L9 (33) Orthogonal test design and results.
| Test number | Time A/h | NaOH B/% | H2O2 C/% | The removal percentage of SO42−/% | The removal percentage of Mn2+/% | The removal percentage of Fe2+/% | pH | COD/(mg L−1) |
|---|---|---|---|---|---|---|---|---|
| 1 | 18 | 4 | 0.5 | 86.20 | 76.44 | 93.57 | 7.89 | 296 |
| 2 | 18 | 5 | 1 | 89.69 | 66.25 | 86.64 | 7.77 | 267 |
| 3 | 18 | 6 | 1.5 | 81.65 | 80.93 | 82.42 | 8.07 | 254 |
| 4 | 24 | 4 | 1 | 82.07 | 72.53 | 87.42 | 7.79 | 252 |
| 5 | 24 | 5 | 1.5 | 79.06 | 75.38 | 84.85 | 7.84 | 240 |
| 6 | 24 | 6 | 0.5 | 85.44 | 79.22 | 86.00 | 7.91 | 227 |
| 7 | 30 | 4 | 1.5 | 90.17 | 75.06 | 89.92 | 7.74 | 280 |
| 8 | 30 | 5 | 0.5 | 82.94 | 69.18 | 90.14 | 7.87 | 305 |
| 9 | 30 | 6 | 1 | 87.33 | 68.61 | 84.78 | 7.91 | 282 |