Table 2 The level of variables
From: Enhanced methane production of vinegar residue by response surface methodology (RSM)
Variables | Factors | Experimental design (Coded level) | ||||
|---|---|---|---|---|---|---|
(Coded Xi) | −1.682 | −1 | 0 | +1 | +1.682 | |
F/I ratio | X1 | 0.5 | 0.7 | 1 | 1.3 | 1.5 |
Organic loading (gVS L−1) | X2 | 13.18 | 20 | 30 | 40 | 46.82 |
Initial pH | X3 | 5.32 | 6 | 7 | 8 | 8.68 |