High Ethanol Concentration (77 g/L) of Industrial Hemp Biomass Achieved Through Optimizing the Relationship between Ethanol Yield/Concentration and Solid Loading

Abstract

In this study, the relationships between ethanol yield/concentration and solid loading (6–21%) were investigated to enhance ethanol titer and avoid a random choice of solid loading for simultaneous saccharification and fermentation (SSF). Alkali-pretreated hemp biomass was used for SSF in four scenarios including Case I: 30 filter paper unit (FPU)-cellulase and 140 fungal xylanase unit (FXU)-hemicellulase/g-solid; Case II: 40 FPU-cellulase and 140 FXU-hemicellulase/g-solid; Case III: 30 FPU-cellulase and 140 FXU-hemicellulase/g-solid with 1% Tween80; and Case IV: 30 FPU-cellulase and 140 FXU-hemicellulase/g-solid with particle size reduction (<0.2 mm). Results showed that bioethanol yield and concentration had a negative linear ( R 2 = 0.76–0.93) and quadratic ( R 2 = 0.96–0.99) correlation with solid loading (6–21%), respectively. As compared to Case I and previous studies, an enhancement in ethanol yield and concentration through increasing cellulase dose (Case II) and adding Tween 80 (Case III) was overestimated, whereas particle size reduction (Case IV) extended the “solid effect”, evidenced by the highest ethanol concentration (77 g/L) achieved from SSF at the focus point of a quadratic model. An interpretation of the relationship between ethanol yield/concentration and solid loading not only avoids a blind selection of solid loading for SSF but also reduces extra enzymes and water consumption.

Recent Advancements in Biological Conversion of Industrial Hemp for Biofuel and Value-Added Products

“…For example, the formation of furfural (0.10-0.25 g/L) and HMF (0.15-0.35 g/L) was reported with hemp after dilute acid pretreatment (1 and 2% H 2 SO 4 ) at 180 • C for 10 min [27]. Dilute alkali pretreatment performed with NaOH was also reported in several previous studies [25,27,28,57]. Alkali pretreatment prevents unwanted sugar degradation by neutralizing released acids during the decomposition of cellulose and hemicellulose by the hydroxide ions from NaOH.…”

“…It can be attributed to the re-condensation of disrupted lignin in case of acid pretreatment, whereas alkali pretreatment unlocks small lignin units [58]. Similarly, in another study, dilute alkali pretreatment performed with 1% NaOH at 170 • C for 30 min increased the glucan content from 40.7% in the raw biomass to 77.5% in the pretreated biomass, with a reduction in lignin from 15.74% to 11.05% after pretreatment [28]. Wawro et al also reported an increase in cellulose content of hemp from 50.8% to 62.7% by NaOH pretreatment (1.5 to 3% NaOH at 90 • C for 5 h) [57].…”

“…Also, ash plays a role in some thermochemical biomass conversion processes as a catalyst [22,23]. [16,[26][27][28][29]. The chemical composition of the separated industrial hemp fractions such as hurds [30,31], fiber and shives [32], and woody core [33] were also tested.…”

“…However, increasing solid loadings after a certain limit can make the process inefficient due to insufficient mixing, as a result of high viscosity and mass transfer limitations [77]. Zhao et al investigated the effect of solid loading (from 6% to 21%) of alkali (NaOH) pretreated hemp on the ethanol concentration and ethanol yields over the course of fermentation [28]. They observed that with solid loading below 15%, SSF was complete within 24 h; however, with higher solid loadings (18% and 21%), there was not enough free liquid water (hydrolysate) present by 48 h of fermentation, indicating mixing and mass transfer limitations.…”

Effective Utilisation of Halophyte Biomass from Saline Soils for Biorefinering Processes

“…After the alkaline treatment, this band disappears completely or significantly loses its intensity, which may indicate a reduction in both lignin and pectin. Going to the lower wavenumber values, the following three more characteristic bands for the cellulose molecule appear: 1160 cm −1 (asymmetric C–O–C stretching vibrations), 1110 cm −1 (C–OH skeletal vibrations) and 1050 cm −1 (C–O–C skeletal vibrations of the pyranose ring) [ 27 ]. These bands, despite the increase in cellulose content after chemical treatment, are reduced.…”