Table 5.

S/N ratio under the optimal conditions.

Effect/Factor	Predicted S/N Ratios under the Optimal Conditions Mean = −15.9350, Sigma = 4.2932
	Parameter Value	Significance of Effect	Standard Error
Repetition	3	0.0540	0.0591
pH	1 (pH = 3)	2.8235	0.0482
K2FeO4	2 (1.200 g/L)	2.0785	0.0482
Time	2 (9 min)	2.1436	0.0482
Expected S/N ratio	-	−8.8354	-

Mean—mean of ETA-value, Sigma—population standard deviation.