Anaerobic degradation as a method for treating high- and
medium-strength biodegradable wastewaters has become a
widely accepted technology in the last few decades with the
development of high-rate reactors such as the upflow anaerobic
sludge blanket (UASB) reactor, anaerobic biofilter and the
anaerobic fluidized bed reactor (AFBR) (Rajeshwari et al., 2000).
The process of anaerobic degradation is a complex and
dynamic system, where microbiological, biochemical and
physico-chemical aspects are closely linked. During anaerobic
treatment, a complex natural community consisting of many
interacting microbial species degrades natural polymers such
as polysaccharides, proteins, nucleic acids and lipids, in the
absence of oxygen, into methane and CO2. The process
involves the hydrolysis of high-molecular-weight carbohydrates,
fats and/or proteins into soluble polymers by means
of enzymatic action of hydrolytic fermentative bacteria and
the conversion of these polymers into organic acids, alcohols,
H2 and CO2. Volatile fatty acids (VFA) and alcohols are then
converted to acetic acid by H2-producing acetogenic bacteria
and finally methanogenic archaea convert acetic acid and H2
gas into CO2 and CH4 (Gujer and Zehnder, 1983; Mosey and
Fernandez, 1989). These processes are considered to be
bacterial in origin and no other processes are considered in the
research literature on anaerobic digestion.