGESTATE

Le programme scientifique est articulé entre des expériences de laboratoire, des outils de modélisation et des compétences pluridisciplinaires. La quantification et la spéciation des contaminants seront évalués pour une sélection de déchets bruts et traités. Les phases porteuses des contaminants et leur comportement (mobilité, phytodisponibilité) seront caractérisés dans des systèmes simplifiés pour affiner notre connaissance des mécanismes mis en jeu. Suite à l’apport au sol d’une sélection de OW, nous quantifierons la proportion de contaminants absorbés par les plantes ou transportés à travers le sol. L’ensemble des résultats expérimentaux et de modélisation acquis dans les WP 1, 2 et 3 alimenteront l’évaluation environnementale qui permettra une comparaison des bilans agro-environnementaux depuis la filière de traitement jusqu’au recyclage agricole des OW.

La quantification et la spéciation des contaminants inorganiques, organiques et biologiques pour l’ensemble des déchets organiques bruts, compostés ou méthanisés échantillonnés sont maintenant acquises ou en cours de finalisation. L’impact du traitement des déchets est notable en terme de concentration et de spéciation des contaminants, mais cet impact est variable entre les familles de contaminants (inorganiques, organiques ou biologiques). Ce premier résultat marquant confirme l’enjeu du projet de proposer un outil de diagnostic pour raisonner le choix du traitement en amont de la mise en œuvre du recyclage.

A mi-projet, il est encore trop tôt pour proposer quelques perspectives thématiques ou techniques dans le prolongement de DIGESTATE.
L’acquisition des données de base va permettre à court terme de développer un premier outil d’évaluation environnemental.

Deux publications et trois présentations lors de conférences ont été réalisés. Ces productions présentent les premiers résultats liés aux contaminants biologiques et inorganiques au sein de divers déchets organiques.

Ever-increasing waste production has prompted the need for new provisions regarding waste management to ensure sustainable development. There is now a global consensus among scientists, economists, politicians and civil society stakeholders on the necessity to recycle resources and close loops in a circular economy. Agricultural recycling makes it possible to effectively and synergistically use livestock, urban and agro-industrial organic waste (OW). From a waste management standpoint, aerobic digestion (composting) and anaerobic digestion are the most obvious and operational processes for OW treatment prior to soil application. Composting OW is seen as an effective method for diverting organic materials from landfills, while reducing the waste volume, eliminating pathogens and creating a stable product suitable for application in crop fields. Anaerobic digestion has also significantly increased in several European countries and represents an opportunity to convert OW into biogas and organic fertilizer (digestate).

The choice of using either raw OW, compost or digestate as fertilizer and soil amendment should be based on a comprehensive assessment of potential benefits and negative effects. Among these negative effects, the lack of understanding regarding the impact of treatments on contaminant speciation, microbial pathogen selection and antimicrobial resistance emergence, and the scarcity of knowledge on the fate of contaminants following soil OW application are key scientific challenges that the DIGESTATE project aims to meet.

The overall objective of DIGESTATE is to develop an original environmental assessment of OW treatments and agricultural recycling. Such environmental assessment involves estimation of environmental consequences (positive and negative) expected to result from OW treatment and recycling scenarios prior to decision making. This assessment will include indicators which are: (i) conventional (agronomic quality of the OW; energy recovery of treatment processes) and (ii) non-standard (fate of contaminants following OW application in water-soil-plant systems).
We will focus our efforts on the ecodynamics of three main classes of contaminants in water-soil-plant systems: (i) trace elements: Cu and Zn, (ii) organic pollutants: PAHs, nonylphenols and pharmaceuticals and (iii) microbial pathogens and antimicrobial resistance genes. We will compare the impact of two major digestion treatments (composting, anaerobic digestion and their combination) on: (i) the speciation of organic and inorganic contaminants, the selection of particular microbial groups and genetic properties in OW, and (ii) the fate (phytoavailability and transport in soil) of contaminants after soil OW application.

The scientific programme is based on laboratory experiments, modeling tools and multidisciplinary approaches. First, contaminant quantification and speciation will be assessed for selected raw and treated OW (WP1). Then fundamental knowledge will be produced on contaminant-bearing phases formed during OW treatment (WP2). After OW spreading on a soil, the proportion of contaminants taken up by plants or transported through the soil will be experimentally quantified (WP3). The experimental and modelling datasets from WP1, 2 and 3 will finally fuel the environmental assessment of OW treatment and recycling based on innovative assessment methodologies (WP4).