Optimising bioethanol production
Lignocellulose, the main structural component of plants, can be used to produce ethanol as fuel. The initial step in the process requires a breakdown of the long lignocellulose molecules to release sugar molecules through enzymatic hydrolysis. This is followed by yeast fermentation to produce ethanol. Despite various bottlenecks in the process, the high energy content of plant lignocellulosic biomass has prompted thorough investigation of its conversion to bioethanol as fuel. The main aim of the EU-funded 'New improvements for ligno-cellulosic ethanol' (NILE) project was to optimise the production of ethanol as a transport biofuel, making the process cost effective. The cost of enzymatic hydrolysis was reduced by improving the performance of fungi-produced cellulaces and by identifying limiting steps in the process. This led to the engineering of two CBH2 enzyme variants that, among other advantages, exhibit improved performance. Although the cost reduction was lower than initially envisaged, extensive research on the actual hydrolysis process produced important outcomes for the production of ethanol from lignocellulose. To enhance the fermentation process scientists developed new yeast strains and optimised the fermentation of complex sugars. The NILE project also developed an improved approach that combines simultaneous saccharification and fermentation. The performance of new enzymes and yeast strains was tested and found to be as efficient in hydrolysis as current commercial enzymes. For management of overall cost, the combustion properties of lignin, the main component of plant cell wall, were also investigated. Lignin hydrolysis residues were proven to serve as alternatives to currently used biofuel. However, this required extra attention to by-products formed during combustion. Assessment of the social and economic impact of the technology indicated that for cellulosic ethanol production to be profitable, optimised supply chains, integrated facilities and a favourable market would be required. The urgent need for renewable energy sources, combined with the fact that testing of bioethanol in engines proved beneficial, make this developing technology an attractive alternative to current energy sources.
