The reverse osmosis systems market is
growing at an annual rate of 8%, “and
desalination, a primary application for RO,
is expected to grow globally at an average
of 11% during the next year.”
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nologies are improving. According to
one estimate, a reverse osmosis (RO)
seawater desalination plant built today
can produce 27 times more water—for
the same capital investment—than
could be achieved in 1980. “It’s now
possible to desalt water for a cost of less
than $1 for every 1,000 gallons,”
reports Tom Decker, vice president for
the Water Business Group of CH2M
Hill, a Denver-based company that provides planning, engineering, design and
program management.
Improving technology and decreasing
costs are boosting the economic viability
and attractiveness of water desalination. According to Decker, in the past 15
years the number of “desal” plants has
tripled from 7,500 facilities in 1993 to
some 21,000 plants today. About two-thirds of these plants process seawater,
while the other one-third mostly
processes brackish groundwater.
As costs come down, economies of
scale can go up. Since RO systems are
modular, operations are easily expandable. Ten years ago most seawater desal
plants ranged in size from 0.2 to 4 million gallons per day (mgd), a CH2M
white paper reports, but most projects
announced in recent years range in size
from 14 to 72 mgd.
According to Marwan Nesicolaci,
vice president of water purification services at Severn Trent Services, a global
supplier of water and wastewater treatment solutions, the reverse osmosis systems market is growing at an annual
rate of 8%, “and desalination, a primary application for RO, is expected to
grow globally an average of 11% during
the next year.”
CIRCLE READER RESPONSE #73
Going with the Flow
Fresh surface water is the most used
source. By contrast, seawater is highly
saline and typically contains more than
35,000 milligrams per liter (mg/l) of
total dissolved solids (TDS). Groundwater taken from subterranean aquifers,
on the other hand, may be fresh or
saline. Groundwater is called brackish
when it contains dissolved solids such as
salts. Concentrations in brackish water
typically range from 1,000 to 10,000
mg/l.
Distillation of seawater has been
employed since Roman times. About
2,000 plants worldwide use a process
called multistage flash distillation.
Under a vacuum that reduces the boiling point of water, a thin film of water is
exposed to high heat so that flash evaporation occurs. After the water is
repeatedly flashed, distilled fresh water
results.
A second method for desalting water
is electrodialysis, a process first used on
a large scale in the late 1950s. Seawater is processed through a container
with positive and negative electrodes on
opposite ends. As salt dissolves in water
and splits into charged particles, these
ions are attracted by the electrodes and
trapped by membranes. The remaining
desalted water is then tapped. However,
the electrical requirements for this
process are high.
According to CM2H Hill’s Decker,
since the late 1990s reverse osmosis has
become the dominant technology for
water desalination. “Though within the
RO market,” he reports, “there are different RO system manufacturers whose
specific technologies vary.”
That observation is affirmed by Tom
Morgan, manager for the North America and Asia Pacific regions of ITT
Water Equipment Technologies. Based
in West Palm Beach, FL, the company
has manufactured RO systems for desal
plants worldwide. “Each manufacturer
has its own niche—for example, a particular size or application,” he says,
