Bioprocessing of renewable resources to commodity bioproducts

Richard Hess Energy Systems and Technologies, Idaho National Laboratory, Idaho Falls, ID, USA Takashi Hirasawa Department of Bioengineering, Tokyo Institute of Technology, Mirodi-ku, Yok

bioconversion of plant biomass to industrial chemicals The chemicals in white bubbles are the industrial commodity bioproducts pertaining to the realm of “white biotechnology”.

Cover illustration/design by Ruchi Uppal.

Rights of Cover Design are owned by Prof Virendra S Bisaria.

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Library of Congress Cataloging-in-Publication Data:

Bioprocessing of renewable resources to commodity bioproducts / edited by Virendra S Bisaria, Akihiko Kondo.

pages cm

Includes bibliographical references and index.

ISBN 978-1-118-17583-5 (hardback)

II Kondo, Akihiko, 1959- editor of compilation.

TP248.27.M53B5626 2014

2013046035 Printed in the United States of America.

10 9 8 7 6 5 4 3 2 1

PREFACE xv

PART I ENABLING PROCESSING TECHNOLOGIES

Michael Sauer, Matthias Steiger, Diethard Mattanovich, and Hans Marx

Kevin L Kenney, J Richard Hess, Nathan A Stevens, William A Smith, Ian J.

Bonner, and David J Muth

v

2.2.1 Analysis Step 1—Defining the Model System 31

Karthik Rajendran and Mohammad J Taherzadeh

4 Enzymatic Hydrolysis of Lignocellulosic Biomass 77

Jonathan J Stickel, Roman Brunecky, Richard T Elander, and James D McMillan

4.3 Enzymatic Hydrolysis at High Concentrations of Biomass Solids 83

Ranjita Biswas, Abhishek Persad, and Virendra S Bisaria

6.5 Formulation Process 153

PART II SPECIFIC COMMODITY BIOPRODUCTS

Tomohisa Hasunuma, Ryosuke Yamada, and Akihiko Kondo

8.3.3 Fermentation of Hemicellulosic Materials 215

9 Fermentative Biobutanol Production: An Old Topic with

Yi Wang, Holger Janssen and Hans P Blaschek

10.3 Bio-Based 1,4-Butanediol 276

Branched-Chain Alcohols: 2-Ketoacid Decarboxylase and an

12.3.3 Isobutanol Production with Bacillus subtilis 337

Kenji Okano, Tsutomu Tanaka, and Akihiko Kondo

14 Microbial Production of 3-Hydroxypropionic Acid From

Renewable Sources: A Green Approach as an Alternative to

Vinod Kumar, Somasundar Ashok, and Sunghoon Park

14.4.2 Synthesis of 3-HP from Glycerol Through the

15 Fumaric Acid Biosynthesis and Accumulation 409

Israel Goldberg and J Stefan Rokem

16 Succinic Acid 435

Boris Litsanov, Melanie Brocker, Marco Oldiges, and Michael Bott

18 Recent Advances for Microbial Production of Xylitol 497

Yong-Cheol Park, Sun-Ki Kim, and Jin-Ho Seo

18.3 Microbial Production of Xylitol 501

19 First and Second Generation Production of Bio-Adipic Acid 519

Jozef Bernhard Johann Henry van Duuren and Christoph Wittmann

For the development of a sustainable, industrial society to meet our demands ofenergy and materials, it is being increasingly realized that we will have to shift fromour dependence on petroleum to the use of renewable resources, such as starch- andcellulose-based plant materials Historically till recently, petroleum-based resourceswere mainly targeted for research and development, and subsequent commercializa-tion of the products derived therefrom However, their rising costs and the anticipatedthreat to the earth’s environment are providing the required incentive to find sustain-able alternative resources Biorefineries, based on renewable resources, shall enablethe production of biofuels as well as commodity chemicals (those produced in excess

of about 1 million tons per year) These processes which are based on drates (such as starch and cellulose) are also favorable from a chemical point of viewbecause the functional groups that are introduced by costly oxidative process stepsinto naphta are already present in them The commodity bioproducts can be produced

carbohy-by microbial processes Most of them are natural products of microorganisms or can

be produced by suitable pathway engineering of industrial organisms As these products contain functional groups, they are extremely useful as starting materials forthe chemical industry for synthesis of a wide variety of products such as polymers,surfactants, lubricants, and resins

bio-To avoid competition with starchy raw materials, which are largely used as food, aswell as to realize the vision of a successful biorefinery, the renewable resource present

in the form of abundant lignocellulosic biomass needs to be efficiently converted to itsconstituent monomers, comprising mainly of hexose (such as glucose, mannose, andgalactose) and pentose sugars (such as xylose and arabinose) Accordingly, the Part I

of the book deals with those enabling technologies that are crucial for the pretreatment(Chapter 3) and hydrolysis of biomass to give sugars in high yield (Chapter 4) bycellulolytic enzymes, primarily cellulase and xylanase (Chapter 5) This first part alsocovers the general aspect and the issues involved in the sustainability of a biorefinery(Chapter 1) and biomass feedstock logistics and the design of biomass feedstocksupply systems (Chapter 2) Chapter 6 describes various bioprocessing technologiesthat in one form or the other will be required to be implemented for the development

of biorefineries

The Part II of the book contains state-of-the-art articles on a few chosen modity bioproducts These bioproducts represent most of those identified by the USDepartment of Energy for intensive investigation for their production from renewableresources While covering these bioproducts, major emphasis has been given to the

com-xv

discipline of metabolic engineering for the development of suitable microbial alysts/cell factories which shall enable their production from renewable resources.Ethanol which remains the most sought-after chemical and biofuel is covered in twochapters While Chapter 7 describes the potential of recombinant bacteria for ethanolproduction, Chapter 8 is concerned mainly with strategies being developed to expandthe genetic potential of the yeasts, already employed by the industry Butanol, anexcellent transportation fuel and a valuable chemical feedstock, is covered in Chapter

biocat-9 with respect to the advances that have taken place in recent years in the well-knownABE fermentation process for its production from renewable feedstock Chapters 10and 11 describe the recent advances being made for bio-based production of butane-diols and propanediols, used extensively as solvent and for production of differenttypes of chemicals, polymers, and so on The feasibility of producing isobutanol,another higher alcohol besides butanol, possessing chemical features close to that

of gasoline, through implementation of the Ehrlich pathway into several potentialhost microorganisms has been dealt with in Chapter 12 Lactic acid (LA), widelyused in the food, pharmaceutical, and polymers industries, is already produced bymicrobial fermentations; Chapter 13, therefore, concentrates on production of LA andLA-based polymers from various genetically modified microorganisms from starchyand cellulosic materials Chapter 14 describes the recent progress in biological pro-duction of 3-hydroxy propionic acid, used for the production of a wide range ofcommercially important chemicals such as acrylic acid, using different microorgan-isms and renewable substrates Chapter 15 reviews the recent research and provides

a critical analysis of future perspectives to develop an economically competitive based process for producing fumaric acid, which is widely used in the food industry.Succinic acid with many applications including the production of important bulk

tetrahydro-furan (THF), is covered in Chapter 16 with respect to its production from varioussubstrates from natural and genetically modified organisms Glutamic acid is themajor amino acid produced by microbial fermentation on an industrial scale Chapter

17 reviews the molecular mechanisms and metabolic engineering of glutamic acid

production by Corynebacterium glutamicum and potential use of glutamic acid as a

building block for producing several other chemicals Xylitol, a natural sugar alcoholwidely used as a sugar substitute in foods, toothpastes, and mouthwashes, is covered

in Chapter 18 with respect to the application of recent approaches of genetic neering, metabolic engineering, and cofactor engineering for its overproduction Newapproaches for production of adipic acid, mainly used as an intermediate reactant forthe production of nylon-6,6, are highlighted in Chapter 19 from several new feed-stocks including lignin-rich streams.The commercial production of some of thesecommodity bioproducts in the near future will have a far reaching effect in catalyzingthe realization of our goal of a sustainable biorefinery

engi-As research and development in this area has not yet achieved its full potential,the field of bioprocessing of renewable resources into commodity bioproducts willcontinue to expand to attain its commercial goal Additionally, new bioproductsand fine chemicals will be added to the existing list of commodity bioproducts, asour capacity to produce sugars from cellulosic residues efficiently and economically

increases and more efficient microbial biocatalysts are developed through application

of modern biotechnology tools

The book also provides a unique perspective to the industry about the scientificproblems and their possible solutions in making a bioprocess work for commercialproduction of these commodity bioproducts The book is suitable for researchers,practitioners, students, and consultants in metabolic engineering, bioprocess engi-neering, and biotechnology

Virendra S BisariaAkihiko Kondo

Somasundar Ashok Department of Chemical and Biomolecular Engineering, Pusan

National University, Jangjeon-dong, Geumjeong-gu, Busan, Republic of Korea

Jozef Bernard Biochemical Engineering Institute, Technische Universit¨at

Braun-schweig, BraunBraun-schweig, Germany

Virendra S Bisaria Department of Biochemical Engineering and Biotechnology,

Indian Institute of Technology Delhi, New Delhi, India

Ranjita Biswas BioEnergy Science Center, Biosciences Division, Oak Ridge

National Laboratory, Oak Ridge, TN, USA

Hans P Blaschek Department of Food Science and Human Nutrition, Institute for

Genomic Biology, Center for Advanced Bioenergy Research (CABER), University

of Illinois at Urbana-Champaign, Urbana, IL, USA

Bastian Blombach Institute of Biochemical Engineering, University of Stuttgart,

Stuttgart, Germany

Ian J Bonner Biofuels and Renewable Energy Technologies, Idaho National

Laboratory, Idaho Falls, ID, USA

Michael Bott IBG-1: Biotechnology, Institute of Bio- and Geosciences, J¨ulich,

Germany

Melanie Brocker IBG-1: Biotechnology, Institute of Bio- and Geosciences, J¨ulich,

Germany

Roman Brunecky Biosciences Center, National Renewable Energy Laboratory,

Golden, CO, USA

Gopal Chotani DuPont Industrial Biosciences, Palo Alto, CA, USA

Bernhard J Eikmanns Institute of Microbiology and Biotechnology, University of

Ulm, Ulm, Germany

Richard T Elander National Bioenergy Center, National Renewable Energy

Laboratory, Golden, CO, USA

Hongxin Fu School of Life Science and Biotechnology, Dalian University of

Technology, Dalian, People’s Republic of China

xix

Israel Goldberg Department of Microbiology and Molecular Genetics, The Institute

of Medical Research Israel-Canada, The Hebrew University—Hadassah MedicalSchool, Jerusalem, Israel

Tomohisa Hasunuma Organization of Advanced Science and Technology, Graduate

School of Engineering, Kobe University, Nada, Kobe, Japan

J Richard Hess Energy Systems and Technologies, Idaho National Laboratory,

Idaho Falls, ID, USA

Takashi Hirasawa Department of Bioengineering, Tokyo Institute of Technology,

Mirodi-ku, Yokohama, Japan

He Huang State Key Laboratory of Materials-Oriented Chemical Engineering,

Col-lege of Biotechnology and Pharmaceutical Engineering, Nanjing Tech University,Nanjing, People’s Republic of China

Holger Janssen Department of Food Science and Human Nutrition, University of

Illinois at Urbana-Champaign, Urbana, IL, USA

Xiao-Jun Ji State Key Laboratory of Materials-Oriented Chemical Engineering,

College of Biotechnology and Pharmaceutical Engineering, Nanjing Tech sity, Nanjing, People’s Republic of China

Univer-Kevin L Kenney Energy Systems and Technologies, Idaho National Laboratory,

Idaho Falls, ID, USA

Sun-Ki Kim Department of Agricultural Biotechnology and Center for Food and

Bioconvergence, Seoul National University, Seoul, Korea

Akihiko Kondo Department of Chemical Science and Engineering, Graduate School

of Engineering, Kobe University, Nada, Kobe, Japan

Vinod Kumar Department of Chemical and Biomolecular Engineering, Pusan

National University, Jangjeon-dong, Geumjeong-gu, Busan, Republic of Korea

Boris Litsanov IBG-1: Biotechnology, Institute of Bio- and Geosciences, J¨ulich,

Germany

Current: Institute of Microbiology, Eidgen¨ossische Technische HochschuleZ¨urich, Z¨urich, Switzerland

Chengwei Ma School of Life Science and Biotechnology, Dalian University of

Technology, Dalian, People’s Republic of China

Hans Marx Department of Biotechnology, BOKU-VIBT University of Natural

Resources and Life Sciences, Vienna, Austria

Diethard Mattanovich Department of Biotechnology, BOKU-VIBT University of

Natural Resources and Life Sciences, Vienna, Austria

Austrian Centre of Industrial Biotechnology (ACIB GmbH), Vienna, Austria

James D McMillan National Bioenergy Center, National Renewable Energy

Laboratory, Golden, CO, USA

Peyman Moslemy DuPont Industrial Biosciences, Palo Alto, CA, USA

Ying Mu School of Life Science and Biotechnology, Dalian University of

Technol-ogy, People’s Republic of China

David J Muth Praxik, LLC, Ames, IA, USA

Kenji Okano Department of Biotechnology, Graduate School of Engineering, Osaka

University, Osaka, Japan

Marco Oldiges IBG-1: Biotechnology, Institute of Bio- and Geosciences, J¨ulich,

Germany

Sunghoon Park Department of Chemical and Biomolecular Engineering, Pusan

National University, Jangjeon-dong, Geumjeong-gu, Busan, Republic of Korea

Yong-Cheol Park Department of Bio and Fermentation Convergence Technology,

Kookmin University, Seoul, Korea

Caroline Peres DuPont Industrial Biosciences, Palo Alto, CA, USA

Abhishek Persad Department of Biochemical Engineering and Biotechnology,

Indian Institute of Technology Delhi, New Delhi, India

Karthik Rajendran School of Engineering, University of Bor˚as, Sweden

J Stefan Rokem Department of Microbiology and Molecular Genetics, The Institute

of Medical Research Israel-Canada, The Hebrew University—Hadassah MedicalSchool, Jerusalem, Israel

Michael Sauer Department of Biotechnology, BOKU-VIBT University of Natural

Resources and Life Sciences, Vienna, Austria

Austrian Centre of Industrial Biotechnology (ACIB GmbH), Vienna, Austria

Alexandra Schuler DuPont Industrial Biosciences, Palo Alto, CA, USA

Jin-Ho Seo Department of Agricultural Biotechnology and Center for Food and

Bioconvergence, Seoul National University, Seoul, Korea

Hiroshi Shimizu Department of Bioinformatic Engineering, Graduate School of

Information Science and Technology, Osaka University, Suita, Osaka, Japan

William A Smith Biofuels and Renewable Energy Technologies, Idaho National

Laboratory, Idaho Falls, ID, USA

Matthias Steiger Department of Biotechnology, BOKU-VIBT University of Natural

Resources and Life Sciences, Vienna, Austria

Austrian Centre of Industrial Biotechnology (ACIB GmbH), Vienna, Austria

Nathan A Stevens Materials and Physical Security, Idaho National Laboratory,

Idaho Falls, ID, USA

Jonathan J Stickel National Bioenergy Center, National Renewable Energy

Laboratory, Golden, CO, USA

Yaqin Sun School of Life Science and Biotechnology, Dalian University of

Technology, Dalian, People’s Republic of China

Mohammad J Taherzadeh School of Engineering, University of Bor˚as, Bor˚as,

Sweden

Tsutomu Tanaka Department of Chemical Science and Engineering, Graduate

School of Engineering, Kobe University, Nada-ku, Kobe, Japan

Jozef Bernhard Johann Henry van Duuren Biochemical Engineering Institute,

Technische Universit¨at Braunschweig, Braunschweig, Germany

Institute of Systems Biotechnology, Saarland University, Saarbr¨ucken,Germany

Yi Wang Department of Food Science and Human Nutrition, Institute for Genomic

Biology, University of Illinois at Urbana-Champaign, Urbana, IL, USA

Christoph Wittmann Institute of Systems Biotechnology, Saarland University,

Saarbr¨ucken, Germany

Zhilong Xiu School of Life Science and Biotechnology, Dalian University of

Technology, Dalian, People’s Republic of China

Ryosuke Yamada Organization of Advanced Science and Technology, Graduate

School of Engineering, Kobe University, Nada, Kobe, Japan

Hideshi Yanase Department of Chemistry and Biotechnology, Graduate School of

Engineering, Tottori University, Tottori, Japan

ENABLING PROCESSING

TECHNOLOGIES

Bioprocessing of Renewable Resources to Commodity Bioproducts, First Edition.

Edited by Virendra S Bisaria and Akihiko Kondo.

© 2014 John Wiley & Sons, Inc Published 2014 by John Wiley & Sons, Inc.

for Sustainability

MICHAEL SAUER, MATTHIAS STEIGER, and DIETHARD MATTANOVICH

Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria

Austrian Centre of Industrial Biotechnology, Vienna, Austria

HANS MARX

Department of Biotechnology, University of Natural Resources and Life Sciences, Vienna, Austria

1.1 Introduction

1.2 Three Levels for Biomass Use

1.3 The Sustainable Removal of Biomass from the Field is Crucial for a SuccessfulBiorefinery

1.4 Making Order: Classification of Biorefineries

1.5 Quantities of Sustainably Available Biomass

1.6 Quantification of Sustainability

1.7 Starch- and Sugar-Based Biorefinery

1.7.1 Sugar Crop Raffination

1.7.2 Starch Crop Raffination

1.8 Oilseed Crops

1.9 Lignocellulosic Feedstock

1.9.1 Biochemical Biorefinery (Fractionation Biorefinery)

1.9.2 Syngas Biorefinery (Gasification Biorefinery)

1.10 Green Biorefinery

1.11 Microalgae

1.12 Future Prospects—Aiming for Higher Value from Biomass

References

Bioprocessing of Renewable Resources to Commodity Bioproducts, First Edition.

Edited by Virendra S Bisaria and Akihiko Kondo.

© 2014 John Wiley & Sons, Inc Published 2014 by John Wiley & Sons, Inc.

3

Our society is highly dependent on fossil non-renewable resources Therefore themain driving force in establishing a new industrial system is sustainability Biorefiner-ies, which are based on renewable biomass, can contribute to such a system However,many current endeavors focus on single technologies and feedstocks such as starch

or vegetable oils that could compete with food or feed Nevertheless, in future itwill be necessary to consider carefully for which purpose land is used to balance theneeds of mankind for food and energy We need to create flexible, zero-waste biore-fineries that can accept a variety of low-value local feedstocks The challenges arethe development of efficient processes for the collection, handling, and pretreatment

of biomass and for the selective conversion of biomass feedstocks into value-addedproducts

1.1 INTRODUCTION

Sustainability is the capacity to endure through renewal, maintenance, or sustenance.This is in contrast to durability, which is the capacity to endure through unchang-ing resistance to change For humans in eco (and social) systems, sustainability isbased on long-term maintenance of responsibility In other words, as the BrundtlandCommission of the United Nations (1987) has coined it: “sustainable development isdevelopment that meets the needs of the present without compromising the ability offuture generations to meet their own needs.”

For true sustainability this includes not only environmental, but also economicand social dimensions of resource use All along the history access and availability

of resources was a main driving force for the development of societies But never

in history was the demand for resources as high as it is now Unfortunately, thedevelopment in the last 100 years was hardly sustainable because our energy demand

is currently met mainly by fossil resources While obviously based on natural carbon,the recycle time for the replenishment of fossil resources (estimated to be 280 millionyears; Liu et al., 2012a) is so high that they can be regarded as nonrenewable incontext with human life Use of this nonrenewable carbon sources is connected withtwo major problems: the first problem is the obvious limitation of these resources.Even avoiding any discussion about the time scale, the limitation of fossil resources

is a fact due to the immense recycle time This implies rising costs for energyand goods followed by increasing conflicts for access and distribution The secondproblem inherently connected with prolonged use of fossil resources is the liberation

of carbon dioxide—a greenhouse gas, which has been sequestered to the ground inancient times Its liberation is connected to various side effects, which shall not bediscussed here in detail However, we consider it commonly accepted that majorpollution of the earth’s atmosphere with greenhouse gasses is something unwanted,which we should strive to avoid for the sake of sustainability

are the only renewable and thereby truly sustainable carbon sources At present,this boils down to photosynthetic organisms as plants, algae, or cyanobacteria as

basis for the production of carbon-containing goods, be it chemicals or fuels Infact, the development of humanity started with the exclusive use of biomass assource for food, energy, and all goods However, fossil resources have overtaken therole as a dominant energy and chemical source since the industrial revolution (Liu

et al., 2012a)

Currently, biomass-derived energy sources supply about 50 EJ (exajoules) ofthe world’s energy The global energy demand was 463 EJ in 2005 and is sup-posed to increase to 691 EJ in 2030 (Lal, 2010) About 10% of the global primaryenergy consumption per year is based on biomass; this corresponds to 75% of theenergy derived from alternative renewable energy sources (Haberl, 2010) Only 2%

of the biomass-derived energy sources are utilized in the transportation sector Therest is consumed for household uses predominantly as firewood (Srirangan et al.,2012) Model calculations suggest that a significant fraction of the energy demandcould be met by the use of biomass The World Energy Council and World EnergyAssessment project estimates that bioenergy could supply a maximum of 250–450EJ/year (probably a quarter of the global energy demand) by the year 2050 (Ragauskas

et al., 2006a,b)

Biomass production by photosynthesis obtains its energy from the sun and its

serve as food and feed, chemical and material, fuel and energy resource A broadand valuable product mix can be created starting from biomass The valorizationpossibilities in a biorefinery are at least as big as in fossil refineries However, whilethe diversity of options allows a large range of configurations, this also impliesdifferent environmental and societal consequences or footprints Decisions taken,regarding the valorization of biomass, should always take at least two critical pointsinto account: the market impact (demands for products, possible displacements ofproducts) and the ecology of the entire production chain (De Meester et al., 2011).Ideally, these decisions are well-thought-out and based on sound assessments toachieve an optimal sustainable development in the post fossil era

1.2 THREE LEVELS FOR BIOMASS USE

Biomass can be used on three different levels:

Food and feed inevitably rely on biomass Materials and products are right nowproduced from fossil resources and biomass If fossil resources are to be avoided or

if they are depleted, biomass remains the only other basis for material production.For heat and power generation a variety of choices exist or are under development,such as solar power, wind energy, or geothermal energy However, liquid fuels fortransportation rely on fixed carbon, which again points to fossil resources or biomass

FIGURE 1.1 Food security, energy security, and climate change are centered around thelimited availability of arable land This constitutes a trilemma, which has to be addressed byour societies.

It is obvious that limited land availability makes it unlikely that biomass will beable to cover all of these demands fully (Ponton, 2009, De Meester et al., 2011).Figure 1.1 outlines the trilemma Maximal valorization of biomass is therefore a keyissue in the future

This means that no biomass fraction should be considered as waste From aneconomic perspective this is a major opportunity for biorefineries From a societalperspective this appears as the major challenge of the future However, focusing on the

question of food or fuel appears not helpful (Karp and Richter, 2011) The pertinent

challenge is how the increasing demands for food and energy can be met in thefuture, particularly when water and land availability will be limited and consideringthat food production requires significant fuel inputs, which are constantly increasingwith intensification of agriculture Food security has once again risen to the top ofgovernment agendas Nevertheless, energy security is arguably an equally importantchallenge impacting food security and climate change

Exemplary, in the United Kingdom, agriculture accounts for only 2% of energyuse However, almost 20% of United Kingdom’s total energy consumption is usedthroughout the whole food production chain (Barling et al., 2008) Consequently,rising fuel prices or fuel shortages have a significant impact on the cost of foodproduction Decisions over land use should therefore be considered within the context

of the bigger framework of all the challenges that lie ahead (Karp and Richter, 2011).Carbon efficiency and energy efficiency are key parameters that should be takeninto account for such decisions As mentioned before—carbon can be obtained fromfossil resources and biomass, while a variety of energy sources are conceivableincluding wind, photovoltaic, photothermic, geothermic, or hydro power The energymixture of the future will be diverse and will also contain a substantial amount ofenergy from biomass, but energy should be seen in this context more as a byproduct

of the biorefinery than the main driving force (This is different for the time being.)One reason for this consideration is the inherent energy content of biomass:essentially the energy stored in biomass is a chemically captured form of solarenergy Energy from biomass can therefore be directly compared with energy obtainedfrom photovoltaic systems Blankenship et al (2011) recently reviewed the energy

efficiency of both technologies They showed that a photovoltaic system coupled withhydrogen generation might capture up to 10–11% of the total solar energy per usedarea In contrast, the solar energy conversion efficiencies of conventional crop plantsusually do not exceed 1% (Blankenship et al., 2011) Only for microalgae grown inbioreactors, yields up to 3% are reported These low efficiencies require a cautiousconsideration of biomass as a mere energy product, and strengthen the importance ofmaterial products obtained from biorefineries as a primary goal.

1.3 THE SUSTAINABLE REMOVAL OF BIOMASS FROM THE FIELD IS CRUCIAL FOR A SUCCESSFUL BIOREFINERY

The key factor for sustainability of currently cultivated biomass is their resourcefootprint This concerns not only the direct land use and transformation and amongstothers the related use of fertilizers, pesticides, fuels, and water for farming, but alsothe mineral balance and quality of the soil (Cherubini, 2010a)

This means that the production chain for biomass-derived goods is more ing than its fossil equivalent In fact, a variety of studies suggest that the agriculturalphase is often the main contributor to the environmental impact of the productionchain of bio-based products (Zah et al., 2007) Sustainable production of biomass

demand-is therefore of utmost importance However, since the demand for bio-feedstock demand-isincreasing, while the arable land remains limited, much emphasis is given to higheragricultural yields However, innovations for yield increase are often not focused

on the simultaneous acceleration of environmental protection (Cassmann and Liska,2007) Often, a blind striving for higher yields tends to cause severe damage to thenatural environment One example is the use of field crop residues These residuesare often seen as a renewable resource, which is freely available In reality suchresidues are often required to enhance soil quality and to prevent erosion and nutrientdepletion Using this part of biomass might thus actually turn out to be a very badchoice in the long term (Reijnders, 2006)

Summing up, it is the production and supply of biomass rather than the demandfor fuel or materials which limits the use of biomass as a renewable resource In thiscontext it is important to note that chemical production requires far lower amounts

of carbon than fuel production For example, in the United States, the chemical ucts segment consumed just over 3% of the total US petroleum consumption in 2007(FitzPatrick et al., 2010) This opens an economic opportunity for the development

prod-of bio-sourced chemical products since the value prod-of the chemical industry is parable to the fuel industry, but requires only a fraction of the biomass (FitzPatrick

com-et al., 2010)

So while the current industrial systems are split into three sectors namely food,bioenergy, and the chemical industry, these three sectors should come together andstrive to valorize the used feedstock to the fullest to obtain the lowest resourcefootprint per (combined) output product(s)

The biorefinery approach is the promising concept, ideally combining the tion of food, materials, and energy from biomass Following the International Energy

produc-Association’s (IEA) definition, a biorefinery is the sustainable processing of biomassinto a spectrum of marketable products (food, feed, materials, chemicals) and energy(fuels, power, heat) (De Jong et al., 2009).

The core technologies of a biorefinery are biochemical, microbial, and chemical processing Energy and waste streams are internally recycled Biochemicalprocesses have the advantage of high selectivity at low processing temperatures.However, they normally require elaborate preprocessing stages and long processingtimes (FitzPatrick et al., 2010; Macrelli et al., 2012) Complementary, thermochem-ical routes include gasification, pyrolysis, and direct combustion to produce oilsand gases These are fast but nonspecific and generally require a high energy input.Biochemical/microbial and thermochemical processing complement each other In

thermo-an integrated system they cthermo-an deliver significthermo-ant advthermo-antages in terms of specificity ofproducts, flexibility, and efficiency

The biorefinery concept that has emerged is analogous to today’s petroleum ies However, many current endeavors focus on single technologies and feedstocksuch as starch or vegetable oils that could compete with food or feed We need

refiner-to create flexible, zero-waste biorefineries that can accept a variety of low-valuelocal feedstock Biorefineries will then be able to compete with existing industries(Clark et al., 2012) Further down the value chain the development of green chem-istry fills the gap between the sustainable resource and the product (Poliakoff andLicense, 2007)

1.4 MAKING ORDER: CLASSIFICATION OF BIOREFINERIES

A variety of classifications of biorefineries have been proposed: some of them sider feedstock, products, or processes A very simple overview and classification ofbiorefineries subdivides them into three types: Phase I, Phase II, and Phase III (Clark

con-et al., 2012)

Phase I biorefineries are integrated facilities limited to a single feedstock (e.g.,

corn or oils) which is converted into a single major product (e.g., ethanol or biodiesel)

Phase II biorefineries produce various end products from a single feedstock.

They might be more flexible depending on product demand, prices, or others Anexample is a biorefinery generating multiple products, ranging from sugar to ethanol,polymer precursors to animal feed, by utilizing sugar beet as the single feedstock.Exemplary, a biorefinery in Pomacle, France produces both ethanol and succinic acid

in addition to beet sugar and glucose from a single facility with many processingstreams (Hatti-Kaul et al., 2007; Le Henaff and Huc, 2008)

Finally, Phase III biorefineries are the most advanced, as they use a variety

of biomass feedstock to yield a mix of products (Figure 1.2) Such biorefineriesemploy a combination of technologies, among them are chemical and/or biologicaltransformations, extractions, and separations Examples for Phase III biorefineriesinclude whole-crop biorefineries encompassing an array of transformations of feed-stock (e.g., corn, or rapeseed) The most promising type of Phase III biorefineries are

Chemical products Thermal energy Aromatic compounds Biofuels Chemical products Nutrition

Glycerol Fatty acids Vegetable oils

Starch Sugar

Fermentation sludge

Syngas Pyrolysis oil

Lignin Hemicellulose

Lignocellulosic + protein feedstock Cellulose

Sugar crop Starch crop Oil crop & algae Lignocellulosic feedstock

FIGURE 1.2 Schematic overview about the processing strategy of different feedstock used

in biorefineries and the various products obtained Processes leading to an energy product areshown as dashed lines Fermentation sludge is the microbial biomass produced during thebioconversion processes

based on lignocellulosic feedstock (e.g., wood, corn stover/cobs) to produce icals, fuels, energy, and other valuable outputs Lignocellulosic biorefineries can besubclassified into various intermediate concepts based on the employed processes.This includes thermochemical biorefineries such as syngas platforms, or biochemical

chem-or microbial bichem-orefineries such as sugar platfchem-orms Sustainability is in the long runonly obtainable with Phase III biorefineries They are expected to expand the rangeand volume of bioproducts on the market as well as to improve the economics ofbiorefinery plants At the same time the expectation is that they optimize the energyand environmental performance and enhance the cost competitiveness of bio-derivedproducts However, the development of such advanced integrated biorefineries isstill ongoing

More precise and detailed classifications of biorefineries rely on four main features:platforms, products, feedstock, and processes (Clark et al., 2012)

Platforms are defined as key intermediates between raw material and final

prod-ucts They are considered as particularly relevant as these can be used to link different

pyrolysis oils

In terms of products, biorefineries can be broadly grouped into energy-driven

and product-driven biorefineries The main goal of energy-driven biorefineries is theproduction of one or more energy carriers (fuels, power, and/or heat) from biomass.The economic profitability of the plant is subsequently maximized by an upgradeand valorization of process residues On the other hand, product-driven biorefineriesare dedicated to the generation of one or more bio-based products The economicprofitability is maximized by production of bioenergy from process residues

Biorefineries can be further classified based on their feedstock For example, the

feedstock can be subdivided into the main classes according to their origin, such asagriculture, forestry, industries, households, and aquaculture (Cherubini, 2010b)

Clearly, the feedstock for biorefineries will change further with the ongoing

tech-nical developments First-generation biorefineries are based on edible feedstock from the agricultural sector (Srirangan et al., 2012), such as sugar and starch Second- generation biorefineries are based on non-edible feedstock, comprising raw material

derived from lignocellulosic biomass and crop waste residues from various

agricul-tural and forestry processes (Nigam and Singh, 2011; Srirangan et al., 2012) generation biorefineries make direct use of photosynthetic bacteria and algae, which

Third-can be cultivated in bioreactors and are thus independent of crop land (Nigam andSingh, 2011)

Processes employed in biorefinery concepts to convert biomass feedstock into

mar-ketable products include biochemical (e.g., anaerobic digestion, microbial tation, enzymatic conversion), chemical (e.g., hydrolysis, transesterification, hydro-genation, oxidation), and thermochemical (e.g., pyrolysis, gasification) processes

fermen-1.5 QUANTITIES OF SUSTAINABLY AVAILABLE BIOMASS

The actual availability of the resources is the basic question to answer, when takingdecisions about which resources to use However, the sustainable and usable amount

of biomass, which is present or possibly present in the future, is difficult to assess.Here we would like to give an overview about some numbers, particularly the orders

Generally speaking, about 75% of the total biomass produced belongs to theclass of carbohydrates However, only 3.5% of these compounds are actually used

by mankind (Tschan et al 2012) Clearly, the theoretical availability of biomassdoes not mean that it is economically feasible or environmentally viable to collect

it for industrial use Parikka (2004) estimated the sustainable worldwide biomassenergy potential to be about 100 EJ/year Only 40% of this biomass is currently usedaccording to Parikka (2004)

Current global bio-based chemical and polymer production (excluding els) is estimated to be around 50 million tonnes ( De Jong et al., 2012) Theglobal petrochemical production of chemicals and polymers is estimated at around

biofu-330 million tonnes ( De Jong et al., 2012)

Figure 1.3, taken from Vennestrøm et al (2011) compares the total US oil sumption with harvested non-food biomass on a weight basis On a weight basis

con-Total consumption

Total petrochemicals Propylene Benzene Ethylene

MethanolButadieneMotor gasoline

EtOH

Biodiesel Oleochemicals Other nonfood bioproducts Energy production

Transportation purposes

Energy production Jet fuel

Total diesel oil

10 Mt/year

Total harvested biomass (nonfood)

FIGURE 1.3 Total US oil consumption compared to potential and currently harvested food biomass divided into its main uses The area of each circle is proportional to the consumedamount From Vennestrøm et al (2011)

non-biomass has a lower energy and carbon density than crude oil In fact, oil containsabout twice the amount of carbon atoms and chemically stored energy as biomass.What becomes clear from this figure is that the orders of magnitude correspond toeach other; however, with an increasing use of biomass in industry at some pointbiomass can become a scarce resource with increasing prizes Feedstock which arevery cheap at the time might become expensive when their industrial use is carried out

on a scale that is comparable to that of current petrochemical processes Large-scaleuse of biomass as feedstock will drastically alter the market Thus, for long-termplanning, the mature market must be considered instead of the current market, which

is by no means a simple task Anyhow, biomass has the potential to fully substitutepetrol as carbon source for the chemical market, if the processes to produce and usethem are sufficiently efficient

1.6 QUANTIFICATION OF SUSTAINABILITY

In the development of sustainable industries, researchers are challenged to find vative technical solutions without losing sight of the economic, societal, and environ-mental impacts of their work (Jenkins and Alles, 2011) Scientific and quantifiablemethods are needed to guide research and industry into the right direction Sustain-ability assessments aimed at quantifying the economic, environmental, and societalimpacts can help to move debates and decision finding to a factual level Science-based methods such as life-cycle analysis (LCA), defined as a holistic approach toquantify environmental impacts throughout the value chain of a product (InternationalOrganization for Standardization, 2006), can be applied as a decision support tool

inno-With LCA the feedstock selection for defined products and the decision of how toproduce the feedstock and the product are set on a factual basis.

For the feedstock, there are logistical and sustainability concerns Each potentialbiorefinery concept has specific coproduct and waste issues to consider Transport is

a general issue in this discussion The biomass resource has to be transported to therefinery; subsequently the products have to be transported to the downstream industryand/or the consumer Of interest is the approach of the company Nature-Works LLCthat currently operates the largest biorefinery in the United States in Blair, Nebraska.The nameplate capacity of the polymer production plant is 140,000 tons of polymerper year Corn is the basis for the production of the bioplastic polylactic acid (PLA)

in a complex multistage process Sixty percent of its corn feedstock is obtained fromthe local area (producers, located less than 40 kilometers from the plant) Severalcompanies in an emergent network are now active on the Blair biorefinery campus(Wells and Zapata, 2012) reducing transportation from one industrial branch to thenext one

1.7 STARCH- AND SUGAR-BASED BIOREFINERY

Starch- and sugar-containing crops are quantitatively the most important products

of today’s agricultural system Most of the existing biorefinery concepts are based

on these plants and they are referred to as first-generation feedstock (vide supra), but

they also constitute the backbone of human nutrition General characteristics of thistype of biorefinery are listed in Table 1.1

The polysaccharide starch is found in most plants as a storage compound; however,only five plants, namely maize, rice, wheat, potatoes, and cassava account for themajority of worldwide produced starch-containing plants Roughly 2.7 billion tons

of these crops are annually harvested The class of sugar-containing crops containsonly two plants namely sugar cane and sugar beet of which about 2 billion tons are

TABLE 1.1 Characteristics of the Starch and Sugar Biorefinery

Starch and sugar crops are already

cultivated worldwide today

Connection between the sugar/starchindustry and classical chemicalindustry is still underdevelopedWell-established industry and the

handling of the different resources is

developed

Direct competition with the food industry

Highly developed technology available

for the primary raffination toward the

platform chemicals saccharose and

starch

Combined production of material andenergetic products needs a betterintegration

A plethora of biochemical fermentations

require fermentable sugars

Fertilizers required for high yieldproduction

1961 0 500

FIGURE 1.4 Worldwide production of the main sugar- and starch-containing crops Datataken from the Food and Agriculture Organization of the United Nations (www.fao.org)

annually harvested The shares of each plant in the overall worldwide productionare shown in Figure 1.4 From this graph, it can be depicted that the overall annualproduction of these crops is rising However, the future growth rate will depend

on three main parameters: land, fertilizer, and plant productivity The production ofnitrogen fertilizers requires a high energy input This directly connects energy pricewith crop price

The starch and sugar processing industry is already highly developed and hasthe technology to readily deal with the conventional crops of today’s agriculture Itsmajor limitation can be seen in the circumstance that only a part of the starch- orsugar-containing plant is implemented in the biorefinery approach In the future, thewhole crop including the stover has to be taken into account in order to develop awhole crop biorefinery concept (Kamm et al., 2006), keeping in mind that only a partcan be used in a sustainable way

The primary biorefinery products of the sugar and starch industry are glucose,fructose, gluconate, and bioethanol (Wagemann et al., 2012) At present, bioethanol

is a fast-growing biorefinery energy product Both in the United States and Brazil,bioethanol is produced in high quantities in order to substitute the dependence onfossil fuels in the transportation sector In both cases, the biorefinery process can

be structured in three steps: (1) obtainment of a solution of fermentable sugars; (2)bioconversion of sugars to ethanol; (3) ethanol separation and purification (Mussatto

et al., 2010) Sugarcane is used as the main feedstock in Brazil whereas the majority

of the bioethanol in the United States is produced from maize More than 35% ofharvested maize grain is used for bioethanol production in the United States (Perlackand Stokes, 2011) and by 2011, 52 million liters of ethanol were produced annually(Jerck et al., 2012) Two other important crops which may be used for biofuelproduction are cassava and sorghum Cassava is grown as an annual crop in thetropical and subtropical countries and has the advantage that it is compatible withcurrent corn ethanol technologies Sorghum is a good alternative feedstock for dryregions, because of its lower water requirements compared to maize and sugarcane(Srirangan et al., 2012)

However, bioethanol is not the only biorefinery product which can be obtainedfrom starch- and sugar-containing crops Microorganisms can directly use sugars as asubstrate and convert them to virtually any product Today products like organic acids(e.g., citric acid, gluconic acid) and amino acids (e.g., glutamate, lysine) are alreadyproduced from sugars in high amounts and are not dependent on fossil resources as

a substrate

1.7.1 Sugar Crop Raffination

After harvesting, the main crop is further treated by a crushing and milling stepthat yields the sugar juice As a by-product the insoluble lignocellulosic material ofthe plant is obtained In case of sugar cane this residue is referred to as sugarcanebagasse This feedstock is currently used (by burning) as an energy resource to drivethe thermal requirements of the sugar plant However, it is also considered a valuablefeedstock for lignocellulosic biorefinery approaches (Dawson and Boopthay, 2008;Cherubini and Strømann 2011; Nigam and Singh, 2011; Macrelli et al., 2012) Thesugar juice obtained can then either be directly used by the fermentation industry as

a substrate or sugar is crystallized stepwise by water evaporation The crystallizedsugar can be used for various purposes including human nutrition and fermentationprocesses, if higher substrate purity is required

1.7.2 Starch Crop Raffination

In a first milling step, the crop is broken up In case of maize, a previous steeping

water and separated from the insoluble fibers, which are a potential feedstock for alignocellulosic biorefinery In successive steps the protein fraction is separated fromthe starch by either protein coagulation (heat or acid treatment) or centrifugationutilizing density differences Starch can be readily hydrolyzed to fermentable glucose

by means of amylases

The processing of starch- and sugar-containing plants has a very long history and

is directly connected to the main function of these crops as nutritional products Thehighest potential for new biorefinery concepts based on sugar- and starch-containingcrops can be expected in the various side products of this industry starting with plantresidues, which are already separated from the crop on the field, and residues frommilling and further processing steps Those product streams often yield only a lowvalue and are currently used as animal feed or for thermal processing (Nitayavardhanaand Khanal, 2012) For example, current flour mills operate at 70–80% grain-to-flouryields Various waste and by-product streams include bran, germ, and endosperm.These by-products contain a high proportion of starch (25–30%) that could be usedfor microbial bioconversion to produce valuable chemicals (Clark et al., 2012)

1.8 OILSEED CROPS

Plants like soybean, sunflower, rapeseed, peanut, oil palm, and coconut contain ahigh fraction of lipids and are referred to as oilseed crops Vegetable oils have a long

30 25 20

tradition as edible oils and are of growing interest for the biofuel industry Over thelast 50 years the production of oilseed crops increased dramatically from around 100million tons to over 800 million tons per year (Figure 1.5) Especially, the cultivation

of oil palms and soybeans was significantly enlarged

General characteristics of this type of biorefinery are listed in Table 1.2

Besides the application as nutritional product, those plants have an importantapplication for production of biofuels also The triglycerides can be modified by atransesterification reaction with short-chain alcohols to produce alkyl esters, mainlymethyl and ethyl esters The product obtained is referred to as biodiesel In thatcase, a fundamental concept of biorefineries was neglected, which requires a suitableapplication for all byproducts because during the transesterification reaction glycerol

is obtained as a byproduct in high amounts The production of 10 tons of biodieselgenerates 1 ton of glycerol Its price decreases with increased biodiesel production.Therefore, new biorefinery concepts need to be developed to convert glycerol to an

TABLE 1.2 Characteristics of the Oil Crop Biorefinery

handling of the different resources is

developed

Fertilizers required for high-yieldproduction

Fatty acids can be directly converted to a

valuable-energy product (biodiesel)

added-value product like 1,2- or 1,3-propanediol, acrolein, or lactic acid (Pfl¨ugl et al.,2012; Posada et al., 2012).

The situation for oil crop plants is comparable with the starch and sugar processingindustry The technology to obtain primary products like vegetable oils and biofuels isalready established and is commercially applied However, secondary refinery streamslike plant residues, seed cakes of pressing and filtration steps, or process byprod-ucts like the above-mentioned glycerol need to be considered in future Processesneed to be developed to add additional value to those products Furthermore, wastestreams like cooking oil can be fed back into the biodiesel production pipeline (Wang

et al., 2007)

1.9 LIGNOCELLULOSIC FEEDSTOCK

The current use of lignocellulosic biomass is primarily the use of wood for tion, construction, and furniture making; cellulose fibers are used for pulp and papermaking or clothing (M¨oller et al., 2007) The global production of forest productshas been estimated by the Food and Agriculture Organization of the United Nations

173 million tons, paper and paperboard production has been 403 million tons, and

211 million tons are produced from recovered paper However, not only wood canserve as feedstock for lignocellulose biorefineries but residues from agriculture canalso be taken into account The lignocellulose feedstock report from the EPOBIOproject (M¨oller et al., 2007) states that the most abundant agricultural residue inEurope is wheat straw, rice straw in Asia, and corn stover in North America

As the systematic cultivation of crops for biorefinery purposes is gaining moreimportance the question arises as to which crops are the most desirable ones To selectthe best possible feedstock several criteria have to be considered From an economicpoint of view the crop has to have a very high biomass yield, low requirement forfertilizers and pesticides, the ability to grow on marginal lands, and the cell wallstructure should allow an easy access for bioconversion methods In addition the cropshould also cover environmental criteria such as low impact on biodiversity, waterand soil quality, low greenhouse gas emission, and high carbon sequestration Based

on these criteria M¨oller et al (2007) selected four candidates, namely poplar, willow,

Miscanthus, and wheat straw for the region of the European Union.

Compared to the availability of fossil resources, areas for biomass cultivation areglobally more evenly distributed, thereby enhancing the security of supply Biore-fineries utilizing lignocellulosic feedstock may even help to a certain extent to combatthe unemployment status of rural areas (Menon and Rao, 2012)

1.9.1 Biochemical Biorefinery (Fractionation Biorefinery)

The term “lignocellulosic biomass” describes the material that constitutes the plantcell wall This includes primarily cellulose (30–50%), hemicellulose (15–35%), and

lignin (10–30%) As a result of the organization and interaction between these meric structures, the plant cell wall is naturally recalcitrant to biological degradation(Himmel et al., 2007).

poly-The lignocellulose biorefinery is one of the most desirable forms of a biorefinery

As mentioned earlier, a Phase III type biorefinery uses virtually any lignocellulosicfeedstock like wood, corn stover/cobs, straw, bagasse, and other lignocellulose-richwaste streams from agriculture, forestry, and municipal areas The accessibility of thedesired fermentable sugars is severely hindered by the assembly of the lignocellulosicbiomass itself; therefore, a pretreatment by milling and grinding followed by a treat-ment with high temperature and pressure is required to access the fibers composed offermentable mono- and oligosaccharides The addition of mild or harsh acids, bases,

or organic substances can further enhance the pulping Depending on the particle sizeand the composition of the biomass that is delivered to the biorefinery, a suitable flowchart of pretreatment steps has to be established Pretreatment techniques can be cat-egorized into physical (milling, irradiation, and extrusion), physicochemical (steamexplosion, ammonia fiber explosion, ammonia recycle percolation, microwave chem-ical, and liquid hot-water pretreatment), chemical (acid, alkaline, green solvents), andbiological processes The pretreatment gives rise to a solid or fluid stream of the threebiomass main components: cellulose, hemicellulose, and lignin These streams arefurther subjected to enzymatic hydrolysis to gain sugars for microbial fermentation.Menon and Rao (2012) conclude that the choice of pretreatment should considerthe overall compatibility of feedstock, enzymes, and organisms to be applied Amore detailed description of pretreatment processes and lignocellulose hydrolysis isgiven in the following chapters of this book The enzymatic conversion of celluloseand hemicellulose to fermentable sugars opens the possibility for the microbial con-version to chemical building blocks for the synthesis of bio-based materials or theconversion to biofuels for transport or energy purposes Saccharification of cellu-lose and hemicellulose to platform compounds d-glucose (from cellulose), d-xylose,l-arabinose, d-mannose, d-glucose, d-galactose, and d-glucuronic acid (from hemi-cellulose) involve a series of hydrolytic enzymes or enzyme complexes to whichChapters 4 and 5 in this book are dedicated

Platform compounds are further converted to products by microbial fermentationprocesses Saccharification and fermentation can be accomplished in a sequentialprocess by separate hydrolysis and fermentation (SHF), or in a consolidated one-pot process known as simultaneous saccharification and fermentation (SSF) of singlesugars or simultaneous saccharification and co-fermentation (SSCF) of all monosac-charides Future developments might even combine the production of saccharolyticenzymes, the hydrolysis of cellulose, and hemicellulose to monomeric sugars andthe fermentation of hexose and pentose sugars in a single process, the so-calledconsolidated biomass processing (CBP) (Menon and Rao 2012)

The most prominent product in the biorefineries nowadays is bioethanol with

a global production volume over 20 billion gallons (or 75 billion liters) in 2011(Alternative Fuels Data Center, 2013) Huge efforts in research and developmentare on the way to broaden the product portfolio of the biorefineries in the future.Screening for new production strains in nature, or microorganisms accessible formetabolic engineering for directed biosynthesis of bioproducts, or a combination of

TABLE 1.3 Characteristics of the Biochemical Biorefinery

The availability of diverse lignocellulosic

raw material is given

Sustainable usage of lignin for materialproduction is still to be establishedThe use of these raw material does not

interfere with food and feed production

Simultaneous fermentation of C6 and C5sugars from the hemicellulose fraction

is still to be optimizedExpertise of pretreatment technologies of

milling and grinding as well as

(thermo)-chemical pretreatment

technologies is established in the pulp

and paper industry sectors

Embedding product streams of thebiorefinery into the chemical industry

is still to be established

Fermentation technologies for the

production of alcohols, organic acids,

amino acids, and other chemical

building blocks from sugars are well

Source: Adapted from Wagemann et al (2012).

both approaches will achieve this aim Part II of this book is dedicated to specificbiocommodity products from biorefineries and future aspects for the production

of those

The remaining lignin that is separated from the sugar stream during the ment process can be used for the production of heat and power, which is done veryfrequently at the moment; nevertheless, it could be used in the future as a source ofvarious aromatic compounds The effective utilization of all the three componentswould play a significant role in the economic viability of an integrated biorefinery.General characteristics of this type of biorefinery are listed in Table 1.3

pretreat-To evaluate the sustainability concerning economic, environmental, and socialaspects the Department of Energy (DOE) is funding integrated biorefinery projects

in pilot, demonstration, and commercial scale The importance of biochemical version is underlined by the fact that four out of five commercial scale plants funded

con-by the DOE are based on biochemical conversion (Department of Energy, 2012)

1.9.2 Syngas Biorefinery (Gasification Biorefinery)

Thermochemical conversion of biomass can be accomplished in three ways that differ

in the amount of oxygen that is supplied to the process By the supply of excess air thebiomass is combusted to generate heat and power When oxygen is depleted from theprocess, the biomass undergoes pyrolysis or liquefaction In the liquefaction biomass

is decomposed into small molecules which then polymerize to oily compounds.Liquids gained from pyrolysis or hydrothermal liquefaction can be further refined

to gasoline, diesel fuel, jet fuel, or chemicals Syngas is produced by gasification

by means of partial combustion of biomass, where only a limited amount of oxygen

is supplied to the process (Demirbas, 2010) Depending on the type of gasifier

Khanal, 2010)

to long-chain hydrocarbons catalyzed by cobalt or iron Before the Fischer–Tropschsynthesis (FTS) the syngas has to be cleaned and conditioned The FTS can beoperated at low temperatures to produce heavy, waxy hydrocarbons or at highertemperatures to produce olefins By further product upgrading the array of productsfrom FTS ranges from diesel, gasoline, methane, ethane, and to light and heavy waxes(Demirbas, 2010)

The microbial conversion of syngas offers some interesting opportunities for thefuture production of biofuels and biochemicals as well According to Munasingheand Khanal (2010), the merits over biochemical biorefinery approaches are the elimi-nations of costly pretreatment steps and enzymes, as well as the usage of all fractionsfrom biomass including the lignin part Compared to the Fischer–Tropsch process

importance

Possible products from syngas fermentation can be ethanol, butanol, lactate,acetate, pyruvate, and butyrate One of the most important factors in syngas fer-mentation is the microbial catalyst itself (anaerobic bacteria from the genera of

Clostridium, Acetobacterium, Butyribacterium) The efficient conversion of syngas

by the microbe can be negatively influenced by impurities like ethylene, ethane,sulfur, and nitrogen-containing gases as well as solid particles of tar, ash, and char

So these impurities have to be avoided by the appropriate choice of gasifier or thesyngas has to be cleaned from these impurities before fermentation The fermentationprocess is influenced by parameters such as pH (depending on the microorganism,

reactor type (stirred tank, bubble column, membrane-based systems), and growthmedia (depending on the microorganism used) Despite the mass transfer limitationsand the quality of the syngas Munasinghe and Khanal (2010) recommend, for futuredevelopment of syngas fermentation, the genetic modification of existing syngas-fermenting microbes to high yield strains especially for solvent production, wherethe pathways to acid production have to be blocked General characteristics of thistype of biorefinery are listed in Table 1.4

1.10 GREEN BIOREFINERY

In contrast to lignocellulose-feedstock biorefineries, where the composite of lignin,cellulose, and hemicellulose are very strong, the green biorefinery uses green biomasssuch as grasses, green crops like lucerne, clover, and green cereals By wet fraction-ation, a fiber-rich press cake and a nutrient-rich green juice is obtained The dried

TABLE 1.4 Characteristics of the Syngas Biorefinery

The gasification of charcoal is well

established and works in large scales,

the expertise of this process can be

translated to biomass gasification

Large scale plants have a high rawmaterial demand

Raw material for biomass gasification are

available by using waste materials

from agriculture and forestry, it does

not interfere with food and feed

production

Construction of industrial scale facilities

is cost intensive

The chemical conversion and refining of

syngas to Fischer–Tropsch diesel fuel,

wax, methane, ethanol, and other

specialty chemicals is established

The potential variety of products is notexploited yet

Complete (holistic) utilization of all

biomass components

Biotechnological conversion of syngas tofermentation products is still in theresearch and development phaseSupply of raw material at a moderateprice has to be secured

Source: Adapted from Wagemann et al (2012).

press cake can serve as fodder, as a raw material for hydrocarbons and chemicals or itcan serve as a raw material for syngas production By separation enzymes, dyes, fla-vorings, carbohydrates, and proteins can be recovered from the press juice The pressjuice can also serve as a feedstock for fermentation where the fermentation broth is asource of lactic acid, amino acids, ethanol, and proteins (Kamm and Kamm, 2004)

1.11 MICROALGAE

Microalgae constitute a further source of industrially usable carbon fixed by synthesis They offer a great potential for exploitation, such as biodiesel production,due to their oil content that can exceed 80% w/w (Amaro et al., 2011) Some possibleadvantages connected to microalgae as feedstock include that their cultivation is notlinked to arable land (it is not linked to land at all, as off-shore cultivation is conceiv-able); they can grow in brackish or salty water and their efficiency in terms of energyuse per hectare is potentially high Following the classical concept of biorefineries,they are interesting because apart from their potential as oil for biodiesel producer, avariety of by-products are accumulated These by-products include valuable omega-3-fatty acids, recombinant proteins, and algal meal containing high amounts of proteins(Subhadra and Grinson-George, 2011) The direct by-product of biodiesel productionfrom oil is glycerol that can be used to grow more algae or which can be converted

photo-to higher-valued chemicals such as 1,3-propanediol

The high oil productivity of microalgae cultures and the possible absence

of competition for arable land and water resources justify the currently high

investments into such projects Nevertheless, care has to be taken with the ation of possible productivities Various studies seem to claim unrealistically highnumbers for the microalgal oil production potential Decades of worldwide researchhave demonstrated that annual productivities beyond 100 tons of algal biomass perhectare appear not attainable at large scale, at least not with current strains andcurrent technologies (Rodolfi et al., 2009) Thus, even under the best conditions arealistic oil yield will not exceed 40 tons per hectare per year This compares toabout 1000 liters of oil per hectare per year which can be typically produced bysunflower or rapeseed, and 6000 liters per hectare per year obtained with oil palms(Chisti, 2007).

evalu-Nevertheless, full commercialization of biodiesel from algae oil has not beenrealized yet Till now the cost of algal biomass production of about US$5/kg issimply not compatible with the low costs required for biofuel production One majorproblem connected to microalgae as oil resource is the large scale cultivation that has

demand for mixing and pumping is very high Light does not penetrate more than afew centimeters into a dense culture of algal cells, so scale-up depends on an increase

of surface area and not volume as is the case for heterotrophic fermentations (Scott

et al., 2010) The costs of scale-up are much debated—estimates of production andcapital costs vary widely This points to the current painful lack of data from real-lifedemonstrations There is a pressing need to conduct pilot studies at realistic scale toassess productivities likely to be achieved in practice

Further drawbacks hindering the large-scale use of microalgae as resource is theenormous water content of the harvested biomass and the intracellular localization ofthe desired oil Drying and oil extraction are very costly, particularly when environ-mentally benign technologies are applied and sustainability is an aim of the endeavor(Singh and Olsen, 2011) Lardon et al (2009) exemplarily calculated that 1 MJ of

energy in biodiesel from Chlorella vulgaris required an energy input of 1.66 MJ for

production Use of the algal biomass for energy generation could turn the balance tothe positive side; however, this shows the significance of technological advancementbefore industrial exploitation of microalgae An important step regarding the down-stream processing is that it should allow the product generation without drying thebiomass For example, Levine et al (2010) have developed a biodiesel productionprocess starting from wet algal biomass with 80% moisture

It is out of question that algal biomass can be utilized for the production of variousbioproducts However, significant improvements in the efficiency, cost structure andability to scale-up algal growth, and lipid extraction are required to establish acommercially viable microalgae-based biorefinery

1.12 FUTURE PROSPECTS—AIMING FOR HIGHER

VALUE FROM BIOMASS

The concepts for biomass valorization are manifold Some existing examples forbiochemical products from bio-derived resources are summarized in Table 1.5