Lignocellulose Conversion: Enzymatic and Microbial Tools for Bioethanol Production

206 Pages·2013·3.396 MB·English

by  Takashi Watanabe (auth.), Vincenza Faraco (eds.)

Vincenza Faraco Editor
Lignocellulose
Conversion
Enzymatic and Microbial Tools for
Bioethanol Production
Lignocellulose Conversion
Vincenza Faraco
Editor
Lignocellulose Conversion
Enzymatic and Microbial Tools
for Bioethanol Production
123
Editor
Vincenza Faraco
Department of Chemical Sciences
Universityof Naples‘‘FedericoII’’
Complesso Universitario MonteS.Angelo
Naples
Italy
ISBN 978-3-642-37860-7 ISBN 978-3-642-37861-4 (eBook)
DOI 10.1007/978-3-642-37861-4
SpringerHeidelbergNewYorkDordrechtLondon
LibraryofCongressControlNumber:2013940305
(cid:2)Springer-VerlagBerlinHeidelberg2013
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Preface
Bioethanol represents one of the most promising biofuels, exhibiting several
advantages, such as high octane number, low cetane number high heat of vapor-
izationand,mostimportantly,reductionofgreenhousegasemissions.Avarietyof
biomass feedstock have been explored for ethanol production including sucrose-
rich crops such as sugarcane and sugar beet, starch-rich crops such as maize and
grain sorghum, and lignocellulosic materials such as woody biomass, herbaceous
perennials, and various wastes.
In the United States, the Department of Energy has set a goal of 60 billion
gallonsofrenewablefuelsperyeartobeproducedby2030.IntheEuropeanUnion
there is a mandatory target to substitute 10 % of transportation fuels with
renewable fuels by 2020. Production of ethanol from corn starch in United States
hasalmostreacheditsfullcapacity.Moreover,ethanolproductionfromthisedible
feedstockposesconcernsaboutcompetitionwithfoodandfeedsupplies.Theonly
sustainablealternative substratefor ethanol productionislignocellulosicbiomass.
LignocellulosicbiomassesarethemostabundantrenewableresourcesonEarth.
The use of lignocellulosic materials for second-generation ethanol production
would minimize the conflict between land use for food (and feed) and energy
production. Moreover, these raw materials are less expensive and they present a
more even geographical distribution than the conventional agricultural feedstock.
Alargefractionoflignocellulosesisrepresentedbyresidualbiomasssuchasagro-
industrial wastes, agricultural and forest crop residues, and the organic and paper
fractions of municipal solid waste that would represent the key response to the
needofincreasingrenewableenergyproduction.Itisworthnotingthatonlysmall
amounts of cellulose, hemicellulose, and lignin composing agricultural residues
are currently exploited, the majority being considered wastes. Moreover, second-
generationethanolproductionanduse showlower greenhouse gas emissions than
the first-generation fuels, reducing environmental impact, particularly in terms of
climate change.
Lignocellulose consists of three types of polymers—cellulose, hemicellulose,
andlignin-bondedbybothnon-covalentandcovalentcrosslinkages.Celluloseisa
highly crystalline linear polymer that is composed of D-glucose units linked by
b-1,4 glycosidic bonds. Hemicellulose is also a polysaccharide, accounting for
v
vi Preface
around 25–35 % of dry wood. It is a very heterogeneous and ramified polymer,
consistingofamixture ofvarious monosaccharides,suchasxyloseandarabinose
(both 5-carbon sugars) and glucose, mannose and galactose (all 6-carbon sugars),
and glucuronic acid. Lignin is present in the cellular wall to give structural sup-
port, mechanical resistance, impermeability, and defense against microbial attack
and oxidative stress. It is an amorphous heteropolymer formed from phenylpro-
pane units joined together by non-hydrolyzable linkages.
Lignocellulose conversion into ethanol commonly involves i) a pretreatment
to remove the barrier of lignin and expose plant cell wall polysaccharides,
ii)enzymaticsaccharificationofsugarswitha(hemi)cellulolyticenzymecocktail,
and iii) fermentation of the sugars with ethanologenic microorganisms. Pretreat-
ment involves the use of acids, alkalis, and/or organic solvents. Numerous pre-
treatment strategies have been developed such as physical treatment, chemical
treatment (alkaline or acid), biological treatment, physicochemical treatment, i.e.,
steam explosion, liquid hot water, ammonia fiber expansion, supercritical fluid
treatment, and thermochemical treatment. Biological pretreatments are also
investigated to reduce use of toxic reagents. After pretreatment, the released cel-
lulose and hemicelluloses are hydrolyzed to monomeric sugars (hexoses and
pentoses) using acid or enzymatic methods. Enzymatic hydrolysis by (hemi)cel-
lulases is the preferred method because of the higher conversion yields and less
corrosiveandtoxicconditionscomparedtotheacidhydrolysis.Fermentationofall
free sugars into ethanol is carried out by yeasts or bacteria.
The cost of enzymes used in the process is considered as one of the key
bottlenecks for producing fuels and chemicals from lignocellulosic biomass.
Severaleffortsareunderwaytoreducethecostandmaximizeenzymeproduction.
Some of the strategies include improving the performance of the enzymes by
increasing the specific activity (through direct evolution and site directed muta-
genesis) and thereby minimizing enzyme dosage or reduce the cost of enzyme
production by improving cellulase titers during fermentation (through process
engineering approaches by using cheap substrates including biomass, producing
enzymes near biorefinery, or expression of enzyme in plants).
The enzymatic hydrolysis may take place in a separate step followed by fer-
mentationcalledseparatehydrolysisandfermentationprocess,oritmaytakeplace
togetherwiththefermentationinasimultaneoussaccharificationandfermentation
of hexoses process or simultaneous saccharification and co-fermentation of both
hexoses and pentoses. The ultimate objective is a one-step consolidated biopro-
cessing of lignocellulose to bioethanol, in which all the steps occur in a single
reactorwhereasinglemicroorganismormicrobialconsortiumconvertspretreated
biomass into ethanol without added enzymes.
Inthisbook,themaintools,thecurrenttechnologicaldevelopments,andfuture
prospects in cellulosic ethanol production and research are described.
The editing work of this book was supported by grant from the Ministero
dell’Università e della Ricerca Scientifica-Industrial Research Project ‘‘Integrated
agro-industrial chains with high energy efficiency for the development of eco-
compatible processes of energy and biochemicals production from renewable
Preface vii
sources and for the land valorization (EnerbioChem)’’ PON01_01966, funded in
the frame of Operative National Programme Research and Competitiveness
2007–2013 D. D. Prot. n. 01/Ric. 18.1.2010.
Contents
1 Introduction: Potential of Cellulosic Ethanol. . . . . . . . . . . . . . . . . 1
Takashi Watanabe
2 Sources for Lignocellulosic Raw Materials for the Production
of Ethanol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Yitzhak Hadar
3 The Pretreatment Step in Lignocellulosic Biomass Conversion:
Current Systems and New Biological Systems. . . . . . . . . . . . . . . . 39
Adenise Lorenci Woiciechowski,
Luciana Porto de Souza Vandenberghe, Susan Grace Karp,
Luiz Alberto Junior Letti, Júlio Cesar de Carvalho,
Adriane Bianchi Pedroni Medeiros, Michele Rigon Spier,
Vincenza Faraco, Vanete Thomaz Soccol and Carlos Ricardo Soccol
4 The Saccharification Step: Trichoderma Reesei Cellulase Hyper
Producer Strains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
Venkatesh Balan, Mingjie Jin, Alan Culbertson
and Nirmal Uppugundla
5 The Saccharification Step: The Main Enzymatic Components . . . . 93
Marie Couturier and Jean-Guy Berrin
6 Extremophilic (Hemi)cellulolytic Microorganisms and Enzymes. . . 111
Beatrice Cobucci-Ponzano, Elena Ionata, Francesco La Cara,
Alessandra Morana, Maria Carmina Ferrara, Luisa Maurelli,
Andrea Strazzulli, Rosa Giglio and Marco Moracci
ix
x Contents
7 The Alcohol Fermentation Step: The Most Common
Ethanologenic Microorganisms Among Yeasts, Bacteria
and Filamentous Fungi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
Parameswaran Binod, Raveendran Sindhu and Ashok Pandey
8 Other Ethanologenic Microorganisms. . . . . . . . . . . . . . . . . . . . . . 151
Eulogio Castro
9 Consolidated Bioprocessing for Improving Cellulosic
Ethanol Production . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
Antonella Amore, Simona Giacobbe and Vincenza Faraco
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
Chapter 1
Introduction: Potential of Cellulosic
Ethanol
Takashi Watanabe
Abstract Conversion of lignocellulosic biomass is emerging as one of the most
important technologies for sustainable production of renewable fuels and chemi-
cals due to its widespread availability, large quantity, non-competitiveness with
foodsupply,potentialasplatformforgreenchemicals,andhighmitigationeffects
on GHG emissions. The process for cellulosic ethanol production by enzymatic
saccharification and fermentation consists of pretreatments exposing plant cell
wall polysaccharides, production of reducing sugars with a (hemi) cellulolytic
enzyme cocktail, and fermentation of the sugars with ethanologenic microorgan-
isms. Simultaneous saccharification and co-fermentation (SSCF) and consolidate
bioprocess (CBP) have been studied as cost-effective integrated processes for
bioethanolproduction.Forthispurpose,ethanologenicmicroorganismshavebeen
engineered to co-utilize hexoses and pentoses at a similar rate and secrete or
display hydrolases on the cell surfaces. In this chapter, the role of bioethanol in
sustainable society, its potential as new platform chemicals, and the current
technological developments and future prospects in bioethanol research are
overviewed.
Contents
1.1 DevelopmentofSustainableSocietyThroughCellulosicFuelEthanol........................ 2
1.2 BioethanolasFeedstockforChemicalIndustry............................................................. 5
1.3 TechnologicalAdvancesandTasksforCellulosicEthanolProduction........................ 7
1.3.1 StrategiestoEnhanceEnzymaticHydrolysisofLignocellulosicBiomass........ 11
1.3.2 GeneticEngineeringofEthanologenicMicroorganismstoImprove
FuelEthanolProduction....................................................................................... 13
1.3.3 ConsolidatedBioprocessingforCellulosicBioethanolProduction.................... 15
T.Watanabe(&)
ResearchInstituteforSustainableHumanosphere,KyotoUniversity,Gokasho,Uji,Kyoto
611-0011,Japan
e-mail:[email protected]
V.Faraco(ed.),LignocelluloseConversion, 1
DOI:10.1007/978-3-642-37861-4_1,(cid:2)Springer-VerlagBerlinHeidelberg2013