Biofuel co-products as livestock feed - Opportunities and challenges

Biofuels: their co-products and water impacts in the context of life-cycle analysis 497FIGURE 17Average water consumption in existing maize dry-mill ethanol plants7Consumptive Water Use (Liter Water/Liter Fuel Ethanol)6543215.84.74.2432.70Phillips et al., 2007 USDA 2003 Keeney and Muller Keeney and Muller20062006Wu 2008 Mueller 2010Source: Wu et al., 2011.TABLE 7Consumptive water use from maize farming to ethanol production in USDA Regions 5, 6 and 7 (litre water per litredenatured ethanol produced)USDA Region Region 5 Region 6 Region 7Share of United States ethanol production capacity (%) (1) 50 15 23Share of United States maize production (%) (2) 50 16 23Maize irrigation, groundwater (3) 12 19 224Maize irrigation, surface water (3) 2 3 12Ethanol production (4) 3 3 3Total (maize irrigation and ethanol production) without co-product allocation 17 25 239Total water consumption with mass-based co-product allocation (5) 11 17 160Notes: (1) Based on 2008 ethanol production capacity in operation (RFA, 2011). (2) Based on 2008 maize production (USDA-NASS, 2011).(3) USDA, 2008. (4) Production-weighted average (Wu, 2008). (5) Mass-based and carbon displacement-based allocation according to theheuristic that one-third of biomass in maize kernel goes to ethanol, one-third goes to CO 2 and one-third goes to DDGS.TABLE 8Water consumption for cellulosic ethanol productionProcessAverage water consumption(litre/litre biofuel)Electricity export(kWh/litre biofuel)Average water consumptionafter co-product allocation(litre/litre biofuel)Biochemical (Humbird et al., 2011) 5.4 (1) 0.47–0.55 (3) 4.5–4.6Gasification (Phillips et al., 2007) 1.9 (1) 0 1.9Pyrolysis (Jones et al., 2009) 2.3 (2) 0 2.3Notes: (1) Cellulosic ethanol produced from switchgrass. (2) Forest residue as feedstocks. (3) Maize stover 1.77 kWh/gal and Switchgrass2.07 kWh/gal, both from a 2000-dry- ton/day ethanol plant. Source: Wu and Chiu, 2011.of ethanol, DDGS and CO 2 emissions during conversion.Irrigation water is allocated with the same ratio (one-thirdassigned to maize, one-third assigned to ethanol).Table 8 compiles water consumption during productionof cellulosic ethanol from maize stover, switchgrass,andforest residue (Wu and Chiu, 2011). No irrigation water isincluded because, in contrast to maize, these feedstocksmay not require irrigation. The electricity generated duringcellulosic ethanol production can displace conventionallyproducedelectricity, the production of which consumes onaverage 1.6 litres per kWh in the United States (Wu andChiu, 2011). As a result, 0.75 to 0.89 litres of water perlitre of cellulosic ethanol are conserved when ethanol is producedvia biochemical technology. The consumptive wateruse attributed to each litre of cellulosic ethanol produced istherefore 4.5 to 4.6 litres.