34,250 research outputs found

    Electro-extractive fermentation for efficient biohydrogen production

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    Electrodialysis, an electrochemical membrane technique, was found to prolong and enhance the production of biohydrogen and purified organic acids via the anaerobic fermentation of glucose by Escherichia coli. Through the design of a model electrodialysis medium using cationic buffer, pH was precisely controlled electrokinetically, i.e. by the regulated extraction of acidic products with coulombic efficiencies of organic acid recovery in the range 50–70% maintained over continuous 30-day experiments. Contrary to\ud previous reports, E. coli produced H2 after aerobic growth in minimal medium without inducers and with a mixture of organic acids dominated by butyrate. The selective separation of organic acids from fermentation provides a potential nitrogen-free carbon source for further biohydrogen production in a parallel photofermentation. A parallel study incorporated this fermentation system into an integrated biohydrogen refinery (IBR) for the conversion of organic waste to hydrogen and energy

    Efficient molasses fermentation under high salinity by inocula of marine and terrestrial origin

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    BACKGROUND: Molasses is a dense and saline by-product of the sugar agroindustry. Its high organic content potentially fuels a myriad of renewable products of industrial interest. However, the biotechnological exploitation of molasses is mainly hampered by the high concentration of salts, an issue that is nowadays tackled through dilution. In the present study, the performance of microbial communities derived from marine sediment was compared to that of communities from a terrestrial environment (anaerobic digester sludge). The aim was to test whether adaptation to salinity represented an advantage for fermenting molasses into renewable chemicals such as volatile fatty acids (VFAs) although high sugar concentrations are uncommon to marine sediment, contrary to anaerobic digesters. RESULTS: Terrestrial and marine microbial communities were enriched in consecutive batches at different initial pH values (pH(i); either 6 or 7) and molasses dilutions (equivalent to organic loading rates (OLRs) of 1 or 5 g(COD) L(−1) d(−1)) to determine the best VFA production conditions. Marine communities were supplied with NaCl to maintain their native salinity. Due to molasses inherent salinity, terrestrial communities experienced conditions comparable to brackish or saline waters (20–47 mS cm(−1)), while marine conditions resembled brine waters (>47 mS cm(−1)). Enrichments at optimal conditions of OLR 5 g(COD) L(-1) d(-1) and pH(i) 7 were transferred into packed-bed biofilm reactors operated continuously. The reactors were first operated at 5 g(COD) L(-1) d(-1), which was later increased to OLR 10 g(COD) L(−1) d(−1). Terrestrial and marine reactors had different gas production and community structures but identical, remarkably high VFA bioconversion yields (above 85%) which were obtained with conductivities up to 90 mS cm(−1). COD-to-VFA conversion rates were comparable to the highest reported in literature while processing other organic leftovers at much lower salinities. CONCLUSIONS: Although salinity represents a major driver for microbial community structure, proper acclimation yielded highly efficient systems treating molasses, irrespective of the inoculum origin. Selection of equivalent pathways in communities derived from different environments suggests that culture conditions select for specific functionalities rather than microbial representatives. Mass balances, microbial community composition, and biochemical analysis indicate that biomass turnover rather than methanogenesis represents the main limitation to further increasing VFA production with molasses. This information is relevant to moving towards molasses fermentation to industrial application. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13068-017-0701-8) contains supplementary material, which is available to authorized users

    Thermodynamic, economic and environmental assessment of energy systems including the use of gas from manure fermentation in the context of the Spanish potential

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    One of the prospective technologies that can be used for energy generation in distributed systems is based on biogas production, usually involving fermentation of various types of biomass and waste. This article aims to bring novelty on the analysis of this type of systems, joining together thermodynamic, economic and environmental aspects for a cross-cutting evaluation of the proposed solutions. The analysis is made for Spain, for which such a solution is very promising due to availability of the feedstock. A detailed simulation model of the proposed system in two different cases was built in Aspen Plus software and Visual Basic for Applications. Case 1 involves production of biogas in manure fermentation process, its upgrading (cleaning and removal of CO2 from the gas) and injection to the grid. Case 2 assumes combustion of the biogas in gas engine to produce electricity and heat that can be used locally and/or sold to the grid. Thermodynamic assessment of these two cases was made to determine the most important parameters and evaluation indices. The results served as input values for the economic analysis and environmental evaluation through Life Cycle Assessment of the energy systems. The results show that the analysed technologies have potential to produce high-value products based on low-quality biomass. Economic evaluation determined the break-even price of biomethane (Case 1) and electricity (Case 2), which for the nominal assumptions reach the values of 16.77 €/GJ and 28.92 €/GJ, respectively. In terms of environmental assessment the system with the use of biogas in gas engine presents around three times better environmental profile than Case 1 in the two categories evaluated, i.e., carbon and energy footprint.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 799439. Dr. Martín-Gamboa states that thanks are due to FCT/MCTES for the financial support to CESAM (UID/AMB/50017/2019), through national funds

    Improvement of Biogas Production by Bioaugmentation

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    Biogas production technologies commonly involve the use of natural anaerobic consortia of microbes. The objective of this study was to elucidate the importance of hydrogen in this complex microbial food chain. Novel laboratory biogas reactor prototypes were designed and constructed. The fates of pure hydrogen-producing cultures of Caldicellulosiruptor saccharolyticus and Enterobacter cloacae were followed in time in thermophilic and mesophilic natural biogas-producing communities, respectively. Molecular biological techniques were applied to study the altered ecosystems. A systematic study in 5-litre CSTR digesters revealed that a key fermentation parameter in the maintenance of an altered population balance is the loading rate of total organic solids. Intensification of the biogas production was observed and the results corroborate that the enhanced biogas productivity is associated with the increased abundance of the hydrogen producers. Fermentation parameters did not indicate signs of failure in the biogas production process. Rational construction of more efficient and sustainable biogas-producing microbial consortia is proposed

    Development of a D-xylose fermenting and inhibitor tolerant industrial Saccharomyces cerevisiae strain with high performance in lignocellulose hydrolysates using metabolic and evolutionary engineering

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    Background: The production of bioethanol from lignocellulose hydrolysates requires a robust, D-xylose-fermenting and inhibitor-tolerant microorganism as catalyst. The purpose of the present work was to develop such a strain from a prime industrial yeast strain, Ethanol Red, used for bioethanol production. Results: An expression cassette containing 13 genes including Clostridium phytofermentans XylA, encoding D-xylose isomerase (XI), and enzymes of the pentose phosphate pathway was inserted in two copies in the genome of Ethanol Red. Subsequent EMS mutagenesis, genome shuffling and selection in D-xylose-enriched lignocellulose hydrolysate, followed by multiple rounds of evolutionary engineering in complex medium with D-xylose, gradually established efficient D-xylose fermentation. The best-performing strain, GS1.11-26, showed a maximum specific D-xylose consumption rate of 1.1 g/g DW/h in synthetic medium, with complete attenuation of 35 g/L D-xylose in about 17 h. In separate hydrolysis and fermentation of lignocellulose hydrolysates of Arundo donax (giant reed), spruce and a wheat straw/hay mixture, the maximum specific D-xylose consumption rate was 0.36, 0.23 and 1.1 g/g DW inoculum/h, and the final ethanol titer was 4.2, 3.9 and 5.8% (v/v), respectively. In simultaneous saccharification and fermentation of Arundo hydrolysate, GS1.11-26 produced 32% more ethanol than the parent strain Ethanol Red, due to efficient D-xylose utilization. The high D-xylose fermentation capacity was stable after extended growth in glucose. Cell extracts of strain GS1.11-26 displayed 17-fold higher XI activity compared to the parent strain, but overexpression of XI alone was not enough to establish D-xylose fermentation. The high D-xylose consumption rate was due to synergistic interaction between the high XI activity and one or more mutations in the genome. The GS1.11-26 had a partial respiratory defect causing a reduced aerobic growth rate. Conclusions: An industrial yeast strain for bioethanol production with lignocellulose hydrolysates has been developed in the genetic background of a strain widely used for commercial bioethanol production. The strain uses glucose and D-xylose with high consumption rates and partial cofermentation in various lignocellulose hydrolysates with very high ethanol yield. The GS1.11-26 strain shows highly promising potential for further development of an all-round robust yeast strain for efficient fermentation of various lignocellulose hydrolysates