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Different variables and their respective levels of BBD.
| Independent variables (Unit) | Symbol | Coded levels |
||
|---|---|---|---|---|
| Lower limit (–1) | Center (0) | Upper limit (+1) | ||
| PAC dosage (mg/L) | A | 50 | 70 | 90 |
| CPAM dosage (mg/L) | B | 20 | 30 | 40 |
| pH |
C |
5.5 |
6.5 |
7.5 |
| Response variables (Unit) | Constraints | |||
| Turbidity removal efficiency (%) | Y1 | Maximize | ||
| COD removal efficiency (%) | Y2 | Maximize | ||
| Zeta potential (mV) | Y3 | Target is zero | ||
| Residual Al concentration (mg/L) | Y4 | Minimize | ||
