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Researchers Identify New Hydrogen- and Ethanol-Producing Bacteria That Withstand High Temperatures

A team of researchers from Finland, Iceland and Taiwan have found new strains of bacteria with the potential of producing hydrogen or ethanol fuels from wastewater now discharged from factories that process sugar beets, potatoes and other plant material.

Fermentations can produce fuels such as hydrogen and ethanol (EtOH) from biomass or organic waste materials. The goal of this research, reported in the Jan./Feb. issue of Energy & Fuels, a bi-monthly journal of the American Chemical Society, was to prospect efficient H2- and EtOH-producing thermophilic microorganisms derived from hot spring environments in Iceland that could withstand higher temperatures than microbes now in use.

Thermophilic H2 fermentation may have many advantages as compared to mesophilic fermentation but has remained less studied. High temperatures favor the stoichiometry of H2 production, resulting in higher H2 yields as compared to mesophilic systems. Furthermore, thermophilic fermentation is considered to have a narrower spectrum of end products as compared to mesophilic fermentation. Elevated temperature conditions may also reduce the enrichment of contaminating microorganisms during H2 fermentation processes. Further, some thermophilic bacteria can produce ethanol from lignocellulosic biomass, a process that is not feasible by brewer’s yeast. The use of inexpensive lignocellulosic materials, such as forestry wastes, agricultural residues, grasses, and other low-cost biomass, can significantly reduce the cost of ethanol production compared to the conventional methods based on yeast fermentation.

—Koskinen et. al.

The team obtained hydrogen- and EtOH-producing enrichment cultures from various hot spring samples over a temperature range of 50–78°C. The temperature dependencies for the most promising enrichments were determined with a temperature-gradient incubator.

One of the enrichments (33HL) produced 2.10 mol of H2/mol of glucose at 59 °C. Another enrichment (9HG), dominated by bacteria closely affiliated with Thermoanaerobacter thermohydrosulfuricus, produced 0.68 mol of H2/mol of glucose, and 1.21 mol of EtOH/mol of glucose at 78 °C.

Hydrogen and EtOH production by 9HG was characterized further in a continuous-flow bioreactor at 74°C. The highest H2 and EtOH yields of 9HG were obtained at pH 6.8 ± 0.3. Lactate production decreased the H2 and EtOH yields in the continuous-flow bioreactor, and the yields were lower than those obtained in the batch fermentations.

Although the enrichments are promising, the team concluded, the full H2 and ethanol production potential of the enrichments has yet to be revealed.




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