Réacteurs à biomasse fixée destinés à la production d'hydrogène par fermentation obscure

Résumé en anglais: "Dark fermentation is the fermentative conversion of organic substrate to biohydrogen (bio-H2) and volatile fatty acids. Fermenting bacteria can utilize complex forms of organic substrate, thus indicating a very interesting potential market of organic waste and wastewater valorisation for the production of bio-H2. The technical feasibility of H2 production from wastewater has been largely investigated in continuous-flow anaerobic biofilm reactors (ABRs) using mixed bacterial cultures. However, many studies have shown low H2 yields and instable H2 production, as the result of the variability of microbial dynamics and metabolic pathways. Therefore, the most important challenge for future research is to improve operation and design of the reactor in order to obtain a stable and efficient H2 production. Metabolic engineering techniques might be a feasible option to redirect metabolic pathways and improve H2 yields. Recent batch studies have shown that sub-dominant bacteria (Desulfovibrio vulgaris) can have a significant effect on H2 production performances of dominant species (Clostridia) (Benomar et al., 2015). In the frame of a global research project from the production to the use of bio-H2 (project Happi-prod, CNRS, France), the H2 production performances of a co-culture of Clostridium acetobutylicum and Desulfovibrio vulgaris were evaluated in two laboratory-scale ABRs. The novelty and the importance of this study consist in the interdisciplinary approach that involves the integrated skills of chemical engineering and microbiology of two research teams applied to the scale-up from batch to continuous-flow experiments: (i) the Waste and Wastewater Treatment Team, laboratory M2P2 UMR CNRS 7340, and (ii) the Extremophile Metabolism Team, laboratory BIP CNRS UMR 7281. Firstly, the effect of various operating parameters, including void hydraulic retention time (HRTv), pH, and inlet water quality, on H2 production performances was investigated in order to establish the best operating conditions for the reactors. Secondly, molecular biology (PCR) and metabolic analyses (HPLC) were performed to evaluate the effects of the main operating parameters on microbial dynamics and metabolic pathways. The results indicated that a stable H2 production was reached after 3-4 days of operation. The main results of the study will be presented, and the effect of the various operating parameters on H2 production rates, H2 content of biogas and H2 yields will be discussed. Finally, a few perspectives and technical challenges to improve reactor performances will be proposed."