This document discusses various methods for water treatment, including reverse osmosis and electrodialysis. Reverse osmosis uses semipermeable membranes and high pressure to filter out salts and impurities from saline water, producing pure water. Electrodialysis uses ion-exchange membranes and an electric current to separate positive and negative ions from water, lowering the salt content through repeated passes between compartments. The document provides definitions and explanations of the processes used in reverse osmosis and electrodialysis to purify water through filtration and separation of ions.

1. WATER TREATMENT
Subject Code: 07AT02
CHEMISTRY FOR BIOLOGIST - II
By
Dr. G. Balakrishnan
Assistant Professor
Department of Chemistry
Vivekananda College
Madurai, Tamil Nadu

2. UNIT- V: POLLUTIONS
Water pollution: Types,
sources,
sewage,
industrial effluents, inorganic
pollutants –
control –
water treatment

3. Desalting or Desalination by Reverse Osmosis
Definition: Reverse Osmosis, commonly referred to as RO, is a
process where you demineralize or deionize water by pushing it
under pressure through a semi-permeable Reverse Osmosis
Membrane.
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4. REVERSE OSMOSIS
This method is based on the principle of compressing
out water from saline water instead of removing salts from
water.
Millions of hollow fibers are bundled together and
dipped in saline water, which acts as a semi-permeable
membrane.
When saline water is subjected to high pressure, water is
literally compressed through the membrane into the
hollow fibers.
Thus pure and fresh water is collected at the opening
ends of the capillaries while salts and impurities remain
on the outer side of the fibers.

5. Electrodialysis
Definition: Electrodialysis is a process by which electrically
charged membranes are used to separate ions from an
aqueous solution by an electrical potential driving force.
https://glossary.periodni.com/glossary.php?en=electrodialysis

6. ELECTRODYALYSIS
 When salty water passes through ion-exchange membranes under
the influence if electric field, positive and negative ions present in
water get separated.
 The tank is divided into three compartments using anion and
cation exchange membranes.
 On passing current, cations from the middle compartment pass
through cation-permeable membrane while anions pass through
anion-permeable membrane.
 Due to movement of ions into the outer compartments, salt content
of water in the middle compartment decreases.
 Water from the outer compartments is discarded while water in the
middle compartment is collected and subjected to electrodialysis
again and again.

8. Thank you