Cellulosic Ethanol

A novel dual-microbe Bacillus/yeast co-culture system is developed for cellulosic bioethanol production. A recombinant cellulosomal Bacillus subtilis that carries eight cellulosomal genes of Clostridium thermocellum, including one scaffolding protein gene (cipA), one cell-surface anchor gene (sdbA), two exo-glucosidase genes (celK and celS), two endoglucanase genes (celA and celR), and two xylanase genes (xynC and xynZ) was constructed. The partner microbes for the dual-microbe combination are the wild type kefir yeast Kluyveromyces marxianus KY3, K. marxianus KY3-NpaBGS, which carries a b-glucosidase (NpaBGS) gene from rumen fungus, and the K. marxianus KR5 strain, that harbors endoglucanase (egIII), exo-glucanase (cbhI) and NpaBGS genes. All three Bacillus/yeast co-culture systems could achieve the cellulose saccharification and ethanol conversion simultaneously better than KR5 alone. The combination of Bacillus/ KY3-NpaBGS outperformed that of Bacillus/KY3, as they could produce b-glucosidase enzyme for the system. Although, KR5 produces two more kinds of cellulases than KY3-NpaBGS. Bacillus/KR5 could not perform better than Bacillus/KY3-NpaBGS. Our results suggest that the dual-microbe Bacillus/yeast coculturing system could leverage the advantages from both microbes and have a great potential for integrating into consolidated bioprocessing system.

Interest in liquid biofuels production and use has increased worldwide as part of government policies to address the growing scarcity and riskiness of petroleum use, and, at least in theory, to help mitigate adverse global climate change. The existing biofuels markets are dominated by U.S. ethanol production based on cornstarch, Brazilian ethanol production based on sugarcane, and European biodiesel production based on rapeseed oil. Other promising efforts have included programs to shift toward the production and use of biofuels based on residues and waste materials from the agricultural and forestry sectors, and perennial grasses, such as switchgrass and miscanthusso-called cellulosic ethanol. This article reviews these efforts and the recent literature in the context of ecological economics and sustainability science. Several common dimensions for sustainable biofuels are discussed: scale (resource assessment, land availability, and land use practices); efficiency (economic and energy); equity (geographic distribution of resources and the "food versus fuel" debate); socio-economic issues; and environmental effects and emissions. Recent proposals have been made for the development of sustainable biofuels criteria, culminating in standards released in Sweden in 2008 and a draft report from the international Roundtable on Sustainable Biofuels. These criteria hold promise for accelerating a shift away from unsustainable biofuels based on grain, such as corn, and toward possible sustainable feedstock and production practices that may be able to meet a variety of social, economic, and environmental sustainability criteria.

Cellulosic ethanol involves the following production steps: physical and/or chemical pretreatment, biological treatment, fermentation and distillation. First three steps are also the bottlenecks for the production of cellulosic ethanol and its co-products. Their production still pose some difficulties in terms of pretreatment, the high cost of enzymes for substrate hydrolysis, the formation of inhibitory compounds in the hydrolyzate, the lack of efficient and viable microorganisms for industrial fermentation of hexose and pentose among others. The solution or minimization of these difficulties may lead to numerous socio-environmental, political, and economic advantages for cellulosic ethanol production. This paper highlights the potential of different substrates, pretreatments, microorganisms and bioprocesses for cellulosic ethanol production.

Hot-air (75 -100°C) pasteurisation (HAP) of birch-wood-based substrate was compared to conventional autoclaving (steam at 121 °C) with regard to shiitake growth and yield, chemical composition of heat-pretreated material and spent mushroom substrate (SMS), enzymatic digestibility of glucan in SMS, and theoretical bioethanol yield. Compared to autoclaving, HAP resulted in faster mycelial growth, earlier fructification, and higher or comparable fruit-body yield. The heat pretreatment methods did not differ regarding the fractions of carbohydrate and lignin in pretreated material and SMS, but HAP typically resulted in lower fractions of extractives. Shiitake cultivation, which reduced the mass fraction of lignin to less than half of the initial without having any major impact on the mass fraction of glucan, enhanced enzymatic hydrolysis of glucan about four-fold. The choice of heating method did not affect enzymatic digestibility. Thus, HAP could substitute autoclaving and facilitate combined shiitake mushroom and bioethanol production.

According to a recent report nearly 42 per cent Indian kids are
malnourished and stunted. The aim of our project was to develop
nutraceutical products using alfalfa as one of the components to
overcome undernourishment particularly among women and
children. The seeds of alfalfa (Medicago sativa) contain more
nutritional property when compared with other leguminous seeds. It
contains 18.9% of protein when compared with egg (13.1%), milk
(3.3%) and beef (16.5%). This paper reports the investigation results
of phytochemical analysis of alfalfa seed extracts using the procedure
of Sadasivam and Manickam (2009). The presence of proteins,
carbohydrates, saponins, phenolic compounds, alkaloids, flavonoids
etc. was observed in sprouted alfalfa seeds extracted by solvents such
as ethanol, petroleum and chloroform. The presences of proteins,
carbohydrates, saponins, alkaloids etc were confirmed by the present
investigation. Thus the cost effective nutraceutical product containing
alfalfa along with other cereals and pulses would serve the humanity
to fight undernourishment in an easy and economical way.

The Energy Policy Act is a bill passed by Congress, and signed into law by President George W.Bush in 2005 which established a bioethanol target in order to offset U.S. dependence on foreign oil. Since then, many different perspectives have contributed to the wealth of data available in regards to bioethanol production from agriculture; responses which have substantiated and criticized almost every step of each process. Two challenges have come to the forefront of the confusing mess of information: 1) challenge for the best energy return on investment [investmentis used here to encompass time, resource, energy, and monetary costs] and 2) challenge for the maximum net greenhouse gas reduction.In 2005, Perlack et al. of the Oak Ridge National Laboratories (ORNL) in cooperation with the Department of Energy (DoE) released the first Billion Ton Study included findings about the feasibility of the government’s proposed bioethanol targets. The report failed to include costs notrelated to the economic scheme of money and resource-related statistics. Since then, seriousquestions have arisen as a result of the ‘push’ to use food for fuel; ethical questions regarding starving and under-represented populations, criticisms regarding the true reductions of emissions, and questions about scalability. My investigation hopes to have covered some of the environmental considerations in the process of finding a better feedstock for the production of bioethanol in the U.S.

Cellulosic ethanol is a sustainable alternative to petroleum as a transportation fuel, which could be made biologically from agricultural and forestry residues, municipal waste, or herbaceous and woody crops. Instead of putting efforts on steps overcoming the natural resistance of plants to biological breakdown, our study proposes a unique pathway to improve the outcome of the process by co-producing high-value nanofibrillated cellulose (NFC), offering a new economic leverage for cellulosic ethanol to compete with fossil fuels in the near future. In this study, glucose has been produced by commercial enzymes while the residual solids are converted into NFC via sonification. Here, we report the morphology of fibers changed through the process and yield of glucose in the enzymatic hydrolysis step.

Banana agricultural waste is one of the potential lignocellulosic substrates which are mostly un-utilized
but sufficiently available in many parts of the world. In the present study, suitability of banana waste for
biofuel production with respect to pretreatment and reducing sugar yield was assessed. The effectiveness
of both acid and alkali pretreatments along with autoclaving, microwave heating and ultrasonication on
different morphological parts of banana (BMPs) was studied. The data were statistically analyzed using
ANOVA and numerical point prediction tool of MINITAB RELEASE 14. Accordingly, the optimum cumulative
conditions for maximum recovery of reducing sugar through acid pretreatment are: leaf (LF) as the
substrate with 25 min of reaction time and 180 C of reaction temperature using microwave. Whereas,
the optimum conditions for alkaline pretreatments are: pith (PH) as the substrate with 51 min of reaction
time and 50 C of reaction temperature using ultrasonication (US).

Bagasse, a major by-product of sugarcane-processing industries, has potential to play a significant role as feedstock for production of cellulosic ethanol, platform chemicals, and bio-based commodities. Pretreatment is essential for efficient processing of lignocellulosic feedstocks by biochemical conversion. In this work, auto-catalyzed (A-HTP) and dilute sulfuric-acid-catalyzed (SA-HTP) hydrothermal pretreatment of sugarcane bagasse was investigated, setting the temperature (175− 205 • C) and the time (4− 51 min) in such a way that the severity factor (SF) was always maintained at one of three predetermined values (2.8, 3.8, and 4.8). The investigation covered the effects of different operational pretreatment conditions on (i) the formation of sugars and water-soluble bioconversion inhibitors, including newly discovered inhibitors such as formaldehyde and p-benzoquinone, in the pretreatment liquid, (ii) the chemical composition and recovery of constituents in the solid phase, as determined using two-step treatment with sulfuric acid, Py-GC/MS, and solid-state NMR, (iii) pseudo-lignin formation, (iv) furan aldehydes in condensates from the gas phase, (v) enzymatic digestibility of pretreated solids, (vi) enzyme inhibition by pretreatment liquids, and (vii) fermentability of pretreatment liquids using Saccharomyces cerevisiae yeast. Glucose and xylose were the predominant sugars in pretreatment liquids from SA-HTP and A-HTP, respectively. For A-HTP, the enzymatic digestibility of the pretreated solids was proportional to the SF, while for SA-HTP no clear trend was observed. The best enzymatic digestibility (above 80%) was achieved for A-HTP performed at SF 4.8. The highest total yields of glucose and xylose, the predominant sugars, were achieved for A-HTP at SF 3.8 and temperatures of 190 • C and 205 • C. The fermentability of the pre-treatment liquids by Saccharomyces cerevisiae was lower for SA-HTP than for A-HTP. The investigation suggests that hydrothermal pretreatment of sugarcane bagasse can be performed with good results without addition of sulfuric acid, but that the conditions must be just harsh enough to almost quantitatively solubilize the hemicelluloses.

This work evaluated the conversion of sugarcane straw into a glucose-rich hydrolysate using a combined process system (CPS) which consists of pretreatment, delignification and enzymatic hydrolysis. The sugarcane straw, with 38.1%, 29.2% and 24.2% of cellulose, hemicellulose and lignin respectively, was submitted to a hydrothermal pretreatment and a delignification process in order to increase the cellulose enzymatic hydrolysis. Straw is the residue to be obtained in sugarcane mills without burning the land previously to the harvesting The CPS, with pretreatment at 190 • C, 10 min, showed 95% of hemicellulose solubilization, 78% of lignin removal and 29% of cellulose degradation. The enzymatic hydrolysis of CPS-cellulignins achieved over 60% cellulose conversion. Considering the cellulose content present in the raw sugarcane straw, only 50% was converted into glucose, due to degradation during the CPS and the enzymatic inefficiency in the hydrolysis stage. In addition, the delignification step did not improve the overall cellulose conversion of the sugarcane straw.

The Policy Research Working Paper Series disseminates the findings of work in progress to encourage the exchange of ideas about development issues. An objective of the series is to get the findings out quickly, even if the presentations are less than fully polished. The papers carry the names of the authors and should be cited accordingly. The findings, interpretations, and conclusions expressed in this paper are entirely those of the authors. They do not necessarily represent the views of the International Bank for Reconstruction and Development/World Bank and its affiliated organizations, or those of the Executive Directors of the World Bank or the governments they represent.

The hydrolysis of cotton bolls, an important agricultural residue in Egypt, with 72% sulphuric acid has been investigated. The cotton bolls were easily hydrolyzable; the rate of hydrolysis was dependent on temperature of reaction and liquor ratio. The optimum saccharification was obtained at 30°C. solid: liquor ratio 7: 1 and reaction time of 30 min. and 60 min in case of cotton bolls and sheaths fraction respectively. The maximum yield of sugar obtained were 58.5% and 38% (based on the original weight) in the case of hydrolysis of cotton bolls and sheaths fraction respectively. The sugar produced from hydrolysis may be fermented to produce ethanol on industrial scale. The sugars produced from hydrolysis may be fermented to produce ethanol on industrial scale (bio-ethanol or bio-fuel).

Polylactides produced from renewable feedstocks, such as corn starch, are being developed as alternatives to plastics derived from petroleum. In addition to corn, other less expensive biomass resources can be readily converted to component sugars (glucose, xylose, etc.) by enzyme and/or chemical treatment for fermentation to optically pure lactic acid to reduce the cost of lactic acid. Lactic acid bacteria used by the industry lack the ability to ferment pentoses (hemicellulose-derived xylose and arabinose), and their growth and fermentation optima also differ from the optimal conditions for the activity of fungal cellulases required for depolymerization of cellulose. To reduce the overall cost of simultaneous saccharification and fermentation (SSF) of cellulose, we have isolated bacterial biocatalysts that can grow and ferment all sugars in the biomass at conditions that are also optimal for fungal cellulases. SSF of Solka Floc cellulose by one such isolate, Bacillus sp. strain 36D1, yielded l(+)-lactic acid at an optical purity higher than 95% with cellulase (Spezyme CE; Genencor International) added at about 10 FPU/g cellulose, with a product yield of about 90% of the expected maximum. Volumetric productivity of SSF to lactic acid was optimal between culture pH values of 4.5 and 5.5 at 50 °C. At a constant pH of 5.0, volumetric productivity of lactic acid was maximal at 55 °C. Strain 36D1 also co-fermented cellulose-derived glucose and sugar cane bagasse hemicellulose-derived xylose simultaneously (SSCF). In a batch SSCF of 40% acid-treated hemicellulose hydrolysate (over-limed) and 20 g/L Solka Floc cellulose, strain 36D1 produced about 35 g/L lactic acid in about 144 h with 15 FPU of Spezyme CE/g cellulose. The maximum volumetric productivity of lactic acid in this SSCF was 6.7 mmol/L (h). Cellulose-derived lactic acid contributed to about 30% of this total lactic acid. These results show that Bacillus sp. strain 36D1 is well-suited for simultaneous saccharification and co-fermentation of all of the biomass-derived sugars to lactic acid.

A kinetic model was developed to predict batch simultaneous saccharification and co-fermentation (SSCF) of paper sludge by the xylose-utilizing yeast Saccharomyces cerevisiae RWB222 and the commercial cellulase preparation Spezyme CP. The model accounts for cellulose and xylan enzymatic hydrolysis and competitive uptake of glucose and xylose. Experimental results show that glucan and xylan enzymatic hydrolysis are highly correlated, and that the low concentrations of xylose encountered during SSCF do not have a significant inhibitory effect on enzymatic hydrolysis. Ethanol is found to not only inhibit the specific growth rate, but also to accelerate cell death. Glucose and xylose uptake rates were found to be competitively inhibitory, but this did not have a large impact during SSCF because the sugar concentrations are low. The model was used to evaluate which constants had the greatest impact on ethanol titer for a fixed substrate loading, enzyme loading, and fermentation time. The cellulose adsorption capacity and cellulose hydrolysis rate constants were found to have the greatest impact among enzymatic hydrolysis related constants, and ethanol yield and maximum ethanol tolerance had the greatest impact among fermentation related constants. Biotechnol. Bioeng. 2009; 104: 920–931. © 2009 Wiley Periodicals, Inc.

This report reviews the current status of second generation biofuels. First generation biofuels continue to be substantially subsidized, and this has contributed to the increasing use of such fuel. However, recent studies claim that the future of biofuels lies in second generation biofuels, in particular biochemical ethanol made from cellulose. Thus, in this report we ask the following three questions: How far is second generation biofuels from being a competitive GHG abatement technology? Is it likely that first generation biofuels will bridge ...

Rice hulls are potential low-cost feedstocks for fuel ethanol production in many countries. Most of the relevant publications are devoted to homogenous (high quality) hulls generated in industrial mills. On the other hand, hulls produced in small-scale mills give rise to hulls containing grain fragments and bran. In the present work, the dilute-acid pretreatment of such heterogeneous rice hulls was investigated based on a central composite rotatable experimental design. The variables were: temperature (140-2108C), biomass load (5-20%), and sulfuric acid concentration (0.5-1.5% based on reaction mixture). A total of 16 experimental runs were carried out, including a 2 3 -plan, two replicates at the central point and six star points. Low temperatures were found to be favorable for the hydrolysis of xylan and of the easily hydrolyzable glucan fraction. High glucose formation (up to 15.3%), attributable to starch hydrolysis, was detected in the hydrolysates obtained under the least severe pretreatment conditions. Several models were developed for predicting the effect of the operational conditions on the yield of pretreated solids, xylan and glucan conversion upon pretreatment, and on enzymatic convertibility of cellulose. The pretreatment temperature exerted the most significant effect on the conversion of the polysaccharides. Optimum results were predicted for the conversion of easily-hydrolyzable glucan in the material pretreated at 140.78C, and for the enzymatic saccharification of cellulose in the material pretreated at 1698C. These results are interpreted that a two-step acid hydrolysis may be the best pretreatment strategy for heterogeneous rice hulls produced in small mills.

The Renewable Fuel Standard mandates in the Energy Independence and Security Act of 2007 will require 36 billion gallons of ethanol to be produced in 2022. The mandates require that 16 of the 36 billion gallons must be produced from cellulosic feedstocks. The potential land ...

This report reviews the current status of second generation biofuels. First generation biofuels continue to be substantially subsidized, and this has contributed to the increasing use of such fuel. However, recent studies claim that the future of biofuels lies in second generation biofuels, in particular biochemical ethanol made from cellulose. Thus, in this report we ask the following three questions: How far is second generation biofuels from being a competitive GHG abatement technology? Is it likely that first generation biofuels will bridge ...

Plant biomass has been recognized globally as an important link to a sustainable energy future because it can be grown universally and converted into liquid transportation fuels or other material through biochemical, thermochemical, or catalytic conversion processes. However, those potential benefits must be viewed in the context of other global societal needs (i.e., food, feed, fiber, potable water, carbon storage in ecosystems, and preservation of native habitats and biodiversity) that must also be met by plant biomass growing on a finite amount of arable land. The development of cellulosic feedstocks for biofuels and other bioproducts must be accomplished in an economically viable, environmentally benign, and socially sustainable manner. This task is feasible throughout the world, as illustrated by examples from Brazil, China, and India.

In the future liquid biofuels will need to be renewable, sustainable, as well as technically and economically viable. This paper provides an overview of the challenges that the biochemical production of cellulosic ethanol process still faces. The main emphasis of the paper is on challenges that emerge from the scale of liquid biofuel production. These challenges include raw material availability, other consumables, and side stream handling. The pretreatment, C5 fermentation, and concentration of sugars in processing need improvements, too. Sustainability issues and greenhouse gas reduction also pose a challenge for implementation and require development of internationally recognized sustainability principles and standards, and certification of sustainable operation. Economics of cellulosic ethanol processes are still also an area under development and debate. Yet, the Energy Independence and Security Act mandate together with the European Union Renewable Energy Directive and other local targets are driving the development and implementation forward towards more significant contribution of biofuels in the transportation sector.

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

The simultaneous saccharification and co-fermentation (SSCF) kinetic model described in the companion paper can predict batch and fed batch fermentations well at solids concentrations up to 62.4 g/L cellulose paper sludge but not in batch fermentation at 82.0 g/L cellulose paper sludge. Four hypotheses for the discrepancy between observation and model prediction at high solids concentration were examined: ethanol inhibition, enzyme deactivation, inhibition by non-metabolizable compounds present in paper sludge, and mass transfer limitation. The results show that mass transfer limitation was responsible for the discrepancy between model and experimental data. The model can predict the value of high paper sludge SSCF in the fermentation period with no mass transfer limitation. The model predicted that maximum ethanol production of fed-batch fermentation was achieved when it was run as close to batch mode as possible with the initial solids loading below the mass transfer limitation threshold. A method for measuring final enzyme activity at the end of fermentation was also developed in this study. Biotechnol. Bioeng. 2009; 104: 932–938. © 2009 Wiley Periodicals, Inc.

The United States (US) and Brazil have been the two leading producers of fuel ethanol since the 1970s. National policies have supported the production and use of ethanol from corn and sugarcane. US support in particular has included exemption from federal gasoline excise taxes, whole or partial exemption from road use (sales) taxes in nine states, a federal production tax credit, and a federal blender's credit. In the last decade the subsidization of grain-based ethanol has been increasingly criticized as economically inefficient and of questionable social benefit. In addition, much greater production of ethanol from corn may conflict with food production needs. A promising development is the acceleration of the technical readiness of cellulosic alcohol fuels, which can be produced from the woody parts of trees and plants, perennial grasses, or residues. This technology is now being commercialized and has greater long-term potential than grain ethanol. Cellulosic ethanol is projected to be much more cost-effective, environmentally beneficial, and have a greater energy output to input ratio than grain ethanol. The technology is being developed in North America, Brazil, Japan and Europe. In this paper, we will review the historical evolution of US federal and state energy policy support for and the currently attractive economics of the production and use of ethanol from biomass. The various energy and economic policies will be reviewed and assessed for their potential effects on cellulosic ethanol development relative to gasoline in the US. r

Switchgrass (Panicum virgatum L.), a warmseason
perennial grass, is an important bioenergy crop
candidate because it produces high biomass yields on
marginal lands and on reclaimed surface mined sites. In
companion studies, dry matter (DM) yields for Cave-in-
Rock, Shawnee, and Carthage cultivars varied from 4.2 to
13.0 Mg ha−1averaged over 6 years at the reclaimed
Hampshire site, and fertilization increased yields of
Cave-in-Rock at Black Castle and Coal Mac sites from
0.3 to 2 Mg ha−1 during the first 3 years. The objective
of these experiments was to compare the impacts of cultivar
and soil amendments on biomass quality and theoretical
ethanol production of switchgrass grown on surface
mines with differing soil characteristics. Biomass
quality was determined for fiber, ash, lignin, digestibility,
and carbohydrate contents via near-infrared reflectance
spectroscopy, and carbohydrates were used to calculate
theoretical ethanol yield (TEY; L Mg−1) and multiplied
by biomass yield to calculate theoretical ethanol production
(TEP; L ha−1). Cultivars at the Hampshire site did not
differ in TEY and ranged from 426 to 457 L Mg−1. Theoretical
ethanol production from Cave-in-Rock at Hampshire
was 7350 L ha−1, which was higher than other cultivars
because of its greater biomass production. This TEP
was higher than in other studies which predicted 4000 to
5000 L ha−1. At the Black Castle and Coal Mac sites,
fertilizer applications slightly affected biomass quality of
switchgrass and TEY, but provided greater TEP as a function
of increased yield. Similar to other findings, total
switchgrass biomass production has more impact than
compositional differences on TEP, so maximizing biomass
production is critical for maximizing potential biofuel
production. With appropriate soil substrates, fertilization,
planning, and management, large areas of reclaimed
surface mines can be converted to switchgrass stands to
produce high biomass quality and yields to support a
bioethanol industry.

External nutrient supplementation and detoxification of hydrolysate significantly increase the production cost of cellulosic ethanol. In this study, we investigated the feasibility of fermenting cellulosic hydrolysates without washing, detoxification or external nutrient supplementation using ethanologens Escherichia coli KO11 and the adapted strain ML01 at low initial cell density (16 mg dry weight/L). The cellulosic hydrolysates were derived from enzymatically digested ammonia fiber expansion (AFEX)treated corn stover and dry distiller's grain and solubles (DDGS) at high solids loading (18% by weight). The adaptation was achieved through selective evolution of KO11 on hydrolysate from AFEX-treated corn stover. All cellulosic hydrolysates tested (36-52 g/L glucose) were fermentable. Regardless of strains, metabolic ethanol yields were near the theoretical limit (0.51 g ethanol/g consumed sugar). Volumetric ethanol productivity of 1.2 g/h/L was achieved in fermentation on DDGS hydrolysate and DDGS improved the fermentability of hydrolysate from corn stover. However, enzymatic hydrolysis and xylose utilization during fermentation were the bottlenecks for ethanol production from corn stover at these experimental conditions. In conclusion, fermentation under the baseline conditions was feasible. Utilization of nutrient-rich feedstocks such as DDGS in fermentation can replace expensive media supplementation.

In this work, dilute sulphuric acid prehydrolysis of residual empty pods of M. oleifera fruits was investigated as pretreatment for enzymatic hydrolysis of cellulose. In experiments performed at 130-190ºC for 10-30 min, corresponding to a severity range between log Ro = 1.9 and log Ro = 4.2, the effect of pretreatment conditions on the recovery of polysaccharides and on the enzymatic convertibility of cellulose was evaluated. Overall cellulose recovery was above 95% in the pretreatments performed at 130 and 160ºC, and between 87 and 90% in the pretreatments at 190ºC, while xylan recovery in the most severe pretreatments was only 24.7-50.2%. The highest sugar concentration in the acid prehydrolysates (15.0 g/L) was obtained in the pretreatment performed at 160ºC and 20 min. The formation of degradation products was low at mild pretreatment conditions, but it increased with the severity. Furfural concentration reached 4.04 g/L at log Ro = 3.1 and decreased again with a further increase of the pretreatment severity. HMF, formic acid and levulinic acid were formed only in the most severe pretreatments. The pretreatment was effective for improving the enzymatic hydrolysis of cellulose, and the highest conversion (84.3%) was achieved in the material pretreated at mid severity (log Ro = 3.1).

The synergetic impacts of ferric chloride aided peracetic acid (FPA) pretreatment were investigated to enhance the total biomass utilization through effective cellulose conversion and high-quality lignin production. The sugarcane bagasse pretreatment with 2% peracetic acid (PAA) and 0.1 mol/L ferric chloride (FeCl 3) effectively removed 57.3% of lignin and 72.2% of xylan while preserving ~ 97% of cellulose from sugarcane bagasse under mild temperature (90 • C). The FPA pretreated sugarcane bagasse was effectively hydrolyzed with a glucose yield of 313.0 mg/g-biomass, which was 4.5 times higher than the yield of untreated biomass (69.75 mg/g-biomass) and 1.6 and 3.6 times higher than that of individual PAA and FeCl 3 pretreated sugarcane bagasse, respectively. The regenerated lignin (FPA lignin) showed great potential for further valorization by preserving the major interunit linkage (up to 86% of β-O-4) without significant carbohydrate contamination and lignin condensation due to its mild reaction conditions. In this study, the combination of PAA and FeCl 3 synergistically enhanced the pretreatment efficiency on sugarcane bagasse and resulted in high fermentable sugar and high-quality lignin production.