# Sustainable Removal of Cr(VI) by Line Peel and Pineapple Core Wastes
## 3 Results and Discussion
### Box-Behnken Analysis
#### 3.4.1 Cr(VI) Removal  
ANOVA analysis is crucial to determine if the model is significant and adequate. It split the total variance of the results into the model inaccuracy and the experimental error, showing if the divergence from the model is significant in comparison with the variation because of residual error [28]. Values of \(F\) and \(p\)-_values_ were employed to specify the model significance and the magnitude of each coefficient. Thus, the obtained \(F\)-_value_ is statistically significant, (typically \(p\)-_values_ \(<\)0.05), this means that the model made a good approach to forecast the output factor and also, that there is a notable connection linking the set of predictions and the dependent factor indicating that the model has significance. The \(F\)-_value_ (66.88) implies the model is significant (\(p\)-_value_\(<\)0.0001) (Table 3). The odds that an \(F\)-_value_ this large would occur due to noise are only 0.01%. The significance of each model term was elucidated based on its \(p\)-_value_. According to these values the terms pH (\(x_{1}\)), PP dosage (\(x_{2}\)), temperature (\(x_{3}\)), PP dosage-temperature (\(x_{2}\)\(x_{3}\)), and the square of pH (\(x_{1}\)\({}^{2}\)) are significant model terms. The high correlation coefficient (R\({}^{2}\) = 0.9885) demonstrated the good connection linking the forecasted and experimental values. In addition, the predicted (Pred R\({}^{2}\)) and the adjusted (Adj R\({}^{2}\)) correlation coefficients are in good concordance. _Adeq-Precision_ measures the ratio signal to noise and a ratio higher than 4 is desirable. A ratio of 27.377 was obtained in this model, which evidences the adequacy of the signal. Thus, the model may be applied to navigate the design space. Furthermore, the variation coefficient percentage (CV) was lower than 15% and according to [PERSON] [29] this value demonstrates exactness and trustworthiness of the performed experiments. The obtained expression of the selected response, Cr(VI) removal, according to the studied variables coded factors is described in the Equation (6):  
\[ \begin{split}\text{Cr(VI) removal (\%)}=65.20-8.45\times x_{1}+6.85\times x_{2}+2.68\times x_{3}-1.03 \times x_{1}x_{2}-1.47\times x_{1}x_{3}+\\ 1.79\times x_{2}x_{3}+8.97\times{x_{1}}^{2}+1.23\times{x_{3}}^{2} \end{split}  \tag{6}\]  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Cr(VI) Removal (\%)**} & \multicolumn{3}{c}{**Total Cr Removal (\%)**} \\ \multirow{2}{*}{**Source**} & _Sum of_ & _Degrees of_ & _Mean_ & \multirow{2}{*}{_F-Values_} & \multirow{2}{*}{_p-Values_} & _Sum of_ & _Degrees of_ & _Mean_ & \multirow{2}{*}{_F-Values_} & \multirow{2}{*}{_p-Values_} \\  & _Squares_ & _Freedom_ & _Square_ & & & & & & & \\ \hline \multirow{2}{*}{**Model**} & 1382.12 & 9 & 153.56 & 66.88 & \ \begin{tabular}{c} \textless{}0.0001 \\ significant \\ \end{tabular}  & 778.51 & 9 & 86.50 & 60.46 & \begin{tabular}{c} \textless{}0.0001 \\ significant \\ \end{tabular}  \\ \(x_{2}\) & 375.79 & 1 & 375.79 & 163.67 & \(<0.0001\) & 72.30 & 1 & 72.30 & 50.54 & 0.0002 \\ \(x_{3}\) & 57.57 & 1 & 57.57 & 25.07 & 0.0016 & 98.63 & 1 & 436.01 & 304.77 & \(<0.0001\) \\ \(x_{1}x_{2}\) & 4.24 & 1 & 4.24 & 1.85 & 0.2162 & 13.25 & 1 & 13.25 & 9.26 & 0.0188 \\ \(x_{1}x_{3}\) & 8.61 & 1 & 8.61 & 3.75 & 0.0940 & 20.48 & 1 & 20.46 & 14.31 & 0.0069 The Pareto analysis of the resulting RSM model equation (Equation (7)) was performed to study the percentage effect (P\({}_{\rm i}\)) of each item on the response [30]. P\({}_{\rm i}\) is calculated as a function of the equation below:  
\[P_{i}=(\beta_{\rm i}^{2}/\sum\beta_{\rm i}^{2})({\rm i}\
eq 0) \tag{7}\]  
The graph corresponding to the Pareto analysis of the Cr(VI) removal response is presented in Figure 3a. As can be observed in this figure, among the variables, the pH (54.1%) and biosorbent dosage (35.6%) are the most significant variables on the Cr(VI) removal. These outcomes are in accord with those reported by [PERSON] et al.