Batch acidogenic fermentation of maize silage occurs in
three metabolic phases characterized by the production of
distinct primary fermentation products and correlating
with the respective bacterial key players. The clostridial
butyric-type fermentation predominates, whereas the
propionic-type fermentation is marginal. The composition
of the inoculum seems to influence the performance of
the hydrolysis and acidogenesis steps. Further studies
should reveal the metabolic dynamics and community
composition when using both a continuous fermentation
regime and solid substrates other than maize silage.
As the metabolite composition of the acidogenesis affects
the subsequent methanogenic performance, process control
and optimization should focus on the first two phases, i.e.,
hydrolysis and acidogenesis of the biogas production when
solid substrates are digested. Especially in plug-flow digesters
or digesters with a separated hydrolysis (two-stage
systems), the control of the acidogenic reactions is important.
More detailed analyses of the hydrolysis and acidogenesis
steps in solid-state fermentation are needed for the
efficient exploitation of more sustainable feedstocks such as
straw or energy crops other than maize.