Table 3.

Experimental pattern for coded variables using 2⁴⁻¹-FFD.

Run	Coded levels of variables				Response (Y, %)
	Aa	Bb	Cc	Dd	*Obs.	**Pred.	***Pred.
1	−1	+1	+1	−1	71.15	67.85	74.55
2	0	0	0	0	93.00	86.16	86.27
3	+1	−1	−1	+1	92.22	88.92	91.94
4	+1	−1	+1	−1	99.61	96.31	99.87
5	0	0	0	0	85.93	86.16	86.27
6	−1	+1	−1	+1	87.03	83.72	84.13
7	+1	+1	+1	+1	99.16	102.5	98.16
8	−1	−1	−1	−1	18.43	21.74	31.33
9	−1	−1	+1	+1	10.20	13.51	****
10	0	0	0	0	85.12	86.16	86.27
11	0	0	0	0	80.59	86.16	86.27
12	+1	+1	−1	−1	88.98	92.30	90.08

Response is shown as observed and predicted % of removal of Cu (II) using BDP.

A, B, C, and D^a are as defined in Table 1.

^*Obs.: experimental values.

^**Pred.: predicted values before response transformation (factorial interactions up to 4th order was considered, prediction is averaged over blocks): Y = 86.16 + 24.14 pH + 15.73 AD – 0.82 HMC + 1.30 CT – 13.35 pH^*AD+ 5.21 pH^*HMC – 0.61 pH^*CT – 15.31 pH^*AD^*HMC^*CT.

^***Pred.: predicted values after response transformation (factorial interactions up to 4th order was considered): Y∧2= 7,443 + 2,887 pH + 1,439 AD – 1,609 pH^*AD + 760 pH^*HMC – 1,286 pH^*AD^*HMC^*CT.

^****Value was not detected by the model.