/ Cheng, Yi / Cravotto, Giancarlo / Gruber-Wölfler, Heidrun / Kralisch, Dana / D. Nigam, Krishna / Saha, Basudeb / Serra, Christophe A.
Growing energy demand and increasing concern for the security of supply of oil tied with the urge to reduce greenhouse gas emissions have led to countries such as the US and European Union (EU) to set targets for replacing petroleum fuels with renewable biofuels.
The US Department of Energy has set a goal for supplying 30% of the gasoline demand with biofuels by 2030, and the EU projects 10% of its transportation fuels to be derived from biofuels by 2020 .
Such fuels derived from crops are termed first-generation biofuels.
However, using crops for fuel production competes with food and is a short-term solution due to limited availability of land.Bioethanol made from sugar (Brazil) or starch (the US) is the most common renewable biofuel today .It is a known substitute to gasoline or an additive to gasoline .The key steps of the process, pretreatment, enzymatic hydrolysis, and fermentation, have undergone considerable amount of research and development over the past decades nearing the process to commercialization.In order for the commercialization to be successful, the process needs to be operated at high dry matter content of biomass, especially in the enzymatic hydrolysis stage that influences ethanol concentration in the final fermentation broth.It is estimated that solids loading of around 30% (w/w) is required to obtain ethanol concentration in the final fermentation broth up to 5%–10% (w/w) , .Operating ethanol production process at high solids loading has its advantages.Corn (42%) is the predominant crop in North America. Wheat also dominates among the crops in Europe (32%).In total, crop residues could replace 28.6% of global gasoline consumption.Therefore, alternative renewable sources of energy such as lignocellulosic biomass will need to be pursued to provide for the shortage in first-generation biofuels.Biofuels derived from lignocellulose (neutral with respect to production of greenhouse gasses) are second-generation biofuels, research into which has escalated over the past decade with a number of pilot plants operating throughout the world , , .