EPA/600/R-12/709
October 2013
A Review of Life-Cycle Based Tools
Used to Assess the Environmental Sustainability of
Biofuels in the United States
Mary Ann Curran, Ph.D.
Life Cycle Assessment Research Center
U.S. Environmental Protection Agency
Cincinnati, Ohio, 45268
Final Report
October 22, 2013
Systems Analysis Branch
Sustainable Technology Division
National Risk Management Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio, 45268
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Disclaimer
The material in this document has been subject to Agency technical and policy review, and
approved for publication as a U.S. Environmental Protection Agency product. The views
expressed by the author, however, are her own, and do not necessarily reflect those of the U.S.
Environmental Protection Agency. Mention of trade names, products, or services does not
convey, and should not be interpreted as conveying, official EPA approval, endorsement, or
recommendation.
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Foreword
The U.S. Environmental Protection Agency (EPA) is charged by Congress with protecting the
Nation's land, air, and water resources. Under a mandate of national environmental laws, the
Agency strives to formulate and implement actions leading to a compatible balance between
human activities and the ability of natural systems to support and nurture life. To meet this
mandate, EPA's research program is providing data and technical support for solving
environmental problems today and building a science knowledge base necessary to manage our
ecological resources wisely, understand how pollutants affect our health, and prevent or reduce
environmental risks in the future.
The National Risk Management Research Laboratory (NRMRL) within the Office of Research
and Development (ORD) is the Agency's center for investigation of technological and
management approaches for preventing and reducing risks from pollution that threaten human
health and the environment. The focus of the Laboratory's research program is on methods and
their cost-effectiveness for prevention and control of pollution to air, land, water, and subsurface
resources; protection of water quality in public water systems; remediation of contaminated
sites, sediments and ground water; prevention and control of indoor air pollution; and
restoration of ecosystems. NRMRL collaborates with both public and private sector partners to
foster technologies that reduce the cost of compliance and to anticipate emerging problems.
NRMRL's research provides solutions to environmental problems by: developing and promoting
technologies that protect and improve the environment; advancing scientific and engineering
information to support regulatory and policy decisions; and providing the technical support and
information transfer to ensure implementation of environmental regulations and strategies at the
national, state, and community levels.
This publication has been produced as part of ORD's strategic research plan. It is published and
made available to assist the user community and to link researchers with their clients. The
production, distribution, and use of biofuels have been analyzed in the literature using several
different life cycle assessment methodologies, leading to variant assessments. These literature
reports attempted to capture benefits and environmental impacts, sometimes even considering
sustainability considerations. The differences in the methodologies raised the question of gaps
that need to be filled for conducting useful life cycle analysis (LCA)-based assessment of
biofuels. This publication is such a gap analysis that points to development needs for satisfying
sustainability and regulatory concerns with respect to various different biofuels development
and their production, distribution and use. A peer-reviewed journal article derived from the data
and information in this report was published in the open literature (Curran MA (2012)
"Assessing Environmental Impacts of Biofuels Using Lifecycle-Based Approaches,"
Management of Environmental Quality: An InternationalJournal, Vol 24(1); 34 - 52). This
report is being made available to the user community by EPA's Office of Research and
Development as supplemental material.
Cynthia Sonich-Mullin, Director
Sally Gutierrez, Director 2004-2011
National Risk Management Research Laboratory
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Abstract
There is no simple answer to the question "are materials from bio-based feedstocks
environmentally preferable?" Bioenergy, as an alternative energy source, might be effective in
reducing fossil fuel use and dependence, slowing or reducing global warming effects, and
providing increased revenue for the farming community. But its production may also contribute
to environmental harm such as degraded soil and water quality. This brings into question how
we define and measure its sustainability.
The issue of environmental sustainability related to bio-based materials is a complicated one.
Achieving sustainability requires a re-thinking of our systems of production, consumption and
waste management and an increased awareness of the need to avoid the shifting of problems,
which often occurs with isolated measures. The environmental advantages should outnumber or
outweigh the disadvantages to the environment and human health. The benefits of bioenergy
have come under increasing scrutiny as researchers look closer at the global environmental
impact of their production. For example, increased demand for corn could result in diverting
corn supplies from making food and feed to making bioethanol, which could in turn affect the
production of competing crops such as soybean, or the conversion of lands to use for corn
production. The overall impacts of these types of shifts are not well understood. If used
properly, bioenergy can help the United States meet its needs while maintaining ample supplies
of food, animal feed, and clean water. To make this happen, well thought out national bioenergy
policies that support the best options are needed for both the short and long-term future.
Life Cycle Assessment (LCA) is a developing tool that can assist decision-makers in evaluating
the comparative potential cradle-to-grave, multi-media environmental impacts of their actions
in order to prevent unintended consequences. Some studies are called "life cycle analysis," but
focus on a particular issue or pollutant of concern such as greenhouse gas emissions or the net
energy gain or loss question. These focused studies fall short of a complete life cycle approach
that helps us recognize how our choices influence each point of the life cycle so that we can
balance potential trade-offs and avoid shifting problems from one medium to another and/or
from one life cycle stage to another.
This report explores how a systems thinking approach, such as LCA, can help decision-makers
view the potential "cradle-to-grave" environmental impacts of various types of biofuels and,
thereby, choose the most favorable options that will keep us on the path toward sustainability.
Ten tools that incorporate a life cycle perspective to evaluate biofuels were studied and
compared: Carbon Management, Ecological Footprint, Exergy Analysis, Fuel Cycle Analysis,
Greenhouse Gas Life Cycle Analysis, Life Cycle Assessment, Life Cycle Risk Assessment,
Material Flow Analysis, Net Energy Balance, and Sustainability Indicators. Discussion on data
and information needs is also provided.
IV
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Contents
Disclaimer ii
Foreword iii
Abstract iv
Acronyms and Abbreviations vii
1.0 Introduction 1
2.0 The Environmental Impacts of Biofuels 3
2.1 Fossil Fuel Use and Depletion 3
2.2 Net Energy Balance 3
2.3 Global Warming 4
2.4 Air Quality Concerns from Combustion in Vehicles 4
2.5 Land Use Impacts from Biofeedstock Supply 5
2.6 Food-for-Fuel 5
2.7 Soil Quality 5
2.8 Water Quality Impacts 6
2.9 Water Availability 6
2.10 Loss of Biodiversity 6
2.11 Introduction of Invasive Species 7
2.12 Socio-Economic Aspects 7
3.0 Life-Cycle Based Analytical Approaches and Tools Selected for Study 8
3.1 Carbon Management 13
3.2 Ecological Footprint 16
3.3 Exergy Analysis 18
3.4 Fuel Cycle Analysis 19
3.5 Greenhouse Gas Life Cycle Analysis 22
3.6 Life Cycle Assessment 25
3.7 Life Cycle Risk Assessment 29
3.8 Material Flow Analysis 32
3.8.1 Material Intensity per Service-Unit 34
3.9 Net Energy Balance 36
3.10 Sustainability Indicators 39
3.10.1 Roundtable on Sustainable Biofuels 39
3.10.2 Sustainability Interagency Working Group 40
4.0 Results 42
5.0 Discussion 45
5.1 Data and Information Needs 46
5.2 Environmental Data 46
5.2.1 Production Data 46
5.2.2 Water Use and Availability 47
5.2.3 Water Quality 47
5.2.4 Land Use Changes 47
5.2.5 Soil Erosion and Sedimentation 48
5.2.6 Human Health Effects 48
5.2.7 Biodiversity 49
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5.2.8 Invasive Species 49
5.2.9 Socio-Economic Impacts 49
6.0 Conclusions 50
7.0 References 51
Figures
Figure 1. Generic Stages of a Product Life Cycle (arrows represent transportation) 8
Figure 2. The Locations of Ethanol Biorefmeries in the United States as of June 2008 12
Figure 3. Flows of Exergy Associated with the Annual Production of Bioethanol from One
Hectare of Corn (GJ ha"1 • yr"1) 18
Figure 4. ED-DuPont Nano Risk Framework 29
Figure 5. Framework for Conducting a Comprehensive Environmental Assessment 30
Figure 6. Aggregate Material Flow Accounting (MFA) Indicators 33
Figure 7. Materials Consumption in the United States by Sector of Origin, 1975-2000 34
Tables
Table 1. Commonly Perceived Environmental and Socioeconomic Pros and Cons of Biofuel
Production and Use Compared to Conventional Gasoline as Observed by the
Author 2
Table 2. Life-Cycle Based Approaches and Tools Used to Evaluate Biofuels 9
Table 3. Draft Sustainability Criteria Developed by the National Biomass R&D Board for
U.S. Biofuels 40
Table 4. The Information or Data Typically Generated by Life-cycle Based Assessment
Approaches Mapped Against Commonly Reported Environmental Concerns
Related to Bio-based Products 44
VI
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Acronyms and Abbreviations
AFOLU Agriculture, Forestry and Other Land Uses
Btu British Thermal Unit
CEA Comprehensive Environmental Assessment
CED Cumulated non-renewable Energy Demand
CH4 Methane
CFIP Combined Heat and Power
CO Carbon Monoxide
CO2 Carbon Dioxide
DDGS Distillers' Dried Grains with Solubles
DOE U.S. Department of Energy
E85 Automotive fuel that is 85% ethanol and 15% gasoline
EBAMM ERG Biofuel Analysis Meta-Model
EC European Commission
EIA Energy Information Administration
EISA Energy Independence and Security Act of 2007
EPA U.S. Environmental Protection Agency
ETOX Ecotoxicity
EU European Union
GHG Greenhouse Gas
GREET Greenhouse gases, Regulated Emissions, and Energy use in Transportation
GWP Global Warming Potential
IPCC Intergovernmental Panel on Climate Change
J Joule
LCA Life Cycle Assessment
LCI Life Cycle Inventory
LCRA Life Cycle Risk Assessment
LLNL Lawrence Livermore National Laboratory
LUC Land Use Change
MAIA Material Intensity Assessment
MIPS Material Intensity Per Service unit
MFA Material Flow Analysis, or Material Flow Accounting
MOVES Motor Vehicle Emission Simulator
MTBE Methyl Tertiary-Butyl Ether
N2O Nitrous Oxide
NAS National Academy of Sciences
NEB Net Energy Balance
NEV Net Energy Value
NRMRL National Risk Management Research Laboratory
NOx Nitrogen oxides
RFS Renewable Fuel Standard
SO2 Sulfur Dioxide
TMR Total Material Requirement
UNESCO United Nations Educational, Scientific and Cultural Organization
USDA U.S. Department of Agriculture
WBCSD World Business Council for Sustainable Development
WRI World Resources Institute
WWF World Wide Fund for Nature (formerly the World Wildlife Fund)
vii
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1.0 Introduction
Energy supplies in the world are dominated by fossil fuels (80%) with biomass resources
providing 10-15% of global energy demand (approximately 500 quadrillion Btu) over the
next several years (U.S. Department of Energy 2009). In order to increase the use of bio-
based energy, policy drivers are being promoted by governments in the United States, the
European Union (EU), and around the globe. The 2003 EU directive on "biofuel and other
renewable fuels" states that 2% of the fuels for transportation should be biofuels by the end of
2005, and 5.75% by the end of 2010. In the United States, President Bush signed into law the
Energy Independence and Security Act of 2007 (EISA), which requires biofuel production to
increase ninefold by 2022 in order to meet the renewable fuel standard for gasoline.
However, these types of policies were originally formed on the notion that fuels are either
renewable or non-renewable; that is, they are viewed as either good or bad (EISA later
included greenhouse gas emission threshold requirements and the EU added sustainability
and greenhouse gas criteria.)
The word "biofuel" covers a variety of products with many different characteristics and a
wide range of potential GHG savings as well as other environmental impacts. Accordingly,
each biofuel must be assessed on its own merits. Of course, the specific advantages and
disadvantages vary depending on whether one is considering biofuels from a cultivated
feedstock (e.g., corn), from a waste material (e.g., corn stover), from a lower maintenance
source (e.g., perennial grasses), or from other next generation feedstocks (e.g., algae).
Careful analysis shows that different biofuels rely on different non-renewables to varying
extents. Furthermore, issues of sustainability and environmental concerns have been raised in
response to the wide-scale production and use of conventional biofuels. For example, corn
grain and soybean production practices are associated with high rates of fertilizer and
pesticide use, extensive water consumption in some regions, and many deleterious
environmental effects such as soil erosion, surface water pollution, air pollution, and
biodiversity losses (Williams, Inman et al. 2009). The issue of environmental impacts related
to bio-based materials, including biofuels, is a complicated one. There is a need to have
appropriate metrics for renewable-based technologies in order to better assess their overall
sustainability.
The environmental and socioeconomic pros and cons of biofuels are readily available in the
open literature (i.e., published reports and on the Internet). At the national, regional and
global levels, three main drivers for the development of bioenergy and biofuels seem to
emerge: climate change, energy security and rural development. The full picture, however, is
much more complex as biofuels differ widely in environmental, social, and economic impacts.
These impacts can occur throughout the life cycle, from the acquisition and processing of
feedstocks, to transport constraints, and air, water, and land quality issues. The overall merits
of biofuels are being openly debated, especially regarding the issue of whether biofuels have
a positive energy balance. The pros and cons held by the general public regarding the
advantages and disadvantages of biofuels are identified in Table 1.
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Table 1. Commonly Perceived Environmental and Socioeconomic Pros and Cons of Biofuel
Production and Use Compared to Conventional Gasoline as Observed by the Author
PROS
Use of renewable feedstocks
Net energy gain
Reduced greenhouse gas emissions
Reduction of imported crude oil
Increased National security
Rural development
Use of waste materials
Corn is a known commodity
CONS
Energy intensive production
Land conversion effects
Food for fuel tradeoff
Increased soil erosion
Runoff of agrochemicals to water
Use of limited water supplies
Threatened and endangered species
Lower energy content
Introduction of invasive species
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2.0 The Environmental Impacts of Biofuels
Public awareness has increased as consumers have become more knowledgeable of the fact
that it is not only the end product, but also the manufacture of biofuels that needs to be
investigated. The following subsections contain brief descriptions of the various global and
regional considerations (from Table 1) that have been drawing attention to discussions about
increasing the production and use of biofuels.
2.1 Fossil Fuel Use and Depletion
The world consumes over 85 million barrels of liquid fuels per day, with the United States
alone consuming over 18 million barrels per day (EIA 2010). Over half of the world's proved
oil reserves are located in the Middle East. How much recoverable crude oil is available is
never precisely known; current estimates range from 1,184 to 1,342 billion barrels (EIA
2010). The debate continues over whether proven world oil reserves can meet increasing
demand.
A reduction in the level of end-use consumption of petroleum is the overarching goal of
biofuel promotion. At the national level, countries are striving to reduce their dependence on
oil from foreign sources. Substituting fossil-based feedstocks with domestic (home-grown)
bio-based feedstocks to produce fuels is one way to accomplish this goal (alternate energy
sources, such as solar cells, and reduced energy demand are other ways).
2.2 Net Energy Balance
Much attention has been given to determining if the manufacture and use of biofuels is a net
gain or a net loss when compared to gasoline. The Net Energy Balance (NEB) of a fuel is
calculated by taking the amount of energy contained in the fuel (a gallon of ethanol contains
roughly 76,000 Btu) and subtracting the amount of energy that goes into its production.
Critics have argued that the net energy gain of the resulting ethanol fuel is modest because
large amounts of energy are required to grow corn and convert it to ethanol (Pimentel 2003).
Some have even calculated that it has a negative net energy value, meaning that ethanol
requires more energy to make than it actually produces. However, other researchers have
concluded that ethanol has a positive net gain (Patzek 2004). While the calculation of NEB
depends on many factors, such as how co-product energy credits are taken into account, the
majority of reports in the open literature indicate that corn-based ethanol provides more
energy than is required to make it, albeit to varying degrees (von Blottnitz and Curran 2007).
Corn farmers using state-of-the-art, energy efficient farming techniques and ethanol plants
integrating state-of-the-art production processes can double the amount of energy contained
in a gallon of ethanol and the by-products compared to the energy needed to grow and
convert the corn into ethanol. Further, as the ethanol industry expands, it may increasingly
rely on more abundant and potentially lower-cost cellulosic crops (i.e., fast growing trees,
grasses, etc.). When that occurs, the net energy of producing ethanol will become even more
attractive (Lorenz and Morris 1995). NEB, however, continues to be one of the most
controversial issues related to bioethanol.
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2.3 Global Warming
Focusing on the greenhouse gas (GHG) carbon dioxide^ using fossil fuels releases carbon that
has been stored underground for millions of years and results in a net addition of CO2 to the
atmosphere. Meanwhile, the argument has been made that biofeedstocks do not add CO2 to
the atmosphere; their use simply recycles what was already there. The Intergovernmental
Panel on Climate Change (IPCC) guidelines instruct that CO2 emissions from biomass (called
biogenic CO2) that are used for energy and fuels be excluded from the total CO2 emissions
figure, that is, they are, in effect, reported as zero, as long as the biomass is grown
sustainably. However, net CO2 emissions are covered in the AFOLU (Agriculture, Forestry
and Other Land Uses) Sector, which considers land use changes (IPCC 2006). Furthermore,
because it takes fossil fuels, such as natural gas and coal, to make biofuels, they are not quite
"carbon neutral."
Production is only part of the story. Engines running on either biofuels or gasoline emit
CO2 in the use phase. A number of recent studies have attempted to assess the total carbon
footprint of biofuels. While research by the USDA has shown that biofuels have the potential
to remove CO2 and other GHGs (such as nitrous oxide, N2O, methane, CH/t, and sulphur
hexafluoride, SF6) from the atmosphere (USDA 2007), others have concluded that the global
warming potential (GWP) of biofuels varies widely from being worse than gasoline to being
about the same (Fargione J, Hill J et al. 2008). This can be attributed to the formation of non-
CO2 global warming compounds. For example, researchers calculated that if new reactive
nitrogen enters the terrestrial biosphere, as when nitrogenous fertilizer is applied to a biofuel
(or any other) crop, then on average 3-5% of that nitrogen will appear in the atmosphere as
N2O. They theorize that this contribution explains the observed increase in the global
atmospheric concentration of N2O that has accompanied large-scale fertilizer nitrogen use
since the beginning of the 20th century (Crutzen, Mosier et al. 2007).
2.4 Air Quality Concerns from Combustion in Vehicles
The distinct dissimilarities in chemical and physical characteristics between the various
biofuels and conventional fossil fuels result in vehicle exhaust emissions that are significantly
different. Because biofuels are relatively new, many of the emission factors that are typically
used to estimate emissions from the combustion of fossil fuels should be re-analyzed for
biofuels. For example, formaldehyde and acetaldehyde emissions are suspected to be higher
from vehicles running on bioethanol (Poulopoulos, Samaras et al. 2001; Biello 2007).
Although formaldehyde and acetaldehyde are naturally occurring and found frequently
throughout the environment, additional emissions may be important due to their role in smog
formation and direct effects on human health. One researcher went so far as to say that if
every vehicle in the United States ran on fuel made primarily from ethanol instead of pure
gasoline, the number of respiratory-related deaths and hospitalizations would likely increase
(Jacobson 2007). Numerous studies on ethanol-oxygenated fuel emissions have been
conducted, including EPA's testing of oxygenated fuels for section 211(b) of the Clean Air
Act (EPA October 15, 2007), the 1999 report to the California Environmental Policy Council
on the health and environmental assessment of the use of ethanol as a fuel oxygenate
(LLNL 1999), and the Auto/Oil Air Quality Improvement Research Program in the 1990s
(Burns, Benson et al. 1991). However, not all possible mixtures of ethanol and gasoline have
been evaluated.
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It remains unclear whether the atmospheric concentrations that might result from a major
shift in urban fuel toward ethanol would be enough to cause significant health impacts. More
research is required on this topic (The Royal Society 2008).
2.5 Land Use Impacts from Biofeedstock Supply
There are many competing demands on land: to grow food, for conservation, urban
development, and recreation. Increasing demand for agricultural products as feedstocks for
bioenergy and biofuels constitutes a significant change for the commodity markets. This is
illustrated in the unprecedented demand for corn arising from expanding bioethanol
production. The use of corn for ethanol has accelerated over recent years. In the four-year
period beginning in the fall of 2005, ethanol increased its share of total U.S. corn use
including exports from 14.2% to 30.5% (Wisner 2009). One impact is likely to be an increase
in land area for feedstocks, either from the reallocation of land from other crops1, the use of
set-aside land taken (within Europe), or from the cultivation of new land in many developing
countries, particularly South and Latin America. Harmful deforestation is already occurring
worldwide to fill the need to expand agricultural lands. Certain land types, such as peat lands,
tropical rain forests, savannas, and grasslands, represent large carbon sinks. Their conversion
to cropland for biofuels will result in greater emissions of soil carbon (Eide 2008). Therefore,
not only should direct impacts to land where biofuel feedstocks are grown be considered, but
also these types of indirect impacts should be considered. Such direct and indirect impacts are
equally important. It is apparent how biofuel development can have major consequences on
land use.
2.6 Food-for-Fuel
Biofuels are produced from the products of conventional food crops such as the starch, sugar,
and oil feedstocks from crops, including wheat, corn, sugar cane, palm oil and rapeseed oil.
Any major switch to biofuels from such crops would create competition with their use as
food and animal feed. In some parts of the world, the economic consequences of such
competition can already be seen as large amounts of productive land are being converted
from food production to biofuel crops, leading to large implications for food availability and
prices. In order to help avoid such competition, future biofuels are likely to be produced from
a much broader range of feedstocks including the lignocellulose in dedicated energy crops
such as perennial grasses, forestry products and by-products, the co-products from food
production, and domestic vegetable waste (The Royal Society 2008).
2.7 Soil Quality
Forms of soil degradation include soil erosion, soil compaction, low organic matter, loss of
soil structure, poor internal drainage, salinization, and soil acidity problems. Typical tillage
and cropping practices lower soil organic matter levels, cause poor soil structure, and result in
compaction, which increases soil erodibility. Carbon compounds in waste biomass left on the
ground, such as corn stover, are consumed by microorganisms and degraded to produce
The increase in corn supplies in the U. S. was obtained by a large increase in the amount of land dedicated to
corn; this shift in land to corn came out of land that previously was used for other crops, most notably soybeans.
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valuable nutrients for future crops. When cellulosic ethanol is produced from feedstocks like
stover, switchgrass, and sawgrass, the nutrients that are required to grow the lignocellulose
are removed and cannot be processed by microorganisms to replenish the soil nutrients. The
soil is then of poorer quality. The widespread human use of biomass, which would normally
compost the field, could threaten these organisms and natural habitats (ETC 2008).
There are also issues related to changes in farming practices that may occur in order to meet
changing market demands. Double cropping, such as harvesting wheat crop by early summer
then planting corn or soybeans on that acreage for harvest in the fall, and switching to
planting continuous corn instead of rotating with soybean could result in needing to apply
more pesticides and fertilizers, which may have longer term impacts.
2.8 Water Quality Impacts
A study from the World Resources Institute (WRI) indicates that the development of a corn-
based ethanol market would only exacerbate problems already associated with large-scale
corn production. Such problems include soil erosion, which can reduce downstream water
quality, algae blooms, and the formation of "dead zones" in waterways inundated with
pesticide and fertilizer runoff (World Resources Institute 2006). For example, it is well-
known that agricultural nutrient releases contribute to hypoxia in the Gulf of Mexico and
eutrophication in the Great Lakes of North America. The input of artificial fertilizers to
increase yield must be carefully monitored in order to prevent or reduce their migration to
surface waters. Improved agronomic practices will undoubtedly play a key role in mitigating
negative environmental impacts through the timing and proper application of fertilizers.
2.9 Water Availability
Globally, pressures on water supply and quality are increasing from a growing population,
per capita usage and the impacts of climate change (UNESCO-WWAP 2006). In some
locations, the availability of water can be an important consideration in biofuel production.
While most often thought of in feedstock production (i.e., crop irrigation), water is required
throughout the entire biofuel supply chain with the distribution of water resources varying
greatly according to location and time. Developments in the agricultural sector for food and
non-food crops will have important implications for water usage and availability. Increased
usage of biofuels will raise demand for water and result in a negative impact on water
supplies (The Royal Society 2008).
2.10 Loss of Biodiversity
Biodiversity, also called biological diversity, plays an important role in ecosystem
functioning, particularly its ability to contribute to essential services such as providing food,
livelihood, and recreation. Over the past few centuries, human activity has resulted in
fundamental and irreversible losses of biodiversity. Globally, habitat conversion for
agriculture and forestry has been a major driver of this loss; for example, more land was
converted to cropland between 1950 and 1980 than between 1700 and 1850 (The Royal
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Society 2008). Converting land to grow a single crop in a large area, or monoculture,
increases yield but reduces biodiversity. Most experts recognize two aspects that must be
considered as indicators of biodiversity: the number of different species in a given area
(species richness) and how common or rare a species is relative to other species in a defined
location or community (relative species abundance). However, there are many outstanding
issues that are yet to be resolved, such as the definitions of species and the identification of a
suitable area in which to measure biodiversity. Researchers continue to seek out more
effective measures of biodiversity to move toward more sustainable practices (Suneetha
2010).
2.11 Introduction of Invasive Species
Invasive plants are introduced species that can thrive in areas beyond their natural range of
dispersal. Ideal energy crops are also commonly found to be an invasive species. For
example, several grasses and woody species are being considered for biofuel production, with
perennial grasses showing the most economic promise. However, these grasses can be
invasive if introduced into some U.S. ecosystems. Not only can they crowd out native
species, threatening riparian areas, they can also alter fire cycles. Internationally, there has
been little success in eradicating or even controlling invading grasses. (Raghu, Anderson et al.
2006).
2.12 Socio-Economic Aspects
Of course, the rate of production and use of agricultural feedstocks, like corn, soybean and
sugar, is affected by global economic markets. At the regional level, Midwest-U.S. corn
growers will likely benefit financially from the increased demand for their product. In
developing countries, areas of high biomass productivity are often areas of low wealth and
earnings. In these areas, the socio-economic benefits of production could be significant. It
will be important to facilitate technology transfer to developing countries, particularly for key
technologies such as those that increase feedstock yield or processing qualities of biomass.
Also, some feedstocks are also used for food and their use for fuel production may result in
price increases. Other feedstocks, such as waste biomass, will not have that impact. Since
different feedstocks result in different impacts, attention is being focused on
diversifying the energy matrix in many countries. As such, many countries are looking to
increase the number and variety of crops that can be cultivated and collected for bioenergy.
Programs are needed to ensure that rural and regional economies benefit from the domestic
production, use, and export of feedstocks (The Royal Society 2008).
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3.0 Life-Cycle Based Analytical Approaches and Tools
Selected for Study
As pointed out previously, the use of renewable resources is not synonymous with
sustainability. A myriad of factors relating to fuel and feedstock production and use must also
be considered. Therefore, we need to use tools to measure the complete process and value
chain before we can evaluate the sustainability of a process or the transformation in industry
(Dewulf and Langenhove 2006).
Several tools have been developed in an attempt to capture the view of the complete value
chain, or life cycle system (see Figure 1). It is common to find studies that are called "life
cycle," but focus on a particular issue or pollutant of concern. For example, one study
may perform a life cycle accounting of GHG emissions and another may focus on the net
energy gain or loss question.
Figure 1. Generic Stages of a Product Life Cycle (arrows represent transportation)
Resource
Acquisition
i
r
Material
Processing
fe
Production
A
I
r\t;L
yut;
Use and
Maintenance
Disposal
These types of narrowly defined studies fall short of a complete, multi-media life cycle
approach, which would enable the United States and others to recognize how our choices
influence each point of the life cycle. Such a perspective would afford the ability to balance
potential trade-offs and avoid shifting problems from one medium to another (e.g., controlling
air emissions, which creates wastewater effluents or soil contamination) or from one life
cycle stage to another (e.g., the raw material acquisition stage, which may affect the
reusability of materials for subsequent product life cycles).
The role of LCA is crucial in determining the values of the various metrics and emissions
along the entire chain of biofuel production and, as such, must be applied to different
processing techniques available now and those that might become available after research,
development and demonstration (RD&D) (The Royal Society 2008). An effective life cycle
approach can identify where potential tradeoffs may occur across different media and across
the life cycle stages (Fava, Denison et al. 1990).
Table 2 lists and briefly describes the following ten analytical approaches and tools that are
commonly used to assess the environmental impacts of biofuels on a life cycle basis:
• Carbon Management/Carbon Footprint
• Ecological Footprint
Exergy Analysis
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• Fuel Cycle Analysis
Greenhouse Gas Life Cycle Analysis
Life Cycle Assessment
Life Cycle Risk Assessment
Material Flow Analysis
Net Energy Balance
Sustainability Indicators
Two themes emerge from reviewing these tools: (1) there seems to be no clear definition of
these terms and (2) there is still variability regarding what each tool measures and what units
are to be used. Accordingly, this paper is intended to discuss general approaches, and not
specific tools, such as EPA's MOVES2 or DOE's GREET3. The ten approaches and tools
listed in Table 2 are discussed in more detail in the following sections.
Table 2. Life-Cycle Based Approaches and Tools Used to Evaluate Biofuels
Common Name
Carbon
Management or
Carbon Footprint
Ecological
Footprint
Description
Measures the total amount
of carbon dioxide (CO2)
emissions that are directly
and indirectly caused by
an activity or are
accumulated over the life
stages of a product,
process, or activity.
Calculates the human
demand on nature by
measuring the land and
sea area required to
provide all the natural
(biological) resources and
services to maintain a
given consumption
pattern, including the
resources it consumes and
the ability to absorb the
waste generated by fossil
and nuclear fuel
consumption. This can
then be compared to
available bio-capacity,
also expressed in land and
sea areas.
Measure
Amount of carbon
dioxide released
Biocapacity and
demand
Units
Total
kilograms
ofCO2
Giga
hectare
(gha)
2 Motor Vehicle Emission Simulator (MOVES)
3 Greenhouse gases, Regulated Emissions, and Energy Use in Transportation (GREET) Model
-------
Table 2. Continued
Exergy Analysis
Fuel Cycle
Analysis
Greenhouse Gas
Life Cycle
Analysis
Life Cycle
Assessment
(LCA)
Life Cycle Risk
Assessment
(LCRA)
Material Flow
Analysis (MFA)
Based on the second law of
thermodynamics, to provide
a mathematical calculation of
the loss of available work
across a system.
Tracks the number of
interdependent processes to
account for energy inputs and
associated releases to air and
water.
Quantifies the total amount
of carbon dioxide (CO2) and
other GHGs that are emitted
over the full life cycle of a
product, process, or service.
Evaluates multi-media,
cradle-to-grave burdens of an
industrial system by
quantifying energy and
materials used and waste
released to the environment
and assessing multiple
potential impacts.
Considers primary and
secondary contaminants,
multiple environmental
media, fate and transport
processes, cumulative and
aggregate exposure, and
ecological and human health
(cancer and noncancer) risks
across the product life cycle.
Quantifies and analyzes the
flows of a material (or
a substance in a "substance
flow analysis") in a well-
defined system usually at the
regional or national level.
Exergy
Energy efficiency,
air emissions
criteria pollutants,
toxics, water
impacts
Greenhouse gases
(GHGs) including
CO2
Multiple, to include
global warming,
ozone depletion,
human health,
ecological health,
eutrophication,
acidification, smog
formation, resource
use, land use, and
water use.
Human health and
ecological impact
Material flows
Joules (J)
Multiple
C02-
equivalents
(C02-eq).
Multiple
Not
applicable
(usually a
probability)
Kilograms
(kg)
10
-------
Table 2. Continued
Net Energy
Balance
Sustainability
Indicators
Determines the net energy
value (NEV) by subtracting
the energy needed to
produce a fuel (input
energy) from the useful
energy in the fuel (output
energy). Net Energy Ratio
(a ratio of less than one
indicates a net energy loss.)
A select group of categories
for which information and
data on the economy,
society and the environment
are needed to determine if
actions are heading toward a
satisfactory outcome.
Indicators for environmental
sustainability include the
state of the environment as
well as future environmental
conditions.
Energy flows
Multiple
Btu
Multiple
Where possible, applications to biofuels, especially corn ethanol, are included if available. Corn
ethanol is a commonly studied biofuel and an important feedstock in biofuels
production in the United States. As of July 15, 2010, the Renewable Fuels Association
reported 200 operating ethanol biorefmeries and another 13 under construction or expanding
(http://www.ethanolrfa.org/blo-refinery-locatlons/). Figure 2 shows that the majority of corn
production occurs along the central corridor of the United States, known as the Corn Belt
States.
11
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Figure 2. The Locations of Ethanol Biorefmeries in the United States as of June 2008
Active
A Corn
A Milo
A Multiple/Other Feedstock
Under Construction/Expanding
0 Corn
• Cellilosic Materials
_ Multiple/Other Feedstock
125 250 375 500 Miles
e. energy. qov.'afdc'pdfe'ethanol refineries. pdf
Data Source: Renewable Fuels Association and Ethanol Producer Magazine, June 2008
12
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3.1 Carbon Management
With the recent urgency associated with global climate change, many methods and tools have
been developed to calculate and account for carbon emissions. The open-access journal
Carbon Balance and Management is dedicated to providing research results aimed at a
comprehensive, policy relevant understanding of the global carbon cycle. According to the
journal's website (http://www.cbmjournal.com/info/about/), the global carbon cycle involves
important interactions between climate, atmospheric carbon dioxide (€62) and the terrestrial
and oceanic biospheres. The carbon management methodology accounts for dissolved
organic carbon, biomass carbon and produced CO2 and identifies potential atmospheric CO2
sources and sinks.
"Carbon Footprint" is a term that has become widely used in relation to carbon management
and the threat of global climate change (for example, http://www.carbonfootprint.com/).
Despite its ubiquitous appearance, there seems to be no clear definition of this term. There is
still much confusion as to what it actually means, what it measures, and what unit is to be
used. While commonly understood to refer to certain gaseous emissions that are relevant to
climate change and associated with human production or consumption activities, there is no
agreement on how to measure or quantify a carbon footprint. Questions remain regarding
whether the carbon components should be weighted and normalized based on their potential
effect in the atmosphere. Other questions that need to be answered include the following:
• Should the carbon footprint include just carbon dioxide (CO2) emissions or other
GHG emissions as well, e.g., methane?
Should it be restricted to carbon-based gases or can it include substances that do not
have a carbon atom in their molecule, e.g., N2O, which is another powerful GHG?
Should the carbon footprint be restricted to substances with a global warming
potential at all since there are gaseous emissions that are carbon-based and relevant to
the environment and health, such as carbon monoxide (CO), which can convert into
CO2 through chemical processes in the atmosphere?
Should the measure include all sources of emissions, including those that do not stem
from fossil fuels, e.g., CO2 emissions from soils? (Wiedmann and Minx 2007)
Sometimes the carbon footprint is expressed in kilograms of carbon rather than in
kilograms of CO2. CO2 can be converted to carbon by multiplying by a factor of 0.27 (1,000
kg CO2 equals 270 kg carbon4). But more commonly, carbon footprinting accounts for all
GHG releases, not only carbon dioxide. Other GHGs that might be emitted, such as methane
and N2O, are also counted in the calculation of a carbon footprint. They are converted into the
amount of CO2 that would cause the same effects on global warming (this is called CO2-
equivalents). This was the approach that was taken in an assessment by the
U.S. Environmental Protection Agency for a life cycle greenhouse gas analysis they
conducted in support of the national Renewable Fuel Standard (RFS) program (EPA
2010).
4 CO2 has an atomic weight of 44 (a carbon atom weighs 12; an oxygen atom weighs 16), therefore, the carbon
content of 1,000 kg CO2 = 1,000 x 12/44 ~ 270.
13
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The assessment of GHG emissions is covered in more detail in a later section (see 3.5
Greenhouse Gas Life Cycle Analysis).
In a calculation for ethanol, most of the carbon footprint falls into one of several categories in
roughly ascending order (depending on the source and process): the fuel used to produce it,
the fuel used to grow or transport the feedstock, the carbon content of the fuel itself, and the
lost carbon not sequestered in the vegetation that would have been on the land used to grow
the feedstock. The main difference across carbon footprint calculations appears to largely
depend on how land use is modeled. Determining where a crop is grown can have a more
significant impact on the outcome than what type of crop is grown (Johnson and Heinen
2008). For example, land use for ethanol feedstock that is already in production will have a
carbon footprint at the low end of the range since there is little net reduction in the carbon
sink. Conversely, converting forests to cropland, or the use of marginal lands that produce
low yields, will have a carbon footprint at the high end of the range (Dikeman 2008).
14
-------
An Example of a Carbon Management (COi) Study
Bias de Oliviera et al. (Bias de Oliveira, Vaughan et al. 2005) calculated the
CC>2 balance for corn ethanol production, distribution, and combustion in the
United States and found a total CC>2 release of 5,030 kg/ha (see
below). They accounted for the generation of CC>2 from the harvesting and
processing of one hectare of corn to produce 3.04 m3 of ethanol. After
gasoline is added to form the mixture, the total fuel volume of 3.58 m3 of E85
will allow the reference vehicle to run for approximately 24,400 km. They
assumed that the production and distribution of gasoline results in 375 kg of
CO2 emitted per m3 of gasoline produced. Consequently, 203 kg of CO2 are
emitted from the production and distribution of the 0.54 m3 of gasoline added
to 3.04 m3 of ethanol to form the E85 mixture. Combustion of this
volume of gasoline emits 1.267 Mg of CC>2.
Total CC>2 released
Process (kg/ha)
Agricultural Inputs 1237
Increase in Soil Organic Carbon -660
Corn Transportation 154
Ethanol Conversion 2721
Ethanol Bistribution 108
Gasoline Portion of E85:
- Production and Bistribution 203
- Combustion 1267
Total 5030
Based upon this example and comparing E85 to an equal amount of gasoline,
the CC>2 emissions for the gasoline portion can be reapportioned to calculate
emissions for 100% gasoline, such that:
(203 + 1267) X (1.00/0.15) = 9800 kg CO2
Adjusting for thermal efficiency: 9800 X 0.75 = 7350 kg CO2
Therefore, according to this data, the comparison of driving a vehicle 24,400
km using the two fuels results in the following CC>2 emissions:
E85 =1.267 MgCO2 Gasoline = 7.350 Mg CO2
Thus, in this analysis, using corn ethanol instead of gasoline can potentially
reduce CC>2 releases by almost one-sixth.
15
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3.2 Ecological Footprint
Ecological Footprint was originally designed to measure the amount of land area a human
population requires to produce the resources it consumes and to absorb its waste under a
prevailing technology. More recent calculations also include water use.
Ecological Footprint measures the amount of cropland, grazing land, forest area, and
fishing grounds that are needed to satisfy humanity's need for food, clothing, shelter, and
products and services. In addition to that, it measures the amount of land required to
sequester our emissions after subtraction of the oceans' absorptive capacity. In modeling land
use, Ecological Footprint expresses all the land area the earth has available for generating
renewable resources using a single unified metric, the global hectare (or global acre). A
global hectare is a mathematical representation of the productivity of real land, established by
Wackernagel in his 1994 Ph.D. thesis (Wackernagel 1994). It is calculated in a manner
that allows a comparison of the productivity of different land types around the globe. It
encompasses all products and services derived from raw materials that came from a land area
(or out of the earth) as well as resulting emissions that need to be absorbed somewhere.
Humanity's Ecological Footprint has been steadily increasing over the past four decades.
According to the Living Planet Report 2006, humanity as a whole uses nearly 25% more
resources than the planet can make available annually. In other words, humanity today
would need 1 1A planets to sustain us. Some people use more while some people use less. If
everybody lived like the average American, we would need more than five planets. Italians
live on about 2 1/3 planets, while the people of Thailand use only 3A of a planet (WWF
2006). Over the years, we have been able to increase biocapacity, mainly through
increased crop yields and expanding area under cultivation; however, this increase has not
been able to keep up with the increase of the world population and increased consumption
(Vos 2007).
16
-------
An Example of Ecological Footprinting
Sustainability Planning Partners (Vos 2007) presented examples of different fuels that can be
used in a typical passenger car. The Toyota Prius hybrid vehicle was added for comparison
purposes as well as the per capita biocapacity available to each person on the planet (1.78 Global
Hectares). Calculations were based on an average annual use of 12,500 miles using the 2006
EPA fuel mileage rating system.
Ecological Footprint of Fueling a Passenger Car for 12,500 miles (Source: Vos 2007)
0*
Global Hectares
<
J*
-------
3.3 Exergy Analysis
"Exergy" was introduced by Rant in 1956 to describe the maximum amount of work that may
be obtained from a thermodynamic system under ideal conditions. Based on the second law
of thermodynamics, it reflects the maximum (mechanical) work possible during a process, i.e.,
available energy that brings the system into equilibrium with the surroundings. Exergy,
therefore, is the potential of a system to cause a change as it achieves equilibrium with its
environment. Thus, exergy has been applied to ecological evaluation, resource accounting,
and environmental impact assessment. The dispersion of pollutants throughout the
environment is thought to be essentially a process that converts the exergy of mixing
embodied in the initial state (the concentrated pollutant) into entropy of the final state (the
dispersed pollutant) (Seager and Theis 2003).
Although exergy analysis is a most useful method as a way to evaluate the thermodynamic
efficiencies of biomass conversion processes, researchers have attempted to apply exergy
calculations to industrial systems to assess environmental impacts. Increased energy
efficiency benefits the environment by avoiding energy use and the corresponding resource
consumption and pollution generation. Exergy and energy analyses are best carried out
together to most effectively find ways to improve industrial systems (Kanoglu, Dincer et al.
2009). Exergy analysis of both utilities and feedstocks as inputs, and products, waste streams
and generated irreversibilities as outputs, shows how efficiently resources are employed
toward products. An exergetic life cycle analysis adopts a life cycle perspective by quantifying
exergy on a cradle-to-grave basis. Figure 3 presents the exergy values along the life cycle
stages of corn ethanol.
Figure 3. Flows of Exergy Associated with the Annual Production of Bioethanol from
One Hectare of Corn (GJ ha1 • yr'1)
46,000
Solar Irradation
46,000
Non-
renewable
Agricultural
Resources
9.92
Renewable
Industrial
4.96
(Source: Dewulf, Langenhove et al. 2005)
-------
Researchers sometimes consider the exergy of the current formation of natural resources from
a small number of exergy inputs (usually solar radiation, tidal forces, and crustal/geothermal
heat). This application not only requires assumptions about reference states, but it also
requires assumptions about the real environments of the past that might have been close to
those reference states.
Because the exergy that is embodied in resources, products, and waste materials has the
potential to cause change in both the industrial environment as well as the natural ecosystem,
exergy and entropy have been proposed not only as a measure for economic losses and
dematerialisation, but also for waste accounting and ecotoxicity. While Dewulf et al. are
supporters of the use of exergy analysis as a tool in environmental impact analysis, claiming
it as possibly the most mature field of application, particularly with respect to resource and
efficiency accounting, they are also quick to point out the tool's deficiencies (Dewulf,
Langenhove et al. 2008). Emissions, for example, have an exergy value because they are not
in thermodynamic equilibrium with the surroundings. However, their exergy value does not
represent their environmental impact. Exergy analysis is much more oriented toward resource
and product, and, hence, efficiency. Nevertheless, efforts to assess environmental impact not
only through resource intake but also through emission generation have been developed
based an exergy analysis.
When compared to other resource accounting methods, exergy has the major advantage that it
is able to weigh different masses in a scientifically sound way that brings mass and energy
into a single scale. Different kinds of resources, including renewable resources (biomass,
solar, wind, hydropower), fossil fuels, nuclear fuels, metal ores, minerals, water resources,
and atmospheric resources, can be quantified on a single scale. The resource category "land
use" is still omitted in most exergy calculations.
Exergy analysis continues to be developed and promoted within the field of
thermodynamics as a way to design and develop more sustainable industrial processes. It is
supported by individuals who believe that exergy is a good method to provide insights into
energy systems to identify potential reductions in thermodynamic losses and efficiency
improvements (Rosen and Bulucea 2009). However, a defensible link between exergy
calculations and environmental impact has yet to be fully demonstrated (Rosen and Dincer
2001; Rosen 2009).
3.4 Fuel Cycle Analysis
Joshi et al. (Joshi, Lave et al. 2000) provide a good description of the general approach for
fuel cycle analysis (more commonly referred to as a "Well-to-Wheel" study by individuals in
the transportation sector). Basically, a fuel cycle analysis attempts to track the number of
interdependent processes to account for energy inputs and associated air and water emissions,
which may include criteria pollutants and toxic compounds. Significant interdependences are
accounted for where other fuels, such as residual oil, coal and electricity, are used as
intermediate energy inputs. The production processes also result in a number of co-products
to which energy and environmental impacts must be allocated. While modeling practices vary
across studies, the basic structure is similar and involves the following features:
19
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For fossil fuels, the fuel cycle is divided into four stages: feedstock extraction;
feedstock transportation and storage; fuel production; and fuel transportation, storage
and distribution.
For biofuels, the biomass farming stage constitutes the feedstock extraction phase.
The major inputs to farming include fertilizers and agricultural chemicals in addition
to energy.
For each of these stages, the energy requirement and fuel mix are estimated.
Depending on the equipment in which the fuel is combusted (boilers, vehicles, ocean
tankers, compressors, etc.), appropriate combustion emission factors are used to
estimate combustion-related emissions.
Non-combustion emissions such as process emissions, venting/flaring and fugitive
emissions are also estimated for each stage.
For biofuels, life cycle energy use and emissions for fertilizers and other inputs are
accounted.
The emissions associated with co-products are allocated using selected criteria.
Relative processing energy intensity is most commonly used as the basis of allocation
for fossil fuels. A common basis for biofuel co-product allocation is less obvious.
These individual stage energy use and emissions are aggregated to estimate full fuel
cycle emissions.
Joshi et al. (Joshi et al. 2000) point out that unavoidable variations occur in modeling large,
complex fuel systems. Accordingly, final estimates of energy use and emissions per GJ
of fuel delivered to a vehicle can vary significantly across studies for gasoline and
bioethanol. Reconciliation of differences is difficult since estimates, calculations and
assumptions are seldom available in published reports.
20
-------
An Example of a Fuel Cycle Analysis
Argonne National Lab (Wang, Saricks et al. 1999) conducted a comparative
analysis of fuel-cycle petroleum use, GHG emissions, and fossil energy use of
fuel ethanol relative to conventional gasoline. The fuel-cycle analysis included
all production, combustion, and transportation stages — from feedstock
recovery to vehicular fuel combustion — for both ethanol and gasoline. The
study modeled emissions of three major GHGs: carbon dioxide (€62),
methane (CFL;), and nitrous oxide (N2O), as well as emissions of five criteria
pollutants: volatile organic compounds [VOCs], carbon monoxide [CO],
nitrogen oxides [NOx], particulate matter with a diameter of less than 10
microns [PMio], and sulfur oxides [SOx].
Reductions in Energy Use and Emissions per Vehicle-Mile for
Corn-Based Ethanol (1999) Compared to Gasoline
E10 E85 E95 E10 E85 E95
Dry Milling Wet Milling
Petroleum 6.4% 74.9% 87.7% 6.1% 72.5% 85.0%
GHGEmissions 1.3% 18.8% 24.9% 0.8% 13.7% 19.1%
Fossil Energy 2.7% 35.0% 44.3% 2.7% 34.4% 42.3%
Reductions in Energy Use and Emissions per Gallon for Corn-Based Ethanol
(1999) Compared to Gasoline
E10 E85 E95 E10 E85 E95
Dry Milling Wet Milling
Petroleum 93.3% 94.9% 94.7% 90.2% 91.9% 91.8%
GHGEmissions 19.2% 23.8% 26.9% 12.4% 17.3% 20.7%
Fossil Energy 40.3% 44.4% 46.5% 39.5% 43.6% 45.7%
The results showed that using a gallon of ethanol, regardless of the blend mix,
can achieve large emissions and energy use benefits, although the benefits are
enhanced slightly for the more efficient vehicle/fuel technologies using E85
and E95. The differences among the per-gallon-of-ethanol results for ethanol
in each of the three blends are caused primarily by the fuel economy
differences of the vehicles fueled by E10, E85, and E95.
21
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3.5 Greenhouse Gas Life Cycle Analysis
Many studies over the past several years have attempted to answer the question of whether or
not biofuel production and use will result in a net reduction of GHG emissions when
compared to gasoline. The Greenhouse Gas Protocol (GHG Protocol) is a joint initiative of
the World Resources Institute (WRI) and the World Business Council for Sustainable
Development (WBCSD). The protocol is intended mainly for corporate or company-level
reporting, but the principles of the protocol can also be applied to a single product. The
protocol categorizes GHG emissions into "direct" and "indirect" emissions. GHG emissions
from the production and use of biofuels are calculated as:
-Ł•• ^ec "l ^p "td ^u ^ccs ~ ^ccr ^ee->
where:
E = total emissions from the use of the fuel;
eec= emissions from the extraction or cultivation of raw materials;
BI= annualized emissions from carbon stock changes caused by land use change;
ep= emissions from processing;
etf= emissions from transport and distribution;
eu= emissions from the fuel in use;
eccs= emission savings from carbon capture and sequestration;
eccr= emission savings from carbon capture and replacement; and
eee= emission savings from excess electricity from cogeneration.
Emissions from the manufacture of machinery and equipment are not taken into account
(European Commission 2008).
The Green Car Congress (Green Car Congress 2009) reports that Emanuela Menichetti and
Martina Otto (2009) reviewed and assessed 30 LCA studies, particularly those relating to the
energy balance and greenhouse gas (GHG) emissions of biofuels produced from a range of
crops and other biomass feedstocks using various conversion technologies (Menichetti and Otto
2009). Among their general observations was that while the number of full LCA studies
continues to increase, it is still relatively small, and that most studies focus on traditional first
generation feedstocks such as corn, sugarcane, rapeseed and wheat. Other reported observations
included:
Most studies only include energy consumption (sometimes only non-renewable
energy, sometimes total energy) and CO2 emissions. A few studies also include other
relevant impact indicators such as acidification potential, eutrophication potential,
ozone depletion potential and various toxicity potentials. However, very few studies
include water use impacts.
Methodologies to develop biodiversity quality indicators are still under discussion. No
study in the review presents results in terms of biodiversity.
22
-------
• Very few studies take into account land use impacts driven by biofuel crop
production. More specifically, only one third of the studies defines an alternative land
use reference system and calculates the carbon stock. Potential impacts in terms of
indirect land use change driven by increased bioenergy demand are not considered in
the sample analyzed.
• The transparency level of reports is quite heterogeneous with respect to hypothesis
and assumptions, yields, heating values, emission factors, and other background
methodological choices. Very few studies include a data quality review according to
the requirements of the ISO standards for LCA.
• Heterogeneity was observed in terms of the treatment of co-products and
allocation methods that were followed.
• Social issues are very often overlooked in the studies. This is not surprising, given the
purely environmental focus of LCA technique.
• Many databases and LCA software programs are used to model data. In particular,
some of the life cycle inventory databases used in the studies appear relatively old.
This affects the quality of results, regardless of the quality of the primary data
collected.
More analysis and research is needed in order to improve the incorporation of land use change
into estimates of GHG emissions from biofuels. The calculation of GHG emissions associated
with biofuels is complicated by the addition of factors associated with both direct and indirect
land use changes. In addition, only recently has the potential for soil to act as a net sink for
carbon begun to be included in studies. Improvements can be made to existing methods by
being more precise in defining system boundaries. In its assessments to inform regulatory
determinations, the U.S. EPA recognizes that as the state of scientific knowledge continues to
evolve in this area, the life cycle GHG assessments for a variety of fuel pathways will
continue to be enhanced. The U.S. EPA is seeking expert advice from the National Academy
of Sciences as well as other experts (EPA 2010).
23
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An Example of a Greenhouse Gas Life Cycle Analysis
As part of proposed revisions to the National Renewable Fuel Standard
program (commonly known as the RFS program), EPA (EPA 2010) analyzed
life cycle greenhouse gas (GHG) emissions from increased renewable fuels
use in order to determine whether or not renewable fuels produced under
varying conditions will meet the greenhouse gas thresholds for the different
fuel types for which the Energy Independence and Security Act establishes
mandates.
The study accounted for secondary or indirect impacts of expanded biofuels
use over a 30-year time horizon with 0% discount rate and a 100-year time
horizon with a 2% discount rate (the figure below shows the results for the
later scenario, comparing gasoline and corn ethanol). They calculated a net
present value of emissions because it provides a common metric for the
direct comparison of life cycle emissions from biofuels and petroleum fuels.
EPA's analysis suggests that the assessment of life cycle GHG emissions for
biofuels is significantly affected by the secondary agricultural sector.
Life Cycle GHG Results for Gasoline and Corn Ethanol, Using 100-Year Net
Present Value with 2% Discount Rate
-jel Procuct :n
Tailpipe
htemational Land Use Change
htemational Farm Inputs and
Pert M2O
Other (He and feedstock
transport)
Domestic Soi' Carbon
Internationa! Livestock
htemational Rice Methane
Domestic R ce Methane
lri|- :-:. «••-
FertN2O
Domestic Livestock
— Cel uios c Threshold
— -'t.oi ' .e:: and Biod esel
"T '&sho c
— Conventional Threshold
Net Emissions *
(Source: EPA 2010)
24
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3.6 Life Cycle Assessment
Life cycle assessment (LCA) accounts for all the inputs and outputs across a product system
from cradle to grave in order to model the potential environmental impacts of resource use
and releases to the environment (International Standards Organization 1997; Environmental
Protection Agency 2006). By including the impacts throughout the product life cycle, LCA
provides a comprehensive view of a product's environmental aspects. It is also valuable in
evaluating the many interdependent processes that are involved in a product system. A
change to one part of this system may have unintended consequences elsewhere. LCA
identifies the potential transfer of environmental impacts from one medium to another (e.g.,
eliminating air emissions by creating a wastewater effluent instead) and/or from one life
cycle stage to another (e.g., from use and reuse of the product to the raw material acquisition
stage). If an LCA were not performed, the transfer might not be recognized and properly
included in the analysis because it is outside of the typical scope or focus of product design
and selection processes.
Quality LCAs require large amounts of input and output data, called the life cycle inventory
(LCI) data. While international activities, such as ecoinvent (ecoinvent Centre 2005) and the
European Commission's International Reference Life Cycle Data System, have been initiated
to assist users in accessing LCI data more easily, LCA practitioners and researchers often
have to develop their own data or modify data from other countries. Having easy access to
consistent LCI data is needed in order for effective LCA applications to continue (NREL
2009).
Inventory data are subjected to life cycle impact assessment models, which seek to establish a
linkage between a system and the potential, related impacts. The impact models are often
derived and simplified versions of more sophisticated models within each of the various
impact categories. Although consensus has yet to be reached on which impact categories
should be included in an LCA, the following are commonly used:
Ozone Depletion • Acidification
Global Warming • Smog Formation
Human Health • Fossil Fuel Use
Ecotoxicity • Land Use
Eutrophication • Water Use
These simplified models are suitable for relative comparisons of the potential to cause human
or environmental damage, but are not indicators of absolute risk or actual damage to human
health or the environment. For example, risk assessments are often very narrowly focused
on a single chemical at a very specific location. In the case of a traditional risk assessment, it
is possible to conduct very detailed modeling of the predicted impacts of the chemical on the
population exposed and even to predict the probability of the population being impacted
by the emission. In the case of LCA, hundreds of chemical emissions (and resource
stressors) that are occurring at various locations are evaluated for their potential impacts in
multiple impact categories. The sheer number of stressors being evaluated, the variety of
locations, and the diversity of impact categories makes it impossible to conduct the
assessment at the same level of rigor as a traditional risk assessment. Instead, models are
based on the accepted models within each of the impact categories using assumptions and
25
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default values as necessary. The resulting impact models are suitable for relative
comparisons, though insufficient for absolute predictions of risk.
Standardized LCA methodology does not include economic factors, such as monetary costs, or
social factors, such as child labor.
Furthermore, LCA results can vary widely depending on how the system boundary is drawn
and the assumptions that are applied to calculate the input and output data (LCI), as well as
the modeling of the environmental impacts. An important variation relates to how the various
co-products from industrial processes are modeled (Curran 2007).
Von Blottnitz and Curran pointed out in 2007 that a full LCA of bioethanol in the United
States is needed (von Blottnitz and Curran 2007). While this still holds true today for the
United States, comparative studies for Europe have been conducted.
26
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An Example of a Life Cycle Assessment of Biofuels
Zah et al. (2007) conducted LCAs of several biofuels (bioethanol, biomethanol, biodiesel
and biogas) in Switzerland using a limited set of impacts: GWP (global warming
potential), CED (cumulated non-renewable energy demand), SMOG (summer smog
potential), EUTR (eutrophication caused by fertilizer use) and ETOX (ecotoxicity).
Calculations were based on the method of ecological scarcity (UBP 06). The emission
standard petrol EUROS, set by the European Union in 2000 for gasoline-powered
passenger cars, was selected as the reference product, i.e., it was set to equal 100%. Zah
et al. list a number of considerations related to this study regarding LCA methodology:
• Although the LCA approach used here is very comprehensive, certain
environmental impacts are covered only incompletely or not at all. For example,
the effects of water utilization are not covered because they differ greatly
depending on local conditions (the quantity of precipitation, ground water level,
etc.). Biodiversity losses are also incomplete because the data is lacking on
tropical ecosystems.
• The assessment approach calculated only the primary environmental impacts of
the process chain, e.g., energy consumption and pollutant emission during the
cultivation of energy rapeseed. Secondary effects were not covered. For instance,
food was grown beforehand on the energy rapeseed field; afterward food had
to be imported, causing additional transports and additional environmental impacts
due to the transports.
• No distinction is made with cultivation biomass (e.g., grain or potatoes) between
harvest waste and biomass produced specifically for fuel production. Nor does
the method differentiate between the use of already cultivated fields and newly
cultivated fallow fields. Therefore, the method neglects the environmental impacts
associated with these aspects of the fields, such as a reduction in biodiversity in
newly cultivated fallow fields.
• On the basis of the data from existing life cycle inventories, most of the results
refer to existing process chains, and thus cover Reference Year 2004. Future
developments are not judged. However, a glimpse of future developments is
provided by the sensitivity analyses and possible optimization potentials.
• Since many allocations have been calculated from sales revenue, and revenue
depends on market dynamics, the results of this study are not "chiseled in stone"
and may have to be verified later.
• The process chains investigated represent only a subset of all production
processes. Many more production paths are conceivable. However, the paths
chosen are considered especially relevant for the current situation in
Switzerland.
• The data from existing life cycle inventories represent average conditions in the
respective production countries (Switzerland, Europe, Brazil, U.S, etc.) and apply
as an integral whole as regards to use in Switzerland. Therefore, the results may
not be applied without qualification to decision situations in partial regions or
individual plants because the environmental impacts in individual cases may
differ radically from the average situation.
The study provides no answers to the questions of the future consequences of a shift to
renewable fuels (e.g., the environmental consequences of agricultural products were to be
grown on such a large scale for energetic utilization that agricultural production as a
whole had to be intensified) or of any possible rebound effects (Zah, Boni et al. 2007).
27
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An Example of a Life Cycle Assessment of Biofuels (continued)
The table below notes the overall environmental Life Cycle Assessment of all unblended biofuels studied in
comparison to a fossil reference. GWP = greenhouse warming potential, CED = cumulated non-renewable
energy demand, SMOG = summer smog potential, EUTR = excessive fertilizer use, ETOX = ecotoxicity.
Reference ( = 100%) is petrol EUROS in each case.
Methane manure, optimized
Methane manure+cosubstrate, optimized
100% Recycled plant oil ME FR
Ethanol whey CH
100% Recycled plant oil ME CH
Methanol fixed bed CH
Methane wood
Methanol fluidized bed CH
Ethanol sugar cane BR
Ethanol grass CH
Ethanol wood CH
Ethanol sweet sorghum CN
Ethanol sugar beets CH
Methane sewage sludge
Methane grass biorefinery
100% Soy ME US
Methane biowaste
100% Palm oil ME MY
100% Rapeseed ME CH
Methane manure+cosubstrate
Methane manure
100% Rapeseed ME RER
Ethanol corn US
Ethanol rye RER
Ethanol potatoes CH
100% Soy ME BR
Natural gas, EURO3
Diesel, low sulphur EURO3
Petrol, low sulphur EURO3
GWP
%
7
14
26
30
30
30
33
35
36
36
37
47
47
50
52
52
55
58
60
65
70
77
93
96
97
105
80
93
100
CED
%
40
40
43
43
43
48
50
52
41
49
48
53
53
55
48
49
42
57
57
40
40
64
79
77
79
70
95
92
100
SMOG
%
52
57
50
70
50
100
90
100
500
75
73
130
90
70
70
210
75
380
65
80
95
160
130
125
73
500
60
74
100
EUTR
%
299
220
65
550
165
110
135
112
265
135
380
500
500
60
500
500
75
348
500
390
410
500
500
500
475
500
67
175
100
ETOX
%
40
40
40
45
40
65
75
70
70
50
45
75
70
40
48
51
50
500
51
46
46
65
105
70
48
500
46
80
100
(Source: Zah, Boni et al. 2007)
28
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3.7 Life Cycle Risk Assessment
Life Cycle Risk Assessment (LCRA) integrates the traditional risk assessment paradigm with
a life cycle perspective. It attempts to examine potential human health and ecological impacts
(both positive and negative) in a broad, systematic manner. The life cycle nature of the
approach indicates that it encompasses a cradle-to-grave framework while accounting for
multi-media environmental fate and transport, exposure, and effects on both ecological
receptors and human health. Other dimensions such as economic, political, security, or
societal factors are typically excluded.
Two examples of LCRA approaches are 1) the Nano Risk Framework that was developed
jointly by Environmental Defense (ED) and DuPont to address concerns related to
nanomaterials and their applications and 2) the EPA's Comprehensive Environmental
Assessment (CEA).
Nano Risk Framework
In 2005, ED and DuPont entered into a partnership to develop a framework for the
responsible development, production, use, and end-of-life disposal or recycling of engineered
nanoscale materials. The resulting "Nano Risk Framework" (Figure 4) develops profiles of
nanomaterials' properties, inherent hazards, and associated exposures throughout the
material's life cycle (ED-DuPont 2007).
Figure 4. ED-DuPont Nano Risk Framework
Iterate
Describe Material
and Application
Assess, prioritize and generate data
(Source: ED-DuPont 2007)
Comprehensive Environmental Assessment
CEA is a life-cycle based approach that was developed by the EPA's National Center for
Environmental Assessment (NCEA) to identify and assess potential risk related to the release
of pollutants (Davis and Thomas 2006). As listed in Column 1 of Figure 5, the life cycle of a
product is typically comprised of several stages, including feedstock production or extraction,
manufacturing processes, distribution, storage, use, and disposal of the product and waste by-
products. At any stage across the life cycle, pollutants may enter one or more environmental
pathways: air, water, and soil (Column 2). It is important to identify these primary
contaminants and, to the extent possible, the transport and transformation processes they
29
-------
undergo. The idea is to characterize the primary as well as secondary or by-product pollutants
associated with the entire life cycle for all relevant media (Column 3). The existence of a
contaminant in the environment does not necessarily mean that humans or other specific
organisms are exposed to it. Thus, CEA is described as going beyond a conventional LCA to
apply exposure assessment, a key feature of risk assessment. As indicated in Column 4,
exposure and dose, i.e., the amount of substance actually taken into an organism, are
relevant to humans and biota generally.
In addition to characterizing exposure and dose, the health and ecological hazards
associated with respective contaminants need to be described qualitatively and quantitatively
(Column 5). To characterize risk quantitatively, the dose-response characteristics of a
toxicant must be considered in relation to exposure potential. Some pollutants may pose low
risk because the exposure potential is low or the hazard potential is low, or both. In other
cases, risk may be relatively high when exposure potential is low, but hazard potential is high,
or vice versa (Davis and Thomas 2006).
Figure 5. Framework for Conducting a Comprehensive Environmental Assessment
(Adapted from Davis and Thomas 2006)
Life Cycle Environmental Fate &
Stages Pathways Transport
Exposure -
Dose
Effects
Feedstocks
Manufacture
Distribution
Storage
Use
Disposal J
Air
Water
Soil
Primary
contaminants
Secondary
contaminants.
Biota
Human
populations
Ecosystems
Human Health
CEA can also involve a broad array of technical experts and stakeholders offering their
individual analytic judgments in a formal, structured manner that leads to a collective
understanding of the trade-offs associated with different fuels (or other technological issues).
-------
An Example of Life Cycle Risk Assessment
The California Energy Policy Council (LLNL 1999) assessed certain potential
environmental and health impacts related to methyl tertiary butyl ether (MTBE) and
ethanol as fuel oxygenates. The California analysis exemplifies some of the key features
of risk assessment in a life cycle framework and considered multi-media impacts of the
two oxygenates in a comparative manner. For example, cancer and noncancer risks
from selected air pollutants associated with MTBE and ethanol are presented below.
Comparative Life Cycle Model Based on Cumulative Cancer Risks and Noncancer
Hazard Indexes (HI) for Selected Air Pollutants in the South Coast Region of California
for MTBE and Ethanol Oxygenates in Gasoline (2003 Projections)
Risk Description
Cumulative lifetime
cancer risk
Cumulative HI for acute
eye irritation
Cumulative HI for acute
respiratory irritation
Cumulative HI for chronic
respiratory irritation
Estimate
Ranee
Upper
Lower
Upper
Lower
Upper
Lower
Upper
Lower
2003 MTBE
1.9X10'4
1.8X10'4
9.6
6.7
3.8
3.7
5.1
5.1
2003 2% EtOH,
bv weight
1.8X10'4
1.7X10'4
9.5
6.6
3.8
3.7
5.1
5.0
(Source: LLNL 1999)
31
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3.8 Material Flow Analysis
Material Flow Analysis or Accounting (MFA) tracks the amounts of materials, ranging from
timber and fuel to metals and agricultural products, as they enter and exit the economy
through various types of transactions. These materials can accumulate in capital stock such as
housing and automobiles or exit to the environment at any phase of their commercial life
cycle, from extraction to processing, manufacturing, use, disposal, or recycling (Wernick and
Irwin 2005).
On a regional as well as national level, MFA is a useful tool for improving resource
management. MFA serves as a system-wide diagnostic procedure related to environmental
problems, supports the planning of adequate management measures and provides for
monitoring the efficacy of those measures. Furthermore, MFA allows early warning and
supports precautionary measures. By quantifying linkages between environmental problems
and human activities, the aggregated information from an MFA study can help detect
potential problem shifting between regions and sectors and can support decision making.
At present, there is no global consensus on MFA methodology, and the United States still
lacks a comprehensive approach for accounting and tracking material flows, but a common
goal is understood. That is, the goal is to analyze the flows (in kilograms) of a material in a
well-defined system, by space and time, in order to identify and quantify material exchanges
between the economy and the natural environment. The term "material" stands for both
substances and material goods. The procedure and some elements of studies that have been
conducted have common features. The core principle of MFA is the mass balance principle,
i.e., the law of conservation of mass where inputs to an economy (extractions + imports) equal
outputs from the economy (consumptions + exports + accumulation + waste). Figure 6
depicts the various flows across the economy that are modeled in an MFA. The procedure
usually consists of four steps: goal and system definition, process chain analysis, accounting
and balancing, and modeling and evaluation. The results of an MFA can be used to minimize
the flow of materials while maximizing the human welfare generated by the flow. As such, it
is a method for evaluating the efficiency of using material resources. The analysis allows for
the monitoring of wastes that are typically unaccounted for in traditional economic analyses
(Rogich, Cassara et al. 2008).
32
-------
Figure 6. Aggregate Material How Accounting (MFA) Indicators
tMft <
DOMESTIC (ENVIRONMENT
tot4l Mdteriiif Hequtfeaittnt TMK — Dornesikc txtraction -+-ki)po*t& •*• Dome&tlc Hidder Ht>'»v* »
Dirwtt M^li^tdl biput rVsrtl - O«J««BV|IC F»1rj«tittr> i Importv >
Direct Mdtcrlml Consumption DMC - DM|- txporti
Pom*»vtic Proc«rt*«Kt Output DPO - tWWC- N«t Add ttinni fa Stock «ft*cjn:k
-------
Researchers at the World Resources Institute (WRI) have been engaged in preparing and
analyzing material flow accounts since 1995. Among their many MFA studies, they provided
a detailed accounting of trends in material flows in four key sectors of the U.S. economy:
metal and minerals, non-renewable organic materials (including fossil fuels), agriculture, and
forestry. Figure 7 shows how agricultural flows increased 30% between 1975 and 2000. WRI
reports that the data show a more than sevenfold increase occurred in the use of grains to
produce ethanol for use in automotive fuels (Rogich, Cassara et al. 2008).
Figure 7. Materials Consumption in the United States by Sector of Origin, 1975-2000
u
s
Q ~
P
!
11
7^
s
7,000
6,000
5,000
4,000
3,000
2,000
1,000
0
Forestry
Agriculture
Nonrencw able Organic Material
Metals and Minerals
1975
1980
1985
1990
1995
2000
(Source: Rogich, Cassara et al. 2008)
3.8.1 Material Intensity per Service-Unit
The concept of Material Intensity per Service-unit (MIPS) was developed by the Wuppertal
Institute in Germany to measure the total mass flow of materials caused by the production,
consumption (including maintenance) and waste disposal/recycling of a defined service unit
or product. The total mass flow for a service unit can consist of overburden, minerals, ores,
fossil fuels, water, air and biomass. MIPS employs a life-cycle perspective to include
the "hidden" flows of a service unit. MIPS only considers input flows to avoid double
counting since input equals output. Also, this approach facilitates accounting since there are
fewer inputs than outputs in the industrial economy. The MIPS approach groups inputs into
five categories: biotic, abiotic, Earth movements, water and air. Energy demands for the
supply of the service unit are also accounted for on a mass basis. To provide additional
information, electricity and fuels were added as a sixth category.
The indicator assigns the same relevance to all materials, e.g., 1 kg of gravel and 1 kg of
plutonium are equal. In different regions, different fuels and raw materials are used as well as
production processes. It is therefore necessary to use the values relevant to each region.
MIPS plays an important role in the promotion of dematerialization. MIPS measures the
use of resources during a product's life cycle. The MIPS indicator is based on the material
flow and the number of services or utilizations provided. Reducing the MIPS of a product is
equivalent to increasing resource productivity. MIPS quantifies the material intensity of a
product or service by adding up the overall material input that humans move or extract to
make that product or provide that service. It puts life cycle thinking at the beginning of the
product chain. See www.mips-online.info for additional information.
34
-------
MIPS is measured in kilogram per unit of service. The material input is calculated in five
categories: abiotic raw materials, biotic raw materials, water, erosion, and air. The Wuppertal
Institute in Germany, which designed material flow analysis, promotes the need to cut
material use by 50% and increase the productivity of materials in a much more efficient and
more equitably distributed manner (Cleaner Production Action 2008).
Following the concept of MIPS, Materials Intensity Assessment (MAIA) is used to
quantify the life-cycle-wide requirement of primary materials for products and services.
Analogous to the quantification of the cumulative energy requirements, MAIA provides
information on basic environmental pressures associated with the magnitude of resource
extraction and the subsequent material flows which end up as waste or emission.
The input of primary raw materials (including energy carriers) is measured in physical units
(kg) and aggregated into five main categories:
• Abiotic Raw Materials (non-regrowing inputs)
• Biotic Raw Materials (regrowing inputs)
• Soil Removal
• Water
• Air (inputs for physico-chemical conversion, usually for combustion, in most
cases are also strongly correlated with carbon dioxide emissions)
(Institute of Environmental Sciences (CML) Leiden University 24 April 2009)
35
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3.9 Net Energy Balance
The life cycle balance, or the Net Energy Balance (NEB), of a biofuel should result in a
positive Net Energy Value (NEV) when compared to conventional fossil fuel in order for it to
be a considered as a viable substitute. However, it is well understood that the conversion of
biomass to bioenergy requires additional energy inputs, most often provided in some form of
fossil fuel. Depending on the processing choices, the cumulative fossil energy demand to
produce biofuels can vary widely. However, the bulk of the studies that have been published
report moderate to strong fossil fuel substitution for bioethanol systems (von Blottnitz and
Curran 2007).
Bioethanol also has its detractors. Often quoted are the works of Pimentel (Pimentel 2003) and
Patzek (Patzek 2004), who have both been critical of bioethanol and other biofuels. Their
studies contend that bioethanol, and biofuels in general, are "energy negative," meaning they
take more energy to produce than is contained in the final product. Perhaps one of the biggest
differences between the conclusions by Pimentel and Patzek and other studies that conclude
positive net gains is the approach to counting energy credits from by-products (Pimentel has
also been criticized for using older production data). Shapouri, Wang and others maintain that
ethanol by-products (such as dried distillers grains, gluten meal, gluten feed, and whey) are
themselves useful products whose market or energy value should be brought into the analysis
to help offset the energy costs of ethanol production (Shapouri, Duffield et al. 2002).
Biofuel production requires energy to grow crops and convert them into biofuels. Hill et al.
(2006) estimated farm energy use for producing corn and soybeans, including both direct and
indirect energy uses such as energy to grow the hybrid or varietal seed planted to produce the
crop, to produce and then power farm machinery and buildings, to produce fertilizers and
pesticides, and to sustain farmers and their households. They also estimated the energy
needed to convert crops into biofuels, including energy use in transporting the crops to
biofuel production facilities, building and operating biofuel production facilities and
sustaining production facility workers and their households. Outputs included the biofuels
themselves as well as co-products, such as distillers dried grains with solubles (DDGS),
which were assigned energy equivalent values. Despite the use of expansive boundaries, Hill
et al. show a positive net energy for corn ethanol. However, the net energy gain for corn
ethanol is small, providing approximately 25% more energy than required for its production.
Corn grain ethanol has a low net energy gain because of the high energy input required to
produce corn and to convert it into ethanol (Hill, Nelson et al. 2006). Almost all the entire net
energy gain is attributable to the energy credit given to ethanol for the DDGS co-product,
which is used as animal feed.
Although energy balances continue to be calculated and discussed, some do not view NEB as
the primary way to address energy security (Dale 2008). Instead, what matters is how
feedstocks such as coal and natural gas can effectively be used to convert corn into a
premium liquid fuel that replaces imported petroleum. This approach reduces the energy
balance issue to looking at the net energy of the liquid fossil fuels used in the production of
corn-ethanol.
36
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Examples of Net Energy Value Calculations
Farrell et al. (Farrell, Plevin et al. 2006) compared the NEV of (Iowa) corn grain ethanol
production to gasoline using the same system boundaries. Even though ethanol
production is a far less efficient process than gasoline production, overall, producing one
MJ of ethanol requires less fossil inputs (0.774 MJ) than is required to produce one MJ of
gasoline (1.19 MJ) As in some NEB models, this study gives energy credits to co-products
that are generated when ethanol is made. Credit is calculated by identifying co-products
that displace products such as dried distiller grains with solubles, corn gluten feed, and
corn oil, thereby partly offsetting the energy required for ethanol production. This is
known as the displacement method (Wang, Saricks et al. 1999).
Gasoline
Ethanol
Net Fossil Inputs
needed for each
MJfuei
1.19
0.774
Net Fossil Ratio
MJfUei produced for each
ssu input*
0.84
1.30
Petroleum Input
MJpetroleum needed for
each MJfUei
1.10
0.04
* Net Fossil Ratio = the inverse of Net Fossil Inputs
The USDA explored how allocation rules and co-product credits can make a difference in
calculating NEV and energy ratios (Shapouri, Duffield et al. 2002). The following
table summarizes the energy requirements by phase of ethanol production on a Btu-per-
gallon basis. It includes energy losses from line loss, venting losses at the ethanol plant,
and losses associated with mining, refining, and transporting raw materials. Also
presented is the NEV of corn ethanol without co-product credits for wet-milling, dry-
milling, and a weighted average of wet and dry milling. The weighted average is based on
two-thirds of U.S. ethanol capacity from wet-milling and one-third from dry-milling. The
average conversion rate for the two processes is 2.525 gallons per bushel. The energy
ratio, i.e., the ratio of energy-out to energy-in, is close to 1 in all three cases. In other
words, the Btu in a gallon of ethanol is about equal to the energy required to produce a
gallon of ethanol even when energy co-products are not considered.
Production phase
Corn production
Corn transport
Ethanol conversion
Ethanol distribution
Total energy used
Net energy value
Energy ratio
(Source: Shapouri,
Milling process
Dry
Wet
Weighted
average
Btu/gal
21,805
2,284
48,772
1,588
74,447
9,513
1.11
Duffielc
21,430
2,246
54,329
1,588
79,503
4,457
1.04
1 et al. 2
21,598
2,263
51,779
1,588
77,228
6,732
1.08
002)
37
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Examples of Net Energy Value Calculations (continued)
The table below presents the NEV and energy ratio results for corn ethanol when energy
credits are included in the calculation. Three conversion processes are considered: wet
mill, dry mill, and a weighted average of wet and dry milling (2 to 1, as described
above). For comparative purposes, the co-product energy values are shown for four
methods: output weight, energy content, market value, and replacement value. With co-
products credit, the average energy ratio increases from 1.08 (shown previously) to
between 1.34 (using a replacement value approach) and 2.22 (using an output weight
basis).
NEV and Energy Ratio Calculations for Corn Ethanol
Energy
Ethanol
Percent
Output weight basis
Wet mill
Dry mill
Weighted average
Energy content:
Wet mill
Dry mill
Weighted average
Market value:
Wet mill
Dry mill
Weighted average
Replacement value:
Wet mill
Dry mill
Weighted average
48
49
48
57
61
58
70
76
72
81
82
81
allocation
Energy use
_ , without co-
Co-products , .
product
credit
Percent Btu/gal
52
51
52
43
39
42
30
24
28
19
18
19
79,503
74,447
77,228
79,503
74,447
77,228
79,503
74,447
77,228
79,503
74,447
77,228
Energy use
with co-
product
credit
Btu/gal
39,987
37,289
37,895
46,000
46,032
45,459
56,129
56,961
56,049
64,699
61,332
62,856
NEV with
co-
products
Btu/gal
44,974
46,672
46,066
37,961
37,929
38,502
27,832
27,000
37,912
19,262
22,629
21,105
Energy
ratio
Btu/gal
2.15
2.25
2.22
1.83
1.82
1.85
1.50
1.47
1.50
1.30
1.37
1.34
(Source: Shapouri, Duffield et al. 2002)
38
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3.10 Sustainability Indicators
In deciding which metrics are important for achieving sustainability goals, most countries agree
on general principles for protecting agricultural lands and ecosystems and for reducing GHG
emissions. These metrics are more popularly known as indicators. Two classes of indicators are
in development by various groups to indicate the state and performance of a system. Those that
indicate the state of a system are known as content indicators and those that measure the
behavior of a system are known as performance indicators (Sikdar 2003). There have been
many initiatives to develop indicators of national-level sustainability, resilience and
vulnerability, but combining them with indicators from other countries can be problematic. The
Socioeconomics Data and Applications Center (SEDAC 2009) sought to make the
acquisition, comparison and analysis of sustainability indicators easier by compiling them in a
single database, incorporating multiple country codes, and condensing the indicator descriptions
into short methodological summaries in an accompanying metadata database. As a result, the
compendium includes 426 indicators from the following six collections:
• 2006 Environmental Performance Index (EPI) (Esty D.C., Levy M.A. et al. 2006)
• 2005 Environmental Sustainability Index (ESI) (Esty D.C., Levy M.A. et al. 2005)
• 2004 Environmental Vulnerability Index (EVI) (Kaly U.L., Pratt C.R. et al. 2004)
• Rio to Johannesburg Dashboard of Sustainability (O'Connor J. and Jesinghaus J. 2002)
• The Wellbeing of Nations (Prescott-Allen R. 2001)
• 2006 National Footprint Accounts (Ecological Footprint and Biocapacity) (Global
Footprint Network 2006)
While the United States is leading on many sustainability issues, it has not yet compiled an
official list of best practices or defined a set of sustainability principles, criteria, or indicators.
However, research to develop a satisfactory list of indicators is on-going; for example, Green
Communities work is being conducted by the EPA (EPA 2009). The following two sections
present examples that are developing sustainability indicators that are specific to biofuels: the
National Roundtable on Sustainable Biofuels and the Sustainability Interagency Working Group
of the National Biomass R&D Board.
3.10.1 Roundtable on Sustainable Biofuels
On August 13, 2008, the Roundtable on Sustainable Biofuels (Board of the Roundtable on
Sustainable Biofuels 2008) announced a new draft of sustainability standards for sustainable
biofuels, developed through global stakeholder discussion around requirements for
sustainable biofuels. The standard includes principles (general tenets of sustainable production)
and criteria (conditions to be met to achieve the principles). The following principles are
proposed by the Roundtable for Sustainable Biofuels:
1. Legality
2. Consultation, Planning, and Monitoring
3. Greenhouse Gas Emissions
4. Human and Labor Rights
5. Rural and Social Development
6. Food Security
7. Conservation
8. Soil
39
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9. Water
10. Air
11. Economic Efficiency, Technology, and Continuous Improvement
12. Land Rights
The group is working on developing indicators to evaluate a farm, producer, or company in
meeting the principles and criteria.
3.10.2 Sustainability Interagency Working Group
In 2008, the National Biomass R&D Board formed the Sustainability Interagency Working
Group, an interagency group led by the U.S. Department of Energy, Department of
Agriculture and the Environmental Protection Agency (Biomass R&D Board 2008; Hecht
2009). Table 3 lists the set of Sustainability criteria that has been drafted by the group for
discussion along the headings of Environmental, Economic, Social, and Energy
Diversification and Security (Hecht 2009).
Table 3. Draft Sustainability Criteria Developed by the National Biomass R&D Board for
U.S. Biofuels
Bin
Environmental
Criterion
Reduce greenhouse gas emissions
Conserve or improve land
productivity and soil quality
Increase water use efficiency and
maintain or improve water quality
Reduce airborne pollutants to
improve air quality:
the production of biofuels
Conserve or improve biological
diversity
Minimize negative land use
change impacts
Description
Life cycle assessment for specific feedstocks
and fuels, processes, and transportation.
Long-term soil quality and productivity of
working lands; conservation and stewardship
practices, soil quality, yield improvement,
management of nutrient and chemical inputs
and retention (plant stock, fertilizers, pesticides,
water) and appropriate pest and disease
management.
Water quality and water use efficiency, water
reuse and treatment.
Emissions of relevant criteria air pollutants and
toxics including those that are associated with
acute or chronic health risks.
Conservation of terrestrial and aquatic
biodiversity and ecosystem services in
compliance with applicable laws, regulations,
Direct and indirect land used for and resulting
from the production of biofuels.
(Adapted from Hecht 2009)
40
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Table 3. Continued
Economic
Social
Energy Diversification
and Security
Enhance resource use and
conversion efficiency and
productivity
Improve cost competitiveness
Enhance economic development
and rural prosperity
Maintain adequate supply of food,
feed, and fiber products to meet
demand
Ensure public health and safety
Comply with relevant legal and
institutional frameworks
Increase workforce capacity
Reduce imported oil and increase
displacement of imported oil-
based products:
Ensure positive net energy
balance
Increase access to affordable
energy
Reduce waste
Reduce production costs
Increase GDP
Impacts of biofuels production and use on the
availability of affordable and secure food,
water, feed, and fiber for domestic consumption
and foreign export.
Protection of public safety and health, including
incidental pollutant exposure, in all aspects of
the biofuels supply, distribution, and use chain.
Compliance with applicable environmental,
land, and labor laws, regulations, treaties,
agreements, and executive orders pertaining to
the biofuels supply and use chain.
Workforce capacity as needed to meet current
and future needs for the biofuels supply chain.
Biofuels as one means to diversifying energy
supply by reducing reliance on imported oil and
ultimately the displacement of oil-based
products.
Net energy balance resulting from life cycle
analysis of biofuels, accounting for the entire
supply chain as compared to fossil fuels.
Long-term availability of biofuels to the public
as compared to fossil fuels
Sustainability Indicators provide broad-based tools that cover a variety of issues, including
biodiversity and social impacts. However, effective metrics that can be used to measure
progress are still needed. Furthermore, the check-list type approach offered by Sustainability
Indicators does not appear to offer a straightforward way to avoid potential trade-offs or
unintended consequences.
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4.0 Results
Table 4 categorizes the ten analytical tools and approaches that were investigated in this
study by the information that each develops and the environmental concerns they measure or
address. A tool may generate data or information that is relevant to a particular environmental
impact, but not necessarily report on that impact. For example, a GHG Life Cycle
Analysis identifies and quantifies GHG emissions without going to the next step of modeling
the potential contribution to global warming. Life Cycle Assessment, on the other hand,
includes such models and reports global warming potential. As can be seen in the table, no
single tool addresses all environmental concerns.
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Table 4. The Information or Data Typically Generated by Life-cycle Based Assessment Approaches Mapped Against Commonly
Reported Environmental Concerns Related to Bio-based Products.
Carbon/GHG
ManaRement
Ecological
Footprint
Energy
Assessments
Fuel Cycle
Analysis
Life Cycle
Assessment
Life Cycle Risk
Assessment
Material Flow
Analysis (MIPS)
Sustainability
Indicators
Resource
Use
Energy
Use
Global
Climate
Change
Air
Quality
Water
Quality
Soil
Quality
Land
Use
Water
Use
Food-
for-Fuel
Bio-
diversity
Invasive
Species
Socio-
Economic
Impacts
/////////////
/////////////
* MIPS: Material Input per Service
Environmental concerns that are currently modeled are represented by dark grey; emerging or quasi applications are indicated by light grey.
Sustainability Indicators is the only approach to address socio-economic impacts as well as various environmental impacts.
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5.0 Discussion
In reviewing the literature, it quickly becomes clear that the early concern in switching from
gasoline (petrofuels) to biofuels was the net energy issue. Numerous researchers calculated,
debated, and debated again whether fuels from biofeedstocks result in an overall gain or a loss
of energy. While the debate continues, the prevailing consensus is that corn-based ethanol, to
varying degrees, has an advantage over gasoline when it comes to energy inputs.
The energy ratio allows for some comparisons to be made between fuel types, however, the
true value of fuels is not reflected in an energy analysis because one kJ of ethanol is more
useful as a fuel for vehicles than one kJ of natural gas or coal. Bruce Dale argues that the net
energy argument is irrelevant and misleading since it assumes all energy carriers are equally
valuable, but they are not (Dale 2008).
Recent awareness of Global Climate Change has driven researchers to study, on a system-
wide basis, CC>2 emissions, which comprise the flip side of the energy coin since much of our
energy is produced from petroleum resources. Because the interest in CC>2 releases has been
driven by concerns of increased global warming effects, the list of air emissions was
expanded to include other GHGs. This expansion had the effect of making approaches such as
Carbon Management, which began as a carbon accounting approach, very similar to Fuel
Cycle Analysis and GHG Analysis.
Exergy analysis continues to be developed and promoted as a way to identify potential
reductions in thermodynamic losses and efficiency improvements, and to address
sustainability issues in a quantitative fashion. For example, researchers at Ohio State
University are developing an ecologically-based life cycle analysis (Eco-LCA™) tool which
emphasizes the essential role of ecosystem goods and services. Eco-LCA™ is both an
economic analysis and an exergy-based calculation of the ecological resource efficiencies of
supply chains (Zhang, Baral et al. 2010). The use of exergy calculations should be further
investigated and developed in order for it to achieve broader acceptance as an environmental
assessment tool.
Ecological Footprinting is widely used around the globe as an indicator of environmental
sustainability. Its appeal is the simplicity of the results that are presented in a single
measurement. However, simplicity is also the weakness of the tool. For example, the
ecological footprint model treats nuclear power the same as it treats coal power, even though
the actual effects of the two modes of power generation are radically different. In addition,
some questions remain regarding the validity of the model and the underlying assumptions.
Life Cycle Assessment attempts to model the entire range of environmental impacts across the
product system (cradle to grave) of biofuels, including global climate change, air quality,
water quality, soil quality, and resource use as well as the potential reduction of fossil fuel use
and GHG emissions. Land use changes and water use impacts can be captured by LCA only if
all the necessary life cycle inventory data are collected.
Material Flow Analysis was originally developed as a way to account for the extraction and
use of materials as they flow through the economy. As such, it can generate useful
information for understanding the potential impacts on our use of natural resources; its main
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goal is dematerialization. Later generations of MFA, including MIPS and MAIA, have
expanded its usefulness to include information on air quality, soil quality and water use.
The use of Sustainability Indicators is the only approach of the ones studied here that takes
biodiversity and social impacts into consideration. However, the implementation of indicators
toward sustainability, especially the application of metrics by which progress can be
measured, has yet to be developed. Furthermore, the check-list type approach offered by
Sustainability Indicators does not appear to offer a straightforward way to avoid potential
trade-offs or unintended consequences. For example, choosing to use more biofuel in order to
reduce greenhouse gas emissions will potentially have resultant impacts to water and soil
quality, as was mentioned earlier. How a checklist allows the user to achieve one goal
without sacrificing another is not clear.
5.1 Data and Information Needs
Effective environmental decision making and public policies need to be based on a broad
range of data and information and not only on single issues, such as fossil fuel dependency,
which can lead to an "all biofuels are good" perspective. In order to capture the entire
spectrum of impacts that are outlined at the outset of this report, a wide array of data i s
needed. In addition, the descriptions of the slate of tools and approaches provided herein
make it clear that more and better data are needed for their full implementation. A summary
of the data and information needed to accurately assess biofuels (not only corn-based ethanol,
but all bio-based fuels) is provided below.
5.2 Environmental Data
5.2.1 Production Data
Biofuel production techniques and farming practices are changing quickly, and becoming
more efficient. Thus, published studies may rely on old data that need to be updated in order
to account for increased efficiencies. Ethanol plants can have distinctly different energy and
GHG emission effects on a full fuel-cycle basis. In particular, GHG emission impacts
can vary significantly—from a 3% increase if coal is the process fuel to a 52% reduction if
wood chips are used (Wang, Wu et al. 2007). Therefore, not only are accurate input and
emissions data for different biofeedstocks needed, data to reflect the types of plants used
to produce corn ethanol are needed as well.
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5.2.2 Water Use and Availability
Water Use in Corn Ethanol Production (Biorefining)
Water usage is a significant, yet not fully recorded, issue in the United States for the ethanol
industry. It is estimated that 3-4 gallons of water are used per gallon of ethanol produced using
the dry milling production process (which is prevalent in 80 percent of U.S. ethanol
production facilities) while 2 to 2.5 gallons of water are used per gallon of gasoline
produced (Aden 2007). However, the amount of water used in the biorefming process is
modest compared to the water used to grow bioenergy crops.
Water Use in Crop Irrigation
Each biofuel feedstock presents unique implications for water resources. Water use varies a
great deal depending on whether the biofuel is grown on irrigated land or not, and whether
there is an increase in overall agricultural production. In the United States, the vast majority
of biofuels are currently grown on non-irrigated land (as much as 96% of field corn used for
ethanol production is not irrigated). For corn that is irrigated, water consumption estimates
are not widely available. For the field corn used for ethanol production that is irrigated, water
use has been reported to be approximately 785 gallons on average for each gallon of ethanol
produced (Aden 2007).
5.2.3 Water Quality
Among the various potential biofuel crops, corn requires the greatest amount of nitrogen and
phosphorous fertilizer per unit of net energy captured in the biofuel. Nitrogen that washes off
farmers' fields into bodies of water causes water quality problems; excess nitrogen washing
into the Mississippi River is known to cause an oxygen-starved "dead zone" in the Gulf of
Mexico (Costello, Griffin et al. 2009). However, the data that represent the amount of
agrochemicals that are applied to the land but run off into adjacent waterways are not readily
available. Simulation models are available for such estimations, but their application is
region-specific and the calculations have not been performed for all the United States.
5.2.4 Land Use Changes
Land Use Change (LUC) issues may be very important but have not been fully explored. It is
projected that the rush to produce corn-based ethanol could see an increase of 10 to 12
million corn acres nationwide, depending if it assumed that per acre crop yield will continue
to increase as it has in the last few decades (from 79 bushels per acre in 1970 to 150 bushels
per acre in 2005). Globally, the conversion of forested, pasture or savannah-type land to
(annual) bioenergy crop cultivation could cause higher GHG emissions from released soil
carbon and cleared biomass than is fixed by the cultivation of energy crops. This leads to a
change in carbon stocks which needs to be considered in the overall GHG balance.
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Along with bringing new land into production, changes in crop rotations and tillage
practices from increased corn production lead to increases in soil erosion and nutrient
loading, particularly in the U.S. Corn Belt and Northern Plains (USDA 2007).
5.2.5 Soil Erosion and Sedimentation
Sedimentation occurs when soil erodes from land and washes down into surface water bodies.
Sediments impair water quality and also carry agricultural and other pollutants. The amount
of sediment eroding from agricultural areas is directly related to land use - the more intensive
the land use the greater the erosion.
Producing biofuels from perennial crops that hold soil and nutrients in place and require
less fertilizers and pesticides, like switchgrass or poplars, is an option to reduce the effects of
sedimentation. There are, however, large uncertainties surrounding the production of
cellulosic ethanol from such crops. Such crops have very little history of use in large-scale
cultivation, so even basic information on water, nitrogen or herbicide use, or impact on soil
erosion or even overall yields is preliminary (The National Academies of Science 2008).
5.2.6 Human Health Effects
Ethanol use in vehicle fuel is increasing worldwide. However, the potential cancer risk and
ozone-related health consequences of a large-scale conversion from gasoline to ethanol have
not been thoroughly examined. Several concerns have been raised regarding the possibility of
emissions from higher ethanol fuels worsening health risks from air pollution (Naidenko
2009). In addition, Jacobsen (2007) concluded the following:
• E85 (85% ethanol fuel, 15% gasoline) may increase ozone-related mortality,
hospitalization, and asthma by about 9% in Los Angeles and 4% in the United States as a
whole relative to 100% gasoline usage.
• Ozone increases in Los Angeles and the Northeast United States are partially offset by
decreases in the Southeast United States
• E85 also increased peroxyacetyl nitrate (PAN) in the United States, but was estimated
to cause little change in cancer risk.
• Due to its ozone effects, future E85 may be a greater overall public health risk than
gasoline.
• Unburned ethanol emissions from E85 may result in a global-scale source of
acetaldehyde larger than that of direct emissions (Jacobson 2007).
The cultivation of bioenergy crops can cause not only land use conflicts, but also direct
impacts on human health depending on the type of crop and harvesting procedures.
Pesticides are the primary cause of health risks for agricultural workers. Air pollutants caused
by field burning can lead to adverse health effects, especially as a result of the cultivation of
sugar cane and palm oil. Furthermore, it is not certain how well workers are educated about
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the health risks of using pesticides. The use of spraying aircraft can cause pesticides to drift
outside of the target area, damage other farmers' crops and harm their animals (Bickel/Dros
2003). Harvesting is dangerous work carried out using sharp tools. Cutting and planting green
cane causes skin irritations. Burned cane can also cause skin irritation. Smoky and polluted
environments are a danger to health, as are the residues of toxins used in weed control.
Medical care is often not available on the plantations. Furthermore, exposure to the sun,
insects and snakes and uncomfortable positions during work all impact on human health
(Zamora et al. 2004).
5.2.7 Biodiversity
The replacement of lands to grow corn can have a large impact on the diversity of species. It
is suspected that higher corn prices, caused by increased ethanol demand, will motivate some
U.S. landowners to convert pastures to row crop production. The impact of land conversion is
not well known, however, it is likely that the destruction of rainforests and other ecosystems
to make new farmland would threaten the continued existence of countless animal and plant
species (Doornbusch and Steenblik 2007).
5.2.8 Invasive Species
Some plants that are being considered as feedstock for biofuel crops are known to be very
invasive. For example, Sorghum Halepense (Johnson grass) is an introduced forage grass that
became an invasive weed in 16 of the 48 contiguous states in which it occurs. The African oil
palm, recommended for biodiesel, has already become invasive in parts of Brazil, turning
areas of threatened forest from a rich mix of trees and plant life into a homogenous layer of
palm leaves. Our understanding of potential impacts of biofeedstock production on wildlife
habitat and the spread of invasive species is in its infancy. The risks of growing these crops
widely need to be evaluated before these crops are planted (Graham 2007).
5.2.9 Socio-Economic Impacts
The definition of sustainability includes the three conditions of economic, social and
environmental "endowments" and "liabilities" that we embrace and pass on to future
generations. In addition to the above environmental assessment tools, there is a need to
incorporate social and economic assessments of biofuels to ensure that overall sustainability
can be addressed. For instance, the cascading effects of large changes in markets are often not
addressed. Potential trade-offs, such as food-for-fuel, should be thoroughly examined (the
surging biofuel industry will use 27% of this year's American corn crop, challenging farmers'
ability to meet food demands). In Mexico, soaring corn prices, sparked by demand from
ethanol plants, doubled the price of tortillas, a staple food (Tillman and Hill 2007).
Instead of a fragmented approach toward sustainable development, one should examine the
linkages between environmental indicators and socio-economic factors that influence and
interact with the indicators. Future research efforts should be directed to further define these
linkages and provide guidance for decision makers to integrate all three facets of
sustainability (environment, economy, and society) into the decision-making process.
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6.0 Conclusions
The benefits, as well as the drawbacks, of biofuels have come under increasing scrutiny as
researchers and policy makers look closer at the global environmental impact of their
production. Unintended consequences may reduce or override the expected benefits. The
widespread deployment of biofuels will have major implications for land use, with associated
environmental impacts that must, in turn, be assessed. For example, diverting corn to make
biofuels could result in shifting production to competing crops, such as soybean, or the
conversion of lands to corn production. The overall impacts of these types of shifts are not
well understood. In order to move toward sustainability, biofuels need to be approached at
the international level in order to capture both global and local issues. If used properly,
biofuels can help us meet our energy needs while maintaining ample supplies of food, animal
feed and clean water supplies. To make this happen, well thought out national biofuels
policies that support the best options are needed for both the short and long-term future.
Various tools and approaches are being applied to closely examine the production and use of
biofuels in order to better understand their potential environmental impact. Ten such tools that
are based on the cradle-to-grave, life cycle concept study were examined in this report in
order to see how the information that they generate relates to the major environmental and
social-economic concerns that are the center of attention in the media and published
literature. Growing concerns over global climate change have led to the promotion of
assessment tools that focus on greenhouse gases, such as Carbon Footprint and Greenhouse
Gas Life Cycle Analysis. Fuel Cycle Analyses have traditionally modeled air emissions and
are also useful for addressing global climate change, as well as other human health-related air
impacts and energy use. Other tools fill very specific niches, such as Ecological Footprint,
which accounts for human demand on nature as measured in land area, and Material Flow
Analysis (MFA), which models the use of natural resources and identifies potential losses as
goods and materials move through the economy. Since no single tool encompasses all possible
environmental impacts, an effective method is needed to integrate these tools into a
framework that supports the decision-making process as we further develop biofuels.
Looking beyond even an integrated, holistic assessment of environmental impacts, it is also
important to consider the economic and social aspects of the full life cycle of biofuels, from
growth of the biomass, transport to the refinery, refining, distribution to consumers, and,
ultimately, end use. Since it is likely that international trade in these commodities is likely to
expand in coming years, it is essential that we use the appropriate assessment tools and
establish a commonly-accepted set of sustainability criteria by which to assess the different
biofuels and biofeedstocks, including food and non-food, and their production systems. A
coherent biofuels policy must address and balance all these factors if biofuels are to make a
sustainable contribution to reducing climate change and improving energy security.
The application of a life cycle view to holistically assess biofuels will be an essential
requirement if we are to achieve the potential that is offered by the newly emerging bio-
economy. Members of the scientific community need to actively communicate and work
together to develop a consensus on what science is needed to support our policy-makers in
delivering sustainable energy systems.
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