| Independent variable | Contact time (5 - 120 min) | Temperature (50˚C - 95˚C) | Adsorbent dose (1 - 6 mass %) |
| Exp. No | X1 | X2 | X3 |
| 1 | 0.000 | 0.000 | 0.000 |
| 2 | 1.000 | 0.000 | 0.000 |
| 3 | −1.000 | 0.000 | 0.000 |
| 4 | 0.500 | 0.866 | 0.000 |
| 5 | −0.500 | −0.866 | 0.000 |
| 6 | 0.500 | −0.866 | 0.000 |
| 7 | −0.500 | 0.866 | 0.000 |
| 8 | 0.500 | 0.289 | 0.816 |
| 9 | −0.500 | −0.289 | −0.816 |
| 10 | 0.500 | −0.866 | −0.816 |
| 11 | 0.000 | 0.577 | −0.816 |
| 12 | −0.500 | 0.289 | 0.816 |
| 13 | 0.000 | −0.577 | 0.816 |