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Highlights • Alkali and acid pretreated biomass slurries were mixed for ethanol production. • This approach saved 40–50% alkali/acid use. • This approach improved fermentability. Abstract Alkali and acid pretreatment based processes for lignocellulosic biofuel production typically consume substantial amount of alkali and acid. In addition, alkali pretreatment generates compounds with high toxicity rendering washing/detoxification inevitable. In this work, alkali (AL) and dilute acid (DA) pretreatment based processes were compared side by side for ethanol production from corn stover (CS) using commercial enzymes and Zymomonas mobilis 8b strain. Next, AL and DA pretreated CS slurries (without removing liquid stream) were mixed to neutralize for enzymatic hydrolysis and ethanol fermentation. The digestibility and fermentability of the mixed pretreated biomass were systematically studied and compared to unmixed pretreated biomass. Results showed that mixed biomass process saved 40–50% alkali/acid use and enhanced fermentability compared to AL-CS. This work suggests that it could be beneficial to have both alkali and acid pretreatments operating in a biorefinery, which could accommodate various feedstocks. [ABSTRACT FROM AUTHOR]

This paper reports on mild acid pretreatment options for the conversion of Agave tequilana leaves into composite sugars for ethanol fermentation. The effect of five different pretreatment conditions (time, temperature and acid concentrations) were assessed in terms of cellulose digestibility, hemicellulose solubilisation and lignin content in leaves of 1.25 years old A. tequilana plants from Rockhampton and 2.5 year plants from Kalamia. Dilute acid pretreatment and enzyme saccharification of A. tequilana leaf bagasse significantly improved total glucose recovery. A recovery of 273 mg/g (70% theoretical) was attained when the bagasse was pretreated with 2.0% H 2 SO 4 for 60 min at 121 °C and saccharified with 6% (w/w) CTec 2. Saccharomyces cerevisiae efficiently fermented crude A. tequilana bagasse and juice hydrolysates within 13 h and 7 h respectively, yielding up to 38.6 g/L and 12.4 g/L. This corresponds to glucose to ethanol conversion rate of 68 and 61% for A. tequilana leaf bagasse and juice, respectively. With further developments, including fermentation of C5 sugars and inulinase saccharification of juices (release of fructose), this process could deliver greater yields, reinforcing its potential as a biofuel feedstock. [ABSTRACT FROM AUTHOR]

In this study, different detoxification treatments (XAD-4 resin adsorption [XAD] and electrodialysis) on oxalic acid pretreated hydrolysate were evaluated. Two different detoxification processes were applied to remove fermentation inhibitors from the oxalic acid pretreated hydrolysate of eucalyptus. The hydrolysates contain sugars (glucose, xylose, and arabinose) and inhibitors. Acetic acid was the main inhibitor in the original hydrolysate, and more total phenolic compounds were generated than hydroxymethyl furfural and furfural. The acetic acid was removed 100% by the electrodialysis process, and total phenolic compounds and furfural were effectively removed from the hydrolysate by XAD. Based on the process order, the combined electrodialysis-XAD process was more effective for ethanol fermentation compared to the combined XAD-electrodialysis process. Ethanol fermentation was successfully performed using the electrodialysis-XAD-treated hydrolysate and achieved a production of 7.83 g/L of ethanol, corresponding to an ethanol yield of 0.40 g/g within 48 h. Fourier transform infrared, X-ray diffractometer, and scanning electron microscopy were used to investigate the characteristics of the raw material and pretreated biomass. The results showed that most of the hemicellulose was degraded during oxalic acid pretreatment. Therefore, the crystallinity value increased from 49.79% to 56.93%. The surface of the raw material was smooth, plump, and compact, whereas the pretreated biomass was more fragmented. [ABSTRACT FROM AUTHOR]

In this study, it was found that soluble polysaccharides (SPs) from rice straw were conjugated with high levels of phenolic compounds. A gradient ethanol precipitation method was used to separate conjugates with different phenolic compound components. These conjugates were mainly composed of disaccharides or trisaccharides and phenolic acids that were mainly p- coumaric acid, ferulic acid, vanillic acid, and vanillin. SPs with more conjugates exhibited better effects on Saccharomyces cerevisiae and ethanol fermentation. The change in the proportion of conjugates in SPs significantly affected the accumulation of intracellular trehalose and glycerol content, indicating the effect of the conjugates on intracellular osmotic stress. Moreover, SPs with more conjugates generated lower intracellular hydrogen peroxide (H 2 O 2) levels. Thus, oligosaccharide and phenolic compound conjugates in SPs promoted yeast growth and ethanol fermentation. For instance, OD value reached 9.4, which was 1.3 times higher than the control group, and ethanol content at 36 h was 36.5 g/L, which was 1.3 times higher than the control. Osmotic pressure alleviation and lowered intracellular H 2 O 2 levels by conjugates are key mechanisms of the SPs during yeast growth and ethanol fermentation. [Display omitted] • SPs from rice straw contained oligosaccharide-phenolic compound conjugates. • The conjugates were mainly composed of disaccharides and phenolic acid. • The conjugates significantly affected SPs to alleviate osmotic stress. • The conjugates could lower intracellular H 2 O 2 levels during ethanol fermentation. [ABSTRACT FROM AUTHOR]

The use of an underutilized and abundant lignocellulosic feedstock residue, wheat bran, was studied for ethanol production using dilute phosphoric acid pretreatment followed by fermentation using edible fungi Neurospora intermedia . Wheat bran was subjected to dilute acid pretreatment at varying acid concentrations (0.5–3.0% w/v), temperature (150–210 °C), and reaction time (5–20 min). The interaction of multiple factors showed the optimum pretreatment conditions at acid concentration of 1.75% (w/v), at 190 °C for 10 min. The maximum total polysaccharide yield of 0.27 ± 0.01 g/g dry biomass loading, corresponding to 66% of the theoretical maximum was observed. Subsequent fermentation with N. intermedia showed 85% of the theoretical maximum ethanol yield from the untreated bran glucose. The effect of the dilute acid pretreatment on the functional groups of the wheat bran cellulose was determined with 78% reduction in the cellulose crystallinity index. The validation of the dilute phosphoric acid pretreatment in a demo plant is also reported for the first time. Enzymatic hydrolysis of pretreated slurry from the demo plant showed 85% total theoretical yield of polysaccharides. Compared to the untreated bran biomass, an increase of 51% was observed in the ethanol yield following pretreatment, with a total ethanol yield of 95% theoretical maximum. Higher yield of ethanol is also attributed to the xylose fermenting capability of the fungi. [ABSTRACT FROM AUTHOR]

Low-lignin content bmr (Brown Mid-Rib)-mutant forage sorghum ( Sorghum bicolor ) grown at Riley and Doniphan counties (Kansas, USA) were compared with wild type high-lignin content forages to evaluate the effect of reduced lignin content in biomass on bioethanol production. Sorghum bagasse ( Sorghum bicolor ), wheat straw ( Triticum aestivum ), switchgrass ( Panicum virgatum ) and miscanthus ( Miscanthus giganteus ) were used as wild type forages. Ground biomass samples were pretreated with 2% sodium hydroxide at 121 °C for 30 min followed by enzymatic hydrolysis using cellulase complex and β-glucosidase at high solid loading (20%, W/V), and the sugars released were fermented using Saccharomyces cerevisiae . Lignin content of all types of biomass was reduced to statistically equal levels (2–4%) after alkali pretreatment irrespective of their initial lignin content. However, saccharification efficiency of the pretreated biomass samples varied significantly from each other and showed a weak relationship between saccharification efficiency and total lignin content in raw and/or pretreated biomass. These results indicated that the reduced total lignin content in bmr -mutant crops does not necessarily benefit bioethanol production. Therefore, number of other factors, including lignin structure, crystallinity of cellulose and type of linkages in cellulose-hemicellulose-lignin complex must be further assessed to evaluate new crop lines for bioethanol production. The Fourier transform infrared spectroscopy (FTIR) peak intensities of ester linkages, aromatic C C linkages and glycosidic linkages for raw, pretreated and hydrolyzed biomass samples are in agreement with the variation in saccharification efficiencies among biomass types. Ethanol yield was more than 95% of the maximum possible theoretical yield based on released glucose in all types of biomass, which showed that biomass after alkali pretreatment followed by washing with water does not inhibit S. cerevisiae , regardless of feedstock sources. [ABSTRACT FROM AUTHOR]

Highlights: [•] Furfural was produced from corn stover by one stage dilute H3PO4 pretreatment process. [•] Maximum furfural yield was obtained at 200°C and 0.75% (v/v) acid dose. [•] Glucose yield was high from solid residues after enzymatic hydrolysis. [•] Ethanol was produced efficiently from glucose by Saccharomyces cerevisiae. [ABSTRACT FROM AUTHOR]

Amaranthus is a fast-growing perennial plant containing large amounts of extractable green proteins and lignocellulose residues. However, it remains to explore optimal Amaranthus biomass process technology for biofuel production. In this study, we examined that mild alkali and acid pretreatments (1% NaOH, 2% H 2 SO 4) were sufficient for near-complete biomass enzymatic saccharification, while 8% Amaranthus endogenous proteins were supplemented into the enzymatic hydrolyses. By performing classic yeast fermentation with all carbon sources from directly-extractable sugars and starch and lignocellulose enzymatic hydrolysis, this work achieved the bioethanol yield up to 23.5% (% dry matter). Notably, with respect to extremely high yield of Amaranthus straw, the maximum bioethanol yield was estimated at 14.46 t/ha/year, which was much higher than those of other major bioenergy crops as previously reported. Furthermore, this work proposed a hypothetic model to elucidate how the complete biomass saccharification was achieved to maximize bioethanol production at large scale, based on the effective wall polymer extraction and distinct lignocellulose feature modification for remarkably enhanced biomass porosity and cellulases adsorption. Hence, this work has demonstrated that Amaranthus could be applied as a novel and leading bioenergy crop, providing a powerful strategy for optimal biomass processing towards high bioethanol production. [Display omitted] • Amaranthus plant is a promising bioenergy crop rich at digestible lignocellulose. • Amaranthus straw was of extractable hemicellulose-lignin complexes. • Endogenous proteins let to 97–99% biomass saccharification with Amaranthus. • Bioethanol yield of 23.47 g/100 g was obtained with Amaranthus straw. [ABSTRACT FROM AUTHOR]

Highlights: [•] We showed that biochar from agricultural residues can remove fermentation inhibitors. [•] We showed a reduced fermentation lag phase when inhibitors were removed. [•] We demonstrated that the biochar can remain in the broth during fermentation. [•] Neither enzyme nor yeast appeared negatively affected by biochar. [ABSTRACT FROM AUTHOR]

• The SPAP removed part of lignin and disrupted the crystalline regions of bamboo. • Glucose yield of SPAP-DS was 89.06 %, which was 4.5 times higher than PAP-DS. • Sulfomethylation contributed to the decrystallize of bamboo cellulose in the subsequent H 3 PO 4 -pretreatment. The sulfomethylation-aided phosphoric acid pretreatment (SPAP) was investigated for bamboo biorefinery. The yield of glucose and xylose were increased from 19.8 % and 13.88 % for H 3 PO 4 -pretreated D. sinicus alone (PAP-DS) to 89.06 % and 72.92 % for SPAP-DS. Ethanol concentration for SPAP-DS was 13.26 g/L, which improved by about 3-folds than PAP-DS. The SPAP-DS exhibited the lower lignin content and cellulose crystallinity, thus resulting in the enzyme accessibility to cellulose increased remarkably. The pre-step of sulfomethylation loosened compact structure of bamboo, which significantly contributed to the decrystallization of cellulose in the following H 3 PO 4 -pretreatment. The study has potential implications in biomass pretreatments, which should target synergistically and simultaneously toward cellulose, hemicellulose, or lignin fraction for obtaining higher bio-based chemical compounds and biofuels. [ABSTRACT FROM AUTHOR]

[Display omitted] • Glucose release rate and viscosity govern ethanol/glycerol ratio disturbance. • The reduced glycerol concentration results from the decreased broth viscosity. • Transcriptomic landscape of cellulase-assisted ethanol production was investigated. In-situ corn fiber conversion enables to greenly convert corn fiber into bioethanol with saving energy and capital expenditure. However, the remaining challenge is to understand how the additive cellulases improve substrate utilization efficiency but reduce the side-product glycerol concentration. Herein, we investigated a comprehensive responses pattern of cellulases-assisted ethanol production on fermentation properties and transcriptomic level. Two determinants, glucose release rate and viscosity, were identified to govern ethanol/glycerol ratio disturbance. The transcriptomic studies revealed three genes in ethanol synthetic and two genes in synthetic glycerol pathway present remarkably up-regulated (up to 4.28-fold) and down-regulated (up to 4.81-fold) under cellulases condition, respectively. Interestingly, 15 upregulated/downregulated genes were commonly obtained in (non-)cellulases and (non-)sodium-polyacrylate transcriptomic landscape, suggesting the reduced glycerol concentration most likely result from the decreased broth viscosity. This obtained knowledge unmask molecular mechanisms of cellulases-assisted ethanol improvement and empower engineers to rationally optimize the biofuel process for higher ethanol concentration. [ABSTRACT FROM AUTHOR]

Abstract: Sorghum (Sorghum bicolor (L.) Moench) is a starch-rich grain similar to maize (Zea mays L.), but sorghum has been underutilized for biobased products and bioenergy. This study was designed to investigate the effects of supercritical-fluid-extrusion (SCFX) of sorghum on ethanol production. Morphology, chemical composition, and thermal properties of extruded sorghum were characterized. Analysis of extruded sorghum showed increased measurable starch content, free sugar content, and high levels of gelatinized starch. SCFX cooked and non-extruded sorghum were further liquefied, saccharified, and fermented to ethanol by using Saccharomyces cervisiae. The ethanol yield increased as sorghum concentration increased from 20 to 40% for both extruded and non-extruded sorghum. Ethanol yields from SCFX cooked sorghum were significantly greater than that from non-extruded sorghum (>5%). [Copyright &y& Elsevier]