Water for bioenergy: A global analysis

Agriculture is by far the largest water user. This chapter reviews studies on the water footprints (WFs) of bioenergy (in the form of bioethanol, biodiesel, and heat and electricity produced from biomass) and compares their results with the WFs of fossil energy and other types of renewables (wind power, solar thermal energy, and hydropower). WFs for bioenergy vary, depending on crop type applied, production location, and agricultural practice. The most water-efficient way to generate bioenergy is to use biomass for heat generation, with electricity generation being the second best option. Biofuel production requires roughly twice as much water as bioelectricity. Regarding biofuels, bioethanol has smaller WFs than biodiesel. For example, the WF of rapeseed biodiesel is four times larger than the WF of sugarcane ethanol and seven times larger than the WF of sugar beet ethanol. Global weighted ethanol WFs increase in the order of sugar beet, potato, sugarcane, maize, cassava, barley, rye, paddy rice, wheat, and sorghum and range between 60 and 400 m3/GJ. For sugar beet, maize, and sugarcane, differences between regions are large. The European Union, northern Africa, and the United States have relatively small WFs for ethanol from sugar beet and maize, while eastern Europe has large WFs. Global weighted average biodiesel WFs increase in the following order: palm oil (95 m3/GJ), soybean and rapeseed (400 m3/GJ), and jatropha (570 m3/GJ). Conversely, the WFs of fossil fuels are relatively small. Finally, the WF of hydropower varies widely between 0.5 and 850 m3/GJ. Our results provide new insight into the impacts of bioenergy on the use and pollution of freshwater. This knowledge is a valuable contribution to future research and for policies concerning energy needs, freshwater availability, and the choice whether to allocate water to food or energy production