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SEAWATER REVERSE OSMOSIS
PLANT(R.O)
The Water and Sewerage Corporation began its efforts
to have a high capacity plant constructed in 1992.
Bids were sought and a joint
venture consortium of the local Bacardi Company limited, a Reverse
Osmosis Engineering Group based in Bermuda, was awarded a contract
to build, own and operate a seawater reverse osmosis plant (SWRO)
for the Corporation in 1996. Under the contractual agreement,
the joint venture company under the name Waterfields Company Limited
was responsible for the design, construction and operation of the
plant. Waterfields Company Limited completed the Primary
construction of the plant and began
producing water in December 1997.
This seawater reverse osmosis plant is designed
to produce up to 2,640,000 US gallons (or 2,200,000 imperial gallons) per
day of high quality portable water.Its design incorporates unique and interesting
features such as diesel-driven high-pressure positive displacement pumps,
work exchanger energy recover system and a 95% second pass RO system.
These
features have resulted in one of most efficient SWRO plants in today’s
market. Currently it is the largest SWRO in the Caribbean.
Seawater, extracted from four deep wells and
containing approximately 39,000 parts per million of salts and other
dissolved solids (total dissolved solids), is fed to four first
pass RO trains at a pressure of 1000
pounds per square inch.
The first pass trains convert
40-45% of the feed water into potable water containing less than 415
parts per million of total dissolved solids.
This
water is further purified by the second pass RO trains which operate
at a pressure of 190 pounds per square inch and produce high quality
potable water having less than 50 parts per million on total
dissolved solids.
The SWO plant is located at Windsor Field adjacent to the Nassau International
Airport and was officially opened on February 23, 1998.
Waterfields Company Limited
delivers approximately 2,400,000 us gallons (2,000,000 imperial gallons)
of high quality water to the Water and Sewerage Corporation of the
Bahamas. The water, upon purchase is blended with the highly saline waters of
the Windsor area wellfeilds to produce a “sweetening” effect and
thus reducing the salinity of the overall product. This blended
water is then chlorinated to kill harmful bacteria before delivery to
consumers. Areas within the distribution zone
include Love Beach, Gambier, Delaport, Cable Beach Strip, and the Prospect
Station which further distributed the water to; Stapledon Gardens, Oaks
Field Bain Town, Nassau Street, Centreville, Palmdale, Pyfroms Addition,
St. James Road and other areas including Paradise Island.
The new BlueHills Osmosis Plant is now fully
operational providing some 5 million gallons of water per day to
customers
Eventually, the Corporation will begin to rely less
on barging of water as water supply for New Providence residence will be
mainly through R.O. plants which is guaranteed to provide better taste,
better quality and greater reliability.
Other
plants planned for New Providence include, one at Perpall's
Tract and later one for eastern New Providence.
It's Happening Now!
R.O. Plant Building
Completed
Wellfields are 92%
completed
Two R.O. units have been
producing 2.0 MIGD since mid May 2006
An additional two (2) R.O.
units may become operational
shortly
New elevated tank is being constructed and erected at the tank section
phase
THE USE OF REVERSE OSMOSIS IN THE FAMILY
ISLANDS
Reverse Osmosis is a method of desalination which employs a semi-permeable membrane (usually a
thin plastic film) to physically separate high quality water from water
the contains salts and other types of impurities including
micro-organisms. Pressure is applied to the saline or feedwater side of
the membrane and purified water passes through and is collected on the
other side of the membrane. The unwanted impurities on the salty side are
then flushed away. Seawater can be used as a source of feedwater, and
therefore this means of producing high quality drinking water can be used
almost anywhere in the world. The drawback is that the feedwater usually
has to be cleaned up, or filtered, before it can be passed though the
membrane and energy is required to create the pressure needed to push the
water molecules through the membrane.
The principle of reverse osmosis is very simple but in practical terms it
requires high maintenance and a sound technical understanding of the
processes involved. Reverse osmosis has many applications. It is used to
desalinate seawater or brackish water for drinking and it is used to
produce high quality water for kidney dialysis, and many other chemical
processes. Even wastewater can be treated by this process.
A
basic reverse osmosis plant comprises a feedwater supply, a pretreatment
filter system, a high pressure pump, and membrane, facilities for product
storage, and a brine disposal system.
In order to
protect the membranes which are expensive and vulnerable items, the
pretreatment system can involve a number of different procedures to make
the water safe for drinking other procedures are employed on the
downstream side of the membranes.
Small plants
usually come in the form of a prefabricated package, but the individual
components can be purchased and assembled to meet specific
requirements.
In the Bahamas the use of reverse osmosis is
widespread. Hundreds of small plants are used in boats to produce water
and plants are now common in many households. Most of the bottled
water supplies in the Bahamas is produced by reverse osmosis. Persons who
live where there is no piped supply of water, and the groundwater quality
is poor, have a choice of collecting rainwater of purifying their
groundwater by means of reverse osmosis. Where the rainfall is low or very
seasonal reverse osmosis is a more reliable option and those that do not
want to deal with and understand the technology involved can pay a person
or a company to operate and maintain their plants. Hotels, marinas, and
restaurants use reverse osmosis throughout the Bahamas. The biggest plant
in use is the 2 m million gallon per day plant operated by Waterfields in
New Providence. There are a large number of companies and individuals
selling reverse osmosis equipment in the Bahamas and it is easy to procure
and install a plant. What is not so simple is operating and maintaining
the plant successfully and the cost of the water is considerably higher
than that of traditional sources such as groundwater.
The reality
of reverse osmosis in this island environment is that it is a godsend for
the Bahamas. This is because there are many inhabited islands that do not
have adequate water resources to meet the needs of the residents, and
there are many situations where water cannot be piped in from other nearby
source areas. In some locations rainwater and groundwater sources did meet
water demands for many years but development and particularly the growth
of tourism has changed this situation. Reverse osmosis already provides
water for the residents of Grand Cay, Moores Island, Black Point and
Farmers Cay, and plans are being finalized for plants to be installed in
Bimini, Long Island, San Salvador, Inagua, and Ragged Island. Other
islands with Bahamian communities that will require the use of reverse
osmosis include Great Harbour Cay, Staniel Cay, Acklins, and Long Cay.
Some islands like the off-shore Abaco cays that do not have any freshwater
resources could obtain their water from the mainland by means of
underwater pipelines, like Harbour Island and Spanish Wells in Eleuthera,
but until the mains are laid small reverse osmosis plants are used by the
commercial enterprises on these cays. Little Exuma and Barreterre do not
have good freshwater resources but water could be supplied from Great
Exuma by pipelines.Alternatively,
local reverse osmosis plants could be utilized.
In early
days New Providence could meet its water demand from groundwater sources,
but this situation has changed because of the growth of the population and
tourism, and changing habits of water use, and there are islands where
this scenario will probably be duplicated in the future. Examples are
Eleuthera, Great Exuma, and Rum Cay. Acklins has good water resources but
unfortunately these are located well away from the population centers and
there is a need for the use of small reverse osmosis plants in sectors of
the island.
In the foreseeable future approximately twenty (20)
populated islands will require water produced by desalination, but this
number could easily increase with development or growth in population.
Presently the best means of desalination on the scale required is reverse
osmosis, and because of various technical considerations the best method
of getting the required plants installed and operated is by means of
private companies with the appropriate experience. All Bahamians can, and
probably do, benefit from the use of reverse osmosis, and what is now
needed is a true appreciation of the value of good quality water, because
this water is not cheap. Technology is constantly changing, however, and
the situation described above could quickly change. What will never change
is the growing demand for water.
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