AWARE-US: Quantifying water stress impacts of energy systems in the United States

The water footprint of hydrogen production

Hydrogen (H2) is the most promising energy carrier for reducing the carbon emissions of the energy sector, but the impact of its production on water resources remains unclear. Here, we quantify the water footprint (WF) of different H2 production pathways accounting for the WF of the primary energy used in the production process, as well as feedstock and infrastructure water requirements. Results suggest that green H2 obtained from water electrolysis powered by renewable energy has the lowest WF (65 ± 2 m3/TJ for wind and 204 ± 79 m3/TJ for solar) mostly due to the low WF of renewable energy. The WF of blue H2 derived from fossil fuels is significantly higher (369 ± 30 m3/TJ for natural gas and 564 ± 82 m3/TJ for coal) due to high WF of fossil fuels as well as the water required for carbon capture and storage (CCS). H2 produced from nuclear energy and biomass have extremely high WF (741 ± 277 m3/TJ for nuclear and > 50,000 m3/TJ for biomass). Considering global and country-based energy scenarios, where the main H2 colors (green and blue) individually account for 15 % of energy consumption, we find that the use of green H2 could reduce the water demand of the energy sector while blue H2 would generally increase it, except in countries already characterized by high water consumption due to reliance on water-intensive energy sources. At the global level, we find that for every 5 % of H2 energy adoption, the energy sector could have water savings between 1 and 4 % for green H2 and increase water consumption between 1 and 5 % for blue H2. These results highlight the potential and criticalities of H2 within the water-energy nexus.

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.

Global spatio-temporal change assessment in interregional water stress footprint in China by a high resolution MRIO model

Developing effective strategies to alleviate increasing water stress in China requires an understanding of how consumption and production drive water stress footprints (WSF) at a high resolution and multiple spatial and temporal scales. However, current Chinese multi-regional input-output (CMRIO) models have limited resolution. Here, we build a high-resolution international MRIO model covering 31 Chinese provinces, 163 sectors, to address this issue, and then analyze the impact of changes in China's interprovincial and international trade patterns on the WSF from 2012 to 2017. We find that China's water stress embodied in inter-provincial trade has increased year after year, to 5606 km³ H₂O-eq in 2017, exceeding 50 % of the total domestic footprint. Domestic water stress transfer is most apparent in the outsourcing of water stress from eastern coastal regions to Central and Western regions, with the top interregional supply chain paths mainly associated with the demand of processed rice and tobacco products. China has transformed into a net exporter of water stress in 2017, with water stress exports to developing countries accounting for 54 % of total exports, up from 51 % in 2012. With deepening globalization, trade between China and developing countries has boosted bilateral economic development, while also exacerbating water stress in China. In addition to agricultural cultivation, industrial products such as plastics and steel exported to meet international industries further contribute to water stress in Northern China. Further identify hotspots of water stress consumption is needed to prioritize actions to relieve regional water stress in a more effective manner, and our study can provide key information.

Improving water scarcity footprint capabilities in arid regions through expansion of characterization factor methods

Water scarcity footprint (WSF) is a recent addition to life cycle assessment methodology that has advanced the understanding of freshwater environmental impact. The Available Water Remaining (AWARE) method is one approach that has gained significant traction in WSF applications. While an effective method for determining WSF, the methodology has limitations that constrain capabilities for determining freshwater environmental impact in arid regions. The primary limitation is the inability to compare regions when more water demand exists than what is available which typically occurs in arid regions. This limitation reduces resolution and therefore decision-making capabilities. This work proposes a novel method for determining WSF in arid regions by capturing and quantifying scarcity when water demand is greater than availability. The approach presented here, called the demand to availability (DTA) method, is intended to be used for small-scale, or subregion analyses in areas where truncation occurs using standard AWARE methods. With the regional specificity, unique characterization factors can be developed to enhance deterministic resolution and ultimately improve decision-making abilities. The DTA methods are presented universally, allowing for application and implementation to any region. A case study was developed to demonstrate the effectiveness of the DTA method by analyzing characterization factors (CFs) and alfalfa WSFs in the arid Southwestern United States. Using the standard AWARE methods, this region originally truncated 38% of counties resulting in zero resolution or decision-making abilities. Results of the case study that used the proposed DTA method show an improved resolution in 100% of these counties, both within CF and alfalfa WSF. Although the proposed method is an improvement for understanding WSFs in arid regions, limitations and constraints still exist and are discussed.

Heavy Metal Adsorption Using Magnetic Nanoparticles for Water Purification: A Critical Review

Research on contamination of groundwater and drinking water is of major importance. Due to the rapid and significant progress in the last decade in nanotechnology and its potential applications to water purification, such as adsorption of heavy metal ion from contaminated water, a wide number of articles have been published. An evaluating frame of the main findings of recent research on heavy metal removal using magnetic nanoparticles, with emphasis on water quality and method applicability, is presented. A large number of articles have been studied with a focus on the synthesis and characterization procedures for bare and modified magnetic nanoparticles as well as on their adsorption capacity and the corresponding desorption process of the methods are presented. The present review analysis shows that the experimental procedures demonstrate high adsorption capacity for pollutants from aquatic solutions. Moreover, reuse of the employed nanoparticles up to five times leads to an efficiency up to 90%. We must mention also that in some rare occasions, nanoparticles have been reused up to 22 times.

Water usage for energy production and supply in China: Decoupled from industrial growth?

The energy industry, one of the largest water consumers in the socioeconomic system, has been constrained by water scarcity in some areas worldwide. Therefore, decoupling water usage from the energy system is a pressing issue for ensuring energy security and maintaining environmental sustainability. This study applied an input-output analysis and the Tapio decoupling index, which may be considered the first attempt to investigate the decoupling degree between water usage, i.e., the direct water withdrawal for energy production (WWEP) from a production-based perspective and the water footprint for energy supply (WFES) from a consumption-based perspective, and industrial growth for five major energy sectors in China from 2002 to 2015. We found that WWEP was roughly three times higher than WFES for the whole energy industry, and both values underwent a considerable decrease during the study period. Production and supply of electricity and heat (PSEH) contributed most to the total WWEP and WFES, and was mainly responsible for the overall decline. Moreover, WFES exceeded WWEP in Processing of petroleum, coking, and processing of nuclear fuel (PPC) and Production and supply of gas (PSG), whose WEFS values accounted for 36.3% and 12.2%, respectively, of the total WFES in 2015. In terms of the decoupling status, only PSEH achieved strong decoupling in both WWEP and WFES, while PPC and PSG presented a better decoupling performance for WWEP than that for WFES. In contrast, Mining and washing of coal and Extraction of petroleum and natural gas performed relatively worse from both perspectives. These results can help provide a foundation and support for effective water conservation policies from both energy production and energy consumption perspectives.

Balancing Water Sustainability and Productivity Objectives in Microalgae Cultivation: Siting Open Ponds by Considering Seasonal Water-Stress Impact Using AWARE-US

Microalgae have great potential as an energy and feed resource. Here we evaluate the water use associated with freshwater algae cultivation and find it is possible to scale U.S. algae biofuel production to 20.8 billion liters of renewable diesel annually without significant water-stress impact. Among potential sites, water-stress is significantly more variable than algae productivity across location and season. Thus, it is possible to reduce water-stress impact, quantified as water scarcity footprint, through the choice of algae site location. We test three site-selection criteria based on (1) biomass productivity, (2) water-use efficiency, and (3) water-stress impact and find that adding water-stress constraints to productivity-based ranking of suitable sites reduces water-stress impact by 97% and water consumption by half, compared with biomass-productivity ranking alone, with little productivity impact (<1.7% per-site on average). With 20.8 billion liters, algae could meet 19.7% of U.S. jet fuel demand with a freshwater demand of less than 1.4% of U.S. irrigation consumption. Evaluating water-stress impact is important because the impact of unit water consumption on water stress varies significantly across regions and seasons. Considering seasonal water balances allows producers to understand the combined seasonal effects of hydrologic flows and productivity, thereby avoiding potential short-term water stress.