Table 3.
Experimental conditions for the RSM and results (COD) for tannery wastewater (K2FeO4 0.127–1.473 g/L, pH 0.95–11.05, Time 0.96–11.05 min). The Envifer® dose was calculated based on pure K2FeO4. (C)—center of plan.
| Run | Experimental Conditions | Experimental Results * | ||
|---|---|---|---|---|
| pH | K2FeO4 (g/L) | Time (min) | COD (g O2/L) | |
| 1 | 3.00 | 0.400 | 3.00 | 7.340 ± 1.100 |
| 2 | 3.00 | 0.400 | 9.00 | 5.570 ± 0.840 |
| 3 | 3.00 | 1.200 | 3.00 | 3.350 ± 0.500 |
| 4 | 3.00 | 1.200 | 9.00 | 1.850 ± 0.280 |
| 5 | 9.00 | 0.400 | 3.00 | 11.800 ± 1.770 |
| 6 | 9.00 | 0.400 | 9.00 | 8.570 ± 1.290 |
| 7 | 9.00 | 1.200 | 3.00 | 8.720 ± 1.310 |
| 8 | 9.00 | 1.200 | 9.00 | 6.980 ± 1.050 |
| 9 | 0.95 | 0.800 | 6.00 | 11.150 ± 1.670 |
| 10 | 11.05 | 0.800 | 6.00 | 8.850 ± 1.330 |
| 11 | 6.00 | 0.127 | 6.00 | 8.900 ± 1.340 |
| 12 | 6.00 | 1.473 | 6.00 | 2.710 ± 0.410 |
| 13 | 6.00 | 0.800 | 0.96 | 7.480 ± 1.120 |
| 14 | 6.00 | 0.800 | 11.05 | 3.150 ± 0.470 |
| 15 (C) | 6.00 | 0.800 | 6.00 | 6.280 ± 0.940 |
| 16 (C) | 6.00 | 0.800 | 6.00 | 6.270 ± 0.940 |
* parameter value ± the measurement uncertainty for an extension factor k = 2.