title: Total solids content: a key parameter of metabolic pathways in dry anaerobic digestion.
abstract: BACKGROUND
  In solid-state anaerobic digestion (AD) bioprocesses, hydrolytic and acidogenic microbial metabolisms have not yet been clarified. Since these stages are particularly important for the establishment of the biological reaction, better knowledge could optimize the process performances by process parameters adjustment.
  
  
  RESULTS
  This study demonstrated the effect of total solids (TS) content on microbial fermentation of wheat straw with six different TS contents ranging from wet to dry conditions (10 to 33% TS). Three groups of metabolic behaviors were distinguished based on wheat straw conversion rates with 2,200, 1,600, and 1,400 mmol.kgVS-1 of fermentative products under wet (10 and 14% TS), dry (19 to 28% TS), and highly dry (28 to 33% TS) conditions, respectively. Furthermore, both wet and dry fermentations showed acetic and butyric acid metabolisms, whereas a mainly butyric acid metabolism occurred in highly dry fermentation.
  
  
  CONCLUSIONS
  Substrate conversion was reduced with no changes of the metabolic pathways until a clear limit at 28% TS content, which corresponded to the threshold value of free water content of wheat straw. This study suggested that metabolic pathways present a limit of TS content for high-solid AD.
authors.affiliation: INRA, UR0050, Laboratoire de Biotechnologie de l'Environnement, Avenue des Etangs, Narbonne F-11100, France. claire.dumas@supagro.inra.fr.
authors.forename: Jean-Charles
authors.initials: JC
authors.lastname: Motte
authors.forename: Eric
authors.initials: E
authors.lastname: Trably
authors.forename: Renaud
authors.initials: R
authors.lastname: Escudié
authors.forename: Jérôme
authors.initials: J
authors.lastname: Hamelin
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Steyer
authors.forename: Nicolas
authors.initials: N
authors.lastname: Bernet
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Delgenes
authors.forename: Claire
authors.initials: C
authors.lastname: Dumas