The release of fermentable carbohydrate from peat by steam explosion and its use in the microbial production of solvents

Steam treatment of peat at 200 degrees C for 3 min, followed by instantaneous decompression (steam explosion), solubilized up to 28% of the dry matter. Seventy-five percent of the solubilized material was carbohydrate, 33% of which was composed of mono- and disaccharides, including galactose, glucose, xylose, mannose, arabinose, and cellobiose, in order of decreasing concentration. The solubilized materials served as the sole source of carbohydrate for growth and solvent production by Clostridium acetobutylicum and C. butylicum which utilized up to 40% of the carbohydrate. Of the saccharides in this mixture, galactose was the least readily utilized. Approximately 30% of the fermentable carbohydrate used was converted to fatty acids and solvents, with the primary fermentation product being butyrate. Clostridium thermohydrosulfuricum was able to utilize ca. 50% of the carbohydrate, and simultaneously produced slightly more than 1 mol ethanol/mol saccharide metabolized. This organism, like other strains tested, used galactose less readily than the other sugars. The residue from the steam explosion process contained 24% cellulose, but it could not serve as a source of carbohydrate for the growth of either Bacteroides succinogenes or Clostridium thermocellum, suggesting that inhibitors were released during the steam treatment.