Conditioning of pretreated substrates for more efficient bioconversion

One of major drawbacks in the pretreatment  of biomass is the formation of degradation compounds that inhibit enzymatic hydrolysis and fermentation. In the steam explosion, a vapor stream that contains a relevant percentage of these byproducts is generated. Moreover, the steam exploded biomass has a relatively low water content, typically 50 wt%, and comes out from the explosion chamber at temperature near 100°C. In this work we assessed the effectiveness of the drying by carrying out SHF and SSF with straw previously steam exploded with a continuous gun (150 kg/h). The conditioning of the pretreated biomass was carried out by a dryer with rotating blades. The standard tests of bioconversion were carried out at flask scale with solid load of 10 wt%, using a mix of cellulosolytic, hemicellulosolitic  and ß-glucosidase enzymes, and a commercial strain of Saccharomyces cerevisiae. The hydrolysis of high concentrated slurry was carried out in the adapted machinery with the rotating blades that was used in the drying step. The yields of glucose conversion into ethanol have indicated that detoxification was very efficient. However, it has been highlighted that drying can depress the yield of enzymatic hydrolysis up to 20%, probably because of the fiber hornification. An energetic analysis and process simulations have been carried out to assess the viability of the drying procedure and the fractionation of the volatile products between the vapor and solid streams. The new developed concept has been patented.