To examine the potential use of synthesis gas as a carbon and energy source in fermentation processes, Rhodospirillum rubrum was cultured on synthesis gas generated from discarded seed corn. The growth rates, growth and poly-beta-hydroxyalkanoates (PHA) yields, and CO oxidation/H(2) evolution rates were evaluated in comparison to the rates observed with an artificial synthesis gas mixture. Depending on the gas conditioning system used, synthesis gas either stimulated or inhibited CO-oxidation rates compared to the observations with the artificial synthesis gas mixture. Inhibitory and stimulatory compounds in synthesis gas could be removed by the addition of activated charcoal, char-tar, or char-ash filters (char, tar, and ash are gasification residues). In batch fermentations, approximately 1.4 mol CO was oxidized per day per g cell protein with the production of 0.75 mol H(2) and 340 mg PHA per day per g cell protein. The PHA produced from R. rubrum grown on synthesis gas was composed of 86% beta-hydroxybutyrate and 14% beta-hydroxyvalerate. Mass transfer of CO into the liquid phase was determined as the rate-limiting step in the fermentation.

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This paper presents a new method for measuring tar concentration in biomass-derived producer gas streams. This solvent-free method is much simpler than the evaporative method of the International Energy Agency (IEA) tar protocol. In tests on producer gas from a fluidized bed biomass gasifier this so-called dry condenser method yielded tar measurements with precision better than 5% and accuracy averaging to within 10% of the IEA tar protocol. Comparisons of water vapor concentrations in producer gas as determined by the two methodologies showed poor agreement, which appears to be due to the low precision of both techniques for this measurement, possibly the result of dissolved hydrocarbons in the recovered aqueous phases.

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