Rapid and entire humification of a substrate
essentially depends on its initial C/N ratio (Beck-Friis et al., 2001 ).
The 10.6% reduction in COD is in agreement with the report of
Wei et al. (2011) in which a high COD removal from the supernatant
of hydrothermally treated municipal sewage sludge by upflow
anaerobic sludge blanket reactor was obtained. The two groups of
bacteria isolated from the digester during the anaerobic digestion
include the acid-formers (Bacillus, Escherichia, Clostridium,
Klebsiella, Proteus and Bacteroides) and a methane former
Methanococcus species.