Reverse Osmosis and Other Treatment Technologies - Global Drinking Water Management and Conservation - page 52

4.2 Water Desalination Technology in Application

Water desalination is a water treatment process that removes salts and other min-
erals from water. Desalination or desalting can be done in a number of ways, but the
result is always the same: freshwater is produced from brackish (up to 10 g of
minerals/L) or seawater (up to 50 g of minerals/L). This is equivalent to saying that
about 3.5 percent of seawater is made up of dissolved salts. According to WHO,
RO will remove 99 percent of all (large molecule) contaminants. But typically, RO
is accompanied by activated carbon

filtration, which will remove any remaining
traces of contaminants. The resulting treated water is then distributed to consumers
for drinking and other purposes (Fig. 4.1 ).
On June 30, 2011, there were 15,988 desalination plants worldwide, and the total
global capacity of all plants in operation was 66.5 million m 3 /day, or approximately
17.6 billion US gallons per day (see Fig. 4.2 ). Saudi Arabia has 6.5 million m 3 /day
of installed capacity.
In the US, there are over 2,000 desalination plants over 32 states, amounting to
6 million m 3 /day of installed capacity. Of this total, 324 have an installed capacity
of over 95 m 3 /day (or 25,000 gallons per day). Their cumulative capacity is over
4.5 million m 3 /day, and 94 percent of these are drinking water treatment plants; the
rest are wastewater treatment plants.
As shown by Dore ( 2005 ), desalination capital and operating costs have been
decreasing. The decrease in costs is partly attributable to tax breaks for R&D in the
US. The year 1952, when the United States federal government passed the Saline

Fig. 4.1 Distribution of the cost components of a typical reverse osmosis desalination plant. (Wilf
2004 )