Assessing county-level water footprints of different cellulosic-biofuel feedstock pathways.

While agricultural residue is considered as a near-term feedstock option for cellulosic biofuels, its sustainability must be evaluated by taking water into account. This study aims to analyze the county-level water footprint for four biofuel pathways in the United States, including bioethanol generated from corn grain, stover, wheat straw, and biodiesel from soybean. The county-level blue water footprint of ethanol from corn grain, stover, and wheat straw shows extremely wide variances with a national average of 31, 132, and 139 L of water per liter biofuel (L(w)/L(bf)), and standard deviation of 133, 323, and 297 L(w)/L(bf), respectively. Soybean biodiesel production results in a blue water footprint of 313 L(w)/L(bf) on the national average with standard deviation of 894 L(w)/L(bf). All biofuels show a greater green water footprint than the blue one. This work elucidates how diverse spatial resolutions affect biofuel water footprints, which can provide detailed insights into biofuels' implications on local water sustainability.