Sampling collection

The WWTP is located in Alcantarilla (Murcia, SE Spain) at the coordinates 37◦55 39 N 1◦14 28 W. This locality has an estimated population of 41,622 people in 2018. The plant has a design flow that exceeds 13,000 m3/day corresponding to 151,667 population equivalent. The treatment included the following steps; (i) mechanical pretreatment, (ii) aerobic biological process as secondary treatment with active sludge with double stage, (iii) coagulation and flocculation, and (iv) sand filter and disinfection with ultraviolet in closed pipes. The device was placed in the wastewater effluent (see Figure 6).

(**a**) Installation of the device (**b**) Device deployed in the effluent

**Figure 6.** Device deployment in Alcantarilla wastewater treatment plant (WWTP).

The sampling procedure involved the acquisition of the analytical data obtained by the sensor daily (average value of 3 daily readings) and the analytical data obtained from 3 daily samples of effluent that were integrated and subsequently analyzed in the laboratory. The samples were stored at 4 ◦C until further analysis. The sampling was carried out during the month of March 2019, and eight samples were compared in the following days 1, 4, 8, 12, 14, 18, 20, and 22.
