environmental impacts of a lignocellulose feedstock biorefinery system: an assessment

b i o m a s s a n d b i o e n e r g y 3 3 ( 2 0 0 9 ) 7 9 3 – 8 0 2

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Environmental impacts of a lignocellulose feedstockbiorefinery system: An assessment

Andreas Uihlein*, Liselotte Schebek

Department of Technology-Induced Material Flow, Institute for Technical Chemistry, Forschungszentrum Karlsruhe GmbH, P.O. Box 3640,

76021 Karlsruhe, Germany

a r t i c l e i n f o

Article history:

Received 3 May 2006

Received in revised form

8 April 2008

Accepted 22 December 2008

Published online 10 February 2009

Keywords:

Life Cycle Assessment

Biorefinery

Lignocellulose feedstock

Environmental impact

* Corresponding author. Tel.: þ49 7247 82 83E-mail address: [email protected]

0961-9534/$ – see front matter ª 2009 Elsevidoi:10.1016/j.biombioe.2008.12.001

a b s t r a c t

Biomass is a sustainable alternative to fossil energy carriers which are used to produce

fuels, electricity, chemicals, and other goods. At the moment, the main biobased products

are obtained by the conversion of biomass to basic products like starch, oil, and cellulose.

In addition, some single chemicals and fuels are produced. Presently, concepts of bio-

refineries which will produce a multitude of biomass-derived products are discussed.

Biorefineries are supposed to contribute to a more sustainable resource supply and to

a reduction in greenhouse gas emissions. However, biobased products and fuels may also

be associated with environmental disadvantages due to, e.g. land use or eutrophication of

water.

We performed a Life Cycle Assessment of a lignocellulose feedstock biorefinery system and

compared it to conventional product alternatives. The biorefinery was found to have the

greatest environmental impacts in the three categories: fossil fuel use, respiratory effects,

and carcinogenics. The environmental impacts predominantly result from the provision of

hydrochloric acid and to a smaller extent also from the provision of process heat. As the

final configuration of the biorefinery cannot be determined yet, various variants of the

biorefinery system were analysed. The optimum variant (acid and heat recoveries) yields

better results than the fossil alternatives, with the total environmental impacts being

approx. 41% lower than those of the fossil counterparts.

For most biorefinery variants analysed, the environmental performance in some impact

categories is better than that of the fossil counterparts while disadvantages can be seen in

other categories.

ª 2009 Elsevier Ltd. All rights reserved.

1. Introduction sources, e.g. wind, water, sun, biomass, geothermal heat;

The world’s economy today highly depends on fossil energy

sources (coal, oil, natural gas) which are used to produce fuels,

electricity, chemicals, and other goods. The utilisation of

these depletable fossil energy sources in the long run is not

considered to be sustainable. As a way out, the use of

renewable resources might serve as an alternative. While the

energy industry can be based on a variety of alternative

30; fax: þ49 7247 82 6715.a.eu (A. Uihlein).

er Ltd. All rights reserved

chemical industry and, to a smaller extent, the production of

fuels will have to rely on biomass as an alternative in the

future [1,2].

At present, some fuels are produced from biomass, such as

ethanol and biodiesel. The main biobased products are

obtained from the conversion of biomass to basic products

like starch, oil, and cellulose. In addition, chemicals like lactic

acid and amino acids are produced, which are mainly used in

.

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the food industry [3]. In contrast to this, conventional refin-

eries use petrochemical raw materials to produce a wide

variety of fuels, chemicals, and consumer goods. Presently,

concepts of biorefineries are being increasingly discussed.

Such biorefineries will produce a multitude of biomass-

derived products which might replace the petroleum-refin-

ery’s products as well as some products which cannot be

manufactured in conventional refineries [3–5]. The three main

biorefinery concepts are the lignocellulose feedstock (LCF)

biorefinery, the whole-crop biorefinery, and the green bio-

refinery [3]. Of these three types, the LCF biorefinery is

considered to be the most promising, as the availability of the

input material (e.g. straw, grass, waste wood) is relatively high

and input material prices are low [3,6].

Biorefineries are supposed to contribute to a more

sustainable resource supply by the conservation of depletable

resources, while allowing for a reduction in greenhouse gas

emissions and other pollutants [1,7,8]. Still, biobased products

and fuels may also be associated with environmental disad-

vantages, e.g. an increased land use, the eutrophication of

water or the pollution of the environment with pesticides.

Moreover, the necessary inputs of auxiliary materials and

energy in the production processes may lead to environ-

mental burdens.

A Life Cycle Assessment (LCA) of a future biorefinery

system was performed in order to analyse whether bio-

refineries are more environmentally friendly than their

conventional (fossil) alternatives. Another aim of the LCA was

to unveil which environmental problems are associated with

biorefinery systems (e.g. acidification, ecotoxicity, ozone layer

depletion) and to identify the steps in the life cycle chain that

are responsible for the impacts (e.g. the provision of the raw

materials, or the production processes). As the LCF biorefinery

seems to be the biorefinery system which will be implemented

first, this biorefinery type was chosen for our analysis [6].

The present article is structured as follows: in Section 2,

a short overview of recent developments in the biorefinery

sector and available technologies will be given. In Section 3,

methodological issues, such as the goal and system definition,

shall be presented. The life cycles and the procedure chosen

for the Life Cycle Impact Assessment will be described.

Section 4 will present some results of our analyses. In Section

5, some conclusions will be drawn from the results.

Goal and scope definition

Inventoryanalysis

Impactassessment

Interpretation

Fig. 1 – The phases of Life Cycle Assessment.

2. Recent developments and biorefinerytechnologies available

The three main biorefinery concepts are the lignocellulose

feedstock (LCF) biorefinery, the whole-crop biorefinery, and

the green biorefinery [3]. The following sections will concen-

trate on LCF biorefinery systems, because this biorefinery type

is regarded as the most promising concept.

Lignocellulose materials are composed of three main

fractions, namely, cellulose, hemicellulose, and lignin [6].

Carbohydrates can be produced from the lignocellulose feed-

stock by (a) diluted acid hydrolysis (at high temperature),

(b) concentrated acid hydrolysis, or (c) biotechnological

methods (enzymes, microorganisms) [6]. Frequently, physical

pre-treatment steps are used.

At present, a multitude of processes are under develop-

ment for LCF biorefineries. Up to now, only pilot plants have

started operation. An example of an LCF biorefinery system is

the technology based on concentrated acid hydrolysis that

was developed by Arkenol in the 1980s. This process is used in

a discontinuous pilot plant with a throughput of 1 t of biomass

per day [9]. Outputs are lignin and a sugar stream containing

C5 and C6 sugars which can then be converted into ethanol

[10]. A first commercial facility will be implemented soon. It

will use rice straw and produce a combination of ethanol,

citric acid, and zeolites [10]. National Renewable Energy

Laboratory, NREL, developed a process for a dilute acid pre-

treatment with a subsequent enzymatic saccharification and

fermentation to produce ethanol. A pilot development unit is

in operation with a throughput of 1 t biomass per day [9].

3. Methodological issues

The Life Cycle Assessment was performed according to the

standard practice as defined by the ISO 14040 series [11] in

general (see Section 3.3). The three main steps of a Life Cycle

Assessment are goal and scope definition, Life Cycle Inventory

(LCI) analysis, and Life Cycle Impact Assessment (LCIA) (Fig. 1).

According to the ISO standards, not only the whole life

cycle of a particular product has to be accounted for in terms

of its ecological implications, but also any by-products arising

from its production. Under certain circumstances, the envi-

ronmental effects of these by-products can tip the balance

with regard to the overall ecological effects of the main

product. Thus, the whole life cycle is balanced. In addition, all

additives and co-products are included and balanced as

credits.

3.1. Goal and scope definition

For our analysis, a simple LCF biorefinery system is defined

and assessed and compared to the conventional product

alternatives (Fig. 2).

The biorefinery uses straw from agriculture as input

material. After transport to the biorefinery, the straw is milled.

filtrationfiltration

cultivation,harvestTmillingpre-hydrolysis pre-hydro-lysatemainhydrolysis mainhy-drolysate

Lignin

ionexchangeXyloseconversion

Xyli te

ionexchangeGlucoseconversionEthanolTuse Tuse(Otto-PC) Tuse

rotat ionfallow

Gaso-line SugarAcrylicbinderTuse Tuse(Otto-PC) Tuse

LegendTTransportprocesscreditProductaggre-gationLegendTTransportprocesscreditProductaggre-gationosso ofstraw

Biorefine ryTrans portUse

Cultivation& harvest

Milling

Pre-hydrolysis

Filtration

Mainhydrolysis

Filtration

T

Pre-hydro-lysate

Ionexchange

XyloseMain hy-drolysate

Con-version

Ionexchange

Glucose

Con-version

Lignin Ethanol XyliteAcrylic

binderGasoline Sugar

Crude oil extraction

Pro-cessing

T

Refining

Crude oil extraction

Pro-cessing

T

Refining

Cultivation& harvest

Sugarextraction

Refining

T

Residue

Residue

Fig. 2 – Schematic life cycle comparison ‘biorefinery vs. conventional products’.

b i o m a s s a n d b i o e n e r g y 3 3 ( 2 0 0 9 ) 7 9 3 – 8 0 2 795

In a first hydrolysis step (pre-hydrolysis), the straw is sepa-

rated into residue and pre-hydrolysate. This pre-hydrolysate

is converted into xylose, which is then converted into xylite.

The residue is hydrolysed again (main hydrolysis), with lignin

and glucose as outputs. Glucose is subsequently converted

into ethanol. The configuration of the biorefinery is mainly

based on the Arkenol process [10]. The system boundaries and

the input and output streams of the biorefinery are shown in

Fig. 3. The provision of the single inputs and processes (e.g.

straw, process heat, wastewater treatment) was calculated

according to Ref. [14] and includes all upstream processes and

emissions (see Section 3.3).

The conventional fossil alternatives are gasoline from

crude oil (for ethanol), sugar from sugar beets (for xylite), and

acrylic binder (for lignin). The outputs of the biorefinery and

the conventional alternatives are assumed to be equivalent,

i.e. to provide the same benefit. Thus, 1 kg xylite replaces 1 kg

sugar (the sweetening effect of xylite is supposed to be the

same as for sugar) and 1 kg lignin replaces 1 kg acrylic binder.

For ethanol, use in a gasoline–ethanol E5 blend (5 vol.%

ethanol) for a passenger car is assumed. For simplification,

engine power and emissions are considered to be equal in

both the cases (E5 and gasoline). As equality of benefits is

taken as a basis, the life cycle steps downstream of the

production (e.g. transport to the end user, use, disposal) do not

have to be included in the analysis.

While setting up the life cycle model, uncertainties con-

cerning some framework conditions were observed, as the

LCF biorefinery is a concept that has not yet been imple-

mented. Since the final configuration of the biorefinery is not

yet clear, many assumptions have to be made. A first LCIA

revealed that especially the provision of hydrochloric acid and

heat influences the environmental impacts of the biorefinery

(see Section 4.1). It was therefore decided to calculate the LCA

for some variants of the biorefinery system. In addition to

a very basic biorefinery without acid and heat recoveries

(variant 1), three additional variants of the biorefinery system

are considered. Variant 2: optimised biorefinery system with

acid recovery; variant 3: optimised biorefinery system

with heat recovery; variant 4: optimised biorefinery system

with acid and heat recoveries.

In a fifth variant, the lignin is assumed to be used to

provide process heat for the biorefinery system and to replace

the process heat provided by natural gas instead of replacing

Electricity

Process heatnatural gas

HCl

Straw

Water Emissions

Biorefinery

Ethanol

Lignin

Xylite

Wastewatertreatment

Product/ser-vice provision

Output

Fig. 3 – Input and output streams of the biorefinery and system boundaries.

Table 1 – Inputs and data assumed for the biorefinerybase case (selection).

Life cycle step Input Unit

Production of straw and transport to biorefinery

Straw production 1000 kg

Transport distance 100 km

Biorefinery

Electricity input – milling 600 MJ

Hydrochloric acid input – pre-hydrolysis 2000 kg

Process heat input – pre-hydrolysis 3250 MJ

Electricity input – ion exchange pre-hydrolysis 135 MJ

Water input – ion exchange pre-hydrolysis 225 kg

Hydrochloric acid input – main hydrolysis 1500 kg

Process heat input – main hydrolysis 2438 MJ

Electricity input – ion exchange main hydrolysis 117 MJ

Water input – ion exchange main hydrolysis 195 kg

Hydrogen input – xylose to xylite conversion 4 kg

Electricity input – glucose to ethanol conversion 23 MJ

Reference: 1000 kg straw input into the biorefinery, data rounded.


acrylic binder. For this variant, the optimised biorefinery

variant (variant 4) was used as the starting point. Variant 6 is

similar to variant 5, but in this case, the lignin was used to

produce electricity instead of process heat.

The infrastructure of the biorefinery is not included in the

LCA, as no appropriate and reliable data are available.

According to Ref. [12], the environmental impacts of the

infrastructure of facilities for producing energy carriers (e.g.

power plants, refineries) amount to about 10% of the envi-

ronmental impacts of the subsequent use of the energy

carrier. In relation to the overall impacts, the omission of the

biorefinery’s infrastructure will thus only lead to errors in the

magnitude of some percent.

LCAs are often performed using a functional unit that

refers to the output/product of a process or a technology (e.g.

1 kg of ethanol in our case). For the biorefinery system under

investigation, it is not clear which of the three products has to

be considered as the main output (the output with the highest

value or quantity or the output the process will be optimised

for). Consequently, the LCI and the life cycle impacts are

calculated for a reference flow of 1000 kg straw entering the

biorefinery. For the LCA, Umberto� Version 5 and for the

conventional product chains, the Ecoinvent v1.01 databases

are applied [13,14]. The life cycles will be described in detail

below.

3.2. Detailed description of the life cycles

3.2.1. Biorefinery life cycle (variant 1)The agricultural production of straw (15% water content) is

calculated using the Ecoinvent standard modules [14].

Subsequently, the straw is transported to the biorefinery. A

distance of 100 km covered by a 32 t lorry is assumed (Table 1).

This distance is chosen, because it is supposed that 100 km

represents the upper limit of transport distance (for economic

reasons). With this ‘worst-case’ assumption, the influence of

the transport on the overall environmental impacts of the

biorefinery system can be determined.

In the biorefinery, the straw is milled in a first step. An

electricity input of 600 kJ kg�1 straw is assumed. After

grinding, the straw is digested with hydrochloric acid (HCl)

in a pre-hydrolysis step. In their laboratory analysis, Kamm

et al. used an HCl (32% w/w) to straw input ratio of 5:1 [15].

According to the US Department of Energy, the total acid

demand is 1.25 kg H2SO4 (70–77% w/w) per kg cellulose/

hemicellulose [16]. Arkenol gives an acid demand (H2SO4) of

0.05 kg per kg dry mass input [10], which is the non-

recovered part of the total acid input only. According to

Ref. [16], the acid loss is not more than 3%. Thus, the total

maximal acid demand (H2SO4, 70–77% w/w) can be


calculated to be about 1.67 kg per kg dry mass input or

1.96 kg per kg straw.

For our analysis, HCl is assumed to be used, because

hydrochloric acid has the advantages of an exothermic

hydrolysis and allows for acid recovery [15]. According to Refs.

[10,16], the input of 1.25–1.96 kg H2SO4 (70% w/w) corresponds

to an input of 0.67–1.06 kg HCl (calculated by average molec-

ular weights). For H2SO4 (77% w/w), the respective amount of

HCl is 0.74–1.16 kg. Similar to the transport distances, an HCl

(30% w/w) to straw ratio of 2:1 (w/w) for the base case was

estimated as a kind of ‘worst-case’ scenario.

The total steam input for the Arkenol process is about

6500 MJ per 1000 kg input of dry mass (with an estimated

energy content of 2 MJ per kg steam) [10]. From this value, the

heat input for each of the two hydrolysis steps is calculated to

be 3.25 MJ per kg input (straw and pre-hydrolysate residue,

respectively).

Then, the suspension is filtered. The proportions are

approx. 25% and 75% w/w of the suspension for the residue

and pre-hydrolysate (plus scrubbing water), respectively. The

pre-hydrolysate is separated into its acid and sugar compo-

nents by an ion exchange step [10,16]. Water (10% of pre-

hydrolysate [w/w]) is added. The electricity demand is

assumed to be 60 kJ per kg pre-hydrolysate. The output of the

separation step is assumed to be xylose and diluted hydro-

chloric acid only. In contrast to this, Kamm et al. found

arabinose, galactase, and other carbohydrates in the pre-

hydrolysate apart from xylose (60–80% w/w) [15]. For simpli-

fication, this is neglected in this paper. The output is specified

to be approx. 10.1% w/w xylose and 89.9% w/w diluted

hydrochloric acid. The diluted hydrochloric acid is passed

onto acid recovery and the wastewater treatment step. In

variant 1, HCl is not recovered.

Then, xylose is converted into xylite via catalytic hydro-

genation. For this process step, an H2 demand of 0.014 kg per

kg xylose is calculated [17].

The pre-hydrolysate residue is used as the input for the

main hydrolysis. The conditions (inputs of water, hydrochloric

acid, etc.) are assumed to be the same as for the pre-hydro-

lysis. The calculated yields are approx. 13.3% w/w and

86.7% w/w of the suspension for the residue (lignin) and the

main hydrolysate, respectively. The ion exchange step is the

same as for the pre-hydrolysate. The outputs are specified to

be glucose and diluted hydrochloric acid (21.0% w/w and

79.0% w/w, respectively). The diluted hydrochloric acid is

passed onto the acid recovery and wastewater treatment step.

Again, the acid used is not recovered in the base case. Then,

glucose is converted into ethanol via fermentation. An elec-

tricity input of 0.05 MJ per kg glucose is estimated. The ethanol

yield is calculated to be 50% w/w, the remainder being CO2 [18].

The outputs of the biorefinery amount to 225 kg ethanol,

253.5 kg xylite, and 300 kg lignin.

3.2.2. Conventional alternativesThe conventional alternative replaced by the ethanol

produced in the biorefinery is gasoline (on a volume basis).

The amount of replaced gasoline is calculated as follows: the

density of ethanol is 0.79 g cm�3. As the density of gasoline is

slightly lower (0.76 g cm�3), about 1.04 kg gasoline per kg

ethanol (about 234 kg in total) is needed. The gasoline

production is calculated using the Ecoinvent standard

modules [14].

The biorefinery produces xylite which is replaced by an

equivalent amount of sugar. As no standard module for sugar

production is provided with the Ecoinvent database, the

balance is set up as follows: (1) cultivation of the sugar beet

and transport to the sugar plant; (2) conversion into sugar

according to Ref. [19].

The biorefinery also produces lignin. Here, acrylic binder is

supposed to be the conventional alternative. The production

of the acrylic binder (equivalent amount) is calculated using

Ecoinvent standard modules.

3.2.3. VariantsFor variant 2, an acid recovery of 95% is assumed. The heat

recovery of variant 3 is defined to be 80%. For variant 4, acid

and heat recoveries are determined to be 95% and 80%,

respectively. For variants 2–4, the life cycles of the conven-

tional alternatives remain unchanged.

In variant 5, lignin is used to provide the process heat for

the biorefinery. A heating value of 17 MJ kg�1 and an efficiency

of 85% are assumed for the lignin boiler [19]. Thus, 4335 MJ

process heat can be provided by lignin. As only 1138 MJ heat is

needed in the biorefinery, there has to be some additional

credit included in the conventional alternatives. We used

conventional process heat that is provided from natural gas

according to Ref. [14] as an alternative. In this variant, the

conventional alternatives thus are process heat (from natural

gas), gasoline (for ethanol), and sugar (for xylite).

Variant 6 is identical to variant 5 but instead of producing

process heat from lignin, electricity is generated (85% effi-

ciency); 4335 MJ electricity can be produced, but only 875 MJ is

needed in the biorefinery. Similar to variant 5, an additional

credit was included (electricity from grid according to

Ref. [14]). The conventional alternatives are electricity (from

grid), gasoline (for ethanol), and sugar (for xylite).

Table 2 shows the differences between the six variants of

the biorefinery system.

3.3. Life Cycle Inventory and Life Cycle ImpactAssessment

After the goal and scope definition and the setting up of the

life cycle steps and life cycle model according to the ISO

standards, the next steps are the Life Cycle Inventory (LCI) and

Life Cycle Impact Assessment (LCIA) [11].

According to the ISO standards, all environmental param-

eters, such as the extraction of minerals and fossil fuels,

emissions into air (e.g. CO2, NOx, SO2, etc.), soils (e.g. heavy

metals), or water (e.g. ammonium, nitrate), are analysed in

a first balancing step for each single process. These are then

added up over the whole life cycle to obtain the Life Cycle

Inventory (LCI).

In our analysis, the Life Cycle Inventories are calculated

separately for the biorefinery and the conventional alterna-

tives. Approximately 850 single outputs and 160 single inputs

are considered. For details of the material flows covered, see

Ref. [14].

In the LCIA, these results are aggregated to the environ-

mental impact categories. For the LCIA, several approaches

Table 2 – Inputs and outputs of the biorefinery variants.

Input Output

Hydrochloricacid (kg)

Process heat(MJ)

Electricity(MJ)

Ethanol(kg)

Lignin(kg)

Xylite(kg)

Process heat(MJ)

Electricity(MJ)

Variant 1 3500 5688 875 225 300 254 0 0

Variant 2 175 5688 875 225 300 254 0 0

Variant 3 3500 1138 875 225 300 254 0 0

Variant 4 175 1138 875 225 300 254 0 0

Variant 5 175 0 875 225 0 254 3200 0

Variant 6 175 1138 0 225 0 254 0 3460

Reference: 1000 kg straw input into the biorefinery, data rounded.


have been developed (for example, see Refs. [20,21]). As

defined in the ISO 14042 standard, these methods classify the

LCI results into environmental impact categories. In our

analysis, the LCIA is performed with the Eco-Indicator99

methodology. The LCI results are assigned to compartments

(e.g. air, soil, water), in which they create environmental

problems. Subsequently, an assignment to environmental

impact categories (e.g. ecotoxicity, climate change, etc.) is

made. The results are translated into damages in three end-

point categories: resources, ecosystem quality, and human

health (e.g. skin cancer due to stratospheric ozone depletion).

Then, the results are normalised to the whole damage in

Europe, and the end-point categories are weighted by a single

score (the Eco-Indicator). For weighting, the hierarchist

perspective is used, which weighs the categories of

ecosystem quality, human health, and resources at a ratio of

4:3:3. For a detailed description of the methodology, see Refs.

[20,22]. The utilisation of a single indicator for the LCIA is not

recommended by the ISO standards because a subjective

weighting step has to be performed. We carefully checked

our results using different Eco-Indicator weighting perspec-

tives and other LCIA methodologies and found similar

results. We are thus confident that our conclusions are quite

robust.

4. Results

4.1. Results for the biorefinery

The LCIAs of the biorefinery and the conventional alternatives

were performed separately. As an example, the results for the

biorefinery variant 1 are shown in Fig. 4 according to the

impact categories and life cycle steps.

The environmental impacts may be assigned to three

impact categories mainly: fossil fuel use, respiratory effects,

and carcinogenics (37.0%, 25.4%, and 17.3% of all environ-

mental impacts, respectively). The respective fractions of the

other impact categories do not exceed 10%.

Three processes dominate the environmental impacts: the

provision of straw, the provision of HCl, and the provision of

process heat. For all impact categories except for carcino-

genics and land occupation, the provision of hydrochloric acid

accounts for more than 65% of the environmental impacts.

Another important process is the provision of straw

(carcinogenics 78.4%, land occupation 88.2%). The provision of

process heat accounts for 19.5% and 25.3% of the impacts in

the categories of climate change and fossil fuel use, respec-

tively. The contributions of other processes are of minor

importance only.

The environmental impacts of the provision of straw are

due to (a) straw production itself and (b) the transports to the

biorefinery. For all impact categories, the transports

contribute 13–34% to the environmental impacts of straw

provision, except for climate change, carcinogenics, and land

occupation where the respective fraction amounts to 1% at the

maximum only. As straw provision plays a major role in

carcinogenics and land occupation only, it may be stated that

even though transport distances are assumed to be high, the

transport process does not play a significant role for the

environmental impacts.

4.2. Results for the conventional alternatives(biorefinery variants 1–4)

The results of the LCIA of the conventional alternatives for the

three different products and the impact categories are shown

in Fig. 5.

Three impact categories dominate the total environmental

impacts: fossil fuel use accounts for 66.2%, land occupation for

16.7%, and respiratory effects for 11.5% of the total impacts.

All other impact categories together account for approx. 5.6%

of the impacts only.

The provision of the acrylic binder accounts for more than

60% of the impacts in four of the 10 impact categories (ionising

radiation, climate change, mineral extraction, and ecotoxicity)

and shows greatest impacts as regards carcinogenics and

respiratory effects. The provision of gasoline dominates two

impact categories (ozone layer depletion, fossil fuels). The

provision of sugar is of minor importance except for land

occupation (95.6%) and acidification and eutrophication

(50.9%). In total, the three products each contribute approxi-

mately a third to the environmental impact.

4.3. Life cycle comparison for the biorefinery variant 4

The comparison of the LCIA of the biorefinery variant 4

(optimised variant) with the conventional alternatives is

illustrated in Fig. 6. The biorefinery shows better results in

most of the impact categories. Nevertheless, the

-25

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Provision of strawProvision of process heatProvision of electricityProvision of hydrochloric acidProvision of water & wastewater treatmentConversion of glucose to ethanolConversion of xylose to xylite

Eco

In

dicato

r-99 P

oin

ts

Environmental impact category

Resources Ecosystem qualityHuman health

Fig. 4 – Life Cycle Impact Assessment of the biorefinery variant 1 according to life cycle steps and impact categories,

calculated for an input of 1000 kg straw.


environmental impacts in three impact categories (ionising

radiation, carcinogenics, and ozone layer depletion) are

greater than those of the conventional alternatives. The main

differences between the biorefinery and the conventional

alternatives exist for carcinogenics and fossil fuels. For

carcinogenics, the biorefinery impacts are mainly due to the

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50

75

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Provision of sugarProvision of acrylic binderProvision of gasoline

Environmenta

Human health

Fig. 5 – Life Cycle Impact Assessment of the conventional altern

impact categories, calculated for an input of 1000 kg straw into

provision of straw (see Fig. 4) while the fossil fuel use of the

alternatives is dominated by the provision of gasoline and

acrylic binder (see Fig. 5).

The total environmental impact of the optimised bio-

refinery (variant 1) is approx. 59% compared to the conven-

tional alternatives.

Min

eral

extra

ctio

n

Foss

il fu

els

Land

occ

upat

ion

Acid

ifica

tion

&eu

troph

icat

ion

Ecot

oxic

ity

l impact category

Resources Ecosystem quality

atives (for variants 1–4) according to the three products and

the biorefinery.

EcoIndicator-99 Points

-100 -50 0 50 100 150 200 250 300

Balance

Conventionalalternatives

Biorefinery

Ionising radiationClimate changeCarcinogenicsRespiratory effectsOzone layer depletionMineral extractionFossil fuelsLand occupationAcidification & eutrophicationEcotoxicity

Fig. 6 – Life cycle comparison: biorefinery (variant 4), conventional alternatives, and balance, calculated for an input of

1000 kg straw into the biorefinery.


4.4. Results for the variants 2–4

Three optimised biorefinery variants have been analysed:

variant 2 with acid recovery; variant 3 with heat recovery;

variant 4 with acid and heat recoveries. The results of the Life

Cycle Assessment show that the recovery of acid and heat

may reduce the environmental impacts of the biorefinery

(to 37.9%, 91.2%, and 29.2% of variant 1, respectively). Variant 2

(acid recovery) and the optimum variant 4 show substantial

reductions which lead to smaller total environmental impacts

(about 23.3% and 41.0%, respectively) compared to the

conventional alternatives (Fig. 7). All variants show advan-

tages for the impact category of fossil fuel use. Variants 2 and

4 also yield better results for climate change, respiratory

effects, mineral extraction, land occupation, acidification and

eutrophication, and ecotoxicity when compared to the

conventional alternatives.

EcoIndicat

-100 -50 0 50

Variant 4

Variant 3

Variant 2

Variant 1

Fig. 7 – Life Cycle Impact comparison: net balance of biorefinery (

input of 1000 kg straw into the biorefinery. Negative values ind

In addition, sensitivity analyses were performed in order to

determine the break-even points, i.e. the minimum percent-

ages of process heat and acid to be recovered in order to result

in equal overall environmental impacts when comparing the

biorefinery system with the conventional alternatives. Con-

cerning acid recovery only, 77% of acid has to be recovered for

the environmental impacts of the biorefinery equaling the

environmental impacts of the conventional alternatives. As

regards acid recovery and heat recovery (80%), approx. 64% of

acid has to be recovered. When process heat only is recovered,

the overall environmental impacts of the biorefinery are still

higher than those of the alternatives even when the recovery

rate is 100% (compare variant 3 in Fig. 7).

In the case of variant 5, lignin is used to provide process

heat instead of being used as a binder. For variant 6, the

lignin is used to provide electricity (see Section 3.2.3).

Process heat and electricity are used to provide the energy

or-99 Points

100 150 200 250


variants 1–4) vs. conventional alternatives, calculated for an

icate advantages of the biorefinery.

EcoIndicator-99 Points

-100 -50 0 50 100 150 200 250

Balance


Biorefinery

Balance


Biorefinery

Varian

t 6

Varian

t 5


Fig. 8 – Life Cycle Impact comparison: biorefinery variant 5 and variant 6 vs. conventional alternatives, calculated for an

input of 1000 kg straw into the biorefinery. Negative values indicate advantages of the biorefinery.


to the biorefinery. The surplus is credited by conventional

energy carriers (see Section 3.2.3). Fig. 8 displays the results

of the LCAs of variant 5 and variant 6 compared to the base

case.

The results show similar patterns for both variants. The

environmental impacts of the biorefinery variants are smaller

compared to conventional alternatives (cf. Fig. 6). Compared

to the starting point (variant 4), the environmental impacts of

the biorefinery system are slightly reduced (about 8% and 6%,

respectively). At the same time, the impacts of the conven-

tional alternatives are reduced by approx. 26% and 24%,

respectively. This is due to the fact that no acrylic binder has

to be provided in this variant. In total, this leads to a decrease

in the environmental advantages of the biorefinery. Under

environmental aspects, the lignin in the biorefinery should

thus better be used to replace the binder instead of producing

heat.

5. Conclusions and outlook

A Life Cycle Assessment of a future lignocellulose feedstock

biorefinery system was performed according to the ISO 14040

series of standards. The biorefinery is assumed to use straw

from agriculture as input and to produce xylite, lignin, and

ethanol. The conventional alternatives are gasoline from

crude oil, sugar from sugar beets, and acrylic binder.

The LCF biorefinery is a concept that has not yet been

implemented in practice. As the final configuration of the

biorefinery is not yet clear, many assumptions had to be made

while setting up the life cycle model. To overcome these

deficits, different variants of the biorefinery system have been

assessed.

From the results of the LCAs of the biorefinery system

variants, the following conclusions can be drawn: the greatest

environmental impacts of the biorefinery system occur in the

four impact categories: fossil fuel use, respiratory effects, land

use, and carcinogenics. The provision of hydrochloric acid

and, to a smaller extent, also the provision of process heat and

straw lead to the greatest environmental impacts. Compared

to the fossil alternatives, all biorefinery system variants cause

higher environmental impacts in the impact categories

carcinogenics and ozone layer depletion.

Three variants of an optimised biorefinery system (acid

recovery, heat recovery, acid and heat recoveries) have been

analysed. Acid recovery in particular will be indispensable in

future biorefinery systems for economic reasons. Further-

more, process heat recovery units are widely used in practice.

It is therefore assumed that the optimised variant 4 (95% acid

and 80% heat recovered) will be implemented in the future

with a higher probability than the other variants. This opti-

mised variant yields better results than the conventional

alternatives. The total environmental impacts are approx. 41%

smaller than for the fossil or conventional chains. In addition

to these optimised variants of the biorefinery system, two

variants with a different use of the biorefinery’s output were

analysed (further integrated biorefinery systems). In these

variants, the lignin produced is used to provide process heat

(variant 5) and electricity (variant 6). Both alternatives lead to

environmental disadvantages. This is due to the fact that for

the conventional alternatives, the provision of process heat/

electricity leads to smaller environmental impacts than the

provision of the acrylic binder.

For all variants of the biorefinery system analysed, the

environmental performance in some impact categories is

worse compared to the fossil counterparts, while advantages

can be seen in other categories. Thus, the results do not

support a clear-cut decision in favour of or against

biorefineries.

Nevertheless, the overall results indicate that future

lignocellulose biorefinery systems will be competitive with

the existing fossil alternatives under the environmental point

of view, especially when some process technologies are

improved.


Acknowledgements

The authors are very grateful to Jens Buchgeister for fruitful

discussions and helpful comments. The authors would also

like to thank the reviewer for the encouraging and thought-

fully suggestions.

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