Regionalized Life-Cycle Water Impacts of Microalgal-Based Biofuels in the United States

While algal biofuels have the potential to reduce the
national
reliance on fossil fuels, high water consumption associated with algal
biomass cultivation represents a major concern potentially compromising
the sustainable commercialization of this technology. This study focuses
on quantifying the water footprint (WF) and water scarcity footprint
(WSF) of renewable diesel derived from algal biomass and provides
insights into where algal cultivation is less water-intensive than
traditional ethanol and biodiesel feedstocks. Results are generated
with an engineering process model developed to predict the life-cycle
water consumption, considering green, blue, and gray water, of algae
facilities across the United States at a high spatiotemporal resolution.
The total WFs for Florida and Arizona are determined to be 13.1 and
17.6 m3 GJ–1, respectively. The blue
WF in Arizona is shown to be 8.5 times larger than in Florida, while
the green WF is 4.5 times smaller, but when combined into a total
WF, there is just a 26% difference between the two locations. The
analysis reveals that the total life-cycle WFs of algal renewable
diesel are smaller than the optimal WFs of corn ethanol and soybean
biodiesel. Algal systems benefit from higher growth rates and offer
the opportunity to manage wastewater streams, therefore generating
smaller green and gray WFs than those of conventional biofuels. The
WSF analysis identifies the Gulf Coast as the most suitable region
for algal cultivation, with cultivation in the western US shown to
exacerbate local water stress levels.