Comparative study of bioethanol production from bagasse pith by Pichia stipitis in free cell system and immobilized electrosprayed micro-beads: SSF and combined hydrolysates fermentation

Abstract

Biofuels production from biomass are receiving special attention due to the availability of raw materials, suitable conversion yield and renewability. The primary objective of this study was comparison of bioethanol productivity from bagasse pith by free and immobilized Pichia stipitis. Alginate micro-beads at various sizes fabricated by electrospray technique. At the first stage, bioethanol production using free cells in two processes including fermentation of combined acid and enzymatic hydrolysates and simultaneous saccharification and fermentation (SSF) was optimized. In fermentation of combined hydrolysates, maximum production equal to 9.53 and 12.68 g/L was observed by free and immobilized cells, respectively at cell concentration 6 %, portion of acid hydrolysate 40 % and total sugar concentration 50 %. Besides, maximum production in SSF equal to 9.93 and 10.62 g/L was obtained by free and immobilized cells, respectively at 6 % cell, 4 g solid and enzyme content of 50 FPU/g solid. However, in SSF fermentation, the beads size had no significant effect on ethanol production while in combined hydrolysates fermentation, bioethanol production considerably affected by the beads size and 13.9 g/L ethanol was obtained in minimum beads size. Additionally, long-term stability of beads was examined in repeated-batch cultures, showing effective bioethanol production up to five reuse cycles.