Life Cycle Assessment and sustainability methodologies for assessing industrial crops, processes and end products

Industrial Crops and Products 34 (2011) 1332–1339

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Life Cycle Assessment and sustainability methodologies for assessing industrial crops, processes and end products M.J. Black a,∗ , C. Whittaker b,c , S.A. Hosseini d , R. Diaz-Chavez a , J. Woods a , R.J. Murphy b a

Porter Alliance, Centre for Environmental Policy, Imperial College London, UK Porter Institute, Department of Biology, Imperial College London, UK North Energy Associates, Watson’s Chambers Business Centre, 5-15 Market Place, Castle Square, Sheffield, S1 2GH, UK d Porter Institute, Centre for Process Systems Engineering, Imperial College London, UK b c

a r t i c l e

i n f o

Article history: Received 15 March 2010 Received in revised form 27 August 2010 Accepted 2 December 2010 Available online 12 January 2011 Keywords: Life Cycle Assessment (LCA) Sustainability Greenhouse gas (GHG) Advanced biofuel technology Lignocellulosic ethanol Willow

a b s t r a c t Providing food, energy and materials for the rising global population is a challenge which is compounded by increased pressure on natural resources such as land, water and fossil sources of raw materials. Greenhouse gas (GHG) emissions from human activities have increased with industrial development and population expansion, and it is anticipated that resulting climate change might further limit agricultural productivity, through changes to weather patterns and global availability/distribution of agriculturally productive land. Growing crops as feedstocks for industrial uses is seen as one way of reducing GHG emissions and dependency on fossil resources. However, determining the extent to which the development of crops for industrial use will effect GHG balances and provide for a more energy efficient manufacturing system requires the development and use of appropriate calculation methodologies. Research at the Porter Institute has identified over 250 different scenarios for bioenergy production systems using commodity crops. In order to rationalise this complexity and diversity, a modular approach to Life Cycle Assessment (LCA) and sustainability analysis has been taken. This allows characterisation of discrete sections of supply chains and enables comparisons to be made between different crop production systems, different process systems and different end product uses. The purposes of this paper are to introduce the concepts of biofuel GHG and sustainability metrics, to introduce the approach taken by our organization and to use the example of UK grown willow in a lignocellulosic ethanol production system to demonstrate how GHG emission outcomes can be reviewed for “new” crops and technologies. The results show a range of variation, in both growing and process systems and how outcomes such as energy and GHG balances can be affected by various activities. LCA methodologies provide data to inform governments and industry of the potential specific supply chains may have for energy and GHG saving. However, methodological approaches can also affect assessment outcomes. Unresolved issues in LCA methodology must also be evaluated e.g. impacts resulting from land use change. Sustainability assessments of crop growing systems, irrespective of the end use, also assist in the assessment of environmental impacts of supply chains. However, it is critical that data continue to be collected, analysed and reviewed, to ensure that the most appropriate crops are grown and processed for the most appropriate end use. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.

1. Introduction In writing an introduction to a paper about Life Cycle Assessment (LCA) and Sustainability analysis of crops for industrial uses it is necessary to take account of three major concerns facing society today. Population growth, depletion of natural resources and

∗ Corresponding author at: Porter Alliance, Rm. 329, Centre for Environmental Policy, Imperial College London, South Kensington Campus, London SW7 2AZ, UK. Tel.: +44 020 7594 9328. E-mail address: [email protected] (M.J. Black).

climate change (from greenhouse gas (GHG) emissions) are major challenges facing mankind in the 21st century. It is widely accepted that human activities and expanding population impact on the environment, and that this impact is disproportionately exacerbated as population increases (Harte, 2007). The relationship between population growth and environmental impact has been discussed in much greater detail by Spiedel et al. (2009). What has been made quite clear is that population growth and demand for products is putting increasing pressure on land resources (forest and croplands are decreasing, as the result of timber extraction, land conversion, soil erosion and desertification); marine resources (depletion of fishery stocks as the result of over

0926-6690/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.indcrop.2010.12.002

M.J. Black et al. / Industrial Crops and Products 34 (2011) 1332–1339

fishing) and water resources (depletion of aquifers and falling water tables, due to over-use and extraction of water) and that, in order to meet the needs of the growing population, intensification of agriculture will be necessary (Godfray et al., 2010). Additionally, further impacts on land and natural resources such as drought, imbalance in water cycles and increased temperatures, are occurring as the result of climate change, resulting from anthropogenic activities. In the developed world, fossil fuels have met between 85% and 93% of energy requirements over the last 50 years (Nehring, 2009). The concept of peak oil is widely accepted, but predictions for peak oil vary and have been proven wrong in the past. According to de Almeida and Silva (2009), there is a consensus amongst market participants that peak oil will occur in the near term, likely before 2015. Beyond peak oil, there is also a profile for oil production which is equally difficult to predict. Data about remaining oil reserves and depletion rates are uncertain, making accurate predictions difficult, and, as with all models, results can depend on methods used to make the predictions. Technological developments, changes in consumer attitude and behaviour, and the development of alternative fuel technologies will also have an influence on oil demands, which cannot be predicted at this time. Nehring (2009) has defined the 3 fossil fuel sectors (solid, liquid and gas) and, taking a longerterm outlook, puts fossil fuel production on a decline, on a per capita basis between 2020 and 2030. On the basis of these predictions, it is apparent that alternatives to fossil fuels (and fossil feedstocks for the chemical industry) are required. Many countries have been looking at renewable energy options such as wind, solar, tidal and bioenergy. For transportation, the options for replacing current fossil-based liquid fuels are limited by engine technologies (including small, large, jet and marine engines, as well as stationary systems). Biofuels currently provide the only renewable option for liquid fuels for internal combustion and jet engines. It is clear that completely replacing liquid fossil fuels with biofuels is an unlikely scenario in the short- or medium-term, particularly if direct competition with food crops is to be avoided. However, replacing a percentage of fossil fuel with biofuel has scope to provide a contribution to reducing demands for fossil fuels, alongside other renewable energies such as solar, wind and tidal energy. Some policies have also taken the approach that biofuels, if produced correctly, can reduce GHG emissions in comparison to fossil fuels. Providing analysis for GHG emissions calculations has led to the development of LCA methodologies for biofuel supply chains, to ensure that biofuels deliver GHG savings. Furthermore, amidst considerable concerns from environmental organisations that biofuels are not sustainable, the UK and the EU have been developing sustainability principles for biofuels. This paper provides a background to LCA and sustainability analysis in policy development for biofuels and outlines the approach taken by the Porter Alliance, Imperial College London, in developing LCA for “new” crops and technologies to inform biofuel development and support policy requirements.

2. Policy background 2.1. UK policy The UK began developing a biofuel policy in 2003, with a view to delivering GHG reductions, through the replacement of fossil fuels with biofuels in road transport fuel. The Renewable Transport Fuels Obligation (the RTFO) commenced in April 2008 and requires obligated parties (fuel suppliers) to ensure that a specified percentage of the road fuel supplied in the UK is made up of renewable fuel. Initially targets were set at 2.5% inclusion (by volume) in 2008–2009, rising to 3.9% in 2009–2010 to 5.25% in 2010–2011 (RTFO, 2007).

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Table 1 UK Renewable Transport Fuels Obligation, Sustainability Principles (RFAb, 2008). Environmental principles 1. Biomass production will not destroy or damage large above or below ground carbon stocks 2. Biomass production will not lead to the destruction of or damage to high biodiversity areas 3. Biomass production does not lead to soil degradation 4. Biomass production does not lead to the contamination or depeletion of water sources 5. Biomass production does not lead to air pollution Social principles 6. Biomass production does not adversely affect workers rights and working relationships 7. Biomass production does not adversely affect existing land rights and community relations

However, concerns about the sustainability of biofuels and in particular, competition for feedstocks which are currently used for food and the impact that increased feedstock production would have on land use, led to The Gallagher Review (RFAa, 2008). The targets have since been revised to 2.5% (by volume) inclusion of biofuel from 2008 and thereafter, a target increase of 0.5% per annum to a maximum of 5% (by volume) in 2013 (RTFO, 2009). In order to ensure that biofuels deliver GHG savings, considerable attention has been paid to developing practical means of reporting GHG emissions from biofuels supply chains. The RTFO includes a carbon reporting methodology, which allows obligated parties to report on GHG emissions for their biofuels derived from known supply chains (RFAc, 2008). GHG emissions calculations (reported as CO2 equivalents) can be made using default data defined in the methodology or obligated parties can use the reporting methodology to calculate individual GHG emissions, if data is available. The RTFO currently provides GHG emission reporting methodology for ethanol from sugarcane, sugar beet, molasses, wheat and corn; Fatty Acid Methyl Ester (FAME) from tallow, used cooking oil, soy, palm, oilseed rape and biomethane from anaerobic digestion of Municiple Solid Waste (MSW) and manure as well as ethanol converted to Ethyl Tertiary Butyl Ether (ETBE). The RTFO policy also has a sustainability component, devised as a “meta-standard”, which defines 5 principles for environmental and 2 principles for socio-economic consideration. These 7 principles (Table 1) are further defined by criteria and indicators which allow existing or independent assurance schemes for feedstock to be benchmarked. Obligated parties can then report sustainability features of their supply chains, based on the Principles, or rely on assurance schemes which have been bench-marked under the RTFO Carbon and Sustainability (C&S) reporting methodology, e.g. Forest Stewardship Council (FSC); Assured Combinable Crops Scheme (ACCS); Linking Environment and Farming (LEAF Marque); Roundtable on Sustainable Palm Oil (RSPO); Roundtable on Responsible Soy (RTRS). Reporting this information is currently voluntary under the RTFO. There is a ‘buy-out’ option for obligated parties and summaries of reported information and the performance of obligated parties are made public at quarterly intervals during the reporting year (April through to end March of the following year). The current format of reporting and the reporting framework provide a robust means of demonstrating the feasibility and practicality of carbon and sustainability reporting and it is expected that this will provide a stepping stone to a mandatory assurance scheme. The RTFO is currently administered through the Renewable Fuels Agency (RFA) which, as well as monitoring the carbon and sustainability reporting, has a programme of activities which reviews and carries out research activities to address on-going issues in the policy and methodology framework.

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2.2. European policy In the European Union (EU) policies which have been developed to promote the use of biofuels fall under the EU Climate Change and Energy Package, which was agreed in December 2008 (EU, 2008). Under this legislation, 27 EU Member States committed to reduce CO2 emissions by 20% by 2020 and to target a 20% share of renewable energies by 2020 i.e. “20–20 in 2020”. It is anticipated that the CO2 reduction commitment will scale up to as much as 30%, under new global climate change agreements with other developed countries. The policies within the Energy and Climate Package, which apply directly to biofuels, are the Fuels Quality Directive (FQD) and the Renewable Energy Directive (RED). These policies address different objectives and are run by separate EU Directorates. The FQD (EU Directive, 2009a) is controlled by the Directorate General for Environment (DG-Environment) and is aimed at the reduction of harmful atmospheric emissions (including GHGs) from transport fuels. The FQD incorporates mandatory monitoring of ‘lifecycle greenhouse gas emissions’ from fuels as of 2009. The RED (EU Directive, 2009b) is controlled by the Directorate General for Transport and Energy (DG-Tren) and is aimed at the promotion of renewable energies such as wind, solar, geothermal, wave, tidal, hydropower, biomass, landfill gas, sewage treatment, plant gas and biogases and includes biofuels. Of the 20% of EU energy to be met from renewable sources by 2020, it is determined that 10% of transport fuel requirements should be from renewable sources. The methodology for GHG reporting and issues around the sustainability of feedstock for biofuel in the FQD have been devised to follow the same methodologies and principles as the RED. Details for GHG methodology and reporting can be found in Article 19 of EU Directive (2009b). Member states can report estimates of GHG savings for typical biofuel supply chains, i.e. default values or can use actual values derived from the calculation methodology found in Annex V of the Directive (EU Directive, 2009b). Briefly, default emission levels have been calculated using the following equation: E(gCO2eq /MJ) = eec + el + ep + etd + eu + esca + eccs + eccr − eee

(1)

where E is the total emissions from the use of the fuel; eec the emissions from the extraction and cultivation of raw materials; el the annualised emissions from carbon stock changes caused by landuse change; ep the emissions from processing; etd the emissions from transport and distribution; eu the emissions from the fuel in use; esca the emission saving from soil carbon accumulation via improved agricultural management eccs the emission saving from carbon capture and geological storage; eccr the emissions saving from carbon capture and replacement; and eee the emissions saving from excess electricity co-generation. Policy recommendation in EU Directive (2009b), is that the EU community should promote the use of sustainable biofuels by developing sustainability criteria. Public consultation with stakeholders, Non Governmental Organisations (NGOs) and governments across EU generally supported the following: • Land with high carbon stocks should not be converted for biofuel production (e.g. wetlands, peatlands). • Land with high biodiversity should not be converted for biofuel production (e.g. forest, grassland). • Biofuels should achieve a minimum level of GHG saving (carbon stock losses would not be included in the calculation). • Biofuels and bioliquids which do not fulfil the sustainability credentials will not be considered as renewable. Developing cohesive sustainability reporting in the RED and FQD is a current topic of discussion and debate amongst policy makers and other organisation in the EU, resulting in a comitology approach to developing sustainability procedures for biofuels. van Dam et al.

(2008) have provided a comprehensive review of developments for sustainability reporting for biomass in the European Union up to 2007. The paper addresses approaches to sustainability, stakeholder engagement and viewpoints on sustainability reporting, and reviews the limitations of sustainability reporting for crop/biomass materials.

3. Feedstock and conversion technologies Achieving biofuel targets which have been set, not only in the UK and EU, but also globally, will require a significant amount of raw material feedstocks as well as a good understanding of the sustainable potential of biofuel supply chains to meet social and environmental needs. This is particularly important in addressing the issues which have been raised about biofuels in recent years by environmental groups and the media, e.g. competition for food, land use change issues, loss of biodiversity and increased GHG emissions (Friends of the Earth, 2008; Greenpeace, 2007; Oxfam, 2008; The Guardian, 2008). Efficiency in the production of feedstock and in the processes used to convert feedstock will affect GHG balances and sustainability and there is much potential to address efficiency in biofuel supply chains. A summary of crops and potential conversion pathways for biofuels, co-products and chemicals is given in Fig. 1. Current biofuel production technologies (first generation or 1G), such as fermentation of sugars to bioethanol or methyl esterification of vegetable oils to biodiesel, rely on existing commodity crops such as sugar cane, maize, wheat and vegetable crops such as palm, soy or oilseed rape. Using these crops and technologies may not necessarily be the most efficient in terms of biofuel yield, in comparison with advanced biofuel technologies (second generation or 2G). Furthermore, the use of food commodity crops for biofuel production has raised questions about food security and potential conflicts between feedstocks for food or biofuel production. However, until advanced technologies are developed to the commercial scale, these are the only means available to meet current liquid road fuel substitution requirements. The use of 2G biofuel conversion systems, such as lignocellulosic ethanol production (where ethanol is derived from the fermentation of sugars from hemicellulose and cellulose fractions of crops instead of from sugar or starch fractions) is seen ultimately as being more land and energy efficient and offering higher GHG savings versus fossil fuels than existing biofuel technologies. However, the conversion steps for 2G biofuels are currently more costly and more material and energy intensive, due to the conditions required to break down the plant cell wall components (Hosseini and Shah, 2009a). The breakdown and separation of plant cell wall structural components by the breakdown and removal of lignin, and cellulose and hemicellulose breakdown to C6 and C5 sugars, requires pre-treatments (e.g. steam explosion; acid treatments; alkali treatments) and/or enzymatic hydrolysis (requiring a cocktail of enzymes depending on the structure of biomass materials) to allow access to C6 sugars for fermentation to ethanol. Further technological developments, such as the engineering of organisms which can ferment C5 sugars to ethanol, are also options for improving ethanol yield from lignocellulosic sources of feedstock (Cripps et al., 2009). The Porter Alliance is a multi-disciplinary, cross-institutional group, whose activities focus on research activities through the supply chain, from crop breeding to end fuel use and engine efficiency. One of the activities within the group is focused on LCA and Sustainability analysis aspects of biofuel supply chains, in an effort to understand and reduce GHG emissions and to enhance energy efficiency and environmental and social benefits of particular biofuel supply chains. The purposes of this paper are to introduce the

M.J. Black et al. / Industrial Crops and Products 34 (2011) 1332–1339

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Fig. 1. Crop conversion routes for fuels and chemicals.

concepts of biofuel GHG and sustainability metrics, to introduce the approach taken by our organization and to use the example of UK grown willow in a lignocellulosic ethanol production system to demonstrate how GHG emission outcomes can be reviewed for “new” crops and technologies. 4. Methodologies The approach to supply chain LCA for biofuel production is a generic approach at the first level, describing a biofuel supply chain for lignocellulosic ethanol via the modules described in Fig. 2. The modules can then be explored for data sensitivity or modification in practices (e.g. difference in feedstock production or process practices). By taking a modular approach at this first level, it is possible to identify and de-couple areas where alternative production practises or new technologies are of interest and to investigate these

Fig. 2. Modular approach to review supply chains for crops and conversion technologies for lignocellulosics to bioethanol pathways.

individually and in depth, before considering the effect on the supply chain LCA as a whole. The model reference system for this study, which explores cellulosic ethanol production, is based on Slade et al. (2009) for softwood or straw feedstock and dilute acid or enzymatic conversion processes. In this case, we demonstrate the decoupling of the feedstock production module and a pre-processing module, which explores the effect of particle size of biomass feedstock on process efficiency for a willow cellulosic ethanol supply chain. 4.1. Feedstock module—Willow (Salix spp.) in the UK Willows (Salix spp.) are one of the two fast-growing, softwood tree species, from the family Salicaeae which are being considered in the UK to supply biomass to meet bioenergy policy requirements and with the potential to supply feedstock for lignocellulosic ethanol production Poplar (Populus spp.) is the other fast-growing, softwood crop under review. When grown for biomass they are managed as short rotation coppice (SRC) crops, which allows harvest every 3–5 years and promotes fast growth and higher yields over time (Karp and Shield, 2008). Willow has been promoted on a number of levels: as a renewable energy source; for diversification for farmers in the UK; as a means of reducing GHG emissions due to decreased fertilizer requirements and as a means of improving carbon sequestration and increasing carbon stocks on land (Aylott et al., 2008). 4.1.1. LCA methodology Willow feedstock production is based on data and methodology presented in the TSEC-BIOSYS final report on the sustainability of biomass supply chains in the UK (Whittaker et al., 2009) which describes SRC willow production for heat and electricity generation at various scales. The willow production system is based on existing supply chains that currently provide fuels to various renewable energy schemes. The primary energy consumption and emissions for willow production are provided for all growing and harvesting activities “to the farm gate” and are based on the systems boundaries described in Fig. 3. The willow feedstock production module is further defined by an activities inventory of all operations involved in site establishment, maintenance and forage (chip) harvesting, and these are presented as “sub”-modules so that the overall feedstock production system can be refined to represent different intensities of production. The results of the LCA are presented as the total primary (fossil) energy inputs (MJ) and GHG emissions (kg of carbon dioxide,

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Fig. 3. Flow chart for the production of 1 oven dry tonne of willow SRC, stored and ready for delivery to the next stage of the supply chain (Whittaker et al., 2009).

methane, nitrous oxide emissions, or by total carbon dioxide equivalents) per oven dry tonne (ODT) of biomass produced. It is assumed that the SRC willow chips are harvested at 50% moisture content (fresh weight basis) therefore for each ODT, two tonnes of material will need storage and transportation to the next stage of the supply chain. The LCA also examines sensitivities of the overall energy requirements and emissions to different cultivation regimes as shown in the following 4 scenarios for different fertilizer regimes: Scenario (1) 100 kg/ha of artificial fertilizers N, P and K. Scenario (2) 100 kg/ha of artificial fertilizers P and K, plus 100 kg N/ha equivalent of slurry. Scenario (3) 100 kg/ha equivalent of slurry. Scenario (4) No fertilizer. The importance of this is that fertilizer requirements of SRC willow may range from site to site, and the availability of slurry may be demand and location specific. Emissions from fertilizer manufacture and application and N2 O emissions from soil are provided separately so that the results can be replicated and re-calculated for various fertilizer regimes. The total GHG emissions of these four Scenarios, are 16.68, 13.15, 11.34 and 8.14 kg CO2 eq./ODT willow, respectively. It is assumed that there is no effect of yield between the scenarios (which may not reflect results in the field) and that any losses in yield will increase the overall emissions per ODT of feedstock. In this case, yield is held static in order to consider the GHG effects of different fertilizer regimes on a particular growing system however, the impact of improving or intensifying crop yield has wider consequences as the result of avoided land use change (Burney

Fig. 4. Comparisons of Greenhouse Gas emissions for 4 scenarios for fertilizer application to SRC willow (Scenario 4 is “no applied fertilizer”) (Whittaker et al., 2009).

et al., 2010). In Fig. 4, ‘material inputs’ represent the GHG emissions that are associated with providing all onsite ‘materials’ such as fertilizers, herbicides and fencing. From Scenarios 1 to 4, the contributions from fertilizer manufacture are 5.4, 1.87, 0.06 and 0 kg CO2 eq./ODT respectively, demonstrating that artificial fertilizers used in Scenarios 1 and 2 are GHG emission-intensive to produce, particularly nitrogen-based fertilizers. Though slurry is a relatively low emission-intensive source of fertilizer, it has a low nitrogen content (approx. 2 kg/m3 ), so providing sufficient quantities for the SRC willow, results in substantial GHG emissions from haulage. GHG emissions also occur from both artificial and organic fertilizers as the result of N2 O emissions from soil, in this case, at a rate of 3.14 kg CO2 eq./ODT, according to the IPCC Guidelines for National Greenhouse Gas Inventories (de Klein et al., 2006). There is also some debate about the inclusion of N2 O emissions from slurry application as, it could be argued that they would have been spread elsewhere on the ‘reference system’, in this case the total GHG emissions for Scenario 3 would be reduced from 11.34 to 8.2 kg CO2 eq./ODT. 4.1.2. Sustainability The most commonly planted, dedicated biomass crops in the UK are SRC (willow and poplar) and grass, in the form of miscanthus (Miscanthus spp.). For these crops, the major environmental impacts are due to changes in land use as the result of biomass crop production; biodiversity impacts; water availability; soil changes and landscape impacts, including impacts on archaeological sites (ADAS, 2006). The impacts of biomass crop production will depend on the area where the energy plantation is situated. Overall, plantations can last 15–20 years and careful planning and judicious site choice for an energy plantation within the landscape, can enhance biodiversity (Woods et al., 2006). Measures to enhance biodiversity include leaving a buffer zone between the plantation and established woodland or hedgerows, to preserve the habitat for biodiversity conservation (Woods et al., 2006). Due to their large leaf area, willow and poplar intercept more rainfall than agricultural crops, reducing the amount of water reaching the soil and the aquifer. Willow species have high transpiration rates and deep root systems and can tap into underground water in times of low rainfall (Woods et al., 2006). SRC willow and poplar have higher water usage than any annual agricultural crop and the high water requirement of willow can constrain its use to areas where sufficient irrigation water is available (RCEP, 2004). Careful choice of site of SRC plantations is therefore extremely important in areas of low rainfall, or in areas where there is a high human consumption of water. Sewage or sewage sludge can be used to irrigate willow and will provide both additional nutrients and water. However, the high heavy metal content of sewage used as fertilizer, can raise concerns over heavy metal content of soils. Willow can also be used to reduce soil contamination through absorption of heavy metals, though this may affect the composition of the ash following the willow’s combustion. According to DEFRA (2002), SRC has large areas of open ground within the crop during establishment. On light, sandy soils this can lead to wind erosion of the soils and on sloping sites, soils can be eroded following heavy rain. During harvesting time, the use of machinery must be carefully considered to avoid erosion. Changing land use from an environmental perspective impacts not only on the physical characteristics of land, such as land carbon stocks, biodiversity and water but also has a visual impact. Changing from arable cropping to willow coppicing or Miscanthus cultivation over a large area, would have a significant impact on the landscape due to the height of the crops (RCEP, 2004). Such impacts can be avoided and several guidelines in England have been produced in recognition of the visual amenity of the landscape (English Heritage, 2006). As part of the RELU-Biomass project in

M.J. Black et al. / Industrial Crops and Products 34 (2011) 1332–1339 Table 2 Area of certified woodland in 2009 in thousands of hectares (FC, 2009).

UK

FC/FS

Non-FC/FS

Total woodland area certified

814

469

128

1. Areas as at 31 March 2009. 2. FC/FS = Forestry Commission/ Forest Service; Non-FC/FS = all other woodland, including some other publicly owned woodland. 3. All certified woodland is under the Forest Stewardship Council (FSC) scheme. 4. The estimates are based on UK data published by FSC, supplemented by data from individual certificates and other sources. Where possible, figures are for the woodland area certified, rather than the land area certified.

the UK (www.relu-biomass.org.uk), a number of these issues have been assessed using a Sustainability Assessment Framework (SAF), to provide information to inform land-use planning in the development and expansions of biomass crop areas (Haughton et al., 2009). In the UK there is currently no certification system in place which addresses the sustainability of dedicated biomass crops, grown for the production of liquid road transport fuels, as required by the RTFO. The sustainability of biomass for bioenergy and biofuel supply chains is currently an area of development in both the UK and the EU. There is however, woodland certification under the UK Forestry Standard which is mandatory for all Forestry Commission (FC) approved planting/felling and there is potential to extend this to agricultural and planning approved forestry. Additionally, the more rigorous voluntary UK Woodland Assurance Standard is internationally compliant against the Forest Stewardship Council (FSC) requirements; this would allow UK forest biomass to be FSC certified (Diaz-Chavez, 2008). The 10 principles of the FSC are as follows: • • • • • • • • • •

Principle 1: Compliance with laws and FSC Principles. Principle 2: Tenure and use rights and responsibilities. Principle 3: Indigenous peoples’ rights. Principle 4: Community relations and worker’s rights. Principle 5: Benefits from the forest. Principle 6: Environmental impact. Principle 7: Management plan. Principle 8: Monitoring and assessment. Principle 9: Maintenance of high conservation value forests. Principle 10: Plantations.

The forest area (including coniferous and broadleaf) in the UK is of 2841 thousand hectares (FC, 2009). The percentage of certified forest area in the UK is mainly under the Forestry Commission/Forestry Service (FC/FS) system and is presented in Table 2. 4.2. Conversion module In 2010, bioethanol is produced at scale, from the direct fermentation of sugar or fermentation of sugar derived from starch. Fermentation technologies for sugar and starch crops are very well developed, but have certain limits namely that the crops utilized often have a high food application value, and their sugar yield per hectare is very low compared with the most prevalent forms of sugar in nature (i.e. cellulose and hemicellulose) (Hamelinck et al., 2005). Furthermore, it has been suggested (Farrel et al., 2006) that only lignocellulosic ethanol offers considerable GHG emission reductions compared with fossil fuel. However, the conversion process for lignocellulosic-based feedstock to ethanol is more complex than processes using sugar or starch based feedstocks (Galbe and Zacchi, 1993; McMillan, 1997; Zaldivar et al., 2001; Hahn-Hägerdal et al., 2006). Although various bioconversion processes are employed for lignocellulosic conversion, a general process includes the main steps shown in Fig. 5.

Lignocellulosic feedstock

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Size Reducon

Pretreatment

Detoxificaon

Disllaon

Fermentaon

Enzymac Hydrolysis

Fig. 5. General process for lignocellulosic-based ethanol production.

Fig. 6. Root cause analysis of lignocellulosic ethanol conversion (Hosseini and Shah, 2009a).

Size reduction and pretreatment are required to make cellulose more accessible to enzymes, so that hydrolysis of the cellulose fraction to glucose can be achieved more rapidly and with greater yield (Wiel et al., 1994). Although numerous pretreatment methods such as steam explosion, lime pretreatment, Ammonia Fiber Explosion (AFEX) and organic solvent pretreatment are extensively reported in the literature, acid pretreatment is still the choice of several model processes (Aden et al., 2002; Mosier et al., 2005). Hydrothermal pretreatment usually involves exposure of lignocellulosic material to a chemical (e.g. acid) at elevated temperatures for a period of time, depending on the physiochemical structure of the biomass, until most C5 sugars are solublised prior to enzymatic hydrolysis. The main drawback of pretreatment is that it leads to the formation, in addition to sugars, of unwanted compounds that are inhibitory to ethanol-producing microorganisms (López et al., 2004). To overcome the negative effect of inhibitors on subsequent process steps it is common to detoxify the hydrolyzate; biological, physical, and chemical methods have been employed for this detoxification (Palmqvist and Hahn-Hägerdal, 2000). Current fuel ethanol research deals with process engineering trends for improving the efficiency of bioethanol production and several studies can be found in the literature focusing on improvement of each processing step. However, in order for lignocellulosic-based bioethanol to be competitive with fossil fuel, further cost and energy reductions in conversion technologies are required. Recent studies by Hosseini and Shah (2009a), have taken a Root Cause Analysis (RCA) approach to identify the causes of inefficiencies within lignocellulosic ethanol conversion. This approach (Fig. 6) identifies 3 of the 4 main causes as being the result inefficient pre-treatment, with 2 of these being the result of low digestibility of fibre. One of the pre-treatments of biomass for lignocellulosic ethanol production is the reduction of particle size. This has been identified as being a significant contributor to overall

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Fig. 7. Severity factor vs. particle size radius for woodchip processing.

incorporated into the conversions module of the supply chain LCA. Pretreatment has been viewed as one of the most expensive and energy intensive processing steps in the lignocellulosic biomass-tofermentable sugars conversion process. A sub-module that models the diffusion of liquid or steam in the biomass and takes into account the interrelationship between chip size and time, allows the energy requirements and GHG emissions for this element of the conversion chain to be derived (and optimized) for a wide variety of feedstock formats. Furthermore, in addition to providing data input to the LCA the sub-module also provides input to overall process improvement by identification of the optimum chip size that permits effective pre-treatment at minimized energy requirement for particle size reduction by grinding. In this example, the proposed optimization method indicates that an average energy saving equivalent to a 5% improvement in the yield of biomass to ethanol conversion process can be achieved. Employing such process modelling approaches enable understanding of how each step in the processing chain affects the overall efficiency, energy consumption and GHG emission of a biofuel supply chain.

5. Discussion

Fig. 8. Energy required for the pretreatment of biomass particles with different radii.

energy requirements in a dilute acid pre-treatment process (Lynd, 2003). A multiscale modelling approach has also been undertaken in order to assess the role of wood chip (particle) size and processing time as factors for improving overall process efficiency (Hosseini and Shah, 2009b). The diffusion of liquid or steam into biomass was modeled to identify the optimum chip size to minimise the energy requirement for grinding and hydration pre-treatments. Reviewing a range of particle sizes from 1 to 10 mm and relying on data reported in the literature for grinding energies and biomass moisture contents (Mani et al., 2004) the model reports severity factor (i.e. the interrelationship of time, temperature and acid concentration (Garrote et al., 1999) and energy as functions of particle size (Figs. 7 and 8). Using the typical data the model implied that at radius of 5 mm, temperature 180 ◦ C and residence of 10 min, it is possible to get the maximum yield with minimum energy input for switchgrass. Our model shows that the severity of all hydrothermal pretreatment methods decreases with increasing chip size. However, in the case of steam explosion, this decrease is sharper (Figs. 7 and 8). Based on typical data used for optimization, it was shown that optimizing biomass chip size can result in up to a 50% improvement in the energy efficiency of pretreatment methods; this can account for up to 5% of the total conversion chain’s yield. It is believed that given the characteristic data of any hydrothermal pretreatment system, the method proposed here could be employed to find the chip size that minimizes the energy requirement of the system. De-coupling this aspect of lignocellulosic pre-treatment allows an extensive analysis to be undertaken using a process modelling approach. The model currently makes a number of assumptions and adopts “typical” values due to lack of data availability specifically for willow biomass chips. However, the modelling approach sets parameters which can then be improved upon as data becomes available. This discrete module can then be

Very recent policy developments in Europe and the USA have focused on implementing ‘sustainable biofuels’. Providing workable methodologies that first, define what is meant by ‘sustainable’, and then implementing assessment criteria and indicators that can lead to either rewards or penalties for biofuel producers and consumers (depending on the performance of those biofuels against environmental, including GHG, economic and social performance), has challenged the scientific and policy making communities. However, in developing methodologies, critical issues have been highlighted for sustainable land management in general, with important lessons for the wider agricultural and forestry sectors. Quantifying the GHG emissions of biofuel supply chains has been a central component of these policy developments, which in some cases have been devised with the primary purpose of reducing GHG emissions from liquid road transport fuels. This has required the development of LCA methodologies which are capable of accounting for the production of biofuels and also co-products, which are important economic contributors to the viability of many biofuel supply chains. Complementing GHG LCA with broader sustainability assessments can ensure that important non-GHG environmental and social impacts are accounted for. The activities associated with growing biomass crops for biofuel production and consequential effects (indirect effects) have been highlighted as being key contributors to GHG emissions. Furthermore, the sustainability criteria for biofuels have been directly attributed to the feedstock production module of biofuel production in the UK policy approach (the RTFO). The advantages of taking a modular approach to a supply chain LCA are that activities which are specific to a particular process (crop-growing or biomass conversion) can be reviewed and revised as new data become available. There are many ongoing issues around both the methodological approaches to LCA and sustainability and achieving consensus on the approaches taken and data used. For LCA, the limitations have been described by Slade et al. (2009) and are attributed to decisions made in designing the LCA (e.g. definition of systems boundaries, allocation of impacts, and choice of data sources); availability of good quality data; loss of resolution in “simplified” models and rebound effects. These issues have been addressed specifically for ethanol from lignocellulosic biomass (Singh et al., in press) taking into consideration methodological design from biomass choice,

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country of origin to functional unit, systems boundaries and the inclusion of land use change in the analysis. The issues embedded in the development and definition of sustainability criteria are equally complex, not least because of the differences in emphasis or value placed on specific criteria by different cultures, communities, organisations or supply chain stakeholders. Aspects of sustainability which are difficult to resolve include the development of practical systems for which evidence can be provided, for the various and diverse supply chains which provide feedstock for bioenergy or biofuel production. As with LCA, the availability of data on land use is also problematic in terms of practical data on carbon stocks, water availability and use, farming practices and biodiversity, as well as historical data on land use and changes in land use. The regulation of sustainability measures, by local or national legislation is not universal and for many countries, for many environmental and social issues, legislation does not exist. In reviewing supply chains based on biomass feedstocks for bioenergy provision there are a range of criteria which must be considered both at the local, national and global level. Methodologies to address LCA and sustainability are advancing although the availability of practical data remains an issue. In developing modules for LCA and sustainability of willow biomass supply chains these factors are being considered and the studies being carried out for willow grown in the UK contribute to the growing body of data available for biomass crops. References ADAS, 2006. Potential Impacts of Future Energy Policy on UK Biodiversity (SD0307). Report for DEFRA. ADAS, UK. Aden, A., Ruth, M., Ibsen, K., Jechura, J., Neeve, Sheehan, J., Wallace, B., Montague, L., Slayton, A., 2002. Lignocellulosic Biomass to Ethanol Process Design and Economics Utilizing Co-current Dilute Acid Prehydrolysis and Enzymatic Hydrolysis for Corn Stover. (Storming Media). Aylott, M.J., Casella, E., Tubby, I., Street, N.R., Smith, P., Taylor, G., 2008. Yield and spatial supply of bioenergy poplar and willow short-rotation coppice in the UK. New Phytologist 178, 358–370. de Almeida, P., Silva, P.D., 2009. The peak of oil production – timings and market recognition. Energy Policy 37, 1267–1276. Burney, J.A., Davis, S.J., Lobell, D.B., 2010. Greenhouse gas mitigation by agricultural intensification. PNAS 107 (26), 12052–12057. Cripps, R.E., Eley, k., Leak, D.J., Rudd, B., Taylor, M., Todd, M., Boakes, S., Martin, S., Atkinson, T., 2009. Metabolic engineering of Geobacillus thermoglucosidasius for high yield ethanol production. Metabolic Engineering 11 (6), 398–408. van Dam, J., Junginger, M., Faaij, A., Jürgens, I., Best, G., Fritsche, U., 2008. Overview of the recent developments in sustainable biomass certification. Biomass and Bioenergy 32, 749–780. DEFRA, 2002. Growing Short Rotation Coppice. Best Practice Guidelines For Applicants to DEFRA’S Energy Crops Scheme. England Rural Development Programme, London, UK. Diaz-Chavez, R., 2008. Sustainability, environmental and social issues. In: RosilloCalle, et al. (Eds.), Evaluation of the Potential for Sustainable Supply of Biomass for Electricity Generation for UK Power Plants. Confidential Report for the Industry in UK. English Heritage, 2006. Biomass Energy and the Historic Environment. English Heritage, UK. EU, 2008. Commission of the European Communities. COM (2008) 30 final., http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=COM:2008:0030:FIN: EN:PDF. EU Directive, 2009a. Directive 2009/30/EC of the European Parliament, PE-CONS 3740/08, 2009. EU Directive, 2009b. Directive 2009/28/ECof the European Parliament, PE-CONS 3736/08, 2009. Farrel, A.E., Plevin, R.J., Turner, B.T., Jones, A.D., O’Hare, M., Kammen, D.M., 2006. Ethanol can contribute to energy and environmental goals. Science 311, 506–508. FC, 2009. Forestry Facts & Figures 2009. A Summary of Statistics about Woodland and Forestry. Forestry Commission, UK. Friends of the Earth, February 2008. Agrofuels: Fuelling or Fooling Europe? Friends of the Earth Briefing document. Galbe, M., Zacchi, G., 1993. Simulation of processes for the conversion of lignocellulosics. In: Bioconversion of Forest and Agricultural Plant Residues , p. 291.

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