Table 3.

Analysis of variance for biosorption of Pb²⁺ by Ulva lactuca biomass obtained by FCCCD.

Source of variance		Degrees of freedom	Sum of square	Mean of square	F-value	P-value	Coefficient estimate
Model		20	1263.97	63.20	61.08	< 0.0001*	96.49
Linear effect	X1	1	2.24	2.24	2.17	0.1518	− 0.26
	X2	1	188.66	188.66	182.32	< 0.0001*	2.36
	X3	1	16.10	16.10	15.56	0.0005*	0.69
	X4	1	159.28	159.28	153.93	< 0.0001*	2.16
	X5	1	79.07	79.07	76.42	< 0.0001*	1.53
Interaction effect	X1X2	1	94.60	94.60	91.42	< 0.0001*	1.72
	X1X3	1	31.09	31.09	30.04	< 0.0001*	− 0.99
	X1X4	1	0.14	0.14	0.13	0.7178	0.07
	X1X5	1	67.86	67.86	65.58	< 0.0001*	1.46
	X2X3	1	0.13	0.13	0.12	0.7281	0.06
	X2X4	1	11.69	11.69	11.30	0.0022*	0.60
	X2X5	1	37.58	37.58	36.32	< 0.0001	− 1.08
	X3X4	1	14.93	14.93	14.43	0.0007*	0.68
	X3X5	1	20.22	20.22	19.55	0.0001*	− 0.80
	X4X5	1	12.50	12.50	12.08	0.0016*	− 0.63
Quadratic effect	X12	1	5.32	5.32	5.14	0.0310*	1.47
	X22	1	7.43	7.43	7.18	0.0120*	− 1.73
	X32	1	22.09	22.09	21.35	< 0.0001*	− 2.99
	X42	1	12.90	12.90	12.46	0.0014*	− 2.28
	X52	1	8.31	8.31	8.03	0.0083*	− 1.83
Error effect	Lack of Fit	22	14.03	0.64	0.28	0.9899
	Pure Error	7	15.97	2.28
R2	0.9768	Std. Dev	1.02
Adj R2	0.9608	Mean	91.48
Pred R2	0.9474	C.V. %	1.11
Adeq Precision	30.32	PRESS	68.01

* Significant values, F: Fishers's function, P: Level of significance, C.V: Coefficient of variation.