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New bioreactor technology was recently developed for bioleaching applications. It consists of ponds where pulp suspension and gas-liquid mass transfer are achieved with floating agitators. Bioleaching reactions are significantly exothermic with high oxygen requirements. Temperature regulation is usually required in bioleaching reactors to maintain biological activity. Contrary to conventional stirred tank reactors, the temperature in ponds cannot be easily regulated through heat exchangers. A numerical strategy was developed to design an industrial application of the concept and to select suitable operating parameters. First, computational fluid dynamics (CFD) was used to model the hydrodynamics of the system and to define the volume of influence of one single agitator, the number of floating agitators and the mechanical power dissipated into the fluid. Then, a numerical model was developed using MatLab to quantify the contribution of the operating and environmental conditions to the heat balance and their influence on temperature regulation. Various scenarios were simulated (equatorial and sub-arctic climates, sulfide concentration, pond geometries). At industrial scale, the environmental conditions have little influence on the heat balance, which is mainly dominated by the reaction enthalpy. It was demonstrated that the temperature could be maintained in a suitable range (40 to 50°C) by controlling the fresh pulp inlet conditions (flow rate, temperature) and the aeration (flow rate, oxygen partial pressure), even at low sulfide concentration (between 5 and 10%).

A new technology of bioreactor was recently developed for bioleaching applications. It consists in ponds where pulp suspension and gas-liquid mass transfer are achieved with floating agitators [1,2]. Bioleaching reactions are significantly exothermic with high oxygen requirements and thus need temperature regulation to maintain biological activity. Contrary to conventional stirred tank reactors, the temperature in ponds may be difficult to regulate through heat exchangers. A numerical strategy was developed to design an industrial demonstration of the concept and to select suitable operating parameters. Firstly, Computational Fluid Dynamics was used to model the system's hydrodynamics and to define the volume of influence of one single agitator, the number of floating agitators and the mechanical power dissipated into the fluid. Then, a heat balance model was developed to characterize the impact of each heat transfer contribution (operating and environmental conditions) on temperature regulation. Various location (equatorial and sub-arctic climates) and geometries (stirred tank, pond) were simulated for the model development. These simulations showed that, for low sulfide concentrations, by controlling aeration (flow rate and oxygen partial pressure) and the fresh pulp inlet conditions (flow rate, temperature), the temperature can be maintained in a suitable range (40 to 50°C).

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International audience; Mesenchymal stromal/stem cells (MSCs) are of great interest in developing new therapies because of their capacity of self-renewal, differentiation and modulation of inflammation or even immunosuppression. However, in vitro expansion is essential before the use of these cells in the clinic, which can lead to changes in the cell properties. The challenge is to optimize the culture conditions and to choose the most appropriate media for the culture of MSC to ensure that they retain their functional properties and thus their therapeutic potential. Moreover, it is necessary to fix parameters related to cell quality that could allow the selection of samples to be used. Currently, the main sources of media supplements used are fetal calf serum (FCS) and human platelet lysate (hPL). The aim of our study was to compare the characteristics and potential of bone marrow and Wharton jelly MSCs cultured in parallel in FCS and in hPL-containing medium. Experiments were performed under hypoxia (2% O2) or normoxia (21% O2) conditions. This study revealed differences in cell behavior depending on the culture condition. The behavior of the cells was related to differential expression of some surface markers and morphological alterations. Cell differentiation capacities were found to be equivalent. These first results confirm the modification of the characteristics of MSCs according to the medium used. These observations must be combined with other functional tests depending on the intended therapeutic application before being able to conclude on the superiority of one culture method over the other.

International audience

International audience