Water pollution can be defined as the
addition of foreign substances(pollutants)
to a water source that affects the physical
chemical and biological properties of
water which in turn decreases the utility of
Only about 3% surface water is fresh water
One- fifth of the world population lacks access
to clean drinking water.
Over 2.6 billion people do not have adequate
More than 2 million children are killed by
diarrheal diseases each year
Earth’s oceans are the most important carbon
sink on the planet along with rain forests
Demand for water will double in next 30 years
Floods are most frequent disaster worldwide
• Heavy metals such as Cd, Hg and
lead. These elements are not present
in our body but get concentrated in
• These elements severely affect the
1. During extraction of Zn Cd is released as
2. Cd alloys in fire detection. automatic
sprinkler, solders, valve seals, high
pressure gas containers. These when
disposed is burnt and cd is released to the
Replaces Ca in bones. And symptoms
similar to those of Rheumatism set in.
Causes ITAI ITAI
increased salivation, acute gastric
liver and kidney damage.
Consumption of contaminated sea food
Increase in chance of prostate and
1. Lead acid industries
2. Galvanized Fe connection
3. Automobile emissions
5.Mining and plumbing
6.Burning of coal and oil
7.Pb enters drinking water from old water pipes
2.Loss of appetite
3.Abdominal pain and anaemia
4.Liver and kidney damage
6.Mental retardation in Children
7.Abnormality in fertility and pregnancy
Lead poisoning also
known as plumbism,
1. Embedded in igneous rocks – Basalt and Granite
in the form Cinnabar – HgS ]
2.Broken thermometers, amalgam tooth fillings,
batteries, pharmaceutical products,
manufacture of Cl and caustic soda
When the amount of Hg exceeds 1-10mg/l, Hg
is converted into methyl Hg, which when
nerve and brain damage
Paralysis followed by death
Affects nervous system and brain
Cause depression and irritability
The disease results in crippling deformi
namata disease- the disease
s to crippling deformity.
fertilizer and chemical
biological degradation of
Deamination of organic N
Hydrolysis of urea
increase pH value of water (increases the
alkalinity), causing stomach disorder .
Produces algae bloom, which in turn reduces
dissolved oxygen, causing damage to aquatic
Blocks oxygen transfer in the gills of fish.
o Fertilizers contain nitrates and phosphates
which in excess over stimulate the growth
of aquatic plants and algae,
o block light to deeper waters while the
organisms are alive;
o when the organisms die, they use up
dissolved oxygen as they decompose,
o diminished amounts of marine life. Such
areas are commonly called dead zones
o causes disease called methanol
globinaemia in children due to high nitrate
concentration- bluish colouration of skin-
conversion of normal Hb into methyl Hb
o nitrates also interfere with oxygen-carrying
capacity of haemoglobin, thereby causing
1. Use fertilizers sparingly
2. Choose one with a low phosphorous number.
3. Don’t fertilize before a rain storm.
4. Use organic fertilizers.
Silt is granular material of a grain size
between sand and clay derived from
soil or rock.
Sediments like silt, sand and minerals
are contributed by soil erosion etc…
They reduce the amount of light
supply to aquatic animals.
What are Sediments?
Impurities in the form of suspended solids
Occur due to soil erosion
Undissolved solids, some of which dissolves
over long periods of time and some of which
practically never go into solution
Run off by agricultural activities, china clay
industry ,construction and steel industry.
Fill up dams, make water cloudy and muddy.
Decrease water quality in a physical way.
Cause physical problems to gill breathers like
SOURCES AND EFFECTS
Detergents, Pesticides, Food Waste,
Radioactive Materials, Thermal
Most common form of water pollution.
Originate from domestic sewage, industrial
effluents and farm wastes.
Some important organic pollutants are
1) Domestic waste – sewage
with organic matter
2) Infectious agents - sewage
from municipalities causing
3) Organic chemicals – pesticides, insecticides etc.
1.Soaps & Detergents
surfactants because they
are surface tension
Mainly two components
1) Lyophilic :- merges with
2) Lyophobic:- merges with
the oil dirt.
Detergents mainly 3
types:- anionic, cationic
Have a poisonous effect on
all types of aquatic life if
they are present in
Destroy the external mucus
layer which protects the
fish from bacteria &
Phosphates in detergents
can lead to algal bloom
that releases toxins and
deplete oxygen in
General term for insecticides, fungicides etc.
Mainly classified as:
Eg: DDT, heptachlor, etc.
chlorophenoxy acid group
Eg: 2,4-dichlorophenoxy acid
Biomagnification: Tendency of pollutants to become
concentrated in successive trophic levels.Eg: DDT,
• One of the most well-known synthetic
• It accumulates in the insulating sheaths
around nerves and prevents the
transmission of impulses by decreasing the
concentration of the concerned enzyme.
Contain Hg which break down soil.
CH3Hg is used as a fungicide in Iraq for wheat
crop. The bread made from this wheat caused
the death of many human beings.
Radioactive materials enter in to water bodies
Production of nuclear power releases
radioactive substances in the environment.
From water they can be transferred to human
body directly or through food chain.
From nuclear power plants and nuclear
reactions. Eg: Sr90, Cs137,Pu248……
Wastes from U and Th mining and refining
Use of radioisotopes in research, agricultural,
industrial and medical applications. Eg. C14,
P32, S35, Ca45, Co60, cs137
From nuclear weapons.
Burns, cancer and molecular disruptions.
high energy radiations can harm genetic material-
genetic effects transmitted to coming
radiations lead to abnormalities in offsprings
Discharge of waste heat into natural waters
is termed as thermal pollution
Large amount of water are used for cooling
purpose in thermal and nuclear power plants.
Water is finally discharged in the water body,
temperature raises to 10-16 degrees.
Rise in temp decreases the dissolved O2 in
Sudden transference of fish to warm water
may result in death.
Decreases disease resistance of fish.
Pollutants present in water become more toxic
at elevated temp.
bring several physiological problems in aquatic
BOD increases with temp.
CONTROL OF THERMAL
Cooling ponds :warm water is sprayed
into cooling ponds using nozzles, quick
cooling takes place due to the formation of
fine droplets having large surface area.
Cooling towers :transfer waste heat to
atmosphere thru evaporation/heat transfer
Warm water is first stored in earth like
ponds. Natural evaporation brings down
temp, then discharged into nearby water
CONTROL OF WATER
Physical Treatment Systems:
//Rely on physical processes
tion and flotation.
removed using gravity.
//Flotation uses diffferences
in particle densities.
CHEMICAL treatment systems:
and disinfection reactions.
Precipitation-uses addition of
chemicals to precipitate dissolved
solids(heavy metals and phosphorus).
Adsorption-activated carbon is used
(GAC-Granulated Activated Carbon
PAC-Powdered Activated Carbon)
causing organisms(bacteria and
Utilize biological activity to remove
pollutant from water streams.
Microorganisms- bacteria- convert
carbonaceous matter into gas.
Microorganism--- aerobic and
Solid pollution control methods:
Spreading the solid waste in compact layers
separated by a thin layer of soil.
biodegradable substances produce CO2 and
Leachate- waste waste water generated from
landfills- treated to avoid ground water
organic matter under
either aerobic or
Carried out in static
a variety of reactors.
paper, food waste,
Solids are burnt in large
reducing the volume of
solid wastes that enter
Can be used for metal
with air pollution control
Importance of Dissolved Oxygen in
Fish growth is inhibited if dissolved Oxygen
concentration is less than 6ppm.
Lower the oxygen concentration,more polluted is
Dissolution of Oxygen into water through the
Photosynthesis causes water to become
supersaturated during the day time.
Dissolved matter is rapidly consumed by
micoorganisms to oxidise matter of sewage.
Sewage is a mixture of domestic and industrial
wastes. It is more than 99% water, but the
remainder contains some ions, suspended solids
and harmful bacteria that must be removed
before the water is released into the sea.
Combination of screens ,filters ,grit chambers &
sedimentation tanks for grit removal.
Screening – removes large suspended or floating
Flocculation – removes smaller suspended
particles. Agitating with mechanical stirrers – small
suspended particles collide to form bigger
aggregates which settle down easily.
Chemical coagulation – sewage treated with
chemical components coagulates to form colloidal
Used coagulants : CaCO3, Alum, FeCl3
COMMONLY USED COAGULANTS ARE
(iii) FERRIC CHLORIDE
TO ENHANCE THE SPEED OF COAGULATION SOMETIMES,
COAGULANT AID SUCH AS ACTIVATED SILICA GEL ETC ARE ALSO
Organic matter is biologically degraded by different
types of microorganisms under controlled
Main processes used duringsecondary treatment
Activated sludge process
A trickling filter consists of a beds of crushed
stone containing biologoical slimes. (A mucous
substance secreted by certain animals)
Waste waster is allowed to percolate through the
stone beds when the organic matter present in
waste water gets adsorbed on slimes and
undergoes decomposition by the bacteria and
fungi present in the slimes
Eg. Food processing, pulp and paper mills,
Sewage is pumped into a huge tank – mixed with
air bubbles and bacteria rich sludge for a
period of 4 to 10 hours. (mechanical aeration)
A gelatinous mass loaded heavily with bacteria
is formed and is called activated sludge.
The carbonaceous matter formed is oxidised to
more stable nitrates, sulphates, and CO2.
The floc thus formed is pumped out to a
sedimentation tank, allowing the sludge to
settle out for reuse
The oxidation ditch is a circular basin lined with
plastic, tar or butyl rubber through which the
Activated sludge is added to the oxidation ditch so
that the microorganisms will digest the waste in the
Longer retention times are needed for better
A pond that contains partially treated
wastewater which is then left to allow the
growth of algae and bacteria which
decompose the rest of the waste.
Oxygen required by the bacteria is provided by
algae present in the pond.
Organic matter undergoes anaerobic oxidation
by bacteria to CH4 ,CO2 & NH3 .
Heavy metal ions are precipitated as
hydroxides and form sludge.
Disposal of sludge
This method consists in digesting the sludge in
circular digestors 6-10 meter deep maintained at
35degree celcius and pH 7-8 for about a month.
Slow fermentation forms gases consisting of about
70% methane and 30% CO2 with other gases.
After treatment, sludge gets converted into a stable
humus material which can be used as a low grade
Other sludge handling methods
Denaturing by drying on sand beds
Denatured sludge is then disposed off by
incineration or composting.
Incineration, however, can lead to air pollution
To remove chemicals in waste water after 10 and
Methods include :
Coagulation & Sedimentation – waste water
treated with chemical coagulants in which
suspended matter gets coagulated and then
Carbon adsorption – waste water filtered
through activated carbon
Chemical Oxidation – Organic contaminants are
oxidized by reagents like O3
The major tertiary methods includes:
1.COAGULATION AND SEDIMENTATION:In
this process,the waste is treated with chemical
coagulants such as alum, ferric chloride ,etc. as
a result of which the suspended matter gets
2.Carbon Adsorption: The waste water is filtered
through activated carbon to eliminate materials
responsible for colour and undesirable tastes and
3.Chemical Oxidation: Organic contaminants are
oxidised by several reagents like ozone and pottassiun
4.Reverse Osmosis : In this process,
waste water is separated from fresh
water by a semipermeable membrane
which allows the water to move to it
but not the dissolved material.
5.Biological Methods: The dissolved
organic materials such as nitrates and
phosphates can be directly removed from
the water by certain aquatic plants such as
Reverse osmosis – waste water separated
from fresh by semipermiable membrane.
applying pressure > osmotic pressure of waste
water, pure water from waste forced to other
side of membrane.
Biological process – Algae and waste
hyacinths consume nitrates and phosphates.
//Both primary and secondary
treatments remove 90% of the oxygen
demanding organic wastes.To remove
chemicals left in the waste water after
primary and secondary
treatment,tertiary treatment is carried
//Primarily chemical methods are used.
contaminants oxidized by several
reagents like ozone and potassium
•Biological Methods://Algae and water
hyacinths grown in ponds can be used
to consume nitrates and phosphates.
Addition of artificial or non artificial
substances, through fertilizers to fresh water
nutrient enrichment of water body
Nitrogen and phosphorus present as
phosphates and nitrates
Rate of increased respiration rates causes
excess organic matter to accumulate in water
stimulating bacterial activity
Causes of Eutrophication
growth of pathogenic organisms due to
decrease of dissolved O2.
species diversity to decrease because of
increased algae growth
increase of turbidity
increase in the rate of sedimentation, shortening
the life span of lakes
obstruction to the flow of water
difficulties in the treatment of water for drinking
extensive fish mortalities in shallow lakes
methaemoglobinaemia in infants by bottle fed
phosphate stripping of water using coagulants
of lime or compounds of Al or Fe
use of micro organism
By treatment of ponds where much of it is
absorbed on to particular matter which will
settle out in the pond itself
Planting of buffer strips (vegetated strip of land
of some 5-50m wide) between farm land and
DESALINATION OF WATER
Desalination is the process of removal of salts
Water containing high concentration of
dissolved salts is called Brackish water.
For example, sea water contains 35000 ppm
of dissolved salts.
Brackish water cannot used for domestic and
DESALI NATI ON OF
Process of removing common salt(NaCl)
Commonly used methods of Desalination
of Water are:
When two solutions of different
concentrations are separated by a semi-
permeable membrane, the solvent
molecules flow from a region of low
concentration to high concentration. This
phenomenon is called osmosis.
The semi permeable membrane is a selective
membranes which does not permit the
passage of dissolved alts. The flow of solvent
molecules continues till the concentration
becomes equal on both sides.
The process of reversing the flow of
solvent molecules by applying pressure in
excess of osmotic pressure, on
concentrated solution side is shown as
(If a hydrostatic pressure in excess of osmotic
pressure is applied on concentrated side, then
solvent molecules are forced o move from
concentrated side to dilute side across the
Pure solvent is seperated from its
contaminates,rather than removing
contaminates from the water
A RO Membrane
Water enters the RO membrane
under pressure and travels from the
feed end to the reject end. Some of
this feed water passes through the
membrane and becomes purified.
This water is called the RO product
water. The contaminants that were
previously in the product water exit
the membrane in the reject water.
Spiral Wound Membrane Element
Several layers of membrane material are sandwiched between spacer
material to form leaves with a feed / reject channel and a product channel.
These leaves are then rolled around a central product collection tube. This
assembly is referred to as a spiral wound membrane element. The spiral
wound membrane element is installed in a pressure vessel. A seal between
the outside of the membrane and the inside of the pressure vessel prevents
the feed water from flowing between the membrane and pressure vessel.
This is called a brine seal. Membranes should always be installed with the
brine seal on the feed end of the vessel. (Before entering the seawater in
reverse osmosis membranes, clarified seawater is pressurized by the High
Pressure Pump typically between 55 and 85 bars, depending on the
temperature and the salinity of the water.
Desalination by reverse osmosis removes
ionic impurities as well as colloidal silica.
Both organic and inorganic contaminants can
Capital and operating expenses are low.
Energy requirement is 30% lower than that of
Operated at a comparatively low temperature.
Electrodialysis is the process of removal of
dissolved salts by migration of ions present in
water towards their respective electrodes,
through ion- selective membranes under the
influence of applied emf.
Electrodialysis (ED) is used to transport salt
ions from one solution through ion-exchange
membranes to another solution under the
influence of an applied electric potential
This is done in a
configuration called an
electrodialysis cell. The
cell consists of a feed
and a concentrate (brine)
compartment formed by
an anion exchange
membrane and a cation
placed between two
The anion selective membrane contains positively charged
functional groups such as R4N+ and only anions pass through it
as cations are repelled by it.
Similarly, the cation selective membrane contains negatively
charged functional groups such as RCOO- or RSO3 and only
cations can pass through it as anions are repelled by it.
When electric current is applied across the electrode, cations (
Na+ions) move towards cathode and anions (CI- ions) move
towards anode through ion selective membranes.
It result in removal of ions from central compartment and pure
water is collected at bottom.
At the cathode,
2e- + 2 H2O → H2 (g)
+ 2 OH-
At the anode,
H2O → 2 H+ + ½ O2
(g) + 2e- or 2 Cl- →
Cl2 (g) + 2e-
It is most compact unit
The cost of installation of the plant and its
operation is economical
If electricity is easily available ,it is best suited