Chapter 1
Introduction to Desalination

Jane Kucera

Nalco Water/an Ecolab Company

Corresponding author: Jane Kucera (jkucera@ecolab.com)

Abstract

The availability of fresh water on the planet is finite, and natural fresh water makes up only about 0.5% entire water supply on Earth. This limited supply, coupled with the growing population of the Earth and the growing industrialization of many developing countries, is driving global fresh water stress and scarcity to the point where more fresh water must be found to meet future needs. Methods to "find" more fresh water include conservation and reduce/reuse/recycle of existing fresh water sources, moving fresh water from water-rich regions to water-poor regions, and "creating" fresh water from other sources, such as oceans and wastewater, using desalination. Of these methods, desalination has proven to be a very viable technique to meet current and future fresh water needs in many areas around the world.

This introductory chapter discusses the history of, and drivers for desalination, and also provides a framework for the detailed discussions about various desalination technologies and opportunities to use renewable energy sources to power the desalination technologies that are presented in this book.

Keywords: Desalination, water scarcity, thermal desalination, membrane desalination, reverse osmosis, renewable energy sources

1.1 Introduction

Desalination: from the root word desalt meaning to "remove salt from" [1]. By convention, the term desalination is defined as the "process of removing dissolved solids, such as salts and minerals, from water" [2]. Other terms that are sometimes used interchangeably with desalination are desalting and desalinization, although these terms have alternate meanings; desalting is conventionally used to mean removing salt from other more valuable products such as food, pharmaceuticals, and oil, while desalinization is used to mean removing salt from soil, such as by leaching [2].

The first practical use of desalination goes back to the sixteenth and seventeenth centuries, when sailors such as Sir Richard Hawkins reported that their men generated fresh water from seawater using shipboard distillation during their voyages [3]. The early twentieth century saw the first desalination facilities developed on the Island of Curaçao and in the Arabian Peninsula [3]. The research into and application of desalination gained momentum in the mid-twentieth century, and the last 30 years has witnessed exponential growth in the construction of desalination facilities.

One could ask the question, "Why desalination?" Desalination has become necessary for several reasons, the most compelling of which may be: 1) the increased demand for fresh water by population growth in arid climates and other geographies with limited access to high-quality, low-salinity water, and 2) the per capital increase in demand for fresh water due to industrialization and urbanization that out paces availability of high-quality water. Research and development over the last 50 years into desalination has resulted in advanced techniques that have made desalination more efficient and cost-effective. Desalination is, and will be in the future, a viable and even necessary technique for generating fresh water from water of relatively low quality. Thus, the title of this book, Desalination: Water from Water.

In this chapter, and in this entire book, we make the case for desalination as one of the major tools for meeting the fresh water needs of a growing and industrializing planet.

1.2 How Much Water is There?

The allocation of the world's water is shown in Figure 1.1. About 97.5%, or 1338 million km3, of the world's water is sea-water [3, 4]. Eighty percent of the remaining water is bound up as snow in permanent glaciers or as permafrost [4]. Hence, only 0.5% of the world's water is readily available as low-salinity groundwater or in lakes or rivers for "direct" use by humans.

Figure 1.1 Allocation of the world's water resources.

1.2.1 Global Water Availability

Some regions of the world are blessed with an abundance of fresh water. This includes areas with relatively low populations and easy access to surface waters, such as northern Russia, Scandinavia, central and southern coastal regions of South America, and northern North America (Canada, Alaska) [2, 5]. More populated areas and areas with repaid industrialization are experiencing more water stress, particularly when located in arid regions.

There are numerous methods to calculate water stress (e.g., The Faulkenmark Indicator [6]), and many maps that display current and projected future water stress. In most cases, water stress is measured by comparing the amount of water used to that which is readily available, as explained by Maplecroft:

"The Maplecroft Water Stress Index evaluates the ratio of total water use (sum of domestic, industrial, and agricultural demand) to renewable water supply, which is the available local runoff (precipitation less evaporation) as delivered through streams, rivers, and shallow groundwater. It does not include access to deep subterranean aquifers of water accumulated over centuries and millennia.

The application of the index is to provide a strategic overview of the current situation of physical water stress at global, continental, regional, and national levels. It does not take account [any] future projection, [or] water management policies, such as desalination, or the extent of water re-use" [5].

Figure 1.2 shows the baseline water stress for the world, as estimated by the World Resources Institute for 2015.

Figure 1.2 Global baseline water stress, 2015. Courtesy of World Resources Institute.

The areas of the world that are not rich in water resources and that also experience un-stable and rapid population growth and industrialization will see water stress significantly increase in the future. Figure 1.3 compares the global water stress in 1995 with that predicted for 2025 [7]. As many as 2.8 billion people will face water stress or scarcity issues by 2025; by 2050, that number could reach 4 billion people [7] (See Figure 1.4 for world-wide 2040 estimates). Water stressed areas will include the south central United States, Eastern Europe, and Asia, while water scarcity (extremely limited access to flush water) will be experienced in the Southwestern United States; Northern, Southern, and Eastern Africa; the Middle East; and most of Asia [2].

Figure 1.3 Global water stress in 1995 and predicted for 2025. Courtesy of Philippe Rekacewicz (Le Monde diplomatique), February 2006.

Figure 1.4 Projected water stress by 2040. Courtesy of World Resources Institute.

1.2.2 Water Demand

The demand for water in developed nations is relatively high. Demand in the United States is about 400 liters per person per day [4]. Some Western countries that have been successful in implementing conservation and reuse measures have seen their demand for water drop to about 150 liters per person per day [4, 8]. However, the limited availability and access to water in some parts of the world, results in much lower consumption in these regions. For example, per capita freshwater consumption in Africa is only about 20 liters per day due to the shortage of suitable water [8]. The World Heath Organization (WHO) deems 15 to 20 liters per person per day is necessary for survival, while 50 liters per person per day is estimated to be needed for operation of basic infrastructure such as hospitals and schools (see Figure 1.5) [4]. The WHO estimates that by 2025, the worldwide demand for fresh water will exceed supply by 56% [8].

Figure 1.5 Global demand for water and World Health Organization basic water requirements (2010).[4, 8].

In addition to population growth, another pressure being exerted on water supply is fact that the per capita water demand is increasing faster than the rate of population growth [9]. According to Global Water Intelligence [10], the per capital water demand has outpaced population growth by a factor of 2. By 2050, global water demand is expected to increase 55% over 2015 demands, primarly due to manufacturing, thermal electricity generation and domestic use [11].

1.2.3 Additional Water Stress Due to Climate Change

While population growth and per capita increase in demand are two major water stressors, the impact of climate change on global water stress cannot be ignored. The effects of climate change actually work synergistically with population growth and increasing demand to strain water supply. As population and industrialization grow, climate change accelerates, leading to more drastic climate events such as drought. A study by the National Center for Atmospheric Research (NCAR) indicates that severe drought is a real possibility for many populous countries [12]. Regions that are projected to experience considerable drought include most of Latin America, the Mediterranean regions, Southeast and Southwest Asia, Africa, the southwest United States, and Australia [9]. Coincidentally, many of these regions are also experiencing increases in population, industrialization and, urbanization, with the corresponding...