Background: Biogas production from lignocellulosic feedstock not competing with food production can contribute
to a sustainable bioenergy system. The hydrolysis is the rate-limiting step in the anaerobic digestion of solid
substrates such as straw. Hence, a detailed understanding of the metabolic processes during the steps of hydrolysis
and acidogenesis is required to improve process control strategies.
Methods: The fermentation products formed during the acidogenic fermentation of maize silage as a model
substrate in a leach-bed process were determined by gas and liquid chromatography. The bacterial community
dynamics was monitored by terminal restriction fragment length polymorphism analysis. The community profiles
were correlated with the process data using multivariate statistics.
Results: The batch process comprised three metabolic phases characterized by different fermentation products.
The bacterial community dynamics correlated with the production of the respective metabolites. In phase 1, lactic
and acetic acid fermentations dominated. Accordingly, bacteria of the genera Lactobacillus and Acetobacter were
detected. In phase 2, the metabolic pathways shifted to butyric acid fermentation, accompanied by the
production of hydrogen and carbon dioxide and a dominance of the genus Clostridium. In phase 3, phylotypes
affiliated with Ruminococcaceae and Lachnospiraceae prevailed, accompanied by the formation of caproic and
acetic acids, and a high gas production rate.
Conclusions: A clostridial butyric-type fermentation was predominant in the acidogenic fermentation of maize
silage, whereas propionic-type fermentation was marginal. As the metabolite composition resulting from
acidogenesis affects the subsequent methanogenic performance, process control should focus on hydrolysis/
acidogenesis when solid substrates are digested.