## 3 Results
### Modeling of Textile WW Treatment in the Laboratory SD Setup
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Exp.** \\ **No.** \\ \end{tabular} } & \multirow{2}{*}{\(Z_{1}\)} & \multirow{2}{*}{\(Z_{2}\)} & \multirow{2}{*}{\(Z_{3}\)} & \multirow{2}{*}{\(X_{1}\)} & \multirow{2}{*}{\(X_{2}\)} & \multirow{2}{*}{\(X_{3}\)} & \({Y_{1\epsilon}\)} & \multirow{2}{*}{\(Y_{1}\)} & \multirow{2}{*}{\({\bf A}\) = (\(Y_{1\epsilon}-Y_{1})\times 100/Y_{1\epsilon}\)} \\  & & & & & & & & \\ \hline
1 & 14 & 150 & 10 & \(-\)1 & \(-\)1 & \(-\)1 & 43.296 & 41.340 & 4.519 \\
2 & 26 & 150 & 10 & 1 & \(-\)1 & \(-\)1 & 32.030 & 34.011 & \(-\)6.185 \\
3 & 14 & 450 & 10 & \(-\)1 & 1 & \(-\)1 & 42.273 & 43.923 & \(-\)3.904 \\
4 & 26 & 450 & 10 & 1 & 1 & \(-\)1 & 39.293 & 36.595 & 6.865 \\
5 & 14 & 150 & 20 & \(-\)1 & \(-\)1 & 1 & 41.434 & 43.676 & \(-\)5.411 \\
6 & 26 & 150 & 20 & 1 & \(-\)1 & 1 & 45.344 & 42.726 & 5.774 \\
7 & 14 & 450 & 20 & \(-\)1 & 1 & 1 & 44.041 & 41.092 & 6.696 \\
8 & 26 & 450 & 20 & 1 & 1 & 1 & 38.641 & 40.142 & \(-\)3.885 \\
9 & 10 & 300 & 15 & \(-\)1.682 & 0 & 0 & 43.482 & 43.864 & \(-\)0.878 \\
10 & 30 & 300 & 15 & \(+\)1.682 & 0 & 0 & 36.034 & 36.902 & \(-\)2.407 \\
11 & 20 & 102 & 15 & 0 & \(-\)1.682 & 0 & 34.916 & 36.190 & \(-\)3.650 \\
12 & 20 & 550 & 15 & 0 & +1.682 & 0 & 35.754 & 36.190 & \(-\)1.220 \\
13 & 20 & 300 & 7 & 0 & 0 & \(-\)1.682 & 41.154 & 41.541 & \(-\)0.941 \\
14 & 20 & 300 & 24 & 0 & 0 & +1.682 & 45.624 & 46.489 & \(-\)1.897 \\
15 & 20 & 300 & 15 & 0 & 0 & 0 & 36.499 & 36.190 & 0.846 \\
16 & 20 & 300 & 15 & 0 & 0 & 0 & 36.406 & 36.190 & 0.592 \\
17 & 20 & 300 & 15 & 0 & 0 & 0 & 36.313 & 36.190 & 0.338 \\
18 & 20 & 300 & 15 & 0 & 0 & 0 & 33.706 & 36.190 & \(-\)7.371 \\
19 & 20 & 300 & 15 & 0 & 0 & 0 & 34.171 & 36.190 & \(-\)5.909 \\
20 & 20 & 300 & 15 & 0 & 0 & 0 & 40.320 & 36.190 & 9.397 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Experimental planning matrix for \(Y_{1}\) (suspended solids removal). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Variable/Value**} & **Real Variable** & **Coded Variable** & **Real Basic Variable** & **Variation Step** \\ \cline{2-5}  & **(z\({}_{i}\))** & **(\(X_{i}\))** & **(\(z_{i0}\))** & **(\(\Delta z_{i0}\))** \\ \hline WW flowrate, [L/h] & \(Z_{1}\) & \(X_{1}\) & 20 & 6 \\ Rotation speed, [rpm] & \(Z_{2}\) & \(X_{2}\) & 300 & 150 \\ Operating time, [min] & \(Z_{3}\) & \(X_{3}\) & 15 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The codification of independent variables in the active central composite rotatable \(2^{3}\) design. The calculated values of the Fisher test were F\({}_{\rm c}\) (\(Y_{1}\)) = 40.560 for \(Y_{1}\) and F\({}_{\rm c}\) (\(Y_{2}\)) = 2.086 for \(Y_{2}\), and related to F\({}_{\rm statistic\_table}\) = 6.59, from which one can conclude that all three tested independent variables (\(X_{1}\), \(X_{2}\), \(X_{3}\)) had a significant importance with respect to the suspended solids removal (\(Y_{1}\)) from the textile WW, and two independent variables (\(X_{2}\) and \(X_{3}\)) had no importance regarding the WW discoloration. Figure 8(a,a1)-(c,c1) and Figure 9a-c illustrate the dependence of the WW suspended solids removal (\(Y_{1}\)) vs. two independent variables (one variable was kept at the basic value) (i.e.,\(Y_{1}\) = \(Y_{1}\)(\(X_{1}\),\(X_{2}\),0); \(Y_{1}\) = \(Y_{1}\)(\(X_{1}\),0,\(X_{3}\)), and \(Y_{1}\) = \(Y_{1}\)(0,\(X_{2}\),\(X_{3}\)) with their isolines) and one independent variable (two variables were maintained at their basic values). Figure 9d illustrates the dependence of textile WW discoloration (\(Y_{2}\)) on one significant independent variable (\(X_{1}\)) (\(X_{2}\) and \(X_{3}\) are constant, at their basic value and not influencing the\(Y_{2}\) value). The variation in the suspended solids removal (\(Y_{1}\)) with the increase inthe WW flowrate (\(X_{1}\)) is obvious in Figure 9a.