This document discusses four methods for obtaining fresh water from seawater: reverse osmosis, electrodialysis, ultrafiltration, and flash evaporation. It provides details on the processes for each method. Reverse osmosis uses pressure to push seawater through a semi-permeable membrane, leaving fresh water on one side and brine on the other. Electrodialysis uses electricity and specialized membranes to separate ionic substances. Ultrafiltration uses pressure to remove solids and pathogens. Flash evaporation involves heating water and then releasing it to a lower pressure environment, causing some water to instantly vaporize.

1. INSTRUCTOR Ali Ibrahim Meris

2. WAYS OF OBTAINING FRESH WATER FROM
SEA WATER
• Reverse osmosis
• Electrodialysis
• Ultrafiltration
• Flash evaporation

3. REVERSE OSMOSIS
• Reverse Osmosis is a technology that is used to remove a
large majority of contaminants from water by pushing the
water under pressure through a semi-permeable membrane
• Osmosis is a physical phenomenon by which two liquids,
in different concentrations, separated by a semi-
permeable membrane, come into contact and tend to
even themselves out. The liquid with the lower
concentration crosses the membrane toward that with
highest concentration.

4. •In reverse osmosis desalination, water is taken
from the sea and receives a first treatment to
eliminate impurities, oil, seaweed, rubbish, and so
on. Once free of organic substances, the saltwater
can be subjected to reverse osmosis.

5. CONT…
• After the filtering, we have two streams: one brine and the
other freshwater. The brine solution is diluted before
being returned to the sea, avoiding high concentrations of
salt which could harm the ecosystem. The freshwater
passes through a remineralization and chlorination
process, after which it is stored in tanks and then sent to
the distribution network for consumption.

6. •98% of the Earth’s water is saltwater, found in seas
and oceans. The other 2% is freshwater, for use by
homes, farms and industry, but 40% of people
cannot access it. Some people have to travel miles
to find freshwater. Could we, however, use
saltwater to supply the places that most need it?
Yes. Desalination technology makes that possible.

8. Electrodialysis
• Electrodialysis (ED) is a membrane technique, during
which ions are transported through a semipermeable
membrane, under the influence of an electric
potential. It is a very versatile technology for the
separation of difficult mixtures.

9. • Electrodialysis uses electricity and specialized
membranes to separate ionic substances from water.
This practice can be used for desalination and
wastewater treatment. To make the process more
sustainable, electrodialysis can be coupled with
renewable sources of energy such as solar and wind
power.

10. Ultrafiltration
• Ultrafiltration (UF) is a pressure-driven barrier to
suspended solids, bacteria, viruses, endotoxins and
other pathogens to produce water with very high
purity and low silt density.
• An ultrafiltration (UF) water system is an efficient means
of removing solids and particulate from your water.
Ultrafiltration systems remove all suspended particulate in
water on a microscopic level. John Woodard.

11. Processes Of
Ultrafiltration
Screening
Sand filtration
Microfiltration
ultrafiltration

12. Flash evaporation
•Flash evaporation (or partial evaporation) is the
partial vapor that occurs when a saturated
liquid stream undergoes a reduction in
pressure by passing through a throttling valve
or other throttling device. This process is one of
the simplest unit operations.
•

13. • With flash evaporators the water is heated in one
compartment before being released into a second
chamber in which the pressure is substantially lower. The
drop in pressure changes the saturation temperature
below the actual temperature, so that some of the water
instantly flashes off as vapor.

14. END
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