ORIGINAL PAPER

Carbon and nitrogen trade-offs in biomass energy production

Lidija Cucek • Jirı Jaromır Klemes •

Zdravko Kravanja

Received: 31 August 2011 / Accepted: 17 January 2012 / Published online: 28 February 2012

� Springer-Verlag 2012

Abstract This contribution provides an overview of

carbon (CFs) and nitrogen footprints (NFs) concerning

their measures and impacts on the ecosystem and human

health. The adversarial relationship between them is illus-

trated by the three biomass energy production applications,

which substitute fossil energy production applications:

(i) domestic wood combustion where different fossil

energy sources (natural gas, coal, and fuel oil) are sup-

plemented, (ii) bioethanol production from corn grain via

the dry-grind process, where petrol is supplemented, and

(iii) rape methyl ester production from rape seed oil via

catalytic trans-esterification, where diesel is supplemented.

The life cycle assessment is applied to assess the CFs and

NFs resulting from different energy production applica-

tions from ‘cradle-to-grave’ span. The results highlighted

that all biomass-derived energy generations have lower

CFs and higher NFs whilst, on the other hand, fossil

energies have higher CFs and lower NFs.

Keywords Carbon footprint � Nitrogen footprint � LCA �Biomass combustion � Bioethanol � Rape methyl ester

Abbreviations

C Carbon

CF Carbon footprint

DDGS Distiller’s dried grains with soluble

FP Footprint

GHG Greenhouse gas

GWP Global warming potential

HCFC Hydrochlorofluorocarbon

HFC Hydrofluorocarbon

HHV Higher heating value

LCA Life cycle assessment

Nr Reactive nitrogen

N Nitrogen

NF Nitrogen footprint

RME Rape methyl ester

US United States of America

Introduction

Insecure energy supply, high energy prices, emissions, and

ever-increasing energy demand are topics of increasing

importance in today’s society (Brandi et al. 2011; Toth

et al. 2011). It is anticipated that global energy consump-

tion will continue to rise by using predominantly fossil

fuels. In 2010, the total world energy consumption was

502.5 EJ (12 Gtoe). World primary energy consumption

grew by 5.6% in 2010. Oil remained the world’s leading

fuel. It represents 33.6% of global energy consumption,

coal accounted for 29.6%, natural gas for 23.8%, nuclear

energy for 5.2% and renewables just for 7.8% of global

energy consumption (BP 2011).

The mankind is rapidly exhausting fossil fuels, as a

consequence of which, in the future, people are going to

depend on non-fossil energy sources. The timing of a

global peak regarding oil production is less certain,

although there is a growing view that maximum production

will occur within the next decade (Curtis 2009). The global

L. Cucek (&) � J. J. Klemes

Centre for Process Integration and Intensification (CPI2),

Research Institute of Chemical and Process Engineering, Faculty

of Information Technology, University of Pannonia, Egyetem u.

10, 8200 Veszprem, Hungary

e-mail: cucek@cpi.uni-pannon.hu

Z. Kravanja

Faculty of Chemistry and Chemical Engineering, University

of Maribor, Smetanova ul 17, 2000 Maribor, Slovenia

123

Clean Techn Environ Policy (2012) 14:389–397

DOI 10.1007/s10098-012-0468-3

peak for coal extraction from the existing coalfields has

been predicted by Patzek and Croft (2010), to occur around

year 2011. Natural gas is performing slightly better, with

the world’s natural gas production peak being predicted

between 2025 and 2066 (Mohr and Evans 2011). Energy

crises, unusual climatic conditions, environmental deteri-

oration, etc., are urgent challenges being handled since the

turn of the twenty-first century (ZTE 2011). Green solu-

tions and environmental protection are becoming the

common issues of this century, and energy saving is

becoming the unavoidable responsibility of industries and

enterprises. However, developing clean and renewable

energy resources ranks as one of the greatest challenges

facing mankind in the medium to long term (Mata et al.

2011). No single energy technology or combination of

technologies exists that can address all challenges descri-

bed above in sustainable manner (Ma et al. 2011).

Also, the human-induced climate change and global

warming are recognised by many as the greatest environ-

mental threats for the twenty-first century (Abbott 2008;

Carter 2007). The main greenhouse gases (GHGs), the

concentrations of which are rising, are carbon dioxide

(CO2), methane (CH4), nitrous oxide (N2O), hydrochloro-

fluorocarbons (HCFCs), hydrofluorocarbons (HFCs) and

ozone (O3) in the lower atmosphere (WMO 2011). CO2 is

the single most important human-emitted GHG in the

atmosphere, contributing approximately 63.5% to the

overall global radiative forcing not considering water

vapour which is continuously within the Earth’s climatic

circulation (WMO 2009). Global dependence on fossil

fuels has led to the release of over 1,100 Gt of CO2 into the

atmosphere since the mid-nineteenth century. Energy-

related GHG emissions, mainly from fossil fuel combus-

tion for heat supply, electricity generation and transport

accounts for around 70% of total emissions, including CO2,

CH4 and some traces of nitrous oxide (N2O) (Sims et al.

2007). Other causes of global warming and climate change

are the clearing of forests, and agricultural activities.

The CO2 global average concentration in the Earth’s

atmosphere was about 388.54 ppm in 2010 (ESRL 2011).

Since the beginning of the industrial revolution in 1750, the

atmospheric concentration of CO2 has increased by

38.76%. The global average concentrations of CH4 and

N2O had reached 1,797 ppb and 321.8 ppb in 2008. They

were higher than those of pre-industrial times by 157 and

19%, respectively (WMO 2009).

Furthermore, the nitrogen (N) deposition represents a

serious threat to biodiversity as claimed by many

researchers, e.g. Hicks et al. (2011), and to the global

environment (Hartmann et al. 2007). N plays a beneficial

and key role in helping to feed the growing population, but

much anthropogenic N is lost into the air, water, and soil

and has a destructive effect on the ecosystem and human

health (Galloway et al. 2008). N emissions into the atmo-

sphere increased substantially over the twentieth century,

mainly in the form of ammonia (NH3) from agriculture and

nitrogen oxides (NOx) from industry (Hicks et al. 2011).

The amount of human-caused reactive or biologically

available reactive nitrogen (Nr) (all N species except N2)

within the global environment has increased by a factor of

12.5 (187 Mt N/y in 2005) since the nineteenth century (15

Mt N/y in 1860) and by a factor of 3.7 since the 1960s (50

Mt N/y), in association with the increased use of fertilizers

(Galloway et al. 2008; UCS 2009). Agriculture is respon-

sible for about 80% of the Nr produced worldwide (UCS

2009). More than half of the synthetic N fertilizer ever used

on the planet has been used since 1985 (Millennium Eco-

system Assessment 2005). Nr is also created by the burning

of fossil fuel and biomass, by manure run-off and by the

planting of legumes.

Several research studies have analysed the carbon

footprint (CF), its impact, minimisation, mitigation, and

even sequestration (Klemes et al. 2006). In ScienceDirect

1,647 articles can be found, most of them in the last

3–4 years (96%). On the other hand, only two studies can

be found on nitrogen footprint (NF), one from 2010 and

one from 2011. In Scopus 1,371 articles on CF can be

found (94% from 2008) and four for NF, two from 2010

and two from 2011. Only two studies have dealt with both,

CF and NF. Cucek et al. (2011) reviewed various footprints

(FPs) with special focus on adversarial relationship

between CF and NF, using a biomass combustion case

study. Xue and Landis (2010) studied nutrient flows during

food production, processing, packaging, and distribution

stages for different food types, then compared the CFs and

NFs for these food crops, and provided some solutions for

reducing N output.

However, some of the research studies performed have

not yet been covered by ScienceDirect and/or Scopus.

Bakshi (2011) and Bakshi and Singh (2011) reviewed the

carbon (C) and N cycles and FPs in industrial products and

investigated CF and NF for biofuels and the US economic

sector. They stressed that corn ethanol, switchgrass and

corn stover have high NF and low CF whilst, on the other

hand, petrol and diesel have low NF and high CF. Singh

and Bakshi (2011) proposed improved C and N metrics,

and compared the old and new CF and NF measures. These

authors studied CF/NF relationships during a bio-fuels case

study. Williams et al. (2006) quantified the resource use

and environmental burdens arising from the productions of

10 commodities. They also quantified a CF/NF for agri-

culture. In agriculture production, NF dominates. They

concluded that CF inadequately describes agriculture, since

it has CF/NF.

Biomass and bioenergy are widely considered as con-

tributors to sustainability (Thornkey et al. 2009; Ladanai

390 L. Cucek et al.

123

and Vinterback 2009). However some questions about their

sustainability have risen over recent years—from among

several works let us select at least a few (e.g. Johnson

2007; Zamboni et al. 2011; Sheehan 2009; Cherubini and

Strømman 2011). In ScienceDirect 37,047 articles can be

found containing the words ‘sustainab*’ and ‘biomass’,

23,520 articles of them also deal with C, 18,101 with N,

416 with CF, but no articles with NF. Often only one FP

(e.g. carbon) is considered (e.g. Manninen 2010; Yuttitham

et al. 2011; Lam et al. 2010a, b), which can lead to

incomplete decisions for sustainable deployment policies.

Several research studies have indicated that lower C

emissions can be achieved by utilizing biomass compared

with energy generated from fossil sources, but higher

amounts of N are emitted into the air and water (e.g.

Cherubini and Strømman 2011; Bauer 2008; Bakshi and

Singh 2011).

This paper starts with an overview of NF and CF defi-

nitions and measures, and is followed by an assessment of

those problems, and even threats, from growing CFs and

NFs. The adversarial relationships between them are pre-

sented on three biomass energy production applications

and suitable substituted fossil energy production applica-

tions: (i) wood logs when burned for heating purposes,

where natural gas, oil or coal are supplemented; (ii) bio-

ethanol, and (iii) biodiesel produced for fuels in passenger

cars, where petrol and diesel are supplemented. All three

case studies demonstrate lower CFs and higher NFs for

biomass energy, and, on the other hand, fossil energy

showed higher CFs and lower NFs.

Carbon and nitrogen footprints

Carbon footprint

CF has become the most covered environmental protection

indicator over the recent years by politicians, media and

consequently researchers (Wiedmann and Minx 2008; Lam

et al. 2010a). CF causes an imbalance within the C cycle. It

usually stands for the amount of CO2 and other GHGs

emitted over the full life cycle of a process or product (UK

POST 2006). The CF is quantified using indicators such as

the global warming potential—GWP (EC 2007), which

stands for the quantities of GHGs that contribute to global

warming and climate change, by considering a specific

time horizon, usually 100 years (IPPC 2009). The land-

based definition of CF stands for the land area required for

the sequestration of atmospheric fossils’ CO2 emissions

through afforestation (De Benedetto and Klemes 2009).

Wiedmann and Minx (2008) proposed that CF is a measure

of exclusive direct and indirect CO2 emissions over a life

cycle.

The following questions should be clarified (Wiedmann

and Minx 2008) because of the various and different def-

initions of CF:

(i) Should only C present in gas emissions be consid-

ered in CF?

(ii) Should the CF consider CO2 only, the most abundant

and potent GHG?

(iii) Should the CF be restricted to C-based gases?

(iv) Can the CF include substances molecules of which

do not contain C (e.g. NOx)?

(v) How the CF should be measured whether, in mass

units of CO2 equivalent, in mass units of CO2, in

mass units of C, per unit of mass, energy, or exergy,

per unit of area, or possibly per unit of time?

The three C gases—carbon monoxide (CO), CH4 and

CO2—are important atmospheric constituents affecting air

quality and the climate (Buchwitz et al. 2006).

CO2 is the most important anthropogenic GHG (IPPC

2007). Increases in CO2 are the single largest climate factor

in forcing contribution to global warming (The National

Academies 2008). CH4 is a GHG with a GWP of 25

(Forster et al. 2007). CH4 emissions have risen due to

agriculture and the usage of fossil fuels. CO is formed

when C in the fuels is not burned completely, and it is

highly toxic. It is a very important air pollutant affecting

local air quality. It can cause harmful health effects by

reducing oxygen delivery to the body’s organs and tissues

(US EPA 2011).

The term global warming considers the continuing rise

in the average temperature of the Earth’s atmosphere and

oceans. Many researchers assume that it is caused by the

increased concentrations of GHGs in the atmosphere

resulting, most likely, from human activities, such as

deforestation, other land use changes and the burning of

fossil fuels. The burning of fossil fuels releases additional

(not released by natural processes) CO2 into the atmo-

sphere. About half of this excess CO2 is absorbed by the

land and oceans, but the remainder accumulates within the

atmosphere and enhances the natural greenhouse effect

(Dilling et al. 2003).

It has been declared that the global average near-surface

atmospheric temperature had already risen by 0.78�C

during the twentieth century, with much of this warming

(0.61�C) occurring over the last 30 years (The National

Academies 2008). Temperatures are predicted to rise by at

least an additional 1.1–6.4�C over the next 100 years. This

warming would cause significant changes in sea level (an

increase of 0.18–0.59 m), ecosystems, the melting of gla-

ciers, the extent of ice and snow, precipitation, water

availability and the probable expansions of subtropical

deserts. Other consequences would include higher maxi-

mum temperatures, fewer colder days, changes in

Carbon and nitrogen trade-offs 391

123

agricultural yields, and an increase in infectious diseases.

Global warming and climate change may also be associated

with deterioration in humans’ health, more intense hurri-

canes, tropical cyclone activity, flooding, drought, wild-

fires, the insect populations, ocean acidification, etc. (The

National Academies 2008; IPPC 2007).

There are various ways of reducing CF (The National

Academies 2008; Levy 2010), such as through

(i) technological developments,

(ii) carbon capture and storage (CSS),

(iii) carbon offsetting,

(iv) reduced energy consumption,

(v) improved energy efficiency, etc.

Nitrogen footprint

N is essential for life. It is the most common element in the

Earth’s atmosphere and a primary component of crucial

biological molecules, including proteins and nucleic acids

such as DNA and RNA. Smil (2001) estimated that in the

mid-1990s, 40% of the global population were dependent

on crops fertilized with Nr. Since 1970 the world’s popu-

lation has increased by 78% and Nr production by 120%

(Galloway et al. 2008). Crops need large amounts of N to

grow, but only Nr can be readily used by most organisms,

including crops.

NF causes an imbalance within the N cycle. The total

NF is calculated as the amount of Nr released into the

environment as a result of human activities (N-Print 2011).

The primary N emission sources are transportation, agri-

culture, power plants and industry.

As a consequence of the growing demand for N and the

inefficiencies in N when used in agriculture, a large share

of the N applied in agriculture is lost to the environment

(UNESCO and SCOPE 2007; Galloway et al. 2003) as

N2O, nitric oxide (NO), NH3 or N2 into the atmosphere, or

to aquatic ecosystems as NO3- (Lal et al. 2011; Galloway

et al. 2003). NOx are produced during the combustion of

biomass or fossil fuels (Galloway et al. 2003).

N2O concentrations have risen primarily because of

agricultural activities and changes in land usage. It is the

largest ozone-depleting substance emitted because of

human activities (NOAA 2009); in the atmosphere, it is a

GHG with a GWP of 298 (Forster et al. 2007) and affects

humans’ health.

NOx emissions have increased by nearly 4 Mt/y. They

play an important role in those atmospheric reactions that

create harmful particulate matter, ground-level ozone

(smog), acid rain, and haze air pollution. They also con-

tribute to eutrophication, degradation in water quality,

causing to fish harm and affecting humans’ health (EDF

2002).

NH3 emissions are increasing rapidly in many parts of

the world as the result of human activities. They contribute

to high concentrations of fine particulate matter and affect

humans’ health, atmospheric visibility, and global radiative

balance. They have direct toxic effects on vegetation, and

atmospheric N deposition, leading to the eutrophication

and acidification of sensitive ecosystems (Sutton et al.

2009).

NO3- is one of the main contaminants causing serious

concern. It seeps into drinking water, where it can become

a health risk. It has been discovered that NO3- causes blue-

baby syndrome or methemoglobinemia and increases the

acidity of water (US EPA 2002). Excess NO3- concen-

trations in aquatic systems lead to eutrophication and algae

blooms (Bhatnagar and Sillanpaa 2011).

Excess N within ecosystems causes eutrophication, an

enhanced greenhouse effect, biodiversity loss, acidificat-

ion, etc. A unique feature is that Nr molecules released into

the environment can cause multiple effects within ecosys-

tems, and on humans’ health. An Nr atom that starts out as

part of NH3 in the Haber–Bosch process is used to produce

fertilizer. Nr is then partly incorporated within the crops

and then partly released as NH3, NO, N2O, N2 or NO3-.

The Nr species can rapidly be interconverted from one Nr

form to another (Galloway et al. 2003).

There are certain methods of reducing NF, through

(N-Print 2011; UCS 2009)

(i) reducing energy consumption,

(ii) changing diets to more sustainably prepared food

and fish,

(iii) consuming less meat,

(iv) reducing food-waste,

(v) crop genetic engineering,

(vi) traditional or enhanced breeding techniques,

(vii) precision farming, and

(viii) cover crops.

Case studies on biomass energy applications

Biomass is a renewable resource that is increasingly being

used to provide low carbon energy. It has potential to be

raw material for production of heat, electricity and trans-

port fuel (Thornkey et al. 2009). However, a review of

scientific studies reporting on biomass potentials showed

that maximum available potential of biomass for energy

purposes in next decades will be capable of around

10–50% fossil fuel substitution (Wenzel 2009). Three case

studies were performed on biomass energy when compared

to fossil energy. Wood is burned to produce heat; corn is

used for bioethanol production and rape seed oil for rape

methyl ester (RME) production. Life cycle assessment

392 L. Cucek et al.

123

(LCA) is used to assess those CFs and NFs associated with

all the stages of energy life cycles from ‘cradle-to-grave’.

The LCA covers the following C and N emissions: CO2,

CO, CH4, NOx, N2O, NO3- and NH3.

Domestic biomass combustion

Fossil-fuelled heat and electricity production are among the

major anthropogenic sources of CO2 emissions today, and

are responsible for the on-going climatic changes to a great

extent (Bauer 2008). Biomass as a fuel has advantages over

CF and GHG emissions, as the CO2 emitted during bio-

mass combustion is absorbed during the biomass growth.

However, heat from burning biomass (wood) produces the

highest NOx emissions.

The CF in this study is composed only of direct and

indirect CO2 emissions, as proposed by Wiedmann and

Minx (2008). NF accounts for NOx which represent the

majority of N emissions (NH3, NOx, N2O). CFs and NFs

from the combustion of wood, natural gas, fuel oil and coal

are presented in Table 1. Both the CFs and NFs were

mostly obtained using the LCA software package GaBi�

(PE, LBP 2011) and the Ecoinvent database (Frischknecht

et al. 2007).

CF and NF from biomass- and fossil-fuelled appliances

differ depending on the emission control at the power

plants, the origins of the fossil fuels, the transportation

mode and the distance of the wood to the user (Bauer

2008). NOx emissions vary significantly among combustion

facilities depending on their design and control. CF from

domestic wood combustion is almost carbon neutral, and

coal has the highest CO2 emissions. Concerning NOx

emissions, natural gas shows the best performance of all

fuel alternatives. Oil and coal burnings cause relatively low

direct NOx emissions. Wood fuel has higher NOx emissions

due to their high N content.

First generation biofuel’s production

The transportation sector relies almost exclusively on

petroleum-based fuels, and about 30% of the world’s fossil

fuel consumption is related to transport. The reduction of

fossil energy reserves and the associated environmental

impact are the two main reasons that lead to considering

the use of alternative fuels within the transportation sector

(Jungbluth et al. 2007). The most used feedstocks for the

current first generation bio-fuel’s production are corn,

wheat, and sugarcane for bioethanol, and soybean, rape

seed and sunflower for biodiesel production. The major

problem is that these feedstocks are also used for food and

feed production. This has been pointed out by Sikdar

(2007) and later by others, e.g. Ajanovic (2011), Kravanja

et al. (2011). The production of fuel from food crops

threatens the safety of food supply and increases the prices

of food, while it only insignificantly increases the share of

biofuels in the world’s total fuel consumption (Winterton

2011). An increase of cultivated fields may lead to biodi-

versity loss, due to the conversion of land not currently in

crop production, such as forest and grassland (Mata et al.

2011). There are also other issues, such as the lower energy

content of biomass per unit of volume compared with oil,

limitations of water availability, and the need to migrate

from the cities to countryside (Winterton 2011).

CFs and NFs from the first generation biofuel chains are

caused throughout all stages of the bio-fuels supply chains.

A petrol- and diesel-fuelled vehicle operation is also

included in the system’s boundary to estimate the differ-

ences in environmental impacts between bioethanol-fuelled

and petrol-fuelled vehicle operations and between RME-

fuelled and diesel-fuelled vehicle operations.

The amounts of biofuels and petroleum-based fuels

substituted by biofuels were evaluated according to the

ratio of their higher heating values (HHVs). The functional

unit of the product systems is 1 GJ of the produced energy.

This study was performed mostly using the LCA soft-

ware package GaBi� (PE, LBP 2011) and Ecoinvent

database (Frischknecht et al. 2007; Jungbluth et al. 2007;

Nemecek and Kagi 2007; Spielmann et al. 2007).

Bioethanol production from corn grain

The most widely used biofuel for transportation worldwide

is bioethanol (IEA 2007). Global bioethanol production

reached 87.1 GL in 2010 (RFA 2011). Approximately 60%

of bioethanol production came from the US. Most ethanol

fuels in the US are made from corn in dry-mill plants

(Wang 2005; Aden 2007).

This case study of bioethanol production from corn

grain was applied to the US conditions. The corn grain is

mainly composed of starch which is milled, slurred with

water, and then hydrolysed into sugars by liquefaction and

saccharification. The sugars are fermented into ethanol

using yeast. The solids are separated from the liquid phase

(mainly ethanol and water), dried, and the co-product dis-

tiller’s dried grains with soluble (DDGS) is obtained. This

can be used as livestock feed. Ethanol recovery is done by

Table 1 Emissions of CO2 and NOx into the air for different types of

fuel (kg/GJ)

CO2 NOx

Wood logs 1.4–4.2 0.21–0.24

Natural gas 61–78 0.028–0.069

Fuel oil 83–97 0.069–0.097

Coal 111–139 0.125–0.167

Carbon and nitrogen trade-offs 393

123

distillation column systems, and through the adsorption of

water on corn grits and/or molecular sieves (Karuppiah

et al. 2008).

The system’s boundary includes corn cultivation,

transportation of corn grain and chemicals, the dry-grind

process, the distribution of bioethanol, plus the bioethanol-

fuelled vehicle operation.

The purity of ethanol fuel (E100), as used in passenger

cars, the so-called flex-vehicles (Brandi et al. 2011), was

assumed to be a fair comparison with petrol. Since no data

were available for E100 passenger car emissions, the

exhaust emissions from the ethanol-fuelled cars were

assumed to be the same as those emissions from the bio-

mass-derived methanol-fuelled cars.

Rape methyl ester production from rape seed oil

Global biodiesel production in 2009 amounted to 17.9 GL,

whilst within the European Union (EU), the biodiesel

production reached 10.2 GL (57%) (Biofuels Platform

2011). Most biodiesels in Europe are made from rape seed

oil (Gupta and Demirbas 2010; Ajanovic 2011).

This case study for RME production from rape seed oil

was applied to European conditions. The rape seed oil is

extracted from rape seed using a solvent (usually hexane).

Solid by-product rape seed meal is mostly used as animal

feed. Most of the biodiesel produced today is made via the

base-catalysed trans-esterification (Gupta and Demirbas

2010). The oil reacts with an alcohol (usually methanol) in

the presence of a catalyst (usually potassium or sodium

hydroxide) to form mono-alkyl esters (biodiesel) and crude

glycerol. Biodiesel and glycerol form two separate layers

allowing the glycerol to be drawn off from the bottom of

the settling vessel. The excess alcohol is removed using a

flash evaporation process or by distillation. The product

from the rape seed oil and methanol is RME.

The system’s scope includes rape seed cultivation,

transportation of rape seed to oil mill, extraction and

refinement of the rape seed oil within the oil mill, the trans-

esterification process, distribution of RME, and also the

RME-fuelled vehicle operations.

The purity of the RME (B100), as used in passenger

cars, was assumed to be a fair comparison with diesel.

Since no data were available for the B100 passenger car

emissions, the exhaust emissions from the RME-fuelled

cars were assumed to be the same as the exhaust emissions

from a RME-fuelled 28-t lorry. Only NOx emissions were

adjusted with an increase of 15% compared with diesel-

fuelled passenger cars (Roy 2011).

Comparisons of footprints for biofuels and fossil fuels

Bioethanol is used as a substitute for petrol, and RME for

diesel fuel which would otherwise be used in the same

engine. Table 2 presents HHVs and those C and N emis-

sions that originated from the whole life cycles of RME,

corn-based ethanol, diesel and petrol. In Fig. 1, the C and

N emissions are presented on a relative scale.

CFs and NFs from biofuels are different depending on

the biomass yield, its moisture and starch or oil content,

nitrogen fertilizer types and levels, harvesting, distances of

biomass to bio-refinery, biofuel to service station, type of

passenger car, conversion rates in biofuel production, etc.

From Table 2 and Fig. 1, it can be seen that CO2

emissions are lower for biofuels compared with fossil fuels

by approximately 41%. Also emissions of CO are lower,

especially CO emissions from ethanol-fuelled passenger

cars, and are 84% lower than those of petrol-fuelled cars.

CH4 emissions are slightly lower for fossil fuels, by

10–15%. NOx emissions are the highest for RME and the

Table 2 HHVs and C and N emissions for transportation fuels

MJ/kg kg CO2/GJ kg CO/GJ kg CH4/GJ kg NOx/GJ kg N2O/GJ kg NO3-/GJ kg NH3/GJ

RME 40.2 56.44 0.128 0.097 0.485 0.1158 1.468 0.128

Ethanol 29.8 57.74 0.1097 0.1105 0.232 0.068 2.929 0.129

Diesel 45.9 95.79 0.157 0.087 0.332 0.0033 0.0013 0.00309

Petrol 46.7 97.78 0.689 0.094 0.248 0.0049 0.0013 0.0112

0

0.2

0.4

0.6

0.8

1

CO

RME

Ethanol

Diesel

Petrol

CO2

CH4

NOx

NH3

NO3-

N2O

Fig. 1 Graphical representation of C and N emissions for transpor-

tation fuels

394 L. Cucek et al.

123

lowest for ethanol (52% lower). All other N emissions,

N2O, NO3- and NH3 are much lower for diesel and petrol

compared with biofuels, by at least 93, 99.9 and 97.6%,

respectively.

Because of more than one C and N emissions, the CFs

and NFs from transportation fuels are also presented in

mass units of C and N per GJ, where NOx is expressed as

nitrogen dioxide (NO2). Table 3 presents the CFs and NFs

for all the four transportation fuels.

It is seen from Table 3 that biofuels have lower CF and

higher NF than fossil fuels. CFs for biofuels are lower by

approximately 41%, whilst NFs are higher by 500–880%.

Conclusions

This contribution overviewed and provided definitions for

the CFs and NFs found in the literature. Furthermore, the C

and N threats on the ecosystems and humans’ health were

explored. Nowadays, both FPs are of great concern and

cause series of environmental threats. CFs and NFs from

different energy production applications were assessed:

FPs originating from wood-fuelled, natural gas, fuel oil and

coal heating; and FPs originating from ethanol, RME, and

petrol- and diesel-powered passenger cars. Although the

FPs from biomass energy strongly differ depending on the

conditions, some conclusions can be provided. All biomass

energy productions have the lowest CF, whilst NF is the

highest; on the other hand, all fossil energy productions

have higher CFs and lower NFs compared with biomass

alternatives.

From the results of these case studies, it can be seen that

when only one FP is considered and evaluated, it most

likely leads to inaccurate conclusions which can lead to

incorrect decisions. Therefore, a complete set or at least

more than one FP (also the potential environmental impact)

has to be considered for LCA to provide valuable results

and conclusions.

In the future, sensitivity analyses of bioenergy should be

provided using the most recent data, because of significant

changes and on-going improvements in, e.g. biomass

yields, the required energy, etc. N capture and N minimi-

sation methods should be addressed for biomass energy

supply chains because of relatively high NF. In addition,

more FPs should be taken into account during analysis, e.g.

water footprint, phosphorus footprint, biodiversity footprint

and others, which are all very important and can seriously

affect ecosystems and humans’ health. Furthermore, the

additional assessment of social and economic footprints

should also be included. This could be done as an extension

of the Environmental Performance Strategy Map (De

Benedetto and Klemes 2009) towards a Sustainability

Performance Strategy Map.

Acknowledgments The financial supports from the project

TAMOP-4.2.2/B-10/1-2010-0025, and from the Slovenian Research

Agency (Program No. P2-0032) are gratefully acknowledged.

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