# Assessment of the Water Quality of WWTPs' Effluents through the Use of Wastewater Quality Index
## 3 Results  
Treated water was collected from 21 Bulgarian WWTPs receiving urban wastewater. The results obtained for six physicochemical indicators--pH, EC, COD, TSS, TN and TP, three priority substances (Cd, Ni and Pb) and one specific substance (Cr) were used for this study (Table 4). The highlighted values, shown in Table 2, mean that the concentrations of these parameters are greater than the maximum allowable concentrations. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**WQI** & \
\begin{tabular}{c} **Water Status** \\ **Original Scale**[53] \\ \end{tabular} & **WQI** &
\begin{tabular}{c} **Water Status** \\ **Modified Scale**[54] \\ \end{tabular} \\ \hline
80–100 & Excellent & 80–100 & Very good \\
65–80 & Good & 65–80 & Good \\
50–65 & Fair & 0–65 & Moderate \\
25–50 & Poor & & \\ \textless{}25 & Very poor & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Water quality categorization scheme. As regards the different water quality parameters, excursions from the environmental water quality standards for the priority [9] and specific pollutants [10] were observed for Pb (14.45 mg/L at PDV), EC (1174 \(\upmu\)S/cm at DMG, 441 \(\upmu\)S/cm at PVN, 991 \(\upmu\)S/cm at RDN) and pH (8.51 at TRO). For the water treatment quality parameters [8], excursions were observed for TP (2.15 mg/L at GAB, 1.61 mg/L at PAZ, 1.70 mg/L at PDV, 2.21 mg/L at PER, 2.82 mg/L POP) and TN (14.2 mg/L at PAZ). These results show that the treatment facilities generally meet the requirements posed by the legislation. The PCA results show that the first five latent factors (PCs) with eigenvalues higher than 1 explain almost 80% of the total variance. The factor loadings of the selected PCs are presented in Table 5.  
The factor loadings reveal the relationships between water quality parameters with significant contributions to the formation of latent factors. For example, there are strong \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**WWTP**} & \multirow{2}{*}{**pH**} & EC & COD & TSS & TP & TN & Cr & Cd & Ni & Pb \\  & & \(\upmu\)S/cm & mg/L & **mg/L** & **mg/L** & **mg/L** & **\(\upmu\)g/L** & **\(\upmu\)g/L** & **\(\upmu\)g/L** \\ \hline BLG & 7.91 & 386 & 16.50 & 2.0 & 0.25 & 5.24 & 2.16 & 0.00008 & 3.36 & 0.36 \\ DMG & 7.77 & **1174** & 17.80 & 3.4 & 0.25 & 13.40 & 2.76 & 0.00008 & 2.54 & 0.25 \\ DPN & 7.80 & 312 & 12.70 & 3.3 & 1.39 & 1.85 & 1.45 & 0.00008 & 2.65 & 0.34 \\ GAB & 8.27 & 232 & 10.80 & 2.4 & **2.15** & 5.40 & 13.94 & 0.09177 & 3.52 & 0.33 \\ KNL & 7.78 & 396 & 16.30 & 4.1 & 1.36 & 4.22 & 1.47 & 0.00008 & 1.89 & 0.72 \\ KZN & 7.57 & 454 & 10.00 & 7.1 & 0.90 & 5.88 & 1.95 & 0.00008 & 2.87 & 0.22 \\ LOV & 8.34 & 589 & 9.61 & 2.2 & 1.63 & 4.19 & 2.09 & 0.00008 & 2.73 & 0.30 \\ MON & 7.92 & 328 & 7.22 & 2.1 & 0.86 & 5.41 & 1.17 & 0.08511 & 2.50 & 0.47 \\ MZD & 8.40 & 711 & 8.78 & 4.3 & 1.63 & 7.22 & 1.47 & 0.00008 & 1.82 & 0.24 \\ PAZ & 8.23 & 346 & 9.83 & 1.7 & **1.61** & **14.20** & 1.77 & 0.00008 & 1.66 & 0.47 \\ PBN & 8.43 & 248 & 23.40 & 6.2 & 1.06 & 6.11 & 2.23 & 0.00008 & 1.91 & 0.37 \\ PDV & 8.28 & 261 & 12.00 & 9.4 & **1.70** & 8.30 & 2.90 & 0.03658 & 4.84 & **14.45** \\ PER & 8.42 & 323 & 12.90 & 1.2 & **2.21** & 6.20 & 1.61 & 0.00008 & 2.15 & 0.19 \\ POP & 8.13 & 485 & 9.62 & 4.0 & **2.82** & 12.20 & 2.78 & 0.00008 & 2.42 & 0.14 \\ PVN & 8.43 & **841** & 10.30 & 1.7 & 0.67 & 8.26 & 3.98 & 0.00008 & 1.77 & 0.57 \\ RDN & 8.39 & **991** & 8.69 & 4.5 & 1.23 & 11.20 & 1.66 & 0.00649 & 2.15 & 0.11 \\ SEV & 8.39 & 267 & 12.30 & 0.1 & 0.52 & 2.00 & 3.38 & 0.00008 & 9.72 & 0.17 \\ SMK & 8.01 & 87.3 & 5.69 & 3.5 & 0.71 & 4.50 & 0.51 & 0.00008 & 1.60 & 0.35 \\ SOF & 7.83 & 222 & 19.00 & 2.1 & 0.25 & 6.60 & 2.74 & 0.00008 & 3.45 & 0.24 \\ SZG & 7.91 & 570 & 11.10 & 1.8 & 0.25 & 6.49 & 1.66 & 0.00008 & 1.78 & 0.16 \\ TRO & **8.51** & 262 & 10.20 & 1.4 & 0.50 & 9.58 & 1.15 & 0.09177 & 2.06 & 0.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Physical-chemical parameters and potentially toxic elements concentration of the collected wastewater effluent samples.