Biodiesel is now recognised as one alternative to petroleum-based diesel. It is renewable and has significantly lower greenhouse emissions - effectively zero if renewable energy is used in its production. It has a number of additional advantages including creation of rural employment and development, improved air quality, and decreased reliance on external sources of oil.

The Story of Biodiesel

Introduction
Global oil supplies are reaching the point where demand may outstrip supply. When this occurs, it is expected that oil prices will increase significantly. In addition, combustion of geological oil and derivatives such as petrol releases greenhouse gases that cause global warming. Biodiesel is seen as one alternative that can help to reduce the sustainability impacts of these events. However, the production and use of biodiesel are not without additional impacts - both positive and negative. The following outlines the production and use of biodiesel, together with the various impacts that these can have on ecological, social, and economic sustainability.

Background
The economies of all industrialised societies are based on consumption of geological oil. These oil supplies are finite and concentrated in areas of political instability. Scarcity will increase prices and have a significant impact on world economies. Combustion of oil and oil-based products such as petrol produces greenhouse gases that are responsible for global warming. Global warming will also have significant impacts on global economies, societies and the environment. For these reasons, alternatives to geological oil and derived products are sought.

An Historical Perspective
In 1895, the first diesel engine was developed by Dr. Rudolf Diesel. This was first demonstrated at the World Exhibition in Paris in 1900. However it wasn't powered by what we now know as diesel, instead it used peanut oil as fuel.1 Thus the first diesel engines were designed to be fueled by vegetable based fuels. However in the early 1900's, new drilling techniques and availability of geological oil lead to petroleum-based fuels (diesel and petrol) becoming cheap and the fuels of choice.

Recently however, there has been increased interest in non-petroleum fuels. This has been for a number of reasons, the most significant of which are global warming and concern over access to oil supplies.

Combustion of petroleum-based diesel and petrol results in emission of carbon dioxide, the most significant greenhouse gas in terms of total contribution to global warming.2 Transport contributed 16.1% of Australia's greenhouse gas emissions in 1999, with road transport making up 83.2% of these.3 Global oil supplies are predicted by various commentators to peak between 2003 and 2020. After this peak, as supply outstrips demand, prices will increase significantly.4 In Australia, oil production is expected to rapidly decline over the next 10 years to approximately half that of current levels. This is expected to result in petroleum-based international trade changing from a surplus of $1.2 billion in 2000/01 to a projected deficit of $7.6 billion by 2009/10, reducing Australia's international competitiveness and Gross Domestic Product (GDP).5

A number of alternative fuels are available (biodiesel, hydrogen, natural gas, ethanol, and methanol), all of which have lower greenhouse gas emissions and reduce oil dependency. It is most likely that all will contribute in some way to the fuel-mix of the future. Here we will look only at biodiesel.

Worldwide Biodiesel Developments
Biodiesel is currently commercially produced in Germany, Italy, Austria, the Czech Republic, Malaysia and the United States, and is most advanced in the United States and Europe, which currently produce 2 billion and 1 billion litres of biodiesel per year respectively.6

In the US, a bill was passed ensuring that all heavy transporting companies source 2% of their fuel from biodiesel. A number of bus and truck companies are trialling a B20 (20% blend of biodiesel and diesel), and the US Army now require new tanks and trucks to be compatible with biodiesel. In 2001 a US Department of Agriculture study concluded that an increase of 195-260 million gallons of biodiesel by 2010 was feasible. The predominately soy-based biodiesel (due to a surplus of soy-oil) would also boost the total crop cash earnings by US$5.2 billion with an average net income increase for farmers of $300 million per year.7

Use of biodiesel is most advanced in Europe. B100 or pure biodiesel is now widely available in Germany, Italy and Austria. In Germany there are over 1000 outlets where biodiesel is cheaper than standard diesel. France, currently the largest user of biodiesel in the world, has a minimum mix of 5% in all diesel sold, with B50 becoming more common and popular.8

In both Europe and the US some diesel car manufacturers have extended their warranties to cover biodiesel. Unfortunately in Australia use of biodiesel in diesel engines usually voids the warranty, despite the fact that biodiesel made to appropriate standards (DIN 51606), is not harmful to modern diesel engines, and has in fact been shown to have benefits such as enhanced lubrication.9

Although in Australia only a very small percentage of cars are diesel, overseas the percentage is far greater and increasing. In 1990, about 3% of British cars were diesel, today this figure is almost 20%. Other European countries are equally high - 28% in France and 39% in Belgium.10

Biodiesel Developments in Australia
Some large-scale biodiesel plant are currently operating in Australia. Current production capacity in Australia is about 18 million litres per year, however plans for establishment of new facilities or expansion of existing ones will increase this capacity to around 90 million litres per year.11 In Wyong NSW, Australian Biodiesel Consultancy and Collex are currently operating a trial biodiesel plant, using recycled cooking oil and tallow that produces 15 million litres per year. In WA, Australian Renewable Fuels plans to complete construction of a 40 million litre per year plant by the end of 2002. It will use low grade tallow and used cooking oils as feedstock and will also annually produce 6,000 tonnes of raw glycerine and 1,800 tonnes of sulphate of potash fertiliser in paste form.12 It will use an improved production technology called a Continuous Trans Esterification Reactor (CTER) that reduces processing time from hours to minutes and can reduce plant capital costs by up to 50%. Within a few years they plan to expand nationally with additional plant.13

In addition to use in transport, biodiesel can be used for stationary electricity generators. These are common in remote locations not connected to the electricity grid - such as mining sites, tourist facilities and homesteads, and account for over a million tonnes of CO2 emissions per year.14 Stanwell Corporation has recently indicated plans to use tallow, waste cooking oil and ethanol to produce biodiesel for electricity production in remote areas.

Sustainability Implications
The sustainability implications of biodiesel are not clear cut. It has a variety of impacts throughout its life cycle, and these differ in nature and extent depending on how it is produced and used. In order to understand its environmental, social and economic impacts, we need to first look at how it is produced.

Production of Biodiesel
Biodiesel can be produced from bio-oils using three different methods.15

The base catalysed reaction is most often used because:

Using this reaction, biodiesel can even be produced at home using appropriate small-scale equipment. The process occurs in two stages as below. Note that although any alcohol can be used, either ethanol or methanol are the most common. In areas where sugar cane is grown, ethanol is most likely.

Stage 1
potassium hydroxide + ethanol › potassium ethoxide + water

KOH + CH3CH2OH › CH3CH2OK + H2O

Stage 2
potassium ethoxide + water + fatty acid triglyceride (oil) › biodiesel (methyl ester) + glycerine + potassium hydroxide

CH3CH2OK + H2O + C3H5(OOCR)3 › 3RCOOCH3 + C3H5(OH)3 + KOH

R = hydrocarbon chain

In modern automated plant, the whole process takes about 8 hours and is shown in Figure 1.

Figure 1: A common automated process for biodiesel production.

From this it can be seen that the potassium hydroxide is reused and the only outputs are biodiesel, glycerine and fatty acids - all of which are harmless. The plant being developed in Australia has minimal impact on the surrounding area because the production, storage and transportation of materials is carried out in sealed vessels and pipes, and no waste is produced.16 Many oil-based substances can be used to produce biodiesel eg. vegetable oils such as canola, soy bean, palm, corn, hemp, coconut, sunflower, and olive, and animal oils such as sardine and tallow (a byproduct of the livestock industry).

Feedstock Production
A significant amount of biodiesel's sustainability impacts occur during production of the various oil feedstocks.

Use of crops as sources of oil may require intensive agricultural practices - for example the use of pesticides and fertilisers. To produce significant amounts of biodiesel would require large areas of land to be converted to crop production.17 For example, to replace the 1.5 billion litres of diesel used per year in WA would require an area of canola 145 km by 145 km square. To put this in perspective, wheat currently takes up an area approximately 204 km by 204 km square - see Figure 2. Use of such large areas of land could restrict other uses such as food and fodder production, and reserves for preservation of biodiversity. As such, this is one of the main issues to be addressed when considering large-scale biodiesel production.

Figure 2: Comparison of areas required to replace Western Australia's diesel consumption with biodiesel.

It has also been shown that canola can have environmental and economic benefits when grown as a "break crop" for wheat. Benefits include better access to soil nitrogen and soil water, reduced chance of disease, and enabling earlier sowing of crops. The potential value of all benefits could be as much as a 40 per cent increase in gross profits over two years.18 The Western Australian Department of Agriculture is establishing a project to develop high-yield oil seen from canola. The 11 year project is expected to result in an increase in yield of 20% within 5 years, which should translate to a price decrease of up to 35% within the life of the project.19 The impacts of crops such as canola are further complicated by moves to introduce crops that have been genetically modified (GM) to be herbicide resistant. An application has been lodged by Monsanto to introduce a GM strain of canola (InVigor® canola - Brassica napus) in 23 local government areas across Victoria, New South Wales, South Australia and Western Australia.20 Possible consequences of this are herbicide tolerant weeds and therefore an increased requirement for spraying, and loss of income for non-GE farmers whose crops may become contaminated.

Use of tallow will enhance the financial viability of the livestock and slaughtering industries. These industries have a number of impacts including soil compaction and erosion, production of methane - a greenhouse gas, and ethical considerations for those opposed to eating meat. Conversely these industries are generally in rural areas with high unemployment so enhancing their financial ability would have social benefits.

Biodiesel Emissions
In order to fully evaluate the sustainability impacts of biodiesel emissions, a full life cycle analysis should be performed i.e. the complete production chain including feedstock production, feedstock transportation, fuel production, fuel distribution and vehicle use.

The Atmospheric Research Division of the CSIRO compared a number of transport fuels in terms of emissions of greenhouse gases and pollutants that negatively impact on health (particulates, oxides of nitrogen, volatile organic compounds and carbon monoxide). Low sulfur diesel, ultra-low sulfur diesel, compressed natural gas, liquefied natural gas, liquefied petroleum gas, ethanol, diesohol, canola oil, biodiesel, and waste oil were compared on a complete life cycle basis.21

Calculation of the total amount of greenhouse gases produced through biodiesel's lifecycle is very complex. These emissions can be divided into those produced during production of biodiesel, and those produced during combustion. The main gases produced during production are CO2 (from combustion of fuels in agricultural equipment and during transport), nitrous oxides (from fertiliser use), and methane (produced during crop and animal production). Thus the amount and types of greenhouse gases produced will depend on the source of biodiesel (eg. crops or animals - further complicated by the use of waste cooking oil), and the production processes. For example it has been shown that biodiesel made from canola emits less greenhouse gases than soy-biodiesel.22 Because of such complications, different studies have produced different results.

The CSIRO report concluded that on average, combustion of biodiesel emits greater quantities of CO2 than conventional diesel for the same energy output.23 However, because it is derived from biomass (and so is only releasing the CO2 that it recently took up), this CO2 does not count towards its total emissions. Thus when the entire life-cycle is taken into account, biodiesel has the lowest level of greenhouse emissions of all fuels tested - See Figures 3 and 4.

Figure 3: Total fossil fuel greenhouse gas emissions (CO2-equivalents) in g/kg for buses.
LS, Low Sulphur; LSD, Low Sulphur Diesel; ULS, Ultra Low Sulphur; LPG, Liquid Petroleum Gas; CNG, Compressed Natural Gas; E95, 95% Ethanol; BD20, 20% Biodiesel / 80% Conventional Diesel; BD100 100% Biodiesel.

 

Figure 4: Total fossil fuel greenhouse gas emissions (CO2-equivalents) in g/kg for non-bus heavy vehicles.
LS, Low Sulphur; LSD, Low Sulphur Diesel; W5, includes 5% waste oil; CNG, Compressed Natural Gas; E95, 95% Ethanol; BD35, 35% Biodiesel / 80% Conventional Diesel; BD100 100% Biodiesel.

Biodiesel's lower lifecycle greenhouse gas emissions are reflected in the energy required to produce it. Approximately 0.62 to 0.70 MJ of input energy is required to produce 1MJ of biodiesel. Conventional diesel requires only 0.10-0.14 MJ of energy to produce 1MJ of fuel, however including the energy content of the diesel itself means that 1.1 to 1.14 MJ of energy are required. Thus, assuming that all the energy used to produce both biodiesel and diesel is derived from petroleum, biodiesel results in a net gain of 0.30 to 0.38 MJ/MJ whereas diesel results in a net loss of 1.1 to 1.14 MJ/MJ.24

It is worth noting that diesel cars are generally much more fuel efficient than petrol cars and so produce less greenhouse gases for the same distance travelled. For example the VW Lupo 3L Tdi uses only 3 litres per 100km, and most use no more than 5L/100km.25 Unfortunately many diesel models are not available in Australia, although as has occurred overseas, it is expected availability will increase.

A large number of studies on "exhaust pipe" emissions have been performed on diesel derived from different sources and used in different types of engines in different countries. The CSIRO report concluded that exhaust emissions from biodiesel, when compared to petroleum diesel have: 96% lower total hydrocarbon; 45% lower carbon monoxide; 13% more oxides of nitrogen; and 28% less particulate matter.26 Table 1 presents data obtained by the U.S. Environmental Protection Agency (EPA) under the Clean Air Act Section 211(b).27

Table 1: Biodiesel Emissions Compared to Conventional Diesel

Emission Type	B100	B20
Total Unburned Hydrocarbons (HC)	-93%	-30%
Carbon Monoxide (a poisonous gas)	-50%	-20%
Particulate Matter	-30%	-22%
NOx (formation of smog and ozone)	+13%	+2%
Sulfates (components of acid rain)	-100%	-20%*
PAH (Polycyclic Aromatic Hydrocarbons)**(possible carcinogens)	-80%	-13%
nPAH (nitrated PAH's)** (possible carcinogens)	-90%	-50%***
Ozone potential of speciated HC	-50%	-10%

* Estimated from B100 result
** Average reduction across all compounds measured
*** 2-nitroflourine results were within test method variability

Thus, compared to petroleum diesel, biodiesel has significantly lower exhaust emissions of a variety of pollutants with significant health impacts - although, on a life cycle basis, high levels of particulates are emitted during production of biodiesel, with the result that it has higher total particulates than diesel.28 However, the particulate matter produced by biodiesel is mainly unburnt fuel which is non-toxic compared to carcinogenic diesel emissions.29 It is also likely that particulates emitted during production will have less of a health impact because production occurs in low population areas.

Interestingly, the benefits conferred by a biodiesel mix are better than proportional, for example, although 100% biodiesel results in a 30% reduction in hydrocarbons, a 20% biodiesel mix results in a 22% reduction. It was also noted that NOx emissions from biodiesel increase or decrease depending on the engine family and testing procedures.30 In addition, due to lower sulphur concentrations, it is now possible to neutralise these NOx emissions using current technology that is hampered by high sulphur levels in conventional diesel.31 The net health benefit of these reduced emissions, according to the Ames Mutagenicity test, is that biodiesel provides a 90% reduction in cancer risks.32

To further complicate things, tailpipe emissions are strongly influenced by the control standards in which the vehicle is sold. Although most vehicles in Japan and Europe are required to be Euro 3 or Euro 4 compliant, vehicles in Australia (since Jan 2002) need be only Euro 2 compliant. To put this in context, a Euro 4 vehicle has NOx and particulate emissions roughly the same as a vehicle running on LPG.33

In conclusion, it seems that the most important determinants of levels of greenhouse gases and other pollutants are the source of biodiesel and the production processes. Thus emphasis should be placed on selecting appropriate processes and feedstocks that over the entire lifecycle minimise these emissions.

Additional Impacts
Biodiesel production and use have a variety of impacts in addition to those outlined above. Additional environmental benefits derive from biodiesel being biodegradable and nontoxic, and include being less damaging than conventional diesel to marine environments such as wetlands, marshes, rivers, and oceans. Use of waste oil reduces waste going to landfill.

Social benefits include employment and development in rural areas during growth of crops and in manufacture and operation of biodiesel plant. In cities, lower pollution levels would improve quality of life and reduce health care costs. Biodiesel is also less combustible and so safer that conventional diesel because its flash point is greater than 150°C- the flash point of conventional diesel is 58°C.34 It is also classified as nontoxic to humans, with the lethal dose being 10 times that of table salt.35

Economic benefits include, in addition to employment, decreased reliance on external supplies of oil and therefore improved national balance of payments, and an increased security of energy supply.

Conclusion
Geologically derived oil is a finite resource, the use of which results in production of greenhouse gases. Biodiesel is one alternative that is renewable and has significantly reduced greenhouse gas emissions. Although biodiesel is gaining worldwide acceptance, especially in the US and Europe, in Australia it is a fledgling industry. Recent developments will significantly increase production, however this is limited by a number of factors, the major one being provision of suitable feedstocks (oils and alcohol) from plant and animal sources. Although the production and use of biodiesel is clearly preferable to geologically-based oil derivatives such as petrol and diesel, it has a number of sustainability impacts. In order to minimise these impacts it is critical that appropriate processes and technologies are used.

Global Significance
Both oil depletion and global warming will have significant local, regional and global impacts. Biodiesel is one means amongst many by which these impacts can be reduced. Although Australian's contribution to both problems is small in terms of global totals, our per capita oil usage and greenhouse gas emissions are amongst the highest in the world.

Sustainability Characteristics

Insight and Innovations

Keywords

Figures

Figure 1: A common automated process for biodiesel production.
From ARF (2002) Australian Renewable Fuels Pty Ltd web site http://www.ausrf.com.au

Figure 2: Comparison of areas required to replace Western Australia's diesel consumption with biodiesel.
From Calais, P. (1998) "The Role Of Liquid Biofuels As Petroleum Replacements In Western Australia", Environmental Science, Murdoch University.

Figure 3: Total fossil fuel greenhouse gas emissions (CO2-equivalents) in g/kg for buses.
From Beer, T., Grant, T., Brown, R. , Edwards, J., Nelson, P., Watson, H. and Williams, D. (2000) "Life-cycle Emissions Analysis of Alternative Fuels for Heavy Vehicles", CSIRO Atmospheric Research, Aspendale, Vic.

Figure 4: Total fossil fuel greenhouse gas emissions (CO2-equivalents) in g/kg for non-bus heavy vehicles.
From Beer, T., Grant, T., Brown, R. , Edwards, J., Nelson, P., Watson, H. and Williams, D. (2000) "Life-cycle Emissions Analysis of Alternative Fuels for Heavy Vehicles", CSIRO Atmospheric Research, Aspendale, Vic.

References

ABARE (2002) "Outlook 2002", Australian Energy News, March, 2002.

AEN (2002) "Clean Burn: Biodiesel at the bowser". Australian Energy News, March, 2002.

AGO (2001) "National Greenhouse Gas Inventory - 1999" Australian Greenhouse Office, Canberra.

ARF (2002) Australian Renewable Fuels Pty LTD web site http://www.ausrf.com.au

BAA (2002) Biodiesel Association of Australia Fact Sheet "Making biodiesel" at http://test.biodiesel.net.au/mambo/index.php

BAA (2002a) Biodiesel Association of Australia Fact Sheet "Emissions" at http://test.biodiesel.net.au/mambo/index.php

BAA (2002b) Biodiesel Association of Australia Fact Sheet "Environmental & Safety Information" at http://www.biodiesel.org.au/

BAA (2002c) Biodiesel Association of Australia Fact Sheet "What is biodiesel?" at http://www.biodiesel.org.au/

Beer, T., Grant, T., Brown, R. , Edwards, J., Nelson, P., Watson, H. and Williams, D. (2000) "Life-cycle Emissions Analysis of Alternative Fuels for Heavy Vehicles", CSIRO Atmospheric Research, Aspendale, Vic.

Calais, P. (1998) "The Role Of Liquid Biofuels As Petroleum Replacements In Western Australia", Environmental Science, Murdoch University.

Campbell, J. B. (2000) "Biodiesel - Will There Be Enough?", New Markets For Bio-Based Energy And Industrial Feedstocks, Agricultural Outlook Forum 2000, from http://www.usda.gov/oce/waob/oc2000/speeches/campbell.txt

CSIRO (2002) "Canola - Giving Wheat A Better Break", CSIRO Plant Industry, CSIRO, Canberra.

Ecofutures (2002) "Australia's fledgling BioDiesel industry taking off in Western Australia", Ecofutures, Feb-April, 2002.

Magoon, L (2001) "Oil Production Curve: Cause for concern", Australian Energy News, Dec, 2001.

OGTR (2001) Office of the Gene Technology Regulator, Application For Licence For Intentional Release Of A GMO Into The Environment: Application No. DIR 010/2001.

Renew (2001) "Biodiesel for sale", Renew Magazine, Alternative Technology Association, Issue 74, 2001.

Renew (2002) "Biodiesel car review", Renew Magazine, Alternative Technology Association, Issue 79, 2002.

Renew (2002a) "Biodiesel car review", Renew Magazine, Alternative Technology Association, Issue 79, 2002.

Scharmer, K. and Gosse, G. (1996) Ecological impact of biodiesel, production and use in Europe. Presented at: 2nd European motor biofuels forum, Graz, Austria.

Sheehan, J., Camobreco, V., Duffield, J., Graboski, M. and Shapouri, H. (1998). Life-cycle inventory of biodiesel and petroleum diesel for use in an urban bus. (Report ; NREL/SR-580-24089) Golden, CO: National Renewable Energy Laboratory. xxiv, 284 p. [http://www.ott.doe.gov/biofuels/lifecycle_pdf.html]

Spataru, A. and Romig, C. (1995) Emissions and engine performance from blends of soya and canola methyl esters with ARB #2 diesel in a DCC 6V92TA MUI engine. (SAE Technical Paper; 952388) Warrendale, Penn.: SAE International. p. 179-188.

Watson, R. T. (1999) "Report to the Fifth Conference of the Parties of the United Nations Framework Convention on Climate Change". Intergovernmental Panel on Climate Change.

WW (2002) Web Wombat Motoring News at http://www.webwombat.com.au/motoring/news_reports/diesel.htm

Endnotes

1 11 13 14 29 34 AEN (2002) "Clean Burn: Biodiesel at the bowser". Australian Energy News, March, 2002.

2 Watson, R. T. (1999) "Report to the Fifth Conference of the Parties of the United Nations Framework Convention on Climate Change". Intergovernmental Panel on Climate Change.

3 AGO (2001) "National Greenhouse Gas Inventory - 1999" Australian Greenhouse Office, Canberra.

4 Magoon, L (2001) "Oil Production Curve: Cause for concern", Australian Energy News, DEC, 2001.

5 ABARE (2002) "Outlook 2002", Australian Energy News, March, 2002.

6 19 Ecofutures (2002) "Australia's fledgling BioDiesel industry taking off in Western Australia", Ecofutures, Feb-April, 2002.

7 Campbell, J. B. (2000) "Biodiesel - Will There Be Enough?", New Markets For Bio-Based Energy And Industrial Feedstocks, Agricultural Outlook Forum 2000, from http://www.usda.gov/oce/waob/oc2000/speeches/campbell.txt

8 9 Renew (2002) "Biodiesel car review", Renew Magazine, Alternative Technology Association, Issue 79, 2002.

10 WW (2002) Web Wombat Motoring News at http://www.webwombat.com.au/motoring/news_reports/diesel.htm

12 16 ARF (2002) Australian Renewable Fuels Pty LTD web site http://www.ausrf.com.au

15 BAA (2002) Biodiesel Association of Australia Fact Sheet "Making biodiesel" at http://test.biodiesel.net.au/mambo/index.php

17 Calais, P. (1998) "The Role Of Liquid Biofuels As Petroleum Replacements In Western Australia", Environmental Science, Murdoch University.

18 CSIRO (2002) "Canola - Giving Wheat A Better Break", CSIRO Plant Industry, CSIRO, Canberra.

20 OGTR (2001) Office of the Gene Technology Regulator, Application For Licence For Intentional Release Of A GMO Into The Environment: Application No. DIR 010/2001.

21 23 26 30 Beer, T., Grant, T., Brown, R. , Edwards, J., Nelson, P., Watson, H. and Williams, D. (2000) "Life-cycle Emissions Analysis of Alternative Fuels for Heavy Vehicles", CSIRO Atmospheric Research, Aspendale, Vic.

22 Spataru, A. and Romig, C. (1995) Emissions and engine performance from blends of Soya and canola methyl esters with ARB #2 diesel in a DCC 6V92TA MUI engine. (SAE Technical Paper; 952388) Warrendale, Penn.: SAE International. p. 179-188.

24 Scharmer, K. and Gosse, G. (1996) Ecological impact of biodiesel, production and use in Europe. Presented at: 2nd European motor biofuels forum, Graz, Austria.

25 33 Renew (2002a) "Biodiesel car review", Renew Magazine, Alternative Technology Association, Issue 79, 2002.

27 BAA (2002a) Biodiesel Association of Australia Fact Sheet "Emissions" at http://test.biodiesel.net.au/mambo/index.php

28 31 Sheehan, J., Camobreco, V., Duffield, J., Graboski, M. and Shapouri, H. (1998). Life-cycle inventory of biodiesel and petroleum diesel for use in an urban bus. (Report ; NREL/SR-580-24089) Golden, CO: National Renewable Energy Laboratory. Xxiv, 284 p. [http://www.ott.doe.gov/biofuels/lifecycle_pdf.html]

32 BAA (2002b) Biodiesel Association of Australia Fact Sheet "Environmental & Safety Information" at http://www.biodiesel.org.au/

35 BAA (2002c) Biodiesel Association of Australia Fact Sheet "What is biodiesel?" at http://www.biodiesel.org.au/

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