Comparative environmental and energy profiles of potential bioenergy production chains in Southern Europe

Journal of Cleaner Production xxx (2014) 1e13

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Comparative environmental and energy profiles of potential bioenergy production chains in Southern Europe Sara González-García a, b, *, Ana Cláudia Dias a, Sónia Clermidy c, d, Antony Benoist d, Véronique Bellon Maurel c, Carles M. Gasol e, Xavier Gabarrell e, Luis Arroja a a

CESAM, Department of Environment and Planning, University of Aveiro, 3810-193 Aveiro, Portugal Department of Chemical Engineering, Institute of Technology, University of Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain Irstea, UMR ITAP, ELSA Group, 351 rue J F Breton, 34 196 Montpellier Cedex 5, France d CIRAD, BioWooEB Research Unit (Biomass, Wood, Energy, Bioproducts), TA B-114/16, 73 rue Jean-François Breton, 34398 Montpellier Cedex 5, France e SosteniPrA (UAB-IRTA-Inèdit), Institute of Environmental Science and Technology (ICTA), Universitat Autònoma de Barcelona (UAB), School of Engineering, Campus de la UAB, Bellaterra (Cerdanyola del Vallès), 08193 Barcelona, Catalonia, Spain b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 24 July 2013 Received in revised form 8 April 2014 Accepted 9 April 2014 Available online xxx

In this study, life cycle assessment (LCA) is used to assess and compare the environmental and energy profiles of three potential bioenergy production chains using different available feedstocks in Southern European countries. Two wastes, vineyard pruning and eucalypt logging residues, and a wooden energy crop, poplar, were examined in detail. The comparative LCA study showed that the use of poplar biomass for bioenergy production has a greater impact than the use of vineyard pruning and logging residues. The contribution from the poplarcultivation-related activities considerably affected the results, as all the activities from field preparation to harvesting have been included within the system boundaries. In contrast, all the activities performed in the vineyard and forest prior to collection of the residues have not been computed in both scenarios since they have been allocated to the driving force of these stands: grapes and roundwood, respectively. The results support the idea that forest and agricultural waste would be an interesting and potential raw material for bioenergy purposes. However, further analysis should focus on these potential bioenergy sources, namely in terms of their availability and technical burning conditions, in order to meet energy requirements. Moreover, the environmental results were compared with others from literature corresponding to electricity production using alternative biomass sources and fossil fuels. In all the categories considered for comparison, environmental benefits were reported for the electricity production using a biomass source. However, these results must be carefully used since other issues e such as production costs, water availability and land use e should be considered. Ó 2014 Elsevier Ltd. All rights reserved.

Keywords: Eucalypt Life cycle assessment Logging residues Populus spp. Short rotation coppice Vineyard pruning residues

1. Introduction 1.1. The role of bioenergy production in Europe The European Union’s energy and climate change strategies (Directive 2009/28/EC) aim to promote the use of energy from

* Corresponding author. Department of Chemical Engineering, University of Santiago de Compostela, E-15782 Santiago de Compostela, Spain. Tel.: þ35 1234370387. E-mail addresses: [email protected], [email protected], sara.gonzalez@ usc.es (S. González-García).

renewable sources. Thus, a share of 20% of renewable energy in the European energy mix has been proposed by 2020 (Directive, 2009/ 28/EC, 2009). In fact, in recent years the share of renewable energy in the European mix has increased considerably (Muench and Guenther, 2013). European countries do not have great reserves of petroleum or natural gas; therefore, they need to import large amounts of fossil fuels (Gasol et al., 2009a). However, fossil fuels are not only used for energy production but also for the major part of material and chemical production as well as transport. From an environmental point of view, increasing dependence on bioenergy systems could result in net reductions of greenhouse gas (GHG) emissions into the atmosphere. Bioenergy systems include a full range of bioenergy products e such as biodiesel, bioethanol,

http://dx.doi.org/10.1016/j.jclepro.2014.04.022 0959-6526/Ó 2014 Elsevier Ltd. All rights reserved.

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biogas, electricity and heat e and all of them are derived from a large spectrum of biomass feedstocks such as wood, grasses, energy crops and agricultural/forest residues (Kaltschmitt et al., 1997; Gold and Seuring, 2011). Thus, increasing biomass-based energy production is an interesting alternative to traditional energy sources; however, its sustainability depends on biomass availability, management and optimised use (European Climate Foundation, 2010). 1.2. Biomass derived bioenergy: advantages and disadvantages The growth of biomass, as a source for energy production, remains slow across Europe. One of the main reasons is the amount of uncertainty surrounding various aspects of the attractiveness of biomass as a renewable energy source. These uncertainties are related to the following areas: (i) the adequate and secure supply of biomass due to the need for food and feed production, (ii) the economic competitiveness as an energy source with or without subsidies; (iii) the environmental benefits in comparison with fossil fuels, and (iv) the frameworks to ensure its sustainability (European Climate Foundation, 2010; Fantozzi and Buratti, 2010; Gold and Seuring, 2011). Several studies have been performed to forecast the contribution of biomass to the future energy supply at a regional and global level (Rentizelas et al., 2009; Gold and Seuring, 2011). According to these studies, biomass use will considerably increase; however, there is no consensus on the maximum level biomass exploitation could achieve (Rentizelas et al., 2009). Furthermore, there is the question of whether biomass use is a carbon-neutral process (Tabata and Okuda, 2012). Carbon dioxide is taken from the atmosphere by photosynthesis and stored temporally in living tissues before releasing back into the atmosphere. Nevertheless, activities involved in the biomass production processes, such as agricultural/ forest practices or even agricultural/forest residues collection, involve GHG emissions derived from energy-intensive operations associated with high diesel requirements; thus, this contribution should not be considered negligible. In addition, the costs of biomass logistical and technological operations constitute important barriers when considering the promotion of biomass utilisation for energy purposes (Buchholz et al., 2009; Iakovou et al., 2010). The term biomass encompasses different fuel types: dedicated energy crops grown on agricultural and/or marginal lands, forestbased products (by-products such as black liquor and sawdust; roundwood and forest residues such as branches and stumps), agricultural residues (straw, stover, etc.) and waste (industrial waste, municipal solid waste, manure, sewage, sludge, recovered wood, etc.). Forest and agricultural activities generate significant amounts of residues suitable for energy purposes (Scarlat et al., 2011). Utilising biomass residues and wastes as energy feedstocks present an important role in the future European energy profile (Heinimö and Junginger, 2009; López-Rodríguez et al., 2009). Many studies have documented biomass residues as forming a significant part of the current and future energy potential (Berndes et al., 2003; Ekman et al., 2013; Gold and Seuring, 2011; Heinimö and Junginger, 2009; Parikka, 2004; Yamamoto et al., 2001). However, the main limitation of this process is the availability of these resources at the local level. Nowadays, special attention is being paid to the promotion of energy crops (herbaceous crops and short rotation coppices e SRC e as potential energy sources related to high biomass and bioenergy yields (Bentini and Martelli, 2013; Xu et al., 2013). However, the high yields derive from intensive management regimes (Bergante et al., 2010; González-García et al., 2012b). In this context, wood biomass from energy plantations is receiving

increasing interest worldwide as a means of meeting regional demands for bioenergy production (McKendry, 2002). Short rotation coppices are gaining special attention in many countries for their multiple advantages related with efficient land use and relatively low economic investments (González-García et al., 2012a). However, apart from environmental and efficiency issues related with the use of these biomass sources, there is a major concern linked to its competitiveness against food and feed crops for land use (Bentini and Martelli, 2013; Gold and Suering, 2011). This competition is more outstanding in developing countries and derives from water and food shortages, losses of diversity, impoverishment of soil quality and increases of food/feed prices. 1.3. Environmental studies of bioenergy production chains e literature review Bioenergy production chains have been assessed in the existing literature from environmental and energy points of view (Wihersaari, 2005; Gasol et al., 2009a; Butnar et al., 2010; Fantozzi and Buratti, 2010; Gold and Seuring, 2011; Whittaker et al., 2011; Muench and Guenther, 2013). Special attention has been paid to GHG emission savings and energy balances of liquid biofuels production; however, electricity and heat represent around 90% of total biomass-derived bioenergy (Muench and Guenther, 2013). Mentzer et al. (2001) defined a “supply chain” as a set of multiple entities directly involved in the upstream and downstream flows of products or services from a source to a customer. In a bioenergy supply chain, the following components should be included: biomass production, harvesting and collection (from single or multiple locations), biomass storage and transport throughout the bioenergy chain (in one or more intermediate locations), loading and unloading processes, biomass pretreatment and bioenergy production (Rentizelas et al., 2009; Iakovou et al., 2010; Gold and Seuring, 2011). Therefore, there is a large variety of bioenergy supply-chain designs that draw very different conclusions, assumptions, methodological choices and environmental results (Muench and Guenther, 2013). The purpose of this study is to assess and compare the environmental impacts and energy balances associated with biomass production and/or management and its further conversion into electricity in a power plant e potentially located in Southern Europe. Three different types of solid biomass available in that region have been proposed for assessment and identified as potential feedstocks: (a) agricultural vineyard pruning residues, (b) logging residues from eucalypt (Eucalyptus globulus) stands, and (c) biomass from energy-dedicated poplar (Populus spp.) plantations. Thus, a dedicated woody energy crop and available agricultural/ forest residues have been considered for analysis. The assessment has been performed by applying life cycle assessment (LCA) methodology in an attributional approach e a common and standardised tool for evaluating and reporting the environmental consequences of services and products (ISO, 2006). This environmental methodology has widely been considered in numerous bioenergy studies in order to determine their environmental profiles and to promote their use instead of conventional systems (Butnar et al., 2010; Gasol et al., 2009a; González-García et al., 2010; Muench and Guenther, 2013; Whittaker et al., 2011). According to published studies, results vary widely depending both on biomass source and methodological choices (Muench and Guenther, 2013). Different methodological choices can be taken into account in an LCA study and there is not a consensus concerning them in spite of the standardisation of LCA. These choices are related to the definition of the system boundaries, the carbon cycle consideration, the selection of the functional unit, allocation procedures or the characterisation method considered (Muench

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and Guenther, 2013). Thus, a comprehensive and transparent analysis must be performed in order to facilitate comparisons between different bioenergy systems. Therefore, these differences and discussions might (re-)define the role of biomass in the future European energy mix. Through this study, that role may be completely reconsidered when only the biomass from waste and residues is used in comparison with that from agricultural and forest lands dedicated to biomass production.

This special type of forestry is concerned with maximisation of wood biomass output per hectare for energy production (Gasol et al., 2009a,b; González-García et al., 2012b). In addition, this crop has proved to be very well suited for biomass production due to its rapid juvenile growth, high photosynthetic capacity, superior growth performance and large wood biomass production in a single growing season (Pontailler et al., 1999; González-García et al., 2012b).

2. Materials and methods

2.2.1. Vineyard pruning residues Vineyards are typical throughout the Mediterranean region. In some countries, such as France, Italy, Portugal and Spain, they assume cultural, economic and aesthetic values which characterise specific regions e as an example, the Douro Valley region is classified as a World Heritage Site. Vineyards require much tending, including annual pruning, which generates a high amount of residual biomass (at least 1 oven dry tonne$ha1) (Spinelli et al., 2010). These residues must be removed from the field before implementing any other tending measures (Spinelli et al., 2012). Until recently, pruning residues were considered as waste without any revenue (Spinelli et al., 2010). This residual biomass can be used as an alternative to other biomass sources for energy and industrial purposes. However, undesirable harvesting conditions make the collection of these residues difficult and involve low biomass yields. The extraction, grinding and storage of viticulture pruning residues in a representative wine field, located in the French region of Languedoc Roussillon (the largest wine growing area in the world), has been considered for assessment in this study.

LCA is defined as a methodology for the comprehensive assessment of the impact that a product or service has on the environment throughout its life cycle. The International Organisation for Standardisation (ISO) provides guidelines for conducting an LCA within the ISO 14040 series (ISO, 2006). LCA is an objective process of evaluating the environmental burdens associated with a product by identifying natural resources consumption and emissions with environmental compartments and identifying and implementing opportunities of attaining environmental improvements (ISO, 2006). 2.1. Goal and functional unit The aim of the study is to assess and compare the environmental and energy impacts on a life cycle horizon of three different potential feedstocks for electricity production: an agricultural residue, a forest residue and an SRC. The reference functional unit for the inventory analysis, and for both environmental and energy assessments, is 1 kWh of electricity produced from each biomass source in a power plant with an energy efficiency of 20%. Only electricity has been considered as the main product of the biomass plant as this is the current widespread situation in Southern European countries such as Portugal. This energy-output functional unit is recommended in numerous bioenergy LCA studies as it comprises energy generation and presents independence from biomass feedstock (Muench and Guenther, 2013). 2.2. Description of biomass sources Three different feedstocks have been considered for assessment in this study: vineyard pruning residues, eucalypt logging residues and wood biomass from dedicated poplar plantations. Eucalypt logging residues represent, on average, 53% of the total logging residues produced in Portugal (Dias and Azevedo, 2004; Mateus, 2007; Viana et al., 2010) and they are one of the main fuels of the existing biomass power plants in that country. These power plants have a total installed capacity of 106 MW (E2P, 2012; DGEG, 2012), and new power plants fuelled by forest biomass are planned in order to achieve an installed capacity of 250 MW by 2020 (Conselho de Ministros, 2010). Eucalypt logging residues may also be a relevant feedstock for other regions such as Northern Spain. Vineyard pruning residues are a potentially important fuel in Southern Europe, as this region encompasses the three major world wine producers: France, Italy and Spain (OIC, 2013). Vineyards require much tending, including an annual pruning. Pruning activities involve the production of residual biomass (Spinelli et al., 2010), which could be used for energy. Currently, this is not the main destination of these residues, which are mainly left in the soil to decay, are burnt in the field, or have industrial uses e e.g., particleboard manufacture (Clermidy, 2012; Ntalos and Grigoriou, 2002). Concerning poplar biomass, this energy woody crop is widely cultivated in numerous European countries such as Italy and Spain.

2.2.2. Eucalypt logging residues Forest management activities (final cutting, thinning, pruning, cleaning, stump removal) involve the production of large amounts of forest residues. Depending on the management regime, the residue yield varies. Commonly, some of the residue is not removed from the forest site; this is to protect the forest floor from damage by heavy machinery and for ecological reasons (Whittaker et al., 2011). In this study, logging residues from eucalypt stands have been considered for assessment as a potential biomass source for energy purposes. Activities carried out in Portuguese eucalypt stands (biomass collection, chipping and loading onto trucks) have been considered for assessment. Portugal has been chosen as the representative European country due to the relevance of eucalypt forest in this country. In fact, eucalypt is the forest species with the largest occupation area in Portugal, accounting for 26% of the total forest area (ICNF, 2013). 2.2.3. Poplar biomass Poplar is an SRC due to its high biomass yields in Mediterranean countries. However, poplar competes with other woody crops in areas having land and water availability (Gasol et al., 2009a); hence, its cultivation in marginal areas is under research. A standard hectare of experimental plot cultivated in Soria (Spain) has been considered in this study. The poplar plantation was established at a density of 10,000 cuttings ha1 in a cultivation period of 16 years and three consecutive cycles of 5 years each (Gasol et al., 2009a). The poplar cultivation was irrigated with water in order to increase the biomass yield (13.5 t ha1 year1 e dry basis). All activities involved in the poplar cultivation process have been considered for assessment such as site preparation, planting, agrochemicals applications, and cuttings, as well as stools killdown and collection. 2.3. System boundaries Three scenarios were defined in this study for potential bioenergy production e taking into account all processes related with

Please cite this article in press as: González-García, S., et al., Comparative environmental and energy profiles of potential bioenergy production chains in Southern Europe, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.04.022

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Fig. 1. Scheme of the vineyard pruning residues system boundary.

the biomass production, management and final combustion in a power plant. It has been assumed that the three biomass sources could be burned in similar power plants. There are not, to date, any power plants operating with poplar and vineyard pruning residues. Information regarding these specific combustion processes was also not available in the literature and databases consulted. However, eucalypt logging residues are a typical biomass source in Portuguese power plants. Thus, air emissions derived from the combustion of the three feedstocks have been estimated e taking into account the biomass composition. The comparison between the three bioenergy systems is based on the electricity produced by means of their combustion in a power plant. Therefore, potential electricity production has been calculated for each feedstock taking into account its low heating value (LHV) and moisture content. A 1 MWe biomass power plant with an efficiency of 20%, regardless of the biomass source, has been considered for assessment. 2.3.1. Scenario A (ScA): vineyard pruning residues This process starts in the field after the grapes have been harvested and ends when the residues delivered to the power plant are burned. The processes presented in Fig. 1 were included within the system boundaries. Pruning residues are extracted from fields and simultaneously grinded in order to reduce the volume. These chips are sent to a container connected to a tractor. Compact vineyard tractors are commonly used in these activities since machinery is constrained by the narrow spaces in the vineyard (Spinelli et al., 2010). An average of 2 t$ha1 (15% moisture) of pruning biomass is collected in the French vineyards under study. The chips are then transported to a cooperative for storage in ventilated storehouses. This transportation is performed with a tractor. Biomass losses of 2.5%, 1% and 2.5% take place in the extraction, transportation and storage steps, respectively. Pruning chips have a density of 190 kg m3, so the load weight is a limiting factor for transport that must be considered in calculations. The harvesting of vineyard pruning residues for energy purposes involves the removal of a nutrient source, and organic matter, from the actual vineyard. Phosphorus (P) and potassium (K) levels in the field are sufficient

for consecutive vineyard activities, but nitrogen (N) loss is a remarkably important and limiting factor. Thus, within the system boundaries, the supply of an organic fertiliser (in this case, compost) has been considered in order to compensate for nitrogen loss. The application of compost in the field (3% N) at a ratio of 350 kg ha1 has been assumed; however, the compost production has been excluded from assessment. Derived emissions from compost application have also been calculated. Finally, vineyard pruning residues are burned in the power plant. Further transport and distribution of electricity to final consumers have been excluded from the system boundaries. The production of the infrastructure and machinery requirements have been included within the system boundaries. 2.3.2. Scenario B (ScB): eucalypt logging residues This process starts in the forest after the final felling and ends when the wood chips are burned at the power plant. Thus, all activities that take place in the forest e such as logging residues forwarding, feeding of the residues into the chipper and the chipping process e were assessed in detail. Wood chips are then transported by trucks to the power plant where they are stored and, finally, burned. An average density of 280 kg m3 has been assumed for the chips obtained from logging residues (Gasol et al., 2009b). Fig. 2 details the processes considered within this scenario. As in Scenario A, the same assumptions have been considered concerning infrastructure and machinery production for the power plant. 2.3.3. Scenario C (ScC): poplar biomass Poplar biomass is cultivated in order to produce biomass for energy purposes. Thus, all activities involved in the cultivation process have been considered within the system boundaries up to the biomass combustion in the power plant. Field preparation activities (such as subsoiling and mechanical weed control), planting, first cutting, fertilising, pesticide application, harvesting and field recovery related activities (stools killdown and collection) were analysed in detail. After the harvesting, the stems are field stored and naturally dried to an average moisture content of 20%. Stems are transported in bales (w310 kg m3 as packed stem density) to

Fig. 2. Scheme of the eucalypt logging residues system boundary.

Please cite this article in press as: González-García, S., et al., Comparative environmental and energy profiles of potential bioenergy production chains in Southern Europe, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.04.022

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Fig. 3. Scheme of the poplar biomass system boundary.

the power plant where they are chipped (according to the delivery schedule), stored and, finally, burned. More detailed information concerning poplar cultivation can be found in Gasol et al. (2009b). Fig. 3 reports all the activities involved within the system boundaries of this scenario. 2.4. Inventory analysis Primary and site-specific inventory data, such as the information concerning operation activities and input rates, were depicted for each scenario in Tables 1e3. For each specific process reported in Figs. 1e3, the following inventory data were considered: the amount of machinery needed for each specific process (tractors, agricultural and forest equipment, trucks), fuel consumption for agricultural and forest activities as well as transport, and electricity requirements for storage activities and infrastructure production. Concerning the poplar-based scenario, besides the field activities, the production of other inputs to the field, such as agrochemicals (fertilisers, herbicides and pesticides), and outputs from the field, such as derived emissions from fertiliser application, have been quantified. In all scenarios, combustion emissions from fossil fuel use in the machinery, as well as heavy-metal emissions from tyre abrasion, have also been included within the systems boundaries. Inventory data related with the vineyard pruning residues collection, distribution and storage in the cooperative and power plants were collected directly from farmers within the framework of the Ecotech-Sudoe project.1 The data collection was performed by means of surveys in vineyards located in the Languedoc

1

http://www.ecotechsudoe.eu.

Roussillon region. Diffuse emissions from compost application were calculated according to Bellon-Maurel et al. (2013). Combustion emissions derived from the machines used in the pruning residues collection activities were taken from the Ecoinvent Ò Database (2007). The same database was considered for collecting the data corresponding to transport activities and the ventilation system in the storage facilities. Combustion emission factors for the power plant have been taken from the existing literature (IPCC, 2006; EMEP/EEA, 2009) and assume a sulphur content of 0.03% (%w/w). Biogenic CO2 emissions derived from the combustion of biomass are compensated with the CO2 uptake during the biomass growth. A short description of inventory data, per functional unit, for Scenario A is displayed in Table 1. Regarding the fuel consumption required in the collection, chipping and loading of eucalypt logging residues onto trucks, the average data for Portuguese stands were considered and taken from Dias (2014). Information relative to the biomass storage at the power plant was taken from the Ecoinvent Ò Database (2007). This information was completed with combustion emission factors and machinery production data also taken from the Ecoinvent Ò Database (2007). In Portuguese eucalypt stands, on average, around 50% of logging residues are left on the forest floor and the remaining 50% are collected for bioenergy (Dias, 2014). Thus, it has been considered that their removal does not involve important nutrient and organic matter losses. Concerning combustion emissions in the power plant, a sulphur content of 0.01% (%w/w) (Gonçalves et al., 2010) and combustion factors have been assumed from the existing literature (IPCC, 2006; EMEP/EEA, 2009). As in Scenario A, biogenic CO2 emissions derived from the combustion of biomass is compensated with the CO2 uptake during the biomass growth. A summary of inventory data related to Scenario B is reported in Table 2.

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Table 1 Data summary for the vineyard pruning residues scenario per kWh of electricity produced (1.48 kg feedstock required). Unit Inputs Materials Diesel Tractor Trailer Agricultural tillage Compost Lubricating oil Energy Electricity (chipping) Electricitya Transport Tractor Truck Outputs Product Electricity Emissions to air CO2 NOx CO SO2 CH4 N2O NMVOC Emissions to water NO 3 PO3 4 a

Value

g g g g kg g

3.24 0.185 0.513 0.310 0.259 1.38$102

kWh kWh

0.03 2.00$105

kg km kg km

14 98

kWh

1

g g g mg mg mg mg

34.7 1.70 1.75 0.642 0.602 72 186

mg mg

1.54 65.4

Storage in field and power plant as well as compost management.

Inventory data corresponding to the agricultural activities carried out in a representative and real poplar plantation (that is, fossil fuel requirements and agrochemicals doses) were taken from Gasol et al. (2009b) and González-García et al. (2010). These primary data were completed with secondary data taken from the Ecoinvent Ò Database (2007) that relate to machinery, fossil fuels and agrochemicals production. Combustion emission factors from the IPCC (2006) and the EMEP/EEA (2003) have been assumed for the poplar-based scenario e taking into account a sulphur content of 0.03% (%w/w). The same assumption, as in the previous scenarios, has been assumed for biogenic CO2 emissions. Table 2 Data summary for the eucalypt logging residues scenario per kWh of electricity produced (2.75 kg feedstock required).

Inputs Materials Diesel Forest machines Forest tillage Lubricating oil Energy Electricity (chipping) Electricity (storage in power plant) Transport Truck Outputs Product Electricity Emissions to air CO2 NOx CO SO2 CH4 N2O NMVOC

Table 3 Data summary for the poplar biomass scenario per kWh of electricity produced (1.55 kg feedstock required).

Unit

Value

g g g g

15.2 1.59 1.75 1.38$102

kWh kWh

0.029 1.20$105

kg km

296

kWh

1

g g g mg mg mg mg

92.5 2.14 1.93 356 632 74.7 218

Inputs Materials Diesel Tractor Agricultural tillage Pesticides Herbicides Mineral fertilizers Lubricating oil Energy Electricity (chipping) Electricity (storage in power plant) Transport Truck Outputs Product Electricity Emissions to air CO2 NOx CO SO2 CH4 N2O NMVOC

Unit

Value

g g g g g g g

1.49 0.137 0.046 0.009 0.023 9.76 1.38$102

kWh kWh

0.031 6.77$106

kg km

166

kWh

1

g g g mg mg mg mg

80.0 1.86 1.62 761 682 615 178

A summary of the inventory data, per functional unit, for Scenario C is shown in Table 3. The uptake of CO2 from the atmosphere was not taken into account within the system boundaries in all scenarios. It has been assumed that the CO2 uptake during the biomass growth (regardless of the scenario) was considered equal to the amount of CO2 released into the atmosphere after the biomass oxidation at the end of its life cycle e in this case, after its combustion (Butnar et al., 2010; Dias and Arroja, 2012). The estimation of the amounts of biomass necessary to produce 1 kWh of electricity (functional unit) has followed the method defined by Butnar et al. (2010) based on the power plant capacity, the operating hours, the efficiency, the low heating value (LHV) and the moisture content for each biomass source (Table 4). Combustion emission factors corresponding to the biomass burning in the power plant have been taken from the IPCC guidelines (IPCC, 2006) and the EMEP/EEA air pollutant emission inventory guidebook (EMEP/EEA, 2013). Inventory data concerning the infrastructure and machinery production in the power plant have been taken from the Ecoinvent Ò Database (2007). 3. Life cycle energy and environmental performance Among the steps defined within the life cycle impact assessment stage of the standardised LCA methodology, only the classification and characterisation stages were undertaken (ISO, 2006). The characterisation factors reported by the Centre of Environmental Science of Leiden University (CML 2001 method) were used (Guinée et al., 2001). The following impact potentials were evaluated according to the CML method v2.05: abiotic depletion potential (ADP), acidification potential (AP), eutrophication potential (EP), global warming potential (GWP), and photochemical oxidants formation potential (POFP). Furthermore, an energy analysis was carried out based on the cumulative non-renewable fossil and nuclear energy demand (CED), computed according to Hischier et al. (2009), as an additional indicator. The choice of these impact categories for the environmental study is based on the fact that they are the most common categories reported in LCA studies

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Table 4 Specifications for the biomass sources and plants under assessment. Biomass source

Moisture content

LHV

Potential energy contenta

Annual biomass requirement

Source

Vineyard pruning residues Eucalypt logging residues Poplar biomass

15% 35% 20%

16.8 MJ kg od1 15.5 MJ kg od1 18.2 MJ kg od1

14.28 MJ kg1 10.08 MJ kg1 14.56 MJ kg1

10,084 t od 14,293 t od 9890 t od

Clermidy (2012) Dias (2014) Gasol et al. (2009a)

Capacity of the power plant: 1 MWe; Annual operation hours: 8000 h; Energy efficiency: 20%. a Potential energy content per kg of biomass with the corresponding moisture content; kg od ¼ kg oven dried (0% moisture content).

of bioenergy systems (Butnar et al., 2010; Gasol et al., 2009a, 2009b; Muench and Guenther, 2013). The software SimaPro 7.3.3 was used for the computational implementation of the inventories (PRé Consultants, 2013). The characterisation results are displayed in Table 5 for each impact category as well as the flow indicator (CED).

A detailed assessment of each scenario is reported below, in which contributions from the processes involved have been quantified in order to identify the environmental hotspots in each scenario.

4. Results

Vineyards require much tending, including an annual pruning. Pruning activities involve the production of residual biomass (Spinelli et al., 2010), which could be used for energy and industrial uses e e.g., particleboard manufacture (Ntalos and Grigoriou, 2002). As indicated in Fig. 1, only activities focussed on the collection and further chipping and storage of residues have been computed in the vineyard pruning process as well as the replacement of nutrients with compost. According to Fig. 4, several processes are responsible for remarkable contributions to the environmental and energy profiles associated with this scenario e with ratios of up to 90% depending on the category. These processes are field activities related with biomass extraction and chipping, biomass transportation from field to power plant, and electricity production. Combustion of biomass in the power plant is the main environmental hotspot. This process presents contributions ranging from 58% to 91% in categories such as AP, EP, GWP and POFP. Biomass combustion emissions were the substances with the most significant responsibility for these environmental burdens. Contributions from agricultural activities to the environmental profile add up to 45% in categories such as ADP and CED (Fig. 4a). A breakdown of the involved activities is shown in Fig. 4b. The use of large machines in the extraction and chipping processes involves significant amounts of diesel (w5.15 L ha1) and the corresponding combustion emissions. Combustion emissions derived from diesel use in agricultural machinery, such as CO2, SO2 and CO, are the main contributing substances. On-field emissions derived from the application of the compost to the field e in order to counteract the nutrient losses derived from the removal of pruning residues e have a small effect in categories such as AP, EP and GWP. It is important to remark on the contribution from diffuse emissions of phosphate to EP. Biomass transport, in Fig. 4b, involves the distribution of chipped biomass from the extraction point to the storage site in the surrounding area (10 km). This activity is carried out by a tractor and is an environmental hotspot mainly due to derived combustion emissions and diesel requirements. According to Fig. 4a, biomass distribution (by truck) from the field storage to power plant (70 km) presents considerable contributions (of up to 41%) in categories such as ADP and CED. Once again, the diesel combustion emissions derived from the truck operations are responsible for environmental impacts. Contributions from storage activities (in field and in power plant) are almost negligible according to Fig. 4a and b.

Considerable differences were identified between the use of biomass derived from a dedicated energy crop and that from agricultural and forest residues. For all selected categories, the environmental and energy impacts decrease when residues are used for energy purposes. The calculated impacts caused by scenarios ScA and ScB are lower than those from the poplar-biomassbased scenario (ScC) e between 9% and 75% in comparison with ScC depending on the category (see Table 5). Contributions from poplar biomass production-related activities are the most significant factor for these results in ScC. The optimum scenario for electricity production, taking into account environmental and energy results (except in POFP and AP), is ScA, which is based on the use of vineyard pruning residues as potential feedstock. This is mainly explained by two factors: (a) lower requirements for fossil fuel and agricultural machinery usage throughout the life cycle (specifically in comparison with ScB), and (b) no requirement of mineral fertiliser application (and production) in comparison with ScC. ScB has the lowest impact in terms of POFP and AP due to the lowest sulphur content of eucalypt biomass in comparison with the other biomass sources. This leads to lower SO2 emission rates during biomass combustion, which have a remarkable affect on both impact categories. As reported before, in scenarios ScA and ScB, only activities performed from residue collection onwards were considered (see Figs. 1 and 2). Other activities carried out previously in the field/ forest were excluded from assessment; they have been allocated to the grapes and roundwood production in ScA and ScB, respectively, because they are performed in order to obtain both products. In contrast, the use of biomass from a dedicated energy crop (in this case, an SRC such as poplar) requires the performance of numerous activities that focus on the production of this feedstock. Therefore, in this case study, all of these activities must be totally allocated to the poplar biomass production. Table 5 Impact assessment results for electricity production systems per functional unit (1 kWh) using vineyard pruning residues (ScA), eucalypt logging residues (ScB) and poplar biomass (ScC) as feedstocks. Impact category

Unit

ScA

ScB

ScC

Abiotic Depletion (ADP) Acidification (AP) Eutrophication (EP) Global Warming (GWP) Photochemical Oxidants Formation (POFP) Cumulative Energy Demand (CED)

kg kg kg kg kg

3.31$104 1.63$103 2.46$104 7.30$102 8.38$105

6.67$104 1.50$103 3.21$104 1.32$101 5.63$105

7.45$104 3.44$103 6.86$104 2.89$101 9.19$105

0.76

1.52

1.72

Sbeq SO2eq PO3 4eq CO2eq C2H4eq

MJeq

4.1. ScA e vineyard pruning residues

4.2. ScB e eucalypt logging residues Eucalypt is a fast-growing species commonly established in order to produce biomass for industrial uses e mainly for pulp and

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scenario are displayed in Fig. 5. According to Fig. 5a, two factors are responsible for w90% of contributions to all of the categories under assessment: the electricity production process and forest activities. Production of electricity is the main hotspot in categories such as AP, EP and POFP, with contributing rates of 66%, 62% and 75%, respectively, of total acidifying, eutrophying and photochemical oxidants emissions produced across the entire bioenergy system. Biomass combustion emissions, such as SO2 and NOx, are the main responsible substances. According to Fig. 5b, if forest activities are assessed in more detail, two processes are responsible for 93% of derived impacts: the forwarding process and the feeding and chipping process. The forwarder and chipper are large machines with significant diesel

100%

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Field activities

60% Contributions

(a) 100%

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(a) 100%

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(b) Fig. 4. Contributions (in %) to each category per processes involved in the vineyard pruning residues based scenario (ScA). (a) Total system; (b) Field activities.

paper manufacture. Significant amounts of logging residues are produced through harvesting activities (w17% of total tree biomass including wood, bark, logging residues and stumps); these residues become potential bioenergy sources. As reported previously, only activities performed from harvesting onwards e collection of residues with a forwarder, chipping at the roadside and loading onto trucks e have been considered for assessment, as well as the delivery of eucalypt chips to the power plant, storage and final conversion into electricity. The remaining forest activities (site preparation, stand establishment, stand tending and wood harvesting) have been excluded as they have been totally allocated to the driving force of these forest stands: the eucalypt logs. Contributions from all processes or activities involved in this forest

Contributions

ADP

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0%

ADP

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Loading onto truck

EP

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Feeding & chipping

POFP

CED

Forwarding

(b) Fig. 5. Contributions (in %) to each category per processes involved in the eucalypt logging residues based scenario (ScB). (a) Total system; (b) Forest activities.

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requirements (1.92 L t1 of logging residues and 3.94 L t1 of chips), which create a large amount of combustion emissions. In fact, the environmental and energy profiles associated with this scenario are related exclusively to diesel consumption. As shown in Fig. 5a and b, the feeding and chipping process has the largest environmental impact within forest activities regardless of the category. Contributions from this activity range from 15% (AP and POFP) to 48% (ADP and CED) of total impacts derived from this bioenergy system. This process involves two activities: the feeding of the logging residues into the chipper and the chipper operation itself. Therefore, the profiles can be partitioned as 17% and 83% for the feeding and chipper operation activities, respectively. Contributions from the forwarding process add from 10% to 24% of the total impacts of the bioenergy system e due to diesel requirements and derived combustion emissions. Finally, distribution of eucalypt chips from the forest to the power plant and the loading of chips onto trucks represent the

9

lowest contributions with average ratios of 10% and 3% of the total, respectively. Once again, chip storage in the power plant presents a negligible contribution (see Fig. 5a). Concerning the contributing substances, AP is associated with NOx and SO2 emissions derived from diesel combustion in the different processes involved throughout the process as well as from the biomass combustion step. NOx also contributes to EP being the main contributing substance. SO2 and CO are the main responsible substances of POFP. 4.3. ScC e poplar biomass Unlike the previous bioenergy stocks we have assessed, poplar biomass is not a residue. Therefore, all the activities involved in the poplar biomass production scenario (including site establishment, tending, management and harvesting) must be included within the analysis. Fig. 6 displays the contribution per process involved for

100%

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Stools killdown & collection Harvesting

Contributions

80%

Fertilizing 60%

Pesticide application First cutting

40%

Planting 20% Field preparation 0%

ADP

AP

EP

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POFP

CED

Chipping

(b) Fig. 6. Contributions (in %) to each category per processes involved in the poplar biomass based scenario (ScC). (a) Total system; (b) Poplar cultivation and management related activities.

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each category assessed. According to Fig. 6a, the activities involved in the poplar cultivation and management are the main factors responsible for the environmental and energy profiles and have contributions ranging from 15% to 84% depending on the category. This hotspot has been broken down in Fig. 6b, in which contributions from all field activities involved in the poplar biomass production are included. Fig. 6b also shows that field-preparationrelated activities contribute 44e86% of total impacts derived from poplar cultivation and management. Field preparation involves numerous agricultural activities prior to the planting step such as subsoiling, rolling, NPK fertilising, weed control and herbicide application. This NPK fertilisation is the field-preparation-related activity with the highest responsibility for environmental burdens and energy profile. Fertilising not only involves emissions from the fertiliser application using a specific machine, but also emissions from the NPK fertiliser production. In agreement with our results, the production of the NPK fertiliser is the main contributor to environmental impacts, in categories such as ADP and CED, due to the large energy requirements associated. Its contribution is also remarkable in GWP. In the remaining categories (AP and EP), the on-field derived emissions from the fertiliser application constitute the main contributing factor e due mainly to NH3. These on-field emissions are also important in GWP due to N2O emissions. After planting, there is another fertilising process, but only with nitrogen (see Fertilising in Fig. 6b). As explained before, the nitrogen-based fertiliser manufacture, the application and the derived on-field emissions have all been taken into account. According to Fig. 6a and b, contributions from this process are within the range of 8e28% concerning total impacts from poplar cultivation and management. If these ratios are analysed in more detail, the production of the nitrogen-based fertiliser is a main contributor in categories such as ADP, GWP, POFP and CED (see Fig. 6b). Diffuse emissions derived from the fertiliser application are important e in terms of POFP due to SO2 emissions, and in terms of GWP due to N2O emissions. Finally, the chipping step is also important, in categories such as ADP, POFP and CED, due to diesel requirements and combustionderived emissions. The remaining processes present almost negligible contributions, which are mainly related with diesel combustion in the corresponding machines (harvesters and stools removal). 5. Discussion 5.1. General remarks This study aims to calculate and compare the environmental impacts and energy flow associated with three different biomass sources, which are potential feedstocks for bioenergy purposes. These biomass sources are: vineyard pruning residues, eucalypt logging residues and poplar biomass. So far, there is no study in which environmental and energy profiles for agricultural and forest residues, as well as SRC, were identified and compared in such detail. This study is of particular importance due to the growing interest in the promotion of bioenergy production from renewable sources in special lignocelluloses residues (Directive, 2009/28/EC, 2009; Domac et al., 2005; Cornelissen et al., 2012). Fossil fuel depletion and the mitigation of climate change are important reasons that support this interest (Cornelissen et al., 2012; Nybakk et al., 2013). In this context, the bioenergy supply must use sustainable sources, creating high GHG emission savings compared to fossil fuels references (McCormick et al., 2007; Cornelissen et al., 2012). Agricultural and forest waste (such as olive tree pruning and forestry residues) are being considered as potential biomass

sources for energy purposes (e.g., for pellets production). Pellets are promising fuels for heat and power production as an alternative to fossil fuels (Carone et al., 2011). In fact, pellet markets are currently undergoing rapid development (Petersen Raymer, 2006). Therefore, waste biomass has emerged as a viable alternative for energy production, encompassing a wide range of potential thermochemical, physicochemical and bio-chemical processes (Iakovou et al., 2010). In addition, biomass waste use for energy purposes is supported by land use savings and water availability as it should avoid competition for land use between biomass production for food, feed and energy use. However, the availability of agricultural and forest waste could be a restriction (Rentizelas et al., 2009; Gold and Seuring, 2011). A better assessment of the potential biomass sources is therefore needed as it can assist bioenergy plants in the selection of the more sustainable feedstock. Specifically, this is required when different types of biomass sources are available for a bioenergy plant. This is the case for some Mediterranean countries (e.g., Spain, Portugal and France) that have experience of vineyards, poplar cultivation and forest practices (Butnar et al., 2010; Dias, 2014). As indicated in Table 5, the use of poplar biomass as a bioenergy feedstock should be the worst option when compared with the use of agricultural and forest residues. Logging and vineyard pruning residues are far better placed than poplar biomass. Energy crops, such as SRC, are known for requiring highly energy-intensive activities in order to promote high biomass yields (Heller et al., 2003, 2004; Butnar et al., 2010; González-García, 2012a, 2012b, 2012c). These activities require diesel consumption with the corresponding combustion emissions, which have an influence on the environmental and energy profiles (Heller et al., 2003, 2004; GonzálezGarcía, 2012c). The same trend is observed not only with the use of SRC for bioenergy systems but also with other dedicated energy crops such as herbaceous crops (e.g., brassica carinata) (Gasol et al., 2007; Butnar et al., 2010). However, it is important to highlight here the perspective considered in this study based on the non-allocation of agricultural and forest activities (prior to the harvesting) to the residues e only taking into account the activities related to the extraction or collection of the residues. Thus, it is expected that this assumption contributes considerably to reducing the profiles corresponding to these biomass sources in comparison with SRC-derived biomass. This assumption has also been considered in other related LCA studies (Dias, 2014). It is widely known that the allocation method considered influences the LCA results. The use of alternative allocation approaches, such as economic allocation, should be avoided according to the existing literature due to the inherent uncertainties resulting from local price differences (Muench and Guenther, 2013). Thus, it is also interesting to note the importance of valorising agricultural and forest residues not only in terms of bioenergy production but also as biomass sources for industrial applications (e.g., particleboards, bioplastics, etc.). Moreover, the heating value and moisture content of the biomass also affect the results (Butnar et al., 2010). Table 4 indicates that poplar biomass presents the highest LHV (18.2 MJ kg od1), followed by pruning residues (16.8 MJ kg od1) and logging residues (15.5 MJ kg od1). Logging residues also present the highest moisture content. Taking into account the power plant capacity (1 MWe), the operating hours (8000 h) and the efficiency (20%), a percentage of logging residues are annually required by the power plant in comparison with the vineyard pruning residues and poplar biomass (42% and 45%, respectively). In addition, changes in land use and farming practices should also be considered when bioenergy systems are assessed. In terms of productivity, poplar cultivation should present the highest yield, and around 0.06 m2 of irrigated land should be required per functional unit. In contrast,

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5.2. Environmental comparison with alternative electricityproduction systems The comparison of electricity-production profiles from biomass sources (residues and dedicated crops) with electricity from other sources, such as fossil fuels (natural gas or coal), has been performed in the existing literature (Heller et al., 2003, 2004; Ecoinvent Ò Database, 2007; Butnar et al., 2010; González-García et al., 2012c). Fig. 7 displays considerable fluctuations in some impact categories (ADP, AP, GWP and POFP) taking into account results available in the existing literature per kWhe. In these studies, different assumptions (conversion efficiencies, capacities, transport distances, allocation approaches, avoided processes, etc.)

300 250 200 ComparaƟve profiles (%)

the use of these agricultural and forest residues should require 14.8 m2 and 37.6 m2 of land, respectively; however, this surface should mainly be dedicated to food and/or other industrial uses. According to the results reported in Table 5, the environmental and energy profile associated with the poplar biomass should be considerably higher than the scenarios based on forest and agricultural residues (depending on the category, up to 4 times higher (e.g., in terms of GWP and in comparison with ScA)). As mentioned previously, a reason for these profiles is the non-allocation of environmental burdens derived from agricultural and forest practices (prior to the collection process) in comparison with the assumption for the poplar-based scenario. According to the results reported, agricultural practices dedicated to the production of poplar biomass are the main hotspot (see Fig. 6) due to the diesel consumption in the machinery as well as the requirement for agrochemicals. However, although environmental burdens were allocated to the residues (regardless of economic- or mass-based allocation approaches assumed), better profiles should be obtained due to the lower market prices and production volumes of residues in comparison with the corresponding driving forces (grapes and roundwood). If the use of logging and pruning residues is compared, the results indicate that the agricultural waste is the best choice in all of the categories except AP and POFP e with reductions in relation to ScB ranging from 23% (in EP) to w50% (in ADP, GWP and CED). Although the similar activities are performed in both scenarios (biomass collection, chipping, storage), except the replacement of nutrients due to the removal of the pruning residues, the forest scenario involves larger machines mainly in the extraction and chipping processes. Larger machines involve larger fossil fuel requirements and corresponding larger combustion emissions. These are the main factors for higher results in terms of ADP, EP, GWP and CED. Concerning the EP and POFP, the contributions to this category are 8% and 9% higher for the vineyard pruning residues scenario than the forest one. SO2 emissions derived from biomass combustion in the power plant are the main contributing substances in both categories e being higher for ScA due to the higher sulphur content in the biomass. The results reported in this study support the idea that forest and agricultural waste would be an interesting and potential raw material for bioenergy purposes. Agricultural residues or wastes e such as straw, leaves, etc., or forest and wood-processing waste e have been promoted in recent years as raw materials not only for the bioenergy sector but also for bio-based industry, giving rise to numerous technological developments (Kretschmer et al., 2013). This increasing interest is also supported by their availability and low associated costs in comparison with dedicated energy crops (EPA, 2007; Kretschmer et al., 2013). Moreover, these biomass sources do not jeopardise agricultural production and forest areas (Kapdan and Kargi, 2006; Shilton et al., 2008; Murphy and Power, 2009; Shupel Ibrahim, 2012).

11

150 100 50 0 ADP

AP

GWP

POFP

10% cofire (biomass & coal)

Fossil fuels

-50 -100 Biomass

Fig. 7. Fluctuations on Abiotic depletion potential (ADP), Acidification potential (AP), Global warming potential (GWP) and Photochemical oxidants formation potential (POFP) derived from electricity production from different biomass/fossil fuels sources. Data taken from literature (Heller et al., 2003, 2004; ecoinvent database Ò, 2007; Butnar et al., 2010; González-García et al., 2012c).

have been established, and different biomass conversion technologies have been considered (Heller et al., 2004). Fig. 7 reports comparative environmental profiles, using the following biomass sources taken from the existing literature, with the corresponding characterisation results: willow biomass combined (co-firing system), or not, with wood residues and coal (Heller et al., 2003, 2004; González-García et al., 2012c), Ethiopian mustard biomass (Butnar et al., 2010) and poplar biomass (Butnar et al., 2010) e as well as the results from our feedstocks. Environmental profiles regarding electricity production from natural gas and coal have also been displayed in Fig. 7. According to these results, environmental benefits are achieved when a biomass source is used for the production of electricity in comparison with the use of fossil fuels. Utilising biomass residues for electricity generation presents benefits. These benefits are related with: (1) exclusion of environmental burdens related with agricultural/forest practices, and (2) conversion into bioenergy avoiding other means of disposal for the residues (e.g., landfill), obtaining a valuable product (i.e., electricity) and, in turn, avoiding derived emissions that would have occurred as a result of that disposal. Establishing dedicated energy crops, such as poplar or willow, requires arable land, and there is alarm over the availability of this limited resource. However, in contrast to the use of biomass residues for energy purposes, dedicated crop biomass availability could be more sustainable due to its high yields. Although the use of biomass sources for electricity potential is interesting from environmental and energy perspectives, further analysis should focus on the availability of these sources and their ability to meet energy requirements. Finally, and in order to have a global view on the issue of biomass for bioenergy purposes, additional aspects should be taken into account such as land use, water availability and production costs. 6. Conclusions The environmental and energy profiles of the three different electricity production scenarios have been assessed through the LCA methodology and adoption of the CML method for

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environmental evaluations. The feedstocks under assessment were two agricultural/forest wastes (vineyard pruning and eucalypt logging residues) and an energy crop (poplar biomass). The results reported that, given the assumptions of this study, the use of poplar biomass for bioenergy production has a greater impact than the use of agricultural and forest residues (from 42% to 45% higher depending on the category). The main reason for these results is the contribution from the plantation-related activities. As the poplar is a dedicated energy crop, all the activities from field preparation to harvesting have been taken into account within the system boundaries. In contrast, all of the activities performed in the vineyard and forest prior to the collection of residues have not been computed, as they have been allocated to the driving force of these stands: grapes and roundwood, respectively. The results reported in this study support the idea (as also reported in other studies) that the use of agricultural wastes and forest residues could provide a potential available raw material not only for bioenergy but also for industrial purposes. However, more research and technological development are required in order to promote their use. Acknowledgements This research has been developed within the framework of the project ECOTECH SUDOE d International Network on LCA and Ecodesign for Eco-innovation (SOE2/P2/E377) funded by the EU Interreg IV B Sudoe Programme. Dr Sara González-García would like to express her gratitude to the Galician Government for financial support (DOG number 62, pages 9405e9410, 1 April 2013) for a Postdoctoral Research Fellowship taken at the University of Aveiro (Portugal). Thanks are also due to FCT (Science and Technology Foundation e Portugal) for the scholarship granted to Dr Ana Cláudia Dias (SFRH/BPD/75788/2011). The authors thank Yago Lorenzo for his help throughout the research. References Bellon-Maurel, V., Clermidy, S., Frizarin, G., Sinfort, C., Roux, P., Ojeda, H., Short, M.D., Peters, G.M., 2013. Streamlining life cycle inventory data generation in agriculture using traceability data information and communication technologies e part II: application to viticulture. J. Clean. Prod. (submitted for publication) June 11th, 2013. Bentini, M., Martelli, R., 2013. Prototype for the harvesting of cultivated herbaceous energy crops, an economic and technical evaluation. Biomass Bioenergy 57, 229e237. Bergante, S., Facciotto, G., Minotta, G., 2010. Identification of the main site factors and management intensity affecting the establishment of short-rotation coppices (SRC) in Northern Italy, through stepwise regression analysis. Central Eur. J. Biol. 5, 522e530. Berndes, G., Hoogwijk, M., van den Broek, R., 2003. The contribution of biomass in the future global energy supply: a review of 17 studies. Biomass Bioenergy 25, 1e28. Buchholz, T., Luzadis, V.A., Volk, T.A., 2009. Sustainability criteria for bioenergy systems: results from an expert survey. J. Clean. Prod. 17, S86eS98. Butnar, I., Rodrigo, J., Gasol, C.M., Castells, F., 2010. Life-cycle assessment of electricity from biomass: case studies of two biocrops in Spain. Biomass Bioenergy 34, 1780e1788. Carone, M.T., Pantaleo, A., Pellerano, A., 2011. Influence of process parameters and biomass characteristics on the durability of pellets from the pruning residues of Olea europaea L. Biomass Bioenergy 35, 402e410. Clermidy, S., 2012. Evaluation environnementale d’une filière potentielle de production d’électricité à partir de sarments de vigne base sur la méthodologie d’analyse de cycle de vie. ESA and CIRAD, Angers and Montpellier, France. Cornelissen, S., Koper, M., Deng, Y.Y., 2012. The role of bioenergy in a fully sustainable global energy system. Biomass Bioenergy 41, 21e33. Conselho de Ministros, 2010. Resolução do Conselho de Ministros n 29/2010. Diário da República, 1.a série, N. 73, pp. 1289e1296. DGEG, 2012. Renováveis estatísticas rápidas n 90. Direcção Geral de Energia e Geologia. Portugal, Lisbon. Dias, A.C., Arroja, L., 2012. Environmental impacts of eucalypt and maritime pine wood production in Portugal. J. Clean. Prod. 37, 368e376. Dias, A.C., 2014. Life cycle assessment of fuel chip production from eucalypt forest residues. Int. J. Life Cycle Assess. http://dx.doi.org/10.1007/s11367-013-0671-4.

Dias, J., Azevedo, J.L.T., 2004. Evaluation of biomass residuals in Portugal Mainland. In: Afgan, N.H., Carvalho, M.D.G. (Eds.), International Conference on New and Renewable Energy Technologies for Sustainable Development, Ponta Delgada, pp. 214e228. Directive 2009/28/EC, 2009. Directive 2009/28/EC of the European Parliament and of the Council of 23 April 2009 on the promotion of the use of energy from renewable sources and amending and subsequently repealing Directives 2001/ 77/EC and 2003/30/EC. Off. J. Eur. Union. L140/16e62. Domac, J., Richards, K., Risovic, S., 2005. Socio-economic drivers in implementing bioenergy projects. Biomass Bioenergy 28, 97e106. Ecoinvent Ò database, 2007. http://www.ecoinvent.org/database/. ECOTECH SUDOE, 2013. International Network in Life Cycle Analysis and Ecodesign for Eco-innovation. http://www.ecotechsudoe.eu. Ekman, A., Campos, M., Lindahl, S., Co, M., Börjesson, P., Nordberl Karlsson, E., Turner, C., 2013. Bioresource utilisation by sustainable technologies in new value-added biorefinery concepts e two case studies from food and forest industry. J. Clean. Prod. 57, 46e58. EMEP/EEA, 2009. EMEP/EEA Air Pollutant Emission Inventory Guidebook 2009. European Environment Agency, Copenhagen. EEA Technical Report 9/2009. EMEP/EEA, 2013. EMEP/EEA Emission Inventory Guidebook. 1.A.1. Energy Industries. Combustion in Energy and Transformation Industries. Available at: http://eea. europa.eu/emep-eea-guidebook (cited January, 2014). EPA e U.S. Environmental Protection Agency, 2007. Biomass Combined Heat and Power Catalog of Technologies. Available at: http://www.epa.gov/chp/ documents/biomass_chp_catalog_part1.pdf (cited January, 2014). European Climate Foundation, 2010. Biomass for Heat and Power. Opportunity and Economics, The Hague, The Netherlands, 72 pp. Available at: http://www. europeanclimate.org/documents/Biomass_report_-_Final.pdf (cited January, 2014). E2P, 2012. Energias endógenas de Portugal e base de dados de fontes renováveis de energia. http://e2p.inegi.up.pt/index.asp. Fantozzi, F., Buratti, C., 2010. Life cycle assessment of biomass chains: wood pellet from short rotation coppice using data measured on a real plant. Biomass Bioenergy 34, 1796e1804. Gasol, C.M., Gabarrell, X., Anton, A., Rigola, M., Carrasco, J., Ciria, P., et al., 2007. Life cycle assessment of a Brassica carinata bioenergy cropping system in southern Europe. Biomass Bioenergy 31, 543e555. Gasol, C.M., Gabarrell, X., Anton, A., Rigola, M., Carrasco, J., Ciria, P., Rieradevall, J., 2009a. LCA of poplar bioenergy system compared with Brassica carinata energy crop and natural gas in regional scenario. Biomass Bioenergy 33, 119e129. Gasol, C.M., Martínez, S., Rigola, M., Rieradevall, J., Anton, A., Carrasco, J., Ciria, P., Gabarrell, X., 2009b. Feasibility assessment of poplar bioenergy systems in the Southern Europe. Renew. Sustain. Energy Rev. 13, 801e812. Gold, S., Seuring, S., 2011. Supply chain and logistics issues of bio-energy production. J. Clean. Prod. 19, 32e42. González-García, S., Gasol, C.M., Gabarrell, X., Rieradevall, J., Moreira, M.T., Feijoo, G., 2010. Environmental profile of ethanol from poplar biomass as transport fuel in Southern Europe. Renew. Energy 35, 1014e1023. González-García, S., Mola-Yudego, B., Dimitriou, I., Aronsson, P., Murphy, R., 2012a. Environmental assessment of energy production based on long term commercial willow plantations in Sweden. Sci. Total Environ. 210e219, 421e422. González-García, S., Bacenetti, J., Murphy, R.J., Fiala, M., 2012b. Present and future environmental impact of poplar cultivation in the Po Valley (Italy) under different crop management system. J. Clean. Prod. 26, 56e66. González-García, S., Iribarren, D., Susmozas, A., Dufour, J., Murphy, R.J., 2012c. Life cycle assessment of two alternative bioenergy systems involving Salix spp. biomass: bioethanol production and power generation. Appl. Energy 95, 111e122. Guinée, J.B., Gorrée, M., Heijungs, R., Huppes, G., Kleijn, R., de Koning, A., van Oers, L., Wegener, A., Suh, S., Udo de Haes, H.A., 2001. Life Cycle Assessment. An Operational Guide to the ISO Standards. Centre of Environmental Science, Leiden, The Netherlands. Heinimö, J., Junginger, M., 2009. Production and trading of biomass for energy e an overview of the global status. Biomass Bioenergy 33, 1310e1320. Heller, C.M., Keoleian, G.A., Volk, T.A., 2003. Life cycle assessment of a willow bioenergy cropping system. Biomass Bioenergy 25, 147e165. Heller, C.M., Keoleian, G.A., Mann, M.K., Volk, T.A., 2004. Life cycle energy and environmental benefits of generating electricity from willow biomass. Renew. Energy 29, 1023e1042. Hischier, R., Weidema, B., Althaus, H.J., Bauer, C., Doka, G., Dones, R., et al., 2009. Implementation of Life Cycle Impact Assessment Methods. Ecoinvent Report No. 3, v2.1. Swiss Centre for Life Cycle Inventories, Dübendorf, Switzerland. Iakovou, E., Karagiannidis, A., Vlachos, D., Toka, A., Malamakis, A., 2010. Waste biomass-to-energy supply chain management: a critical synthesis. Waste Manag. 30, 1860e1870. ICNF, 2013. IFN6 e Áreas dos usos do solo e das espécies florestais de Portugal continental. Resultados preliminares. Instituto da Conservação da Natureza e das Florestas, Lisbon, Portugal. IPCC, 2006. Guidelines for Natural Greenhouse Gas Inventories. Chapter 2. Stationary Combustion. Available at: http://www.ipcc-nggip.iges.or.jp/public/ 2006gl/pdf/2_Volume2/V2_2_Ch2_Stationary_Combustion.pdf (cited January, 2014). ISO, 2006. ISO 14040. Environmental management e Life cycle assessment e Principles and framework. International Organization for Standardization.

Please cite this article in press as: González-García, S., et al., Comparative environmental and energy profiles of potential bioenergy production chains in Southern Europe, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.04.022

S. González-García et al. / Journal of Cleaner Production xxx (2014) 1e13 Kapdan, I.K., Kargi, F., 2006. Bio-hydrogen production from waste materials. Enzyme Microb. Technol. 38, 569e582. Kaltschmitt, M., Reinhardt, G.A., Stelzer, T., 1997. Life cycle analysis of biofuels under different environmental aspects. Biomass Bioenergy 2, 121e134. Kretschmer, B., Buckwell, A., Smith, C., Watkins, E., Allen, B., 2013. Technology Options for Feeding 10 Billion People e Recycling Agricultural, Forestry & Food Wastes and Residues for Sustainable Bioenergy and Biomaterials. Institute for European Environmental Policy. Available at: http://www.europarl.europa.eu/ stoa/ (cited January, 2014). López-Rodríguez, F., Pérez Atanet, C., Cuadros Blázquez, F., Ruiz Celma, A., 2009. Spatial assessment of the bioenergy potential of forest residues in the western province of Spain, Caceres. Biomass Bioenergy 33, 1358e1366. Mateus, T., 2007. O Potencial energético da floresta portuguesa: análise do potencial energético disponível para as centrais termoeléctricas a biomassa florestal lançadas a concurso. Faculdade de Engenharia da Universidade do Porto, Porto, Portugal. McKendry, P., 2002. Energy production from biomass (part 1): overview of biomass. Review paper. Bioresource Technol. 83, 37e46. McCormick, K., Kåberger, T., 2007. Key barriers for bioenergy in Europe: economic conditions, know-how and institutional capacity, and supply chain co-ordination. Biomass Bioenergy 31, 443e452. Mentzer, J.T., DeWitt, W., Keebler, J.S., Min, S., Nix, N.W., Smith, C.D., Zacharia, Z.G., 2001. Defining supply chain management. J. Bus. Logist. 22 (2), 1e25. Muench, S., Guenther, E., 2013. A systematic review of bioenergy life cycle assessments. Appl. Energy 112, 257e273. Murphy, J.D., Power, N.M., 2009. An argument for using biomethane generated from grass as a biofuel in Ireland. Biomass Bioenergy 33, 504e512. Ntalos, G.A., Griogoriou, A.H., 2002. Characterization and utilisation of vine prunings as a wood substitute for particleboard production. Indus. Crops Prod. 16, 59e68. Nybakk, E., Lunnan, A., 2013. Introduction to special issue on bioenergy markets. Biomass Bioenergy 57, 1e3. OIC, 2013. Statistical Report on World Vitiviniculture. International Organisation of Vine and Wine, Paris, France. Parikka, M., 2004. Global biomass fuel resources. Biomass Bioenergy 27 (6), 613e620. Petersen Raymer, A.K., 2006. A comparison of avoided greenhouse gas emissions when using different kinds of wood energy. Biomass Bioenergy 30, 605e617.

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Pontailler, J.Y., Ceulemans, R., Guittet, J., 1999. Biomass yield of poplar after five 2year coppice rotations. Forestry 72 (2), 157e163. PRé Consultants, 2013. http://www.pre.nl (cited June, 2013). Rentizelas, A.A., Tolis, A.J., Tatsiopoulos, I.P., 2009. Logistics issues of biomass: the storage problem and the multi-biomass supply chain. Renew. Sustain. Energy Rev. 13, 887e894. Scarlat, N., Blujdea, V., Dallemand, J.F., 2011. Assessment of the availability of agricultural and forest residues for bioenergy production in Romania. Biomass Bioenergy 35, 1995e2005. Shilton, A.N., Mara, D.D., Craggs, R., Powell, N., 2008. Solar-powered aeration and disinfection, anaerobic co-digestion, biological CO2 scrubbing and biofuel production: the energy and carbon management opportunities of waste stabilisation ponds. Water Sci. Technol. 58, 253e258. Shupel Ibrahim, E., 2012. Biomass Potentials for Bioenergy Production from Buildup areas. Doctoral thesis. Faculty of Geo-Information Science and Earth Observation. University of Twente, Twente, The Netherlands. Spinelli, R., Magagnotti, N., Nati, C., 2010. Harvesting vineyard pruning residues for energy use. Biosyst. Eng. 105, 316e322. Spinelli, R., Nati, C., Pari, L., Mescalchin, E., Magagnotti, N., 2012. Production and quality of biomass fuels from mechanized collection and processing of vineyard pruning residues. Appl. Energy 89, 374e379. Tabata, T., Okuda, T., 2012. Life cycle assessment of woody biomass energy utilization: case study in Gifu Prefecture, Japan. Energy 45, 944e951. Viana, H., Cohen, W.B., Lopes, D., Aranha, J., 2010. Assessment of forest biomass for use as energy. GIS-based analysis of geographical availability and locations of wood-fired power plants in Portugal. Appl. Energy 87, 2551e2560. Whittaker, C., Mortimer, N., Murphy, R., Matthews, R., 2011. Energy and greenhouse gas balance of the use of forest residues for bioenergy production in the UK. Biomass Bioenergy 35, 4581e4594. Wihersaari, M., 2005. Greenhouse gas emissions from final harvest fuel chip production in Finland. Biomass Bioenergy 28, 435e443. Xu, X., Li, S., Fu, Y., Zhuang, D., 2013. An analysis of the geographic distribution of energy crops and their potential for bioenergy production. Biomass Bioenergy 59, 325e335. Yamamoto, H., Fujino, J., Yamaji, K., 2001. Evaluation of bioenergy potential with a multi-regional global-land-use-and-energy model. Biomass Bioenergy 21 (3), 185e203.

Please cite this article in press as: González-García, S., et al., Comparative environmental and energy profiles of potential bioenergy production chains in Southern Europe, Journal of Cleaner Production (2014), http://dx.doi.org/10.1016/j.jclepro.2014.04.022