Environmental Engineering Reference
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mentioned above. Nevertheless, the three factors that are comparable and have the
largest effect on the cost of desalination per unit of fresh water produced are the
feed-water salinity level, energy costs, and plant size, which show economies of
scale (Winter et al. 2002 ).
4.4.1 Feed-Water Salinity Level
An increase in the salt content of the feed-water increases the operating costs as
desalination takes longer and/or uses more equipment. Brackish water can be
desalted most economically on a large scale by RO (Larson and Leitner 1979 ;
Glueckstern and Kantor 1983 ). RO brackish water desalination costs about
$1.50
$2.50 US per 1,000 gallons. As shown by Dore ( 2005 ), seawater desali-
nation on a large scale by RO can be obtained for about US $0.5 per cubic meter.
-
4.4.2 Energy Requirements
The energy required for desalination can represent about 44 percent of operating
costs under distillation as described above (see Fig. 4.1 ). The energy requirements
for employing various RO and Distillation treatments are presented in Table 4.1 and
clearly show that RO requires the lowest energy demand. This is a result of immense
heating required for water evaporation in the process of distillation. For this reason,
between the two best technological options (i.e. RO and distillation), RO takes the
lead, also in seawater desalination (Sackinger 1982 and Glueckstern 1999 ). Wood
( 1982 ) observed that rising world energy prices would alter the relative costs of
different desalination methods, increasingly favoring RO. But the development and
application of renewable energy could change this picture. For example, in
Australia, the Perth Desalination Plant produces up to 38 million gallons per day
using power from the Emu Downs Wind Farm. The 48 turbines at the wind farm
produce 80 MW/day, more than three times the needs of the plant (Mydens 2007 ).
Since 2008, Australia has added
five large-scale desalination plants. These facilities
have a production capacity ranging from 36 to 120 million gallons per day and all
use renewable energy sources including wind, solar, and wave energy (Furukawa
2013 ).
4.4.3 Economies of Scale
According to Mielke, the economies of scale favoring larger plants are particularly
signi
cant for plants with capacities smaller than 3 million gallons per day (Mielke
1999 ). The distillation processes bene
t most from economies of scale, while for
RO such economies of scale lead to a fall in unit costs at a lower rate. Nevertheless,
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