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This may be the author’s version of a work that was
submitted/acceptedfor publication in the following source:
Cox, Kelly, Renouf, Marguerite, Dargan, Aidan, Turner,
Christopher, &Klein-Marcuschamer, Daniel(2014)Environmental
life cycle assessment (LCA) of aviation biofuel from microal-gae,
Pongamia pinnata, and sugarcane molasses.Biofuels, Bioproducts and
Biorefining, 8(4), pp. 579-593.
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1
Environmental life cycle assessment (LCA) of aviation biofuel
from microalgae, 1
Pongamia pinnata, and sugarcane molasses 2
Kelly Cox, Boeing Research and Technology Australia, Brisbane
Technology Centre, Brisbane, 3
QLD, Australia. 4
Marguerite Renouf, University of Queensland, School of
Geography, Planning and Environmental 5
Management, St. Lucia, QLD, Australia. 6
Aidan Dargan, Boeing Research and Technology Australia, Brisbane
Technology Centre, Brisbane, 7
QLD, Australia. 8
Christopher Turner, University of Queensland, Australian
Institute of Bioengineering and 9
Nanotechnology, St. Lucia, QLD, Australia. 10
Daniel Klein-Marcuschamer, University of Queensland, Australian
Institute for Bioengineering 11
and Nanotechnology, St Lucia, Australia; Joint BioEnergy
Institute, Deconstruction Division, 12
Emeryville, CA, USA; Lawrence Berkeley National Laboratory,
Physical Biosciences Division, 13
Berkeley, CA, USA 14
Correspondence to: Kelly Cox, Boeing Research and Technology
Australia, Brisbane, QLD, 15
Australia. 16
E-mail: [email protected] 17
18
ABSTRACT 19
The environmental benefits and trade-offs of automotive biofuels
are well known, but less is known 20
about aviation biofuels. We modeled the environmental impacts of
three pathways for aviation 21
biofuel in Australia (from microalgae, pongamia, and sugarcane
molasses) using attributional life 22
cycle assessments (LCA), applying both economic allocation and
system expansion. Based on 23
economic allocation, sugarcane molasses has the better fossil
energy ratio FER (1.7 MJ out/MJ in) 24
and GHG abatement (73% less than aviation kerosene) of the
three, but with the trade-offs of higher 25
water use and eutrophication potential. Microalgae and pongamia
have lower FER and GHG 26
-
2
abatement (1.0 and 1.1; 53% and 43%), but mostly avoid the
eutrophication and reduce the water use 1
trade-offs. All have similar and relatively low land use
intensities. If produced on land where existing 2
carbon stocks are not compromised, the sugarcane and microalgae
pathways would currently meet a 3
50% GHG abatement requirement, and some GHG mitigation would be
required for the pongamia 4
pathway to achieve this. This is reasonably promising given the
early developmental status of these 5
pathways. Based on system expansion, microalgae and pongamia
pathways had lower impacts than 6
the sugarcane pathway for all categories except energy input,
highlighting the positive aspects of 7
these “next–generation” feedstocks. The low fossil energy
conservation potentials of these pathways 8
was found to be a, and significant energy efficiencies will be
needed before they can effect fossil 9
energy conservation. Energy recovery from processing residues
(base case) was preferable over their 10
use as animal feed (variant case), and crucial for favourable
energy and GHG conservation. However 11
this finding is at odds with the economic preferences identified
in a companion technoeconomic 12
study. 13
14
Supporting information can be found in the online version of
this article. 15
Keywords: LCA; environmental impact; energy; greenhouse gas;
alternative fuel; jet fuel; 16
17
1. INTRODUCTION 18
The aviation industry contributes around three percent of the
radiative forcing from energy-related 19
greenhouse gas (GHG) emissions.1 The International Air Transport
Association (IATA) has set a 20
target to halve emissions from the global aviation sector by
2050 compared with 2005 levels, and one 21
strategy is the use of aviation biofuels (IATA (www.iata.org)).
While biofuels alone are not expected 22
to achieve this target, they can make a substantial contribution
depending on the feedstock and 23
production pathway.2 Identification and development of optimal
GHG saving pathways will require 24
collaboration between government, the aviation industry,
research organisations and fuel 25
manufacturers. The Queensland Sustainable Aviation Fuel
Initiative (QSAFI) project is such a 26
collaboration established to assess the feasibility of three
pathways for aviation biofuels in Australia, 27
-
3
based on molasses from sugarcane (Saccharum spp.),
photoautotrophic microalgae (Nannochloropsis 1
spp.) and pongamia seeds (Pongamia pinnata). The focus was on
aviation turbine fuels. A 2
companion technoeconomic study has been published previously in
this journal.3 The current work 3
assesses the environmental impacts of the pathways using
environmental life cycle assessment 4
(LCA) based on the same process models, data and assumptions as
the technoeconomic study 5
(QSAFI (www.aibn.uq.edu.au/qsafi)). 6
Past LCA studies of biofuels generally have found them to offer
fossil energy conservation and GHG 7
mitigation, but the extent varies depending on the feedstock and
the production pathway, and the 8
assessment methodology applied.4-7 Greater recognition of GHG
emissions associated with land use 9
change has introduced caution for first-generation biofuels that
necessitate expanded agricultural 10
production.5, 8 Impacts from nitrogen use have also been
highlighted, both in regards to emissions of 11
nitrous oxide (N2O) and eutrophication potential.9-12 Other
issues are increased stress on water 12
resources13-15 and land use change (both direct and indirect) in
relation to the loss of eco-system 13
services16 and competition with food production.17, 18 With
increasing recognition of the 14
environmental constraints of large-scale bio-production,19, 20
and the development of environmental 15
criteria for future investment in bio-production,21, 22 it is
important for environmental implications of 16
new biofuel pathways to be fully understood so that their GHG
abatement potential can be harnessed 17
sustainably. 18
The aim of this study was to evaluate the life cycle
environmental impacts of the three selected 19
production pathways, to test if they are sustainable
alternatives to their fossil-fuel equivalent. This 20
was done by comparing the (expected) GHG savings relative to
aviation kerosene with current GHG 21
abatement standards,21, 22 and by considering other
environmental impacts (land use, water use, 22
eutrophication, ecotoxicity). The environmental assessment was
also considered alongside the 23
companion technoeconomic assessment3 to draw out synergies and
conflicts between economic and 24
environmental objectives. 25
The three assessed feedstocks are promising because they can be
produced in commercial quantities 26
under Queensland conditions. Sugarcane molasses is a by-product
of producing raw sugar from 27
-
4
sugarcane, a major commercial crop in Queensland. Molasses is
preferred over cane juice as a 1
fermentation substrate in the Australian context as it reduces
diversion of sucrose away from raw 2
sugar production, which is the industry’s core focus. Pongamia
is a leguminous, oilseed tree native 3
to India that has become naturalized in Australia. While not yet
domesticated or grown 4
commercially, it has been the subject of research because of its
potential to produce commercial 5
quantities of oil in Australian conditions.23 Microalgae are a
family of simple-structured 6
photosynthetic organisms with high photosynthetic efficiency and
lipid content, which can be 7
converted into microalgae oil. Microalgae are promising because
they have the potential for high 8
biomass productivity per unit area, they can be grown without
the need for arable land or fresh water, 9
and can utilise seawater, brackish waters and wastewaters.24 The
engineering processes for producing 10
aviation fuel modelled in this study are based on a suite of
technologies currently being investigated 11
in Queensland, and described further in 2.2. They do not
represent aviation biofuel production in 12
general, and are in the early stages of development. 13
The production of first- and second-generation biofuels from
sugarcane has been extensively 14
assessed using LCA. Sugarcane has consistently been shown to be
amongst the best energy and 15
GHG saver relative to other feedstocks,4, 6, 7 but the
first-generation pathways (from molasses and 16
cane juice) have potentially significant land-use, water-use and
water quality trade-offs associated 17
with most first-generation biofuels.25 In effect, sugarcane
biofuels can be regarded as the reference 18
case against which to compare other pathways. There have been
far fewer LCA studies of algae 19
biofuels, and those available have found that the promise of
high productivity has not yet translated 20
into favorable GHG abatement due to its early development
status,26, 27 but other environmental 21
considerations have not been well examined. No published studies
of the environmental profile of 22
pongamia-derived biofuels were identified. 23
Past research relates almost entirely to automotive biofuels,
with very few published studies of 24
aviation biofuels.2 The different processes involved in
producing and utilizing aviation biofuels 25
means that findings for automotive biofuels cannot be directly
transposed, so examination of the 26
aviation biofuel pathways is warranted. This is the first
environmental examination of pongamia oil 27
-
5
as substrate for biofuel, and the first to examine a range of
environmental impacts, beyond energy 1
and GHG conservation, for microalgae. 2
2. MATERIALS AND METHODS 3
2.1. Overview 4
Scenarios were defined for each production pathway, which are
mostly based on developmental 5
processes. An LCA was undertaken for each scenario with the aid
of Simapro software V7.3.3 (Pre 6
Consulting (www.pre-sustainability.com)) to generate
quantitative indicators of environmental 7
impacts per 100 MJ of fuel used. Methods were consistent with
the International Standard for LCA.28 8
An attributional rather than consequential assessment was
considered appropriate. Attributional LCA 9
evaluates the performance of systems using a static approach,
whereas consequential LCAs consider 10
changes to a system 29. 11
All processes within the life cycle of each feedstock and
processing pathway were assessed within 12
the scope of the LCA (from ‘cradle to grave’), and impacts
assigned to their products and by-13
products. Economic allocation (EA) was used as the default
approach for assigning impact to the 14
multiple products so the results could be compared with the GHG
abatement standards which 15
stipulate EA.30 However results were also generated using system
expansion (SE), as different 16
approaches are known to be influential.6, 31, 32 The other
sensitivity considered was the utilisation 17
route for processing residues (meals) from pongamia and
microalgae processing, with two 18
alternatives modelled. 19
Environmental impacts were quantified using mid-point indicators
considered most important for 20
Australian agriculture-based processes,33 namely fossil energy
input, consumptive water use, global 21
warming potential (GWP),34 eutrophication,35 ecotoxicity,36 and
land occupation as a course proxy 22
for impacts to ecosystem services. 23
To test how the impacts of the aviation biofuels compared with
those of the fossil fuels they 24
substitute and to estimate their GHG abatement potential, the
results were compared with results 25
generated for aviation kerosene using life cycle inventory data
for Australian production.37 The 26
biofuels modelled were assumed to have properties within the
operational specifications of 27
-
6
acceptable jet fuel.38 In the absence of information about
combustion characteristics, emissions from 1
combustion in jet engines were also assumed to be equivalent.
2
To distinguish discernible differences between the fuels,
uncertainty ranges were generated using the 3
Monte Carlo function in Simapro. This was run over 500
iterations to generate 95% confidence 4
ranges based on known data ranges or assigned data quality
pedigrees. 5
The reader is referred to the supporting information in the
online version of this paper for the data 6
used in the analysis. 7
2.2. Scenario Descriptions 8
Assumed processes for each scenario are summarised in Fig. 1 and
production outputs from each 9
stage are detailed in Table 1. 10
2.2.1. Feedstock production (sugarcane, pongamia seed and
microalgae) 11
For the sugarcane scenario state average sugarcane production
parameters reported by Renouf et 12
al.,39 were used. A growing cycle of six years was assumed,
comprising one plant crop, four ratoon 13
crops, and a fallow period. Sugarcane production in Queensland
is highly mechanised, employing 14
machinery for all stages of crop cultivation, mechanical
harvesting, and truck and rail transport of the 15
harvested sugarcane to the mill. Nutrients are applied as
synthetic fertilizers, and pesticides are 16
applied to control insect pests and weeds. Nitrous oxide (N2O)
emissions from nitrogen fertiliser 17
application were assumed to be 0.0125 kg N2O-N/kg applied N in
line with national GHG 18
methodology.40 Higher emissions are possible in some conditions
(0.04 kg N2O-N/kg applied N on 19
average41), and the sensitivity of results to higher emissions
was considered. Irrigation water is 20
applied to 60% of the crop. Around 61% is harvested ‘green’ with
harvest residues (trash) retained in 21
the field. The other 39% is burnt prior to harvest with no
retention of trash. Harvested sugarcane is 22
moved short distances by tractor to transport sidings for onward
transport to sugar mills, which is 23
mostly by rail using the extensive sugarcane rail network, and
to a lesser extent by road trucks. 24
The pongamia scenario is based on trial pongamia plantations at
a couple of sites in Queensland, and 25
.production parameters were based on estimates from these
research trials. It assumes a network of 26
pongamia plantations located in an inland region of Queensland
within 100 km of the processing 27
-
7
plant, and where supplementary irrigation of 1ML/ha/yr was
assumed to be required. Planting 1
densities were assumed to be 500 trees/ha, producing seeds over
25 years after a 5 year establishment 2
phase (Scott PT, 2013, pers. comm.). Each tree is assumed to
produce 30 kg seed pods/tree/yr 3
resulting in a yield of 9.7 t seed/ha/yr42 containing 40% oil,
or 3.9 t oil/ha.42, 43 . This assumed yield 4
is within the observed yield range (3-5 t oil/ha) (Scott PT,
2013, pers. comm.), and would be 5
representative of yield on agricultural land. Seeds are
harvested using an umbrella shaker and the 6
kernels extracted from the pods on-site using machines similar
to those used to de-shell peanuts. 7
Waste pods are applied as mulch for weed control 8
For the microalgae scenario, a hypothetical site was defined in
the absence of a full-scale production 9
facility to model. The scenario assumes production of
Nannochloropsis spp. in salt water in 10
compacted clay race-way ponds. Yield was assumed to be 20 g
DM/m2/day, which is conservative, 11
being at the low end of yield reported in other studies.44-47
Production is assumed to occur on the 12
Queensland coast, in proximity to sources of carbon dioxide
(CO2)-rich flue gas and sea water. Sea 13
water and ground water are fed into the ponds along with
nutrients (phosphate and nitrate), aerated 14
and mixed with paddlewheels and injected with the CO2.
Microalgae are harvested once the required 15
concentration is achieved. Anoxic conditions that promote N2O
emissions were assumed to not be 16
present in the algae ponds and therefore direct N2O emissions
were assumed to be zero or 17
insignificant.48 However indirect emissions of N2O from the N
contained in wastewaters from the 18
algae process were accounted for in line with national GHG
inventory methodology.40 19
2.2.2. Feedstock processing (to molasses, pongamia oil and
microalgae oil) 20
Sugarcane milling was modelled on a typical Queensland sugar
mill consistent with the 21
technoeconomic study.3 Cane is first crushed to extract juice,
with the leftover fibre (bagasse) 22
combusted in a mill boiler to produce steam and electricity used
internally to power the mill. Surplus 23
electricity is assumed to be exported to the grid rather than to
the downstream fuel production 24
process because of inconsistencies in the timing of supply.
Molasses is a co-product from the sugar 25
crystallisation process, containing residual sugars that are not
further recovered. This scenario 26
assumes the use of A-grade molasses in fermentation and fuel
refining. Other milling residues (mill 27
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8
mud and boiler ash) are applied to cane fields, and wastewater
is treated in aerobic ponds prior to 1
discharge to local rivers. 2
For pongamia, the kernels are first processed through a drying
and flaking mill, then oil is recovered 3
using hexane solvent extraction and degumming to clean the oil.
For microalgae, the harvested algae 4
slurry is first centrifugally concentrated to a dense paste,
then subjected to hexane solvent extraction 5
and de-gumming. Energy requirements for pongamia and algae
processing are met by grid electricity 6
and natural gas by default, but some portion of energy demand
can be met by bio-gas generated from 7
by-products in some cases. A phospholipid co-product is produced
from both the pongamia and 8
microalgae processes and is assumed to be a substitute for
lecithin, a food additive. 9
The residual pongamia meal and hulls, and algae meal are assumed
to be utilised in two different 10
ways. The base case assumes they are anaerobically digested to
produce biogas, which is combusted 11
in a methane boiler to generate steam and electricity for
feedstock processing and fuel production 12
Digestion effluent is discharged to the local sewerage system
after treatment in the case of pongamia, 13
and in the case of microalgae returned to the ponds to recycle
water and nutrients. The variant case 14
assumes they are used as protein-rich animal feed and all energy
requirements met by fossil fuels. 15
2.2.3. Fuel production 16
For the sugarcane scenario, molasses is first fermented to
produce farnesene. Residual fermentation 17
effluent is applied to cane fields. The farnesene then undergoes
an emulsion dispersion process with 18
the addition of tergitol, sodium chloride and sodium hydroxide
to produce oil. Hydrogen is then 19
added in a hydrocracking process to break down the oil followed
by distillation. For the pongamia 20
and microalgae scenarios, the triacylglyceride oils are
extracted and then refined into aviation fuel 21
using hexane extraction followed by a proprietary Honeywell
UOPTM process, which involves 22
hydrogenation to produce synthetic hydrocarbons followed by
selective hydrocracking and 23
distillation. Aviation fuel is the primary product from all
these processes, co-produced with naphtha 24
and diesel. Light gases are also produced but are combusted in
boilers to produce process heat. 25
Further details can be found in the technoeconomic study.3
26
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9
2.3. System boundaries and data sources 1
The following aspects were included in the ‘cradle to grave’
system boundaries: 2
feedstock production – sugarcane,39 pongamia seeds,49 and
microalgae;3 3
feedstock processing - sugarcane milling, oil extraction from
pongamia and microalgae;3 4
fuel production – molasses fermentation, hexane extraction and
UOP process, hydrocracking and 5
distillation;3 6
combustion and energy generation from bagasse (in the sugarcane
scenario), biogas (in the 7
pongamia and microalgae scenarios) and light gas (in all
scenarios); 8
anaerobic digestion of processing residues – algae meal,
pongamia hulls and meal;3 9
land application of residues – sugarcane mill mud and boiler
ash,50 effluent from molasses 10
fermentation, and biomass from pongamia and algae meal
digestion; 11
production and supply of inputs for all the above processes
(fuels, electricity, fertilisers, 12
pesticides, process chemicals);37 13
transport of inputs, and transport of feedstock to the
processing plants (harvested sugarcane, 14
harvested seed, algae slurry); 15
emissions to air and water from sugarcane and pongamia growing,
algae ponds, pre-harvest 16
burning of sugarcane,39, 40 feedstock processing and oil
refining,3 and wastewater discharges; 17
production of agricultural machinery for sugarcane and pongamia,
and pond construction for 18
microalgae;37 and 19
combustion of the produced aviation fuels in jet aircraft.37
20
The blending and distribution of fuels were assumed to be
equivalent for all compared fuels, and 21
hence not included. Transport of substrate (molasses and oils)
from feedstock processing to the fuel 22
production plant was not included as these were assumed to be
co-located. Land transformation for 23
establishment was not included as specific geographic locations
were not known and outside the 24
scope of the study. The construction of processing plants and
the removal of the pongamia trees at 25
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10
the end of their production life were not included, as the
impacts amortized over the very large 1
production output over the life time of the plants / trees were
considered to be insignificant. 2
When system expansion was applied, boundaries were expanded to
account for avoided production 3
of commodities substituted by co-products (sorghum grain, lupin
grain, naphtha and diesel). 37 4
Environmental input and output data can be found in the
supporting information provided with the 5
online version of this paper. 6
2.4. Economic allocation (EA) 7
For economic allocation, impacts were assigned to multiple
products based on the percentage 8
contribution of each product to the economic value of all
products, using current trading prices 9
(Table 1). 10
For the sugar mill, impacts were allocated to raw sugar and
molasses. Bagasse was modeled as a 11
waste, hence exported electricity produced from its combustion
(the default disposal method) was 12
not considered a product, and instead avoided production of the
average electricity mix in 13
Queensland was assumed. 14
For pongamia processing, impacts were allocated to the oil and
the co-produced phospholipid. In the 15
base case, digestion of pongamia hulls and meal was modeled as a
service process as it is conducted 16
for the purpose of energy production (over the default disposal
route which is animal feed). Hence 17
the electricity and steam from combustion of the resulting
biogas, which are utilised in the 18
downstream fuel production process, are also co-products with
very small proportions of impacts 19
allocated to them. In the variant case, pongamia biomass is
combined with the phospholipids and 20
used as animal feed instead, which was modeled as a waste
treatment process. 21
For microalgae processing, impacts were allocated to the oil and
the co-produced phospholipid in the 22
base case, and in the variant case to the oil and the meal. For
the base case, digestion of algae slurry 23
was modeled as a waste treatment process (being the default
disposal method due to its high water 24
content). Hence electricity and steam from combustion of the
resulting biogas, which are fully 25
utilised in algae processing and fuel production, were not
considered co-products. In the variant case 26
-
11
algae slurry is dried and combined with the phospholipids and
utilised as animal feed, making it an 1
additional co-product with some impacts allocated to it. 2
For the fuel production process in each scenario, impacts were
allocated to the aviation fuel, diesel 3
and naphtha. 4
2.5. System Expansion 5
For system expansion all impacts are assigned to the determining
products, and the system expanded 6
to account for increased or decreased production of commodities
displaced by the co-products.51 7
Quantities of substituted products were estimated based on
qualified estimates of rates of substitution 8
(Table 1). 9
For the sugarcane mill, raw sugar is the determining product and
molasses is the co-product. As 10
molasses is the feedstock of interest (whose default use is for
animal feed), the impact of using it for 11
fuel production is taken to be increased production and use of
sorghum grain, the marginal feedstock 12
for animal feed by virtue of its substitutable energy content.
13
For microalgae and pongamia processing, oil is the determining
product. Co-production of 14
phospholipids (in the base case) and animal feed (in the variant
case) is assumed to decrease 15
production of lupin grain Lupin grain was assumed to be the
marginal feedstock for animal feed, by 16
virtue of its substitutable protein content. Therefore the
avoided impacts of avoided animal feed 17
production (lupin grain) were taken into account. 18
For the fuel production processes aviation fuel is the
determining product, and co-production of 19
diesel and naphtha are assumed to decrease the production and
use of diesel and naphtha from fossil 20
fuels. 21
3. RESULTS 22
The contributional profile of results generated using EA (Fig. 2
right hand columns) show the 23
sources of environmental impacts across the life cycle of the
assessed biofuels when only the 24
attributes of the production systems are considered. 25
Fossil energy input (Fig. 2(a)) for all feedstocks is dominated
by electricity and/or chemical inputs to 26
feedstock processing and fuel production. The embodied energy of
chemicals used in fuel production 27
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12
(mostly hydrogen used in hydrocracking) is the most significant
(45-55% for the pongamia 1
scenarios, 40-50% for the microalgae scenarios, and 58% for the
sugarcane scenario), followed by 2
electricity input (34-35% for the pongamia scenarios, 43-45% for
the microalgae scenarios). There is 3
no fossil-energy input to sugarcane milling because all energy
needs are met by bagasse combustion. 4
Molasses fermentation is also less energy intensive than the
hexane extraction and UOP processes 5
required for the oil substrates. This makes sugarcane molasses
the least energy intensive of the three 6
feedstocks. Microalgae production requires significant energy
for operating the ponds making it the 7
most energy-intensive feedstock overall. 8
GHG emissions contributing to GWP (Fig. 2(b)) originate from
fossil-energy use, but also field 9
emissions of N2O from growing sugarcane and pongamia, and N2O
and methane (CH4) from pre-10
harvest burning of sugarcane. For the pongamia and microalgae
scenarios, which require a higher 11
input of electricity, the associated GHG emissions are
significant (45-50% for the pongamia 12
scenarios, 63-68% for the microalgae scenarios) because the
electricity mix is dominated by 13
emissions-intensive black-coal electricity. The energy
self-sufficiency of sugarcane milling along 14
with the credit for displaced grid electricity means the
sugarcane scenario has the lowest GWP. In 15
situations where N2O emissions are higher (0.04 kg N2O-N/kg
applied N)41, the allocated GWP 16
result would increase from 2.2 to 3.2 kg CO2eq/ 100MJ, but would
still be lower than the other 17
feedstocks. 18
Sources of eutrophication potential (Fig. 2(c)) common to all
scenarios are nitrogen oxide (NOx) 19
exhaust gases from fuel combustion in jet engines, from
combustion of bagasse, biogas and light 20
gases, and from other fossil-fuels. The sugarcane scenario also
has the potential for field emissions of 21
nutrients (N and P) to waterways from sugarcane growing,
resulting in it having higher 22
eutrophication potential than the pongamia and microalgae cases.
While pongamia is a legume tree 23
with no nitrogen requirements, there was assumed to be some
fertiliser application in the 24
establishment phase. However no nutrient losses to water were
assumed due to the inland location 25
with less rainfall. The risk of nutrient loss is low for
microalgae production because it occurs within 26
-
13
a controlled production process rather than an agricultural
process thereby avoiding nutrient 1
exchanges with water bodies. 2
The sources of eco-toxicity potential (Fig. 2(d)) when the
Australian toxicity method36 is used are 3
predominantly releases of heavy metals and organic compounds
from production of electricity and 4
chemicals. The energy self-sufficiency of sugarcane milling
along with the credit for displacement of 5
grid electricity means the sugarcane scenario has the lowest
eco-toxicity potential using this method. 6
However if a different eco-toxicity method were used (such as
Recipe52), which applies less 7
weighting to the toxicity impacts of metals and organics and
more to pesticides, then the outcome 8
would be different. Potential losses of pesticide would be more
significant for the sugarcane scenario 9
and would likely lead to it having the highest eco-toxicity
potential. Due to the sensitivity of the 10
results to the eco-toxicity impact assessment method and
consequently uncertainty in the eco-toxicity 11
results generated here, less emphasis has been placed on the
eco-toxicity results when interpreting 12
findings. 13
The process responsible for water use is feedstock production –
irrigation for sugarcane and 14
pongamia growing, and water feed of the algae ponds to
compensate for evaporative losses. The 15
pongamia case has the lowest water use intensity (Table 2). In
contrast sugarcane growing in 16
Australia can rely heavily on irrigation, but it is highly
variable.39 In wetter growing regions where 17
no irrigation is required (as in the far north of Queensland),
water use intensity may be comparable 18
with the other feedstocks. In the scenario modelled here, which
represents average conditions, the 19
sugarcane molasses pathway has the highest water-use intensity.
20
Feedstock production is also the process responsible for land
occupation. Land use per unit of fuel is 21
lowest for the pongamia case (Table 2) owing to its higher
overall fuel productivity per hectare (2.5 t 22
fuel/ha for pongamia, 0.7 for sugarcane molasses and 0.4 for
microalgae). However land use 23
intensities for all three pathways are relatively low when
compared with the broader range of first 24
and second generation automotive biofuel pathways (2-20
m2/100MJ).7 The land use intensity for 25
algae from this study (6.8 m2/100MJ) was higher than reported in
other past studies (0.3 m2/100MJ)7 26
because more realistic (conservative) productivity was assumed.
27
-
14
3.1. Influence of alternative allocation approach 1
When SE is applied, impacts occurring outside the system
boundary due to co-product utilization are 2
also accounted for (Fig. 2 left hand columns). For all
scenarios, there are avoided energy and GWP 3
impacts when naphtha and diesel from biofuel refining displace
the production and use of naphtha 4
and diesel from crude oil. For the pongamia and algae variant
cases, there are avoided energy, GWP, 5
eutrophication, land use and water use impacts when
phospholipids and algae / pongamia meals 6
displace lupin grain as animal feed. For the sugarcane scenario,
the impacts of feedstock production 7
and processing are those of sorghum grain rather than sugarcane,
and can be seen to be considerable. 8
3.2. Influence of different co-product utilisation routes 9
The fate of processing meals in the microalgae and pongamia
scenarios was found to influence 10
results (Fig. 2). Impacts are lower when the meals are used for
energy production (the base case ), 11
than when used as animal feed (the variant case) . In the EA
analysis, even though the impacts 12
allocated to oil are lower in the variant cases (allocation
reduced from 99% to 78% in the pongamia 13
scenario, and 97% to 50% in the microalgae scenario), this is
offset by the increased dependency on 14
grid electricity. In the SE analysis the effect of lower
fossil-fuel energy demand in the base case is 15
greater than the effect of avoided lupin grain production in the
variant case. Therefore energy 16
recovery from meal is the environmentally preferred route for
utilising processing residues, which 17
was also observed in another LCA study of processing
alternatives in Australian algae systems.53 The 18
discussions that follow will focus on the
environmentally-preferred base case scenarios. 19
3.3. Ranking the aviation biofuels 20
Table 3 summarises the rankings of the base case aviation
biofuel scenarios to aid the interpretation 21
of the results. It shows that different conclusions may be drawn
about their relative environmental 22
impacts of the different pathways depending on which assessment
approach is taken. 23
The EA results, as discussed in the previous section, only
consider the attributes of the production 24
system and show the sugarcane molasses pathway to be best in
terms of fossil energy input and GHG 25
emissions. However the algae and pongamia pathways have lower
eutrophication potential and use 26
less water, and all have similarly favourable land use
intensities. 27
-
15
The SE results on the other hand, also consider the wider
product displacement effects and are 1
thought to provide a truer reflection of actual impacts.51 They
show the algae base case pathway to 2
have the least impacts for all categories except for fossil
energy input. Its advantages stem from the 3
fact that feedstock is produced in a contained system which
avoids the impacts of agricultural 4
production (N2O emissions, water use and nutrient and pesticide
losses to water), and that processing 5
residues (meal) are produced as a slurry that can be readily
digested to biogas to enable some degree 6
of energy self-sufficiency. However its low FER flags the need
to pursue more energy-efficient algae 7
harvesting and separation. The base case pongamia scenario also
shows promise, as the perennial 8
nature and nitrogen- and water-efficient features of this legume
tree crop minimise many of the 9
impacts of the agricultural production phase, and it also
generates residues for energy self-10
sufficiency. This study is the first to quantify the promising
characteristics of these two “next- 11
generation” pathways. 12
Sugarcane usually ranks as a preferred first-generation
feedstock in terms of GHG offsets and land 13
utilisation when the substrate is cane juice4, 6, 7, 54, due to
the very high yields of fermentable substrate 14
and the production of surplus energy. However in this study the
substrate is molasses and the SE 15
results show that diverting molasses away from its existing use
and necessitating substitute grain 16
production disadvantages the pathway modelled in this study..
17
Overall, the very large confidence ranges generated by the Monte
Carlo analysis (Fig. 2) mean that 18
uncertainties in the results are too high to confidently discern
any particular preferences amongst the 19
pathways assessed at this stage. A gauge of the relative
environmental performance of the fuels can 20
be gained by comparing the results with current standards and
criteria for sustainable biofuel 21
production (in the next section). 22
3.4. Evaluating the biofuels against aviation kerosene and GHG
abatement standards 23
The results were compared with aviation kerosene (Table 2), from
which GHG abatement potentials 24
for the biofuels were calculated for comparison against the
criteria of the Roundtable for Sustainable 25
Biofuels (RSB)22 and the European Union (EU) Directive for the
use of energy from renewable 26
-
16
sources.21 Only the EA results are considered to be consistent
with these standards which stipulate 1
EA in their methods.30 2
The fossil-energy inputs for all the base case biofuel scenarios
are lower than for kerosene (Table 2). 3
However for the pongamia- and microalgae-derived fuels it is
only marginally lower, requiring 4
almost as much fossil fuels to produce as kerosene. The
less-preferred variant cases have energy-5
intensities higher than kerosene (Fig. 2). The fossil energy
ratios (FER) (MJ out / MJ in) are 1.7 for 6
sugarcane molasses, 1.1 for pongamia and 1.0 for microalgae,
compared with 0.92 for kerosene. 7
These are low compared with the range of values reported for
automotive biofuels (1-7)55 This is 8
attributed to the higher energy demand for producing aviation
fuels via the assessed pathways, 9
compared with the less energy-intensive processes for producing
automotive fuels. The FER would 10
be expected to improve as the energy efficiency of these
technologies develops over time. 11
GWP of all the base case biofuel scenarios are lower than
kerosene. GHG abatement (i.e. the 12
percentage reduction in GHG emissions relative to the reference
fossil fuel, aviation kerosene) was 13
calculated to be 73% for sugarcane, 53% for microalgae and 43%
for pongamia. All pathways would 14
meet the minimum GHG abatement currently stipulated by the EU
Directive (35%), but only the 15
sugarcane and algae pathways would meet those of the current RSB
or the EU Directive from 2017 16
(both 50%). The pongamia pathway would require some GHG
mitigation to achieve this. 17
For all the biofuels, land occupation, water use and
eco-toxicity potential are considerably higher 18
than for kerosene. This is consistent with the finding from
other LCA studies of bio-products that 19
have considered impacts other than GHG emissions.56, 57 However,
for the base case microalgae and 20
pongamia pathways eutrophication is not discernibly higher than
kerosene and water use is lower 21
than sugarcane. 22
These findings are consistent with the previously established
trade-off between energy and 23
greenhouse savings and other environmental protection
objectives. A novel observation is that the 24
“next-generation” pathways based on microalgae and pongamia can
reduce or eliminate the water 25
use and eutrophication impacts. 26
-
17
3.5. Comparing economic and environmental objectives 1
The companion technoeconomic analysis3 found it was economically
preferable to sell the co-2
produced meals from algae and pongamia as animal feed rather
than recover energy from them. This 3
preference was most marked in the algae system, and less so in
the pongamia system. In contrast, the 4
findings of the LCA suggest the environmental benefits of
decreased reliance on grid electricity 5
when energy is recovered from meal far outweigh the benefits of
diverting it to animal feed. 6
3.6. Applicability of the models and results 7
The results of the LCA are specific to the processes modelled
and thus the results should not be 8
generalised. One limitation is that efficiencies of the systems
modelled depend on the technologies 9
used by each production route. The process models were developed
using publicly available data 10
whenever possible to ensure transparency and reproducibility of
the models. However, this meant 11
that the most efficient scenarios may not have been assessed,
for the sake of achieving higher data 12
integrity by modelling established and proven processes. An
example is the choice of the algae 13
harvesting process. Dissolved air flotation (DAF) is potentially
less energy intensive, but insufficient 14
data was available to model this technology accurately. 15
Another caveat concerns the methods used for representing water
and land use impacts, which only 16
consider consumptive water use and land occupation without
consideration of the status of water and 17
land resources used. This was because the geographic locations
of the production systems were left 18
unspecified. The land occupation and water use results should be
regarded as general indicators 19
based on the attributes of the production system. 20
4. CONCLUSIONS 21
When only the attributes of the three production pathways were
considered (economic allocation), 22
the sugarcane molasses pathway was found to have the better
fossil energy ratio FER (1.7 MJ out/MJ 23
in) and GHG abatement (73% less than aviation kerosene) of the
three pathways assessed. This is 24
mostly due to the production of surplus energy when sugarcane is
processed and the lower energy-25
intensity of the fermentation process compared to the oil
extraction processes. The downsides of the 26
sugarcane pathway are higher water use and eutrophication
potential. These observations are 27
-
18
consistent with past LCA studies that have compared and ranked
biofuel feedstocks, and found 1
sugarcane to be a preferred feedstock in terms of GHG abatement.
As such, the sugarcane pathway 2
has been used as a reference against which to compare the
microalgae and pongamia pathways. 3
The microalgae and pongamia pathways were found to have less
favourable FER and GHG 4
abatement (1.0 and 1.1; 53% and 43%) than sugarcane. 5
If produced on land where existing carbon stocks are not
compromised, the sugarcane and algae 6
pathways would currently meet the 50% GHG abatement requirement
of the Roundtable for 7
Sustainable Biofuels and the European Directive (from 2017).
Some GHG mitigation would be 8
required as part of future process developments for the pongamia
pathway to achieve this. However 9
the microalgae and pongamia pathways mostly avoid the
eutrophication and reduce the water use 10
trade-offs that are downsides for the sugarcane pathway. 11
The microalgae and pongamia pathways consume only marginally
less fossil fuel than does aviation 12
kerosene, and the sugarcane molasses pathway is at the low end
of compared with biofuels generally. 13
This is a considerable limitation and a point of difference with
automotive biofuels. Significant 14
energy efficiencies will need to be found for these processes
before they can effectively conserve 15
fossil energy.All pathways were found to have similar and
relatively low land use intensities when 16
considered against the broader range of biofuel feedstocks. The
land use intensity for microalgae was 17
higher than previously reported as it was based on more
realistic (conservative) biomass 18
productivities. No clear conclusions could be drawn in relation
to eco-toxicity potentials due to 19
uncertainty regarding the choice of impact assessment method.
20
When the product displacement effects of co-product utilisation
were considered (system expansion), 21
which is arguably a truer reflection of impacts, the microalgae
and pongamia pathways had lower 22
impacts than the sugarcane pathway for all categories except
energy input. This highlights the 23
positive aspects of these “next-generation” feedstocks which had
not been well quantified previously. 24
Energy recovery from processing residues (base case) was found
to be preferable over their use as 25
animal feed (variant case), and crucial for favourable energy
and GHG conservation. However this 26
finding is at odds with the economic preferences identified in
the companion technoeconomic study. 27
-
19
This suggests that economic versus environmental trade-offs may
need to be grappled with in the 1
future development of these technologies. 2
These findings suggest that each pathway holds some
opportunities for being sustainable routes for 3
aviation biofuel production. . The sugarcane molasses pathway
can conserve fossil energy and 4
mitigate GHG emissions, but displacement effects when molasses
feedstock is diverted away from 5
existing uses will need to be managed. The microalgae and
pongamia pathways can avoid the water 6
use and water quality impacts, but energy efficiency will be
crucial for fossil energy conservation 7
and GHG abatement. Other pathways such as conversion of
lignocellulose, which have been shown 8
to be promising for automotive biofuels, 6, 58 may also be
better options for aviation biofuels, and 9
should be explored. 10
5. ACKNOWLEDGEMENTS 11
This work was conducted by Boeing Research and Technology
Australia as part of their contribution 12
to the Queensland Sustainable Aviation Fuel Initiative (QSAFI)
project. Recognition goes to Brad 13
Wheatley and Shaun Jellett (Boeing Research and Technology) for
their contributions in the early 14
stages of the project. The authors acknowledge the valuable
input from Tim Grant (Life Cycle 15
Strategies Pty Ltd) in reviewing the work and providing guidance
of appropriate allocation and 16
system expansion approaches. Thanks also go to the QSAFI
consortium partners – Queensland State 17
Government, University of Queensland, James Cook University, IOR
Energy, Mackay Sugar 18
Limited and Virgin Australia. DKM acknowledges help from the DOE
Joint BioEnergy Institute 19
(http://www.jbei.org) supported by the US Department of Energy,
Office of Science, Office of 20
Biological and Environmental Research, through contract
DE-AC02-05CH11231 between Lawrence 21
Berkeley National Laboratory and the US Department of Energy.
The authors are also grateful for 22
the useful input provided by the anonymous reviewers. 23
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Tables 1
Table 1 Production outputs from each stage1, allocation factors
and substitute products 2 Values in parentheses are allocation
factors used in economic allocation. 3 Values underlined represent
the assumed increased (+ve) or decreased (-ve) production of
substitute products, used in 4 system expansion. 5 Products
Intermediary products Substitute products
Unit Sugarcane scenario Pongamia scenarios Microalgae
scenarios
Base case Variant case Base case Variant
case Feedstock production, per ha per year Sugarcane t 85 - -
Pongamia seed t - 18 - Microalgae (solids) 2 t - - 19
Processing of sugarcane, per tonne feedstock processed Raw sugar
kg 62.7 (64.9%)3 - - Molasses (A-grade) kg 146.8 (35.1%) 3 - -
Bagasse (to co-generation) kg 309.7 - -
Electricity from bagasse (exported) kWh 13.9 - Electricity from
natural gas (substituting bagasse electricity) kWh -13.9
4 - -
Sorghum (substituting molasses) kg +125.65 - -
Processing of pongamia seeds and microalgae solids, per tonne
feedstock processed
Oil kg - 286.9 (98.9%) 6 286.9
(78%) 6 44.2
(97.2%) 10 44.2
(50.4%) 10
Phospholipids kg - 22.3 (0.8%) 6 - 13.6
(2.8%) 10 -
Pongamia meal (animal feed) kg - - 531.2 (21.9%) 9 -
Algae meal(animal feed) kg - - - - 318.8 (49.6%) 9
Electricity from biogas kWh - 96.7 (0.08% )7 - 83.6 -
Steam from biogas kg - 928.6 (0.22% )7 - 148.8 -
Lupin (substituting phospholipids) kg - -20.2 8 - -12.3 8 -
Lupin (substituting meal) kg - - -398.3 9 - -239.1 9 Fuel
production (per tonne substrate - oil or molasses) Aviation fuel kg
53.5 (47.2%) 11 480.3 (47.2%) 11 467.4 (47.2%) 11 Naphtha kg 28.9
(40.8%) 11 259.3 (40.8%) 11 252.3 (40.8%) 11 Diesel kg 8.0 (12%) 11
72.2 (12%) 11 70.3 (12%) 11 Light gases (used internally) GJ 0.85
7.69 7.48 1 All production quantities are based on process
modelling by the technoeconomic study.3 6 2 Harvested microalgae
slurry contains 30%(wt) microalgae solids. 7 3 Derived from trading
prices: raw sugar (2011-2012) A$520/t,59 molasses (2013) A$120/t
(Sucrogen, unpublished). 8 4 Bagasse-electricity is assumed to
substitute electricity generated from Queensland natural gas (1:1).
9 5 Molasses was assumed to be a substitute for sorghum grain
(0.568 kg sorghum / kg molasses, based on calorific values) (USDA
10 Agricultural Research Service (http://ndb.nal.usda.gov/)). 11 6
Derived from estimated economic values of generated products.
Pongamia oil value was based on qualified estimates (A$2776/t) 12
(Scott PT, 2013, pers. comm.). Phospholipid value was based on the
value of lecithin (A$293/t) (ICIS (www.icis.com)). 13 7 Electricity
value was based on wholesale price for electricity in Queensland
(A$0.024/kWh) (AEMO (www.aemo.com.ua)). Steam 14 values based on a
published estimate (A$10/t).60 15 8 Phospholipids were assumed to
substitute lupin grain for both the pongamia and microalgae
scenarios (0.905 kg lupins/ kg 16 phospholipids, based on calorific
values) (USDA Agricultural Research Service
(http://ndb.nal.usda.gov/)). 17 9 When pongamia or microalgae meal
are utilised as animal feed (along with the phospholipid product)
they were assumed to 18 substitute lupin grain (0.75 kg lupins/ kg
meal, based on protein content) (USDA Agricultural Research Service
19 (http://ndb.nal.usda.gov/)). Their economic value as animal feed
was based on the economic value of soybean (A$421/t). The 20
economic value of lupins in the ABARES Commodities Statistics is
$250 (6-yr average). 21 10 Derived from estimated economic values
of generated products. Algae oil value was based on a qualified
estimate (A$3,090/t) 22 (Borowitzka MA, 2013, pers. comm.).
Phospholipid value based on the value of lecithin (A$293/t)
(www.icis.com)). 23 11 Derived from average trading prices (2013):
aviation fuel A$987/t (IATA (www.iata.org)), naphtha A$1580/t
(Recochem 24 (www.recochem.com.au), diesel A$1674/t (AIP
(www.aip.com.au/pricing)). 25
26
-
24
Table 2 Life cycle impact assessment results for aviation
biofuels (base case scenarios) compared with aviation 1 kerosene
(per 100 MJ fuel consumed) 2 Impact category Unit System expansion
Allocation
Sugarcane Pongamia Microalgae Sugarcane Pongamia Microalgae
Kerosene
Fossil energy input MJ 85.2 121.0 134.3 58.7 93.0 99.2 108.6
Global warming potential (GWP) kg CO2eq 8.0 4.7 2.7 2.2 4.7 3.8
8.2
Eutrophication kg PO4eq 0.044 0.012 0.011 0.015 0.009 0.009
0.007
Eco-toxicity -Australian method DAY 51.1E-08 1.1E-09 8.6E-10
1.4E-10 5.2E-10 4.2E-10 4.1E-11
Water use kL 14.7 1.18 1.39 1.56 0.55 0.64 0.001
Land use m2.a 38.9 7.8 7.0 5.1 4.5 6.8 0.003
3
Table 3 Ranking the environmental impacts of the assessed
aviation biofuels 4 ■ Lower impact, ■ Moderate impact; ■ Higher
impact 5
System expansion Economic allocation
Sugarcane Pongamia Microalgae Sugarcane Pongamia Microalgae
Fossil energy input ■ ■ ■ ■ ■ ■ Global warming potential (GWP) ■
■ ■ ■ ■ ■ Eutrophication ■ ■ ■ ■ ■ ■ Water use ■ ■ ■ ■ ■ ■ Land use
■ ■ ■ ■ ■ ■ 6