4. Conclusions
Using an enzyme cocktail of Cellic® CTec 2 (0.87 FPU/g substrate) together with Novozyme® 188 (2 U g−1 substrate), 94.7% (w/w of theoretical) yield of ethanol was obtained from steam exploded duckweed substrate (1% w/w). However increasing substrate concentration lowered the yield substantially. Improved ethanol yields at the higher substrate concentration could be achieved using higher yeast titres, and/or preconditioning the yeast in pretreatment liquor so that the yeast could metabolise fermentation inhibitors. Nearly 70% (w/w of theoretical ethanol) or 3.5% (v/v) (equivalent to 13.5% g/g DM) was achieved from concentrated substrate (20% w/v).