Resources, Conservation and Recycling 54 (2010) 923–930
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Resources, Conservation and Recycling
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Life cycle assessment of raw materials for non-wood pulp mills: Hemp and flax
S. González-García ∗, A. Hospido, G. Feijoo, M.T. MoreiraDepartment of Chemical Engineering, School of Engineering, University of Santiago de Compostela, 15782-Santiago de Compostela, Spain
a r t i c l e i n f o
Article history:Received 29 April 2008Received in revised form 29 January 2010Accepted 31 January 2010
Keywords:Environmental impactFlaxHempLCALife Cycle AssessmentNon-wood fibre production
a b s t r a c t
At the present time, there is a remarkable increasing interest for using non-woody fibres as raw materialsfor pulp mills. The present study aims to identify and quantify the environmental impacts associated withthe production of hemp and flax fibres for speciality paper pulp by using the Life Cycle Assessment (fromnow, LCA) methodology. One ton of fibre entering the pulp mill was used as functional unit in bothsystems.
Inventory data for the foreground system (agricultural inputs and outputs) were obtained directly fromgrowers (Spanish plantations and expert advisors) and combined, when necessary, with bibliographicsources. Data for the background system such as production of chemicals and pesticides, machinery orelectricity were taken from the Ecoinvent database.
The CML baseline 2000 methodology was selected to quantify the potential environmental impactassociated to the crops. Specifically global warming (GWP), acidification (AP), eutrophication (EP) andphotochemical oxidant formation (POP) were evaluated. In addition, two flow indicators were considered:energy (EU) and pesticide use (PU).
Production of hemp fibre reported higher values for all the impact categories analyzed. On the contrary,flow indicators were more intensive in the flax scenario due to irrigation and pesticide consumption. LCAtool aided to identify the hot spots, so that a proposal for upgrading alternatives to reduce environmental
impacts could be made. Production and use of fertilizers as well as the stage of scutching were identifiedas the hot spots in both crops; in addition, harvesting has also significant contribution in hemp productionand irrigation regarding the flax scenario. Future work will be focused on the study of non-wood fibre
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. Introduction
Paper pulp manufacturing is the first non-food industrial uti-ization of plant biomass (Gutierrez et al., 2001). Paper is defined assheet mainly constituted by recycled or virgin fibres of cellulose,nd its properties and resistance depend on its fibrous composition,istribution in the sheet as well as number and strength of inter-bre bonds. In theory, all vascular plants in nature can be used asources of cellulosic fibres for paper and pulp manufacture; how-ver, both availability and production costs limit the natural sourcef fibre (García Hortal and Jimenez Alcaide, 2005).
Nowadays wood fibres constitute the main virgin source of
aper pulp raw materials in developed countries (Sigoillot et al.,005). However, in the last years the pulp and paper sector haseen facing several problems related to the shortage of forest indus-ry traditional resources. As a result, there is an increasing interest
in using non-wood fibres, mainly for specialty paper production,and many fast growing annual as well as perennial plants havebeen identified, cultivated and studied for their suitability for pulpand paper manufacture (García et al., 2003). Among the non-woodplants, straw has been used in Asia, Africa, Eastern Europe and LatinAmerica for the production of paper pulp as well as in Spain andother European countries for manufacturing of high-quality pulpsfor speciality papers (Hedjazi et al., 2009; Sigoillot et al., 2005; Zhaoet al., 2006). Several reasons support this interest: their easy avail-ability as agricultural waste (such as wheat straw, rice straw orsugar cane bagasse), avoiding shortage of forest resources, goodyields and stable productions of annual plants, farmers can receivesubsidies for their cultivation and fibres present a wide range ofcharacteristics and chemical composition (higher yields of cellu-lose and lower lignin contents in comparison with these of woods)(Ye and Farriol, 2007). In addition, non-wood paper pulps are eas-ier to obtain because of the linkages nature (Camarero et al., 2004;
Sigoillot et al., 2005).
This paper is focused on the environmental study of hemp andflax straw as potential sources of fibre from which high qualitypaper products are produced. Both crops have been two of the mostimportant fibre crops in Europe, although hemp is more widespread
han flax in NE Spain (Lloveras et al., 2006). Hemp and flax are theaw materials used in a Spanish specialty paper pulp mill with aong experience in chemical and mechanical treatments of non-
ood fibres coming from annual plants. Besides, this factory cane considered representative of the present movements related tohe growing interest in applying green biotechnology to cookingnd bleaching processes to reduce pollution as well as improve theuality of pulp produced (Hedjazi et al., 2009).
Hemp and flax cultivation have excellent agronomic charac-eristics, they can also be excellent predecessors in crop rotation,nd in addition can provide high fibre yields (Casa et al., 1999;orchs and Lloveras, 2003; Lloveras et al., 2006; Svennerstedt andvensson, 2006; Zentner et al., 1989). Bast fibres (phloem) derivedrom the vascular bundles of the plant stem mixed approximatelyith 15% of core fibres (xylem) are used as raw material in pulpaking (Ebskamp, 2002). These crops were considered in the study
ecause they both are two of the most important non-wood rawaterials used nowadays for speciality paper pulp (Camarero et
l., 2004; Lloveras et al., 2006) and their environmental evaluationnd comparison is recommended to evaluate possible differencesn their production.
An agricultural process, as the cultivation of hemp or flax,ncludes not only field operations but also impacts related to theost-preparation of product, extraction of raw materials (fuels,inerals, . . .) as well as production and transportation of system
nputs (fertilizers, pesticides, machinery, . . .) and their effects muste taken into account in order to achieve a holistic evaluation of theystem. In this sense, Life Cycle Assessment (LCA), a methodologyhat aims to analyse products, processes or services from an envi-onmental perspective, has been shown to be an useful and valuableool for environmental evaluation of agricultural systems (Audsleyt al., 1997; Brentrup et al., 2001; Halberg, 1999; Lewis et al., 1999;ilà i Canals, 2003; Milà i Canals et al., 2006; Payraudeau and van
er Werf, 2005; Pizzigallo et al., 2006; van der Werf, 2002a; van dererf and Petit, 2002b; van der Werf et al., 2007).The approach is not only gathering the inventory data for each
rop (taking into account field operations, fibre processing andransport to the gate of pulp mill) but also identification of ‘hotpots’ and discussion of some improvement opportunities with theim of comparison between two agricultural systems with similarnal products.
. Materials and methods
.1. LCA methodology
The purpose of this LCA study is to determine which non-oody fibre (hemp or flax), from an environmental point of view,
s more favourable for its use as raw material in high quality paperulp manufacturing. Two plantations located in NE Spain repre-enting the ‘state of the art’ production system and suppliers ofbres to a Spanish pulp mill were considered as agricultural stan-ard scenarios for hemp and flax production (season 2003–2006nd 2000–2001, respectively). Data for foreground system (agri-ultural inputs and outputs, and agricultural standard practices)ere obtained from expert advisors and personal communica-
ions with Spanish growers, and complemented when necessaryith bibliographic sources (Casa et al., 1999; Easson and Molloy,
000; Gorchs and Lloveras, 2003; Lloveras et al., 2006; van dererf, 2004; Zah et al., 2007). Climatic conditions in the region
re regarded as Mediterranean with a minimum annual precipi-ation of 700 mm and 400 to 900 m over sea level. The soil textureas loam with clay 23.5%, organic matter 2.4% and CaCO3 equiv-
lent 22%, pH (water) is about 8.3 (Lloveras et al., 2006). Dataor background system (agro-chemical and pesticide production,
tion and Recycling 54 (2010) 923–930
machinery production and transportation) were taken from theEcoinvent database (Dones et al., 2004; Nemecek et al., 2004;Spielmann et al., 2004).
The function of the agricultural systems under study is to pro-duce non-wood pulp fibre and therefore the functional unit wasdefined as “1 ton of fibre ready to be processed in a pulp mill”. More-over, both fibres have a very similar yield in terms of pulp and theycan be used in the same proportion in the pulp mill. The selectionof functional unit seems to be in agreement with other agricul-tural LCA studies with different types of products (Brentrup et al.,2004a,b; Charles et al., 2006; Milà i Canals et al., 2006; Ramjeawon,2004), where mass-based functional units were also selected.
As the focus of this study was the fibre production, no poste-rior processing (either the fibre or the by-products: woody coreand dust) was included within the system boundaries. The systemboundaries included then all the life cycle stages from the cradle(raw materials production) to the pulp mill gate as described below.Although the specific period of growth in both crops is quite short(3–5 months), a 12-month seasonal period was considered heresince soil preparation activities were also included and no rotationcrops activities take place in the field.
The impact assessment phase was carried out following theCML baseline 2000 methodology (Guinée et al., 2001) and in par-ticular the impact categories usually used in an agricultural LCA(global warming (GWP), acidification (AP), eutrophication (EP) andphotochemical oxidant formation (POP)) were analyzed as wellas two flow indicators concerning to the use of non-renewableenergy resources and pesticide active substance consumption. Theselection of these impact categories seems to be suitable for theevaluation of crops related to industrial products (van der Werf andTurunen, 2008). SimaPro 7.0 (PRé Consultants) was used to performthe impact assessment stage.
2.2. Hemp system description/production
Hemp (Cannabis sativa L.) is a slender and annual herbaceouscrop which depending on its handling and agro-chemical aspectscan supply up to 20 tonnes of dry matter per hectare (Struik et al.,2000). Nowadays, this crop is awakening great interest as a renew-able source for many industrial products such as paper-making,horse bedding, house building and insulation materials or biodiesel(Acosta Casas and Rieradevall i Pons, 2005; Gorchs and Lloveras,2003; van der Werf and Turunen, 2006; Yates, 2006).
Historically, hemp was grown for its fibre for industrial appli-cations for millennia throughout Europe and, due to a recentrelaxation of cropping rules within the European Union, there hasbeen a renewed increase in interest in the crop. In Spain hemp culti-vation has never stopped and at the present time, it is mainly grownin NE Spain (Gorchs and Lloveras, 2003).
System boundaries cover up to (and including) the agriculturalproduction subsystem (comprising: soil management, fertilisation,sowing and harvesting), straw processing subsystem (that is tosay the stems post-treatment once harvested: retting, sun drying,scutching, baling and storage) and transportation of the fibre balesto the pulp mill gate (Fig. 1).
The establishment of hemp crop consists in the seedbed prepa-ration with a combination of both plough and rotary harrow.Fertilizers application is prior to seeding. Sowing date is aroundlate April, Spanish cultivars are seeded and a cereal drill is usuallyused. Harvesting is around middle August and does not requiredspecial equipment (Gorchs and Lloveras, 2003). Machinery for for-
age harvest is generally used. Hemp is cut and spread out over thesoil in windrows to be retted (dew retting). This step can last upto 3 weeks and to help the process, the hemp bundles are periodi-cally turned over. When the moisture content is 11–14%, the strawis mechanically scutched in order to separate the valuable fibres
S. González-García et al. / Resources, Conservation and Recycling 54 (2010) 923–930 925
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ig. 1. Subsystems included in the LCA of fibre hemp/flax production: System boundccurs at hemp production and spotted boxes at flax production.
rom the woody core in the retted straw. Roughly, the average fibreontent in the retted straw is 33%. Next, bales of fibre (325 kg perale) are formed with a round baler and storage (van der Werf,002a).
Inventory data of global process of hemp cultivation and pro-essing is shown in Table 1. Production of sowing seed is consideredn the same way as the fibre production system although withome differences regarding sowing rate (lower), harvesting dateup to one more month) and energy consumption in seed process-ng (Martínez et al., 2007; Narain and Singh, 1988).
Inventory data related to the production of fertilizers used in theystem (ammonium nitrate, potassium chloride and triple superhosphate) were taken from the Ecoinvent database (Nemecek etl., 2004). The use of agro-chemicals is an important source of
utrient related emissions in field with an important contribu-ion to global warming, acidification and eutrophication (Charlest al., 2006). Emissions rates are variable due to the influence ofoil type, climatic conditions and agricultural practices and it is
able 1nventory of fibre hemp crop (Data per tonne of fibre).
Inputs
Materialsa Units Value Energy Units Value
Seeds kg 50.00 Electricity forscutching
kWh 336
Fertilizers TransportationAmmonium nitrate kg N 85.00 Fertilizers t km 90.48Triple superphosphate kg P2O5 65.00 Fibre bales t km 180.00Potassium chloride kg K2O 125.00Diesel kg 74.85Agricultural machinery kg 23.05
Outputs
Products and co-products Units Value
Straw (11–14% moisture) t 3.00Fibre t 1.00Woody core t 1.50Hemp dust t 0.50
a Supplemental irrigation is not required as rainfall during growing season isnough.
and process chain. White boxes are common for both cultivations, black boxes only
necessary to develop an entire mineral balance for each particu-lar scenario to determine emissions from fertilizers. However, thelack of data made that impossible and the calculation of nutrientrelated emissions (ammonia, nitrate, nitrogen, nitrous and nitro-gen oxides, phosphate) was done by means of emission factorsproposed by several authors (Arrouays et al., 2002; Audsley et al.,1997; EMEP/CORINAIR, 2006).
Hemp crop is rarely threatened by dangerous pest so no pes-ticides or herbicides are required. Supply of irrigated water isunnecessary, due to sufficient annual rainfall.
Yields can vary largely depending on producers, climatic con-ditions, region, soil characteristics, sowing and harvesting date,and the type of seed sown (Bennett et al., 2006; Forrest andYoung, 2006; Keller et al., 2001 Mediavilla et al., 2001; Schäfer andHonermeier, 2006; Struik et al., 2000). For example, an increase upto 50% in total fibre yield can be obtained increasing the seed ratein 100% depending on seed type (Bennett et al., 2006).
2.3. Flax system description/production
Flax is an annual plant with slender stems. It is native to theregion extending from the eastern Mediterranean to India; how-ever, it has always been a minor crop in Spain in comparison tohemp (Lloveras et al., 2006). It is also a bast fibre plant, i.e. its fibresare derived from the outer part of the stem. This crop is sown forboth its seeds (linseed or seed flax) and fibres (fibre flax), which arealternative types of the same specie, Linum usitatissimum. They bothcan be used as dual purpose crops under specific conditions (Eassonand Molloy, 2000). The present study deals with the simultaneousproduction of seed for re-sowing and straw.
As presented for hemp, flax system covers up to (and including)the agricultural production, straw processing and final transportfrom plantation to pulp mill gate (see Fig. 1). The agricultural pro-duction subsystem is similar to hemp but there are also somedifferences which are: smaller fertilizers consumption, the neces-
sity of irrigation and the requirement of pesticides application.Inventory data of global process of flax cultivation and processingis shown in Table 2.
The straw processing subsystem is the same as hemp, althoughthe fibre bales size are considered as different at 250 kg per bale.
926 S. González-García et al. / Resources, Conservation and Recycling 54 (2010) 923–930
Table 2Inventory for fibre flax crop (data per tonnes of fibre).
Inputs
Materials Units Value Energy Units Value
Seeds kg 68.15 Electricity for scutching kWh 414.88Fertilizers TransportationCalcium ammonium nitrate kg N 30.06 Fertilizers t km 88.00Triple superphosphate kg P2O5 41.76 Herbicides kg km 47.70Potassium chloride kg K2O 41.76 Fibre bales t km 107.63HerbicidesMCPA (40%) g 467.66Supplemental irrigation a m3 3340Diesel kg 60.67Agricultural machinery kg 11.36
Outputs
Products and co-products Units Value
Straw (11–14% moisture) t 3.70Fibre t 1.00
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dominated by two substances (N2O (20%) and CO2 fossil (79%)),which are mainly emitted from energy production, nitrate basedfertilizer production and application:
Table 3Environmental impacts of the cultivation, production and supply of hemp and flaxfibre.
Unit Hemp Flax
Impact categoriesAcidification (AP) kg SO2 eq. t−1 9.39 3.22Eutrophication (EP) kg PO4
−3 eq. t−1 14.6 2.28Global Warming (GWP) kg CO2 eq. t−1 1600 437Photochemical Oxidant kg C H eq. t−1 0.213 0.114
Woody core tSeeds (9% moisture) t
a As rainfall is not significant during growing season, irrigation is required.
pproximately, fibre yield is around 27% of retted straw. Finally,bre bales are delivered to the same pulp mill for their processing.
Sowing date is at the end of March and the seed rate is lowerhan hemp scenario. In addition, the upper part of the plant is cutnd threshed by a combined harvester in order to separate seedsrom the rest of the plant and the straw is laid over the field in rowso the dew retting stage.
As for the hemp scenario, inventory data related to the produc-ion of fertilizers (calcium nitrate ammonium, potassium chloridend triple super phosphate) and of pesticides (chlorophenoxy com-ound) consumed by the crop came from the Ecoinvent databaseNemecek et al., 2004).
Plant protection substances are applied in order to controlrganisms to improve the productivity of arable farming systems.evertheless, a part of the substances applied impact upon ter-
estrial and aquatic ecosystems as well as humans via wind drift,vaporation, leaching or surface run-off (Brentrup et al., 2004a).missions of synthetic pesticides to air, surface water, groundwa-er and soil were estimated according to the method proposed byauschild (2000).
.4. Allocation procedures
Allocation (partitioning of input or output flows of a unit pro-ess to the product under study) was needed along the study asoth agricultural processes yield more than one product. So, fibreemp cultivation also produces woody core and dust, and economicllocation was applied as fibre is the driving-force for hemp cultiva-ion and large differences in market prices are present (Gorchs andloveras, 2003). On the other hand, fibre flax cultivation yield alsoeeds, which are used for sowing and the surplus, is sold for otherims (oils, animal feed, flours). Unlike fibre hemp crop, there areo big differences in the market prices for flax stem and seed (vaner Werf and Turunen, 2006) and therefore results from mass orconomic allocation would be similar. For this reason, mass-basedllocation was considered.
. Results
Among the steps defined by the impact assessment stage in theCA methodology (ISO 14040, 2006), only the classification andharacterization stages have been considered. Normalization andvaluation were excluded since they are optional elements and
2.700.37
according to the goal and scope defined here, would not provideextra useful information.
Table 3 shows the environmental impact associated to theproduction of both crops, being flax the scenario that producesless impact in all the impact categories analyzed as well as non-renewable resources use, while hemp presents lower values forthe pesticide active substance consumption.
3.1. Global warming potential (GWP)
Emissions of gases with specific radioactive characteristics likecarbon dioxide (CO2) and nitrous oxide (N2O) lead to an unnatu-ral warming of Earth’s surface. This impact is commonly knownas global warming. In the hemp system, the production (specifi-cally ammonium nitrate) and use of fertilizers were identified asthe principal elements (70% of total GWP) responsible of emissionscontribute to this effect (Fig. 2) Regarding individual substances,N2O (58%) and CO2 fossil (42%) emissions dominated the contribu-tions to global warming mainly due to the application of nitrogento soil, nitric acid production and combustion of fossil fuels to thegeneration of electricity required.
Concerning to flax scenario, fertilizers production and use aswell as field operations (specifically irrigation process) were themain responsible (Fig. 2). This environmental category was again
Formation (POP)2 4
Flow indicatorsEnergy resources (EU) GJ t−1 13.2 12.4Pesticide use (PU) kg active
ingredient t−1– 1.18 × 10−4
S. González-García et al. / Resources, Conservation and Recycling 54 (2010) 923–930 927
Fig. 2. Relative contributions to GWP for fibre hemp and fibre flax scenarios. “Fieldopp
3
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Fopp
perations” refers to agricultural practices including scutching and baling. “Trans-ort” refers to transportation of fertilizers, pesticides (if the case) and fibre bales toulp mill. “Others” refers to the remaining processes.
.2. Acidification potential (AP)
Acidification is an impact category due mainly to emission ofcidificating substances, which causes important effects in the soil,roundwater, ecosystems and materials. In the hemp scenario,cidification was mainly due to mineral based fertilizers produc-ion and use (57%), and the scutching process (field operation)Fig. 3). Energy related emissions are the main contributions tohis category: Sulphur dioxide (SO2) originated from combustionf sulphur-containing fossil fuels (41%), ammonia (NH3) emissionsssociated to fertilizers use and production (34%), as well as nitro-en oxides (NOx) from combustion (25%).
Regarding the flax scenario, field operations such as irrigationnd scutching processes are mainly responsible for the results inhis impact category (more than 50% of total contributions), fol-owed by fertilizers production and use (Fig. 3): SO2 and NOx
missions represent approximately 47% and 20% respectively. NH3mitted as consequence of nitrogen application (volatilization) anditrate based fertilizer production stands for one third of the acid-
fication impact.NH3 emissions are strongly dependent on the nitrogen-fertilizer
ate: this type of emissions increase with increasing N-fertilizerates applied, so it will be needed to apply the optimum amount.
ig. 3. Relative contributions to AP for fibre hemp and fibre flax scenarios. “Fieldperations” refers to agricultural practices including scutching and baling. “Trans-ort” refers to transportation of fertilizers, pesticides (if the case) and fibre bales toulp mill. “Others” refers to the remaining processes.
Fig. 4. Relative contributions to EP for fibre hemp and fibre flax scenarios. “Fieldoperations” refers to agricultural practices including scutching and baling. “Trans-port” refers to transportation of fertilizers, pesticides (if the case) and fibre bales topulp mill. “Others” refers to the remaining processes.
3.3. Eutrophication potential (EP)
Eutrophication covers all potential impacts of having highenvironmental level of macronutrients, specifically nitrogen andphosphorus emissions to air, water and soil. This situation mightcause serious damages in both aquatic and terrestrial ecosystems.
In the hemp scenario, the use of fertilizers is the principal sourcecontributes to this impact category, followed by fertilizers produc-tion (Fig. 4). Nitrate (NO3
−) leaching, nitrogen and also phosphateemissions contribute to approximately 90% of the whole effect.
Regarding the flax scenario, fertilizers usage and productionare again the main factors responsible (Fig. 4). Nitrogen relatedemissions, phosphate and NO3
− leaching associated to fertilizingprocess are responsible of almost 65% of total.
3.4. Photo-oxidant formation potential (POP)
Photo-oxidant formation is the formation of reactive chemicalcompounds that are damaging to human health, ecosystems andcrops, by the action of sunlight on certain primary air pollutants.Photo-oxidants may be formed in the troposphere under the influ-ence of ultraviolet light by means of VOCs and CO in the presenceof NOx. Generally, Photo-oxidant formation potential is known assummer smog which is different from winter smog as it is charac-terised by high levels of inorganic compounds (particles, SO2 andCO). However, CML baseline 2000 methodology does not distin-guish between them and includes both in the same impact categoryunder the name Photo-oxidant formation potential (Guinée et al.,2001).
In the hemp system, field operations contribute to 50% of POP,being scutching process the main contributor to this category(Fig. 5). Fertilizers production involves almost the 40% of total con-tributions, specifically P-based fertilizer production. POP showsimportant contributions from energy-related emissions: SO2 andCO, which represent 71% and 17% of the total emissions, respec-tively. With regard to flax scenario, field operations (irrigation andscutching) are the main responsible (Fig. 5) and their contributionadds up to 67% of total. As in the case of hemp system, SO2 means66% of the emissions contribute to this category followed by CO(26%)
3.5. Non-renewable energy use (EU)
Non-renewable energy use refers to the depletion of energeticresources such as coal, crude oil, natural gas or uranium. Total
928 S. González-García et al. / Resources, Conservation and Recycling 54 (2010) 923–930
Fig. 5. Relative contributions to POP for fibre hemp and fibre flax scenarios. “Fieldoperations” refers to agricultural practices including scutching and baling. “Trans-pp
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Fopp
Table 4Processes that contribute more than 10% (hot spots) to impact categories or flowsin the fibre hemp system.
ort” refers to transportation of fertilizers, pesticides (if the case) and fibre bales to
ulp mill. “Others” refers to the remaining processes.
nergy use of the hemp and/or flax system (agricultural production,traw processing and transport subsystems) is 13.2 and 12.4 GJ t−1
13.2 and 18.6 GJ ha−1) respectively. These values were calculatedsing the Lower Heating Values proposed by Eco-indicator 95ethodology (Goedkoop et al., 1995). Other published studies of
imilar annual plants crops (Cardone et al., 2003; Martínez et al.,007; van der Werf, 2004; van der Werf and Turunen, 2006) havestimated results in the same range, obviously depending on thentensity of the cultivation among other factors. In particular, vaner Werf (2004) reported 11.4 GJ ha−1 for hemp crop, a figure that
s lower to our value where transport was included and other dif-erences occur (i.e. amount of fertilizers used).
Although fertilizers production is an important element foremp crop representing 39% of energy use (Fig. 6), field operationsre the main contributors in flax scenario (89%) as it is shown inig. 6, specifically irrigation process which involves 71% of total. Inhe case of hemp system, scutching and harvesting stage mean the7% and 11%, respectively. Oil crude, natural gas and uranium arehe main energy resources used in both systems (79% and 71% for
emp and flax, respectively).
ig. 6. Relative contributions to EU for fibre hemp and fibre flax scenarios. “Fieldperations” refers to agricultural practices including scutching and baling. “Trans-ort” refers to transportation of fertilizers, pesticides (if the case) and fibre bales toulp mill. “Others” refers to the remaining processes.
EU 17.0 Uranium 36.6
HarvestingEU 11.2 Oil crude 75.6
3.6. Pesticide use (PU)
Hemp crop does not require pesticide application. However,most agricultural productions rely on the use of chemicals to main-tain high crop yields (Margni et al., 2002). Flax fibre production isone of them and therefore plant protectors are applied, specificallyherbicides as they do not defend well from weeds, are applied. Dif-ferent types and rates of herbicide application have been reported(Easson and Molloy, 2000; Lloveras et al., 2006; Schmidt et al., 2004;van der Werf and Turunen, 2006; www.infoagro.com) and a dosageof 0.468 kg of active ingredient, (4-chloro-2-methylphenoxy) aceticacid, per ton of fibre was used here. Emissions of synthetic pesti-cides to air, surface water, groundwater and soil were estimatedaccording to Hauschild (2000) methodology taking into accountphysico-chemical characteristics of the active ingredient. In addi-tion, given the organic nature of the herbicide, degradation rate hasbeen considered in this case determined from the time of harvest-ing and the herbicide half-life for microbial degradation.
3.7. Identification of the hot spots
To summarise the results, Tables 4 and 5 present the processes,as well as the main substances within them, that are responsi-ble for the highest contributions to impact categories and energyuse in both scenarios. Those elements are generally named hotspots and their identification helps to improve the environmen-tal performance of the systems under study. Results are presentedas percentage of the total value for each impact category or flowindicator.
4. Discussion
The present study shows that four processes represent animportant contribution for many impact categories in both crops:fertilisation (including the production of the compounds), irriga-tion, harvesting and scutching.
The use of Nitrogen-based fertilizers (ammonium nitrate for
hemp and calcium ammonium nitrate for flax) is an importantsource of nutrient related emissions. In some situations, the typeof fertilizers used is the main driver of the emissions at the wholefarm level and changing the type of fertilizers could reduce theemissions and therefore, the environmental impact (Brentrup et al.,
GWP 11.1 CO2 98.8AP 22.2 SO2 87.9POP 22.9 SO2 96.2
004b; Charles et al., 2006). Nitrogen based fertilizers use lead toifferent N2O, NH3, NOx emissions and NO3
− leaching rates, whichontribute considerably to eutrophication, acidification and globalarming potential. The systems studied (flax and hemp) presentifferent NO3
− leaching rates not only due to mineral based fer-ilizer rate applied but also due to differences on the nitrogenontent of seeds and stems as well as on the NH3 volatilizationate.
NO3− leaching was identified as the greatest cause of eutroph-
cation potential in fibre hemp crop and therefore its reductionould have important consequences. In general, the optimization
f nitrogen fertilization and the reduction of the period betweenarvest and the establishment of the next crop are the main actionso reduce NO3
− leaching (Gustafson et al., 2000). As in this study itas considered that fertilization level was the optimum, the second
lternative seems to be the best option to prevent NO3− flushed
way from the soil. Other related agricultural studies show sim-lar results regarding eutrophication and acidification potentialsBrentrup et al., 2004b; Charles et al., 2006; Martínez et al., 2007;an der Werf, 2004).
The manufacture of nitrogen based fertilizers involves impor-ant emissions of greenhouse gases, typically CO2 and N2O, as wells other gaseous inorganic compounds (NH3). Reducing N2O emis-ions during their production (scrubbing techniques) would lead toreduction in the GWP associated (Brentrup et al., 2004b).
Energy related emissions (NOx, SOx, CO2) associated to fossiluels combustion are also of great importance and a change in fuelype could lead to their reduction and as a result to their impactn the categories under study. The increasing utilisation of renew-ble energy sources, for example, electricity from wind and hydroource, would lead to reduce CO2 fossil and SOx emissions consid-rably.
With regard to energy resources use, hemp scenario is morentensive than flax. Agricultural activities (field operations) areighly mechanized and have high energy consumption, up to 48%nd 89% of total in hemp and flax scenarios respectively. Specifi-ally, scutching and harvesting stage appear as main contributors inemp system, while the high electricity consumption due to irriga-
ion (71% of the total) dominates the energy use for flax production.
Pesticide use entails important damages to human health andcosystem: groundwater becomes too toxic for human consump-ion and biological activity in the soil is impaired, resulting damage
tion and Recycling 54 (2010) 923–930 929
to vegetation (Goedkoop et al., 1995). Pesticides use was zero forhemp crop. In the case of flax scenario, 0.468 kg of active ingre-dient was used. That amount is similar than other similar studies(Lloveras et al., 2006; van der Werf and Turunen, 2006). Field emis-sions associated to pesticide consumption were analyzed with agreat detail according to the method proposed by Hauschild (2000).
Finally, straw yields reported here can be considered unusuallylow, specifically for hemp crop where higher values (up to 8 t ha−1)have been reported from similar Spanish regions (Lloveras et al.,2006) and from other countries (Amaducci et al., 2000; Struik etal., 2000; van der Werf, 2002a; van der Werf, 2004) . Values werechecked with growers and they considered that the reasons can beshort vegetative period of the plants and/or meteorological condi-tions. Regarding flax, values can be also considered low althoughsimilar results have been reported for Spain (Lloveras et al., 2006)and European countries (Schmidt et al., 2004). Different climate andagricultural conditions in Europe cause large differences in yieldfrom one year to another and from one country to another (Schmidtet al., 2004).
In order to check the possible influence of analysing an unusu-ally low yield for hemp cultivation, a sensitivity analysis was carriedout by using higher straw yields (but keeping the same inputs andoutputs) from the same region although under different meteoro-logical conditions (different year) and irrigating conditions (Gorchsand Lloveras, 2003; Lloveras et al., 2006): 6 and 8 t ha−1. As expectedhemp scenario result in less environmental impact for all theimpact categories analyzed, so the conclusions from the compari-son are not affected as hemp stays as a preferable option from anenvironmental point of view. Besides, energy use per ton is logicallylower when higher yields are used and therefore support even morethe choice of hemp.
5. Conclusions
This study dealt with the field production, processing and trans-portation of two types of non-wood annual crops, flax and hemp,considering fibre as main product. An environmental comparisonwas carried out in order to know more about these two crops thatare used as non-wood cellulosic fibre for the manufacture of spe-ciality paper pulp.
System boundaries were covered from soil management up tostraw processing and transportation of fibre bales to pulp mill. Pro-duction of all inputs for each system (fertilizers, pesticides, seeds,energy carriers) and their supply was also included, as well asmachinery production, use and maintenance.
According to the results, both systems are low-input and low-impact crops in front of other agricultural crops i.e. potato orsugar beet. Nevertheless, energy consumption should be a focusof attention, specifically in the irrigating and scutching processes.In addition, a reduction of environmental impacts associated to theuse of fertilizers should be considered, as a decrease in the impactcategories and in particular, eutrophication potential, should alsobe obtained.
6. Future outlook
Future work will focus on the study of non-wood fibre process-ing stages in order to get a complete picture of the non-wood pulpproduction process.
This project has been developed within the framework of theBIORENEW Integrated Project (Project reference: NMP2-CT-2006-026456). S. González-García would like to express her gratitude
o the Spanish Ministry of Education for financial support (Granteference AP2005-2374) and A. Hospido to the Xunta de GaliciaIsidro Parga Pondal programme).
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