Ethanol Production from Whole Sugarcane Using Solid-State Fermentation

Conventional sugarcane-to-ethanol conversion occurs via a series of process steps, inter alia, energy-intensive juice extraction and concentration, followed by fermentation of the extracted juice under submerged (liquid) fermentation conditions. Solid-state fermentation (SStF), occurring in the absence of free water, is a promising alternative approach, potentially offering higher product concentrations, reduced water requirements and liquid effluent from the process, and elimination of the substantial energy requirements of the juice extraction step. While SStF has been applied to various substrates, such as sweet sorghum, there is a lack of studies considering the SStF of sugarcane, which is considered a more challenging substrate. The present study investigated the SStF of whole, milled sugarcane in 3-L horizontal, rotating reactors, to assess the effect of inoculum size, mixing speed, and particle size on ethanol production. The maximum ethanol concentration and yield were 86.7 g/L and 6.15 g/100 g wet mass (90.5% of the theoretical maximum), respectively, achieved at an inoculum size of 5% (w/w), rotation speed of 5 rpm, and particle size range of 8 to 20 mm. The fermentation was scaled up to a 50 L solid-state reactor, applying intermittent mixing to obtain a similar ethanol concentration and yield of 87.5 g/L and 6.61 g/100 g wet mass, respectively.