Simultaneous hydrolysis and fermentation of lignocellulose versus separated hydrolysis and fermentation for ethanol production

Second generation of biofuels relay mostly on lignocellulose as raw materials. There are several technologies applied to obtain ethanol from lignocellulose. In this study we try to compare the productivity and efficiency of two technologies: simultaneous hydrolysis (saccharification) and fermentation (SSF) and separated hydrolysis and fermentation (SHF). We used a BlueSens equipment with CO(2) ant EtOH cap sensors mounted on the fermentation flasks. In the first part we have studied how the size and type of inoculums and agitation influence the production o ethanol. In the next steps, we applied the two technologies to hydrolyze and ferment different types of cellulose from agriculture. The biomass was pretreated using alkaline and steam combined method The cellulases used for hydrolysis are Trichoderma cellulases Onozuka from Merk, Aspergillus cellulases from Fluka, and cellobiase from Novo. The results show that the type of the yeasts is very important, especially for SSF technology, where high temperature is applied to ferment and hydrolyze in the same time. Also, the size of inoculums influence the speed of fermentation. Regarding the rate of hydrolysis and ethanol production, in case of Avicel cellulose, the hydrolysis rate is between 21 - 24% (in a fermentation medium of 10% cellulose). As for wheat straw and corn stalks, the rate of hydrolysis is much higher, over 80%. The ethanol production from lignocellulosic biomass is higher in SSF than in SHE The results indicate that SSF is more efficient that SHF in terms of total production time, energy consumption and total production costs.