Imidazole Pretreatment of Oil Palm Empty Fruit Bunches for Ethanol and Succinic Acid Co-production by Saccharomyces cerevisiae and Pichia stipitis

Oil palm empty fruit bunches (OPEFB) were pretreated with imidazole aiming to reduce the biomass recalcitrance and to co-produce ethanol and succinic acid. For such as purpose, two different yeasts (Saccharomyces cerevisiae and Pichia stipitis) were evaluated and compared. Imidazole pretreatment of OPEFB at 180 °C for 1 h achieved a removal of 81.5% of lignin and a solid recovery of 53.0%. Enzymatic hydrolysis (24 h) of imidazole-pretreated OPEFB achieved 96.2% and 98.8% of glucose and xylose yields, respectively. Fermentation of the enzymatic hydrolysate with S. cerevisiae resulted in higher ethanol titer (8.9 g/L) and productivity (0.75 g/L/h) with lower fermentation time (12 h) compared to the fermentation (48 h) using P. stipitis (6.3 g/L and 0.13 g/L/h). Additionally, 1.11 g/L and 1.83 g/L of succinic acid were produced by S. cerevisiae (12 h) and P. stipitis (48 h), respectively. From a biorefinery sight, a total of 132.5 kg of ethanol and 16.4 kg of succinic acid could be produced from a ton of raw OPEFB, employing S. cerevisiae in a 12-h fermentation of the enzymatic hydrolysate obtained from imidazole-pretreated OPEFB. The results showed great potential of imidazole-pretreated OPEFB for ethanol production using S. cerevisiae, leading to efficient lignocellulosic biomass valorization and minimization of the agro-industrial waste.