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In the future liquid biofuels will need to be renewable, sustainable, as well as technically and economically viable. This paper provides an overview of the challenges that the biochemical production of cellulosic ethanol process still faces. The main emphasis of the paper is on challenges that emerge from the scale of liquid biofuel production. These challenges include raw material availability, other consumables, and side stream handling. The pretreatment, C5 fermentation, and concentration of sugars in processing need improvements, too. Sustainability issues and greenhouse gas reduction also pose a challenge for implementation and require development of internationally recognized sustainability principles and standards, and certification of sustainable operation. Economics of cellulosic ethanol processes are still also an area under development and debate. Yet, the Energy Independence and Security Act mandate together with the European Union Renewable Energy Directive and other local targets are driving the development and implementation forward towards more significant contribution of biofuels in the transportation sector. [ABSTRACT FROM AUTHOR]

Abstract: Reduction of the emissions of greenhouses gases, increasing the share of renewable energy sources (RES) in the energy balance, increasing electricity production from renewable energy sources and decreasing energy dependency represent the main goals of all current strategies in Europe. Biomass co-firing in large coal-based thermal power plants provides a considerable opportunity to increase the share of RES in the primary energy balance and the share of electricity from RES in gross electricity consumption in a country. Biomass-coal co-firing means reducing CO2 and SO2, emissions and it may also reduce NO x emissions, and also represents a near-term, low-risk, low-cost and sustainable energy development. Biomass-coal co-firing is the most effective measure to reduce CO2 emissions, because it substitutes coal, which has the most intensive CO2 emissions per kWh electricity production, by biomass, with a zero net emission of CO2. Biomass co-firing experience worldwide are reviewed in this paper. Biomass co-firing has been successfully demonstrated in over 150 installations worldwide for most combinations of fuels and boiler types in the range of 50–700MWe, although a number of very small plants have also been involved. More than a hundred of these have been in Europe. A key indicator for the assessment of biomass co-firing is intrduced and used to evaluate all available biomass co-firing technologies. [Copyright &y& Elsevier]