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 5

Effects of individual factors and interaction effects on adsorption of Cr (VI).

Source	Sum of square	Df.	Mean square	F-value	value
Model	1518.60	9	168.73	5077.33	<0.0001	Significant
A-pH	5.54	1	5.54	166.73	<0.0001
B-dose	68.18	1	68.18	2051.65	<0.0001
C-contact time	39.87	1	39.87	1199.57	<0.0001
AB	2.16	1	2.16	65.09	<0.0001
AC	5.31	1	5.31	159.90	<0.0001
BC	0.3961	1	0.3961	11.92	0.0062
A^2	594.25	1	594.25	17881.53	<0.0001
B^2	201.78	1	201.78	6071.79	<0.0001
C^2	861.81	1	861.81	25932.63	<0.0001
Residual	0.3323	10	0.0332
Lack of fit	0.1612	5	0.0322	0.9419	0.5254	Not significant
Pure error	0.1711	5	0.0342
Cor total	1518.93	19