COMMENT pubs.acs.org/est
Water Energy Nexus Featuring peer-reviewed articles published in 2010 and 2011, this research shows progress on the water energy nexus— a hotbed of research with global implications for energy and environmental policies. Editor Jerald L. Schnoor comments on selection of these articles in this editorial appearing in the June 15, 2011 issue and on the Water Energy Nexus virtual issue Web site, http://pubs.acs.org/page/esthag/vi/1. As interest in water and energy resources grows, Environmental Science & Technology encourages continued submission of high-quality and impactful manuscripts. f you want more water, you need energy. And if you want more energy, it’s likely you’ll need an abundant supply of water to produce it. The two resources are inextricably intertwined. Such a fascinating topic, and that’s why we offer this ES&T Virtual Issue on the Water Energy Nexus. Here we seek to coalesce our content into one location for easy discovery and reading. Twenty-four articles are highlighted, including extraction of energy from algae and wastewater, and development of water supplies from groundwater and saline waters. Perhaps the greatest energy story of the 21st century (so far) is our ability to pump natural gas from shale formations. We may have as much as 1000 trillion cubic feet of newly available gas (Amy Myers Jaffe, “Shale Gas Will Rock the World”, May 10, 2010 Wall Street Journal, http://online.wsj.com/article/ SB10001424052702303491304575187880596301668.html). But the method of hydraulic fracturing requires millions of gallons of water and numerous toxic chemicals in “fracking fluids” (Kargbo et al., Environ. Sci. Technol. DOI 10.1021/ es903811p). Likewise, development of gasoline from tar sands is known to have a large water footprint (Chavez-Rodriquez and Nebra, Environ. Sci. Technol. DOI 10.1021/es101187h). The greatest water story of the 21st century is probably our increasing ability to reuse wastewater (both domestic sewage and industrial) for drinking water supplies through the development of high-pressure membranes and reverse osmosis. Still, energy requirements to force the water through membranes can be huge. Recovering some power by microbial fuel cells during water treatment, reuse, and desalination processes appears feasible, if not yet economical (Environ. Sci. Technol. DOI 10.1021/ es104325z; Environ. Sci. Technol. DOI 10.1021/es1022202; Environ. Sci. Technol. DOI 10.1021/es1025646; Environ. Sci. Technol. DOI 10.1021/es1009345; Environ. Sci. Technol. DOI 10.1021/es100852a). Wastewater is increasingly recognized as a resource—a resource from which we seek to harvest water, nutrients, and energy. Power generation represents the largest water withdrawal in the U.S. (Blackhurst et al., Environ. Sci. Technol. DOI 10.1021/ es903147k). Once-through cooling water is still the norm for 43% of existing power plants. But Li et al. (Environ. Sci. Technol. DOI 10.1021/es1040305) show that cooling water for electrical power stations may be provided economically from municipal wastewater if technical and policy challenges can be met. The greatest consumptive use of water remains irrigation. That is why irrigation of feedstocks for production of biofuels results in such an enormous water footprint (see “Water Footprint of U.S.
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Transportation Fuels” by Scown et al., Environ. Sci. Technol. DOI 10.1021/es102633h). But even nonirrigated crops use substantial amounts of water in the conversion process like that for sugar cane in Brazil (Environ. Sci. Technol. DOI 10.1021/es101187h). Of life cycle assessment papers submitted to ES&T these days, more concern biofuels than perhaps any other single topic. The world seeks greater energy security by substituting domestic biofuels for imported petroleum in transportation fuels, but the environmental impacts can be daunting. All politics are local. And all water energy portfolios ultimately must be studied at the local scale. That is the tactic that Perrone et al. (Environ. Sci. Technol. DOI 10.1021/es103230n) have taken while examining one of the most water-short cities in the U.S., Tuscon, Arizona. They found that “recycled water” uses, by far, the least amount of energy, and that natural gas was the fuel requiring the least amount of water to develop. “No country uses as much energy as that which strikes its buildings every day”, says Denis Hayes, cofounder of Earth Day. If we could harvest all that solar, there should be no energy shortages. But severe energy stress exists in the world today, and even solar buildings have a substantial water footprint (Batlles et al., Environ. Sci. Technol. DOI 10.1021/es9027088). The Water Energy Nexus will become ever more important in coming years. The world needs both commodities desperately. Communities with severe water stress relieve their situation in one of three ways: (1) importing water from upstream sources or via interbasin transfers; (2) pumping groundwater unsustainably; or (3) reusing wastewater or saline waters. Only the last solution is sustainable in the long run. Countries with energy stress attempt to increase production of domestic energy resources and to avoid imports of petroleum by making biofuels. All of these solutions have substantial environmental impacts.
Jerald L. Schnoor Editor
’ AUTHOR INFORMATION Corresponding Author
[email protected].
Published: June 13, 2011 5065
dx.doi.org/10.1021/es2016632 | Environ. Sci. Technol. 2011, 45, 5065–5065
