*2.1. WWTP Characteristics*

The WWTP is located in the Southwest of Spain, specifically in Caravaca de la Cruz (Murcia). It was designed to treat an average daily flow of 8000 m3, serving 85,000 population equivalent (p.e.). Firstly, as can be seen in Figure 1, the raw water is pre-treated by means of a screening system (pore size of 10 mm and 3 mm) and an aerated grit and grease removal system. The secondary treatment consists of an anoxic tank with a capacity of 950 m<sup>3</sup> with two agitators, two carousel-type aeration tanks with a total volume of 19,000 m<sup>3</sup> and two secondary decanters placed in series. Finally, the tertiary treatment consists of coagulation-flocculation tank, lamellar decanter, rapid sand filter (RSF) and UV disinfection system.

**Figure 1.** Scheme of WWTP analysed in this work (asterisks indicate sampling points).

The sludge recovered from the secondary and tertiary treatment is mixed, thickened by settling, and finally, dewatered by means of centrifugation, up to 78–86% moisture content (*w*/*w*).
