Biofuel co-products as livestock feed - Opportunities and challenges

483Chapter 27Biofuels: their co-products and waterimpacts in the context of life-cycle analysisMichael Wang and Jennifer DunnCenter for Transportation Research, Argonne National Laboratory, Argonne, IL 60439, United States of AmericaE-mail for correspondence: mqwang@anl.govABSTRACTLife-cycle analysis (LCA) of biofuels, including maize ethanol, sugar cane ethanol, cellulosic ethanol and biodiesel,must incorporate the impact of co-products. Distillers grain with solubles, an animal feed co-produced with maizeethanol, is one such co-product. Electricity, a significant co-product of cellulosic ethanol production, can providesignificant greenhouse gas credits over the life cycle of a biofuel. This chapter examines biofuel production technologiesand biofuel co-products, and methods for allocating energy and water consumption and environmentalburdens among the biofuel and its co-products. Allocation methodologies include displacement, mass-based,energy-based, market-value-based and process purpose. It is also possible to combine these approaches in a hybridmethodology. We present LCA results (energy consumption and GHG emissions) for maize and cellulosic ethanol,and examine the effect of co-product allocation methodologies on these results. We also discuss water consumptionin the life cycle of maize and cellulosic ethanol. As biofuel production technology matures, it is likely that theportfolio of biofuel co-products will evolve, requiring LCA practitioners to re-assess their effect on the life-cycleimpacts of biofuels.INTRODUCTIONLife-cycle analysis (LCA) is a tool to systematically examinethe energy and environmental impacts of products, processesand systems (Allen and Shonnard, 2002; ISO, 2006).Its application to biofuel production has expanded rapidly inrecent years, but not without controversy. Applying LCA tobiofuels raises issues such as accounting for greenhouse gas(GHG) emissions from land-use change (LUC), allocatingthe environmental impacts of biofuel production among coproducts,including animal feed, and assessing the impactof biofuel production on water quality and consumption.In this chapter we present recent advances in the applicationof LCA to biofuels, including the impact of technologydevelopments, improved estimates of LUC impacts,advancements in the understanding of animal feed as aco-product of ethanol plants, and advances in quantifyingwater consumption impacts of biofuel production.BIOFUEL PRODUCTION TECHNOLOGIESProduction of biofuels in the United States has escalatedsince the United States began its fuel ethanol programmein 1980. United States production of maize ethanol was 76million litres in 2000. In 2010, it had increased to 49 billionlitres (RFA, 2011). Production of bio-ethanol is increasingworldwide. In the European Union (EU), for example,3.7 billion litres of ethanol were produced in 2009, upsix-fold from 2002 (ePure, 2010). In Brazil, which is thesecond-largest ethanol producer in the world, ethanolaccounts for 40 percent of the gasoline market (Wang etal., 2008). Brazil’s 2008/2009 ethanol production was 28billion litres, more than double production in 1990-1991(UNICA, 2011).Biofuels can be classified as first, second or third generation.First-generation biofuels derive from cereal, oiland sugar crops, which are converted to fuels with maturetechnology. Of the first-generation fuels, maize ethanolhas received the most attention in the LCA arena. Figure 1depicts the life cycle of this biofuel, which is the mostwidespread fuel alternative to gasoline in the United States.Ethanol plants use dry- or wet-milling technologies.In wet-milling plants, maize kernels are soaked in SO 2 -containing water. De-germing of the kernels and oil extractionfrom the germs follows. The remaining kernel materialis ground, producing starch and gluten. The former isfermented to ethanol. In dry-milling plants, starch in milledmaize kernels is fermented into ethanol. Residual materialsare generated that have value as commercial animal feed,called distillers grain with solubles (DGS), which can be soldin wet (WDGS) or dried form (DDGS). Integration of maizefractionation in the dry-milling process permits productionof germ and fibre co-product streams from whole maizekernels prior to fermentation. Front-end fractionation has