Optimization and Modeling of Cr (VI) Removal from Tannery Wastewater onto Activated Carbon Prepared from Coffee Husk and Sulfuric Acid (H₂SO₄) as Activating Agent by Using Central Composite Design (CCD)

Table 6

Fit summary for model selection.

Source	Sequential -value	Lack of fit -value	Adjusted R^2	Predicted R^2
Linear	0.7336	<0.0001	−0.0987	−0.2781
2FI	0.9946	<0.0001	−0.0987	−1.2223
Quadratic	<0.0001	0.5254	0.9996	0.9990	Suggested
Cubic	0.4253	0.4949	0.9996	0.9996	Aliased