Cellulosic Energy Cropping Systems E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Serie: Wiley Series in Renewable Resources
• Sprache: Englisch

Seitenzahl: 806

Veröffentlichungsjahr: 2014

Beschreibung

Cellulosic Energy Cropping Systems presents a comprehensive overview of how cellulosic energy crops can be sustainably produced and converted to affordable energy through liquid fuels, heat and electricity.

The book begins with an introduction to cellulosic feedstocks, discussing their potential as a large-scale sustainable energy source, and technologies for the production of liquid fuels, heat and electricity. Subsequent chapters examine miscanthus, switchgrass, sugarcane and energy cane, sorghums and crop residues, reviewing their phylogeny, cultural practices, and opportunities for genetic improvement. This is followed by a detailed focus on woody crops, including eucalyptus, pine, poplar and willow. Critical logistical issues associated with both herbaceous and woody feedstocks are reviewed, and alternate strategies for harvesting, transporting, and storing cellulosic materials are also examined. The final sectionof the booktackles the challenge of achieving long-term sustainability, addressing economic, environmental and social factors.

Cellulosic Energy Cropping Systems is a valuable resource for academics, students and industry professionals working in the field of biomass cultivation and conversion, bioenergy, crop science and agriculture.

Topics covered include:

• Identifying suitable cellulosic energy crops that are adapted to a wide range of climates and soils
• Best management practices for sustainably growing, harvesting, storing, transporting and pre-processing these crops
• The development of integrated cellulosic energy cropping systems for supplying commercial processing plants
• Challenges and opportunities for the long-term sustainability of cellulosic energy crops

 This book was conceived and initiated by David I. Bransby, Professor of Energy and Forage Crops in the Department of Crop, Soil and Environmental Sciences at Auburn University, USA.

 For more information on the Wiley Series in Renewable Resources, visit www.wiley.com/go/rrs

Leseprobe

Contents

Cover

Cellulosic Energy Cropping Systems

Title Page

Copyright

Dedication

Foreword

Series Preface

Preface

List of Contributors

Chapter 1: Introduction to Cellulosic Energy Crops

1.1 Cellulosic Biomass: Definition, Photosynthesis, and Composition

1.2 Cellulosic Biomass Properties and Their Relevance to Downstream Processing

1.3 Desirable Traits and Potential Supply of Cellulosic Energy Crops

1.4 The Case for Cellulosic Energy Crops

References

Chapter 2: Conversion Technologies for the Production of Liquid Fuels and Biochemicals

2.1 Introduction

2.2 Biomass Conversion Technologies

2.3 (Bio)Chemical Conversion Route

2.4 Thermochemical Conversion Route

2.5 Summary and Conclusions

Acknowledgement

References

Chapter 3: Technologies for Production of Heat and Electricity

3.1 Introduction

3.2 Combustion

3.3 Repowering

3.4 Gasification

3.5 Pyrolysis

3.6 Direct Hydrothermal Liquefaction

3.7 Anaerobic Digestion

3.8 Integrated Biorefineries

3.9 Summary

References

Chapter 4: Miscanthus Genetics and Agronomy for Bioenergy Feedstock

4.1 Introduction

4.2 Phylogeny, Growth, Yield and Chemical Composition

4.3 Cultural Practices

4.4 Genetic Improvement

4.5 Conclusion

References

Chapter 5: Switchgrass

5.1 Overview

5.2 Phylogeny, Growth, Yield and Chemical Composition

5.3 Cultural Practices

5.4 Genetic Improvement

5.5 Summary

References

Chapter 6: Sugarcane, Energy Cane and Napier Grass

6.1 Sugar and Energy Cane

6.2 Napier grass

References

Chapter 7: Sorghum

7.1 Introduction

7.2 Sorghum Phenology, Genetic Structure and Types

7.3 Cultural Practices

7.4 Genetic Improvement

7.5 Summary and Conclusions

References

Chapter 8: Crop Residues

8.1 Overview

8.2 Corn Stover

8.3 Wheat Straw

8.4 Future Opportunities

References

Chapter 9: Eucalyptus

9.1 Phylogeny, Growth, Yield and Chemical Composition

9.2 Cultural Practices

9.3 Genetic Improvement

References

Chapter 10: Pine

10.1 Introduction

10.2 Cultural Practices

10.3 Harvesting

10.4 Genetic Improvement

10.5 Economics

10.6 Government Regulations

10.7 Final Comments

References

Chapter 11: Poplar

11.1 Introduction

11.2 Cultural Practices

11.3 Genetic Improvement

11.4 Utilization

11.5 Carbon Sequestration and Soil Response

References

Chapter 12: Development and Deployment of Willow Biomass Crops

12.1 Introduction

12.2 Shrub Willow Characteristics

12.3 Production Systems for Willow Biomass Crops

12.4 Willow Biomass Crop Economics

12.5 Environmental and Rural Development Benefits

12.6 Commercial Development

12.7 Conclusions

References

Chapter 13: Herbaceous Biomass Logistics

13.1 Introduction

13.2 Typical Biomass Logistics Constraints

13.3 Linkage in Logistics Chain

13.4 Plant Size

13.5 Harvesting

13.6 Highway Hauling

13.7 Development of Concept for Multibale Handling Unit

13.8 Functionality Analysis for Rack System Concept

13.9 Cost Analysis for 24-h Hauling Using Rack System Concept

13.10 Summary

Appendix 13.A Cost to Operate Workhorse Forklift (Example for Equipment Cost Calculations)

Appendix 13.B Operational Plan for “Rack System” Example

B.1 Operation Plan for SSL Loading

B.2 Influence of SSL Size on Rack Loading Operations

B.3 Total Trucks Required – 24-h Hauling

B.4 Total Racks Required – 24-h Hauling

References

Chapter 14: Woody Biomass Logistics

14.1 Introduction

14.2 Overview of the Woody Biomass Supply Chain

14.3 Woody Biomass from Dedicated Energy Crops

14.4 Woody Biomass from Stand Thinning

14.5 Logging Residues

14.6 Harvesting and Processing Systems and Equipment

14.7 Woody Biomass Transportation

14.8 Pretreatment

14.9 Handling and Storage

14.10 Logistics Management

References

Chapter 15: Economic Sustainability of Cellulosic Energy Cropping Systems

15.1 Introduction

15.2 Economics of Crop Production

15.3 Risk and Uncertainty

15.4 Risk Mitigation and Management

15.5 Supply, Demand and Prices

15.6 The Start-Up Barrier

15.7 Elements of Sustainability

15.8 Policy

15.9 Summary

References

Chapter 16: Environmental Sustainability of Cellulosic Energy Cropping Systems

16.1 Introduction

16.2 Greenhouse Gas Effects

16.3 Soil Properties

16.4 Water Quantity and Quality

16.5 Invasive Species Effects/Mitigation/Enhancement

16.6 Wildlife and Biodiversity

16.7 Conclusions

References

Chapter 17: Social Sustainability of Cellulosic Energy Cropping Systems

17.1 Introduction

17.2 Standards for Social Sustainability

17.3 Forest-Based Biofuels

17.4 Biofuel Social Sustainability Standards

17.5 Summary and Conclusions

References

Chapter 18: Commercialization of Cellulosic Energy Cropping Systems

18.1 Overview

18.2 Introduction

18.3 Land Availability

18.4 Crop Selection and Contracting

18.5 Financing Establishment

18.6 Agronomic Efficiencies and Management

18.7 Identifying and Addressing Risks

18.8 Conclusion

References

Chapter 19: Selected Global Examples of Cellulosic Cropping System Trends

19.1 Overview

19.2 Cellulosic Ethanol in Brazil

19.3 Cellulosic Bioenergy in China

19.4 Bioenergy in India

19.5 Summary

Acknowledgements

References

Index

Wiley Series in Renewable Resources

Series Editor

Christian V. Stevens – Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium

Titles in the Series

Wood Modification – Chemical, Thermal and Other Processes

Callum A. S. Hill

Renewables – Based Technology – Sustainability Assessment

Jo Dewulf & Herman Van Langenhove

Introduction to Chemicals from Biomass

James H. Clark & Fabien E.I. Deswarte

Biofuels

Wim Soetaert & Erick Vandamme

Handbook of Natural Colorants

Thomas Bechtold & Rita Mussak

Surfactants from Renewable Resources

Mikael Kjellin & Ingegärd Johansson

Industrial Application of Natural Fibres – Structure, Properties and Technical Applications

Jörg Müssig

Thermochemical Processing of Biomass – Conversion into Fuels, Chemicals and Power

Robert C. Brown

Biorefinery Co-Products: Phytochemicals, Primary Metabolites and Value-Added Biomass Processing

Chantal Bergeron, Danielle Julie Carrier & Shri Ramaswamy

Aqueous Pretreatment of Plant Biomass for Biological and Chemical Conversion to Fuels and Chemicals

Charles E. Wyman

Bio-Based Plastics: Materials and Applications

Stephan Kabasci

Introduction to Wood and Natural Fiber Composites

Douglas Stokke, Qinglin Wu & Guangping Han

Forthcoming Titles

Cellulose Nanocrystals: Properties, Production and Applications

Wadood Hamad

Introduction to Chemicals from Biomass, 2nd edition

James Clark & Fabien Deswarte

Lignin and Lignans as Renewable Raw Materials: Chemistry, Technology and Applications

Francisco García Calvo-Flores, José A. Dobado, Joaquín Isac García & Francisco J. Martin-Martinez

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Library of Congress Cataloging-in-Publication Data

Karlen, D. L. (Douglas L.) Cellulosic energy cropping systems / editor, Douglas L. Karlen. pages cm. Includes index. ISBN 978-1-119-99194-6 (cloth) 1. Energy crops. 2. Biomass energy. 3. Cellulose--Biotechnology. 4. Cellulose--Chemistry. I. Title. SB288.K37 2014 333.95′39--dc23 2013037386

A catalogue record for this book is available from the British Library.

ISBN: 9781119991946

This book was conceived and initiated by Dr. David I. Bransby, and it is to him that the final product is dedicated. David is a professor in the Agronomy and Soils Department in the College of Agriculture at Auburn University in Auburn, Alabama, U.S.A. A native of South Africa, David arrived at Auburn in 1987 to teach and conduct research in forage and livestock management. Shortly thereafter, he was asked to provide oversight and leadership for a federal, multistate grant focused on high-yielding, low-input herbaceous plants that could be converted to bioenergy. David insisted he was not qualified because he knew nothing about converting biomass to energy and even thought “it was a crazy idea.” He was quickly reassured that “nobody else knew anything about it, either; renewable energy was a totally new area.”

David immediately began learning all he could about the production of energy from biomass while simultaneously educating himself, as an immigrant, about U.S. agriculture. Suddenly he realized that the two topics could provide a nearly perfect union. He surmised that the major commodities were often being overproduced and that the government response through decades of farm programs had created “stagnation in U.S. agriculture by discouraging new ideas and change.”

Nearly three decades later, David has built two research and outreach programs, one in forage and livestock management and one in energy crops and bioenergy, that have both received national and international recognition. A cornerstone of these programs has been David's emphasis on outreach, built on a philosophy that “the ultimate goal of applied research should be to benefit society, and this goal cannot be achieved without getting involved in outreach.” Through his personal involvement with many different stakeholder groups, David concludes that he has “gathered valuable information that has helped me design more relevant research and improve the content of the courses I teach.”

David is convinced that biofuels made from switchgrass and other agricultural crops and by-products can reduce America's dependence on foreign oil, strengthen farm economies and revitalize rural communities. “Energy crops, while not a total solution, would help by giving farmers new markets and reducing their dependence on farm subsidies.” He has continued his endeavors because “I believe this is really important stuff. It's going to play a major role in our country's future.”

Foreword

This volume on cellulosic energy cropping systems is a valuable addition to the Wiley Series on Renewable Resources. The editor, Doug Karlen, has provided guidance for fifty expert co-authors from around the world to make meaningful contributions that detail an extremely diverse and complex topic. The result is an easy-to-use source of cutting edge information with an international perspective on all aspects of cellulosic energy cropping systems that will be extremely beneficial to students, the private sector, legislators and lay people alike. Chapters are well organized; the information provided is based largely on scientific research but also includes valuable observations, ideas and advice that are not available in refereed scientific journals. For those who wish to review any particular topic in more detail, a comprehensive list of references is provided at the end of each chapter.

As efforts to commercialize numerous biofuel, biopower, and bioproduct conversion processes around the world steadily increase, it has become evident that optimization of the connection between the feedstock and conversion phases in the supply chain is often a very major challenge, and potentially poses the greatest risk of project failure. In particular, understanding by managers in the feedstock phase of needs in the conversion phase are often tenuous, and vice versa. In this regard, chapter sequence is helpful: following an excellent broad introduction to cellulosic energy crops in the first chapter, overviews of conversion technologies for production of biofuels, and of biomass heat and power are provided in Chapters 2 and 3, respectively. This ensures that the reader has a basic understanding of these processes prior to reviewing information on cellulosic energy crops; for those who wish to explore these topics further, considerably more information is provided in other volumes of the Wiley Series on Renewable Resources.

The heart of this volume comprises comprehensive accounts of current best management practices for production of both herbaceous (Miscanthus, switchgrass, sugarcane, energy cane, napier grass, sorghum and crop residues) and woody (eucalyptus, pine, poplar and willow) cellulosic energy feedstocks that offer most potential globally. While the importance of a systems approach is emphasized or implied throughout, separate chapters on logistics of herbaceous and woody energy crops address this issue in detail. The all-important topic of sustainability is covered in the next three chapters, one each on economic, environmental and social sustainability. Never before have new crops been scrutinized and regulated, as much as is expected for cellulosic energy crops, due largely to a substantial increase in international awareness of global climate change and its impact on society. The final two chapters provide accounts of challenges and solutions related to commercialization of cellulosic cropping systems in the fledgling industry, and selected global examples of these systems.

In summary, this volume provides a unique and comprehensive source of up-to-date information on cellulosic energy cropping systems that is valuable to anyone interested in this topic: it will be prescribed reading for both undergraduate and graduate students who register for my course on Bioenergy and the Environment.

David Bransby Professor, Energy Crops and Bioenergy Auburn University, U.S.A.

Series Preface

Renewable resources, their use and modification are involved in a multitude of important processes with a major influence on our everyday lives. Applications can be found in the energy sector, chemistry, pharmacy, the textile industry, paints and coatings, to name but a few.

The area interconnects several scientific disciplines (agriculture, biochemistry, chemistry, technology, environmental sciences, forestry…), which makes it very difficult to have an expert view on the complicated interaction. Therefore, the idea to create a series of scientific books, focusing on specific topics concerning renewable resources, has been very opportune and can help to clarify some of the underlying connections in this area.

In a very fast changing world, trends are not only characteristic for fashion and political standpoints; also, science is not free from hypes and buzzwords. The use of renewable resources is again more important nowadays; however, it is not part of a hype or a fashion. As the lively discussions among scientists continue about how many years we will still be able to use fossil fuels – opinions ranging from 50 years to 500 years – they do agree that the reserve is limited and that it is essential not only to search for new energy carriers but also for new material sources.

In this respect, renewable resources are a crucial area in the search for alternatives for fossil-based raw materials and energy. In the field of energy supply, biomass and renewable-based resources will be part of the solution alongside other alternatives such as solar energy, wind energy, hydraulic power, hydrogen technology and nuclear energy.

In the field of material sciences, the impact of renewable resources will probably be even bigger. Integral utilization of crops and the use of waste streams in certain industries will grow in importance, leading to a more sustainable way of producing materials.

Although our society was much more (almost exclusively) based on renewable resources centuries ago, this disappeared in the Western world in the nineteenth century. Now it is time to focus again on this field of research. However, it should not mean a ‘retour à la nature’, but it should be a multidisciplinary effort on a highly technological level to perform research towards new opportunities, to develop new crops and products from renewable resources. This will be essential to guarantee a level of comfort for a growing number of people living on our planet. It is ‘the’ challenge for the coming generations of scientists to develop more sustainable ways to create prosperity and to fight poverty and hunger in the world. A global approach is certainly favoured.

This challenge can only be dealt with if scientists are attracted to this area and are recognized for their efforts in this interdisciplinary field. It is, therefore, also essential that consumers recognize the fate of renewable resources in a number of products.

Furthermore, scientists do need to communicate and discuss the relevance of their work. The use and modification of renewable resources may not follow the path of the genetic engineering concept in view of consumer acceptance in Europe. Related to this aspect, the series will certainly help to increase the visibility of the importance of renewable resources.

Being convinced of the value of the renewables approach for the industrial world, as well as for developing countries, I was myself delighted to collaborate on this series of books focusing on different aspects of renewable resources. I hope that readers become aware of the complexity, the interaction and interconnections, and the challenges of this field and that they will help to communicate on the importance of renewable resources.

I certainly want to thank the people of Wiley's Chichester office, especially David Hughes, Jenny Cossham and Lyn Roberts, in seeing the need for such a series of books on renewable resources, for initiating and supporting it and for helping to carry the project to the end.

Last, but not least, I want to thank my family, especially my wife Hilde and children Paulien and Pieter-Jan, for their patience and for giving me the time to work on the series when other activities seemed to be more inviting.

Christian V. Stevens, Faculty of Bioscience Engineering Ghent University, Belgium Series Editor ‘Renewable Resources’ June 2005

Preface

As stated in the Dedication, this book was conceived and initiated by Dr. David I. Bransby, who strongly believes that “research should not be an end in itself, but the first step in a process for generating and transferring information or technologies that are of value to the communities we serve.” David chose to focus the book on plant biomass because even though fats and oils can be used for bioenergy production, plant biomass is more abundant than animal biomass and thus offers much greater potential for energy production. Plant biomass can provide a variety of inputs including starch, oil, and sugar, but it is the lignocellulosic (cellulosic) biomass itself that is most abundant. Composed of cellulose, hemi-cellulose, and lignin these cell wall components are renewed on an annual basis around the globe.

There are also numerous technologies that are ready or under development for converting cellulosic biomass to heat, electricity and/or liquid fuels. With that in mind, David set out to produce a book that provided comprehensive documentation of how cellulosic energy crops such as switchgrass, Miscanthus, and sorghum and the cellulosic fraction of sugarcane, maize and wheat residues could be sustainably produced and converted to affordable energy through liquid fuels and electricity. Unfortunately, due to an on-going battle with diabetes, David was unable to complete the project. I am very humbled to have been able to pick up the gauntlet and with the outstanding help of many of my friends and colleagues complete this very important project. It is our hope as editor and authors of this work that readers around the globe will catch hold of David's inspiration and continue the ground-breaking work in the area, building new programs where none existed before, and continuing to build an awareness of the potential benefits of bioenergy to the public at large and to policy makers. The target audience for this book is society as a whole, but especially those elected officials who are often ultimately responsible for building new programs through their critical enabling legislation.

The book is divided into five sections. The first (I) provides general background related not only to the challenges and various potential cellulosic feedstocks (Chapter 1) but also to technologies for production of liquid fuels and biochemicals (Chapter 2) or production of heat and electricity (Chapter 3). Section II hones in on each of the herbaceous crops that have been identified as a potential cellulosic feedstock for not only bioenergy but also bioproduct development. Miscanthus (Chapter 4), switchgrass (Chapter 5), sugarcane and energy cane (Chapter 6), sorghums (Chapter 7) and crop residues (Chapter 8) are examined in detail by reviewing their phylogeny, cultural practices, and opportunities for genetic improvement. Section III follows a similar format although the focus is on woody crops, including eucalyptus (Chapter 9), pine (Chapter 10), poplar (Chapter 11), and willow (Chapter 12).

Section IV moves toward David's ultimate goal of commercialization by reviewing critical logistical issues associated with both herbaceous (Chapter 13) and woody (Chapter 14) feedstocks. Alternate strategies for harvesting, transporting, and storing various cellulosic materials are examined. Finally, Section V tackles the challenge where “the rubber meets the road”, that is, moving the technology from the researchers to society as a whole.

To achieve long-term sustainability, emerging cellulosic bioenergy and/or bioproducts industries must meet three crucial and equally important challenges. One is that the new enterprise(s) must be economical (Chapter 15). The second is they must not have adverse environmental impacts (Chapter 16), and, finally, they must be socially acceptable (Chapter 17). The final two chapters are intended to provide readers with case study examples of an actual bioenergy commercialization project (Chapter 18) and a glimpse at activities in Brazil, China, and India (Chapter 19).

In summary, to meet ever increasing global needs for sustainable food, feed, fiber, and fuel supplies, greater attention must be given to soil, water, and air resources. Redirecting from an increased trajectory of expanded row crops to cellulosic energy crops and crop rotations is one component needed to achieve the intensified productivity required for high quality agricultural products that are economically viable, socially acceptable, and adaptable. This book is intended to help: (1) identify suitable cellulosic energy crops that are adapted to a wide range of climates and soils; (2) develop best management practices for sustainably growing, harvesting, storing, transporting and pre-processing these crops with minimal negative impacts on the environment and food production; (3) develop integrated cellulosic energy cropping systems for supplying commercial processing plants; and (4) educating landowners, technology owners, students, policy makers and the general public on how to use cellulosic energy crops to maximize the many benefits they offer. It is my hope that we have successfully provided the information in a format that will enable all of us to achieve this important twenty-first century goal.

Douglas L. Karlen USDA, Agricultural Research Service, National Laboratory for Agriculture and the Environment U.S.A.

List of Contributors

Lawrence P. Abrahamson College of Environmental Science and Forestry, State University of New York, U.S.A.

Nathaniel Anderson Rocky Mountain Research Station, USDA Forest Service, U.S.A.

William F. Anderson Crop Genetics and Breeding Research Unit, USDA Agricultural Research Service, U.S.A.

Tom Anthonis Centre of Expertise for Industrial Biotechnology and Biocatalysis, Faculty of Bioscience Engineering, Ghent University, Belgium

Stéphanie Arnoult Joint Research Unit INRA/USTL Abiotic Stress and Differentiation of Cultivated Plants (UMR SADV), Experimental Unit Crops Innovation Environment – Picardy (INRA EU GCIE Picardy), INRA (l'Institut National de la Recherche Agronomique), France

Nicolas Beaudoin Research Unit Agro resources and environmental impacts (INRA UR AgroImpact), INRA (l'Institut National de la Recherche Agronomique), France

Linda Bethencourt Joint Research Unit INRA/USTL Abiotic Stress and Differentiation of Cultivated Plants (UMR SADV), INRA (l'Institut National de la Recherche Agronomique), France

Hubert Boizard Research Unit Agro resources and environmental impacts (INRA UR AgroImpact), INRA (l'Institut National de la Recherche Agronomique), France

Antonio Bonomi Brazilian Bioethanol Science and Technology Laboratory (CTBE)/Brazilian Center of Research in Energy and Materials (CNPEM), Brazil

Maryse Brancourt-Hulmel Joint Research Unit INRA/USTL Abiotic Stress and Differentiation of Cultivated Plants (UMR SADV), Research Unit Agro resources and environmental impacts (INRA UR AgroImpact), INRA (l'Institut National de la Recherche Agronomique), France

Thomas Buchholz Gund Institute for Ecological Economics, University of Vermont, U.S.A., and Spatial Informatics Group, LLC, U.S.A.

Kara G. Cafferty Idaho National Laboratory, U.S.A.

Jesse Caputo College of Environmental Science and Forestry, State University of New York, U.S.A.

Michael Casler U.S. Dairy Forage Research Center, USDA Agricultural Research Service, U.S.A.

John S. Cundiff Biological Systems Engineering, Virginia Tech, U.S.A.

Michael W. Cunningham ArborGen Inc., U.S.A.

Camille Dauchy Joint Research Unit INRA/USTL Abiotic Stress and Differentiation of Cultivated Plants (UMR SADV), INRA (l'Institut National de la Recherche Agronomique), France

Adam Davis Global Change and Photosynthesis Research Unit, USDA Agricultural Research Service, U.S.A.

Charlotte Demay Research Unit Agro resources and environmental impacts (INRA UR AgroImpact), INRA (l'Institut National de la Recherche Agronomique), France

Sofie Dobbelaere Centre of Expertise for Industrial Biotechnology and Biocatalysis, Faculty of Bioscience Engineering, Ghent University, Belgium

Mark Eisenbies College of Environmental Science and Forestry, State University of New York, U.S.A.

Fabien Ferchaud Research Unit Agro resources and environmental impacts (INRA UR AgroImpact), INRA (l'Institut National de la Recherche Agronomique), France

Cornelia Butler Flora Harkin Institute, Iowa State University, U.S.A.

Henrique Continho Junqueira Franco Brazilian Bioethanol Science and Technology Laboratory (CTBE)/Brazilian Center of Research in Energy and Materials (CNPEM), Brazil

Marcelo Valadares Galdos Brazilian Bioethanol Science and Technology Laboratory (CTBE)/Brazilian Center of Research in Energy and Materials (CNPEM), Brazil

John Hogland Rocky Mountain Research Station, USDA Forest Service, U.S.A.

David R. Huggins Land Management and Water Conservation Research Unit, USDA Agricultural Research Service, U.S.A.

Sam W. Jackson Genera Energy, Inc, U.S.A.

Jacob J. Jacobson Idaho National Laboratory, U.S.A.

Douglas L. Karlen National Laboratory for Agriculture and the Environment, USDA Agricultural Research Service, U.S.A.

Robert Keefe Department of Forest, Rangeland and Fire Sciences, University of Idaho, U.S.A.

Andrzej Klasa Department of Agricultural Chemistry and Environmental Protection, Warmia and Mazury University in Olsztyn, Poland

Mark Laser Thayer School of Engineering, Dartmouth College, U.S.A.

D.K. Lee Department of Crop Sciences, University of Illinois, U.S.A.

Jihong Li MOST-USDA Joint Research Center for Biofuels, Institute of New Energy Technology, Tsinghua University, China

Shi-Zhong Li MOST-USDA Joint Research Center for Biofuels, Institute of New Energy Technology, Tsinghua University, China

Richard Lowrance Southeast Watershed Research Laboratory, USDA Agricultural Research Service, U.S.A.

Lee Lynd Thayer School of Engineering, Dartmouth College, U.S.A.

Rob Mitchell Grain, Forage, and Bioenergy Research Unit, USDA Agricultural Research Service, U.S.A.

Ken Muhlenfeld Southern Union Community College, U.S.A.

Leslie Ovard Biofuels and Renewable Energy Technologies, Idaho National Laboratory, U.S.A.

Sarita Cândida Rabelo Brazilian Bioethanol Science and Technology Laboratory (CTBE)/Brazilian Center of Research in Energy and Materials (CNPEM), Brazil

Edward P. Richard, Jr. Sugarcane Research Unit, USDA Agricultural Research Service, U.S.A.

William L. Rooney Department of Soil & Crop Sciences, Texas A&M University, U.S.A.

Emeline Rosiau Joint Research Unit INRA/USTL Abiotic Stress and Differentiation of Cultivated Plants (UMR SADV), Experimental Unit Crops Innovation Environment – Picardy (INRA EU GCIE Picardy), INRA (l'Institut National de la Recherche Agronomique), France

Mathew Smidt School of Forestry and Wildlife Sciences, Auburn University, U.S.A.

Wim Soetaert Centre of Expertise for Industrial Biotechnology and Biocatalysis, Faculty of Bioscience Engineering, Ghent University, Belgium

David B. South School of Forestry and Wildlife Sciences, Auburn University, U.S.A.

Bijay Tamang ArborGen Inc., U.S.A.

Jaya Shankar Tumuluru Biofuels and Renewable Energy Technologies, Idaho National Laboratory, U.S.A.

Timothy A. Volk College of Environmental Science and Forestry, State University of New York, U.S.A.

Kelly D. Zering Department of Agricultural and Resource Economics, North Carolina State University, U.S.A.

1

Introduction to Cellulosic Energy Crops

Mark Laser and Lee Lynd

Thayer School of Engineering, Dartmouth College, U.S.A.

1.1 Cellulosic Biomass: Definition, Photosynthesis, and Composition

Plants, through photosynthesis, convert solar energy, carbon dioxide, and water into sugars and other derived organic materials, referred to as biomass, and release oxygen as a by-product. Humans have long used plant biomass for a variety of applications, such as fuel for warmth and cooking, lumber and other building materials, textiles, and papermaking. More recently, plant biomass has been considered as a feedstock for biofuels production – the focus of this book – with first-generation fuels being made from edible portions of plants, including starch, sucrose, and seed oils. Next-generation biofuels will be produced from non-edible cell wall components (described below) that comprise the majority of plant biomass.

Photosynthesis consists of two stages: a series of light-dependent reactions that are independent of temperature (light reactions) and a series of temperature-dependent reactions that are independent of light (dark reactions). The light reactions convert light energy into chemical energy in the form of adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH). The dark reactions, in turn, use the chemical energy stored in ATP and NADPH to convert carbon dioxide and water into carbohydrate.

About half of the light energy falls outside the photosynthetically active spectrum; some of the available energy is reflected away and not captured. Further energy is lost during the light absorption process, and during carbohydrate synthesis and respiration. As a result, photosynthesis typically converts less than 1% of the available solar energy into chemical energy stored in the chemical bonds of the structural components of biomass [1].

Plants have evolved three photosynthetic pathways, each in response to distinct environmental conditions. One is called the C3 pathway because the initial product of carbon fixation is a three-carbon compound (phosphoglyceric acid, or PGA). When carbon dioxide levels inside a leaf become low, especially on hot dry days, a plant is forced to close its stomata (microscopic pores on the surface of land plants) to prevent excess water loss. If the plant continues to fix carbon when its stomata are closed, carbon dioxide is depleted and oxygen accumulates in the leaf. To alleviate this situation, the plant uses a process called photorespiration in which a molecule ordinarily used in carbon fixation (ribulose-1,5-bisphosphate, or RuBP) combines instead with oxygen, catalyzed by the enzyme RuBisCO, which also figures prominently in carbon fixation. This reduces photosynthetic efficiency in two ways: firstly, it creates competition between oxygen and carbon dioxide for the active sites of RuBisCO – sites that take up oxygen are not available for carbon dioxide; secondly, the process re-releases carbon dioxide that had been fixed. Photorespiration reduces photosynthetic efficiency by 35–50%, depending upon environmental conditions, with warm, arid habitats promoting greater photorespiration [1].

In response, many plant species in warm, dry climates have evolved two alternative photosynthetic pathways – the C4 pathway and crassulacean acid metabolism (CAM) photosynthesis, both of which significantly reduce photorespiration and enhance efficiency. Both convert carbon dioxide into a four-carbon intermediate using the enzyme phosphoenolpyruvate (PEP) carboxylase – which does not react with oxygen – rather than RuBisCO. C4 plants fix carbon dioxide during the day; CAM plants, to keep stomata closed during the day, fix carbon dioxide at night [2].

The highest reported solar energy conversion efficiency is about 2.4% for C3 plants and 3.7% for C4 species [3]. CAM plants are estimated to be 15% more efficient than C3 plants, but 10% less efficient than C4 plants [4]. Zhu et al. [3] estimate the theoretical maximum efficiency to be 4.6 and 6% for C3 and C4 crops, respectively. The C3 pathway is the oldest – originating around 2800 million years ago – and most widespread, both taxonomically and environmentally, accounting for about 95% of total plant species [5]. C4 photosynthesis is found in about 1% of plant species [5] and is most prevalent in grasses, with about 50% of the species using the pathway [6]. CAM occurs in about 4% of total plant species [5].

The energy crops considered in this volume all have either a C3 or C4 photosynthetic pathway. They include:

C3 pathway: wheat straw, eucalyptus, poplar, willow, pineC4 pathway: miscanthus, switchgrass, sugarcane, energy cane, sorghum, corn stover.

Though not considered here, examples of potential energy crops having the CAM pathway include agave and opuntia. More detailed treatments of photosynthesis are available elsewhere [2,7].

Each of the above plant species contains cellulosic biomass, that is, the fibrous, generally inedible portions of plants, rich in the polysaccharide cellulose, which make up the majority of all plant material. Cellulosic biomass can generally be grouped into four categories: herbaceous plants, woody plants, aquatic plants, and residual material such corn stover, sugarcane bagasse, paper sludge, and animal manure. Terrestrial cellulosic energy crops and agricultural crop residues are the primary focus of this book.

Cellulosic biomass contains varying amounts of cellulose, hemicellulose, lignin, protein, ash, and extractives. Cellulose, a structural component of the primary cell wall in plants, generally comprises the largest fraction, with 40–50% on a dry weight basis being typical. The material is a polymer of glucose, a six-carbon sugar, joined by 1–4 beta-linkages. Linear cellulose chains, which have an average molecular weight of about 100 000, are generally arrayed in parallel and held together with extensive hydrogen bonding forming macromolecular fibers 3–6 nm in diameter called microfibrils. The material is well ordered, largely crystalline, and highly recalcitrant to rapid reaction under many conditions.

Hemicellulose, another polysaccharide – one that binds tightly, but non-covalently, to the surface of each cellulose microfibril – usually comprises 20–35% of the dry mass of biomass. In contrast to cellulose, hemicellulose is composed of multiple sugars – the identity and proportion of which depend on the type of plant – and has a heterogeneous, non-crystalline branched structure. As a result, hemicellulose is generally more reactive than cellulose and is readily hydrolyzed by dilute acid or base as well as hemicellulase enzymes. Xylose, a five-carbon sugar, is the dominant constituent of hemicellulose in plants other than softwoods; for softwoods, mannose is often the most abundant sugar.

Lignin is an amorphous polymer of phenyl–propane subunits (six-carbon rings linked to three-carbon chains) joined together by ether and carbon–carbon linkages, and covalently bound to hemicellulose. The subunits may have zero, one, or two methoxyl groups attached to the rings, giving rise to three structures – denoted I, II, and III, respectively. The proportions of each structure depend on the plant type. Structure I is commonly found in grasses, structure II in softwoods, and structure III in hardwoods. Lignin both creates a net around carbohydrate-rich microfibrils in plant cell walls and penetrates the interstitial space in the cell wall, driving out water and strengthening the wall. The dry mass fraction of lignin in plants typically ranges from 7–30%. Leafy herbaceous plants are generally at the low end of this range, woody plants at the high end, with softwoods having more lignin than hardwoods.

Smaller amounts of protein and minerals are also present in plant tissues. As plants mature, wall composition shifts from moderate levels of protein and almost no lignin to very low concentrations of protein and substantial amounts of lignin. Protein content can be significant (e.g. 10% dry mass) in early-season herbaceous crops, but is relatively low in late-season harvests and minimal in most woody crops.

Plants require a variety of inorganic minerals for proper growth, including both macronutrients (N, P, K, Ca, S, Mg) and micronutrients, or trace elements (B, Cl, Mn, Fe, Zn, Cu, Mo, Ni, Se, Na, Si). Plant roots, mediated by transport proteins, absorb mineral nutrients as ions in soil water. Each mineral participates in distinct biological functions within the plant. Nitrogen, for example, is involved in all aspects of plant metabolism, with its foremost function being to provide amino groups in amino acids, the building blocks of every protein. Potassium, meanwhile, is essential for activating a multitude of enzymes, including pyruvate kinases involved in glycolysis, and is one of the most important contributors to cell turgidity in plants. Another vital macronutrient, calcium, is essential for providing structure and rigidity to cell walls, and is used as a signaling compound in response to mechanical stimuli, pathogen attack, temperature shock, drought, and changes in nutrient status. When plant biomass is converted to fuels, chemicals, electricity, and/or heat, inorganic minerals remain as ash, with the amount residual ash being dependent upon plant species. Herbaceous plant species typically have higher levels of ash (e.g. 5–10% dry mass) than do woody species (<2% dry mass).

The term “extractives” is also commonly used when characterizing the composition of plant biomass. Extractives are materials in the biomass that can be dissolved in a solvent (typically water and/or ethanol), including resins, fats and fatty acids, phenolics, phytosterols, salts, minerals, soluble sugars, and other compounds.

More detailed consideration of the composition of cellulosic biomass can be found elsewhere [8,9]. Representative compositions for many of the biomass crops considered in subsequent chapters are listed in Table 1.1.

Table 1.1 Representative compositions, proximate analysis, ultimate analysis, and energy density for several lignocellulosic feedstocks.

1.2 Cellulosic Biomass Properties and Their Relevance to Downstream Processing

The choice of biomass feedstock is a critical driver in determining key performance metrics of bioenergy – including economic viability, scale of production (both at individual facilities and in aggregate), and environmental impact. For commodities such as fuels or electricity, feedstock cost typically represents two-thirds of the product cost, or more [26]; therefore, selecting a cost-effective feedstock is essential. As is discussed in Part IV of this book, the logistics of growing, harvesting, storing, and transporting biomass – unique for a given feedstock type – affects the feasible size of the processing facility, which, in turn, impacts the overall sector scale. Each feedstock also has a particular set of environmental attributes – for example, water use, wildlife habitat, soil quality, and so on – that significantly affects the environmental performance of the bioenergy system.

In assessing the suitability of a biomass feedstock for a given conversion process, several material properties are important to consider, including: (1) moisture content; (2) energy density; (3) fixed carbon/volatile matter ratio; (4) ash content; (5) alkali metal content; and (6) carbohydrate/lignin ratio. The first five properties are especially important in thermochemical processing. For biological conversion, the first and last properties are of primary concern.

1.2.1 Moisture Content

Biomass moisture content is defined as the amount of water in the biomass expressed as a percentage of the material's weight; reporting on a wet basis is most common. Moisture content at harvest for woody feedstocks is usually 40–60% (wet basis); for herbaceous crops, it typically ranges from 10 to 70% (wet basis) depending upon the species, climate, geographic location, and stage of maturation. Biomass net energy density per unit mass decreases with increasing moisture content. Transport efficiency of biomass feedstock, therefore, decreases as moisture content increases. Storage of high-moisture biomass is also less efficient, both because of reduced energy density and increased probability of biological degradation, fire risk, and mold formation. Moisture content also affects downstream processing, especially for thermochemical conversion. High-moisture feedstocks must be dried to levels of less than 50% for conventional combustion and less than 20% for gasification and pyrolysis. In biological processing for which some form of thermal pretreatment is used, moisture content can also significantly affect the energy efficiency of the process.

1.2.2 Energy Density

Energy density, often termed “heating value”, refers to the amount of energy released per unit fuel combusted, usually measured in terms of energy content per unit mass for solids (e.g. MJ/kg) and per unit volume for liquids (e.g. MJ/l). Energy density can be expressed in two forms, higher heating value (HHV) or lower heating value (LHV). HHV represents the total energy released when the fuel is combusted in air, including the latent heat contained in the resulting water vapor product – the maximum potentially recoverable energy from a given feedstock. The latent heat contained in the water vapor, however, typically cannot be used effectively. LHV, therefore, is the appropriate value to use when quantifying the energy available for subsequent use. As noted above, moisture content significantly affects biomass feedstock energy density. Freshly cut wood, for example, might have as much as 60% moisture and a relatively low energy content (e.g., 6 MJ/kg). In contrast, oven-dried wood with little moisture might have up to 18 MJ/kg. Representative LHV values for many of the biomass crops considered in subsequent chapters are listed in Table 1.1.

1.2.3 Fixed Carbon/Volatile Matter Ratio

Fuel analysis that quantifies the amount of chemical energy stored as volatile matter (VM) and fixed carbon (FC) has been developed for solid fuels such as coal. The VM of a solid fuel is the portion released as gas (including moisture) by heating to 950°C in the absence of air for seven minutes; the FC is the mass remaining after the volatiles have been driven off, excluding the ash and moisture contents. Fuel analysis based upon VM content, ash, and moisture, with the FC determined by difference, is termed the proximate analysis of a fuel. Elemental analysis of a fuel, presented as C, N, H, O and S, together with the ash content, is termed the ultimate analysis of a fuel. The ratio of FC to VM provides an indication of the ease with which the solid fuel can be ignited and subsequently gasified, or oxidized, depending on how the fuel is to be converted. Representative proximate and ultimate analyses for many of the biomass crops considered in subsequent chapters are listed in Table 1.1.

1.2.4 Ash Content

Conversion of biomass feedstock, either thermochemically or biochemically, results in a solid residue. In themochemical processing via combustion in air, the residue consists solely of ash. For biochemical processing, it contains both ash and other unconverted material, especially lignin. The bioprocess residue can be further processed thermochemically to yield ash as the final solid residue. The ash content negatively affects the energy density of the feedstock. Ash can also pose operational problems in thermochemical processing, such as slagging in which the ash melts and fuses together. Relatively low-cost control measures, such as leaching the raw feedstock with water and using different mineral additives (e.g. kaolinite, clinochlore, ankerite), can be used to reduce negative effects [27]. Potential end uses of ash include mineral agricultural fertilizer [28] and construction material additive [29]. Representative ash content values for many of the biomass crops considered in subsequent chapters are listed in Table 1.1. As can be seen from the table, herbaceous feedstocks tend to have higher ash contents (e.g. ≥5%) than woody feedstocks (e.g. <2%).

1.2.5 Alkali Metal Content

During thermochemical conversion, alkali metals (Na, K, Mg, P, Ca) present in the ash react with silica – originating both from the biomass itself and from soil introduced during harvesting – to produce a sticky, mobile liquid phase that can contribute to slagging, deposition, and corrosion of process equipment. As noted above, water leaching and fuel additives can be used to reduce the damaging effects of ash components, including alkali metals.

1.2.6 Carbohydrate/Lignin Ratio

In biological processing, carbohydrate present in cellulose (and potentially hemicellulose) is converted to fuels and/or chemicals, while the lignin fraction remains unaffected. Furthermore, the recalcitrance of cellulosic biomass to bioconversion typically increases with increasing lignin content, requiring more severe pretreatment, which decreases process efficiency. Bioconversion processes, therefore, favor feedstocks with high carbohydrate to lignin ratios. Representative cellulose, hemicellulose, and lignin values for many of the biomass crops considered in subsequent chapters are listed in Table 1.1.

1.3 Desirable Traits and Potential Supply of Cellulosic Energy Crops

Given the world's finite land resource, the most important trait for cellulosic energy crops is productivity – the annual dry matter produced per unit land area. As listed in Table 1.1, productivity of the crops considered in this book ranges from 0.1 to 1.75 Mg/ha/yr (dry basis) for wheat straw, to as high as 44 Mg/ha/yr (dry basis) for miscanthus. The best energy crops will also have few inputs and low production costs. Easily established, robust perennial crops having long life spans (e.g. ≥10 years) are favored over annual crops, as are those having low fertilizer, pesticide, and insecticide requirements. Native, non-invasive species that provide good habitats for wildlife are preferred.

Feedstocks used in thermochemical processing should be harvested when moisture content is relatively low to minimize preliminary energy intensive drying. Low moisture is not as critical in bioconversion feedstocks, for which wet storage can sometimes be a viable option. Ideally, ash content should be low (e.g. <1%), ash melting temperatures should be high (e.g. >1500°C), with low levels of particularly damaging elements, including alkali metals, alkaline earth metals, silicon, chlorine, and sulfur.

Conventional plant breeding – which involves manipulating the genes of a species via selection and hybridization so that desired genes are packaged together in the same plant and as many detrimental genes as possible are excluded – has traditionally been used to enhance desired agronomic traits such as productivity, water use efficiency, and crop lifespan. Breeding systems have been developed, and continue to be developed, that can be used to improve virtually all plant species. The productivity of corn, for example, has more than quadrupled since the 1930s largely through conventional breeding [30]. Biomass productivity can potentially be increased even further using more sophisticated biotechnology techniques. Recent molecular and genetic studies have identified a number of regulators of plant biomass production – for example, vegetative meristem activities, cell elongation, photosynthetic efficiency, and secondary wall biosynthesis – that might be manipulated to enhance energy crop yields [31].

The potential to produce viable energy feedstocks is vast. A detailed study led by the Oak Ridge National Laboratory estimates that the United States could produce 602–1009 million dry tons annually by 2022, and 767–1305 million annual dry tons by 2030, at a price of $60 per dry ton [32]. (The low value in the range assumes a 1% annual increase in yield; the high value, a 4% annual increase.) This excludes resources that are currently being used, such as corn grain and forest products industry residues. When currently used resources are included, the total biomass estimate jumps to over one billion dry tons per year for the lower productivity case – enough to displace about half of the country's current gasoline consumption (134 billion gallons/year) if converted to ethanol at a yield of 100 gallons/dry ton. Estimates for the global annual supply of biomass feedstocks range from 100 to 400 EJ/year – equivalent to 6 to 24 billion dry tons. If converted to ethanol, this represents 120–460% of current global gasoline consumption (338 billion gallons/year).

1.4 The Case for Cellulosic Energy Crops

With ever-increasing indications that resource use is exceeding the planet's biocapacity [33] – largely driven by non-renewable fossil fuel consumption – it is clear that humankind must shift to sustainable practices in order for a peaceful, equitable, and thriving future to be possible. Furthermore, given mounting evidence of climate change – to the point that some say we are now living in a new geologic epoch, the Anthropocene [34] – this transformation must begin now and be completed within decades, not centuries. Indeed, it is fair to characterize this transition, moving from finite resource capital to renewable resource income, as the defining challenge of our time.

Most sustainable paths from primary resources to human needs pass through either plant biomass or renewable electricity, with biomass being the only foreseeable source of organic fuels, chemicals, and materials, as well as food. In comparison, other large-scale sustainable energy sources are most readily converted to electricity and heat. Because liquid organic fuels have a greater energy density than batteries, both today and with anticipated improvements in battery technology, it is reasonable to expect that organic fuels will meet a significant fraction of transportation energy demand for the indefinite future. This is particularly true for long-distance travel via personal vehicles and for heavy-duty applications, such as aviation and long-haul trucking, which account for more than half of global transportation energy [35]. Biofuels would, therefore, appear to be an essential component of tomorrow's sustainable world rather than a discretionary option.

Cellulosic biomass energy potentially offers many environmental benefits that contribute to its sustainability, some of which are:

Fossil fuel displacement.Lower emissions of greenhouse gases and other air pollutants.Enhanced soil quality.Reduced soil erosion.Reduced nutrient run-off.Enhanced biodiversity.

Demirbas [36], Rowe et al. [37], Arjum [38], and Skinner et al. [39] provide more detailed reviews and discussion of these and other potential benefits.

In addition to the environment, cellulosic biomass energy also has the potential to enhance energy security and rural economic development. Nations dependent upon petroleum face increasing security costs to ensure the steady supply of oil. The United States, for example, according to the RAND Corporation [40], spends about $75.5–93 billion per year – representing between 12 and 15% of its current defense budget – to secure the supply and transit of oil. Furthermore, major oil supplying countries hold leverage over nations relying upon imports, as the oil producers control price stability. This directly affects foreign policy, forcing import nations to prioritize stability over values such as democracy, transparency, and human rights. Even if a country could produce 100% of the oil it uses, its consumers would still be vulnerable to global price fluctuations based on supply disruptions in unstable regions. Beyond consumerism, modern militaries invest for the long term – new airplanes, ships, and vehicles are expected to last decades. This requires alternative energy sources to be able to accommodate infrastructure that is likely to be in place for years.

In recognition of this, the United States Department of Defense has developed an alternative fuels policy to “ensure operational military readiness, improve battle space effectiveness,” and increase “the ability to use multiple, reliable fuel sources [41].” Consistent with this, the US Navy has plans to deploy a “Great Green Fleet” strike group of ships and aircraft running entirely on alternative fuel blends – including cellulosic fuels – by 2016 [42]. It also has a goal of meeting 50% of its total energy consumption from alternative sources by 2020. To help enable these goals, the Navy – together with the Departments of Energy and Agriculture – signed a Memorandum of Understanding (MOU) to “assist the development and support of a sustainable commercial biofuels industry [43].” The MOU calls for $510 million in funding over three years to develop advanced biofuels that meet military specifications, are price competitively with petroleum, are at geographically diverse locations with ready market access, and have no significant impact on the food supply.

A cellulosic biofuels industry, by generating demand for agricultural products, has the potential to significantly increase employment in rural areas in sectors ranging from farming to feedstock transportation to plant construction and operation. Workers would be required in a variety of occupations, including: scientists and engineers conducting research and development; construction workers building plants and maintaining infrastructure; agricultural workers growing and harvesting energy crops; plant workers processing feedstocks into fuel; and sales workers selling the biofuels. Brazil's sugar/ethanol industry directly employs about 489 000 workers, with an additional 511 000 workers engaged in supporting agricultural activities [44]; the United States corn ethanol industry directly employs about 400 000 [45]. A study forecasting the impact of advanced biofuels on the US economy estimates that the industry could create over 800 000 jobs by 2022 [46].

Cellulosic biofuels also have the potential to promote rural economic activity within developing nations and improve the lives of the world's poor. Farmers would have increased demand for their products, including crop residues from existing crops, and employ additional workers to produce the energy feedstocks. They would also be able to make use of degraded or marginal land not suitable for food production. Care must be taken, however, to include small landholders in the sector's development and to adequately invest in local workforce training for feedstock production, production facilities construction, and process operation. In addition, to the extent possible, the sector should be developed around existing industries, such as sugarcane processing, to lower investment barriers [47]. Also, selection of feedstock supply chains that do not compromise food security is critical. Significant potential exists to actually enhance food security through bioenergy production – by using inedible crops grown on marginal land, for example, or integrating production of food, animal feed, and bioenergy. One can envision many benefits that might be realized: employment and development of marketable skills; introduction of agricultural infrastructure and knowledge; energy democratization, self-sufficiency, and availability for agricultural processing; and an economically rewarding way to restore degraded land. Bioenergy could potentially improve both food security and economic security for the rural poor [48].

Such benefits, however, are by no means guaranteed. The environmental impact of biomass energy very much depends upon how the given system is designed and implemented. Detractors of bioenergy have called into question its sustainability, citing a number of concerns, including:

Food versus fuel.Land use change (direct and indirect).Water use.Invasive species.Biodiversity.

This productive debate has prompted an expanding literature analyzing and discussing the keys to “getting biofuels right,” so that the promise of sustainable bioenergy can be realized [49–51]. To minimize both competition with food production and land use change effects, multiple classes of feedstocks are available, including energy crops grown on abandoned agricultural lands; food crop residues such as corn stover and wheat straw; sustainably harvested forest residues; double crops grown between the summer growing seasons of conventional row crops; mixed cropping systems in which food and energy crops are grown simultaneously; municipal and industrial wastes; and harvesting invasive species for bioenergy [49,50,52–54]. Water use can be minimized by selecting crops having low irrigation requirements, by using non-potable sources such as wastewater or high-saline water for any necessary irrigation [55,56], and using subsurface drip irrigation to minimize evaporative losses [57]. The potential for non-native energy crops becoming invasive can be limited by proper preliminary risk assessment, including test plots [58], regular monitoring and stewardship programs [59], and by using sterile plant varieties [60]. The impact of a given energy crop upon biodiversity depends strongly on specific regional circumstances, the type of land and land use shifts involved, and the associated management practices [61]. Herbaceous perennial crops, in particular, appear to be capable of providing suitable habitats for a variety of species, especially with careful attention to crop placement and when mixed cultures are used [62–65]. By incorporating many of the above strategies, Dale et al. [51] calculated that, using the 114 million hectares of cropland currently allocated in the United States for animal feed, corn ethanol, and exports, 400 billion liters of cellulosic ethanol (80% of current gasoline demand) could be made – all while producing the same amount of food. In summarizing their findings, the authors write:

Our analysis shows that the U.S. can produce very large amounts of biofuels, maintain domestic food supplies, continue our contribution to international food supplies, increase soil fertility, and significantly reduce GHGs. If so, then integrating biofuel production with animal feed production may also be a pathway available to many other countries. Resolving the apparent “food versus fuel” conflict seems to be more a matter of making the right choices rather than hard resource and technical constraints. If we so choose, we can quite readily adapt our agricultural system to produce food, animal feed, and sustainable biofuels.

Any human activity involving new technology can potentially be harmful if not thoughtfully planned and appropriately conducted. The early-generation Altamont Pass wind farm in California, for example, unwittingly located on a major bird migratory route, results in thousands of bird deaths every year [66]. To remedy the problem, the farm's owners are installing new, less destructive turbines and shutting down a significant fraction of the turbines during the migration season [67]. In the case of cellulosic biomass, if care is taken to address the key concerns noted above, the resource could very likely contribute substantially – indeed, uniquely and essentially, by accommodating energy services not easily met by other means – towards achieving a sustainable global energy future. Kline et al. [50] succinctly capture the promise of this vision:

When biofuel crops are grown in appropriate places and under sustainable conditions, they offer a host of benefits: reduced fossil fuel use; diversified fuel supplies; increased employment; decreased greenhouse gas emissions; enhanced habitat for wildlife; improved soil and water quality; and more stable global land use, thereby reducing pressure to clear new land.

This book – through detailed consideration of cellulosic energy crop production; the logistics of feedstock harvest, storage, and transport; and commercial deployment that is mindful of economic, environmental, and social concerns – seeks to disseminate knowledge that can help make large-scale, sustainable bioenergy a reality.

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