4.1 Introduction

Here we will consider climate effects and non-greenhouse gas emissions associated with the life cycles of transport biofuels. Considering the whole seed-to-wheel life cycle of transport biofuels is important because at each stage, there may be signifi­cant environmental impacts. In cropping plants, there are usually inputs of fossil fu­els (needed to power tractors and generate N fertilizer) and emissions of substances such as N2O and nitrate (both derived from nitrogen fertilizers) and pesticides. The effects thereof may be substantial. For instance, Donner and Kucharik (2008) have shown that a US bioethanol production of 15 billion gallons would increase the an­nual average flux of dissolved inorganic fixed nitrogen (N) in the Mississippi and Atchafalaya rivers by 10-34%. And it has been argued that in Brazil, ethanol pro­duction from sugar cane will contribute to a rapidly changing tropical biogeochem­ical N cycle, because the N fertilizer use efficiency of production is low: about 30% of N fertilizer ends up in sugar cane tissue (Galloway et al. 2008).

Also the choice of plants grown as biofuel feedstocks may matter, as plants, for instance, differ in their production of isoprene, which may contribute oxidizing smog (Royal Society 2008). The stage of processing biomass to transport biofuels is associated with energy use and process-related emissions. For instance, dry mill fuel ethanol production leads to significant emissions of ethanol, acetaldehyde, acetic acid and ethylacetate (Brady and Pratt 2007). Leakage from storage facilities for bioethyl-tertiary-butylether (ETBE) may have a significant impact on groundwater quality (Rosell et al. 2007). And the stage of driving is important, because driving a car on biofuels generates emissions which may be different from those of fossil fuels.

This chapter starts with an overview of the different types of uncertainty related to life cycle studies (Sect. 4.2). After that, most attention will be given to life cycle emissions of biofuels based on terrestrial plants and wastes. These are considered in Sects. 4.3 to 4.5. Section 4.6 will deal with possibilities to reduce the life cycle emissions associated with the biofuels considered here.

L. Reijnders, M. A.J. Huibregts, Biofuls for Road Transport © Springer 2009