# Assessment of the Water Quality of WWTPs' Effluents through the Use of Wastewater Quality Index
## 3 Results
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & **PC1** & **PC2** & **PC3** & **PC4** & **PC5** \\ \hline pH & \(-\)0.032 & 0.097 & 0.021 & 0.209 & **0.893** \\ EC & \(-\)0.124 & **0.813** & \(-\)0.083 & \(-\)0.147 & \(-\)0.013 \\ COD & 0.121 & 0.068 & \(-\)0.032 & \(-\)**0.812** & \(-\)0.083 \\ TSS & **0.906** & 0.116 & \(-\)0.034 & 0.009 & \(-\)0.213 \\ TP & 0.307 & 0.097 & 0.269 & **0.589** & 0.316 \\ TN & 0.138 & **0.845** & \(-\)0.037 & 0.107 & 0.133 \\ Cr & \(-\)0.054 & 0.010 & **0.933** & \(-\)0.085 & 0.174 \\ Cd & 0.117 & \(-\)0.223 & **0.820** & 0.289 & \(-\)0.125 \\ Ni & 0.054 & \(-\)**0.520** & 0.179 & \(-\)0.465 & 0.458 \\ Pb & **0.884** & \(-\)0.128 & 0.073 & \(-\)0.031 & 0.193 \\ Eigenvalue & 1.767 & 1.749 & 1.663 & 1.391 & 1.260 \\ Explained & & & & & \\ variance \% & 17.67 & 17.49 & 16.63 & 13.91 & 12.60 \\ \hline \hline \end{tabular} Note: The maximum factor loadings in absolute value for each water quality parameter are given in bold.  
\end{table} 
Table 5: Factor loadings for the first five latent factors. correlations between TSS and Pb in PC1, between EC and TN in PC2 and between Cd and Cr in PC3. The factor loadings of PC4 reflect the strong negative correlation between COD and TP. Furthermore, the weights of parameters (\(\text{w}_{\text{i}}\)) are calculated according to the Equation (6). The calculated relative weights for water quality parameters according to the approaches described earlier are presented in Table 6.  
It could be noticed that relative weights obtained by equal weightage and PCA-based approaches are closer than expert judgment ones. The calculated WWQIs for the investigated WWTPs are presented in Figure 3.  
The three approaches for the calculations give similar results, where the expert judgment gives higher WWQI (cleaner water), as opposed to the PCA-based and equal weightage, giving nearly equal results. The only exceptions are Pernik (PER) and Plovdiv (PDV), with the highest WWQIs calculated by an equal weightage approach. The wastewater outlet status classifications of investigated WWTPs, based on applied WWQIs according to the modified WQI schemes, are presented in Table 7. There is full agreement between the three approaches used for the calculation of WWQI, excluding the classification of the WWTP located near Pernik (PER). Generally, the status of WWTP outlets is \"good\" to \"very good\" with the only exceptions being PDV and PAZ, for which a \"moderate\" status is given based on the WWQI. \begin{table}
\begin{tabular}{c c c c} \hline  & \multicolumn{3}{c}{\(\text{\bf{W}}_{\text{i}}\)} \\ \cline{2-4}
**Water Quality Parameter** & & \(\text{\bf WWQI}_{\text{N}}\) & \(\text{\bf WWQI}_{\text{Exp}}\) & \(\text{\bf WWQI}_{\text{PCA}}\) \\ \hline pH & 0.1 & 0.051 & 0.097 \\ EC & 0.1 & 0.077 & 0.102 \\ TSS & 0.1 & 0.077 & 0.092 \\ COD & 0.1 & 0.103 & 0.101 \\ TN & 0.1 & 0.103 & 0.097 \\ TP & 0.1 & 0.103 & 0.099 \\ Cd & 0.1 & 0.103 & 0.097 \\ Cr & 0.1 & 0.128 & 0.101 \\ Ni & 0.1 & 0.128 & 0.102 \\ Pb & 0.1 & 0.128 & 0.112 \\ - & \(\sum\text{w}_{\text{i}}=1.0\) & \(\sum\text{w}_{\text{i}}=1.0\) & \(\sum\text{w}_{\text{i}}=1.0\) \\ \hline \end{tabular}
\end{table} 
Table 6: Relative weights assigned to the water quality parameters. Figure 3: Calculated WWQI values for the outlets of the investigated WWTPs (n = 21).