Environmental Engineering Reference
In-Depth Information
24
20
16
12
8
4
0
1940
1955
1970
1985
2000
-4
Year
Fig. 4.4 Integrated moving average model forecast (Dore 2005 )
Based on the cost information from US plants that have been using RO to
produce drinking water through desalination, Dore used an autoregressive inte-
grated moving average model (ARIMA) to forecast the change in real seawater
desalination unit costs. The obtained model is shown graphically in Fig. 4.4 .
Figure 4.4 shows a steady decrease in real seawater desalination unit costs from
1940 to 1988, as well as a further decrease in forecasted costs up to the year 2005.
The blue line represents the upper 95 percent con
dence interval of the forecast and
the red line represents the 95 percent lower con
dence interval of the forecast. The
green line is the predicted value. From Fig. 4.4 we see that real unit costs of
desalination are expected to continue their downward trend. For the year 2000 the
real unit cost of seawater desalination was expected to lie within $0.00 to $3.54 per
1,000 gallons (3.79 m 3 ). For the year 2005 this cost was expected to fall even
further and lie within $0.00 to $2.42 per 1,000 gallons (Dore 2005 ).
Based on this forecast and the fact that the cost of obtaining and treating water
from conventional sources has been increasing, we can expect that desalination
costs will soon be competitive with those of conventional water treatment pro-
cesses. This suggests that desalination could become an important source of
drinking water even when the feed water does not require desalting.
4.3 Desalination Processes
Desalination processes can be divided into two categories: (a) thermal methods,
which involve heating water to its boiling point to produce water vapor and (b)
membrane processes, which employ a membrane to move either water or salt to
induce two zones of differing concentrations to produce freshwater. Desalination
facilities use one of
five basic technologies to extract potable water from sea and
brackish water. The
five technologies include RO, distillation, electrodialysis, ion
exchange, and freeze desalination. These technologies are classi
ed as thermal or
membrane processes in Table 4.2 .
 
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