Table 4.
The Box–Behnken experimental design with three independent variables
| Run # | Initial pH value | (NH4)2SO4 (g) | Fermentation time (days) | aYs (g/L) | |||
|---|---|---|---|---|---|---|---|
| X 1 | Code | X 2 | Code | X 3 | Code | ||
| 1 | 5.0 | − 1 | 0.3 | − 1 | 4.0 | 0 | 2.67 ± 0.06 |
| 2 | 5.0 | − 1 | 0.5 | 1 | 4.0 | 0 | 2.67 ± 0.11 |
| 3 | 6.0 | 1 | 0.3 | − 1 | 4.0 | 0 | 4.66 ± 0.12 |
| 4 | 6.0 | 1 | 0.5 | 1 | 4.0 | 0 | 6.17 ± 0.10 |
| 5 | 5.5 | 0 | 0.5 | − 1 | 5.0 | − 1 | 5.33 ± 0.12 |
| 6 | 5.5 | 0 | 0.3 | − 1 | 5.0 | 1 | 5.00 ± 0.16 |
| 7 | 5.5 | 0 | 0.5 | 1 | 3.0 | − 1 | 2.67 ± 0.11 |
| 8 | 5.5 | 0 | 0.5 | 1 | 5.0 | 1 | 4.00 ± 0.08 |
| 9 | 5.0 | − 1 | 0.4 | 0 | 3.0 | − 1 | 2.75 ± 0.03 |
| 10 | 6.0 | 1 | 0.4 | 0 | 3.0 | − 1 | 8.33 ± 0.11 |
| 11 | 5.0 | − 1 | 0.4 | 0 | 5.0 | 1 | 4.95 ± 0.14 |
| 12 | 6.0 | 1 | 0.4 | 0 | 5.0 | 1 | 5.88 ± 0.05 |
| 13 | 5.5 | 0 | 0.4 | 0 | 4.0 | 0 | 8.12 ± 0.12 |
| 14 | 5.5 | 0 | 0.4 | 0 | 4.0 | 0 | 6.70 ± 0.10 |
| 15 | 5.5 | 0 | 0.4 | 0 | 4.0 | 0 | 8.44 ± 0.15 |
The center point was replicated three times to estimate the experimental errors
aYs represented average ethanol production of triplicate experiments