A. AZAPAGIC, The University of Manchester, UK and

H. STICHNOTHE, Johann Heinrich von Thunen Institut — Institute of Agricultural Technology and Biosystems Engineering, Germany

Abstract: Biofuels have a potential to reduce carbon dioxide emissions from transport because the biomass used in their production is considered carbon neutral. This is the main reason for a growing interest in biofuels. However, there are certain aspects, particularly of the first-generation biofuels, which may render them unsustainable, including the increased use of land and competition with food production. Therefore, sustainability of biofuels should be assessed carefully, considering all relevant environmental, economic and social aspects. To prevent shifting the impacts along the supply chains, sustainability should be assessed considering the whole life cycle of biofuels, including cultivation of the feedstock and biofuel production processes. This chapter reviews various sustainability aspects of biofuels and illustrates how environmental and economic sustainability can be assessed on a life cycle basis. The environmental impacts considered include water use, global warming, acidification, eutrophication and loss of biodiversity while economic aspects include feedstock costs, capital costs and biofuel prices. Future viability of biofuels is also discussed.

Key words: biofuels, environmental impacts, economic costs, life cycle assessment, sustainability assessment.

3.1 Introduction

Biofuels can be produced from a range of biomass sources using different production routes, as discussed throughout this book. Depending on the type of the bio-feedstock used, they are referred to as first-, second — or third-generation biofuels (OECD and IEA, 2008). First-generation biofuels are produced commercially from conventional food crops, including wheat, maize, corn, sugar cane, rapeseed, sunflower seeds and palm oil. The most common first-generation biofuels are bioethanol, biodiesel, vegetable oil and biogas.

Second-generation biofuels are produced from non-food sources and include dedicated energy crops (e. g. perennial grasses, short-rotation coppice willow and other lignocellulosic plants) and waste biomass (e. g. agricultural, forestry and municipal solid waste). Two main processing routes used to produce these fuels are: thermo-chemical and bio-chemical. The former is used mainly for the production of biodiesel and the latter for bioethanol. Other second-generation fuels under development include: biohydrogen, biomethanol, dimethylfuran (DMF), bio-dimethylether (bio-DME), Fischer-Tropsch diesel, biohydrogen diesel and mixed alcohols (Brigenzu et al., 2009).

Third-generation biofuels are still under development and the main bio­feedstock being considered are algae for the production of biodiesel via the thermo-chemical route. Other sources of third-generation biofuels could include alcohols such as bio-propanol or bio-butanol; however, they are not expected to enter the market before 2050 (OECD and IEA, 2008).

Currently, the majority of the global biofuel production is from food crops with bioethanol representing over 80% of liquid biofuels by energy content (Brigenzu et al, 2009); however, the importance of the second — and third-generation fuels is growing.

Biofuels have a potential to reduce the carbon dioxide (CO2) emissions because the biomass used in their production is considered carbon neutral. This is based on the assumption that the amount of carbon released during combustion of biofuels in the use phase is equivalent to the amount of carbon sequestered during the growth of biomass from which the fuels were derived. Further attractive features of biofuels over fossil fuels are that they provide security of supply as they can be produced domestically by many countries. Furthermore, they require only minimal changes in the distribution system and production technologies. Biofuels also have a potential to stimulate rural development (Rajagopal and Zilberman,

2007) . Thus, the expectations from biofuels as a source of ‘sustainable’ energy are high.

However, there are certain aspects, particularly of the first-generation biofuels, which may render them less sustainable. For example, while the intensification of agriculture to increase crop production per land unit may lead to lower greenhouse gas (GHG) emissions per unit of product, the increased use of land, energy, fertilisers and pesticides will reduce the net GHG benefits and cause further environmental damage, including release of soil carbon, leaching of nutrients and loss of biodiversity. Other risks associated with large-scale production of the first — generation biofuels include competition with food production, leading to increased costs of food and in some cases, food poverty (Bird et al., 2008; Escobar et al., 2009; Fargione et al, 2008; Searchinger et al, 2008).

Therefore, sustainability of biofuels should be assessed carefully, considering all relevant environmental, economic and social aspects (The Royal Society,

2008) . Furthermore, to prevent shifting the burdens along the supply chains, sustainability should be assessed taking a systems approach and considering the whole life cycle of biofuels, including cultivation of the feedstock and biofuel production processes (Azapagic, 2006; Fehrenbach et al, 2007; Stichnothe and Azapagic, 2009; The Royal Society, 2008; US EPA, 2009). The life cycle approach is also required by various legislative acts related to biofuels, including the European Union (EU) Renewable Energy Directive (EC, 2009), the German Sustainability Biofuel Ordinance (GFG, 2007), the Swiss Directive on Mineral Oil Tax Redemption for Biofuels (SFG, 2007), the UK Renewable Transport Fuel Obligation (DfT, 2008) and the US Energy Independency and Security Act (USFG, 2007).

This chapter discusses how the main sustainability issues associated with biofuels can be assessed on a life cycle basis, considering different bio-feedstocks and production routes.