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Algae's high productivity provides potential resource advantages over other fuel crops. However, demand for land, water, and nutrients must be minimized to avoid impacts on food production. We apply our national-scale open-pond, growth, and resource models to assess several biomass to fuel technological pathways based on Chlorella sp. We compare resource demands between hydrothermal liquefaction (HTL) and lipid extraction (LE) to meet 1.89E+10 and 7.95E+10 L yr−1 renewable diesel targets. We estimate nutrient demands where post-fuel biomass is consumed as co-products and recycling by anaerobic digestion (AD) or catalytic hydrothermal gasification (CHG). Sites are prioritized based on fuel value relative to a set of site-specific resource costs. The highest priority sites are located along the Gulf of Mexico coast, but potential sites exist nationwide. Compared to LE, HTL reduces land requirements at least 50%, freshwater consumption at least 33%, and saline groundwater by 85%. Without recycling, nitrogen (N) and phosphorous (P) demand is reduced 44%, but remains significant relative to current U.S. agricultural consumption. The most nutrient-efficient pathways are LE + CHG for N and HTL + CHG for P (by 52%). Resource gains for HTL + CHG are offset by a 284% increase in N consumption relative to LE + CHG (with potential for further recycling). Nutrient recycling is essential to effective use of alternative nutrient sources. While modeling of availability and costs remains, for HTL + CHG at the 7.95E+10 L yr−1 production target, municipal sources can offset up to 20% of N and 49% of P demand and animal manure could potentially satisfy demands. |
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