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Life cycle assessment of hemp hurds use in second generationethanol production

Sara Gonzalez-Garcıa a,*, Lin Luo b,1, Ma Teresa Moreira a, Gumersindo Feijoo a,Gjalt Huppes b

aDepartment of Chemical Engineering, School of Engineering, University of Santiago de Compostela, 15782 Santiago de Compostela, Spainb Institute of Environmental Sciences (CML), Leiden University, P.O. Box 9518, 2300 RA, Leiden, The Netherlands

a r t i c l e i n f o

Article history:

Received 25 November 2009

Received in revised form

10 October 2011

Accepted 22 October 2011

Available online 16 November 2011

Keywords:

Allocation

Ethanol

Gasoline

Hemp hurds

Life cycle assessment

Cannabis sativa

* Corresponding author. Division of Biology,South Kensington Campus, London SW7 2A

E-mail addresses: s.gonzalez-garcia@imp1 Present address: European Commission,

0961-9534/$ e see front matter ª 2011 Elsevdoi:10.1016/j.biombioe.2011.10.041

a b s t r a c t

Resource depletion, climate change and environmental pollution are priority topics in

international environmental policy. The use of renewable resources for energy production

is an interesting alternative to fossil fuels. Lignocellulosic biomass as a feedstock to

produce ethanol may replace petrol as a transport fuel. A comprehensive Life Cycle

Assessment was conducted on ethanol produced from hemp hurds (a by-product from

dedicated fibre crops) in an enzymatic hydrolysis process that converts lignocellulosic

biomass into ethanol. The environmental performance of two ethanol fuel blends, E10 and

E85, in a flexi fuel vehicle was analyzed and compared. The environmental impact was

determined by selecting two different allocation approaches (mass and economic alloca-

tion). A sensitivity analysis was conducted and four scenarios were evaluated, involving

different allocation coefficients, taking into account market prices for agricultural products

and the production volume of each product. The results show that ethanol-based fuels can

offer improved environmental performance in impact categories such as global warming,

as well as a decrease in energy resources based on fossil fuels. However, the use of petrol is

the best option in terms of other impact categories, such as photochemical oxidants

formation, acidification and eutrophication. The choice of allocation approach significantly

affects the environmental performance and influences the question which fuel (E10 or E85)

has smaller environmental impacts.

ª 2011 Elsevier Ltd. All rights reserved.

1. Introduction Nowadays, 40% of the total energy consumptionworldwide

The continuing increase in energy consumption, high over-

seas energy dependence and increasing crude oil prices have

motivated more and more support for the use of renewable

energies. Hence, renewable energy is seen as a long-term key

to sources of energy supply in the future [1].

Department of Life ScienZ, United Kingdom.erial.ac.uk, sara.gonzalezJRC, Institute for Energy aier Ltd. All rights reserve

is in the form of liquid fuels such as petrol and diesel [2]. In

fact, the transport sector is almost fully dependent on this

kind of fuel. Hence, special attention has been given to the

potential use of biomass for the production of biofuel to be

used in vehicles. The use of biofuels seems to present envi-

ronmental, energy and socioeconomic advantages relative to

ces, Sir Alexander Fleming Building, Imperial College of London,

@usc.es (S. Gonzalez-Garcıa).nd Transport, P.O. Box 2, 1755-ZG Petten, The Netherlands.

d.

b i om a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9 269

fossil fuel consumption, and the substitution of fossil fuels by

biofuels can be a useful tool to implement the European

policies on the mitigation of greenhouse gas (GHG) emissions

and reduce the dependence on fossil energy supplies. Among

biofuels, ethanol is one of the most environmentally

appealing. It can be blended with petrol (the ethanol volume

fraction is usually 10%e85%) to operate in flexible fuel vehicles

(FFV) and even as 100% ethanol in dedicated vehicles [1,3].

Ethanol is nowadays produced from sugar (such as sugar

cane in Brazil) or starch (such as corn grain in the USA) on

a large scale. However, these rawmaterials can also be used as

food and animal feed. In order to avoid conflicts between food/

feed and industrial uses and an increase in starch price,

lignocellulosic biomass such as agricultural residues, herba-

ceous crops or forestry residues are being studied in detail.

These raw materials are abundant and inexpensive, with

a high content of cellulose and hemicellulose, the main

sources of ethanol [4].

Hemp (Cannabis sativa) is a versatile fibre crop cultivated in

Europe that can supplyfibresandseeds for important industrial

applications. Therefore, the areas under hemp cultivation have

considerably increased since 2003 [5]. A potential use for the

hemp seeds is the biodiesel production. In fact, several papers

can be found in the literature concerning the feasibility of

converting hemp seeds into biodiesel [6,7]. Bast fibres are being

used in specialized sectors such as speciality paper pulp, the

motor industry, construction and textile sectors. The fibres are

obtained by retting hemp stem to separate the fibres fromnon-

fibre components known as hurds. Hemp hurds are the woody

and lignified inner tissues and are considered a by-product of

fibreproduction. The ratio of hurds to fibres canvary from1.5 to

more than 2 [5]. Although new uses for the hurd are under

development, they are mainly used in animal bedding (95%)

and the construction sector (w5%). The chemical composition

of hemp hurds is similar to that of wood species, with

a high content of cellulose and hemicelluloses [8]. Therefore,

hemp hurds could be considered as a potential lignocellulosic

biomass for second generation ethanol production.

Several studies have evaluated the environmental perfor-

mance of cellulosic feedstocks and the subsequent use of the

fuel in vehicles [9e17] achieving different results mainly due

to the lack of a commercial cellulosic ethanol production line

[13]. A general conclusion fromall these studies is that ethanol

as a liquid fuel would have environmental advantages in

terms of reducing non-renewable energy consumption and

greenhouse gas (GHG) emissions. However, ethanol applica-

tion could have adverse effects on acidification and eutro-

phication, due to emissions related to agricultural activities.

This paper aims to assess the environmental performance

of ethanol produced from hemp hurds, using the Life Cycle

Assessment (LCA) approach. An LCA quantifies the environ-

mental impacts of a product or process, provides information

concerning the stage or stages of the production chain that are

likely to cause the highest environmental impacts and helps

to suggest improvements. The present study involves an LCA

on ethanol applications for E10 (blend with a volume fraction

of 10% ethanol and 90% petrol) and E85 (blend with a volume

fraction of 85% ethanol and 15% petrol) fuels, to compare their

environmental profiles in terms of fossil fuel use (natural

gas, crude oil, hard coal and brown coal), global warming,

acidification, eutrophication and photochemical oxidant

formation. One of the problems identified was the competi-

tion with other uses for the hurds, since the use of hemp

hurds for ethanol production competes with their use in

building and insulation materials as well as in animal

bedding. Solving this problem required an allocation process,

and a sensitivity analysis was conducted based on the

market prices of hurds (economic allocation) and mass based

allocation.

The environmental performance shown in this paper

reflects the advantages and disadvantages of using ethanol

blends instead of conventional petrol as well as the influence

of the allocation approach.

2. Life cycle assessment

2.1. Ethanol fuel and functional unit

Ethanol is currently used as a vehicle fuel mainly in two ways.

The first involves ethanol being blended with petrol in a blend

with a volume fraction of 5e20% ethanol, for use in vehicles

without engine modifications. The second involves using

ethanol almost in its pure form (85e100%) in vehicles with

modified engines. In the present study, ethanol was assumed

to be used in two blends: E10 (volume fraction of 10% ethanol

and 90% petrol) and E85 (volume fraction of 85% ethanol and

15% petrol) in a medium-sized FFV. LCA methodology was

used to compare the environmental performance of both

blends with the use of conventional petrol (CG) in a “well to

wheel” analysis.

The function investigated in the study is that of driving an

FFV. There are different ways of defining the functional unit

(FU), and the influence of this choice on the results is partic-

ularly important when the results of the LCA are to be used as

a decision support tool. In addition, the choice of the FU is

highly dependent on the aim of the study. In this study, the FU

chosen to compare the life cycle flows was based on the

distance travelled by vehicles with the vehicle tank full of CG.

The average fuel economy of the FFV under study when

running on CG, E10 and E85 was assumed to be 15.15 km kg�1,

14.49 km kg�1 and 10.87 km kg�1, respectively. If 36 kg of CG

fills up the tank of an FFV, it drives for 545 km. Driving this

distance with E10 and E85 would require about 37.6 kg and

50.2 kg, respectively.

2.2. System boundaries

Fig. 1 shows the main subsystems and processes included

within the system boundaries of the ethanol system under

study. The system includes hemp cultivation, transport of

hurds to the ethanol plant, conversion into ethanol, transport

and distribution of ethanol and ethanol blends combustion in

FFVs.

2.2.1. Hemp Culture (SubSystem 1)The first step in the ethanol production is biomass cultivation.

A standard hectare plot located in the Ebro Valley (NE Spain;

41.35N, 0.78W) was selected for assessment [18]. In this case

study, hemp hurds are a by-product of hemp crops whose

Soil management Fertilizing

SowingHarvesting

Retting Scutching

Baling Bales storage

Feedstock storage & handling

Pretreatment & Conditioning

Saccharification & Co-fermentation

Destillation & Dehydratation

WWTP

Energy productionEn

zym

e pr

oduc

tion

Storage

Utilities:-Water system

-Air system

Chemicals production

Petrol production Blending step

Storage E85

Combustion E10

Nutrients production

LandfillGypsum

Syrup& solid residues

Ethanol

Slu

dg

e &

Bio

ga

s

Electricity SteamLandfillAsh

Storage E10

Combustion E85

Petrol storage

Ethanol storage

FIBRES

DUST

HURDS

ETHANOL

E85

SubSystem1: HEMP CULTURE

SubSystem 2: BALES FORMATION & DISTRIBUTION

SubSystem 3: ETHANOL PROCESSING

SubSystem 4: ETHANOL BLENDS PRODUCTION

SubSystem 5: ETHANOL BLENDS USE

Production & Transport:Machinery Fossil Fuels Fertilizers Seeds

TransportSystemboundary

CO2

Offgas

Combustionemissions

Agrochemical emissions

CO2

Water

Other production

Other production

Subsystemactivities

Legend:E10

Fig. 1 e System boundary for hemp hurds based ethanol blends life cycle.

b i om a s s an d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9270

driving force is the production of fibres for speciality paper

pulp manufacture. The production of fertilizers (ammonium

nitrate, potassium chloride and triple superphosphate),

diffuse emissions from fertilizer application and emissions

from agricultural activities using diesel machinery (chiselling,

harrowing, fertilizing, sowing, harvesting, haying, scutching)

were taken into account in this subsystem, as well as the

transport of all consumable materials up to the farm gate. In

addition, CO2 is fixed when photosynthesis occurs in hemp

growth, which is beneficial from the perspective of mitigating

climate change. The fixation of CO2 was estimated by the C-

content in the dry matter multiplied by the stoichiometric

factor 44/12, based on the assumption that the carbon in the

biomass is completely taken from air.

2.2.2. Bale formation and distribution (SubSystem 2)The next step is the formation of hurd bales from the hurds

obtained in the scutching step which were previously sun

dried up to amoisture content inmass fraction of 11e14% [18].

Bales are subsequently stored before being transported to the

ethanol plant in 16 t lorries. The average distance of delivery

was assumed to be 180 km, because this is the average

distance between the plantation and the pulp mill (destina-

tion of fibres, motivation of hemp crop), located in Tortosa (NE

Spain; 40.8N, 0.52E).

2.2.3. Ethanol processing (SubSystem 3)In the ethanol plant, hemp hurds are converted to ethanol by

means of biological conversion [10,13]. The material and

b i om a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9 271

energy balances for ethanol production as well as ethanol

yield, are based on the ethanol conversion technology from

corn stover reported by the National Renewable Energy

Laboratory [19], assuming that the efficiency of ethanol

production is similar to the one obtained from other crops. In

this case, feedstock composition was adapted to the compo-

sition of hemp hurds (Table 1).

The conversion of the dry biomass involves enzyme-

catalyzed hydrolysis, followed by fermentation and distilla-

tion stages. The model considered in this study assumes that

all sugars obtained from cellulose and hemicellulose content

are transformed into ethanol since a genetically modified

strain is used to convert both C5 and C6 sugars into ethanol

[19]. The pre-treatment step uses dilute sulphuric acid in order

to convertmost of the hemicellulose portion to soluble sugars.

The glucan in the hemicellulose and a small portion of the

cellulose are converted to glucose. Remaining hemicellulose

carbohydrates are assumed to have the same reactions and

conversions as xylan [19]. Following the pre-treatment, there

is a solideliquid separation to remove the cellulose (solids)

from the soluble sugars, which are sent to fermentation for

ethanol production. The cellulose is sent to saccharification,

where enzyme is used to obtain mainly glucose. After that,

this glucose is fermented to ethanol.

Treatment of the wastewater from distillation and evapo-

ration condensates produces biogas. The lignin fraction

presents in the biomass as well as other solids and biogas, are

used as fuel to meet the energy requirements of the plant

(electricity and steam). A conversion efficiency around 50%

was assumed. The production of the enzymes consumed in

the conversion process was included within the subsystem

boundaries. Transports of all consumable materials up to the

plant gate and the landfill of gypsum and ashes generated in

the ethanol production process were also included in this

subsystem.

2.2.4. Ethanol blends production (SubSystem 4)The distribution of ethanol from the ethanol plant to a petrol

station was assumed to be by 32 t diesel lorries over an

average distance of 20 km [20]. The production of the petrol as

well as its transport to the petrol station, the mixture of petrol

Table 1 e Assumed composition (dry mass basis) offeedstock delivered to the refinery gate [8].

Component Mass fraction

Cellulose 0.374

Hemicellulose 0.276

Xylan 0.211

Arabinan 0.029

Other sugar polymers 0.036

Lignin 0.180

Acetatea 0.029

Ash 0.052

Others 0.089

Total 1.00

a Acetate represents the acetate groups present in the hemi-

cellulose polymer. They are converted to acetic acid in the prehy-

drolysis reactor.

and ethanol to produce the blends under study (E10 and E85)

and their regional storage were also included within the

subsystem boundaries. Fuel quality control has been assumed

to take place and is not extensively discussed in the scope of

the study. In practice, ethanol could be blended with gasoline

at terminals near the end users. Establishing new infrastruc-

ture for the blending terminals has not been considered

within the scope of the present study, thus this optionwas not

assumed here.

2.2.5. Ethanol blends use (SubSystem 5)The previously described combustion of fuels in a represen-

tative FFV was evaluated and emissions were calculated

according to the quantities of ethanol and petrol necessary to

drive a distance of 545 km. Manufacture, maintenance and

disposal of the FFV were excluded from the subsystem

boundaries.

2.3. Allocation procedures

Allocation (partitioning of input or output flows of a unit

process to the product under study) is one of the most critical

issues in LCA. The ISO 14044 recommends avoiding allocation

whenever possible either through subdivision of processes or

by expanding the system limits to include the additional

functions related to them [21]. If avoiding allocation is not

possible, the ISO 14044 recommends using methods to allo-

cate. In this study, allocation approach was needed as this

agricultural crop yield more than one product. Allocation may

be performed from an economic or physical relationships

point of view (mass/weight or energy content). Each allocation

method has its advantages and disadvantages, and the choice

of allocation procedure depends on the goal of the study.

Hemp crop produces large amounts of hurds as a by-product

during fibre separation (fibre being the main product) as well

as hemp dust. Economic allocationwas considered as the base

case, since it represents a measure to promote production.

The economic allocation approach is interesting not only in

view of the different market prices of agricultural products

[22], but also because of the large differences in the market

value of hemp hurds reported in the literature on this subject

[22,23]. According to previous studies, feedstock cultivation is

an important contributor to the environmental profile [9,24].

Therefore, a sensitivity analysis of allocation coefficients was

carried out to evaluate the dependence on agricultural activ-

ities. Thus, we also considered mass based allocation in the

analysis, as specified in ISO 14044 [21], for two reasons: (i)

market prices of these products fluctuate depending on

demand and (ii) more hurds than fibres are produced per

hectare (mass ratio: 1.5:1).

Four scenarios were designed, and Table 2 provides brief

descriptions of the economic values and allocation factors:

� Scenario A (ScA) is the base case and corresponds to an

economic allocation, assuming that the mean market price

for the hurds at the farm gate is the same as that for other

lignocellulosic biomass, such as corn stover used for ethanol

production, that is, 25 V t�1 [19].

� Scenario B (ScB) also corresponds to an economic allocation,

but assumes a market price for the lignocellulosic feedstock

Table 2 e Partitioning fraction for mass and economic allocation.

Products t ha�1 V kg�1 ScA V kg�1 ScB V kg�1 ScC ScD

Fibres 1.0 0.265a 86.3% 0.265a 65.5% 0.750c 71.1% 33.3%

Hurds 1.5 0.025b 12.2% 0.090a 33.4% 0.200c 28.5% 50.0%

Dust 0.5 0.009a 1.5% 0.009a 1.1% 0.009a 0.4% 16.7%

Total 3.0 100% 100% 100% 100%

a Data from [19].

b [22].

c [23].

b i om a s s an d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9272

of 90 V t�1. This is the average price for hemp hurds sold in

France for building purposes, without including biomass

transport costs [22]. This value fits with market values re-

ported by other authors [25,26].

� Scenario C (ScC) also represents an economic allocation, but

assumes a market price of 200 V t�1 [23]. This value is

significantly higher than the values in ScA and ScB, and the

authors did not report whether this consideration includes

transport costs.

Biomass transport cost is an economic key factor, since it

depends on several factors: form and bulk density of biomass,

distance covered to reach the final destination and transport

infrastructure [27e29]. The traditional way of dealing with

biomass transport cost is to consider a distance fixed cost

(DFC) and a distance variable cost (DVC) for the transport

equipment [30]. Since biomass is commonly transported by

Table 3 e Data sources for the life cycle inventory of hemp hu

Subsystem Data required

SS1 Fuel use Hemp f

Fertilizer use

Labour use

Consumable materials transport

(mode, capacity and distance)

Researc

(see Tab

Diffuse emissions Researc

SS2 Fuel use Hemp f

Weight of bales

Hurds bales transport (mode,

capacity and distance)

Researc

(see Tab

SS3 Production capacity Researc

Chemicals use

Nutrient use

Enzyme production

Landfill operation

Energy requirements

Industrial equipment use

Wastewater treatment plant

Consumable materials transport

(mode, capacity and distance)

Researc

(see Tab

SS4 Petrol production and transport

(mode, capacity and distance)

Researc

(see Tab

Ethanol transport (mode, capacity

and distance)

Ethanol, Petrol and Blends storage

SS5 Fuel use Researc

Emission data of car driving

lorry, DFC should be the cost of loading, unloading and

stacking at the final destination, and DVC should be the

hauling cost for transport of biomass, depending on distance

travelled, weight of biomass transported, moisture and road

quality. Several authors have proposed equations to calculate

the transport costs [27,30,31]. Moreover, an increase in the

demand for ethanol might be expected to increase the market

price as well. However, we do not take transport cost into

account due to the uncertainty and lack of information about

feedstocks supply for ethanol production. All scenarios based

on economic allocation take market prices at the farm gate

into account and do not include the corresponding transport

from farm to final industry.

� Scenario D (ScD) corresponds to mass based allocation

taking into account the total weight production for each

agricultural product.

rds based ethanol manufacture.

Data sources Collecting method

armers Research report [32] Questionnaires Interviews

Literature review

h reports [33] Assumptions

le 4)

h reports [34e37]

armers Research report [32] Literature review

Questionnaires

h report [33] Assumptions

le 4)

h reports [19,33,38e42] Literature review

h report [33] Assumptions

le 4)

h reports [12,33,39] Assumptions

le 4)

Literature review

h reports [42,43] Literature review

Table 5 e Mass balance of the hemp culture (kg haL1).

Quantity

N-fertilizer 85

K2O 125

P2O5 65

Diesel use 74

Hemp straw (11e14% moisture)a 3000

Ethanol produced 413

a 50% hurds, 33% fibres, 16.7% dust [18]

b i om a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9 273

Table 2 shows the corresponding allocation ratios for each

product and allocation method.

Regarding ethanol production, allocation was avoided

because almost all electricity and steam produced from

wastes in the biorefinery is consumed in the ethanol process.

There is a surplus of electricity and steam but it was not

included in the analysis since the surplus energy is low and

steam was vented to the atmosphere. Surplus electricity

(270 kJ kg�1 ethanol) could be sold to the grid. In addition, solid

residues generated in the biorefinery, such as gypsum and

ash, are sent to landfill and were thus regarded as wastes.

Thus, all the environmental burdens of the SS3 were allocated

to ethanol (the main product).

2.4. Data collection

Themost laborious step in the implementation of LCA studies

is the collection of inventory data to build the life cycle

inventory (LCI). Moreover, high quality data is essential for

a reliable evaluation. We handled a large amount of data,

including fertilizer production, diffuse emissions from fertil-

izer application, transport systems and ethanol production.

The procedure for the LCI of the system under study is

summarized in Table 3. As this table shows, data for the study

was collected from different sources and by different

methods, including field data, interviews, research reports

and literature, to ensure the reliability of the study. Table 4

describes the hypotheses that were considered regarding

transport activities in the ethanol life cycle.

To evaluate the environmental performance of hemp hurd

production and distribution to the ethanol plant, a standard

hectare plot was selected from the 700 ha cultivated in the

region under study (the Ebro Valley, NE Spain) [18]. This region

was chosen because hemp is a traditional crop in the area.

The selected plot was characterized by the values shown in

Table 5. Data from the ethanol production subsystem (mass

and energy balances) is summarized in Table 6.

Table 4 eHypotheses about transport activities related toethanol life cycle.

Materials Transportmode

Capacity(t)

Averagedistance(km)

Fertilizers from wholesalers

to farm

Diesel lorry 28 308a

Hurds bales from farm to

ethanol plant

Diesel lorry 16 180a

Chemicals from wholesalers

to ethanol plant

Diesel lorry 16 50a

Solid wastes from ethanol

plant to landfill

Diesel lorry 16 20a

Ethanol from ethanol plant

to blending refinery

Diesel lorry 32 20b

Ethanol blends to regional

storage

Diesel lorry 32 34c

a Average distance.

b Data from [20].

c Data from [32].

3. Results

Life Cycle Impact Assessment was conducted using charac-

terization factors from CML methodology [37]. The following

parameters were considered in the analysis: global warming

(GW), photochemical oxidants formation (PO), acidification

(A), eutrophication (E) and fossil fuel extraction (FF). Special

attention was paid to the GHG emissions and fossil fuel use to

satisfy the two challenges for the EU in terms of transport

fuels [44], viz. (i) reducing GHG emissions and (ii) protecting

energy supply.

3.1. Environmental performance of E10 and E85 incomparison with CG in the base case

Tables 7and 8 summarize the LCA characterization results for

CG, E10-a and E85-a. Change represents the impacts of

substituting either of the two alternative fuels for CG. Nega-

tive change implies a reduction in environmental load

compared to CG, while positive change implies an increase in

the environmental load.

According to our results, contributions to GW, PO, A and E

are increased by a shift from CG to ethanol blends. GHG

emissions are due mostly to three global warming gases: CO2,

N2O and CH4. N2O and CH4 emissions increase when changing

from CG to ethanol blends, since they come from the culti-

vation step, especially due to N-based fertilizers and the use of

agricultural machinery. CO2 emissions also increase because

Table 6 e Mass and energy balances (per t of ethanol) ofthe ethanol processing subsystem.

Electricity(kWh)

Steam(MJ)

Residue(kg)

Feedstock storage &

handling

�56a e þ70

Pre-treatment &

conditioning

�66a �5023 þ274

Saccharification &

fermentation

�65a e

Distillation & dehydration �40a �1052 e

Wastewater treatment

plant

�56a e

Enzyme production �680a e

Ethanol storage �1a e

Utilities �129a e

Energy production þ1168 þ 6075 þ75

-100

-50

0

50

100

150

200

250

300

CG E10-a E85-a

GW

as C

O2eq

p

er F

U (kg

)

Chemicals

Fossil fuels

Transport

Blend use

EtOH plant

Agriculture

N2O emissions

CO2 uptake

Fig. 2 e Contributions (in kg) to global warming (GW) as CO2

equivalent per functional unit for the base case (ScA).

Table 7 e Potential environmental impacts estimated perfunctional unit for the base case (ScA).

Category CG E10-a E85-a

Value % Change Value % Change

GW as CO2 eq (kg) 139 149 þ7.1 232 þ67

PO as C2H4 eq (g) 87.3 90.5 þ3.8 138 þ58

A as SO2 eq (g) 404 407 þ0.8 472 þ17

E as PO4�3 eq (g) 41 103 þ151 709 þ1633

b i om a s s an d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9274

of the low effect of CO2 uptake during the biomass growth. CG

and E10 yielded similar performances (with minor differences

in terms of GHG emissions) because the fuel economy of both

fuels is quite similar and a low percentage of ethanol in the

blend was considered. Fig. 2 shows the contributions of the

main processes involved in the life cycle for CG and ethanol-

based fuels. In CG and E10, the main contributor to GW is

the use of the blend, followed by petrol production. This result

is due to the high proportion of petrol in the blend (volume

fraction of 90%).

Using E85 as a transport fuel radically changes the results

and the ethanol conversion step is now the main key issue,

followed by fuel use. Electricity production and distillation are

the main stages responsible for the impact of the ethanol

plant. Regarding the remaining impact categories (PO, A and

E), the results show the same behaviour as GW, and the

percentage of positive change is higher when E85 is used.

Therefore, using CG is also more advantageous than ethanol-

based fuels. Higher impacts from the upstream activities

(agricultural, biorefinery and blending related activities) for

ethanol blends govern the net impacts of the fuel life cycle

relative to CG in all these impact categories. Agricultural

activities are among the main contributors, due to the

increased CO and NMVOC emissions from the use of diesel in

agricultural machinery and hurd bale transport from farm to

plant, which contribute to PO (Fig. 3a); the SO2 and NOx

emissions from fertilizer production and diesel combustion,

which contribute to A (Fig. 3b); and finally nitrate leakage and

N2O from N-fertilizer application, which contributes to E

(Fig. 3c). It is interesting to note that diffuse emissions from

fertilizer application are responsible for more than 56% and

88% of total contributions to E for E10 and E85, respectively.

Specifically, nitrate leakage represents 39% and 61% of the

total eutrophying emissions for these two ethanol-based

fuels.

Table 8 e Contributions to fossil fuel extraction (FF)expressed in coal equivalent per functional unit for thebase case (ScA).

Fossil fuels CG E10-a E85-a

Value % Change Value % Change

Coal (kg) 2.20 2.15 �2.2 3.97 þ80.2

Natural gas (kg) 4.44 4.42 �0.4 4.72 þ6.3

Crude (kg) 78.25 73.44 �6.2 26.63 �66.0

Total (kg) 84.89 80.01 �5.8 35.32 �58.4

Regarding FF, Table 8 shows clear advantages of using E10

and E85 instead of CG as a transport fuel, in terms of reducing

fossil fuel consump4tion. Although shifting from CG to

ethanol blends entails the consumption of more liquid fuel by

agricultural machinery (usually diesel), less petrol is neces-

sary to propel the cars, hence the reduction of up to 58.4% in

total fossil fuel consumption is obtained when E85 is used.

3.2. Sensitivity analysis: effect of changing allocationratio between agricultural products

Numerous authors have reported that feedstock cultivation

contributes significantly to environmental impacts, but

particularly to global warming, acidification and eutrophica-

tion [9,13,45,46]. For this reason, a sensitivity analysis was

applied for the allocation factors in our agricultural

subsystem. The results of the sensitivity analysis of changes

in the allocation coefficient between hemp hurds and the

other agricultural products (hemp fibres and hemp dust) are

shown in Fig. 4 (for E10 scenarios) and Fig. 5 (for E85 scenarios).

All the results are displayed as percentages relative to CG.

According to Fig. 4, the use of the E10 blend results in

a slightly better environmental performance than CG in terms

of GW (reduction of 0.5% of contributing emissions) when

a high allocation ratio is assumed (ScD, mass allocation ratio:

50%). This result is mainly influenced by the highest contri-

bution of the agricultural activities, which implies a greater

effect of the CO2 uptake during biomass growth. Thus, the CO2

taken up during the biomass growth can slightly reduce the

equivalent CO2 emissions from other processes such as agri-

cultural machinery, ethanol conversion and blend use,

resulting in reduced GHG emissions. Fig. 6 shows the contri-

butions to GW from the main processes involved in the life

cycle of the fuels. E10 fuels also present a better environ-

mental profile than CG in terms of FF, regardless of the allo-

cation factor chosen. However, the reduction of the

consumption of fossil fuels is greater when allocation ratios

are lowest (ScA, economic allocation ratio: 12.2%), due to the

fact that less of the diesel required for the agricultural activ-

ities is allocated to the hemp hurds.

Concerning the remaining categories under study (PO, A

and E), the results show the expected behaviour: increasing

the allocation ratio for the hemp shives contributes to an

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

CG E10-a E85-a

PO

as

C2H

4e

q (

kg

)

Use Upstream

0

0.1

0.2

0.3

0.4

0.5

CG E10-a E85-a

A a

s S

O2

eq

(k

g)

Use Upstream

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

CG E10-a E85-a

E a

s P

O4

-3

eq

(k

g)

Use Upstream

a

b

c

Fig. 3 e Life cycle equivalent emissions comparison (per

functional unit) of the different fuels under study for the

base scenario (ScA): CG, E10-a and E85-a. (a) Contributions

to photochemical oxidants formation expressed as net

C2H4 eq emissions. (b) Contributions to acidification

expressed as net SO2 eq emissions. (c) Contributions to

eutrophication expressed as net PO34 eq emissions.

b i om a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9 275

increase in the contributions from hemp cultivation (diffuse

emissions from fertilizer application, fertilizer production and

combustion emissions from agricultural machinery use).

Using E85 as a transport fuel (Fig. 5) results in the same

trend as E10, although the net emissions are considerably

increased relative to the use of E10 and CG in terms of PO, A

and E. This proves the influence on the environmental results

of the activities relating to feedstock cultivation. With regard

to GHG emissions, CO2, CH4 andN2O are themain contributors

to GW. Fig. 7 compares the life cycle GHG emissions for each

fuel and scenario under study.

Using E85 results in increased N2O emissions in compar-

ison with the use of CG and E10 fuels, as more ethanol is

involved in the fuel life cycle and higher amounts of N2O are

thus released into the atmosphere. In addition, the emission

of nitrous oxide increases with the allocation ratio because

agricultural activities play a major role in the life cycle.

Regarding CO2 emissions, using E85 as a transport fuel results

in lower CO2 emissions from petrol production than the use of

CG or E10. This is due to the fact that E85 has the lowest

percentage of petrol in the blend. In contrast, E85 use

produces more emissions from the ethanol production plant

and from fossil fuel extraction relating to agricultural activi-

ties (diesel for machinery and fertilizer production). As

a result, the contributions to GW could be increased,

depending on the allocation factor. Thus, high allocation

ratios (scenario ScD in our study) imply that more CO2 taken

up by agricultural production is assigned to the hemp hurds

than to the other by-products, offsetting the CO2 emissions.

Quite the opposite occurs at low allocation ratios (scenarios

ScA, ScB and ScC in this study), where it is not possible to

offset the GHG emissions. Fig. 8 shows the contributions to

GW from themain processes involved in the E85 fuel life cycle.

Finally, CH4 emissions are slightly reducedwhen shifting from

CG to E85, due to the lower fossil fuel requirements.

In relation to the contributions to FF, the higher the

reductions of fossil fuel consumption for E85 blends, the lower

the allocation factor for the hurds (Fig. 5), and they are also

reduced when shifting from E10 to E85 for identical allocation

ratios. The main causes of these results are the lower

assignment of diesel for agricultural activities to the hurds

and the lower proportion of petrol in the fuel used to propel

the car, respectively.

Regarding the remaining categories (PO, A and E), shifting

fromCG to E85 fuels increases the emissions which contribute

to these impact categories, the increase being higher for

higher allocation ratios. This result is highly influenced by the

contributions from upstream activities, especially from

activities relating to feedstock cultivation. In addition,

a comparison of the use of E85 and E10 shows that these

corresponding emissions are also increased by the use of E85,

due to the fact that there is more ethanol in the blend and

there are more emissions from the feedstock cultivation and

ethanol production stages. The environmental impacts from

the ethanol production cycle (especially agricultural activities)

play amore dominant role in a high-level ethanol-petrol blend

than in a low-level one.

4. Discussion

Asmentioned above, there are a few obstacles and constraints

that need to be overcome if second-generation ethanol is to be

regarded as a sustainable and cost-effective source of energy.

Nowadays, biofuels are commercially uncompetitive with

fossil fuels (petrol anddiesel) in Europebecause the technology

is still being developed. Although lignocellulosic biomass is

0%

20%

40%

60%

80%

100%

120%

GW PO A FF

Re

lativ

e p

erfo

rm

an

ce

(%

)

0%

200%

400%

600%

800%

E

Re

lativ

e p

erfo

rm

an

ce

(%

)

CG E10-a E10-b E10-c E10-d

Fig. 4 e Relative environmental profile of the E10 scenarios compared with CG as the base case (index [ 100). Acronyms:

GW [ global warming; PO [ photochemical oxidants formation; A [ acidification; E [ eutrophication; FF [ fossil fuel

extraction.

b i om a s s an d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9276

abundantand inexpensive, not all cellulose biomass is suitable

and can be used as feedstock, due to the constraints of the

present technology used to hydrolyze the biomass efficiently

in terms of cost and energy consumption [2].

We have reviewed a number of papers presenting LCA

studies of different ethanolepetrol blends from lignocellulosic

feedstocks [9,10,47] and sugar crops [11,24,46,48,49]. This

review shows that the choices of system boundaries, the

definition of the functional unit and allocation procedures

play an important role in the LCA of ethanol blends. This

paper has aimed to analyze the influence of the allocation

procedures on the environmental results for the feedstock

cultivation stage, since the driving force of this kind of crop is

the production of fibres for paper pulpmanufacture, and there

are large differences in market prices between the fibres and

the other by-products (hurds and dust). In addition, their

production differs greatly in terms of weight.

Several previous studies have presented ethanol-based

fuels as an interesting alternative fuel which can offer an

opportunity to reduce GHG emissions and other polluting

emissions, as well as amore reliable energy supply [50]. When

0%

50%

100%

150%

200%

250%

300%

GW PO A

Rela

tive p

erfo

rm

an

ce (%

)

CG E85-a E85-b

Fig. 5 e Relative environmental profile of the E85 scenarios com

GW [ global warming; PO [ photochemical oxidants formatio

extraction.

one process results in two or more valuable product outputs

(known as co-products), allocation of emissions and resources

used in the production of the products may be necessary. Co-

product allocation procedures are very important for agricul-

tural systems, because these systems usually produce more

than one economic output, and the allocation procedure can

markedly modify the results. The diversity of allocation

approaches has causedmuch debate among LCA practitioners

and researchers. Curran [51] determined the impact of

different allocation procedures upon the use of ethanol blends

and petrol fuels. In that study, several allocation procedures

(mass, volume, economic, energy and demand based) were

applied to the petrol and ethanol production plant, but not to

the biomass production system, since the stover (considered

to be feedstock) was regarded as waste. According to Curran’s

study, the allocation methodology does not alter the final

environmental results when comparing systems, and ethanol

blends are always the best option in terms of GW. Nguyen and

Gheewala [11] analyzed the influence of the economic allo-

cation approach applied to the products obtained in sugar

milling, since the molasses obtained in this step from the

FF0%

1800%

3600%

5400%

7200%

E

Re

lativ

e p

erfo

rm

an

ce

(%

)

E85-c E85-d

pared with CG as the baseline (index [ 100). Acronyms:

n; A [ acidification; E [ eutrophication; FF [ fossil fuel

-20%

0%

20%

40%

60%

80%

100%

CG E10-a E10-b E10-c E10-d

GW

-c

on

trib

utio

ns

Chemicals

Fossil fuels

Transport

Blend use

EtOH plant

Agriculture

N2O emissions

CO2 uptake

Fig. 6 e Contributions to global warming (GW) in % for CG

and E10 scenarios according to the sensitivity analysis for

the allocation factors.

-60%

-40%

-20%

0%

20%

40%

60%

80%

100%

CG E85-a E85-b E85-c E85-d

GW

-c

on

trib

utio

ns

Chemicals

Fossil fuels

Transport

Blend use

EtOH plant

Agriculture

N2O emissions

CO2 uptake

Fig. 8 e Contributions to global warming (GW) in % for CG

and E85 scenarios according to the sensitivity analysis for

the allocation factors.

b i om a s s a n d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9 277

sugar cane are used as feedstock in the ethanol plant.

According to this study, the only large differences that were

predicted related to N2O emissions. These emissions from N

fertilization in agriculture are among the main factors which

could help to increase GHG emissions from ethanol use

compared to fossil fuels.

In the ethanol-based fuel life cycle, the agricultural activ-

ities related to the production of the feedstock have been

identified as environmental key factors in several impact

categories, such as acidification, eutrophication and global

warming [10,11,46,51]. Hence, the impact of the agricultural

product allocation approaches on the environmental results.

Biomass crops such as sugar cane and cassava should not

require allocation, since they are the only product. In hemp

production; however, allocation is unavoidable because the

production of hurds is impossible without the simultaneous

production of fibres and dust. The growing crop is an impor-

tant sink for atmospheric CO2, as this gas is used in the

photosynthesis process to build the organic carbon

compounds used in growth. The CO2 fixed in the part of the

biomass exported from the land has three final destinations:

the fibres, the hurds and (for a small fraction) the dust.

Economic allocation was applied in the baseline scenario

(scenario A), but in view of the large differences in market

value for hemp hurds found in the literature [22,23], we

CG E10-a E10-b E10-cCO2 136.9 145.1 136.4 138.0N2O 0.1 1.9 4.9 4.2CH4 2.0 1.9 2.0 2.0

0

45

90

135

180

225

GW

as

CO

2e

q p

er F

U (

kg

)

Fig. 7 e Life cycle GHG emissions comparison between CG and et

analysis for the allocation factors.

constructed two more scenarios, also based on economic

allocation (scenarios B and C). The sensitivity analysis was

supplemented with a fourth scenario, based on mass based

allocation (scenario D) as explained above.

Our results show that the use of ethanol blends as trans-

port fuel in an FFV could reduce GHG emissions by more or

less remarkable amounts, depending on the percentage of

ethanol in the blend and the allocation ratio assumed between

hurds, fibres and dust, which does not agree with with

Curran’s results [51]. The reductions obtained when

comparing biofuels with CG would be greater when using

a higher allocation ratio and a higher ethanol percentage in

the blend (Figs. 4 and 5). However, the use of economic allo-

cation (with a low allocation coefficient for the hurds)

completely changes the results, and ethanol blends then do

not reduce GHG emissions. Although the lower level of crude

oil consumption implies that less CO2 is emitted from petrol

production when shifting from CG to ethanol, the allocation

ratio between agricultural products is considerably lower for

hurds in the economic allocation, so most of the CO2 taken up

by agricultural production is allocated to the fibres, and it

cannot offset the CO2 emissions from fossil fuels.

Regarding the impacts on PO, A and E, our results are in

agreement with those of other published papers. These

E10-d E85-a E85-b E85-c E85-d129.3 211.1 116.7 138.5 43.3

7.3 19.0 51.6 44.1 76.92.1 1.5 2.8 2.5 3.8

hanol-based fuels (E10 and E85) according to the sensitivity

b i om a s s an d b i o e n e r g y 3 6 ( 2 0 1 2 ) 2 6 8e2 7 9278

impact categories are increased when shifting from CG to

ethanol blends, as feedstock cultivation contributes signifi-

cantly to all these impact categories [9e11,24].

For fossil fuel requirements, shifting from CG to ethanol

blends always reduces their consumption (especially that of

crude oil). Higher reductions were observed in the economic

allocation than in the mass based allocation approach. This

result is influenced by the lower assignment factor of the

agricultural activities to the hemp hurds. In addition, greater

reductions are achieved for blendswith a higher percentage of

ethanol, mainly due to the reduction of petrol in the blend

(Figs. 4 and 5).

5. Conclusions

The production and use of ethanol as an alternative fuel to

conventional petrol in an FFV could allow an improvement of

some environmental impacts, as well as a reduction of the

dependence on fossil fuels. Second generation ethanol has the

potential to become the major source of renewable energy in

theworld, and lignocellulosic feedstocks could help to achieve

these proposals. However, there are vehement protests

around the world against the idea of using land to grow crops

dedicated to fuel while there aremillions of people who suffer

from famine and malnutrition. Agricultural and forest waste

as well as by-products such as hurds and shives from ligno-

cellulosic fibre crops could be an interesting alternative to

avoid all the controversy.

The use of different allocation procedures can affect the

environmental results. Hence the importance of avoiding

allocation if possible, since the selection of the allocation

factors strongly affects the conclusions of the study.

The use of biomass for fuels would increase acidification,

eutrophication and photochemical oxidants formation,

particularly because of fertilizer-related burdens from

biomass cultivation as well as from the ethanol production

plant. Therefore, efforts should be made to reduce these

burdens and improve the environmental profile.

Acknowledgements

This work has been partially financed by the Xunta de Galicia

(Project Reference GRC 2010/37). Dr. S. Gonzalez-Garcıa would

like to express her gratitude to the Spanish Ministry of

Education for financial support e Grant reference AP2005-

2374, during which this paper was prepared and e Grant

reference EX2009-0740 for a Postdoctoral Research Fellowship

taken at Imperial College London (UK), during which this

paper was revised.

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