Environmental Engineering Reference
In-Depth Information
Table 9.1
Water use for different power generation technologies.
Withdrawal (m
3
/MWh)
Consumption
(m
3
/MWh)
Open-loop cooling
Closed-loop tower
Closed-loop pond
Coal
76-190
1.1-2.3
1.9-2.3
1-1.8
Natural gas
28-76
0.9
—
0.4-0.7
∼
Nuclear
95-228
1.9-4.2
3.0-4.2
1.5-2.7
Geothermal
—
7.6
—
5.0
∼
Solar
2.8-3.5
—
2.8-3.5
Hydroelectric
17 (evaporation)
Fuel extraction
Withdrawal
Consumption
Coal
0.4-0.9
0.02-0.3
Natural gas
0.04
Uranium
0.2-0.6
Adapted from Department of Energy, 2006.
groundwater overpumping, which leads to lower levels and desiccation of wetlands. A similar
effect is produced by water diversion for irrigation projects. Excessive extraction of water in
the upper part of rivers results in less water available downstream. This not only results in
diminished volume of water but also in lost of habitats for fish and other aquatic animals and
for ecosystems depending on those rivers. A good example is the Aral Sea, which used to be
66,100 km
2
in 1960 and was reduced to 17,000 km
2
in 2004 after the Soviet Union diverted the
rivers that feed it for irrigation projects. By 1980, fisheries were all extinct because fish were
killed as a result of high salinity (Zavialov, 2005). In addition, the exposure of the sea bed has
increased suspended particles in the air with the subsequent impact on public health (O'Hara
et al., 2000).
Many rivers in the world are running low on water because of overuse and change in pre-
cipitation patterns. Examples of rivers that are running dry are the Amu Darya, one of the
rivers that fed the Aral Sea; the Colorado in the United States; the Fen and Yellow in China;
the Ganges in India; the Indus that supports Pakistan's agriculture; and the Nile in Northern
Africa (Brown, 2005).
Desalinization
In coastal areas where freshwater is in short supply, people have been producing a drinking
water by desalinization of seawater. Seawater contains on average 35 g/L of dissolved salts that
can be transformed into drinking water if the content of total dissolved solids is reduced to
levels less than 1.0 g/L, which is considered freshwater (“Thirsty? How 'bout a cool refreshing
cup of seawater,” n.d.), and preferably to 0.6 g/L of total dissolve solids (World Health
Organization [WHO], 2004) (Table 9.2). Another resource that can be used to produce fresh-
water via desalination is “brackish water,” which is water with a salt content between that of
seawater and freshwater. The advantage of using brackish water is that it requires less energy to
transform it into drinking water in comparison with seawater. Brackish water is available in
estuaries, internal seas and lakes, mangrove swamps, coastal lakes, and marshlands.
There are two basic ways to desalinate water: distillation and reverse osmosis. Distillation
plants, which use multistage flash distillation and vacuum distillation, heat and evaporate
