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Did
you know?
Reverse osmosis is the finest water filtration method known. This process will
allow the removal of particles as small as ions from a solution. It is used
to purify water and remove salts and other impurities in order to improve the
color, taste or properties of the fluid. R.O. uses a membrane that is semi-permeable,
allowing the fluid that is being purified to pass through it, while rejecting
other ions and contaminants from passing.
This technology uses a process
known as crossflow to allow the r.o. membrane to continually clean itself. This
is the reason of why an r.o. element can last many years before clogging or
need replacement. This
water purification process requires a driving force to push the fluid through
the membrane, and the most common force is household water pressure or pressure
from a booster pump. The higher the pressure, the larger the driving force and
efficiency.
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Can
you make seawater drinkable?
Anyone
who has ever seen a great, or even not so good movie about life on the
ocean knows that humans just can't drink seawater. After all, it's full
of salt that typically dehydrates the human body. But what if we could
make seawater safer to drink? It turns out that we can and the process
is called desalination. Desalination is a process that removes dissolved
minerals (including but not limited to salt) from seawater, brackish water,
or treated wastewater. A number of technologies have been developed for
desalination, including reverse osmosis (RO), distillation, electrodialysis,
and vacuum freezing. So why is seawater such an attractive water resource?
Here's
a few reasons why...Seawater provides an unlimited, reliable water supply
for coastal populations worldwide; brackish water is a plentiful, relatively
drought-proof water resource for inland populations and reduces dependency
on imported water. And, of all the Earth's water, 97 percent is salt water,
only 1 percent is fresh water available for humans to drink, and 2 percent
is frozen. Of the more than 7,500 desalination plants in operation worldwide,
60% are located in the Middle East. The world's largest plant in Saudi
Arabia produces 128 MGD of desalted water. In contrast, 12% of the world's
capacity is produced in the Americas, with most of the plants located
in the Caribbean and Florida.
To
date, only a limited number of desalination plants have been built along
the California coast, primarily because the cost of desalination is generally
higher than the costs of other water supply alternatives available in
California (e.g., water transfers and groundwater pumping). However, as
drought conditions occur and concern over water availability increases,
desalination projects are being proposed at numerous locations in the
state. Desalination costs are decreasing as technology improves and more
plants are built. Today there are more than 15,000 desalination plants
in 120 countries. The desalination market is forecast to grow more than
$70 billion in the next 20 years. About half of the world's desalted water
is produced with heat to distill fresh water from seawater.
The
distillation process mimics the natural water cycle in that salt water
is heated, producing water vapor that is in turn condensed to form fresh
water. One such treatment process is called Multi-Stage Flash Distillation.
Another desalination treatment process with the most expanded use is membrane-based
reverse osmosis,. In this process, pressure is applied to the water, which
allows water to flow through a membrane, leaving the ions, salts, and
other dissolved solids and nonvolatile organics behind. Some examples
of U.S. cities currently using, or planning to use desalination include:
Tampa Bay Water has constructed a 25-million-gallon-per-day desalination
facility in Apollo Beach in Hillsborough County, FL. The facility began
operating intermittently in March 2003 and is expected to be fully functional
by 2006; El Paso Water Utilities and Fort Bliss officials are collaborating
to build the country's largest inland desalination plant. The plant will
draw brackish water from an underground aquifer that provides about 40
percent of El Paso's municipal water supply. Construction of the 27.5-million-gallon-per-day
facility began in September 2005 and should be completed in 2007;The
Groundwater Recovery Enhancement and Treatment (GREAT) program in Oxnard,
CA will blend desalted groundwater with high-quality water the city buys
from a neighboring water district. Oxnard broke ground on the project
in May 2004, and it should be completed in 2006 or 2007.
There
are a number of ways to forestall this, however. One of those ways - desalination
- is already being used across the country to stretch water supplies,
clean up polluted water and provide protection for aquifers. The technique
is ancient, dating back to the 4th century B.C. when, according to the
National Water Supply Improvement Association, Greek sailors used simple
evaporation to desalinate seawater. The technology, however, is far more
modern. Desalination - separating saline water into fresh water and water
containing the concentrated salts - is accomplished in two main ways:
through distillation or use of membranes. Nearly 60 percent of the world's
desalted water is produced via the first method by heating salty water
to produce water vapor that is then condensed to form fresh water. The
second process uses membranes to separate the salts from the water.
In reverse osmosis (RO) facilities, water is forced through bundles of
membranes under pressure, leaving behind impurities. In electrodialysis
reversal (EDR) plants, an electrical current transfers ions through membranes,
resulting in desalted water and concentrates. Worldwide, desalting plants
have the capacity to produce 3.5 billion gallons of water a day, nearly
enough to provide 15 gallons a day for every American. Some nations, such
as Saudi Arabia and Malta, desalt ocean water to produce fresh water for
public and industrial consumption. In the United States, most desalting
plants treat brackish water, a process that costs one-third to one-fourth
as much as the treat involved in desalting ocean water. The product water
is used for direct supply, reserves or groundwater recharge.
According
to the American Desalting Association (ADA), other uses include irrigation,
wastewater treatment and water purification. Hospitals, resorts, manufacturing
plants, oil rigs and pleasure boats also employ desalination technology.
During the Persian Gulf War, the Army had mobile desalination units that
could produce 3,000 gallons per hour of potable water from brackish pools.
In a 1988 report, the Congressional Office of Technology Assessment suggested
desalination could find application in treating contaminated groundwater,
be it runoff from mines, agriculture, landfills or storage tanks. Of desalting
in general, the report noted, "Desalination should be included as a viable
option in any evaluation of water-supply alternatives."
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