## 3 Results and Discussion  
In all analyzed towns, similar trends were observed in respect of the BOD concentration of sewage flowing into the treatment plant (Figure 1). The highest values of this indicator were recorded in 2019, and the lowest in 2020, when catering and hotel facilities were closed many times. In 2021, the BOD concentrations of sewage from the largest towns studied (D and E) returned to levels similar to those of 2019. On the other hand, in smaller towns (A, B, C) with greater importance of tourist facilities, the BOD concentration recorded in 2021 was higher than in 2020 but lower than in 2019. This was due to the restrictions on the operation of catering and hotel facilities in the first four months of 2021 and the \"slowdown in tourist traffic\" observed around the world during the COVID-19 pandemic [32]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Town**} & \multirow{2}{*}{**Area**} & \multirow{2}{*}{**Population**} & \multirow{2}{*}{**Beds in Hotels**} & \multirow{2}{*}{**Beds in Hotels**} & \multirow{2}{*}{**Food**} & \multicolumn{2}{c}{**Average Daily Flow**} \\  & & & & & & **Places** & **2019** & **2020** & **2021** \\ \cline{2-7}  & \multirow{2}{*}{**km2**} & \multirow{2}{*}{**PE**} & \multirow{2}{*}{**Number**} & \multicolumn{2}{c}{**Number/**} & \multicolumn{2}{c}{**Places/**} & \multirow{2}{*}{**m3/d**} & \multirow{2}{*}{} \\  & & & & & **1000 PE** & & & **m3/d** & \\ \hline A & 8.85 & 4000 & 1500 & 375 & 13.00 & 1274 & 1150 & 1224 \\ B & 10.87 & 11,000 & 383 & 35 & 3.20 & 1845 & 1757 & 2064 \\ C & 11.79 & 22,000 & 230 & 10 & 0.91 & 2684 & 2379 & 3434 \\ D & 13.72 & 33,000 & 1160 & 35 & 1.30 & 6931 & 681 The scale of the problem is most evident in the example of town A, which is an exclusively tourist destination (Table 4), as indicated by the number of beds in hotel facilities per 1000 inhabitants (375) and the number of places where meals are served (13). In this town, the closing of tourist and catering facilities was observed to have a significant impact on the concentration of organic compounds in sewage discharged to the treatment plant. The BOD and COD values (Figure 2) in 2020 accounted for 62.3% and 66.4%, respectively, of the values recorded in the year preceding the pandemic (2019). The annual load of pollutants discharged to the treatment plant in 2020 (Table 5) amounted to 169,159 kg BOD/year and was lower by 131,702 kg BOD compared to 2019 (300,861 kg BOD/year). Similarly large changes were recorded in town C, where BOD and COD concentrations recorded in 2020 accounted for 52.8% and 51.5%, respectively, of the values recorded in  
Figure 1: Average BOD concentration of raw wastewater in 2019–2021. Figure 2: Average COD concentration of raw wastewater in 2019–2021. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{4}{c}{**Load, \(\mathbf{10^{3}}\)-kg/Year**} & \multicolumn{4}{c}{**Load, \(\mathbf{10^{3}}\)-kg/Year**} & \multicolumn{4}{c}{**Load, \(\mathbf{10^{3}}\)-kg/Year**} \\ \cline{2-13}  & \multicolumn{4}{c}{**2019**} & \multicolumn{4}{c}{**2020**} & \multicolumn{4}{c}{**2021**} \\ \cline{2-13}  & **A** & **B** & **C** & **D** & **E** & **A** & **B** & **C** & **D** & **E** & **A** & **B** & **C** & **D** & **E** \\ \hline BOD & 301 & 211 & 409 & 1816 & 7135 & 169 & 192 & 192 & 1658 & 6519 & 205 & 261 & 322 & 1860 & 7752 \\ COD & 642 & 737 & 827 & 3668 & 13,823 & 384 & 627 & 377 & 3415 & 13,967 & 293 & 800 & 591 & 3775 & 15,100 \\ SS & 231 & 382 & 321 & 1627 & 6872 & 97 & 312 & 126 & 1551 & 7032 & 203 & 382 & 213 & 1651 & 7602 \\ TN & 40 & 62 & 84 & 232 & 1301 & 30 & 51 & 48 & 231 & 1248 & 40 & 62 & 101 & 249 & 1406 \\ TP & 5 & 13 & 9 & 35 & 184 & 4 & 11 & 6 & 35 & 194 & 5 & 13 & 10 & 37 & 224 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Pollution loads in 2019–2021. the year preceding the pandemic (2019).