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in the production phase. Sewage sludge and manure can be used as by‐product of the systems for bioenergy generation purposes without additional water requirement for the production phase. Algae production systems need a large quantity of water, however, in a closed system where most of the water is recycled, the water footprint is between 1.4 – 5.8 m³/kg of dry algal biomass produced (Martins et al., 2018).

Table 3.1 Evapotranspiration and water footprint of some crops for energy purposes.

Feedstock	ETm3/GJ feedstock*	Water footprintm3/kg feedstock*	Reference
Sugarcane	18–124	0.12–0.59	Berndes, 2002; Fraiture and Berndes, 2009
Sugar beet	48–151	0.11–1.11	Berndes, 2002; Fraiture and Berndes, 2009
Corn	37–190	0.48–1.43	Berndes, 2002; Fraiture and Berndes, 2009; Postel, 1998
Wheat	21–199	0.28–1.67	Berndes, 2002; Fraiture and Berndes, 2009; Postel, 1998
Sweet sorghum		0.18	Bennett and Anex, 2008
Grain sorghum		2.67	Critchley et al., 1991
Cassava		0.55	Liu et al., 2007
Sweet potato		0.23	Liu et al., 2007
Rapeseed	46–81	0.83–2.2	Berndes, 2002
Oil palm		3.2	Berndes, 2002
Soybean		1.43–2.5	Postel, 1998
Canola		1.8	Bauder, 2019
Lignocellulosic crops	7–68	0.11–1	Berndes, 2002; Robins et al., 2009

      ^* ET and water footprint for the production of some agricultural crops, including starch, lignocellulosic, and oil containing crops.

      3.2.3. Water Use in Biomass Conversion to Biofuels

Biomass processing uses water for buffers and media preparation, pretreatment, cleaning, heating, waste heat recovery, cooling, as well as the reactant and fluidizing agent. Processing phase in bioethanol industry uses water mainly for cooling purpose (Phillips et al., 2007). While water use in processing phase may be recycled, there are water losses primarily due to evaporation from cooling towers and utility systems (Phillips et al., 2007). In the US, 1 L of ethanol production from corn grain requires ~3 L of water (University of Illinois Extension, 2009). Table 3.2 summarizes the water footprint of biofuels from different feedstocks. Ethanol production from sugarcane in Brazil requires large amount of water for washing, condensing the vapor, and cooling the fermentation broth (Stone et al., 2013).

Most of the biorefineries are located in the same regions of biomass production, which reduces the transportation and logistics costs; however, the large quantities of water demand by the biorefineries exert pressure on the limited water resources. For example, corn ethanol biorefineries in the US are mainly located in the Midwest, where there is already a pressing need for water in biomass production, food production, and processing systems (Phillips et al., 2007). Water use in the corn ethanol industry in the US is taken from the local aquifer (Phillips et al., 2007). Due to the concerns over water use in bioprocessing, there is an interest in using improved systems to avoid evaporation and leaks (Stone et al., 2013). One solution is use of “zero discharge” system that recycles water in the ethanol industry and avoids the discharge (Phillips et al., 2007). Cooling systems is a main water consumer in ethanol biorefineries (Phillips et al., 2007). Air cooling can be implemented to replace the cooling water. Biodiesel production industry also requires large amount of water, ranging from 119 m³/GJ for biodiesel production from canola, to 444 m³/GJ for biodiesel production from palm (Table 3.2). Different conversion phases of corn to ethanol and soybean to biodiesel are presented in Figure 3.2.

Table 3.2 Water footprint of biofuels from different feedstocks.

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Fuel	Feedstock	Water footprint (m3/GJ energy)*	Reference
Bioethanol	Sugarcane	20–63	Postel, 1998
	Sugar beet	96	Yang et al., 2009
	Corn	87–90	Postel, 1998
	Sweet sorghum	31	Berndes, 2002
	Grain sorghum	319	Critchley et al., 1991
	Cassava	113	Yang et al., 2009
	Sweet potato	78	Yang et al., 2009
	Switchgrass	67	Robins et al., 2009
Biodiesel	Rapeseed	165	Yang et al., 2009
	Palm	444	Yang et al., 2009
	Soybean	237	Critchley et al., 1991
	Canola