Green Energy and Technology

Life Cycle Assessment of Renewable Energy Sources

Anoop SinghDeepak PantStig Irving Olsen Editors

Life-Cycle Assessment of Biomethanefrom Lignocellulosic Biomass

Abdul-Sattar Nizami and Iqbal Mohammed Ismail

Abstract This chapter evaluates the life-cycle assessment (LCA) studies ofbiomethane produced from lignocellulosic biomass as a biofuel and it is releasedinto the environment in comparison with other bioenergy systems. A case study ofgrass biomethane that is produced by anaerobic digestion (AD) of grass silage andused as a transport fuel is described. The production of biomethane from AD is awell-known technological procedure that fulfills the requirements imposed by theenvironment, agronomy, and legislation in developing rural economies and sus-tainable biofuel production. All across Europe, the biomethane yield from variouslignocellulosic biomass ranges from 10 to 1,150 m3 h-1. The LCA studies havebeen gaining importance over the past few years to analyze biofuel sources fromcradle to grave in determining optimal biofuel strategies. Included in these, LCAstudies is the indirect input of biofuel production processes, related emissions andwaste as well as the fate of downstream products. Eighty-nine percent of green-house gas (GHG) emission savings are achieved by AD of grass silage to producebiomethane as a transport fuel.

A.-S. Nizami (&) � I. M. IsmailCenter of Excellent in Enviromental Studies (CEES), King Abdulaziz Universty (KAU),PO Box 80216, Jeddah 21589, Saudi Arabiae-mail: nizami_pk@yahoo.com

I. M. Ismaile-mail: iqbal30@hotmail.com

A. Singh et al. (eds.), Life Cycle Assessment of Renewable Energy Sources,Green Energy and Technology, DOI: 10.1007/978-1-4471-5364-1_4,� Springer-Verlag London 2013

79

1 Introduction

1.1 Lignocellulosic Biofuels, Renewable Directive,and Sustainability

Large-scale replacement of fossil fuels with renewable energy sources is necessarydue to energy security and climate change in the form of greenhouse gas (GHG)emissions (Farrell et al. 2006). Thus, there is an emerging utilization of ligno-cellulosic biomass, which is the largest source of renewable carbohydrates forbioenergy production (Jørgensen et al. 2007). The lignocellulosic biomass is anattractive feedstock for anaerobic digestion (AD) that produces biomethane to beused as a biofuel. However, according to the EU renewable directive of 2009,‘‘… the GHG emission saving from the use of biofuels and bioliquids taken intoaccount… shall be at least 35 %, whereas from 2017, GHG emission savings shallbe at least 50 %’’ (EC 2009). Thus, the renewable directive (EC 2009) promotesnonfood feedstocks including perennial grasses, forest, and agricultural residues,energy crops, organic fraction of municipal solid waste (OFMSW), and other likesubstrates for biofuel production. Grasses are one of the lignocellulosic biomassfor producing enriched biomethane as a transport fuel (Peeters 2009; Eisentraut2010; Singh et al. 2010a). Biomethane from lignocellulosic biomass has a betterenergy balance when compared to first-generation liquid transport biofuels (Korreset al. 2011). Many European countries are seeking biofuels to meet sustainabilitycriteria and to achieve GHG emission savings targets (Korres et al. 2010).

1.2 Significance of LCA Studies for Biofuels

The generation of biofuels is facing the challenges of becoming full commer-cialization (Singh et al. 2010b), which is expected in near future due to improvedprocess technologies and value-added products (IEA 2009). Thus, to ascertainoptimal biofuel strategies, it is necessary to take into account environmentalimpacts of biofuel and bioproducts (by-products) from cradle to grave. The indi-rect input in the biofuel production process, related emissions and wastes as wellas the fate of downstream products are all included in life-cycle assessment (LCA)studies. Thus, the overall assessment and impact evaluation of biofuels is carriedout in a systematic manner. Nevertheless, LCA can also bring inaccurate andunsuitable actions for the industry, policy-making sectors, and people’s perceptionif not exercised correctly (Korres et al. 2011).

80 A.-S. Nizami and I. M. Ismail

1.3 Anaerobic Digestion: A Source of Biofuel

AD is a process where organic waste and lignocellulosic biomass are convertedinto biogas and digestate for value-added products. The organic wastes includeslaughterhouse waste, agricultural slurries and residues, and OFMSW. Accordingto Prasad et al. (2007), among the entire biomass available in the world ligno-cellulosic biomass consisting of industrial, agricultural, and forest residues is themainstream feedstock for biogas production. Different potential feedstocks forbiogas production are listed in Table 1. The biogas produced can be used for theproduction of electricity or heating purposes at combined heat and power (CHP)units. Biogas can be further purified and upgraded to enriched biomethane(*97 % CH4, *3 % CO2 and some minor constituents) and can be injected intothe gas grid or used as gaseous biofuel for transport and heating purposes. Theenriched biomethane used as a transport fuel has recently started to gain consid-eration in many European countries, such as in Sweden, Austria, France, andSwitzerland (Korres et al. 2011). All across Europe, the biomethane yield fromvarious lignocellulosic biomass ranges from 10 to 1,150 m3 h-1 (Dena et al.2009). The methane (CH4) yield of various feedstocks is exemplified in Table 2.AD brings a promising perspective for stakeholders in the discussion of carbontrading and carbon neutral production chains, when doing an LCA study.

The aim of this chapter is to evaluate the LCA studies of biomethane producedfrom lignocellulosic biomass as a biofuel and its release into the environment incomparison with other bioenergy systems. A case study of grass biomethane,produced by AD of grass silage and used as a transport fuel, is described.

Table 1 Different feedstocks for biogas production

Agricultural residues Municipal waste and residues• Livestock manure • Sewage sludge• Animal mortalities • Municipal solid waste• Citrus waste • Food residuals• Green waste • Organic fraction of municipal

solid waste• Agricultural slurries• Sugarcane bagasseEnergy crops Industrial origin• Energy maize • Wastewater• Grass • Industrial sludges• Miscanthus • Industrial byproducts• Oilseed rape • Slaughterhouse waste• Sugar beet • Animal fats• Sweet sorghum • Biosolids• Switchgrass • Spent beverages• Willow

Life-Cycle Assessment of Biomethane 81

2 Methodology

2.1 Life-Cycle Assessment

According to International Organization for Standardization 14000 (ISO 2006),there are four phases of an LCA procedure, including (1) the goal, scope definition,and functional unit, (2) inventory analysis, (3) impact assessment, and (4) inter-pretation. An LCA provides systematic view and complete assessment of a productthroughout its life cycle (Payraudeau et al. 2007). It is important to consider thewhole life cycle due to efficient energy management of renewable sources andtheir GHG emissions. The scientific community considers LCA as one of the bestmethod for calculating the environmental burden associated with bioenergy pro-duction (Consoli et al. 1993). The renewable directive (EC 2009) has providedguidelines for the LCA of biofuels. An LCA of biofuels must evaluate GHG

Table 2 Methane yield of different feedstocks

Feedstocks Methane yield(m3 CH4 kg-1 volatilesolid added)

Feedstocks Methane yield(m3 CH4 kg-1 volatilesolid added)

Barley 353–658 Sorghum 295–372Triticale 337–555 Peas 390Alfalfa 340–500 Reed canary

grass340–430

Sudan grass 213–303 Flax 212Jerusalem artichoke 300–370 Straw 242–324Oats grain 250–295 Rice straw 278Maize, whole crop 205–450 MSW 278–320Grass 298–467 Food waste 373Hemp 355–409 Wheat grain 384–426Sunflower 154–400 Clover 300–350Wheat straw 290 Potatoes 276–400Oilseed rape 240–340 Chaff 270–316Leaves 417–453 Kale 240–334Sugar beet 236–381 Turnip 314Rye grain 283–492 Rhubarb 320–490Fodder beet 420–500 Miscanthus 179–218Nettle 120–420 Sludge 260Chicken litter 290 Pig manure 310Cattle manure 160 Source separated

food waste300–529

OFMSW 158–400 Timothy 345–375Cocksfoot 315

Chandra et al. 2012; Jha et al. 2011; Li et al. 2010; Cho and Park 1995; Juanga 2005; Murphyet al. 2011; Browne and Murphy 2012; János and Elza 2008

82 A.-S. Nizami and I. M. Ismail

emission reductions of carbon dioxide (CO2), nitrous oxide (N2O), and CH4 in theglobal-warming potential (GWP) with relation to fossil fuel replacement (Korreset al. 2011). According to Gerin et al. (2008), there should be a net reduction andgain in GHG emissions and bioenergy, respectively, in LCA studies of biomethaneproduced from lignocellulosic biomass. In Figure 1, a comprehensive presentationof the whole cycle of lignocellulosic biomethane is shown, where GHG emissionsare calculated based on energy inputs and outputs.

2.2 Goal, Scope, and Functional Unit

As a first step in conducting an LCA, goal, scope, and functional unit are defined.The goal addresses the intended applications to the intended audience, while scopehas to be compatible with the goal of study and well defined (Singh et al. 2010a).The functional unit is an element of the product or system, which must be mea-surable and definable. It is used as a quantitative tool for the comparative analysisof bioenergy systems (Casey and Holden 2005). In AD, biomethane is the mainproduct, and thus, the functional unit is described in m3 biomethane per year.

Ploughing (machinery and Soil C-N)

Rolling/harrowing (machinery)

Lime (manufacture)

Lime application (machinery)

Seed (production)

Sowing (machinery)

Ground preparation

Sowing

Raw

material p

rod

uctio

n

ph

ase

Fertilizer (manufacture)Fertilizer (machinery)

Mowing (machinery)

Fossil fuel

Electricity

Electricity

Bio

meth

ane p

rod

uctio

n

ph

ase

Distribution/pumping

Compression

Cleaning + upgrading

Macerating

Transport / storage

Harvesting (2 cuts)

Establishment and maintenance

Collecting (machinery)

Heat

Fuel (digestate usage) Transport

Anaerobic digestion

Electricity

Fig. 1 A flow chart of lignocellulosic biomethane production system

Life-Cycle Assessment of Biomethane 83

The environmental impact as a result of different operations is expressed in g CO2

equivalent (CO2 eq.) MJ-1 energy replaced.

2.3 System Boundaries

The system boundaries are determined initially by the goal and scope of the study.They are further linked with energy inputs and outputs of unit processes, where allof the direct and indirect emissions from agriculture, transportation and process arecalibrated (Singh et al. 2010a). The system boundaries for the GHG emission ofbiomethane produced from lignocellulosic biomass are examined from cradle tograve. The production of the lignocellulosic biomass is the cradle and enrichedbiomethane as a transport biofuel is the grave. The EU directive 2009/28/EC,Annex V, C-13 states that ‘‘… emissions from the fuel in use shall be taken to bezero for biofuels and bioliquids’’ (EC 2009). Thus, emissions from biomethanecombustion (often taking place in vehicles) are not considered in LCA studies(Korres et al. 2010, 2011).

2.4 Impact Category

To determine the potential impact of GHG emissions of CO2, N2O, CH4, the termGWP is used. GWP is defined as the collective outcome between the presentinstant and a certain time in the future resulted in a unit mass of gas released in thepresent (Casey and Holden 2005; Korres et al. 2010). A GWP of one (1) refers tothe release of 1 kg CO2 (Korres et al. 2011). According to EC (2009), the GWP ofNO2 and CH4 on one (1) kg basis is 296 and 23, respectively. The followingformula is used to calculate the volume of GHG emission in terms of CO2

(EC 2009).GHG (t of CO2 eq.) = CO2 (t) ? 23 9 CH4 (t) ? 296 9 N2 O (t).

3 LCA of Biomethane from Lignocellulosic Biomass

3.1 Sustainability Criteria and Energy Efficiency

The energy efficiency of a biofuel source is determined by considering all energyinputs and outputs over the entire product production cycle (Salter and Banks2009). For example, biodiesel production in Europe is accomplished using rapeseed oil that covers about 80 % of the land set aside for nonfood energy crops(Bauen 2005). Similarly, the rape seed biodiesel and wheat bioethanol both yield

84 A.-S. Nizami and I. M. Ismail

less gross and net energy in comparison with palm oil biodiesel, grass biomethane,and sugarcane bioethanol (Fig. 2). The option to import substrates for biodieselproduction from tropical countries, such as Indonesia and Malaysia, is not a viableoption as they result in a high demand for the production of palm oil, which is 80 %of the global production (Korres et al. 2011). Consequently, deforestation isoccurring at an annual rate of 1.5 % (Fargione et al. 2008). There are no net GHGemission savings with a change in land use (Reinhard and Zah 2009). According toDirective 2009/28/EC, palm oil biodiesel is not considered as biofuel because itneeds to achieve GHG savings of 60 % by 2020 (EC 2009). The increase in palm oilproduction causes habitat loss, drainage of peatlands, and land conflicts (Colchesteret al. 2006). Similar issues of deforestation, decarbonization, and soil degradationoccur with the production of sugarcane ethanol (Goldemberg et al. 2008).According to Korres et al. (2010, 2011), biofuel in form of enriched biomethaneproduced from lignocellulosic biomass like grass silage is much better for Europethan rape seed biodiesel and wheat ethanol (Fig. 2). The low-input indigenousperennial grasses provide biofuel with more useable energy, GHG savings and lesspollution related to agrochemical procedures than arable crops per hectare. Thearable crops can be corn grain ethanol or soybean biodiesel (Tilman et al. 2006;Korres et al. 2011). The benefits of producing biomethane as a transport fuel fromlignocellulosic biomass through the AD process are shown in Fig. 3.

3.2 GHG Emissions

Korres et al. (2010) assessed the GHG emissions of enriched biomethane as atransport biofuel produced by grass silage in place of diesel as69.74 g CO2 eq. MJ-1 energy replaced or 6,904 kg CO2 eq. ha-1 yr-1. This was

Rapeseed biodiesel

Wheat ethanol

Palm oil biodiesel

Sugarcane ethanol

Grass biomethane

Net energy 25 4 74 120 69

Gross 46 66 120 135 122

0

50

100

150

200

250

300

En

erg

y (G

J h

a-1a-1

)

energy

Fig. 2 The net and gross energy of different biofuels systems (Korres et al. 2010, 2011; Smythet al. 2009)

Life-Cycle Assessment of Biomethane 85

determined by considering different scenarios such as improved vehicle efficiency,electricity from wind, use of wood chips for AD heating requirements and carbonsequestration of 0.6 t C ha-1 yr-1; a minimum value for most European perma-nent crops and grasslands. All of them results in GHG emission savings of up to89.4 %. This achievement meets the EU directive 2009/28/EC requirements of60 % GHG savings by 2018 (EC 2009). The crop production and AD process arethe main GHG emissions contributors in grass biomethane (Fig. 4). Among theindirect GHG emissions, potassium and nitrogen fertilizers are the main contrib-utors to agricultural emissions. The digester heating is the largest contributor in thebiomethane production process (Korres et al. 2011).

The wheat ethanol, rapeseed biodiesel, and sunflower biodiesel do not meet the60 % GHG emission savings in comparison with grass biomethane (Fig. 5).According to Thornley et al. (2009), issues of high nitrogen and pesticiderequirements are associated with rape seed biodiesel, which impacts the GHGsavings. Furthermore, the associated technology is poor. The low GHG savingswith wheat ethanol is due to the emission of N2O during cultivation and lowbiofuel yields (Smith et al. 2005; Börjesson 2009). Similarly, sunflower biodieselonly fulfills the conversion rate necessary to achieve 35 % GHG emission savingsfrom 30 % of arable land (Ragaglini et al. 2010). Nevertheless, there are envi-ronmental benefits reported with sunflower biodiesel (Sanz-Requena et al. 2010).The biomethane production on farms from manure, which is an easily accessiblesubstrate result in higher GHG emission savings (Korres et al. 2011). Nevertheless,

Energy Advantages

- High quality fuel production- Surplus heat and electricity

production- Energy imports reduction

- Decentralized power system promotion

- Fossil fuels reduction

Economic Advantages

- Profit centres from transformation of waste liabilities

- Valuing of Negative-value feedstocks - Water consumption reduction

- Self-sufficiency increment

Environmental Advantages

-Odour elimination- Pathogens reduction

- Sanitized compost production- Inrorganic fertilizer reduction

- GHGs emission reduction- Carbon sequestration promotion

- Recycled water reuse- Groundwater and surface water

resources protection

Biomethane from Lignocellulosic

Biomass

Fig. 3 Benefits of lignocellulosic biomethane production system

86 A.-S. Nizami and I. M. Ismail

the problem of high water contents, low biogas production rates, and high econ-omies are barriers in AD of manure (Gerin et al. 2008). To overcome this problem,manure can be codigested with other lignocellulosic feedstocks. This results inhigher biomethane production (Jagadabhi et al. 2008) with improved digestermicrobiology (Nizami and Murphy 2010).

3.3 Digestate: A Source of Fertilizer and Bioproducts

AD results in a residual digestate. This digestate can be a great source of com-mercial fertilizer. This additional environmental benefit included in the biofuelprocess chain lowers the production costs and loss to the environment andincreases the process efficiency (Cherubini et al. 2009). The use of maize and grasssilage as AD feedstocks and their digestate used as fertilizer have been studied byGerin et al. (2008). Matsunaka et al. (2006) studied the Timothy grass for digestatepurposes. They observed the benefit of nitrogen uptake by the grass digestate,especially during the spring. Liquid and fiber components are obtained fromdigestate (Salter and Banks 2009) and some of the liquid can be re-used to enhancethe digestion process (Berglund and Börjesson 2006). The rest is processed intoliquid biofertilizer or can be used for many practical purposes (Fig. 5). The soliddigestate can be processed into either soil conditioner or high value insulatingmaterials (Grass2004; Salter and Bank 2009). The concept of using biomethane asa biofuel and digestate for value-added products evolves into the concept of

0

5

10

15

20

25

30

35

40

Cro

p p

rod

uct

ion

Her

bic

ide

vola

tiliz

atio

n

Lim

e d

isso

luti

on

N2O

em

issi

on

s

Tra

nsp

ort

atio

n

An

aero

bic

dig

esti

on

pla

nt

Up

gra

din

g

To

tal p

roce

ssin

g

Bio

gas

loss

es

Agriculture Transportation Biomethane production process

g C

O2

e M

J-1 en

erg

y re

pla

ced

Direct GHG emissions

Indirect GHG emissions

Total GHG emissions

emis

sio

n

Fig. 4 The direct, indirect, and total GHG emissions from grass biomethane production (Korreset al. 2010, 2011)

Life-Cycle Assessment of Biomethane 87

biorefinery (Kamm et al. 1998; Nardoslawsky 1999; Kamm and Kamm 2004).According to Korres et al. (2010), these value-added products that emerge inaddition to the biofuel (Fig. 6) will also help to reduce GHG emissions. However,calculation of these bioproducts GHG emissions is needed, as they are shaped intomarketable products at additional energy and financial cost.

89.40%

80%

62% 61%58%

45%

32%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Grass-Biomethane (0.6 t/ha/year C sequestration)

Biogas from Municipal Solid Waste (MSW)

Palm oil-Biodiesel Sugarcane- Ethanol

Sunflower-Biodiesel Rapeseed-Biodiesel Wheat-Ethanol

% C

O2

savi

ngs

Fig. 5 The % CO2 savings of different biofuel systems (Korres et al. 2010, 2011; Smyth et al.2009)

Feedstock

Biofuel

Dig

estate

Liquid digestateS

olid digestate

Value added products

Biofertilizer

Chemicals

Proteins

CarbohydratesEnzymes

Dyes

Fibre for making insulation boards and textile

Soil conditionerSyngas

Solid fuelAnimal fodder

ChemicalsHydrocarbons

Value added products

Bioreactor

Fig. 6 Value-added products of digestate (Kamm and Kamm 2004; Korres et al. 2011)

88 A.-S. Nizami and I. M. Ismail

4 Scenarios to Increase Sustainability of Biomethanefrom Lignocellulosic Biomass

4.1 The Potential of CO2 and GHG savings

A large portion of biogas consists of CO2 (40–50 %), which is removed duringbiogas upgrading to achieve enriched biomethane as a transport fuel. The range ofCO2 removal during upgrading is 1.62–1.86 kg CO2 m-3 (Power and Murphy2009). This CO2 removal is an additional source of GHG emission and thus can beminimized by its use in the AD (Fig. 7). Using CO2 as a pretreatment option toaccelerate the hydrolysis of cellulose (one of the major components in lignocel-lulosic biomass) is observed and described by Zheng et al. (1995), 1998 and Clarket al. (2006). The cellulose crystallinity, lignin sealing and cross-linkage ofhemicellulose around cellulose are barriers in the attachment of enzymes andmicrobes to the cellulosic surfaces (Nizami et al. 2009; Fan et al. 1987). This is anissue that impacts the efficiency of lignocellulosic biomass undergoing cellulosehydrolysis (Kim and Hong 2001). The use of CO2 as a pretreatment option in theAD process is preferred due to less expensive, clean, less energy demanding, easyto recover in a nontoxic manner and nonflammable properties in comparison withthe physical, chemical, thermal, and steam explosion pretreatments (Chahal et al.1981; Zheng et al. 1995; Kim and Hong 2000, 2001). The CO2 can be used in twodifferent forms: first in an explosive form at a high pressure where it disrupts the

Biogas production

CH4

Biomethane

CO2

Biofertilizer

CO2

CO2

Lignocellulosic Biomass

Fig. 7 The CO2 movementthrough various subsystemsinvolved in thelignocellulosic biomethanesystem

Life-Cycle Assessment of Biomethane 89

cellulose structure and second in a dissolved form where it forms carbonic acid.Carbonic acid is a weak acid that dissolves hemicellulose without toxicity andcorrosivity to the AD process. These processes result in porous cellulosic surfaces,which are easily accessible to enzymatic and microbial activity (Zheng et al. 1998;Kim and Hong 1999, 2000, 2001). Thus, the use of CO2 in biogas production hasuntapped potential that will not only enhance the efficiency of the process withreduced economic and energy requirements but will also decrease GHG emissionstremendously. Nevertheless, the use of CO2 as a pretreatment option is limited tothe ethanol industry in a supercritical CO2 explosion form, where it increasesglucose yield by 50 % and overall ethanol yield by 70 % (Zheng et al. 1998).

4.2 Digester Configurations and GHG Savings

Continuous stirred tank reactors (CSTR) are widely used to digest slurries andrepresent a simple and robust technology (Smyth et al. 2009; Mähnert et al. 2005).The addition of a separate preprocessing tank with chopper pump, screw-feeder,and flushing system (Weiland 2003) does increase the energy demand when usingfor lignocellulosic biomass. Therefore, the values for GHG emission of CSTRswill be higher than other digester configuration such as a dry batch digester orleach beds digester coupled with an up flow anaerobic sludge blanket (UASB)reactor (Nizami et al. 2009). In dry batch, leach beds, and UASB, there is lessrequirement for mechanical or electrical feeding and mixing (Köttner 2002; Niz-ami and Murphy 2010). This comparison of anaerobic digester configurations willassist developers and farmers in selecting digester types and digester processessuitable to digest lignocellulosic biomass with least GHG emissions.

4.3 Biogas Losses and Engine Efficiency

On average, the rate of biogas loss from AD to enriched biomethane production is7.41 %, which accounts for indirect GHG emissions between 8.44 and8.86 kg CO2 m-3 of biogas (Power and Murphy 2009). Nizami et al. (2009),suggested a closed-loop monitoring system equipped with sensory devices foranaerobic digester (Nizami et al. 2009). The application of nanotechnology toidentify, monitor, and record these losses using sensory chips and devices is at theinfancy stage in the scientific community. Moreover, comparing the GHG emis-sions of various digester configurations will assist the development of differentcomponent of the digester as we attempt to reduce energy loss. Above all, vehicleengines must be improved, as existing engines are less efficient in utilizing bi-omethane and greater in their release of GHG (Power and Murphy 2009).According to Korres et al. (2010), an improvement of 18 % can be achieved by theimprovements in engine efficiency to a similar km MJ-1 as diesel.

90 A.-S. Nizami and I. M. Ismail

5 Conclusion

Lignocellulosic biomass is available in substantial quantities all over the globe andis a promising source of biofuel when digested anaerobically in a digester. LCAstudies are important in analyzing biofuel sources from cradle to grave to deter-mine optimal biofuel strategies. Grass and grass silage have recently been con-sidered in many European countries as the crop of transport fuel. These feedstocksare perennial in nature and have high yields and volatile contents, which makethem beneficial feedstocks for biomethane production. A GHG emission savings of89 % is achieved by grass silage if digested anaerobically and biomethane is usedas a transport fuel.

References

Bauen A (2005) Biomass in Europe. In: Silveira S (ed) Bioenergy-realizing the potential.Elsevier, Amsterdam, pp 19–30

Berglund M, Börjesson P (2006) Assessment of energy performance in the life cycle of biogasproduction. Biomass Bioenergy 30:254–266. doi:10.1016/j.biombioe.2005.11.011

IEA Bioenergy (2009) Sustainable bioenergy—a reliable energy option. Report prepared for IEABioenergy Implementing Agreement. www.ieabioenergy.org

Börjesson P (2009) Good or bad bioethanol from a greenhouse gas perspective-what determinesthis? Appl Energy 86:589–594. doi:10.1016/j.apenergy.2008.11.025

Browne JD, Murphy JD (2012) Assessment of the resource associated with biomethane from foodwaste. Appl Energy Accepted

Casey JW, Holden NM (2005) Analysis of greenhouse gas emissions from the average Irish milkproduction system. Agric Syst 86:97–114

Chahal DS, Mcguirc S, Pikor H, et al (1981) In: Proceedings of the 2nd world congress ofchemical engineering. Montreal, Canada, October, 4–9

Chandra R, Takeuchi H, Hasegawa T (2012) Methane production from lignocellulosicagricultural crop wastes: A review in context to second generation of biofuel production.Renew Sustain Energy Rev 16:1462–1476

Cherubini F, Bird ND, Cowie A et al (2009) Energy-and greenhouse gas-based LCA of biofueland bioenergy systems: key issues, ranges and recommendations. Resour Conserv Recycl53:434–447. doi:10.1016/j.resconrec.2009.03.013

Cho JK, Park SC (1995) Biochemical methane potential and solid state anaerobic digestion ofKorean food wastes’. Bioresour Technol 52(3):245–253

Clark JH, Budarin V, Deswarte FEI et al (2006) Green chemistry and the biorefinery: apartnership for a sustainable future. Green Chem 8:853–860

Colchester M, Jiwan N, Andiko et al (2006) Promised land: palm oil and land acquisition inIndonesia: implications for local communities and Indigenous Peoples. Forest PeoplesProgramme/Perkumpulan Sawit Watch, London/Bogor

Consoli F, Allen D, Boustead I, et al (1993) Guidelines for life-cycle assessment: a ‘‘Code ofpractice’’. In: Proceedings of society of environmental toxicology and chemistry (SETAC).SETAC Workshop, Sesimbra, 31 Mar–3 Apr

Dena HM, Kontges A, Rostek S (2009) Biogaspartner—a joint initiative. Biogas grid injection inGermany and Europe-Market, Technology and Players. German Energy Agency, HP Druck,Berlin

Life-Cycle Assessment of Biomethane 91

EC (2009) Directive 2009/28/EC of the European parliament and of the council of 23 April 2009on the promotion of the use of energy from renewable sources and amending andsubsequently repealing Directives 2001/77/EC and 2003/30/EC. Official J Eur Union, L140/16–62

Eisentraut A (2010) Sustainable production of second generation biofuels, information paper.International Energy Agency, Paris

Fan LT, Gharpuray MM, Lee Y-H (1987) Cellulose hydrolysis. Springer, BerlinFargione J, Hill J, Tilman D et al (2008) Land clearing and the biofuel carbon debt. Science

319:1235–1238. doi:10.1126/science.1152747Farrell AE, Plevin RJ, Turner BT et al (2006) Ethanol can contribute to energy and environmental

goals. Science 311:506–508Gerin PA, Vliegen F, Jossart JM (2008) Energy and CO2 balance of maize and grass as energy

crops for anaerobic digestion. Bioresour Technol 99:2620–2627. doi:10.1016/j.biortech.2007.04.049

Goldemberg J, Teixeira CS, Guardabassi P (2008) The sustainability of ethanol production fromsugarcane. Energy Policy 36:2086–2097. doi:10.1016/j.enpol.2008.02.028

Grass S (2004) Utilisation of grass for production of fibres, protein and energy. Biomass andagriculture: sustainability, markets and policies. Biomass Project Services, Switzerland,pp 169–177

ISO (2006) International Standardization Organization (ISO), Environmental management–lifecycle assessment-principles and framework, ISO 14040

Jagadabhi PS, Lehtomäki A, Rintala J (2008) Co-digestion of grass silage and cow manure in aCSTR by re-circulation of alkali treated solids of the digestate. Environ Technol29:1085–1093. doi:10.1080/09593330802180385

János T, Elza K (2008) Input materials of biogas production. Lecture on Environmentaltechnology. Debreceni Egyetem a TÁMOP 4.1.2 pályázat keretein belül. Available from:http://www.tankonyvtar.hu/en/tartalom/tamop425/0032_kornyezettechnologia_en/ch01s02.html

Jha AK, Li J, Nies L et al (2011) Research advances in dry anaerobic digestion process of solidorganic wastes. Afr J Biotechnol 10:14242–14253

Jørgensen H, Kristensen JB, Felby C (2007) Enzymatic conversion of lignocellulose intofermentable sugars: challanges and opportunities. Biofuels. Bioprod Biorefin 1:119–134

Juanga JP (2005) Optimizing dry anaerobic digestion of organic fraction of municipal solidwaste. M.E. thesis, Asian Institute of Technology, Bankok

Kamm B, Kamm M (2004) Principles of biorefineries. Appl Microbiol Biotechnol 64:137–145Kamm B, Kamm M, Soyez K (1998) The green biorefinery, concept of technology. In:

Proceedings of (1st international symposium on green biorefinery) Neuruppin, Society ofEcological Technology and System Analysis, Berlin

Kim KH, Hong J (1999) Equilibrium solubilities of spearmint oil components in supercriticalcarbon dioxide. Fluid Phase Equil 164:107–115

Kim KH, Hong J (2000) Dynamic extraction of spearmint oil components by using supercriticalCO2. Sep Sci Technol 35:315–322

Kim KH, Hong J (2001) Supercritical CO2 pretreatment of lignocellulose enhances enzymaticcellulose hydrolysis. Bioresour Technol 77:139–144

Korres NE, Singh A, Nizami AS et al (2010) Is grass biomethane a sustainable transport biofuel?Biofuels Bioprod Bioref 4:310–325. doi:10.1002/bbb.228

Korres NE, Thamsiriroj T, Smyth BM et al (2011) Grass biomethane for agriculture and energy.In: Sustainable Agriculture Reviews, vol 7. Springer, London Ltd, pp 5–49, DOI: 10.1007/978-94-007-1521-9_2

Köttner M (2002) Biogas and fertilizer production from solid waste and biomass through dryfermentation in batch method. In: Wilderer, P, Moletta, R (eds) Anaerobic digestion of solidwastes III. IWA Publishing, London

92 A.-S. Nizami and I. M. Ismail

Li D, Yuan Z, Sun Y (2010) Semi-dry mesophilic anaerobic digestion of water sorted organicfraction of municipal solid waste (WS-OFMSW). Bioresour Technol 101:2722–2728

Mähnert P, Heiermann M, Linke B (2005) Batch- and semi- continuous production from differentgrass species. Agric Eng Int: CIGRE E J V11, Manuscript EE 05 010

Matsunaka T, Sawamoto T, Ishimura H et al (2006) Efficient use of digested cattle slurry frombiogas plant with respect to nitrogen recycling in grassland. Int Congr Ser 1293:242–252

Murphy JD, Braun R, Weiland P et al (2011) Biogas from crop digestion. IEA Bioenergy Task37. Web access: http://www.iea-biogas.net/

Narodoslawsky M (1999) Green biorefinery. In: Proceedings of 2nd international symposium ongreen biorefinery, SUSTAIN, Feldbach

Nizami AS, Murphy JD (2010) What type of digester configurations should be employed toproduce biomethane from grass silage? Renew Sustain Energy Rev 14:1558–1568

Nizami AS, Korres NE, Murphy JD (2009) A review of the integrated process for the productionof grass biomethane. Environ Sci Technol 43:8496–8508

Payraudeau S, van der Werf HMG, Vertes F (2007) Analysis of the uncertainty associated withthe estimation of nitrogen losses from farming systems. Agric Syst 94:416–430. doi:10.1016/j.agsy.2006.11.014

Peeters A (2009) Importance, evolution, environmental impact and future challenges ofgrasslands and grassland-based systems in Europe. Grassl Sci 55:113–125. doi:10.1111/j.1744-697X.2009.00154.x

Power MP, Murphy JD (2009) Which is the preferable transport fuel on a greenhouse gas basis;biomethane or ethanol? Biomass Bioenergy 33(10):1403–1412 doi: 10. 1016/j. biombioe.2009. 06.044

Prasad S, Singh A, Joshi HC (2007) Ethanol as an alternative fuel from agricultural, industrialand urban residues. Resour Conserv Recycl 50:1–39

Ragaglini G, Triana F, Villani R et al (2010) Can sunflower provide biofuel for in-land demand?an integrated assessment of sustainability at regional scale. Energy. doi:10.1016/j.energy.2010.03.009

Reinhard J, Zah R (2009) Global environmental consequences of increased biodieselconsumption in Switzerland: consequential life cycle assessment. J Cleaner Prod 17(Supple-ment 1):S46–S56. doi:10.1016/j.jclepro.2009.05.003Salter

Salter A, Banks CJ (2009) Establishing an energy balance for crop-based digestion. Water SciTechnol IWA 59(6):1053

Sanz Requena JF, Guimaraes AC, Quiros Alpera S et al (2010) Life cycle assessment (LCA) ofthe biofuel production process from sunflower oil, rapeseed oil and soybean oil. Fuel ProcessTechnol 92:190–199. doi:0.1016/j.fuproc.2010.03.004

Singh A, Pant D, Korres NE et al (2010a) Key issues in life cycle assessment of ethanolproduction from lignocellulosic biomass: challenges and perspectives. Bioresour Technol101:5003–5012. doi:10.1016/j.biortech.2009.11.062

Singh A, Korres NE, Murphy JD (2010b) Grass and anaerobic digestion for biomethaneproduction: a sustainable option. In: Grassland Science in Europe, the official peer-reviewed.Proceedings of European Grassland Federation, General Meeting, Kiel, 29 Aug–2 Sept 2010

Smith TC, Kindred DR, Brosnan JM et al (2005) Wheat as a feedstock for alcohol production.Research Review no. 61, Home-Grown Cereals Authority

Smyth B, Murphy JD, O’Brien C (2009) What is the energy balance of grass biomethane inIreland and other temperate northern European climates? Renew Sustain Energy Rev13(9):2349–2360 doi:10.1016/j.rser.2009.04.003

Thornley P, Upham P, Tomei J (2009) Sustainability constraints on UK bioenergy development.Energy Policy 37:5623–5635. doi:10.1016/j.enpol.2009.08.028

Tilman D, Hill J, Lehman C (2006) Carbon-negative biofuels from low-input high diversitygrassland biomass. Science 314:1598–1600. doi:10.1126/science.1133306

Weiland P (2003) Production and energetic use of biogas from energy crops and wastes inGermany. Appl Biochem Biotechnol 109(1–3):263–274

Life-Cycle Assessment of Biomethane 93

Zheng Y, Lin HM, Wen J et al (1995) Supercritical carbon dioxide explosion as a pretreatmentfor cellulose hydrolysis. Biotechnol Lett 17:845–850

Zheng Y, Lin H-M, Tsao GT (1998) Pretreatment for cellulose hydrolysis by carbon dioxideexplosion. Biotechnol Prog 14:890–896

94 A.-S. Nizami and I. M. Ismail