tions of an ethanol plant are shown in Figure 5-1. Pure water is required for the slurry operation with whole corn, followed by liquefaction to liberate sugars from starch via hydrolysis. This is followed by fermentation and distillation operations.

Current estimates of the consumptive water use from these facilities are in the range of 4 gallons of water per gallon of ethanol produced (gal/gal) (Pate et al., 2007). For perspective, consumptive water use in petroleum refining is about 1.5 gal/gal (Pate et al., 2007). Overall water use in biorefineries may be as high as 7 gal/gal, but this number has been consistently decreasing over time and as of 2005 was only slightly over 4 gal/gal in 2005 (Phillips et al., 2007). Thus for a 100 million gallon per year plant, a little over 400 million gallons of water per year would be withdrawn from aquifers or surface water sources (1.1 million gallons per day). The overall water balance for a typical bioethanol plant using corn is shown in Figure 5-2.

FIGURE 5-1 Process schematic and unit operations of ethanol production facility from whole corn kernels. DDGS is “dry distillers grains with solubles.”

SOURCE: Parkin et al. (2007).