Anaerobic digestion of C1–C4 light oxygenated organic compounds derived from the torrefaction of lignocellulosic materials

• First paper on the anaerobic digestion of the aqueous phase derived from the torrefaction of lignocellulosic materials.
• The concentrations of the aqueous phase rich in C1–C4 that maximizes the production of bio-gas were measured.
• A linear correlation was determined between the optimal concentration at which a torrefaction aqueous phase can be AD and the content of HAA + phenols in the aqueous phase.

This paper reports the anaerobic digestion (AD) of the aqueous phase rich in C1–C4 oxygenated organic compounds derived from the torrefaction of six lignocellulosic materials (corn stover, annual rye straw pellet, pea hay, sorghum biomass, arundo donax and red fir wood) in an Auger reactor. The content of some of the most important C1–C4 compositions found in the aqueous phase measured by GC/MS is reported. Some of the compounds identified in the torrefaction aqueous phase produced (acetic acid, acetol, hydroxyacetaldehyde and phenol 2-methoxy) were anaerobically digested. The optimal concentration at which acetol and acetic acid could be digested was 1.5 and 1 mass % respectively. Much lower optimal concentrations were obtained for hydroxyacetaldehyde (HAA) and phenol 2-methoxy (0.01 mass %) which were found to be the main inhibitors. At 200 h and at the optimal concentration obtained for acetic acid, acetol, HAA and phenol-2 methoxy the yield of biogas produced was 363, 50, 600 and 4100 ml/g respectively. The AD of the aqueous phase obtained from the torrefaction of the six biomasses studied was conducted at the same conditions used for the model compounds. The optimal concentration these aqueous phases could be digested was: 2.5, 1.5, 1.5, 1.5, 0.5 and 0.5 mass % for the pea hay, corn stover, arundo donax, annual rye, sorghum biomass and red fir wood respectively. At 500 h and the optimal concentrations the yield of bio-gas produced was 106, 85, 91, 53, 32 and 88 ml/g of aqueous phase for pea hay, corn stover, arundo donax, annual rye straw, sorghum biomass and red fir wood respectively. A linear correlation was obtained between the optimal concentration at which a torrefaction aqueous phase can be AD and the content of HAA + phenols.