A deep discussion on the evolution and applicability of the anaerobic technology for the treatment of domestic sewage is presented elsewhere(Lettinga et al., 1993; Seghezzo et al., 1998; von
Sperling and Chernicharo, 2005), where the several favourable characteristics of the anaerobic
processes are highlighted, such as low cost, operational simplicity, no energy consumption and
low production of solids. These advantages, associated with the favourable environmental conditions in warm-climate regions, where hightemperatures prevail practically throughout theyear, have contributed to establish the anaerobic
systems, particularly the UASB reactors, in anoutstanding position.