# Simultaneous Electrochemical Removal of Selenium and Strontium from Aqueous Solution
## Appendix A  
Table A1 contains the experimental matrix obtained using DesignExpert software and the corresponding responses (removal efficiencies for Se and Sr). Tables A2 and A3 show the results of the ANOVA for the reduced quartic model. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Source** & \
\begin{tabular}{c} **Sum of** \\ **Squares** \\ \end{tabular} & **df** &
\begin{tabular}{c} **Mean** \\ **Square** \\ \end{tabular} & **F-Value** & \(p\)**-Value** & \\ \hline Model & 5147.08 & 44 & 116.98 & 24.66 & \textless{}0.0001 & Significant \\ A—I & 891.74 & 1 & 891.74 & 187.95 & \textless{}0.0001 & \\ B—electrode number & 0.5269 & 1 & 0.5269 & 0.1111 & 0.7402 & \\ C—t & 1066.63 & 1 & 1066.63 & 224.82 & \textless{}0.0001 & \\ D—material & 501.39 & 1 & 501.39 & 105.68 & \textless{}0.0001 & \\ E—pH & 237.45 & 2 & 118.72 & 25.02 & \textless{}0.0001 & \\ AB & 6.61 & 1 & 6.61 & 1.39 & 0.2427 & \\ AC & 616.67 & 1 & 616.67 & 129.98 & \textless{}0.0001 & \\ AD & 132.76 & 1 & 132.76 & 27.98 & \textless{}0.0001 & \\ AE & 76.15 & 2 & 38.07 & 8.02 & 0.0008 & \\ BC & 12.91 & 1 & 12.91 & 2.72 & 0.1045 & \\ BD & 14.69 & 1 & 14.69 & 3.10 & 0.0838 & \\ BE & 6.54 & 2 & 3.27 & 0.6898 & 0.5058 & \\ CD & 270.76 & 1 & 270.76 & 57.07 & \textless{}0.0001 & \\ CE & 55.31 & 2 & 27.65 & 5.83 & 0.0050 & \\ DE & 10.65 & 2 & 5.32 & 1.12 & 0.3328 & \\ A\({}^{2}\) & 76.78 & 1 & 76.78 & 16.18 & 0.0002 & \\ B\({}^{2}\) & 18.10 & 1 & 18.10 & 3.81 & 0.0557 & \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Results of ANOVA analysis for reduced quartic model describing electrochemical removal of selenium. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & \
\begin{tabular}{c} **Sum of** \\ **Squares** \\ \end{tabular} & **df** &
\begin{tabular}{c} **Mean** \\ **Square** \\ \end{tabular} & **F-Value** & \(p\)**-Value** & \\ \hline Model & 5147.08 & 44 & 116.98 & 24.66 & \textless{}0.0001 & Significant \\ A—I & 891.74 & 1 & 891.74 & 187.95 & \textless{}0.0001 & \\ B—electrode number & 0.5269 & 1 & 0.5269 & 0.1111 & 0.7402 & \\ C—t & 1066.63 & 1 & 1066.63 & 224.82 & \textless{}0.0001 & \\ D—material & 501.39 & 1 & 501.39 & 105.68 & \textless{}0.0001 & \\ E—pH & 237.45 & 2 & 118.72 & 25.02 & \textless{}0.0001 & \\ AB & 6.61 & 1 & 6.61 & 1.39 & 0.2427 & \\ AC & 616.67 & 1 & 616.67 & 129.98 & \textless{}0.0001 & \\ AD & 132.76 & 1 & 132.76 & 27.98 & \textless{}0.0001 & \\ AE & 76.15 & 2 & 38.07 & 8.02 & 0.0008 & \\ BC & 12.91 & 1 & 12.91 & 2.72 & 0.1045 & \\ BD & 14.69 & 1 & 14.69 & 3.10 & 0.0838 & \\ BE & 6.54 & 2 & 3.27 & 0.6898 & 0.5058 & \\ CD & 270.76 & 1 & 270.76 & 57.07 & \textless{}0.0001 & \\ CE & 55.31 & 2 & 27.65 & 5.83 & 0.0050 & \\ DE & 10.65 & 2 & 5.32 & 1.12 & 0.3328 & \\ A\({}^{2}\) & 76.78 & 1 & 76.78 & 16.18 & 0.0002 & \\ B\({}^{2}\) & 18.10 & 1 & 18.10 & 3.81 & 0.0557 & \\ \hline \hline \end{tabular}
\end{table} 
Table 11: Results of ANOVA analysis for reduced quartic model describing electrochemical removal of selenium. The obtained models could be described by the equations listed in Table A4 (the value of each term is multiplied by its according coefficient). The equations, expressed in terms of actual factors, allowed for predictions about the response based on the specific levels of each factor, where the levels were designated in their original units. However, this equation was not suitable for assessing the relative importance of each factor, as the coefficients were adjusted to fit the units of each factor, and the intercept did not lie at the center of the design space.