ARTICLE pubs.acs.org/est
Biodiesel Production in a Semiarid Environment: A Life Cycle Assessment Approach Wahidul K. Biswas,*,† Louise Barton,‡ and Daniel Carter§ †
Centre of Excellence in Cleaner Production, Curtin University, Bentley, Western Australia 6845, Australia School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Western Australia 6009, Australia § Department of Agriculture and Food WA, 3 Baron-Hay Court, South Perth, Western Australia 6151, Australia ‡
ABSTRACT: While the use of biodiesel appears to be a promising alternative to petroleum fuel, the replacement of fossil fuel by biofuel may not bring about the intended climate cooling because of the increased soil N2O emissions due to N-fertilizer applications. Using a life cycle assessment approach, we assessed the influence of soil nitrous oxide (N2O) emissions on the life cycle global warming potential of the production and combustion of biodiesel from canola oil produced in a semiarid climate. Utilizing locally measured soil N2O emissions, rather than the Intergovernmental Panel on Climate Change (IPCC) default values, decreased greenhouse gas (GHG) emissions from the production and combustion of 1 GJ biodiesel from 63 to 37 carbon dioxide equivalents (CO2-e)/GJ. GHG were 1.1 to 2.1 times lower than those from petroleum or petroleum-based diesel depending on which soil N2O emission factors were included in the analysis. The advantages of utilizing biodiesel rapidly declined when blended with petroleum diesel. Mitigation strategies that decrease emissions from the production and application of N fertilizers may further decrease the life cycle GHG emissions in the production and combustion of biodiesel.
’ INTRODUCTION Life cycle assessment (LCA) of greenhouse gas (GHG) emissions from biodiesel production has mainly focused on biodiesel production from soybean and rapeseed (or canola) oils produced in Argentina, Brazil, China, South Africa, and the USA,1-5 with very few studies conducted for semiarid climates.6,7 Most of LCA studies have utilized international default values proposed by the Intergovernmental Panel on Climate Change (IPCC) for calculating soil nitrous oxide (N2O) emissions8 and have not taken into account nitrous oxide (N2O) emission from nitrogen leaching or ammonia (NH3) volatilization.1-7,9,10 Crutzen et al.,11 who took into account IPCC default values both for direct field emissions and from nitrogen leaching and volatilization, concluded that the replacement of fossil fuels by biofuels may not bring the intended climate cooling due to the accompanying N2O emissions resulting from the application of synthetic N fertilizer to the biofuel crop. However, recent fieldbased research concluded that annual soil N2O emissions from the application of N fertilizer to canola in the semiarid region of southwestern Australia were 17 times lower than that predicted using the IPCC default value,12 suggesting that the LCA of GHG emissions from biodiesel production in semiarid regions may not be influenced by soil N2O emissions to the same extent as temperate climates.11 Semiarid and arid land regions constitute one-third of the global land area13 and are widely used for agricultural production, so understanding GHG emissions from biodiesel production from these regions is required to better understand global terrestrial trace gas losses. Consequently, the overall objective of this study was to assess the influence of soil N2O emissions on the life cycle global warming potential of the production and combustion of biodiesel from canola oil produced in a semiarid climate. Specifically the study (a) compared the GHG emissions r 2011 American Chemical Society
of biodiesel usage, calculated using a locally derived N2O emission value, with that using the Australian and IPCC international default values, (b) compared the GHG emissions of biodiesel usage with petroleum diesel, and (c) identified GHG mitigation potentials for reducing GHG emissions from the production and combustion of biodiesel.
’ MATERIALS AND METHODS LCA of Biodiesel and Associated Coproducts. The goal of the LCA study was to estimate the total GHG emitted due to production and combustion of biodiesel from canola oil in a semiarid climate of southwestern Australia. The functional unit that determines the scope and system boundary of this LCA is the production and combustion of 1 GJ (gigajoule) of canolabased biodiesel. A life cycle inventory (LCI) was developed that consisted of inputs (e.g., fertilizers, pesticides) and outputs [e.g., carbon dioxide (CO2), methane (CH4), and (N2O)] of three stages: prefarm, on-farm, and postfarm (Table 1). Prefarm data included the emissions from the production and transportation of inputs to the field to produce a canola crop, such as N fertilizer, pesticides, and diesel. A 30 tonne articulated truck, which is widely used in the rural Australia, traveled 180 km to carry fertilizers, pesticides, and herbicides to the site of the canola production in the present study (Cunderdin, 31°360 S, 117°130 E). Received: September 18, 2010 Accepted: February 10, 2011 Revised: February 9, 2011 Published: March 07, 2011 3069
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Table 1. Life Cycle Inventory of the Production and Combustion of 1 GJ of Biodiesel Using Local N2O Emission Value (scenario 3a) units
per GJ
urea production
kg
12.59
superphosphate production
kg
2.65
pesticide production
kg
0.04
herbicide production transportation of inputs from producer to paddock
kg tkmb
0.25 2.74
farm machinery production, seeder (9 m width)
USDc
0.05
farm machinery production, harvester (10 m header)
USD
0.19
farm machinery production, sprayer
USD
0.03
Prefarm
(20 m boom spray) On-Farm emissions from fertilizer applications, direct N2O-N
kg
5.45 10-3
emissions from fertilizer applications, CO2
kg
9.23
emissions from fertilizer applications, CH4 farm machinery operationsd, seeding
kg MJ
5.18 10-4 3.46
farm machinery operations, harvester (10 m header)
MJ
farm machinery operation, sprayer (20 m boom spray) MJ
3.46 10.4
Postfarm canola seed to canola oil
kWh
2.07
canola oil to biodiesel
kWh
0.61
transportation, from farm to canola oil factory
tkm
6
transportation, from canola oil factory to biodiesel
tkm
3
plant coproducts, protein meal
kg
coproducts, glycerol
kg
5.2
emissions from combustione, CO2 biogenic
kg
67.81
emissions from combustion, N2O
kg
0.00
emissions from combustion, CH4
kg
9.80 10-4
59.2
The value of direct soil N2O-N emissions measured at the present field site in southwestern Australia12 in partnership with indirect emission factors used by the Australian Government.23 b The unit for transport library is tonne-kilometer (tkm). c A USA input-output database was used to calculate the GHG emitted from manufacturing farm machinery.17 Since the US input-output database contains 1998 price values, the 1998 price of machinery in AUD per tonne of canola seeds produced was converted to 1998 US dollars by multiplying by 0.6. d Farm machinery consumes 1 for the present field site.24,25 The IPCC methodology predicts that leaching will only occur when Et/P is between 0.8 and 1.8 N2O-N emissions from NH3 volatilization from fertilizer application were calculated using the IPCC default value 8 in all scenarios, as this value was not determined at the present site; furthermore, this IPCC default value is currently used to calculate the Australian GHG inventory. The IPCC methodology assumes 10% of N fertilizer applied will be emitted as NH3 via ammonia volatilization, with 1% of the NH3 then emitted as N2O-N following atmospheric deposition. The value of N2O-N is multiplied with 44/12 to convert N2O-N to N2O. GHG Allocation for Coproducts. GHG emissions were allocated to each of the coproducts of the biodiesel production (protein meal, glycerol). The allocation could be calculated by either using the physical value of the inputs used for producing the coproducts [i.e., when the coproduct amount is determined by the mass flow of the inputs and outputs of the coproducing process26] or by using the economic value of coproducts. The physical values of inputs and outputs could not be differentiated for coproducts due to the absence of mass balance information of biological processes for canola production, so an economic allocation method was used to calculate the GHG emissions from the inputs and outputs of the coproducts.18,27 The use of one allocation method does not have a large impact on the LCA results when comparing production systems producing the same product (i.e., biodiesel production for three N2O-N emission factor scenarios).28 The allocation factors used to partition the greenhouse emissions to the various products (biodiesel, glycerol, and protein
Figure 1. GHG emissions from the production and combustion of biodiesel (BD) and petroleum diesel. Biodiesel emissions have been calculated using three scenarios: Scenerio 1, direct and indirect N2O emission factors from the IPCC; Scenario 2, direct and indirect N2O emission factors used by the Australian Government; Scenario 3, local direct soil N2O emission value and indirect N2O emission factors used by the Australian Government.
meal) were derived using the ratio of market values or sale proceeds in 2009 (Table 3) and following consultation with local industries (Australian Renewable Fuel, Perth, P. Duca, Pers. Comm.; Aus-Oil, Kojonup, Perth, J. Slee, Pers. Comm.). Consequently 65% of total GHG emissions due to production of canola oil and protein meal was allocated to canola oil, while 96% of the total GHG emissions emitted due to the production of biodiesel and glycerol was allocated to biodiesel. Comparison of Biodiesel with Petroleum Diesel. GHG emissions from the production and combustion of 1 GJ of biodiesel were compared with those emitted from production and combustion of 1 GJ from either petroleum diesel or a biodiesel blend (BD20, 20% biodiesel and 80% petroleum diesel). GHG emissions from the production and combustion of Australian diesel were obtained from the Commonwealth Scientific and Industrial Research Organization [CSIRO6,7]. BD20 (i.e., 20:80, biodiesel:petroleum diesel) was the selected blend, as it is the dominant biodiesel/petroleum diesel blend in the Australian market.7
’ RESULTS AND DISCUSSION GHG Emissions from Biodiesel Production and Combustion in a Semiarid Climate. The total GHG emissions from the
production and combustion of 1 GJ of biodiesel produced from canola oil varied depending upon which N2O emission data were utilized in the LCA (Figure 1). In the present study, 63 kg of CO2-e was emitted when the direct and indirect N2O emission factors were sourced from the IPCC (Scenario 1), 44 kg of CO2-e when the LCA utilized direct and indirect N2O emission factors currently used by the Australian Government (Scenario 2), and 37 kg of CO2-e when direct soil N2O emissions measured at the present field site in southwestern Australia12 were used in partnership with indirect emission factors used by the Australian Government (Scenario 3) (Figure 1). The incorporation of sitespecific N2O emission data in the present study (Scenario 3) decreased the total GHG emissions from the production and combustion of biodiesel produced from canola oil by 41% in comparison to that calculated using IPCC default values (Scenario 1) and by 19% in comparison to that calculated using emission factors currently used by the Australian government (Scenario 2). 3071
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Table 4. Reported GHG Emissions from 1 GJ of Biodiesel Production and Combustion GHG emissions feed stocks algae canola/rapeseed
soybean
(kg CO2 -e/GJ) -31.0 37
a, ref 10 current study (scenario 3)
43.3
b, ref 6
40.1
a, ref 9
115.0
c, ref 2
29.4 386.0 - 978.0
waste vegetable oil
references
ref 1 c, ref 5
48.2
a, ref 4
29.8 23.6
ref 3 ref 29
7.1
Figure 2. GHG emissions from the production and combustion of biodiesel (BD100) (Scenario 3), a blend of biodiesel and petroleum diesel (BD20), and petroleum diesel.
b, ref 30
a
Extrapolated by using the power consumption value of a 30 tonne articulated truck (i.e., 0.89 MJ/t-km).10 b Extrapolated by using the power consumption value of a 30 t articulated truck for each km traveled (10 MJ/km).6 c Extrapolated by using an average calorific value of biodiesel (36 MJ/kg).36
The total GHG emissions from the production and combustion of 1 GJ of biodiesel produced from canola oil in a semiarid climate was of similar magnitude to other values reported for biodiesel produced from vegetable oil in other locations (Table 41-6,9,29). However, the GHG emissions calculated in the present paper were approximately 5 times higher than that for biodiesel produced from waste vegetable oil30 (i.e., 7.1 kg CO2-e/ GJ), but the pre- and on-farm stages were excluded from the waste vegetable oil analysis. By contrast, GHG emissions from the production and combustion of biodiesel from the current study were 10 to 26 times lower than that from biodiesel produced from rapeseed (or canola) in Brazil,5 as the Brazilian analysis included the loss of CO2 sequestration resulting from clearing the land of native forest for soybean cultivation. Accounting for all GHG emissions associated with the production and combustion of biodiesel is essential for accurately assessing the ‘carbon footprint’ of biodiesel production its combustion. The total GHG emissions from the production and combustion of 1 GJ of biodiesel produced from canola oil estimated in the present study was influenced by the inclusion of NH3 volatilization. For example, including N2O emissions resulting from the deposition of volatilized N contributed 9% to the GHG emissions in Scenario 3. The current study, and that of Crutzen et al.,11 appears to be the only analyses that have taken into account both direct and indirect N2O emissions when assessing the global warming impact of biodiesel production from vegetable oil. The GHG emissions from the production and combustion of biodiesel produced from canola oil in the present study were greater than zero and therefore not carbon neutral. This finding is consistent with previously published studies investigating GHG from the production and combustion of biodiesel from vegetable oils, where emissions have ranged from 7.1 to 978 kg CO2-e/GJ (Table 4). By contrast, the production of biodiesel from other plant-based materials such as algae (-31 kg CO2-e/GJ, Table 4) has been shown to sequester more atmospheric GHG emissions than that associated with the production and subsequent combustion. Comparison of GHG Emissions from Biodiesel with Petroleum Diesel. The relative GHG emissions from biodiesel,
produced in a semiarid climate, and petroleum diesel differ depending on the soil N2O emission factors utilized in the LCA. The GHG emissions from the production and consumption of 1 GJ of biodiesel were 19% lower than that of petroleum diesel when using the IPCC default N2O emission factors (Scenario 1; Figure 1). Utilizing current Australian N2O emission factors (Scenario 2), life cycle GHG emissions of biodiesel were 45% lower than that of petroleum diesel, with a further 8% decline achieved when the locally measured value of N2O emissions (Scenario 3) was included in the LCA. Our findings contrast with Crutzen et al.,11 who concluded that the replacement of petroleum diesel by biodiesel did not decrease GHG from fuel production and consumption because of the accompanying soil N2O emissions from crop production. Since BD20 (20:80, biodiesel:petroleum diesel) is widely available in Australia,9 the production and combustion stages of BD20 was compared with pure biodiesel (Scenario 3) and petroleum diesel. The production of biodiesel emitted more GHG emissions (37 kg CO2-e) than the production of diesel (11 kg CO2-e) (Figure 2). However, the GHG emissions from the combustion of biodiesel (0 0.02 kg CO2-e) were less than those from the diesel combustion (67 kg CO2-e). Consequently, the life cycle GHG emissions from the production and combustion of biodiesel were 52% lower than petroleum diesel. The advantages of utilizing biodiesel rapidly declined when blended with petroleum diesel, with GHG emissions from the production and combustion of BD20 only 10% less than that of petroleum diesel (Figure 2). Sources and Mitigation of GHG Emissions from Biodiesel Production and Combustion. GHG emissions from the production and combustion of biodiesel may be further lowered by identifying, and then mitigating, significant sources of GHG emissions. In the present study, when local N2O soil emissions values were included (Scenario 3), the GHG emissions from the production of fertilizer were the single greatest source of GHG emissions (11 kg CO2-e/GJ, 29% of the total life cycle emission), followed by CO2 emissions from the hydrolysis of urea (9 kg CO2-e/GJ, 25%) and the production of herbicide (6 kg CO2-e/ GJ, 16%) (Table 5). Indirect N2O emissions from NH3 volatilization accounted for 9% (3 kg CO2-e/GJ of the total GHG emissions), while direct soil N2O emissions represented 5% (2 kg CO2-e/GJ) GHG emissions from the production and combustion of biodiesel (Table 5). The GHG emissions from the production and application of fertilizer, including direct and indirect N2O emissions, and CO2 3072
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Table 5. Contribution of Inputs and Outputs to GHG Emissions (CO2 equivalents) from the Production and Combustion of 1 GJ of Biodiesel Produced from Canola Oil kg CO2-e % of the total Prefarm fertilizer production
10.7
pesticide production
0.5
1
herbicide production
5.8
16
farm machinery production transportation
0.2 0.3
1 1
17.5
48
direct soil N2O emissions
1.7
5
indirect soil N2O emissions (NH3 volatilization)
2.8
7
soil CO2 emissions (urea hydrolysis)
9.2
25
farm machinery operation
2.2
6
15.9
43
1.5 0.6
4 2
subtotal
29
On-Farm
subtotal Postfarm conversion of seeds to canola oil conversion of canola oil to biodiesel combustion of biodiesel
0.0
0
transportation
1.3
3
subtotal
3.4
9
36.8
100
total
emissions due to urea hydrolysis, accounted for 67% (25 kg CO2e/GJ) of the total life cycle GHG emissions of biodiesel. Mitigation strategies need to address GHG emissions from fertilizer production and application in order to further decrease GHG emissions from the production and combustion of biodiesel. For example, in Denmark, approximately 50% of on-farm emissions from wheat production was mitigated by substituting chemical fertilizers with organic fertilizer.31 This was because 50% less energy was needed to manufacture the organic fertilizer than the inorganic fertilizer. However, the appropriateness of substituting synthetic N fertilizer with organic fertilizer requires further research in semiarid regions from a life cycle perspective to ensure that this substitution is acceptable. Incorporating legumes in cropping rotations may also provide another opportunity to decrease GHG emissions from biodiesel production by decreasing N-fertilizer inputs.18,32,33 Industrial symbiosis, where industries collaborate to exchange products and byproduct, may also minimize CO2 emissions from the manufacture of fertilizer.34 For example, in the present process, 70 000 tonnes of CO2 produced by the local fertilizer company at their ammonia plant is sold annually to a nearby alumina processing plant, thereby mitigating some of the emissions associated with fertilizer production.34 To the best of our knowledge, this is the first study to incorporate local soil N2O emission data in an LCA of GHG emissions from the production and combustion of biodiesel. The GHG emissions from the production and combustion of biodiesel produced from canola in a semiarid climate of Western Australia were equivalent to 37 kg of CO2-e/GJ when utilizing a local value for direct soil N2O emissions and accounting for indirect soil N2O emissions, which was 41% less than the value
estimated using IPCC default values. This finding demonstrates the importance of utilizing regionally specific data when assessing GHG from the production and consumption of biodiesel. GHG emissions from the production and combustion of biodiesel were 53% lower than that from petroleum diesel when utilizing a local value for direct soil N2O emission factors. The advantage of utilizing biodiesel decreased as biodiesel was blended with petroleum diesel. A large proportion of the GHG emissions from biodiesel production was from the production and application of chemical fertilizers, suggesting that GHG emissions could be further lowered by decreasing the reliance on chemical fertilizers or introducing industrial symbiosis during the fertilizer manufacturing process.
’ AUTHOR INFORMATION Corresponding Author
*Phone: þ61 8 9266 4520; fax: þ61 8 9266 4811; e-mail:
[email protected].
’ ACKNOWLEDGMENT This research was funded by the Department of Agriculture and Food Western Australia, Department of Climate Change, and the Grains Research & Development Corporation, Australia. Comments made by three anonymous reviewers improved the manuscript. ’ REFERENCES (1) Huo, H.; Wang, M.; Bloyd, C.; Putsche, V. Life Cycle Assessment of Energy Use and Greenhouse Gas Emissions of Soybean-Derived Biodiesel and Renewable Fuels. Environ. Sci. Technol. 2009, 43 (3), 750–756. (2) Harding, K. G.; Dennis, J. S.; von Blottnitz, H.; Harrison, S. T. L. A life cycle comparison between inorganic and biological catalysis for the production of biodiesel. J. Cleaner Prod. 2007, 16, 1368-1378. (3) Hu, Z.; Tan, P.; Yan, X.; Lou, D. Life cycle energy, environment and economic assessment of soybean based biodiesel as an alternative automotive fuel in China. Energy 2008, 33, 1654-1658. (4) Panichelli, L.; Dauriat, A.; Gnansounou, E. Life cycle assessment of soybean-based biodiesel in Argentina for export. Int. J. Life Cycle Assess. 2009, 14 (2), 144-159. (5) Reijnders, L.; Huijbregts, M. A. J. Biogenic greenhouse gas emissions linked to the life cycles of biodiesel derived European rapeseed and Brazilian soybeans. J. Cleaner Prod. 2008, (16) 477-482. (6) Greenhouse and Air Quality Emissions of Biodiesel Blends in Australia; Report No. KS54C/1/F2.27; Commonwealth Scientific and Industrial Research Organisation: Canberra, Australia, 2007; http:// www.csiro.au/files/files/phim.pdf. (7) Life Cycle Assessment of Environmental Outcomes and Greenhouse Gas Emissions from Biofuels Production in Western Australia; Report KN29A/WA/F2.5; Commonwealth Scientific and Industrial Research Organisation: Canberra, Australia, 2008; http://www.agric.wa.gov.au/ objtwr/imported_assets/content/sust/biofuel/csiro_wa_biofuels_lca_ report.pdf. (8) 2006 IPCC Guidelines for National Greenhouse Gas Inventorie; Intergovernmental Panel on Climate Change (IPCC): Geneva, 2006; http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/4_Vol.4/V4_11_ Ch11_N2O&CO2.pdf. (9) Beer, T.; Grant, T.; Williams, D.; Watson, H. Fuel-cycle Greenhouse Gas Emissions from Alternative Fuels in Australian Heavy Vehicles. Atmos. Environ. 2002, 36 (4), 753-763. (10) Campbell, P. K.; Beer, T.; Batten, D. Greenhouse gas sequestration by algae- energy and greenhouse gas life cycle studies. Presented 3073
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