2-29: Detoxification of steam exploded biomass by steaming

One of major drawbacks of the thermic pretreatments of biomass is the formation of degradation compounds that inhibit the enzymatic hydrolysis and the fermentation. The most abundant inhibitors (furfurals, low molecular weight acid and the fragments of lignin) can be removed by washing the substrate, but this procedure sweeps away also the soluble hemicellulose and produces a dilute liquid stream. In this work it has been investigated the removal of volatile inhibitors from the steam exploded biomass by using an additional stream of steam. Alternatively, the inhibitors can be removed by drying the substrate (like in oven at 60°C overnight) but this procedure leads to the hornification of the substrate that depresses the saccharification yield. The steaming has been applied to a pretreated Arundo donax (210 °C, 6 min); the detoxified product has been tested in the SSF procedure to obtain bioethanol, using an optimised mix of enzymes (cellulosolytic, hemicellulosoyitic, β-glucosidase), and a commercial strain of Saccharomyces cerevisiae.  The bioconversion has been carried out in flasks with solid load of 7 wt%. The results have been compared with other detoxification procedures i.e. washing with water and drying. The high yields of glucose conversion into ethanol have confirmed the efficiency of the detoxification, while no ethanol has been obtained using the substrate not detoxified. The final ethanol yields (respect to the theoretical from cellulose) have been: 58% using steaming, 54% using water washing, 49% using drying. It has been used a device submitted for patent to carry out the steaming.