8-03: The novel method of improving steam pretreatment to bioethanol process: the effect of biomass moisture content on bioethanol yields from steam pretreated switchgrass and sugarcane bagasse

The role of physical and chemical characteristics of biomass has been extensively studied in relation to production of bioethanol and other products. Equally important, however, is the role of biomass processing prior to pretreatment.

This study aimed to determine the effect of moisture content of three different feedstocks on overall ethanol yield via steam pretreatment and simultaneous saccharification and fermentation process (SSF). Switchgrass and sugarcane bagasse from two sources were either soaked in water (~80% moisture) or left dry (~12% moisture), and half each of these were impregnated with 3% w/w SO₂ and all were steam pretreated. The overall ethanol yield after simultaneous saccharification and fermentation of hexoses was 18-28% higher in samples that were soaked prior to SO₂ addition than in SO₂-catalysed samples that were not soaked.

The implications of this work cannot be understated. By simply increasing the moisture content of biomass prior to SO₂-catalysis and steam pretreatment, the yield of ethanol can be greatly increased. This represents a promising means of increasing commercial ethanol yields through simply monitoring and altering moisture of biomass as it enters the process. Improved solids digestibility also represents a potential cost savings in that reduced enzyme loadings are required for the same ethanol yield. These results also go a long way towards explaining discrepancies in the literature in overall ethanol yields from similar feedstocks in different labs. Unless the moisture content of the starting biomass is the same, it is difficult to compare the results of experiments utilizing the same biomass.