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(a) Consumption through evaporation

(a) Consumption through evaporation the number of new plants has led to a 254% increase in total water consumption for this type of fuel processing in the U.S. (Lloyd and Larsen 2007).

Impact of Shift toward Biofuels

For various reasons, a shift toward CO2-neutral and renewable energy carriers, such as biomass, is currently being heavily promoted. First-generation biofuels are produced from food crops, which are specifically grown for ethanol production. By contrast, second-generation biofuels are made from waste but have not yet reached the stage of commercial viability. Gerbens-Leenes et al. (2008) tried to determine the impact that a shift toward biofuels might have on water use and availability by comparing the water footprints for the currently most important primary energy carriers. The water footprint consisted of three components of virtual water: (a) green water, which referrs to rainwater that is evaporated during the production process, (b) blue water, which refers to surface and groundwater applied for irrigation that evaporated during production, and (c) gray water, which is defined as the amount of water being polluted during the production process. For the assessment of biomass, food crops such as sugar cane providing ethanol and rapeseed providing biodiesel were considered as well as energy crops such as poplar, which provides heat. A third category of biomass for energy (i.e., organic wastes) was excluded from the study. Table 14.2 shows that the water footprints of biomass differ greatly, depending on the crop, the agricultural system applied, and the climatic conditions. Whereas the water footprint of maize was generally favorable, the one from rapeseed was not. For some crops that are specifically grown for energy

Table 14.2 Average total water footprints (m3/GJ) for selected primary energy carriers (after Gerbens-Leenes et al. 2008). Only the numbers for the biomass energy carriers are country specific; the others are averages.

Primary energy carrier

Netherlands

United States

Brazil

Zimbabwe

Maize

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