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

Abstract

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 m 3 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.

Global Life Cycle and Techno-Economic Assessment of Algal-Based Biofuels

“…More recently, research on alkaliphilic strains has found their ability to directly capture CO 2 from ambient air. , This not only eliminates co-location requirements but also reduces the economic and environmental penalty of concentrating and compressing CO 2 . − Aside from land and CO 2 , a freshwater supply is required to make up for evaporation losses in open ponds. Although algal biofuels generate lower water footprints than biofuels from terrestrial crops, algal cultivation can exacerbate water stress in arid regions. Cultivation of marine strains would expand potential locations to areas with available saline and brackish water resources.…”

“…59−61 Aside from land and CO 2 , a freshwater supply is required to make up for evaporation losses in open ponds. Although algal biofuels generate lower water footprints than biofuels from terrestrial crops, 20 algal cultivation can exacerbate water stress in arid regions. Cultivation of marine strains would expand potential locations to areas with available saline and brackish water resources.…”

“…10 In addition, a holistic sustainability assessment requires concurrent evaluation of environmental and technoeconomic aspects, but predictive spatial modeling is often only integrated into life cycle models with studies typically excluding techno-economic modeling. 20,24 Based on the current state of the field, a global sustainability assessment considering region-specific climate conditions, supply-chain environmental impacts, and economic factors is necessary to understand the actual sustainability potential of microalgal RD, particularly in regions with favorable climatic conditions for microalgal cultivation but for which limited data is available. This study integrates dynamic engineering process models with global weather datasets and spatially explicit sustainability data to investigate the environmental and economic implications of large-scale production of microalgal-derived RD around the globe.…”

“…This modeling framework reduces the uncertainty that productivity inputs introduce to process models and subsequently propagates to LCA and TEA outputs . However, spatiotemporal analyses have been often limited to regions with suboptimal weather conditions for algal cultivation such as the United States (U.S.) − and a restricted number of global case study locations. − Aside from process modeling limitations, the scarcity of life cycle data for location-specific supply chains constrains the focus of LCAs to specific regions as well as environmental impacts [e.g., global warming potential (GWP)]. ,, Similarly, TEAs usually use regional average economic data and ignore the effects of local cost factors (e.g., labor expenses) on process economics . In addition, a holistic sustainability assessment requires concurrent evaluation of environmental and techno-economic aspects, but predictive spatial modeling is often only integrated into life cycle models with studies typically excluding techno-economic modeling. , Based on the current state of the field, a global sustainability assessment considering region-specific climate conditions, supply-chain environmental impacts, and economic factors is necessary to understand the actual sustainability potential of microalgal RD, particularly in regions with favorable climatic conditions for microalgal cultivation but for which limited data is available.…”

“…21−23 Aside from process modeling limitations, the scarcity of life cycle data for location-specific supply chains constrains the focus of LCAs to specific regions as well as environmental impacts [e.g., global warming potential (GWP)]. 10,20,24 Similarly, TEAs usually use regional average economic data and ignore the effects of local cost factors (e.g., labor expenses) on process economics. 10 In addition, a holistic sustainability assessment requires concurrent evaluation of environmental and technoeconomic aspects, but predictive spatial modeling is often only integrated into life cycle models with studies typically excluding techno-economic modeling.…”