Microbiology of synthesis gas fermentation for biofuel production 朱琴娥

Background What we shoud do with these problem?

What way we can obtain clean and sustainable energy supply?

Method Ⅰ Shorting: the conversion rate is very low.

Method Ⅱ Gasification coal chemistry Fossil fuelsbiomass Gasification Syngas AcetateEthanolButyrateOthers production Source and application of syngas

Syngas (CO,H 2 O)

WGS: Syngas fermentation Higher specificity biocatalysting Lower energy costs Resistance to catalyst poisoning Independence of a fixed H2:CO ratio

For example: Clostridium ljungdahlii commercial process step: Biomass gasification Syngas fermentation Distillation of ethanol from the reactor effluent

The way of stimulate gas/liquid mass transfer rate  High gas and liquid flow rates  Large specific gas–liquid interfacial areas  Increased gas solubility (increased pressure or solvents) Question? Sparingly soluble gases result in low conversion rate……

 Continuous stirred tank reactors (CSTR)  Membrane biofilm reactor (MBfR)  Biotrickling filter  Monolith biofilm reactors

Carboxydotrophic thermophiles Before Carboxydocella sporoproducens Desulfotomaculum carboxydivorans both convert CO to acetate optimum growth temperatures of 55 ℃ and 80 ℃ doubling times of 10 h and 7 h others might also grow organotrophically Recently carboxydotrophic hydrogenogens Chemolithoautotrophically through the conversion of CO and H2O to H2 and CO2. optimum growth temperatures of 55 ℃ and 80 ℃ growth rates between 1 and 2 h encode CO dehydrogenases Thermoanaerobacter tengcongensis Archaeoglobus fulgidus

The acetyl-CoA pathway and CO dehydrogenase

Metabolic engineering Metabolic engineering of these organisms with the aim of producing of a specific compound can thus be accompanied by the formation of undesired byproducts, which are formed to satisfy the redox balance Additional separation techniques are then required to obtain a purified product. CO 2 CO oxidation NADPH NADP + Dehydrogenation ATP ADP

Syngas fermentation is an attractive technology for the production of biofuels and chemicals. A process for ethanol production from syngas is already available, and pureH2 production is possible as well. At present, suitable thermophiles for the production of organic compoundsfrom syngas are not available, although their use could offer potential advantages over the use of mesophiles. Thermophiles that employ CO as a substrate for theproduction of chemicals could be selected based on theidentification of CO dehydrogenase genes in their genome. Better still would be the isolation of new thermophiles that use CO or syngas as a substrate at conditionsthat resemble expected bioreactor conditions. Conclusions