| Factor | Unit | Factor levels | ||||
| −α | −1 | 0 | 1 | +α | ||
| Catalyst dosage | mg | 6.364 | 20 | 40 | 60 | 73.636 |
| pH | - | 1.273 | 4 | 8 | 12 | 14.727 |
| UV irradiation time | min | 6.364 | 20 | 40 | 60 | 73.636 |