Table 5. The range analysis of active carbon on F ratio obtained from the L9 (33) orthogonal experiment
| No. | (A) | (B) | (C) | F ratio |
| 1 | 1 | 1 | 1 | 12.09 |
| 2 | 1 | 2 | 2 | 23.48 |
| 3 | 1 | 3 | 3 | 14.23 |
| 4 | 2 | 1 | 2 | 21.50 |
| 5 | 2 | 2 | 3 | 25.79 |
| 6 | 2 | 3 | 1 | 18.98 |
| 7 | 3 | 1 | 3 | 13.89 |
| 8 | 3 | 2 | 1 | 19.63 |
| 9 | 3 | 3 | 2 | 16.90 |
| K1 | 16.60 | 15.83 | 16.90 | |
| K2 | 22.09 | 22.97 | 20.63 | |
| K3 | 16.81 | 16.70 | 17.97 | |
| Best level | A2 | B2 | C2 | |
| R | 5.49 | 7.14 | 3.73 | |
| R order | B>A>C | | | |
Three controllable variables, including time (A), temperature (B), and pH (C) were selected for optimization.
F ratio, Fischer's ratio.