Abstract
BackgroundSimultaneous saccharification and fermentation (SSF) is a promising process for bioconversion of lignocellulosic biomass. High glucan loading for hydrolysis and fermentation is an efficient approach to reduce the capital costs for bio-based products production. The SSF of steam-exploded corn stover (SECS) for ethanol production at high glucan loading and high temperature was investigated in this study.ResultsGlucan conversion of corn stover biomass pretreated by steam explosion was maintained at approximately 71 to 79% at an enzyme loading of 30 filter paper units (FPU)/g glucan, and 74 to 82% at an enzyme loading of 60 FPU/g glucan, with glucan loading varying from 3 to 12%. Glucan conversion decreased obviously with glucan loading beyond 15%. The results indicated that the mixture was most efficient in enzymatic hydrolysis of SECS at 3 to 12% glucan loading. The optimal SSF conditions of SECS using a novel Saccharomyces cerevisiae were inoculation optical density (OD)600 = 4.0, initial pH 4.8, 50% nutrients added, 36 hours pre-hydrolysis time, 39°C, and 12% glucan loading (20% solid loading). With the addition of 2% Tween 20, glucan conversion, ethanol yield, final ethanol concentration reached 78.6%, 77.2%, and 59.8 g/L, respectively, under the optimal conditions. The results suggested that the solid and degradation products’ inhibitory effect on the hydrolysis and fermentation of SECS were also not obvious at high glucan loading. Additionally, glucan conversion and final ethanol concentration in SSF of SECS increased by 13.6% and 18.7%, respectively, compared with separate hydrolysis and fermentation (SHF).ConclusionsOur research suggested that high glucan loading (6 to 12% glucan loading) and high temperature (39°C) significantly improved the SSF performance of SECS using a thermal- and ethanol-tolerant strain of S. cerevisiae due to the removal of degradation products, sugar feedback, and solid’s inhibitory effects. Furthermore, the surfactant addition obviously increased ethanol yield in SSF process of SECS.
Highlights
Simultaneous saccharification and fermentation (SSF) is a promising process for bioconversion of lignocellulosic biomass
Enzymatic hydrolysis steam explosion pretreatment (SEP) was adopted to break down the structure of the lignocellulosic matrix to facilitate hydrolysis and fermentation
The results show that higher enzyme loading resulted in higher glucan conversion of either washed steam-exploded corn stover (SECS) (Figure 1A) or whole slurry (Figure 1B)
Summary
Simultaneous saccharification and fermentation (SSF) is a promising process for bioconversion of lignocellulosic biomass. High glucan loading for hydrolysis and fermentation is an efficient approach to reduce the capital costs for bio-based products production. The SSF of steam-exploded corn stover (SECS) for ethanol production at high glucan loading and high temperature was investigated in this study. LCE production requires the following three major processes: pretreatment, enzymatic hydrolysis, and fermentation. Pretreatment is a necessary step for breaking down the lignin-carbohydrate complex (LCC) structures, which increases cellulose accessibility to enzymes in hydrolysis and improves ethanol yield in fermentation [8,9,10]. Steam-exploded biomass was found to be highly digestible and highly fermentable, and it should be suitable for bio-based products refining [4,14,15]
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