BackgroundPure bacterial strains give better yields when producing H2 than mixed, natural communities. However the main drawback with the pure cultures is the need to perform the fermentations under sterile conditions. Therefore, H2 production using artificial co-cultures, composed of well characterized strains, is one of the directions currently undertaken in the field of biohydrogen research.ResultsFour pure Clostridium cultures, including C. butyricum CWBI1009, C. pasteurianum DSM525, C. beijerinckii DSM1820 and C. felsineum DSM749, and three different co-cultures composed of (1) C. pasteurianum and C. felsineum, (2) C. butyricum and C. felsineum, (3) C. butyricum and C. pasteurianum, were grown in 20 L batch bioreactors. In the first part of the study a strategy composed of three-culture sequences was developed to determine the optimal pH for H2 production (sequence 1); and the H2-producing potential of each pure strain and co-culture, during glucose (sequence 2) and starch (sequence 3) fermentations at the optimal pH. The best H2 yields were obtained for starch fermentations, and the highest yield of 2.91 mol H2/ mol hexose was reported for C. butyricum. By contrast, the biogas production rates were higher for glucose fermentations and the highest value of 1.5 L biogas/ h was observed for the co-culture (1). In general co-cultures produced H2 at higher rates than the pure Clostridium cultures, without negatively affecting the H2 yields. Interestingly, all the Clostridium strains and co-cultures were shown to utilize lactate (present in a starch-containing medium), and C. beijerinckii was able to re-consume formate producing additional H2. In the second part of the study the co-culture (3) was used to produce H2 during 13 days of glucose fermentation in a sequencing batch reactor (SBR). In addition, the species dynamics, as monitored by qPCR (quantitative real-time PCR), showed a stable coexistence of C. pasteurianum and C. butyricum during this fermentation.ConclusionsThe four pure Clostridium strains and the artificial co-cultures tested in this study were shown to efficiently produce H2 using glucose and starch as carbon sources. The artificial co-cultures produced H2 at higher rates than the pure strains, while the H2 yields were only slightly affected.

The production rates and yields were investigated at 30 °C in a 2.3 l bioreactor operated in 19 batch and sequenced-batch mode using glucose and starch as substrates. In order to study the 20 precise effect of a stable pH on hydrogen production, and the metabolite pathway involved, 21 cultures were conducted with pH controlled at different levels ranging from 4.7 to 7.3 22 (maximum range of 0.15 pH unit around the pH level). For glucose the maximum yield (1.7 23 mol H 2 mol -1 glucose) was measured when the pH was maintained at 5.

In this paper, a simple and rapid method was developed in order to assess in comparative tests the production of binary biogas mixtures containing CO 2 and another gaseous compound such as hydrogen or methane. This method was validated and experimented for the characterisation of the biochemical hydrogen potential of different pure strains and mixed cultures of hydrogen-producing bacteria (HPB) growing on glucose.The experimental results compared the hydrogen production yield of 19 different pure strains and sludges : facultative and strict anaerobic HPB strains along with anaerobic digester sludges thermally pre-treated or not. Significant yields variations were recorded even between different strains of the same species by i.e. about 20% for three Clostridium butyricum strains. The pure Clostridium butyricum and pasteurianum strains achieved the highest yields i.e. up to 1,36 mol H 2 /mol glucose compared to the yields achieved by the sludges and the tested Escherichia and Citrobacter strains.

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Fermentative hydrogen production has often been described as inhibited by its own gas production. In this work, hydrogen production by Clostridium butyricum was investigated in batch Biochemical Hydrogen Potential (BHP) tests and in a 2.5 L Anaerobic Sequenced Batch Reactor (AnSBR) under different operating conditions regarding liquid-to-gas mass transfer.Through the addition of both stirring up to 400 RPM and nitrogen sparging, the yields were enhanced from 1.6 to 3.1 mol H2 ·mol glucose -1 and the maximum hydrogen production rates from 140 to 278 mL·h -1 . These original results were achieved with a pure Clostridium strain. They showed that hydrogen production was improved by a higher liquid-to-gas hydrogen transfer resulting in a lower dissolved hydrogen concentration in the culture medium and therefore in a lower bacterial inhibition. In addition, biohydrogen partitioning between the gas and the liquid phase did not conform to Henry's Law due to critical supersaturation phenomena up to seven-fold higher than the equilibrium conditions. Therefore dissolved hydrogen concentration should be systematically measured instead of the headspace hydrogen partial pressure. A model was proposed to correlate H 2 production yield and rate by the pure C.butyricum strain CWBI1009 with mass transfer coefficient K L a.

Lung PET/CT is a promising imaging modality for regional lung function assessment. Our aim was to develop and validate a fast, simple, and fully automated GMP compliant [68Ga]Ga-MAA labeling procedure, using a commercially available [99mTc]Tc-MAA kit, a direct gallium-68 eluate and including a purification of the [68Ga]Ga-MAA.Method: The synthesis parameters (pH, heating temperature) were manually determined. Automated 68Ga-labeling of MAA was then developed on a miniAIO (Trasis®, Ans, Belgium) module. An innovative automated process was developed for the purification. The process was then optimized and adapted to automate both the [68Ga]Ga-MAA synthesis and the isolation of gallium-68 eluate required for the pulmonary ventilation PET/CT.Results: The 15-min process demonstrated high reliability and reproducibility, with high synthesis yield (>95 %). Mean [68Ga]Ga-MAA radiochemical purity was 99 % ± 0.6 %. The 68Ga-labeled MAA particles size and morphology remained unchanged.Conclusion: A fast, user friendly, and fully automated process to produce GMP [68Ga]Ga-MAA for clinical use was developed. This automated process combining the advantages of using a non-modified MAA commercial kit, a gallium-68 eluate without pre-purification and an efficient final purification of the [68Ga]Ga-MAA may facilitate the implementation of lung PET/CT imaging in nuclear medicine departments.

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A horizontal tubular fixed bed bioreactor (HFBR) and an anaerobic biodisc-like reactor (AnBDR) were designed to both fix Clostridium biomass and enable rapid transfer of the hydrogen produced to gas phase in order to decrease the strong effect of H 2 partial pressure and H 2 supersaturation on the performances of Clostridium strains. The highest H 2 production rate (703 mL H 2 /L.h) and yield (302 mL/g glucose consumed i.e. 2.4 mol/mol) with the pure culture 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 g/L.h. These results are about 2.3 and 1.3-fold higher than those achieved in the same bioreactor with 500 mL liquid medium and with the same glucose consumption rate. Therefore, our experimentations and a short review of the literature reported in this paper emphasize the relevance of performing bioreactors with high L/G transfer.Keywords: Clostridium; hydrogen production; biofilm; bioreactor; pure strain CWBI -ULg 2/35 IntroductionThe fermentative production of hydrogen has drawn increased attention in recent years. This biological process called "dark fermentation" (DF) offers new opportunities to produce "green" energy from various renewable resources and organic wastes [1][2][3]. While significant improvements have been made in development of such alternative H 2 production systems, more technical progress and cost reduction needs to occur for them to compete with current large scale technologies e.g. methane-reforming process. By contrast, for local and smaller scale DF and some other opportunities, biohydrogen production processes would be cost competitive since the feedstocks are available almost anywhere and crucial interest is paid for both energy independence and efficient utilization [4,5]. However, optimization is still needed for DF regarding the bioreactor design, rapid removal and purification of gases, use of cheaper feedstock, genetic and molecular engineering to redirect metabolic pathway [6][7][8][9][10].Moreover, DF is only likely to be viable as an industrial process if integrated with a process that maximizes energy recovery from the fermentation end-products. The traditional methaneproducing anaerobic digestion process is the most promising since about 10 to 30 % more energy could be generated in the two-stage integrated system comparing to a single stage methanogenic process [11]. Besides, very prospective processes to convert acetate from DF spent medium exist such as further biohydrogen production (towards the maximum theoretical yield of 12 mol/mol glucose) by photosynthetic non-sulfur bacteria or direct electricity production in microbial fuel cells [6,11].In the past decades, most studies on biohydrogen production processes dealt with suspended culture systems such as the conventional (dis-)continuous stirred tank reactors (CSTR) since they are relatively simple and easy to operate. These investigations, several times reviewed [5,10,12,13], enabled to optimize number of operating parameters such as the ...