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International audience; Bioleaching of sulfidic mine wastes from the Iberian pyrite belt was studied in the framework of the H2020 project RAWMINA to recover critical raw materials and to remove sulfides. The study focused on the process development and optimization, and on the understanding of the mechanisms involved. Bioleaching tests were performed using a microbial consortium (Leptospirillum ferriphilum, Acidithiobacillus caldus and Sulfobacillus spp.) in 2-L stirred tank reactors (STRs) maintained at 42 °C at different operating conditions (solid content, pH control and CO2-enrichment of the gas phase). Main results showed good recovery of Co (~100%), Cu (75%) and Sb (~50%), little effect of CO2 gas enrichment on the microbial growth and a negative influence of low pH (< 1) on iron oxidation kinetics. Then, two continuous STRs in series (total volume of 6-L) were used to test the optimized operating conditions. This test also allowed increasing microorganisms' resistance to low-pH.

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International audience; Soil, surface water and groundwater in Martinique and Guadeloupe (French West Indies) are contaminated with chlordecone (CLD; C10Cl10O), a very persistent organochlorine pesticide. In soils, its persistence is estimated as several decades in nitisols, centuries in ferralsols and half a millennium in andosols. CLD accumulates in food chains. Long-term chronic exposure to CLD through food and drinking water can have consequences for human health.

In the framework of the H2020 project CROCODILE, the recovery of Co from oxidized ores by reductive bioleaching has been studied. The objective is to reduce Fe(III) into Fe(II) to enhance the dissolution of Co from New-Caledonian limonites, mainly composed of goethite and Mn oxides. This study focused on the Fe(III) bioreduction which is the rate-limiting mechanism of this process. In a first step, biomass growth was sustained by aerobic bio-oxidation of elemental sulfur. In a second step, the biomass anaerobically reduced Fe(III) into Fe(II). This study aims at optimizing the biomass growth on elemental sulfur and assessing the influence of the biomass concentration on the second step, i.e. the Fe(III) bioreduction rate and yield, both in batch and continuous mode. Parameters, such as pH, nutrient medium composition and sulfur concentration, were optimized. Kinetics of S biooxidation followed by Fe(III) bioreduction were determined in stirred tank reactors (STR) operated at 35 °C. The consortium was mainly composed of Acidithiobacillus ferrooxidans, Acidithiobacillus ferriphilus, Acidithiobacillus ferridurans and Sulfobacillus thermosulfidooxidans. In batch mode, the increase in numbers of bacteria from 4.10 8 cell/mL to 3.10 9 cell/mL resulted in an increase of the mean Fe(III) bioreduction rate from 2 to 10 mg/L/h (compared to 0.13 mg/L/h in the abiotic control). In continuous mode, after the optimization of the nutrient medium composition, the bioreduction rate reached up to 20 mg/L/h.

Soil is recognized as a major component of the functioning of terrestrial ecosystems and a key element for the provision of Ecosystem Services (ES). In a context of tensions over their use, the ecological rehabilitation of abandoned sites (industrial, urban or agricultural wasteland) is an opportunity to make territories more resilient to the consequences of climate change (Climate and Resilience Law, 2021) and to meet the objectives of preserving and restoring biodiversity (Biodiversity Plan, 2018). The question then arises of the reversibility of this soil degradation via refunctionalization, i.e. the restoration of ecological processes that should ultimately lead to the provision of ecosystem services adapted to these new uses. One of the obstacles to the success of ecological rehabilitation projects is linked to the difficulty of recreating functional ecosystems starting from degraded soil (compacted, sterile, impermeable). As part of the BioTubes project (https://expertises.ademe.fr/content/biotubes-bio-technosolsurbains-faveur-biodiversite-services-ecosystemiques), a urban wasteland was rehabilitated (Figure 1) using different ecological engineering paths including, soil decompaction or importation, controlled inoculation by microorganisms and sowing & planting of local plant species. The functioning of these soils, from which stems their ability to provide ES, is based on their physico-chemical but also biological parameters, in particular those of microbial communities and nematodes, which play a fundamental role in bio-geochemical cycles. For 3 years, monitoring of activity, biomass and microbial and nematofauna diversity were carried out in parallel with physico-chemical parameters and plant diversity in order to identify (bio)indicators that are witnesses of effective rehabilitation. In particular, this work has focused on integrating indicator measurements to reflect the state of soil ecological functions (Figure 2, carbon storage and dynamics, nutrient supply, habitat for biodiversity).