Cost-effective production of cellulosic ethanol from sweet sorghum stalks via the integration of advanced solid-state fermentation and alkali-distillation

S. Li
Tsinghua University,

Keywords: alkaline pretreatment,advanced solid-state fermentation (ASSF),sweet sorghum, black liquor recycle


Pretreatment and waste water treatment are two of the most critical and challenging areas in cellulosic ethanol production. For the cost-effective production of cellulosic ethanol from sweet sorghum stalks, we developed a novel technology of integrating advanced solid-state fermentation (ASSF) and alkali-distillation without black liquor emission. Sweet sorghum has been considered as a viable energy crop for ethanol production, the soluble sugar in sweet sorghum stalks can be easily converted into ethanol by ASSF technology which uses the crushed stalks as culture substrates directly, and the fermented bagasse after distillation is rich with homocelluloses (70%). In the present research, an integrated process combined ASSF and alkaline distillation was designed to produce cellulosic ethanol cost-effectively. NaOH solution was added during ethanol distillation process after ASSF as an alkali pretreatment to avoid energy-intensive pretreatment of cellulosic ethanol, direct enzymatic saccharification of alkali pretreated fermented bagasse without solid and liquid separation, solid washing, and detoxification significantly improved saccharification and subsequent ethanol fermentation, and the so-called black liquor (alkali distillate) was recycled to treat fermented bagasse after ASSF. Compared with ethanol production from traditionally washed substrate, the fermentable sugars conversion and ethanol theoretical yield from alkali distillation pretreated whole slurry of a fermented bagasse improved from 44.06 % and 44.85% to 65.14% and 61.81%, respectively. It’s a promising process to cost-effectively produce cellulosic ethanol without waste water treatment issues at commercial scale.