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Unformatted text preview: Energy and Air Emission Effects of Water Supply J E N N I F E R R . S T O K E S A N D A R P A D H O R V A T H * Department of Civil and Environmental Engineering, 215 McLaughlin Hall, University of California, Berkeley, California 94720-1712 Received June 29, 2008. Revised manuscript received December 15, 2008. Accepted February 17, 2009. Life-cycle air emission effects of supplying water are explored using a hybrid life-cycle assessment. For the typically sized U.S. utility analyzed, recycled water is preferable to desalination and comparable to importation. Seawater desalination has an energy and air emission footprint that is 1.5- 2.4 times larger than that of imported water. However, some desalination modes fare better; brackish groundwater is 53- 66% as environmentally intensive as seawater desalination. The annual water needs (326 m 3 ) of a typical Californian that is met with imported water requires 5.8 GJ of energy and creates 360 kg of CO 2 equivalent emissions. With seawater desalination, energy use would increase to 14 GJ and 800 kg of CO 2 equivalent emissions. Meeting the water demand of California with desalination would consume 52% of the state’s electricity. Supply options were reassessed using alternative electricity mixes, including the average mix of the United States and several renewable sources. Desalination using solar thermal energy has lower greenhouse gas emissions than that of imported and recycled water (using California’s electricity mix), but using the U.S. mix increases the environmental footprint by 1.5 times. A comparison with a more energy-intensive international scenario shows that CO 2 equivalent emissions for desalination in Dubai are 1.6 times larger than in California. The methods, decision support tool (WEST), and results of this study should persuade decision makers to make informed water policy choices by including energy consumption and material use effects in the decision-making process. 1. Introduction Drinking water scarcity is an issue in many parts of the world. By 2025, 1.8 billion people will be living in areas likely to experience absolute water scarcity ( 1 ). More than 40% of the world’s population may face serious water shortages if they must rely solely on locally available freshwater ( 2 ). Some of these places experience scarcity due to climate and others because infrastructure is unavailable; however, in some places, both issues are problematic. The western United States is especially impacted by scarcity. For example, California’s population is expected to increase by 14 million people by 2030. If we assume water use rates for the year 2000 are representative values, demand will increase by 40% in the same period ( 3 ). Much of this growth will occur in the more arid areas of the state, where the scarcity will be acute ( 4 ). Currently, most water in arid areas is imported via major conveyance networks that comprisemorethan4800kmofpipelines,tunnels,andcanals, and dozens of pump stations, e.g., the State Water Projectand dozens of pump stations, e....
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This note was uploaded on 05/08/2011 for the course CE 11 taught by Professor Horvath during the Spring '11 term at University of California, Berkeley.
- Spring '11
- Environmental Engineering