Wastes recycling of non-sterile cellulosic ethanol production from low-temperature pilot-scale enzymatic saccharification of alkali-treated sugarcane bagasse

Abstract

High energy consumption has been one of bottlenecks for bioconversion of lignocellulose into biofuels and biochemicals. A self-designed pilot-scale device with recycling of black liquor (BL) and waste washing water (WWW) was constructed to conduct low-temperature pretreatment and high-solid enzymatic hydrolysis of sugarcane bagasse (SCB) at ordinary atmospheric pressure. Results showed that enzymatic hydrolysis of WWW-washed BL-WWW-NaOH-treated SCB at 30% solid concentration for 72 h achieved 91.59 g/L glucose with glucan conversion of 70.94%. The pretreatment unit shared only 19.68%–22.43% of total energy consumption and 8.32%–8.81% of total cost. The non-sterile enzymatic hydrolysate could be directly fermented by BL-adapted yeasts to maximally produce 44.82 g/L ethanol at 48 h, while the sterile hydrolysate could not be fermented. 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, furancarboxaldehyde and 5-hydroxymethylfurfural might be the dominant inhibitors in the sterile enzymatic hydrolysate for ethanol production. Finally, a low-emission strategy for cellulosic ethanol production with low energy consumption was proposed.