Biofuel co-products as livestock feed - Opportunities and challenges

Biofuels: their co-products and water impacts in the context of life-cycle analysis 491TABLE 4Distillers grain with solubles displacement ratios at the feedlot levelDisplacement ratio between DGS and conventional feed(kg/kg of DGS on a DM basis)Dry DGSWet DGSLivestock Maize Soybean Meal Urea Maize Soybean Meal UreaBeef Cattle 1.203 0.000 0.068 1.276 0.000 0.037Dairy Cattle 0.445 0.545 0.000 0.445 0.545 0.000Swine 0.577 0.419 0.000Poultry 0.552 0.483 0.000Average 0.751 0.320 0.024Source: Arora, Wu and Wang, 2010.Dry and Wet DGS Combined0.788 0.304 0.022FIGURE 9GHG emissions as a result of land use changes associated with maize ethanol (g CO 2 e/MJ)100FAPRI80gCO 2e/MJ604020FAPRI & FASOMGTAP - unrevisedGTAP - revised0Searchinger et al.,2008EPA 2010 CARB 2009 Hertel et al.,2010Tyner et al.,2010(2001 baseline)Tyner et al.,2010(2006baseline,partiallyupdated)Tyner et al.,2010(2006baseline,updatedthrough 2015)demand trends without ethanol production (the so-calledreference case for global food supply and demand), andaccurate modelling of the substitution of conventionalanimal feed with DGS. One model that permits calculationof LUC is Purdue University’s Global Trade Analysis Project(GTAP) model, which has been developed primarily toevaluate global agricultural commodity trade linkages.GTAP has recently been modified to model maizeethanol production. Figure 9 compares the revised GTAPmodel predictions of GHG emissions resulting from LUCwith previous studies for maize ethanol programmes. Theprevious studies either used other models (Iowa StateUniversity’s Food and Agricultural Policy Research Institute(FAPRI) model, Texas A&M’s Forest and Agricultural SectorOptimization Model (FASOM)) or older GTAP versions.The most recent GTAP model version predicts significantlylower LUC and resulting GHG emissions than previousstudies. For example, Searchinger et al. (2008), whoused the FAPRI model, predicted GHG emissions (in gCO 2 e/MJ of ethanol) that were 70 percent higher than calculationsby California Air Resources Board (CARB, 2009) andHertel et al. (2010), who used an earlier version of GTAP.Revisions to GTAP resulted in an estimate of GHG emissions85 percent below that of Searchinger et al. (2008), asreflected in the results of Tyner et al. (2010).Although the advances made in this work are significant,it should be noted that research is ongoing to furtherreduce uncertainties in incorporating LUC into economicmodels. In particular, uncertainties still exist in CGE models,including (1) modelling of DGS and other co-produced animalfeeds; (2) global growth in food supply and demand;(3) global available land types and their potential grainproduction yields; and (4) below- and above-ground carbonstocks for different land cover types.BIOFUEL LCA RESULTSFigure 10 displays life-cycle carbon dioxide equivalent(CO 2 e) emissions for petroleum gasoline, six types of maizeethanol, three types of cellulosic ethanol, and sugar caneethanol. Maize ethanol produced at coal-powered plants