Although a few pioneering studies attempted cost estimates of wood-derived ethanol from the 1980s onward, they focused on aspects of the technological processes required rather than making firm conclusions about market prices.24,25 Swedish studies appear to have been the first to present detailed cost breakdowns for ethanol production from accessible large-scale woody biomass sources.26,27 The first of the two to be published was highly unusual in that it used recent advances in pentose utilization by recombinant bacteria to model a pentose stream process, that is, using the solubilized sugars from the pretreatment of wood (willow) feedstock — the procedure involved the impregna­tion of the material with SO2 and subsequent steaming — and included a detoxification procedure to reduce the levels of inhibitors from the hydrolysate.26 The fermentation with Escherichia coli KO11 (chapter 3, section 3.3.2.1) was assumed to consume 96%

[49] The authors did not discriminate between xylose and xylooligosaccharides or between xylose and arabinose, and the implicit assumption was that more than 95% of the available pentoses were in a readily metabolizable form, that is, monomeric xylose.

A very similar analysis of three different approaches to utilizing the full carbo­hydrate potential of pine wood, digesting the cellulose component with concentrated acid, dilute acid, and enzymatic methods, calculated a full manufacturing costs for ethanol of between 500 and 530/l ($1.89-2.01/gallon).27 The bulk of the production cost (up to 57.5%) was accounted for by the financial costs of installing the hardware for generating fermentable carbohydrates (hexoses as well as pentoses) in more com­plex total processes with longer cycle times.