A cascade biorefinery concept was proposed for the first time to produce furfural and subsequent volatile fatty acids production using corn stover as biomass. In the first step, Subcritical water pre-treatment was used to extract furfural from hemicellulose into the liquid phase, while the solid phase, rich in cellulose and lignin, was fermented anaerobically in the second step to produce volatile fatty acids (VFA). A subcritical water treatment combined with CO2 as pressurizing agent was used both as a pre-treatment of the biomass, and for the production of furfural from the hemicellulose fraction of the lignocellulosic biomass. After 1h at 180 °C and 50 bar, a furfural yield of 29 % was obtained in the liquid phase. Acetic and formic acid were generated as side products of the treatment. Following this treatment, 49.4 % of the initial solids were recovered, with a marked reduction in hemicellulose content (from 33 % to 5 %) and an increase in both cellulose (from 39 % to 62 %) and lignin (from 21 % to 33 %). This solid was then subjected to anaerobic fermentation. Inoculum type was a key parameter, with 12 % higher volatile fatty acids production when cow rumen was used compared to anaerobic digestion (AD) sludge from a wastewater treatment plant. Pre-treatment of corn stover did not improve organic matter biodegradation, probably due to its high lignin content. However, the proposed cascade biorefinery showed to be successful for the consecutive production of two value-added products using low value corn stover as the raw material.
