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This study investigated the effects of pretreatment using an acetone–butanol–ethanol (ABE) mixture with and without H2SO4 (H+) as a catalyst on sugar recovery from Salix schwerinii biomass. The sugar recovery was susceptible to both the temperature and the catalyst. Moreover, the relatively higher concentration of ABE (H+ABE4) at 200 °C yielded glucose recovery of 85.5% from the pretreated solid, higher than the recovery under other conditions. This result was mainly attributed to the compositional changes in the biomass, as the xylan and lignin were removed in large quantities by ABE pretreatment at 200 °C. Correspondingly, xylose recovery of 53.8% and glucose recovery of 12.1% were obtained from the liquid in which more sugar degradation products were formed. Ultimately, a fermentation broth containing a low concentration of ABE was successfully employed for pretreatment and showed great potential in producing fermentable sugars from S. schwerinii for biobutanol production.

This study investigated whether the effectiveness of pretreatment is limited by a size reduction of Norway spruce wood in biobutanol production. The spruce was milled, chipped, and mashed for hydrogen peroxide-acetic acid (HPAC) and dilute acid (DA) pretreatment. Sugar recoveries from chipped and mashed spruce after enzymatic hydrolysis were higher than from milled spruce, and the recoveries were not correlated with the spruce fiber length. HPAC pretreatment resulted in almost 100% glucose and 88% total reducing sugars recoveries from chipped spruce, which were apparently higher than DA pretreatment, demonstrating greater effectiveness of HPAC pretreatment on sugar production. The butanol and ABE yield from chipped spruce were 126.5 and 201.2 g/kg pretreated spruce, respectively. The yields decreased with decreasing particle size due to biomass loss in the pretreatment. The results suggested that Norway spruce chipped to a 20 mm length is applicable to the production of platform sugars for butanol fermentation.

This study assessed the energy and environmental impacts in terms of second-generation (2G) bioethanol production, renewable electricity generation and greenhouse gas (GHG) emissions reduction potential of surplus rice straw (SRS) in India. National rice production database, and standard procedures for life cycle assessment of rice straw to 2G bioethanol production using two different pretreatment technologies namely, dilute acid (DA) and steam explosion (SE) pretreatments were explored for the analysis. Two scenarios (benchmark and resource-efficient) were constructed to evaluate the availability of SRS and to determine the potential from 2020 to 21 to 2030–31. Under benchmark for the year 2030–31, the potential from SRS using DA and SE pretreatment methods for the production of 2G bioethanol and the surplus renewable electricity generation were estimated to be 10,547 and 11,165 million L; and 5295 and 6928 GWh, respectively, and the corresponding GHG emissions reduction potential were assessed to be 11,954 and 14,375 kt CO2eq., respectively while generated renewable electricity replaces crude oil-driven grid electricity, and 11,498 and 14,498 kt CO2eq., respectively while generated renewable electricity replaces coal-driven grid electricity. The study revealed that both the availability of SRS and the choice of pretreatment method play decisive roles in the determination of its potential.

The sustainability of transportation biofuel production value chains is under discussion as a consequence of the implementation of the European Union Bioeconomy Strategy and renewable energy production. Greenhouse gas emissions from the biomass produced for biofuel, and the energy required during the production process are, in many cases, greater than the emission reductions from the biofuels that are produced and used to replace fossil fuels. In this study, the sustainability of bioethanol production from short rotation coppice Salix schwerinii was considered from cultivation and harvesting to biofuel production and distribution. The sustainability of the full value chain was evaluated according to the European Union Renewable Energy Directive and calculations of greenhouse gas emission savings (%) from biofuel production were compared to a reference fossil fuel (gasoline). For comparison, four bioethanol production scenarios were developed, and specific attention was focused on the utilization of waste-based organic fertilizers (for biomass production) and on carbon dioxide capture at the fermentation stage, and their effects on value chain greenhouse gas emissions. Based on our evaluation, Salix bioethanol production achieved 60% emission savings compared to the fossil reference (requirement for installations that will commence operations until end of December 2020). When waste based organic fertilizers were used in the Salix biomass production, 65% emission savings were achieved (requirement for the installations that will commence operations from 2021). Moreover, the value chain sustainability and greenhouse gas emissions balance were improved by the carbon dioxide captured during the bioethanol fermentation stage.

The present study investigated the ability of pressurized microwave pretreatment to convert softwood lignocellulose to fermentable monosaccharides. Norway spruce lignocellulose was subjected to microwave pretreatment (600 and 1200 W) under high pressure at different temperatures. Microwave pretreatment at mild acid concentrations (0.05–0.1 % H2SO4), temperatures of 170 and 200 °C, and a very short incubation time (5 min) released 84–100 % of hemicellulosic monosaccharides (mannose, galactose, and xylose). In addition, minimal amounts of degradation products (5-(hydroxymethyl)-2-furaldehyde, levulinic acid) were formed. The highest yield of fermentable sugars was 75 %, after both the pressurized microwave pretreatment with conditions 0.05 % H2SO4/600 W/200 °C/5 min and enzymatic hydrolysis with 20 FPU Celluclast 1.5 L, 400 nkat of Novozyme 188, and polyethyleneglycol (PEG) 4000 (0.3 g/g of pretreated material). Results showed that already 0.05 % H2SO4 used in microwave pretreatment could effectively liberate hemicellulose monosaccharides without serious monosaccharide degradation and form a basis for enzymatic hydrolysis.

This study aims to improve enzymatic sugar production from dilute sulfuric acid-pretreated barley straw for acetone–butanol–ethanol (ABE) fermentation. The effects of additive xylanase and surfactants (polyethylene glycol [PEG] and Tween) in an enzymatic reaction system on straw hydrolysis yields were investigated. By combined application of 2 g/100 g dry-matter (DM) xylanase and PEG 4000, the glucose yield was increased from 53.2% to 86.9% and the xylose yield was increased from 36.2% to 70.2%, which were considerably higher than results obtained with xylanase or surfactant alone. The ABE fermentation of enzymatic hydrolysate produced 10.8 g/L ABE, in which 7.9 g/L was butanol. The enhanced sugar production increased the ABE yield from 93.8 to 135.0 g/kg pretreated straw. The combined application of xylanase and surfactants has a large potential to improve sugar production from barley straw pretreated with a mild acid and that the hydrolysate showed good fermentability in ABE production.

This study aims to efficiently use hemicellulose-based biomass for ABE (acetone–butanol–ethanol) production by co-fermentation with starch-based biomass. Two processes were investigated: (I) co-fermentation of sugars derived from hemicellulose and starch in a mixture of barley straw and grain that was pretreated with dilute acid; (II) co-fermentation of straw hemicellulosic hydrolysate and gelatinized grain slurry in which the straw was pretreated with dilute acid. The two processes produced 11.3 and 13.5 g/L ABE that contains 7.4 and 7.8 g/L butanol, respectively. In process I, pretreatment with 1.0% H 2 SO 4 resulted in better ABE fermentability than with 1.5% H 2 SO 4 , but only 19% of pentoses were consumed. In process II, 95% of pentoses were utilized even in the hemicellulosic hydrolysate pretreated with more severe condition (1.5% H 2 SO 4 ). The results suggest that process II is more favorable for hemicellulosic biomass utilization, and it is also attractive for sustainable biofuel production due to great biomass availability.

This study aims to improve acetone-butanol-ethanol production from the hydrolysates of lignocellulosic material by supplementing starchy slurry as nutrients. In the fermentations of glucose, xylose and the hydrolysates of Salix schwerinii, the normal supplements such as buffer, minerals, and vitamins solutions were replaced with the barley starchy slurry. The ABE production was increased from 0.86 to 14.7 g/L by supplementation of starchy slurry in the fermentation of xylose and the utilization of xylose increased from 29% to 81%. In the fermentations of hemicellulosic and enzymatic hydrolysates from S. schwerinii, the ABE yields were increased from 0 and 0.26 to 0.35 and 0.33 g/g sugars, respectively. The results suggested that the starchy slurry supplied the essential nutrients for ABE fermentation. The starchy slurry as supplement could improve the ABE production from both hemicellulosic and cellulosic hydrolysate of lignocelluloses, and it is particularly helpful for enhancing the utilization of xylose from hemicelluloses., final draft, peerReviewed

Lignocellulosic biomass (LCB), the most abundant renewable feedstock for bioenergy generation, is commonly converted to second generation bioalcohols, the main drop-in fuels for petroleum gasoline, through three technologies based on sugar, carboxylic acid and syngas platforms. The hybridization of either any two or three platforms altogether is a novel concept aimed at improvement of yield and quality (high heating value) of bioalcohols. This article reviews the present status of the integration techniques of hybrid platforms with an overall assessment of their advancement with respect to their individual counterpart as well as the challenges involved. It has been indicated that to extract the maximum benefit of hybridization, research studies should be spurred in the fields of kinetic analysis of all thermochemical and biochemical processes, microbial interaction, optimization of process parameters (pH, temperature), performance analysis of engine for the utilization of mixed product bioalcohols, sustainability analysis through the development of mathematical models for lab-scale operations and process simulation models for large scale units along with life cycle assessment. Moreover, pyrolysis of LCB has been identified as a unique central process for the supply of all intermediate compounds, namely, sugar, carboxylic acid and syngas during the hybrid networking of three platform technologies. In this context, the scheme of CONVER-B, a joint research project under the INNO-INDIGO partnership program, aiming at sustainable integration of the platforms to produce bio-alcohols from LCBs leaving zero effluent simultaneously with carbon sequestration potential has been introduced and discussed.

Large numbers of Finnish lakes accumulate biomass sediments due to large nutrient inputs from forest areas, agricultural and industrial activities. The theoretical biofuel production potential was studied for lake bottom biomass from mesotrophic (ML) and eutrophic lakes (EL) in eastern Finland. Methane potentials of the EL and ML biomass were 136.6 ml g−1 volatile solid and 38.9 ml g−1 volatile solid, respectively. The estimated ethanol yields of the EL and ML biomass from fermentation were 137 l tonne−1, and 40 l tonne−1, whereas the yields from mixed alcohol synthesis after gasification were 244.5 l tonne−1 and 57.1 l tonne−1, respectively. The ash from both lake bottom biomass contained harmful elements below the detectable limit, and therefore, could be used as fertilizer. Techno-economic estimation showed that bioethanol production from the fermentation of EL biomass is the most profitable process and is a potential non-food lignocellulosic biomass source for the biorefining industry.

This study investigated the effects of pretreatment conditions, dilute sulfuric acid concentration and treatment time, on the carbohydrate solubility of a mixture of barley straw and grain. The conditions were expressed as combined severity (CS) to evaluate sugar recovery from pretreated samples. Enzymatic hydrolysates from the lignocellulose pretreatment residues were also included to the results. CS was positively correlating with glucose recovery in all conditions, but in higher acid concentrations CS did not predict xylose recovery. It appeared that the residual xylan better indicate the xylose release. An optimal fermentable sugar yield from the mixture of barley straw and grain was obtained by maintaining the CS at around 1.38, corresponding to an overall glucose yield of 96% and a xylose yield of 57%.