High solid loading and multiple-fed simultaneous saccharification and co-fermentation (mf-SSCF) of rice straw for high titer ethanol production at low cost

Efficient ethanol production using dilute acid pretreated rice straw was investigated in multiple-fed simultaneous saccharification and co-fermentation (mf-SSCF) for producing high titer ethanol at a low cost. The mf-SSCF was performed at very high solid loading (29.5% w/v) by multiple feeding of dilute acid pretreated rice straw without any detoxification, solid-liquid separation, and sterilization. After 72 h, an ethanol titer of 68.72 g L−1 was attained with higher ethanol yield (0.42 g g−1) and productivity (0.95 g L−1 h−1). Only magnesium sulfate (6 g L−1) was added as nutrient component and aqueous ammonia was used for pH adjustment of pretreated slurry to 5, which also provides ammonium ions as a nitrogen source for yeast during ethanol fermentation. Almost no water was added in the mf-SSCF process; therefore, higher ethanol titer (8.7 % v/v) was achieved, which further reduce distillation, water input, and treatment cost. These results suggest that the mf-SSCF process has great potential for the production of high titer ethanol on a commercial scale due to the consolidation and simplification of the process at a low cost.