Table 2 Analysis of variance for biosorption of Congo red by Ulva lactuca biomass obtained by FCCCD.

Model

20

22,728.56

1136.43

271.25

 < 0.0001*

93.67

Linear effect

X₁

1

261.77

261.77

62.48

 < 0.0001*

− 2.77

X₂

1

11.38

11.38

2.72

0.1101

0.58

X₃

1

1172.94

1172.94

279.96

 < 0.0001*

5.87

X₄

1

1504.90

1504.90

359.19

 < 0.0001*

− 6.65

X₅

1

1466.42

1466.42

350.01

 < 0.0001*

− 6.57

Interaction effect

X₁X₂

1

227.64

227.64

54.33

 < 0.0001*

− 2.67

X₁X₃

1

45.20

45.20

10.79

0.0027*

− 1.19

X₁X₄

1

319.98

319.98

76.37

 < 0.0001*

3.16

X₁X₅

1

28.67

28.67

6.84

0.0140*

0.95

X₂X₃

1

381.09

381.09

90.96

 < 0.0001*

3.45

X₂X₄

1

520.60

520.60

124.26

 < 0.0001*

− 4.03

X₂X₅

1

346.17

346.17

82.63

 < 0.0001*

− 3.29

X₃X₄

1

656.76

656.76

156.76

 < 0.0001*

4.53

X₃X₅

1

315.44

315.44

75.29

 < 0.0001*

3.14

X₄X₅

1

440.97

440.97

105.25

 < 0.0001*

− 3.71

Quadratic effect

X₁²

1

16.47

16.47

3.93

0.0569

2.58

X₂²

1

14.66

14.66

3.50

0.0716

− 2.43

X₃²

1

32.76

32.76

7.82

0.0091*

− 3.64

X₄²

1

62.06

62.06

14.81

0.0006*

− 5.01

X₅²

1

2219.22

2219.22

529.69

 < 0.0001*

− 29.95

Error effect

Lack of Fit

22

107.87

4.90

2.52

0.1062

Pure Error

7

13.63

1.95

R²

0.9947

Std. Dev

2.05

Adj R²

0.9910

Mean

67.52

Pred R²

0.9843

C.V. %

3.03

Adeq Precision

63.80

PRESS

358.04