Some characteristics of these organic residues were determined in samples previously air dried, homogenized and sieved (b2 mm) (Table 1). The pH was determined in a residue/water suspension (1/2.5 w/v ratio). Organic carbon (OC) content was determined by oxidation (Walkley–Black method). Dissolved organic carbon (DOC) was determined in a suspension of residue (1/100 w/v ratio) in Milli-Q ultrapure water after residue shaking (24 h at 20 °C), centrifugation (20 minat 10,000 rpm), and filtering (Minisart NY 25 filter 0.45 μm, Sartorius Stedim Biotech, Germany) using a Shimadzu 5050 (Shimadzu,