Table 4.
Substrate, product and by-product concentrations and yields obtained from SHF (A) and SSF (B) experiments
| A) | ||||||
| Bark content (% of DM) | 0 | 10 | 30 | 50 | 100 | |
| Enzymatic hydrolysis step in SHF | Glucose concentration (g/L) | 80.6 ± 0.1 | 66.5 ± 0.7 | 61.8 ± 1.8 | 48.5 ± 0.5 | 34.0 ± 0.5 |
| Glucose yield (% of the theoretical) | 89.8 ± 0.3 | 81.6 ± 1.0 | 81.9 ± 3.3 | 67.9 ± 1.1 | 53.3 ± 0.9 | |
| Fermentation step in SHF | Total hexose sugar concentration (g/L) | 3.5 ± 0 | 3.1 ± 0 | 2.9 ± 2.1 | 1.0 ± 0.7 | 1.1 ± 0 |
| Glycerol concentration (g/L) | 5.2 ± 0 | 4.5 ± 0.1 | 4.2 ± 0.1 | 3.6 ± 0 | 3.0 ± 0.1 | |
| Volumetric ethanol productivitya (g/L⋅h) | 1.7 ± 0 | 2.0 ± 0 | 2.3 ± 1.2 | 2.8 ± 0.1 | 3.2 ± 0 | |
| Ethanol concentration (g/L) | 41.5 ± 0.8 | 36.1 ± 1.8 | 32.8 ± 0.4 | 28.2 ± 0.1 | 18.1 ± 0 | |
| Ethanol yield (% of the theoretical) | 93.1 ± 0.1 | 92.0 ± 0 | 93.8 ± 0.8 | 96.2 ± 0.9 | 95.0 ± 0.2 | |
| SHF | Overall ethanol yield (% of the theoretical) | 83.6 | 75.1 | 76.8 | 65.3 | 50.7 |
| B) | ||||||
| Bark content (% of DM) | 0 | 10 | 30 | 50 | 100 | |
| SSF | Total hexose sugar concentration (g/L) | 4.2 ± 0.3 | 1.9 ± 0.1 | 2.2 ± 0.1 | 2.4 ± 0.1 | 3.3 ± 0.1 |
| Glycerol concentration (g/L) | 4.8 ± 0.1 | 4.2 ± 0.2 | 3.8 ± 0.1 | 3.4 ± 0 | 3.6 ± 1.4 | |
| Volumetric ethanol productivitya (g/L⋅h) | 1.7 ± 0.1 | 1.8 ± 0.3 | 2.5 ± 0 | 2.9 ± 0.1 | 4.0 ± 0.1 | |
| Ethanol concentration (g/L) | 45.8 ± 0.8 | 39.3 ± 0.9 | 34.5 ± 0.4 | 29.4 ± 0.1 | 20.9 ± 0 | |
| Overall ethanol yield (% of the theoretical) | 85.4 ± 1.9 | 81.1 ± 2.3 | 77.5 ± 1.3 | 70.5 ± 0.4 | 59.3 ± 0.1 | |
aCalculated for the first two hours.
SSF and SHF experiments of steam-pretreated wood and bark mixtures were performed at 10% WIS loading, pH 5 using Cellic CTec3 enzyme cocktail (20 FPU/g WIS) and an industrial S. cerevisiae strain, Ethanol Red (5 g/L). DM, dry matter; SHF, separate hydrolysis and fermentation; SSF, simultaneous saccharification and fermentation; WIS, water-insoluble solids.