Isabel C. Escobar*
Chemical and Environmental Engineering Department, The University of Toledo, 2801 West Bancroft Street, MS 305, Toledo, OH 43606-3390, USA
According to the International Water Management Institute (IWMI), one in three people globally endures some form of water scarcity, one-quarter of the world's population lives in areas where water is physically scarce, and over one billion people live where water is economically scarce, or places where "water is available in rivers and aquifers, but the infrastructure is lacking to make this water available to people.'' Fig. 1 shows a United Nations history of global water scarcity since 1950, and a projection to 2025. The World Water Institute states that water scarcity is not a factor of absolute quantity; rather, it is a relative concept comparing the availability of water to actual use. In the United States and Europe, the average individual uses between 200 and 600 liters of water per day (UN - Coping with Water Scarcity, 2007 World Water Day, http://www.unwater.org/wwd07), compared to the 20 liters deemed to be the minimum daily requirement for drinking, washing, cooking, and sanitation. A significant cause of water scarcity is agriculture since crop production requires up to 70 times more water than is used in drinking and other domestic purposes. IWMI approximates that each calorie consumed as food requires about 1 liter of water to produce. Such unsustainable consumption levels have led to localized areas of water scarcity and significantly altered freshwater ecosystems.
Existing water supplies may be limited in quantity or quality for meeting the increasing demands from population growth and industry expansion. In many arid and semi-arid areas, providing the large volume of water required for industrial, agricultural, recreational, and potable applications is especially difficult. So, searching for "new" water sources is a task for researchers in the water works field. Municipal wastewater, which comprises between 75% and 80% of consumed water in most cities, is one of the most reliable sources of
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Sustainability Science and Engineering, Volume 2 ISSN 1871-2711, DOI 10.1016/S1871-2711(09)00201-3 © 2010 Elsevier B.V. All rights reserved.
Global water1 availability
Global water1 availability
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water, since its volume varies little throughout the year. Through suitable treatment, reclaimed wastewater can meet various water quality requirements for potential wastewater reuse/recycle . Recycled water can be used in numerous applications to satisfy many water demands such as agricultural and landscape irrigation, industrial processes, toilet flushing, or replenishing a groundwater basin, depending on the level of treatment. Usually, treatment includes four stages: primary, secondary, tertiary or advanced, and disinfection. Among the many available treatment alternatives, membrane filtration technologies are attractive treatment options since they can meet stringent regulation standards.
Membrane processes are now a proven and reliable method of providing high-quality, cost-effective water. Membrane technologies have immediate applications to treatment of fresh, brackish, and seawaters, as well as wastewater reclamation. With innovative module design and engineering, micro- and ultrafiltrations have become effective and economical for drinking water production, particularly for removal of microorganisms. Membrane bioreactors are being developed for municipal and industrial water recycling. Various membrane processes are also used to remove contaminants from industrial wastewaters. The use of membrane technologies for aqueous separations has become very popular over the past 20 years. Successful use of membranes was first seen with desalination of brackish water and seawater. However, improvements in materials and manufacturing technology, mechanical configuration, and cleaning have expanded membrane technology to the treatment of waters of varying quality. Communities are searching for alternatives to conventional treatment for the production of high-quality effluents, and membrane technologies are emerging as treatment of choice for communities, as such technologies become better understood and widely available .
The United Nations declared 2005-2015 the "Water for Life'' Decade because water is crucial for sustainable development. The goals of the ''Water for Life'' Decade are to reduce by half the proportion of people without access to safe drinking water, to stop unsustainable exploitation of water resources, to aim to develop integrated water resource management and water efficiency plans, and to halve the proportion of people who do not have access to basic sanitation. Providing safe, clean water in a sustainable fashion is the focus of this book as it covers the fundamental and practical concepts and issues dealing with the application of different technologies for sustainable water treatment. It describes and compares the effectiveness of desalination versus water recycling for long-term sustainable water use.
 I.C. Escobar, Membrane developed systems for water and wastewater treatment, Environmental Progress 24(4) (2005) 355-357.
 I.C. Escobar, S. Ritchie, Foreword: Selected water/wastewater membrane-related presentations from the North American, Environmental Progress 27(2) (2008) 169-172.
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