1. Introduction
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 high
temperatures prevail practically throughout the
year, have contributed to establish the anaerobic
systems, particularly the UASB reactors, in an
outstanding position.
Nowadays, it can be said that the high-rate
anaerobic reactors used for treatment of domestic
sewage are a consolidated technology in some
warm-climate countries, especially in Brazil, Colombia
and India, with several treatment systems operating in
full scale (population equivalents from a few thousand up to around one million inhabitants). In
Brazil, practically all the wastewater treatment
feasibility studies include anaerobic reactors as
one of the main options. Undoubtedly, a great
contribution to the consolidation and dissemination of the anaerobic technology for the treatment
of domestic sewage in Brazil came from the
National Research Programme on Basic Sanitation – PROSAB, which has been carried out since
1997 (Chernicharo et al. 2001a). Therefore, for the
purpose of this paper, the advances on post treatment of anaerobic effluents will be mainly focussed on the Brazilian experience, that is believed
to reflect also the reality of other warm climate
countries.