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1
Introduction
1.1 INTEREST IN ALGAL BIOFUELS
P
etroleum-based fuels have been the primary type of transportation fuel in the United
States for decades. Until the 1960s, domestic production of these fuels met the vast
majority of the nation's demand. U.S. oil production peaked in the 1970s, but demand
continued to grow. The desire to reduce reliance on foreign oil imports and to improve
energy security sparked interests in research and development (R&D) of alternative fuels.
In 1978, the U.S. Department of Energy's (DOE) Office of Fuels Development initiated the
Aquatic Species Program whose goal is to produce renewable transportation fuels from
algae (Sheehan et al., 1998). That program furthered the understanding of algae's potential
as a feedstock for fuel through its development and characterization of a large collection
of oil-producing algae, its research to improve understanding of the biological triggers for
enhancing oil production in algae, and its work on demonstrating open-pond systems for
large-scale algae cultivation (Sheehan et al., 1998). Biofuels derived from algae and cyano-
bacteria1 were considered a promising alternative fuel for improving energy security for
the following reasons:
· Microalgae, macroalgae,2 and cyanobacteria convert solar energy to chemical en-
ergy for their growth and development through the process of photosynthesis.
Some species also can be grown in heterotrophic conditions, where an exogenous
source of organic carbon is provided.
1Cyanobacteria, also called cyanoprokaryotes, were historically known as blue-green algae. For simplicity,
biofuels derived from macroalgae, microalgae, and cyanobacteria grown under photosynthetic conditions all are
referred to as algal biofuels.
2Macroalgae are multicellular algae that lack true roots and leaves. Macroalgae are found in fresh water and
marine water, soil, and growing on other organisms.
11
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12 SUSTAINABLE DEVELOPMENT OF ALGAL BIOFUELS
· Unicellular algae and cyanobacteria have the advantage of being able to complete
a reproductive cycle in a matter of hours or a few days. Therefore, they can be har-
vested on a daily or weekly basis.
· The oil productivity of many species of algae exceeds that of oil crops (Patil et al.,
2008).
During its two decades of operation, the Aquatic Species Program built a collection
of more than 3,000 species of oil-producing microalgae (Sheehan et al., 1998). Program
research shed light on algal physiology and biochemistry and the relationship between oil
content in cells and algal productivity. Efforts also were made to demonstrate the feasibility
of large-scale cultivation of algae in open ponds (Sheehan et al., 1998). The Aquatic Species
Program was terminated in 1996 when DOE was under budget pressure. At that time, the
price of oil was less than $20 per barrel (EIA, 1999). In contrast, a technoeconomic analysis
conducted in 1982 estimated algal biofuels would cost about $60 per barrel of oil equivalent
under an optimistic scenario and about $120 per barrel of oil equivalent under a conserva-
tive scenario (Benemann et al., 1982).
Volatile oil prices observed from 2000 to the present renewed interests in alternative
fuels. In addition, mounting evidence of global climate change raised concern over the
carbon footprint of using fossil fuels. Greenhouse gases (GHG)--such as carbon dioxide
(CO2), nitrous oxide, and methane--are heat-trapping gases that produce a warming effect
on the Earth's atmosphere. CO2 emissions from burning of fossil fuels account for a large
portion of GHG emissions (NRC, 2011a). In the United States, the use of petroleum-based
fuel in the transportation sector accounted for 30 percent of the nation's CO2 emissions in
2009. Although using algal biofuels for transportation would produce tailpipe emissions
comparable to those from using petroleum-based fuels, algae and cyanobacteria take up
CO2 during growth and thereby offset some of the CO2 emissions (Brune et al., 2009). In
addition, the net impact on CO2 emissions also depends on the quantity of fossil fuels used
throughout the algal biofuel production pathway. Life-cycle assessment (LCA), discussed
later in this chapter, attempts to account for and aggregate the energy requirements and
CO2 impacts over the whole production pathway.
Domestic production of renewable fuels including algal biofuels has the potential to
meet the dual goals of improving energy security and decreasing GHG emissions from
the transportation sector. However, a dramatic decrease in foreign oil importation and
reduction in GHG emissions in the United States will require the production and use of
multiple alternative transportation fuels. Biofuels produced from algal feedstock could be
one of the alternatives. The number of startup companies working on the development of
algal biofuels has been increasing, and some oil companies are investing in algal biofuels
(Mascarelli, 2009; Mouawad, 2009). The U.S. military is interested in substituting part of
its fuel use with renewable energy sources including algal biofuel (Physorg.com, 2010),
and the Defense Advanced Research Projects Agency funded projects for developing tech-
nologies to produce affordable algal biofuels (Lundquist et al., 2010). Given the interest in
algal biofuels, the DOE Energy Efficiency and Renewable Energy's (DOE-EERE) Office of
Biomass Program (OBP) held a workshop in 2008 "to discuss and identify the critical barri-
ers currently preventing the economical production of algal biofuels at a commercial scale"
(DOE, 2010). DOE and private companies are actively investing in R&D for algal biofuels
to resolve technical barriers, improve feasibility of large-scale production, and reduce costs.
In addition to developing production technologies, any developing industry also needs to
consider sustainability. Addressing sustainability concerns and challenges as the industry
develops can help ensure its success well into the future. Ignoring sustainability at the
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INTRODUCTION 13
BOX 1-1
Statement of Task
The committee is tasked to examine the promise of sustainable development of algal biofuels, identify
potential concerns and unforeseen sustainability challenges and unintended consequences for a range of
approaches to algal biofuel production, explore ways to address those challenges, and suggest appropri-
ate indicators and metrics that can inform future assessments of environmental performance and social
acceptance associated with sustainability. Although economics is an important aspect of sustainability, the
study will not assess costs of algal biofuels. Algal biofuel production approaches and technical systems
are still emerging, and facilities have not reached commercial scale. Public data on the economics of algal
biofuel production is sparse. Therefore, it is premature for the committee to conduct generalized economic
analyses of algal biofuels.
The committee will:
· Identify the potential sustainability concerns for commercial production (including larger centralized
and smaller distributed facilities) of algal biofuels associated with a selected number of different
pathways of biomass production and conversion. Potential concerns to be addressed could include
the availability and use of land, water, and nutrient resources; human health and safety associated
with feedstock cultivation and processing; potential toxicity associated with algal metabolites and
their adverse impacts on downstream coproducts; and other impacts that are of social and envi-
ronmental concern.
· Identify information or data gaps related to the impacts of algal biofuel production.
· Suggest indicators and metrics to be used to assess sustainability concerns across the algal biofuel
supply chain and data to be collected now to establish baseline and to assess sustainability. Identify
indicators that are most critical to address or have the greatest potential for improvement through
DOE intervention. This input will inform DOE-EERE OBP's broader analysis of biofuels and bioenergy
sustainability.
· Using selected approaches as illustrations, discuss whether any, or combinations of, the identified
challenges could present major sustainability concerns. Are there preferred cost and benefit analyses
that could best aid in the decision-making process, and could those decisions be performance based
and technology neutral?
outset might exacerbate the sustainability issues for future generations and make it difficult
for an industry to successfully scale-up (Azapagic and Perdan, 2000).
At the request of DOE-EERE's OBP, the National Research Council (NRC) appointed
an independent committee to examine the sustainable development of algal biofuels. (See
Appendix A for committee membership.) The purpose of this study is to identify and an-
ticipate sustainability concerns associated with large-scale deployment of algal biofuels,
discuss potential mitigation strategies, and suggest indicators and metrics that could be
used and data that could be collected to evaluate sustainability across the biofuel supply
chain to monitor progress as the industry develops (Box 1-1).
1.2 SUSTAINABLE DEVELOPMENT OF BIOFUELS
1.2.1 Defining Sustainable Development
"Sustainable development is development that meets the needs of the present with-
out compromising the ability of future generations to meet their own needs" (United
Nations, 1987). Most definitions of sustainability include and integrate an economic, an
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14 SUSTAINABLE DEVELOPMENT OF ALGAL BIOFUELS
environmental, and a social dimension (Hammond, 2000; IISD, 2011; United Nations, 2011).
A recent NRC report identified four key societal sustainability goals for agriculture. Those
goals are:
· "Satisfy human food, feed, and fiber needs, and contribute to biofuel needs.
· Enhance environmental quality and resource base.
· Sustain the economic viability of agriculture.
· Enhance the quality of life for farmers, farm workers, and society as a whole."
(NRC, 2010b; p.23)
In the context of algal biofuels, the goals of sustainable development can be framed as
follows:
· Contribute to energy security, particularly the domestic supply of transportation
fuel.
· Maintain and enhance the natural resource base and environmental quality.
· Produce fuel that is economically viable.
· Enhance the quality of life for society as a whole.
The four aspects of sustainability are interconnected in many ways, some of which are
synergistic or mutually reinforcing, others of which might involve tradeoffs among goals.
An example of synergy could be technological improvements in algae and cyanobacteria
production and in processing the biomass to fuels. Those improvements would enhance
fuel yield, contribute to energy security, increase resource use efficiency, and reduce cost
of production, and therefore contribute to transportation fuel needs and improve environ-
mental, economic, and social sustainability. An example of a tradeoff could be pollutant
management, which would contribute to maintaining environmental quality and minimiz-
ing human-health impacts but could add to the cost of production.
1.2.2 Components of Sustainable Biofuel Development
As in the case of plant-based biofuels (NRC, 2011b), algal biofuels could provide op-
portunities to improve energy security, reduce GHG emissions, and maintain and enhance
the resource base and environmental quality, but their production also could raise sustain-
ability concerns. Whether those opportunities will be realized depends on how the industry
develops. It is prudent to consider potential sustainability concerns that might arise and
to avoid or mitigate them as the industry develops. Sustainability of plant-based biofuels
has been discussed, and criteria for assessments have been developed by various entities
over the past decade (ESA, 2008; Markevicius et al., 2010; NRC, 2010a,c). Examples of sus-
tainability criteria are shown in Table 1-1. Many of the sustainability criteria apply to algal
biofuels.
1.2.2.1 Energy Security
Whether and how much algal biofuels would contribute to energy security depends in
part on the resources (for example, land and water) available for algal biofuel production,
the productivity of algae cultivation, the yield of the processing of algae to fuel, and the
ability to integrate the various components of algal biofuel production into one functional
system and to scale it up. Resource limitations bound how much algal biofuel could be
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INTRODUCTION 15
TABLE 1-1 Examples of Sustainability Criteria Used to Evaluate Plant-Based Biofuels.
Sustainability Criteria Explanation
Economic
· Cost of production Cost competitiveness with respect to other fuel alternatives.
· Economic development Effects on the standard of living and economic health.
· Fiscal effects Effects on fiscal balances.
· Employment Employment creation.
Resource Use and Environmental
· Energy balance Energy output in fuel per unit of energy input to make the fuel
over its life cycle.
· Resource use including land and water Land and water requirements to produce one unit of fuel.
· Pollutant emissions including GHG and Emissions (for example, CO2 and sulfur oxides) over the life
criteria pollutants cycle of one unit of fuel.
· Biodiversity Effects on ecological species and communities (for example,
habitat destruction or enhancement).
Social
· Competition for resources being used for Effects of resource use (for example, water and nutrients) for
other human activities biofuel production on other activities (for example, farming
food crops and animals).
· Cultural acceptability Acceptability of the effects of biofuel production.
· Visual impacts Perception of landscape aesthetics.
· Health effects Effects of emissions (for example, air-quality emissions) on
human health.
produced, but technological progress could enhance the productivity of algal feedstock
and fuel yield.
1.2.2.2 Economics
Cost of production is an important aspect of sustainable development that applies to
all nonpetroleum-based alternative fuels including algal biofuels. Alternative fuels are not
likely to penetrate the fuel markets if they are much more expensive for consumers than
other fuel alternatives (NRC, 2008, 2011b). Although government policies and subsidies can
facilitate and accelerate the market penetration of biofuels, the biofuels eventually would
have to become economically viable without subsidy. Brazilian ethanol was heavily subsi-
dized when Brazil's National Alcohol Program was initiated, but the government subsidies
gradually were phased out in the 1990s. Sugar-cane ethanol has been economically viable
in Brazil since 2003 (Solomon, 2010).
As discussed in Box 1-1, the committee was not asked to analyze costs of algal biofuels.
Published estimates for costs of algal oil and algal biofuels span a wide range of about $1-
$25 per gallon (Williams and Laurens, 2010; Gallagher, 2011; and references cited therein).
The wide range reflects a number of factors including when the estimate was made. The
cost estimates reported in the literature were not in constant dollars and therefore are not
directly comparable. Some cost estimates were for algal oil before upgrading to fuels. A
wide range of technologies could be used in an algal biofuel production system resulting
in varying costs. This range in estimated costs reflects the immaturity of algal biofuel pro-
duction and the uncertainties associated with a developing industry (Williams and Lau-
rens, 2010). It is still premature to analyze and draw any conclusions about the economic
sustainability of algal biofuels, particularly when costs likely will decrease with ongoing
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16 SUSTAINABLE DEVELOPMENT OF ALGAL BIOFUELS
technological developments. Although this report does not address costs of algal biofuels,
it makes occasional reference to economics if there are known critical synergies or tradeoffs
between economics, productivity, resource use, and environmental effects.
1.2.2.3 Resource Use and Environmental Effects
Land, water, and nutrients are required for cultivating plants and algae. Cropland acre-
age in the United States has been decreasing in the past few decades (Nickerson et al., 2011),
and the water levels of some aquifers used for irrigated agriculture have been declining
(NRC, 2001). Nutrient runoff from row-crop agriculture into surface water and its environ-
mental effects has raised concerns (NRC, 2009). Some of these concerns for resource use
and availability and for the environment might be alleviated by developing algal biofuels
because the production of algae and cyanobacteria biomass does not require high-quality
land resources, as in the case of the production of sugar cane or corn for ethanol, and soy-
bean or other oilseeds for biodiesel (Schenk et al., 2008). Algae and cyanobacteria can be
grown in saline waters or nutrient-rich wastewater that is not suitable for agriculture or
human consumption (Woertz et al., 2009; Bhatnagar et al., 2010; Chinnasamy et al., 2010;
Craggs et al., 2011). In addition, enriching algae and cyanobacteria cultures with CO2 and
other nutrients helps maximize photosynthetic algal biomass production on a large scale.
One suggestion is to co-locate algal biomass production sites with stationary industrial CO 2
emission sources like fossil fuel-fired power plants to integrate the plant CO2 emissions
with the algal cultivation system. Another suggestion is to locate algal biomass produc-
tion facilities near wastewater sources, such as municipal wastewater treatment plants.
Algae cultivation systems can use the nutrients present in wastewater that has undergone
primary or secondary treatment thereby serving as a nutrient removal component of waste-
water treatment. An important issue then to assess is the number of potential sites for algae
cultivation that are near both a source of CO2, such as fossil-fired power plants, and a source
of nonpotable water, such as wastewater or saline water. Resource use and maintaining
the quality of the natural resource base necessary for developing algal biofuels will play a
role in the sustainable development of algal biofuel. This report focuses on the sustainable
development of algal biofuels with respect to resource use and effects on the environment.
1.2.2.4 Social Well Being
Although biomass production of algae and cyanobacteria is not likely to compete for
high-quality arable land with crops, there could be social concerns about land use that
need to be considered in the development of algal biofuels. For example, situating algae
and cyanobacteria biomass production in the U.S. desert Southwest could be perceived
as a good use of low-value land by some, but as an intrusion into pristine land by others.
Similarly, the use of genetically engineered organisms in production systems could affect
social acceptability. This report discusses how the resource use and environmental effects
of large-scale algal biofuel production could affect the social acceptability of algal biofuels.
1.2.3 Sustainability of Transportation Fuel
The preceding section mentioned some potential sustainability concerns for large-scale
development of algal biofuels (which will be discussed in detail in later chapters along with
opportunities to mitigate them), but the sustainability of algal biofuels cannot be viewed
in isolation and needs to be put into the broader context of the transportation-fuel sector
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INTRODUCTION 17
for two reasons. First, there is not one alternative fuel that can replace all the petroleum-
based fuels used in U.S. transportation. Few options are available to reduce petroleum
use (NAS-NAE-NRC, 2009), and algal biofuels could become a future option for reduc-
ing petroleum use and GHG emissions from the transportation sector. Second, every fuel
source has its positive and negative effects on the resource base or other aspects of the
environment. Therefore, the overall sustainabilities of different fuels have to be compared
to assess whether replacing one fuel with another would contribute to improving sustain-
ability. Therefore, the committee cautions that the report is not to be read as a mere list of
sustainability concerns, but as a discussion of resource use and environmental effects that
need to be compared with those of other fuels to see which fuel option is more sustainable
or better balances the various sustainability objectives.
1.3 TOOLS AND METHODOLOGIES FOR ASSESSING
SUSTAINABLE DEVELOPMENT OF ALGAL BIOFUELS
This section presents a brief overview of the tools and methodologies used for assessing
the sustainability of algal biofuels in this report. The objective here is not to provide results
from the application of these methodologies to algal biofuels, but to provide a brief descrip-
tion of the approaches used in this report and how they help meet the overall objectives
of providing indicators and approaches to measuring the sustainability of algal biofuels.
It focuses on several basic concepts: the systems analysis framework, indicators of sus-
tainability, LCA, and futures or scenario analysis. Indicators are repeated measurements,
observations, or model results that "are used to represent or serve as proxies for impacts
of outcomes of concerns" (NRC 2010b, p.32). LCA and futures analysis are methodologies
for estimating resource use and environmental effects. Systems analysis is an integrating
conceptual approach for evaluating impacts of algal biofuels.
1.3.1 Systems Analysis Framework
As Holmes and Wolman (2001) have pointed out, the systems analysis approach em-
phasizes the development of comprehensive strategies and impact assessments by inte-
grating all "critical physical, biological, socioeconomic, and engineering processes and
constraints into a unified framework" (Figure 1-1). Typically quantitative models are used
to define the most effective outcome or tradeoffs among multiple outcomes for a given set
of system inputs. Historically, the application of this methodology involved "elucidating
the objective(s) in the solution, developing a comprehensive description [of the system],
formulating alternative solutions, and [quantitatively] analyzing the alternatives with re-
spect to the magnitude and distribution of their consequences" (Holmes and Wolman, 2001,
p. 177). The systems analysis framework is particularly applicable to algal biofuels. Of all
of the current renewable energy alternatives, biofuels derived from algae and plant-based
resources represent one of the most complex systems integration challenges. Part of the
complexity is due to the diverse set of feedstocks, and logistical and conversion technolo-
gies that designers of bioenergy systems can select from as major components of a biofuel
industrial ecology. In addition, many of these technologies are at different evolutionary
stages of development ranging from an intriguing possibility to large-scale pilot demon-
strations. Further adding to this complexity is the diverse way that these technologies can
be integrated to design and implement advanced biofuel systems. This diversity in the
mixing of technologies and the possible integration schemes is a driver for innovation as
currently seen in the diverse commercial approaches to algal biofuel development. At the
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18 SUSTAINABLE DEVELOPMENT OF ALGAL BIOFUELS
Raw Material Acquisition Products
Facilities and
Water Effluents
Infrastructure Manufacturing, Processing, and
Formulation
Energy Air Emissions
Materials Use, Reuse, or Maintenance Solid Wastes
System Inputs System Outputs
Recycling
Waste Management
Distribution and Transportation
FIGURE 1-1 Schematic representation of a production system, including system inputs and
outputs.
same time, this diversity creates challenges for documenting critical material, energy, and
monetary flows needed to assess performance.
Understanding the performance of alternative designs for producing liquid fuels from
algae requires the adoption of a systems framework for assessing alternative designs. The
systems framework illustrates the interdependent nature of the individual supply chain
components and the system inputs and outputs. The understanding developed from such
a representation is fundamental for applying a wide array of sustainability tools such as
LCA, engineering process modeling, and cost-benefit analysis.
1.3.2 Indicators
Biofuel sustainability indicators are metrics of defined aspects of sustainability that rep-
resent system status or progress toward sustainability goals. Some researchers and institu-
tions distinguish between definitions of indicators and metrics, while others see substantial
overlap in the concepts. The definition of an indicator used in this report is "a measure that
is somehow indicative of some unmeasurable environmental goal such as environmental
integrity, ecosystem health, or sustainable resources" (Suter, 2001). Indication of sustainable
development of algal biofuels is indirect, through the union of metrics of resource use, other
environmental impacts, social acceptance (all considered in this report), and economics and
energy security (not considered in this report). Specific metrics of water quality or quantity
or GHG emissions, for example, are viewed as indicators of sustainability or sustainable
development.
Because sustainability includes environmental, economic, and social dimensions (in
addition to energy and energy security, which may be classified separately), indicators
also typically are divided among these categories. Categories of resource requirement
indicators that have been discussed for biofuels include total and consumptive water use,
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INTRODUCTION 19
nutrient use, total land use, and net energy return, and categories of environmental indica-
tors include net GHG emissions, water quality, and biodiversity. This report emphasizes
the sustainability of the broad environment and thus presents categories of indicators of
aspects of the environment that are pertinent to algal biofuels. This report also emphasizes
the sustainability of resource use that determines the viability of the biofuel system. Indica-
tors at this interface between environmental and economic sustainability also are presented
and discussed in this report. Specific sustainability indicators pertaining to other aspects
of the economy (for example, international trade, profitability, employment) are beyond
the scope of this study, though clearly these will influence and be influenced by indicators
of environmental sustainability. Social indicators of biofuel sustainability often are not
derived or considered, but such potential indicators for algal biofuels could be developed.
However, the focus of this study is on environmental sustainability and indicators related
to environmental impacts and natural resource requirements.
Because sustainable development implies progress toward sustainability goals, it is
important to understand baselines for indicators of sustainability. Moreover, the attribu-
tion of particular environmental and social effects to algal biofuel production requires an
understanding of baseline and reference conditions. An appropriate definition of a baseline
is conditions that would have prevailed in the absence of algal biofuel production. In prin-
ciple, the baseline incorporates dynamic land-use and associated environmental changes
in the region, but in practice it is often simpler and more certain to consider the conditions
that prevailed prior to biofuel production.
The use of particular units can influence the way that sustainability indicators are
interpreted (Turnhout et al., 2007; Corbière-Nicollier et al., 2011; Efroymson et al., 2012).
Units may include volume or mass of resources required; concentrations, emissions, or
loadings of chemicals to environmental media; and abundance of organisms or habitat
area. The units may have denominators of land area, energy produced, or volume of fuel.
Choosing a denominator such as land area or volume of fuel can facilitate comparisons
between alternative land uses or fuels but also can add to the uncertainty associated with
an indicator. For example, land area may include the area for infrastructure or the area for
infrastructure plus a buffer. Including time as a factor in an indicator allows the duration of
an environmental effect to be considered. Including coproduct quantities in the divisor of
an indicator can imply that decision makers have determined that part of an effect should
be formally attributed to the coproduct.3
Sustainability and sustainable development encompass diverse goals and targets that
relate to dynamic human values. Movement toward sustainability cannot be assessed un-
less the specific goals are defined and targets and metrics for aspects of sustainability are
selected. Many international organizations are developing sustainability indicators for bio-
fuels. These include the Roundtable on Sustainable Biofuels (RSB), the G-8-endorsed Global
Bioenergy Partnership (GBEP), and others (van Dam et al., 2008). Additional organizations
have been created to promote sustainable biofuel industries, such as the Council on Sustain-
able Biomass Production in the United States (CSBP, 2010). The International Sustainability
and Carbon Certification system for biomass and bioenergy has been implemented globally
by 750 stakeholders from 45 countries (ISCC, 2012). Some organizations recommend a large
number of sustainability indicators. For example, RSB (2011) recommends more than 200
3Coproducts are commercial products such as nutrient supplements, animal feedstuff, or chemical feedstocks
that can be coproduced from the pathways that produce algal biofuels and marketed. For example, after lipids
have been extracted from algal biomass, the lipid-extracted biomass might be processed to become animal feed-
stuff or animal feed supplements.
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20 SUSTAINABLE DEVELOPMENT OF ALGAL BIOFUELS
indicators and measures of biofuel sustainability. A challenge is to winnow generic lists of
biofuel sustainability indicators to a suite that is appropriate for a particular assessment
problem and is technically and economically practical (McBride et al., 2011; Efroymson et
al., 2012). Many of the efforts to develop generic biofuel sustainability indicators have fo-
cused on plant-based biofuels--corn ethanol, cellulosic biofuels, and agricultural biodiesel.
Therefore, some recommended indicators may not be pertinent to algal biofuels, and some
important potential indicators may not appear on previously published lists.
Turnhout et al. (2007) suggested that the successful application of indicators is specific
to each situation. What typically leads to a sustainability assessment is a decision or other
purpose, combined with sustainability goals. Sustainability goals may include concepts
such as efficient use of resources, maintenance of water quality, maintenance of biodiver-
sity, and minimization of waste (Sydorovych and Wossink, 2008). Indicators would have to
be selected to reflect goals. Moreover, the context of a biofuel sustainability assessment is
important for selecting, measuring, and interpreting sustainability indicators (Efroymson
et al., 2012). The context for the application of sustainability indicators includes the purpose
of the assessment, the region, the scale of analysis, the relevant policies context, the decision
context (including stakeholders), and available data on baselines and reference scenarios
(Efroymson et al., 2012).
A sustainability assessment for algal biofuel production may entail comparing algal
biofuels with business-as-usual scenarios for energy use (that is, using mostly petroleum-
based gasoline in transportation as is done today), alternative energy sources (for example,
other biofuels or other algal biofuel pathways), previous land uses or land uses that would
have occurred in the absence of biofuel production, or alternative sites for the facility. These
comparisons may lead assessors to prioritize various sustainability indicators differently
and may lead to different measurement or modeling methods and units.
1.3.3 Life-Cycle Assessment
LCA is a set of methods, databases, and tools that aims to characterize the environ-
mental impacts over a life cycle of a product or service. LCA is defined as "a systematic
set of procedures for compiling and examining the inputs and outputs of materials and
energy and the associated environmental impacts directly attributable to the functioning
of a product or service system throughout its life cycle" (ISO, 2006). The life cycle in the
context of algal biofuel production refers to a chain of activities that includes extraction of
raw resources, producing materials, manufacturing, transportation, use, and disposal (Bau-
mann and Tillman, 2004; EPA, 2006). Figure 1-1 shows a schematic of the chain of activities
involved in a production system, and LCA attempts to account for and aggregate a resource
requirement or an environmental impact over the whole pathway. However, it is generally
infeasible to analyze every process in a life cycle. Data and knowledge limitations imply
that LCA entails selection of a "system boundary" that delineates processes included in the
analysis versus those excluded.
One approach to LCA involves numerical modeling of material flows in supply chains.
The idea is to map a target product to a set of activities or processes (or sectors) and use in-
put-output tables to estimate cumulative material flows per unit product. An input-output
table delineates requirements of inputs to generate a set of outputs (for example, iron ore,
coal, and electricity as inputs for crude steel as an output). This input-output approach has
the advantage of being able to rely on economy sector level data to quantify the relationship
between energy, resources, and the final products (Miller and Blair, 2009). However, given
the nascent nature of algal biofuel production, the LCAs discussed in this study will focus
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INTRODUCTION 21
primarily on the process analysis approach to LCA that uses specific information on the
energy, nutrients, and emissions associated with each component of the process, which is
combined to get a complete LCA of resource requirements. The process approach to LCA
is a bottom-up approach that builds a full supply-chain estimate through the examination
of the individual components. In contrast, the economic input-output approach to LCA
(EIOLCA) (Bullard and Herendeen, 1975; Hendrickson et al., 2006) is a top-down approach
that uses a holistic model of an economy divided into sectors, with the input-output table
describing economic transactions between sectors (Leontief, 1970). To briefly address un-
certainty in LCA models, the bottom-up process method suffers from variations in defin-
ing the system boundary when data on part of the supply chain are unavailable, while
the EIOLCA has error associated with the aggregation of processes into economic sectors
(Williams et al., 2009). Hybrid LCA is a set of methods that aims to combine process and
EIOLCA methods to reduce uncertainty (for example, Bullard et al., 1978).
A second component of LCA, impact assessment, interprets life-cycle material flows in
terms of environmental impacts. A major thrust of impact assessment is mapping flows to
multiple types of impacts (for example, climate change, resource availability, and human
toxicity) and developing ways to inform decision-making tools to navigate these multiple
impacts (Baumann and Tillman, 2004; EPA, 2006). Many of the LCAs done for other biofuels
are reviewed in the NRC report Renewable Fuel Standard: Potential Economic and Environmen-
tal Effects of U.S. Biofuel Policy (NRC, 2011b).
LCA can provide important insights into the sustainability of algal biofuels. Algal bio-
fuels potentially have lower GHG emissions compared to petroleum-based fuels and they
might not generate significant new negative impacts. Estimates of life-cycle GHG emis-
sions for other biofuels span a wide range depending on the feedstock type, management
practices used to grow feedstock, and whether any land-use changes were incurred. Algal
biofuels thus need to be vetted with LCA and other approaches. Also, mass-scale agricul-
tural systems induce significant material inputs of water and nutrients and emit various
pollutants. LCA can help characterize material flows associated with such requirements for
an algal biofuel industry.
There are challenges to using LCA to assess sustainability of algal biofuels. These chal-
lenges, including the issues associated with defining the system boundary for LCA analysis,
are discussed in other publications (NAS-NAE-NRC, 2010; NRC, 2011b). LCA primarily is
formulated as a retrospective description of existing supply chains. Algal biofuel produc-
tion is in early development and there are limited historical data. In addition, technological
progress and scale-up will affect future material flows but are challenging to forecast.
In addition to LCAs for assessing environmental variables, social LCAs are being de-
veloped to compare social impacts of products, processes, or companies, and to identify
potential areas of improvements (Jorgensen et al., 2008). Social LCA is in early development
stage, and consensus has yet to be reached on the impact categories to be included and how
they would be measured (Dreyer et al., 2006; Jorgensen et al., 2008).
1.3.4 Scenario Analysis
A scenario is a characterization of a possible future. Scenarios take many different forms
and can be constructed in many different ways (Chermack et al., 2001). Generally, scenarios
"provide conceptual and quantitative frameworks to describe and assess" an activity or
technology (NAS-NAE-NRC, 2010, p.292). Scenarios typically "use qualitative analysis
and quantitative assumptions to integrate the environmental, technologic, economic, and
deployment-related elements" into a framework to compare alternative possible outcomes
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22 SUSTAINABLE DEVELOPMENT OF ALGAL BIOFUELS
(NAS-NAE-NRC, 2010, p.292). Scenarios do not simply extrapolate historical data but try
to develop internally consistent sets of conditions that are needed to occur to attain a given
set of outcomes. For example, scenarios for algal biofuels might look at potential system
design, resource requirements, and infrastructure needs required to reach a given percent-
age of the liquid fluids market. Scenarios can help define the environmental and resource
sustainability issues that might accompany a greatly expanded algal biofuel production
system.
Scenarios are a part of a more general future analysis. Elements of future analysis
include trend projections, systems modeling, and scenarios; the analysis can combine these
elements in different ways. Trend projection involves extrapolation of retrospective infor-
mation to the future. A central element of the trend projection process is simply deciding
on a functional form for the trend, such as linear, exponential, or some other relationship
(Craig et al., 2002). Further, trend analysis is best for known systems where there is a large
quantity of historical data, which is not true for algal biofuels. Systems modeling consists of
identifying relationships between variables of interest (Ibid). For example, an econometric
model finds the optimal statistical fit between variables that are assumed to be related by a
predefined functional form. A systems dynamics model develops causal relationships be-
tween quantities of interest and evolves the future from some initial condition using these
relationships. Future issues relevant to the sustainability of algal biofuels include: how indi-
vidual technology elements will develop (for example, algae cultivation), how technology
elements will combine to yield a fuel production system, and how the production system
will link to natural systems (for example, salt versus fresh water).
1.4 STUDY SCOPE AND APPROACH
Algal biofuels can be produced from a variety of feedstocks (autotrophic microalgae
and cyanobacteria, heterotrophic microalgae, and macroalgae) using different processing
technologies (for example, transesterification of algal oil, thermochemical conversion of
algal biomass such as gasification and pyrolysis, or direct synthesis of alcohol). Examining
the promise of different combinations of feedstocks and processing technologies to sustain-
ably develop algal biofuels within the timeframe of this study was not feasible. Therefore,
the committee limited the scope of the report in three ways following the guidance of the
study sponsor and the committee's expert judgment.
First, this study focuses on biofuel production systems that use autotrophic microal-
gae as a feedstock in the United States. Heterotrophic approaches for algae cultivation are
excluded because DOE-EERE considers production of biofuel using heterotrophic algae
as a biochemical pathway to convert another feedstock (a sugar source such as cellulosic
biomass) rather than a pathway that directly produces fuels from algae (Pate, 2011). The ex-
clusion of the heterotrophic pathways is not a judgment on the validity of these approaches.
Second, the study sponsor indicated macroalgae as a feedstock was of lower priority for
this study than microalgae and cyanobacteria and suggested that the committee could
consider macroalgae if time and budget allowed. The committee could not fully address
the sustainability of using macroalgae as a feedstock not only because of time and budget
constraints, but also because of the sparse literature on this topic. The focus on microalgae
also is consistent with the research and investment patterns in algal biofuels. Third, the
study relies on published literature so that the well-studied topics are emphasized more
often than less well-studied topics relative to others in the report.
The committee developed its report based on members' expertise and information
gathered from the public record. In its examination of publicly available information, the
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INTRODUCTION 23
committee relied on peer-reviewed papers; reports produced by government agencies and
other interested parties; and documents filed as part of regulatory activities, including
patent applications and environmental-impact assessments. In addition, the committee
gathered information through presentations at open committee meetings from government
agencies, companies, and others involved in the algal biofuel supply chain, researchers
from academia, and other groups. The information gathered at these public meetings was
augmented by public webinars and solicitation of information from algal biofuel compa-
nies. The information gathered during these activities helped form the basis for the descrip-
tion of the algal biofuel supply chain, resource requirements, and impacts discussed in
subsequent chapters. In analyzing this information, the committee relied on the methods
described earlier.
1.5 STRUCTURE OF REPORT
The report addresses the statement of task in the following ways. Chapter 2 provides
an overview of algal biofuel supply chain and examples of different cultivation, harvest-
ing, dewatering, processing, and coproduction methods that could be used in producing
algal biofuels. Chapter 3 introduces selected algal biofuel production systems as examples
to illustrate challenges and sustainability concerns of algal biofuel production and possible
tradeoffs among sustainability goals. Chapters 4 and 5 discuss potential concerns related
to resource use (for example, availability of land, water, and nutrient resources) and en-
vironmental effects and how some of those concerns might affect social acceptability of
algal biofuels, respectively. For each category of resource use and environmental effect,
indicators and metrics to be employed and data to be collected to assess sustainability are
suggested. Chapter 6 summarizes the sustainability challenges for each of the selected algal
biofuel production systems introduced in Chapter 3 and uses them to illustrate benefits and
tradeoffs of each system.
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