Prior studies have estimated that a liter of bioethanol requires 263-784 L of water from corn farm to fuel pump, but these estimates have failed to account for the widely varied regional irrigation practices. By using regional time-series agricultural and ethanol production data in the U.S., this paper estimates the state-level field-to-pump water requirement of bioethanol across the nation. The results indicate that bioethanol's water requirements can range from 5 to 2138 L per liter of ethanol depending on regional irrigation practices. The results also show that as the ethanol industry expands to areas that apply more irrigated water than others, consumptive water appropriation by bioethanol in the U.S. has increased 246% from 1.9 to 6.1 trillion liters between 2005 and 2008, whereas U.S. bioethanol production has increased only 133% from 15 to 34 billion liters during the same period. The results highlight the need to take regional specifics into account when implementing biofuel mandates.

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.

The 2011 US Billion-Ton Update 1 estimates that there are enough agricultural and forest resources to sustainably provide enough biomass to displace approximately 30% of the country's current petroleum consumption. A portion of these resources are inaccessible at current cost targets with conventional feedstock supply systems because of their remoteness or low yields. Reliable analyses and projections of US biofuels production depend on assumptions about the supply system and biorefi nery capacity, which, in turn, depend on economics, feedstock logistics, and sustainability. A cross-functional team has examined optimal combinations of advances in feedstock supply systems and biorefi nery capacities with rigorous design information, improved crop yield and agronomic practices, and improved estimates of sustainable biomass availability. Biochemical-conversion-to-ethanol is analyzed for conventional bale-based system and advanced uniform-format feedstock supply system designs. The latter involves 'pre-processing' biomass into a higher-density, aerobically stable, easily transportable format that can supply large-scale biorefi neries. Feedstock supply costs, logistics and processing costs are analyzed and compared, taking into account environmental sustainability metrics.

[1] A spatially explicit life cycle water analysis framework is proposed, in which a standardized water footprint methodology is coupled with hydrologic modeling to assess blue water, green water (rainfall), and agricultural grey water discharge in the production of biofuel feedstock at county-level resolution. Grey water is simulated via SWAT, a watershed model. Evapotranspiration (ET) estimates generated with the Penman-Monteith equation and crop parameters were verified by using remote sensing results, a satellite-imagery-derived data set, and other field measurements. Crop irrigation survey data are used to corroborate the estimate of irrigation ET. An application of the concept is presented in a case study for corn-stover-based ethanol grown in Iowa (United States) within the Upper Mississippi River basin. Results show vast spatial variations in the water footprint of stover ethanol from county to county. Producing 1 L of ethanol from corn stover growing in the Iowa counties studied requires from 4.6 to 13.1 L of blue water (with an average of 5.4 L), a majority (86%) of which is consumed in the biorefinery. The county-level green water (rainfall) footprint ranges from 760 to 1000 L L À1. The grey water footprint varies considerably, ranging from 44 to 1579 L, a 35-fold difference, with a county average of 518 L. This framework can be a useful tool for watershed-or county-level biofuel sustainability metric analysis to address the heterogeneity of the water footprint for biofuels.Citation: Wu, M., Y. Chiu, and Y. Demissie (2012), Quantifying the regional water footprint of biofuel production by incorporating hydrologic modeling, Water Resour. Res., 48, W10518,

The 2011 US Billion-Ton Update estimates that by 2030 there will be enough agricultural and forest resources to sustainably provide at least one billion dry tons of biomass annually, enough to displace approximately 30% of the country's current petroleum consumption. A portion of these resources are inaccessible at current cost targets with conventional feedstock supply systems because of their remoteness or low yields. Reliable analyses and projections of US biofuels production depend on assumptions about the supply system and biorefi nery capacity, which, in turn, depend upon economic value, feedstock logistics, and sustainability. A cross-functional team has examined combinations of advances in feedstock supply systems and biorefi nery capacities with rigorous design information, improved crop yield and agronomic practices, and improved estimates of sustainable Modeling and Analysis: Thermochemical conversion and refinery sizing Th e previous study did not consider woody biomass supply systems, account for variability in biomass ash content throughout the supply chain, or look at biorefi nery scale impacts for thermochemical conversion processes.In this paper, we analyze the infl uences of biorefi nery size, biomass supply system designs, and feedstock specifications on process economics and environmental sustainability metrics for southeastern (SE) US woody feedstocks converted into ethanol through a thermochemical process. Th e woody feedstocks include logging residues, which are low cost at the forest landing (i.e. roadside aft er harvest, chipping, and loading on a truck), but because of ash, may not be the least expensive for the conversion process. Because of this diff erence, this report also analyzes the impact of costs incurred between landing and the throat of the conversion system ('reactor throat'), including the costs of feedstock pre-processing. Th e analyses compared options of performing pre-processing operations at the landing or depot, such as ash removal, or letting the conversion process handle the upgrading of the material. Th e analyses support upgrading the material near the point of extraction rather than allowing the conversion facilities to handle the upgrades. Illustrative casesTh e SE USA is projected to be highly productive for the emerging biorefi nery industry. 4 One potential challenge with developing supply chains in the SE (Fig. 1) is that the resource base is made up of various types of herbaceous and woody biomass resources. Table 1 shows the primary biomass categories and potentially available quantities biomass availability. A previous report on biochemical refi nery capacity noted that under advanced feedstock logistic supply systems that include depots and pre-processing operations there are cost advantages that support larger biorefi neries up to 10 000 DMT/day facilities compared to the smaller 2000 DMT/day facilities. This report focuses on analyzing conventional versus advanced depot biomass supply systems for a thermochemical conversion and refi nery sizi...