Influence of pH and stirring on the hydrogen production by a pure Clostridium strain.

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Optimisation of culture conditions for biological hydrogen production by Citrobacter freundii CWBI952 in batch, sequenced-batch and semicontinuous operating mode

Investigations were carried out to determine the effect of the pH, the nitrogen source, iron and the dilution rate (h 1) on fermentative hydrogen production from glucose by the newly isolated strain Citrobacter freundii CWBI952. The hydrogen production rate (HPR), hydrogen yield, biomass and soluble metabolites were monitored at 30 C in 100 mL serum bottles and in a 2.3 L bioreactor operated in batch, sequenced-batch and semicontinuous mode. The results indicate that hydrogen production activity, formate biosynthesis and glucose intake rates are very sensitive to the culture pH, and that additional formate bioconversion and production of hydrogen with lower biomass yields can be obtained at pH 5.9. In a further series of cultures casein peptone was replaced by (NH4)2SO4, a low cost alternative nitrogen source. The ammonia-based substitute was found to be suitable for H2 production when a concentration of 0.045 g/L FeSO4 was provided. Optimal overall performances (ca. an HPR of 33.2 mL H2/L h and a yield of 0:83 molH2 =molglucose) were obtained in the semicontinuous culture applying the previously optimized parameters for pH, nitrogen, and iron with a dilution rate of 0.012 h 1 and degassing of biogas by N2 at a 28 mL/min flow rate.Micro-H2 : Production microbiologique d’hydrogène : Etude des processus microalgal et bacterie

Physicochemical And Biochemical Characterization Of Non-Biodegradable Cellulose In Miocene Gymnosperm Wood From The Entre-Sambre-Et-Meuse, Southern Belgium

Specimens of Miocene fossil wood from the Entre-Sambre-et-Meuse karsts (southern Belgium) were examined using physicochemical and biochemical techniques in order to understand the reasons for the exceptional preservation of these fossilized remains after 15 million years. Structural and chemical changes were assessed by comparing the structural features of the fossil samples with those of their modern counterpart, Metaseguoia. Solid state C-13 nuclear magnetic resonance (NMR) and microscopic analysis showed good preservation of the cellulose structure in the fossil wood from the Florennes peat deposit. Despite the substantial cellulose fraction available in the fossil tissue, an enzymatic degradation test and a biochemical methane potential assay showed that the fossil cellulose could not be degraded by cellulases and anaerobic microorganisms usually involved in the biodegradation of organic matter. Moreover, the cellulose structure (crystallinity and surface area) seemed to have no effect on cellulose biodegradability in these Miocene fossil wood samples. On the basis of our observations, we suggest that the presence of a modified lignin structure could greatly influence cellulose preservation/biodegradability

Genome-wide transcriptional analysis suggests hydrogenase- and nitrogenase-mediated hydrogen production in Clostridium butyricum CWBI 1009

[en] Background: Molecular hydrogen, given its pollution-free combustion, has great potential to replace fossil fuels infuture transportation and energy production. However, current industrial hydrogen production processes, such assteam reforming of methane, contribute significantly to the greenhouse effect. Therefore alternative methods, inparticular the use of fermentative microorganisms, have attracted scientific interest in recent years. However thelow overall yield obtained is a major challenge in biological H2 production. Thus, a thorough and detailedunderstanding of the relationships between genome content, gene expression patterns, pathway utilisation andmetabolite synthesis is required to optimise the yield of biohydrogen production pathways.Results: In this study transcriptomic and proteomic analyses of the hydrogen-producing bacterium Clostridiumbutyricum CWBI 1009 were carried out to provide a biomolecular overview of the changes that occur when themetabolism shifts to H2 production. The growth, H2-production, and glucose-fermentation profiles were monitoredin 20 L batch bioreactors under unregulated-pH and fixed-pH conditions (pH 7.3 and 5.2). Conspicuous differenceswere observed in the bioreactor performances and cellular metabolisms for all the tested metabolites, and theywere pH dependent. During unregulated-pH glucose fermentation increased H2 production was associated withconcurrent strong up-regulation of the nitrogenase coding genes. However, no such concurrent up-regulation ofthe [FeFe] hydrogenase genes was observed. During the fixed pH 5.2 fermentation, by contrast, the expressionlevels for the [FeFe] hydrogenase coding genes were higher than during the unregulated-pH fermentation, whilethe nitrogenase transcripts were less abundant. The overall results suggest, for the first time, that environmentalfactors may determine whether H2 production in C. butyricum CWBI 1009 is mediated by the hydrogenases and/orthe nitrogenase.Conclusions: This work, contributing to the field of dark fermentative hydrogen production, provides amultidisciplinary approach for the investigation of the processes involved in the molecular H2 metabolism ofclostridia. In addition, it lays the groundwork for further optimisation of biohydrogen production pathways basedon genetic engineering techniques.info:eu-repo/semantics/publishe

Production de biohydrogène à partir de biomasses

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Valorisation de la biomasse par biométhanisation : Comment tirer profit des déchets organiques

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Biohydrogen production from carbohydrate substrates using dark-fermentation process

Hydrogen (H2) is being considered as an ideal and clean energy carrier since the utilization of hydrogen, either via combustion or via fuel cells, results in pure water. The recent advances to produce biohydrogen from renewable sources such as biomass and particularly by fermentation of carbohydrate-rich substrates from agriculture and agro-industries appear promising. Such a process called “dark fermentation” enables both organic waste treatment and renewable energy production to be coupled. In the thesis different hydrogen-producing microorganisms were studied and some environmental parameters and bioreactors have been investigated in order to improve the hydrogen production yields and rates. The experimental results compared the hydrogen production yield of 19 different pure strains and sludges : facultative and strict anaerobic H2-producing strains along with anaerobic digester sludges thermally pre-treated (to enrich the microflora in high H2-producers) or not. Significant yields variations were recorded even between different strains of the same species (up to 20% of variation). The pure Clostridium butyricum (C. but.) strains achieved the highest yields i.e. up to 172 L H2 produced per kilogram of glucose consumed (1.38 mol H2 / mol glucose). Two efficient H2-producing strains (C. but. CWBI1009 and Citrobacter freundii CWBI952) were further studied in order to determine the optimum culture conditions for the production of hydrogen. A 2.3 L bioreactor was operated at 30 °C in batch and sequenced-batch mode using glucose and starch as substrates. For glucose the maximum yield (211 L H2 / kg or 1.7 mol H2 / mol glucose) was measured with the C. but. strain when the pH was maintained at 5.2. In sequenced-batch reactor a 35% increase in H2 yield was obtained with removal–addition of 40% of the culture medium at the beginning of each sequence. For operation in continuous mode, original bioreactors such as an anaerobic biodisc reactor (AnBDR) were designed to both fix biomass and enable rapid liquid to gas transfer of hydrogen produced since H2 partial pressure and H2 supersaturation are known as hardly affecting hydrogen production performances. The highest and stable H2 production rate (703 L H2 per hour and per m³ of liquid volume inside the bioreactor) and yield (302 L / kg glucose consumed i.e. 2.4 mol/mol) with the pure culture of C. but. CWBI1009 were recorded in the AnBDR with 300 mL culture medium (total volume 2.3 L) at pH 5.2 and a glucose loading rate of 2.87 kg / m³.h. These results achieved with pure strains are relevant compared to the highest H2 yields and rates reported in the literature with mixed cultures and achieved in reactors, such as trickle bed bioreactors, with high gas transfer performances. Moreover, the soluble metabolites, mainly acetate and butyrate, contained in the spent medium of the dark fermentation bioreactor were efficiently converted to methane in a second anaerobic digester (20 L continuously stirred tank) with a methane yield of about 170 L/kg COD initially fed in the first stage. These results demonstrate that a two-step anaerobic digestion process may be carried out in two successive bioreactors, both with specific and optimized parameters, in order to generate separated biogas flows containing either H2 or CH4. In addition to the advantages related to both gaseous molecule properties, many technological improvements would be achieved by this way : better hydrolysis, higher process stability, etc. The general discussion highlights the central and relevant position of the 2-stage anaerobic digestion process in the panorama of technologies able to both treat raw or residual organic matter and to produce energy or energy vectors for stationary or mobile end-use. The technical, economical and environmental aspects have been considered.L’hydrogène (H2) est considéré comme un vecteur d’énergie idéal et propre : son utilisation dans des piles à combustible ou sa combustion résulte essentiellement en un rejet d’eau. Les dernières avancées au niveau de la valorisation énergétique de la biomasse laissent entrevoir une place non négligeable pour la production de biohydrogène par fermentation de substrats riches en composés carbohydratés tels que les sous-produits d'origine agricole ou eaux résiduaires des industries agro-alimentaires. Un tel procédé appelé “dark fermentation” permet de coupler épuration d’une charge organique et production d’énergie renouvelable. Dans la thèse, différents types de microorganismes producteurs d'hydrogène ainsi que plusieurs paramètres environnementaux et bioréacteurs ont été étudiés en vue d'améliorer les productivités et rendements de production d’hydrogène. Les expérimentations ont permis de comparer les rendements de production d’hydrogène de 19 souches pures et cultures mixtes différentes : souches pures de bactéries anaérobies facultatives ou strictes ainsi que des boues de digesteurs anaérobies, après d’éventuels traitements thermiques pour enrichir la microflore en microorganismes hyper producteurs d’H2. Des variations significatives de rendement ont été enregistrées même pour des souches de la même espèce (jusqu’à 20 % de variation). Les rendements les plus élevés, de l’ordre de 172 L H2 produits par kilogramme de glucose consommé (1.38 mol H2 / mol glucose), ont été atteints par les souches pures de Clostridium butyricum (C. but.). Deux souches productrices d’H2 particulièrement intéressantes (C. but. CWBI1009 et Citrobacter freundii CWBI952) ont été étudiées de façon plus approfondie dans l’optique de déterminer les conditions de culture optimales pour la production d’H2. Ces travaux ont été menés en bioréacteur de 2.3L à 30°C en mode batch et séquentiel avec le glucose ou l’amidon comme substrat. Le rendement d’H2 maximum a été mesuré sur glucose (211 L H2 / kg ou 1.7 mol H2 / mol glucose) avec la souche C. but. au pH contrôlé à une valeur de 5.2. En mode séquentiel, 35% d’augmentation du rendement ont pu être obtenus en opérant un retrait/ajout de 40% du milieu de culture en début de chaque séquence. Pour les opérations en mode continu, des bioréacteurs originaux tels qu’un réacteur à biodisque anaérobie (AnBDR) ont été mis en œuvre pour, à la fois immobiliser la biomasse et permettre un transfert rapide vers la phase gazeuse de l’hydrogène produit en phase liquide. Il s’agit ainsi de pallier l’impact de la pression partielle et de la sursaturation en H2 affectant lourdement les rendements et productivités d’H2. Les performances les plus remarquables en productivité d’H2 (703 L H2 par heure et par m³ de volume liquide au sein du bioréacteur) et rendement (302 L / kg glucose dégradé, soit 2.4 mol/mol) ont été enregistrées avec la souche pure de C. but. CWBI1009 dans l’AnBDR avec 300 mL de milieu de culture (volume total de 2.3 L) au pH de 5.2 et avec une charge organique en glucose de 2.87 kg / m³.h. Ces résultats importants obtenus avec des souches pures sont comparables aux meilleurs rendements et productivités d’H2 rapportés dans la littérature pour des cultures mixtes et concernant des réacteurs à haut pouvoir de transfert gazeux tels que les bioréacteurs à lit arrosé. De plus, les métabolites solubles, principalement l’acétate et le butyrate, contenus dans l’effluent du bioréacteur de dark fermentation ont pu être convertis efficacement en méthane dans un second bioréacteur anaérobie (à cuve agitée de 20 L) avec un rendement en méthane de l’ordre de 170 ml/g DCO initialement introduite dans le premier bioréacteur. Ces résultats démontrent la faisabilité d’une digestion anaérobie classique en deux étages, optimisés individuellement pour produire deux types de biogaz contenant soit de l’H2 ou du CH4. En plus des avantages liés aux propriétés intrinsèques de ces deux molécules gazeuses, plusieurs améliorations du procédé peuvent être visées de cette manière : hydrolyse plus approfondie, plus grande stabilité du procédé, etc. La discussion générale met en évidence le rôle central et important du procédé de digestion anaérobie en deux phases dans le panel des technologies capables à la fois de traiter des matières premières organiques ou résiduelles et de produire de l’énergie ou un vecteur énergétique pour des applications stationnaires ou mobiles. Les aspects techniques, économiques et environnementaux ont été pris en considération

Potential association of acidogenic bacteria and highly effective sulfate reducers for bioconversion of gypsum industrial by-product

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Valorisation énergétique des déchets organiques par biométhanisation

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Introduction aux biotechnologies industrielles et applications

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