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Benchmarking the Environmental Performance of the Jatropha Biodiesel System through a Generic Life Cycle Assessment J. Almeida,† W. M. J. Achten,†,* M. P. Duarte,‡ B. Mendes,‡ and B. Muys † † ‡
Division Forest, Nature and Landscape, Katholieke Universiteit Leuven, Celestijnenlaan 200 E Box 2411, BE-3001 Leuven, Belgium UBIA, Grupo de Disciplinas da Ecologia da Hidrosfera, Faculdade de Ci^encias e Tecnologia, FCT, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
bS Supporting Information ABSTRACT: In addition to available country or site-specific life cycle studies on Jatropha biodiesel we present a generic, location-independent life cycle assessment and provide a general but in-depth analysis of the environmental performance of Jatropha biodiesel for transportation. Additionally, we assess the influence of changes in byproduct use and production chain. In our assessments, we went beyond the impact on energy requirement and global warming by including impacts on ozone layer and terrestrial acidification and eutrophication. The basic Jatropha biodiesel system consumes eight times less nonrenewable energy than conventional diesel and reduces greenhouse gas emissions by 51%. This result coincides with the lower limit of the range of reduction percentages available in literature for this system and for other liquid biofuels. The impact on the ozone layer is also lower than that provoked by fossil diesel, although eutrophication and acidification increase eight times. This study investigates the general impact trends of the Jatropha system, although not considering land-use change. The results are useful as a benchmark against which other biodiesel systems can be evaluated, to calculate repayment times for land-use change induced carbon loss or as guideline with default values for assessing the environmental performance of specific variants of the system.
’ INTRODUCTION Biofuels have been hyped as renewable liquid energy sources that reduce nations’ dependency on fossil fuels and as a climate change mitigation option.1 Investigating if biofuels are a good option to reduce greenhouse gas (GHG) emissions compared to the fossil fuel system relies on the quantification of such reductions. This needs in-depth analysis and depends on many aspects of the biofuel production and use process (“well-to-wheel”). Life cycle assessment (LCA) is considered as one of the best available tools for such analysis.2 Among the available biofuel crops, Jatropha curcas L. (further called Jatropha) received much attention as a nonfood feedstock.3 Jatropha produces toxic oil and is a perennial with a clear drought avoidance strategy and relatively higher water use efficiency.4 As such, Jatropha would not compete with food production or with the maintenance of forest ecosystem services (e.g., biomass carbon stocks),5 therefore minimizing biofuels’ pressure on land.6 However, due to the lack of scientific knowledge, industrial Jatropha production and expansion has been risky.7,8 Currently, science is catching up with the made investments through r 2011 American Chemical Society
acquired insights in aspects such as optimal agro-practices and biophysical limits,9,10 crop behavior (e.g., refs 1014) and byproduct use (e.g., refs 15, 16). Several location-specific LCA studies on Jatropha biodiesel have been published recently, pointing to a favorable GHG and energy balance.1725 Most of these studies only consider energy and/or GHG balance, while other impact categories are also important to get insight into the overall environmental performance of a biofuel system.2 Further aspects such as water footprint and land-use impacts are still under discussion.5,14,26,27 In this paper we present a generic, location-independent LCA providing a general and profound insight into the environmental performance of the production and use of Jatropha biodiesel. With this study we aim to (i) broaden the scope of available information on the system’s performance by assessing environmental impacts Received: January 21, 2011 Accepted: May 10, 2011 Revised: April 22, 2011 Published: May 17, 2011 5447
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Figure 1. System boundaries of the Jatropha system, the reference system and the system boundary expansion. *: byproducts refer to scenario A.
beyond the energy and GHG balance; (ii) provide benchmark values of these impacts useful in the evaluation of specific Jatropha projects; (iii) assess the influence of changes in yield, byproduct use and production chain setup on the environmental performance; and (iv) identify performance improvement options.
’ MATERIALS AND METHODS The LCA exercise was executed in accordance to the International Organization for Standardization guidelines (ISO 1404043). Goal, Scope, and System Boundaries. The Jatropha system was analyzed from “well-to-wheel”, from Jatropha cultivation to biodiesel consumption (Figure 1). Operations included field preparation and nursery, cultivation, harvesting, oil extraction, transesterification, end use and transportation of inputs and outputs. Construction and maintenance of infrastructure and equipment were accounted at all stages. Following the typical setup of most current Jatropha activities, a decentralized production chain with local consumption of biodiesel was modeled as base scenario (Figure 1). The environmental performance of the Jatropha biodiesel system was evaluated by quantifying its nonrenewable energy requirement (NRER) [MJ], global warming potential (GWP) [kg CO2-eq], ozone layer depletion (OLD) [kg CFC-11-eq] and terrestrial eutrophication and acidification (TEA) [kg SO2-eq]. The results were reported per megajoule (MJ) of biodiesel delivered by the system. This measure is the functional unit (FU). The performance of the Jatropha system was compared to the performance of fossil diesel, which is the reference system. The reference system includes crude oil extraction, refining, regional distribution and storage, end use, and intermediate transportation (Figure 1). In all scenarios the allocation of environmental burdens to byproduct was avoided by expanding the system boundaries.28 By-products were included in the Jatropha system and their functional equivalents in the reference system. Hence, the system was debited with the environmental burdens of the production of the functionally equivalent products in the reference system (Figure 1). Scenarios. The base scenario represents the current situation of Jatropha cultivation, as based on the questionnaires and expert
interviews (see Data Collection). Other scenarios look at (A) alternative byproduct usage (proposed as a potential life cycle system improvement24) and (B) product chain centralization (a probable way forward 29): Scenario A. In this scenario anaerobic digestion of the seed cake is added to the system. The biogas and effluent produced during this step avoid natural gas and inorganic fertilizer production in the reference system. Scenario B. In this scenario the locally extracted oil is transported to a centralized transesterification unit, which requires an extra transportation step between extraction and transesterification. Life Cycle Inventory Analysis. Data Collection. The primary data provided insight both into the actual practices and hand input (materials, water, and energy) and output (product and byproduct quantities). The data were gathered from (i) questionnaires submitted to Jatropha entrepreneurs with replies from Mexico, Brazil, and Tanzania with a response rate of 43%; (ii) direct observations and consultation with experts in 25 Jatropha sites spread throughout eight Indian states (100% response rate); (iii) literature set in India and Thailand (Supporting Information (SI) Figure S1, Table S10). Background data were acquired from life cycle inventory databases Ecoinvent (Swiss Centre for Life Cycle Inventories, Switzerland), BUWAL 250 (Swiss Department of the Environment, Transport, Energy and Communications, Switzerland) and ETH-ESU 96 (Swiss Federal Institute of Technology Zurich, Switzerland). Transport occurs at nearly all stages of the product system and is an influential contribution in a LCA.30 Jatropha plantations were listed from visited sites and information divulged in online literature or conveyed by the questionnaires and personal communications with entrepreneurs. Distances were calculated between these and input production locations (SI Figure S1, Tables S1023). Descriptive statistics (mean ( standard deviation) were calculated for the inventory data. The resulting means used in the LCA are given in Table 1. Production System. The production system is based on a rotation period of 20 years, 2500 plants ha1 10,31 yielding an average 4.3 t ha1 of dry seeds (direct observations and literature17,18,32,33). A sensitivity analysis was executed to acquire insight into the effect of the yield on the LCA results in each 5448
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Table 1. Key Inputs and Outputs of The Jatropha System Presented per 1 Megajoule of Produced Biodiesel input fertilization in establishment
amount
unit
N
2.8
g
P K
0.89 1.86
g g
N
6.63
g
P
2.15
g
K
4.79
g
irigated water
0.56
m3
methanol
1.36
g
sodium hydroxide
0.22
g
fertilization in cultivation
electricity transport
road freight
26.08 1.03
Wh km
rail freight
0.6
km
sea freight
8.17
km
output
amount
biodiesel
25.6
unit g
fertilizer field emissions
N2O
0.094
g
NO3
2.82
g
biodiesel end use emissions
NH3 NOx
0.94 54.69
g mg
3.42
mg
PM seed cake
133.31
g
glycerine
4.55
g
impact category (see below). Seedlings are grown in polybags in nurseries.10,31 Prior to transplantation, the field is prepared with a tractor working 6 h ha1 (questionnaires). The use of fertilizer during plantation establishment and rotation period is based on direct observations and literature 17,18 (Table 1). NO3, NH3 and N2O field emissions to air and water from N application were included according to IPCC guidelines.34 Pests are prevented by using pyrethroid insecticides (questionnaires). Oil is extracted by cold pressing with an electric screw press17 with an extraction rate of 16.32 kg oil per 100 kg dry seed.35 Transesterification converts 97% of the oil mass into biodiesel.35 Reagents and catalyst inputs follow a 0.2 methanol: oil and a 0.01 NaOH:oil mass ratio,35 with methanol having a recovery ratio of 0.739 (own data) (Table 1). The exhaust emissions of biodiesel combustion correspond to emission profile of a Toyota Hilux pick-up truck,34,36 adjusted for biodiesel characteristics.37 Assumptions. Based on on-field experience, questionnaires and literature review we assumed manual weeding, pruning and harvesting. Information about Jatropha’s irrigation practice is scarce and imprecise. It is known that optimal growth levels occur in regions with 1500 mm rainfall.38 We assumed that the seed cake is applied as soil amendment,10 but not in the Jatropha fields of its origin, as indicated by questionnaire responses. It was further assumed that the supplied energy follows the energy mix prevalent in the regions where Jatropha is produced: coalgenerated electricity and fossil diesel for transportation.39 Impact Assessment. Environmental impact assessment was executed with SimaPro LCA software (PRe, The Netherlands) using IMPACT2002þ method. For each impact the share of the different contributing production phases (Jatropha cultivation, including nursery and field preparation, oil extraction, biogas production (in scenario A
only), oil transesterification and end use) are indicated. The avoided production burdens of products analogue to Jatropha byproduct are credited to the production phase of the byproduct. Transportation is part of the burden of the hauled commodity. Sensitivity Analysis. In general, yield has an important role in the overall environmental impact of a land-based system. Yield showed great variability among literature and direct observations. Keeping all yield-independent variables constant, the LCA was executed for the base scenario for seven yield values (0.5, 1; 1.5; 2, 2.5, 3.5, and 5 t ha1) based on the global yield classification used by Trabucco et al.38
’ RESULTS AND DISCUSSION Nonrenewable Energy Requirement. The results show a favorable performance of Jatropha-based biodiesel system regarding the fossil alternative. The base system (0.48 MJ FU1) consumes nearly 8 times less per FU than the reference system (3.88 MJ FU1) (reduction of 88%) (Figure 2). Cultivation consumes much more energy than the remaining phases (68% of total). This contradiction with literature 18,19,21,23 is a combined effect of different input quantities (namely fertilizers and methanol) and different allocation options (SI Table S16). Scenario B consumes ca. 5 times less than the reference system (reduction of 78%). This is a consequence of the additional expenditure in hauling oil to centralized transesterification units. Biogas production from seed cake (scenario A) reduces NRER by 105%. As the extraction phase is not credited for the seed cake as fertilizer anymore, its contribution to the NRER increases compared to the base scenario. However, the production of biogas and its effluent (credited to ‘biogas production’ in Figure 2) offsets this increase. Global Warming Potential. The base system reduces GHG emissions by 51% compared to the reference system (0.05 kg CO2-eq FU1 versus 0.1 kg CO2-eq FU1). This result represents the lower part of the range of reduction percentages available in literature (4972%).20,21 In contrast to what was found with NRER, the base and A scenarios show about the same reduction in terms of GWP (54%). If seed cake is used to replace an energy source more pollutant than natural gas (e.g., coal), the GHG savings are higher.4 Scenario B shows a lower GWP reduction (30.5%) than the base scenario, owing to the extra transportation step. The cultivation phase is the main contributor in all scenarios (76% in the base system, 55% and 74% in scenarios A and B). The fertilizer chain (production, transport, and field emissions from application) represents the largest share in this contribution: 91%. This observation coincides with previous Jatropha biodiesel LCA studies.17,18,20,22 End use contributes with 4%. The credit attributed to the transesterification step for the avoidance of glycerin production reduces the overall GWP impact of the system in this step. Ozone Layer Depletion. Opting for Jatropha biodiesel instead of fossil diesel has a clear advantage in terms of ozone layer depletion (Figure 2). The base system emits 8.8 109 kg CFC11-eq FU1, in contrast to an emission of 2.1 108 kg CFC11-eq FU1 in the reference system. The main contributor to this result is the avoidance of glycerin production, which overcompensates the impact of the remaining phases. While scenario A has a similar result, the transport burden in scenario B slightly increases the CFC11-eq emissions compared to the base scenario. 5449
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Figure 2. Life cycle impacts of the Jatropha biodiesel (b: total impact) compared to the reference system (-).The bar stacks represent the contribution of different production phases. Impact categories: nonrenewable energy requirement (NRER), global warming potential (GWP), ozone layer depletion (OLD) and terrestrial acidification and eutrophication (TAE).
Figure 3. Sensitivity analysis of NRER (A) and GWP (B) regarding yield variation by 0.5, 1; 1.5; 2, 2.5, 3.5, and 5 t ha1. “Base” is the reference yield of 4.3 t ha1 considered in the base system.
Terrestrial Acidification and Eutrophication. Different from what we had found for the previous impact categories, TAE potential is greater in the biodiesel system than in the reference system. The base scenario scores 1.1 102 kg SO2-eq FU1 versus 1.3 103 kg SO2-eq FU1 in the reference system, which is an 8 times increase (Figure 2). Reinhardt et al.17 estimated a 4.5 times increase of acidification and 3.5 times increase of eutrophication impact FU1. The discrepancy is owed to lower fertilization levels. The cultivation phase is the biggest contributor to this impact (92%, 86%, and 87% in the base, A and B scenarios respectively) owing mainly to NH3 and NO3 field emissions from fertilizer application. Since this phase is common to the base system and the alternative scenarios, this impact category shows the same impact trend in all scenarios. Scenario B, which
bears additional SO2-eq emissions due to the transport of oil to centralized transesterification plants, shows only a slightly increased impact. The few credits arise from seed cake use, but are negligible. Sensitivity Analysis. NRER and GWP show little variation above yields of 1.5 t ha1 but are high below that yield level (Figure 3). TAE behaves similarly, while OLD shows little or no sensitivity to yield. Although its decrease curve is pronounced, the total amplification factor of the impact in TAE is lower than in NRER and GWP. Figure 3 shows that with a yield of 0.5 t ha1 the Jatropha biodiesel system outperforms the reference system in terms of NRER. In fact, the reference system shows lower GWP if Jatropha yields are lower than 1 t ha1. 5450
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Environmental Science & Technology Life Cycle Interpretation. Interpreting LCA results and gaining insight in the overall environmental performance of a production system is not straightforward. It depends on the evaluation of the relative importance of each environmental impact category and their trade-offs. Although several impact assessment methodologies are available to perform such evaluations, we opted into work with a methodology which enables the presentation and discussion of impacts and trade-offs in their basic units. The LCA outcome presented in this paper suggests that Jatropha biodiesel system is a promising alternative transportation fuel system to fossil diesel. The NRER, GWP, and OLD are considerably lower than the reference system. One important contribution to this positive balance arises from seed-cake use. The extent to which it does so depends on its finality: energy generation is more favorable than artificial fertilizer displacement (confirming Reinhardt et al.17). The trade-offs for these benefits are higher eutrophication and acidification. This increase is a general trend in a shift from a fossil to biodiesel system, and is mainly triggered by nitrogen related burdens during the agricultural phase.40 The results indicate that the Jatropha biodiesel system has roughly half of the GWP of the equivalent fossil system. It should be noted that these figures do not include land-use change impact, hence omitting a potential large impact through carbon stock loss,41,42 as exemplified by Bailis and Baka43 and Lapola et al.44 Compared to other biofuels, Jatropha’s GWP reduction rate falls among the lower values available in literature. Studies on palm oil biodiesel point to GWP reductions from 38% to 79.5%4549 and other fuels such as sunflower, soy, and rapeseed biodiesel (4065% reductions),2,45 switchgrass, and corn stover ethanol (57% and 65%)50 and soybean fuels (5774%),51 but these crops often grow in more humid climates and might provoke a bigger carbon debt due to land-use change. The reliability of the results of a LCA depends largely on scope and inventory attributes. Our scope and inventory involved several types of data sources which increased data completeness. However, great variability leads to high uncertainty. This is not unexpected owing to the system’s immatureness and the nature of this LCA. Still, it does not compromise result fitness as corroborated by the sensitivity analysis, which probed the impacts of variability around the yield. The average seed yield is a crucial factor in the distribution of impact per FU and is quite high in this study (4.3 t ha1 yr1). The yields that were accounted for in inventory were very wideranged, which echoes a scientific knowledge gap.38,41 The wide range can be caused by different climatic and abiotic conditions, or different chemical, physical or management inputs, factors which are inherently variable as well. The sensitivity analysis shows us that a yield of 0.5 t ha1 yr1 is minimal necessary to attain improvement in NRER. Improvement of GWP compared to the fossil fuel system only comes above 1 t ha1 yr1. Hence, despite Jatropha’s variable yields,35 the performance of its biodiesel relatively to conventional fossil diesel can be expected to be positive in terms of NRER and GWP. The influence of the yield on the other impact categories is negligible and is unlikely to alter the system’s position relative to the reference system. Fertilizers are the main stressors in the environmental performance of the entire system, followed by the remaining inputs of the cultivation phase. Hence, optimized cultivation practices (e.g., soil amendment, pruning, spacing, irrigation) could considerably reduce environmental impacts. System enhancement should also
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involve seizing byproduct maximum potential. However, byproduct use is only realistic if it has a place on the market. Further improvement options lie in investing in superior seed lines and in plant breeding programs or choosing to deploy Jatropha activities in areas best suited, which can attain the double goal of increasing yield and minimizing cultivation inputs.52 Still, our results suggest that aiming at yield improvement does not offer much room for impact mitigation. In general, educated management options based on scientifically solid information tend to reduce environmental impacts, besides leading to sound investments. By using averages of both inputs and outputs we came to the generic trend of the environmental (site- and country-independent) performance of the Jatropha system for transportation biodiesel. Impact results show the inherent potential of the Jatropha system. They are useful as benchmark values against which improvements can be measured. Likewise, they could be used as guideline if it is impossible to assess the environmental performance of a specific situation (e.g., in carbon credit application through the UNFCCC Clean Development Mechanism Energy Projects).
’ ASSOCIATED CONTENT
bS
Supporting Information. Figure 1, questionnaire, and additional information. This material is available free of charge via the Internet at http://pubs.acs.org
’ AUTHOR INFORMATION Corresponding Author
*Phone: þ32 (0) 16 329721; fax: þ32 (0) 16 329760; e-mail:
[email protected].
’ ACKNOWLEDGMENT This research is funded by the Flemish Interuniversity Council, University Development Co-operation (VLIR-UOS) and is a contribution of the R&D Platform on Climate and Development Cooperation (KLIMOS). All questionnaire respondents are acknowledged for sharing their information. We thank Dr. Carolin Spirinckx of VITO (Flemish Institute for Technological Research) and Antonio Trabucco and Omid Azadibougar of K.U. Leuven for their collaboration. The constructive comments, edits, and suggestions of three anonymous reviewers are greatly acknowledged. ’ REFERENCES (1) Verrastro, F.; Ladislaw, S. Providing energy security in an interdependent world. The Washington Q. 2007, 30 (4), 95–104. (2) Cherubini, F.; Bird, N.; Cowie, A.; Jungmeier, G. Energy-and greenhouse gas-based LCA of biofuel and bioenergy systems: Key issues, ranges and recommendations. Resour. Conserv. Recycl. 2009, 53, 434–447. (3) G€ubitz, G.; Mittelbach, M.; Trabi, M. Exploitation of the tropical oil seed plant Jatropha curcas L. Bioresour. Technol. 1999, 67 (1), 73–82. (4) Maes, W. H.; Achten, W. M. J.; Reubens, B.; Raes, D.; Samson, R.; Muys, B. Plant-water relationships and growth strategies of Jatropha curcas L. seedlings under different levels of drought stress. J. Arid Environ. 2009, 73 (10), 877–884. (5) Makkar, H. P. S.; Becker, K. Jatropha curcas, a promising crop for the generation of biodiesel and value-added coproducts. Eur. J. Lipid Sci. Technol. 2009, 111 (8), 773–787. 5451
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