Influence of High Solid Concentration on Enzymatic Hydrolysis and Fermentation of Steam-Exploded Corn Stover Biomass

Abstract

Steam-exploded corn stover biomass was used as the substrate for fed-batch separate enzymatic hydrolysis and fermentation (SHF) to investigate the solid concentration ranging from 10% to 30% (w/w) on the lignocellulose enzymatic hydrolysis and fermentation. The treatment of washing the steam-exploded material was also evaluated by experiments. The results showed that cellulose conversion changed little with increasing solid concentration, and fermentation by Saccharomyces cerevisiae revealed a nearly same ethanol yield with the water-washed steam-exploded corn stover. For the washed material at 30% substrate concentration, i.e., 30% water insoluble solids (WIS), enzymatic hydrolysis yielded 103.3 g/l glucose solution and a cellulose conversion of 72.5%, thus a high ethanol level up to 49.5 g/l. With the unwashed steam-exploded corn stover, though a cellulose conversion of 70.9% was obtained in hydrolysis at 30% solid concentration (27.9% WIS), its hydrolysate did not ferment at all, and the hydrolysate of 20% solid loading containing 3.3 g/l acetic acid and 145 mg/l furfural already exerted a strong inhibition on the fermentation and ethanol production.

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“…Shorter hydrolysis times were required for low substrate loadings as compared to longer hydrolysis times for high substrate loading, which was in agreement to reported work on CMC and corn stover using cellulase (Al-Zuhair 2008; Lu et al 2010). This may be due to high initial viscosity at high substrate loadings which poses mass transfer limitations, resulting in a low conversion efficiency (Ioelovich and Morag 2012;Lu et al 2010;Mussatto et al 2008;Sarkar and Etters 2004). End-product inhibition on cellulases by cellobiose was avoided by supplementing b-glucosidase using Novozyme 188 (Teeri 1997).…”

“…The results for reducing sugars showed that at higher substrate loadings, the initial rate of reaction was faster, hence the higher production of sugars in agreement with Gan et al (2003). Shorter hydrolysis times were required for low substrate loadings as compared to longer hydrolysis times for high substrate loading, which was in agreement to reported work on CMC and corn stover using cellulase (Al-Zuhair 2008; Lu et al 2010). This may be due to high initial viscosity at high substrate loadings which poses mass transfer limitations, resulting in a low conversion efficiency (Ioelovich and Morag 2012;Lu et al 2010;Mussatto et al 2008;Sarkar and Etters 2004).…”

“…As the reaction proceeds, hydrolysis slows down as there will be changes in substrate structure, with easily hydrolysable substrate getting depleted, enzymes may become adsorbed on residual substrate and lignin, enzymes may become deactivated, end-product inhibition may occur as well as mass transfer limitations, especially at high substrate loadings 1999). Glucose was released rapidly at the beginning of hydrolysis at low substrate loading (Lu et al 2010). The fast rate of glucose release may be due to the removal/ hydrolysis of the first layer of cellulose (Gan et al 2003).…”

“…End-product inhibition on cellulases by cellobiose was avoided by supplementing b-glucosidase using Novozyme 188 (Teeri 1997). High substrate loading results in increased sugar concentration, which assisted in lowering capital operational costs associated with reduced reactor volume, reduced energy costs and ethanol separation (Hodge et al 2009;Lu et al 2010;Zhang et al 2010). However, the limitation of high solids is that more energy is required for mixing and there is a build-up of residual solids.…”

Application of Response Surface Methodology to Optimize Alkali Concentration, Corn Stover Particle Size, and Extruder Parameters for Maximum Sugar Recovery

“…The particle size of rice straw and silvergrass inversely influenced the acetic acid formation in dilute acid pretreatment (Guo et al, 2008); however, it was not confirmed in this study. The acetic acid concentration was lower than dilute acid Hodge et al, 2008), formic acid (Xu et al, 2009a), lime , alkali ), hydrothermal pretreatment (Öhgren et al, 2006;Lu et al, 2010) of corn stover; compared to other feedstocks listed in the table. NaOH has higher reactivity with hemicellulose than cellulose due to amorphous characteristics of hemicellulose (Lai, 2001).…”