## 2 Materials and Methods
### Wastewater Treatment Plant (WWTP) and Sampling Points  
Five Portuguese WWTPs (Evora, Reguengos de Monsaraz (RM), Borba, Redondo, and Portel) were evaluated across at least four sampling campaigns conducted in 2020. The main sampling periods were conducted in January, June, September, and November.  
The monitoring campaign included a total number of 77 samples and 2002 measurements. The samples included influents and effluents of each WWTP and surface waters upstream and downstream of the WWTPs.  
The selected WWTPs were in the Evora district, whose capital is Evora city. It is the second biggest Portuguese district, with an area of 7393 km\({}^{2}\) and 170,000 inhabitants, which is integrated into the Alentejo region of Portugal and corresponds entirely to the Central Alentejo subregion (Figure 1). This region is frequently affected by severe drought and high temperatures in the summer season. Table 1 summarizes the information on the five WWTPs of the Evora district.  
The Evora WWTP is the biggest of these target facilities. Only Evora WWTP receives hospital effluents. The remaining facilities receive mainly domestic sewage.  
It was impossible to collect upstream samples in Redondo WWTP because this sampling point is on private property.  
All five WWTPs processes started with some form of pretreatment with the objective of removing grease and large solids from the wastewater that could damage the unit operations downstream.  
The activated sludge conventional process (ASCP) is by far the most widely used for sewage biological secondary treatment.  
In the bioreactor, which operates in continuous mode, the suspended microorganisms consume the colloidal and dissolved organic matter by aerobic biodegradation. Therefore, the reactor is aerated to provide dissolved oxygen. Evora WWTP uses two reactors in series, the first for nutrient removal and the second for digestion of organic matter. In the settling tank or clarifier, the activated sludge (flocculated biomass) is gravitationally separated from the treated wastewater and the effluent overflows into the receiving waterbody, after a filtration step and before being discharged.  
The long-term activated sludge process (LT-ASP) was adopted for activating sludge in order to obtain the highest efficiency in the biological treatment, wherein the aeration periods were higher than in the conventional process. The three WWTPs that use this treatment process (Reguengos de Monsaraz, Borba and Redondo) all have a similar operation, with the use of oxidation ditches, followed by settlers.  
Waste stabilization ponds (WSPs) consist of open basins that use natural processes to treat domestic wastewater. The most common types of WSPs are anaerobic ponds, facultative ponds, maturation or polishing ponds, aerated ponds, and high-rate algal ponds (HRAPs). WSP systems require large areas of open land, making them ideal in smaller towns and rural settings; however, they are used successfully in many urban environments as well, often in combination with other sanitation technologies. One of the biggest advantages of WSPs is that they are easy and inexpensive to operate and maintain, and generally do not rely on mechanized equipment or expensive material or energy inputs. The Portel WWTP is equipped with an anaerobic waste stabilization pond followed by two facultative stabilization ponds.  
Figures S1-S4 of Supplementary Material show diagrams for each type of treatment performed in the studied facilities.