Greener bioethanol production
First-generation ethanol is produced by converting sugars directly to ethanol. When using plant waste as biomass, the lignocellulose structure of the biomass must first be broken down into hemicelluloses and cellulose. These polysaccharides can then be further broken down into sugars (saccharification) by enzymes. It is this pre-treatment process that has hampered the production of second-generation ethanol. This led to funding by the EU for the BABETHANOL project. Researchers examined a new process called combined extrusion-saccharification (CES), which requires much less energy, water, chemicals, detoxification and wastewater treatment than current approaches. CES is based on the thermo-mechanical deconstruction of the biomass matrix by extrusion. The saccharification enzymes will then have better access to the carbohydrates for further breakdown into sugars. Researchers tested the technology in the laboratory before embarking on pilot studies of diverse biomass sources such as blue agave bagasse (Mexico), oil palm empty fruit bunches (Costa Rica), sweet corn cob (France), barley straw (Spain), sugar cane bagasse (Brazil), vineyard pruning residues (Chile) and eucalyptus forest residues (Uruguay). Although they found that the process generates twice as much energy as it consumes, researchers felt the carbon footprint could still be improved on. They also decided that saccharification performances could be enhanced through the addition of efficient enzymes and that the fermentation performance needs optimisation. A financial evaluation revealed that material supply is a major contributor to cost. Ideally ethanol plants should be located within 100 km of the biomass source. This would also create socioeconomic benefits for local populations. Tequila producers in Mexico and the corn-producing cooperatives in southern France have already expressed interest in exploiting BABETHANOL research results. Once this environmentally friendly process is ready for industrialisation, it will be applicable to a range of lignocellulosic feedstocks in European and Latin American countries.
