WATER POLLUTION AND CONTROL

WATER POLLUTION AND CONTROL
Dr. Subash Thanappan PhD
Associate Professor
Department of Civil Engineering

Eutrophication is the gradual increase in the concentration of phosphorus, nitrogen, and other
plant nutrients in an aging aquatic ecosystem such as a lake. The productivity or fertility of such
an ecosystem naturally increases as the amount of organic material that can be broken down into
nutrients increases. This material enters the ecosystem primarily by runoff from land that carries
debris and products of the reproduction and death of terrestrial organisms. Water blooms, or
great concentrations of algae and microscopic organisms, often develop on the surface,
preventing the light penetration and oxygen absorption necessary for underwater life. Eutrophic
waters are often murky and may support fewer large animals, such as fish and birds, than noneutrophic
waters.
Eutrophication, or nutrient pollution, is a major environmental concern for lakes, tributaries,
rivers, estuaries and coastal waters. Eutrophication refers to an increase in nutrients, especially
nitrogen and phosphorus, which leads to an explosive increase in the growth of algae, called
algal blooms. Eutrophication also includes the increased input of sedimentary material. There are
two types of eutrophication: natural and cultural. Furthermore, there are two types of sources for
the nutrients and sedimentary materials: point and nonpoint.
Natural Eutrophication
Water bodies under Eutrophication
Over centuries, gradual buildup of nutrients, sediments and organic material begin to fill many
lake basins. As the lakes become more eutrophic, they are able to support more living organisms,
including damaging algae, as a result of higher nutrient levels. At the same time, their littoral
area increases as a result of sedimentary buildup. Eventually, this process not only affects the
water quality but allows colonization by terrestrial vegetation in the expanding shallows. The
length of this process depends on the characteristics of the lake basin, the watershed and the
climate.

Cultural Eutrophication
The alteration of nutrient input to water basins by human activity can dramatically increase
eutrophication, leading to major ecological changes in decades, rather than centuries. Cultural
eutrophication is primarily associated with phosphorus, which is found in fertilizers and partially
treated sewage. Phosphorus has been found to be one of the strongest stimulators of algae
growth. One of the primary sources of man-caused sedimentary eutrophication is soil erosion
caused by the removal of trees and vegetation. The health of aquatic habitats is directly tied to
the human activity that takes place throughout the entirety of their watersheds, requiring
effective land management and environmental policy.
Eutrophication Sources
Point sources are definitive, localized sources of nutrients and sedimentary pollution. A primary
point source is municipal and industrial wastewater runoff. Additional point sources include
runoff and leaching from waste disposal systems, animal feedlots, hog and chicken farming
operations and industrial sites. Large construction sites are also a frequent point source for
sedimentary runoff. Nonpoint sources are diffuse sources of nutrients and sedimentary pollution.
A primary nonpoint source of eutrophication is runoff from agriculture and pastures. Other
possible nonpoint sources include runoff from urban areas without sewer systems and abandoned
mines, as well as leaching from septic tanks. Atmospheric deposition is another source of
nonpoint eutrophication.
Definitions:
Solvent : is a component of solution that is present in greater amount and act as the dissolving
medium ex) water : Universal solvent
Solute: the component present in lesser quantity and it is the component being dissolved.
Salts, Sugar, starch
Ex.
Solution: Mixture of Solvent and Solute
Concentration: amount of solute present in a solution / amount of solvent
Conditions for Potable Water:
1) Tasteless, Odorless; and Colorless
2) Free from “Pathogenic Bacteria”.
3) Free from “Permanent hardness”
4) Non-Corrosive
5) pH: (6.5 – 8.5)
6) Stain Free
7) Free from Toxic Substances (Lead, Arsenic, Cadmium, Chromium, Silver, Barium,
Copper etc)
Health Hazards of water Pollution

1) “Phosphorous and Nitrates” ↔Nutrients ↔ O2 consuming Algae ↔Depletion of DO
level ↔ Killing of Fishes and other aquatic organisms { Pre-aging of water bodies.
This phenomena is referred to be “ Eutrophication”.
2) “Industrial Effluents” ↔ Toxic Substances ↔ *Kill the aquatic organisms
*may reach the human body through the contaminated food (Fish).
3. Blue Baby Disease (Mathemoglobinea)
‣ Excess “Nitrates” in water.
‣ Changes the Skin Colour of Babies of Age < 5 Years to “Blue Colour”.
‣ In the extreme case, may die.
4. Tooth Decay (Dental Debris)
Spotting on Teeth; Discoloration; Dropping
Due to “Excess Fluoride”.
5. Oil Pollution
● Reduces DO Level >>>Killing Fishes
6. Thermal Pollution
●Kills many “Water Birds” and “Water Animals”.
7. Thermal Radio Active Pollutants
● Radio Active Pollutants from “ Nuclear Power Station”
● Enters the Human Body through Food and water
● Accumulates in Liver; Blood; Bones and Muscles.
8. The excess sodium and chloride in drinking water may induce heart failure (Brooker and
Johnson, 1984) and hyper tension (Hussain & Ikbal 2003).
Sources of Water Pollution
● Point Sources (Easily Identifiable)
Industries like Textile, Chemical, Dye, Paper, NPS, TPS etc
● Non-Point Sources (Cannot be identified easily)
Use of Fertilizers; Pesticides; Storm Run Off; Surface Run Off; Tillage Practices; Crop
Pattern Changes etc.
Physical Characteristics of water
Turbidity (5-10 ppm Allowable)
● Muddy or Turbid in appearance
● Large no of Suspended Matter such as Clay and Silt
● Any other “Finely divided Organic materials”.
Tastes and Odours
● Dissolved Organic Materials
● Inorganic salts
●Dissolved Gases (H2S, CO2, CH4, O2, N2 etc)
Temperature ( 10 0 C – 25 0 C)
●Ideal Temp: 10 0 C
Temp > 25 0 c : Objectionable
Colour
● Excessive growth of Algae

● Aquatic Micro Organisms
● Dissolved Organic matter from
‘Decaying Vegetation’
● Inorganic materials (Colored Soil)
Chemical Characteristics of water
●Total Solids and Suspended Solids ( limited to 500 ppm)
● pH Value (6.5 – 8.5) ● Hardness ↔ Nil
● Chloride Content (should not be greater than 250 ppm)
●Nitrogen Content ●Dissolved Gases
● Metals and other Chemical Substances
pH value:
● Logarithm of Reciprocal of Hydrogen ION.
● Indicator of Acidity and Alkalinity of Water.
Hardness: Total hardness of water is caused by calcium and magnesium ions.
● Temporary Hardness: (Bi-carbonates and carbonates of Ca and Mg)
* can be removed by Simple Boiling
● Permanent Hardness: (Chlorides, Nitrates and Sulphates of Ca and Mg)
* Can not be removed by Simple boiling, but requires some spl treatments.
Chloride Content:
● in the form of “Sodium Chloride” (Common Salt)
●Their Conc. Above 250 mg/lit ↔ “Salty Taste”.
Nitrogen Content
● (Indication of Organic Matter)
* Free Ammonia (<0.15 ppm)
* Nitrates (limited to 45 ppm)
* Nitrites (Nil);
* Organic N2 (0.3 ppm)
Dissolved gases
● Various gases which may dissolved in water due to its contact with ‘atmoshere’.
• Nitrogen (N2)
• (Oxygen (O2) < saturation level) ↔ Organic matter ↔ water Suspicious
• Methane (CH4) ↔ Explosive Tendency
• Hydrogen Sulphide (H2S) ↔ Bad taste, even in small conc.
• CO2 ↔ Bad taste and Corrosion
Metals and other Chemical Substances
• Iron
• Manganese
• Copper
• Lead
• Cadmium
• Arsenic
• Fluoride etc
Biological Characteristics of water

● Algae
● Fungi
● Bacteria
● Viruses
Algae
● Type of “Plant” that grows and flourishes in the presence of “Sun Light”.
● Seven types of Algae
●3 Groups – (Dia’to’maceae; Chloro PhylCeae; Cyanophycea)
ex ) PLAKTON: Microscopic plant (Swim or Float)
: Serve as Food for Fish and Sea Creatures
: may cause “Stain” on Kitchen Vessels; affect the industries like Laudaries, Dyeworks;
Paper Mills etc.
● Chlorophyll/ Conversion of CO2, Water and other Simple Substances into “Organic Carbon
Compounds”.
● Covering the Reservoir
● Exclude the Sun light reaching the water body, thus DO Depletion.
Fungi
● Plants which grow with out ‘Sun light’.
● Live on other Plants and Animals
ex) TOASTOOLS ---fairly large in size
Others ----- Microscopic in size
Bacteria
● Minute Single Cell Organisms
● having “NO Chlorophyll”
● Pathogenic and Non-Pathogenic
● Pathogenic Bacteria - - Serious water borne diseases like Typhoid; Cholera; Dysentery.
● Aerobic / Anaerobic / Facultative
Rain water collects Bacteria and Viruses from the Dry Dust, Smog present in the Air. Initial rain
washes away most of these dusts -----Highly Contaminated with bacteria and other Organisms.
No. of bacteria in 1 Teaspoon of Rain water: (5 – 225)
Water falling as “Snow” ↔ picks More Bacteria, because ‘Snow-flake’ has Large Surface than
rain drops. Most of bacteria requires O2; Consume DO and Decompose the organic
matter.
“Coliforms” are the rod shaped bacteria, which are ‘Non-pathogenic’. Ex) E- Coli (Escherichia
Coli) and B- Coli: (Bacterium and Coli)
“Coliform Index” is used to measure the Coliform Bacteria present in water.
● Harmful Bacteria and Harmless Bacteria
BACTERIOLOGICAL TEST
1. Agar Plate Count Test or Total Count Test
i) In this test, the ‘Diluted Samples’ ( Water samples diluted with sterilized water) are
prepared first and placed in ‘Incubator’ for 24 hrs at 37 deg C.

ii) During this period, ‘Bacterial Colonies’ are formed in the sample, will be counted with
the help of ‘Microscope’.
Again, the other diluted sample is to be placed in the incubator for 48 hrs at 20 deg C.
iv) The bacterial Colonies formed in this case will be counted.
v) The two results are added to know the total number of colonies. This is known as “ Total
Counts”.
vi) It is then converted to colonies per cc.
Note: Bacteria are cultivated on a medium of ‘agar’ having different dilutions of sample of water
with sterilized water.
For potable water, the total count should not exceed 100 per cc.
2. B-Coli Test
There are 3- phases.
Phase-1 Presumptive test
i) A known amount of diluted sample of water is taken in a ‘Fermentation Tube’ containing
‘ Lactose Broth’.
ii) The tube is kept at a temp of 37 de C for 48 hrs.
iii) After this period, if ‘Gas’ is seen in the tube, then this is an indication of presence of B-
Coli. This result is +ve and the sample of water is ‘Unsafe’ for drinking. If No gas is
seen, then water sample is free from B-Coli. This – ve result is safe for drinking.
Phase -2 Confirmed test
A small Quantity of sample ( from presumptive test) is taken to another fermentation tube
containing ‘ Green lactose Bile’ and kept for 48 hrs at 37 Deg C.
If gas seen, +ve.
If gas not seen, – ve.
Phase -3 Completed test
It is for 24 Hrs at 37 Deg C. If the bacterial colonies are found, the result is +ve. So, the “
Completed test” must be done.
●The samples from the previous test are taken into “Lactose broth fermentation tube” and “Agar
tube”.
● Both tubes are then kept for 24 hrs at 37 Deg C.
● After this period, if gas is seen, the result is +ve. and concluded that the water is ‘Unsafe” for
drinking.
B-Coli Index = No. of B-coli / cc of sample
1) A no of presumptive tests are carried out with dilution ratio of water sample with
sterilized water.
2) For each test, the % of +ve result is recorded.
3) The difference between the successive percent is found out.
4) This difference is multiplied by the reciprocals of quantity of mixture. (ie Water sample
and Sterilized water).
5) Sum of such values = B-Coli Index
For Potable water, B-Coli: (3 – 10)

Sequence of Water Treatment Unit
1. Intake Point: (To collect water from the source)
2. Pump House: (To transfer water from Intake well to the treatment Units)
3. Plain Sedimentation Tank
4. Coagulation Tank
5. Filtration Unit
6. Chlorination Unit
7. Water Softening Tank
8. Overhead Reservoir
I. Sedimentation
Purpose of Sedimentation
1. To reduce ‘Heavy Sediment Load’ before the water enters the coagulation tank.
2. To make the coagulation process very easy
3. To reduce the amount of coagulants.
4. To reduce the cost of coagulation process
5. To make the working of other treatment processes more efficient.
Theory of Sedimentation
Discrete Particles: The particles which do not change their size, Shape, and Weight
while settling down in a fluid.
Ex) Suspended particles in Water has Discrete particles such as ‘Inorganic Solids (G=
2.65) and ‘Organic Solids’ (G=1.04)
With G>1.20, Particles settle down by Gravitational force. This phenomenon of
settlement is known as “Hydraulic Subsidence”.
The process of settlement depends on:
i) Velocity of flow
ii) Size and Shape of the particles
iii) Viscosity of Water
According to Stoke’s law,
V=418(S-S1)d 2 {(3T+70)/100}
S= Sp gravity of particle
S1 = Sp gravity of Water
d= Dia. of Particle
T=Temperature in 0 C
Note:1
The particles are given maximum opportunity to settle down
--- by decreasing the velocity of flow
--- by increasing the length of travel in the
Sedimentation tank.
Note-2
The lighter particles can not settle down by the gravitational force, are converted to
“Settleable Size” by the application of some Co-agulants” in Water.

II. Coagulation Tank
• To remove the “lighter Suspended Particles” by the application of “Coagulants”.
Coagulants Used:
1. Aluminium Sulphate
2. Chlorinated Coppers
3. Ferrous Sulphate and Lime
4. Magnesium Carbonate
5. Sodium Aluminate
Floc Formation:
Coagulants → Water → a thick gelatinous precipitate (Floc).
This “floc” has the property of attracting the Suspended impurities in Water and settle
down to the bottom of tank.
The phenomenon of the formulation of floc is known as “Flocculation”. The efficiency
of flocculation depends upon:
i) Dose of Coagulant
ii) Mixing of Coagulants
iii) pH value
iv) Note-1While settling down, the floc attracts more and more suspended impurities and
thus the size of floc goes on increasing and ultimately the surface area of the floc
becomes sufficient to arrest “ Colloidal particles”, “Organic matters”, and “some amount
of bacteria”.
v) Note-2 It is observed that the ions of floc possess positive electric charge while the
colloidal particles possess negative electric charge. So, the floc attracts the colloidal
particles while travel towards the bottom of the tank.
Step involved with Flocculation Process:
1. Jar test for finding the dose of coagulant
2. Sedimentation tanks used: (Rectangular / Circular / Hooper Bottom tank)
3. Coagulation tank: It consists of the following component:
i) Inlet chamber ii) Feeding Device iii) Mixing device iv) Flocculation chamber v) Sludge
removal vi) collection of clear water .
Mixing devices:
• Flash Mixer → Deflecting wall/ Driving Unit (Fan) → rotated by electric motor through
vertical shaft → Mixed water rises up→ outlet
• Deflector Plate Mixer → Deflecting wall/ Deflecting Plate → Mixing of water by the
agitation of deflecting plate → outlet pipe.
• Flocculator → “Vertical shaft” /”Horizontal shaft”.
Horizontal shaft → several paddles
Rotation of Horizontal shaft → Revolving of paddles at a very slow speed at about 2 to
3 rpm.
*Several Jars of capacity 1-2 lit.
Procedure for Jar Test

*Jars are placed in a Base plate.
*Spindles are provided in each jars.
*The spindles carry ‘paddles’ at its lower ends.
*Again the spindles are geared with the ‘Horizontal shaft’ which is rotated by ‘driving
unit’ (motor).
*The raw water is pored into the jars and different quantities of coagulants are added to
it in each jar.
*The motor is operated with the speed of 80 rpm and thus the paddles are rotated and
mixing is done rapidly.
*After 5 minutes, the speed has been reduced to 20 rpm and the mixing continued for
about 10 minutes.
*Then the driving is stooped.
*After about 30 minutes, the formation of flocs in each jar is observed.
*The amount of coagulants which produce good floc is considered as the required
quantity for the treatment of that particular sample of water.
III. Filtration of water
(To remove some of the Colloidal particles and Some bacteria)
Classification of Filters:
• Gravity Filters
Slow Sand Filter (Using Fine Sand)
Rapid Sand Filter (Using Coarse Sand)
• Pressure Filters (through a closed cylinder)
a) Enclosure Tank: Rectangular/ Brick masonry/ Inside surface Plastered with rich CM (1:3)/
Depth: 2- 3.5 m
Surface area: 100 – 2000 Sq. mt
b) Under Drain System:
c) Base material: Clean Gravels of different sizes/placed over the under drain system in 4 layers
of 15 cm thick each.
1 st layer: (20-40 mm);
Intermediate: (6-20mm);
Top: (3-6mm)
Theory of SSF:
Water→ → →Percolation slowly through the Filtering media
↘ ↘ ↘

“Improvement of Physical, Chemical and Biological
characteristics of water” takes place considerably.
• Its not suitable for large scale
• It is suitable for drinking water in small towns
Function of SSF
Water from coagulation tank
↘
“Inlet Chamber” through inlet pipe
↘
Water is allowed to stand over the sand bed → Water percolates through the sand
bed → Gravel bed (Base material) → Under drain →Outlet Chamber
Rate of Filtration: 100-200 lit/hr/Sq.mt of surface area
Efficiency: 25% colour removal; 95% bacteria removal; 50% Turbidity removal
Rapid Sand Filter
1. Enclosure tank: Surface Area: 30-60 Sq.mt
Depth:2-4 m.
2. Under Drain System
3.Base Materials:
* Bottom: (20-40mm)
* Intermeiate-1 st : (12-20mm)
* Intermediate-2 nd : (6-12mm)
* Top: (3-6 mm)
4. Filter media of sand:
Coarse Sand (0.35- 0.65 mm)
Cu: 1.20-1.80
Depth: 60-100mm
5. Other Appurtenance:
• Air Compressor – for sending the compressed air through the UDS at the time of washing
the filter.

• Troughs-provided on the top of sand layer for carrying the dirty water at the time of
washing.
• Rate control- to control the rate of flow.
• V1 = Inlet Valve
• V2= To storage reservoir
• V3=To wash water drain
• V4=From “wash water storage tank” to “Central drain”
• V5=Valve between “Central drain” to “wash water drain”
• V6= Valve to supply Compressed Air to “Gravel layer”
Working of RSF:
• In the normal working condition, the valves V1 and V2 are kept ‘Open’ and the other
valves are ‘Closed’.
• Water enters the Inlet chamber through inlet.
• Water ‘uniformly’ spread over the filter media.
• Filtered water is collected in the ‘Central drain’ through ‘lateral drains’.
• Finally, water is taken to the ‘Storage tank’.
Washing of Filter:
a) During washing, the valves V1 and V2 are ‘Closed’.
b) The valves ‘V4’and ‘ V6’ are opened. The wash water and compressed air are forced
through the UDS.
c) After some time, ‘V6’ is closed and the valve ‘V3’ is opened so that the dirty water is
removed through the ‘wash water drain’.
d) When washing is over, the valves V3 and V4 are closed. But V1 and V5 are kept open for
some time.
e) Finally, the valve V5 is closed and V1 remains open.
Now, the valve ‘V2’ is opened to start the normal work.
Rate of Filtration: Very high (3000-6000 lit/hr/sqm)
Efficiency:
• It can remove turbidity to the extent of 30-45 ppm
• It is highly efficient in removing the colour.
• It is less efficient in removing the bacteria.
Comparison between SSF and RSF
Particulars SSF RSF
Area Large area Small area
Quality of
Sand
Fine sand (0.20-0.35mm) Coarse Sand( 0.35-
0.65mm)
Base
Gravel (3-65mm)
Gravel (3-40mm)
Materials
Method of
Cleaning
Scraping the top layer of sand to a
thick of about 25 mm
Back washing by Water and
Compressed air
Period of
1 to 3 months 2 to 3 days
Cleaning
Supervision Skilled supervision is not
req.
Skilled Supervision is req.

Rate of
Filtration
100-200 lit/hr/ sq.mt of
surface area
3000 – 6000 lit/ hr/sq.mt of
surface area.
Efficiency High in removing Bacteria Less in removing Bacteria
Suitability for Towns For large Cities
Economy Not economical economical
Disinfection of water Disinfection of water
• The process of destroying harmful bacteria from water and making it safe for drinking is
known as “Disinfection”.
• The substances used for this purpose are known as “Disinfectants”.
• The common disinfectants are: Lime; Iodine and Bromine; Ozone; Potassium
Permanganate; Silver; Chlorine etc.
Method of disinfection:
• By Boiling (100 C, 10-15 min)
• By Iodine and Bromine (8-10 ppm)/ small pallets
• By Excess Lime – increases the pH value-increases alkalinity-detrimental to bacteria
Note: With pH 9-10, 99% bacteria removal.
• By Ozone (2-5 ppm, 5-10 min)
• By Potassium Permanganate (Powerful oxidizing agent, 2-3 ppm, 2-3 hrs)
• By Silver (Silver foils are spread over the filter media, water passes through it, kills
bacteria)
• By Chlorine* -- Very fast; cheap; reliable
• The Process of disinfection of water by the application of chlorine is known as
“Chlorination”. The term Chlorination indicates the destruction of bacteria from drinking
water and waste water in order to protect the public health from water-borne diseases.
• Cl2+H2O →→→HOCL +HCl
• (Hypochlorous Acid)
• After sometime, HOCl is further ionized as follow:
• HOCL →→→H + +OCl –
• Note-1: At high pH value (>8.5), the chlorine is practically ‘inactive’. But at low pH
(<7), the chlorine is very active.
• Note-2:
• Free Chlorine
• ↨ (partly unites with)
• the cell structure of bacteria
• ↓
• Chloro-products (Harmful to bacteria)
Application of Chlorine
Chlorine ---- Gaseous form / Liquid form
Chloromines --- Some amount of ‘Ammonia’ will be added to water along with chlorine.
Mono-chloramines *Dichloramine * Nitrogen trichloride
Bleaching Powder - -- Calcium hypochlorite

BP→water →hypochlorite ions(OCl) OCl+ H + →HOCl (Hypochlorous acid)
[Hypo-chlorination]
Chlorine dioxide – (Cl gas →sodium chlorite) in a closed cylinder.
Forms of Chlorination
1. Plain Chlorination 2. Pre-chlorination 3. Post chlorination 4. Double
chlorination
5. Break point chlorination 6. Super chlorination 7. Dechlorination
Plain Chlorination: (When the raw water is supplied to consumers by applying chlorine
treatment only).
• In case of clear raw water, does not require any primary treatments. Generally, in case of
emergencies, for military purpose, training camps, survey camps etc.
Pre-chlorination: (Advance dose of chlorine)
In rainy season, when the raw water is highly contaminated, a dose of chlorine is added to raw
water before it enters the sedimentation tank.
Post Chlorination: (When chlorine is added to water after all the treatments are over and just
before it enters the distribution system).
Double Chlorination: (When both pre-chlorination and post-chlorination are adopted in water
supply scheme to safeguard the public health from ‘epidemic’).
Break Point Chlorination:
(Method of determining the chlorine demand of raw water)
• There is No Chlorine demand in Pure water.
• If Chlorine is added to water, the chlorine will come as “Residual chlorine”.
Stages:
Chorine → contaminated water →kills bacteria and oxidize the organic matter.
• In the beginning, the chlorine goes on killing the bacteria and then it starts accumulating
upto a certain point A.
• If the dose of chlorine goes on increasing, it will start emitting ‘bad smell’.
• But after sometime, the bad smell suddenly disappears. This critical point is known as “
Break Point (B).
Note: The actual dose of chlorine should be determined very carefully by finding the break point
formation.
Super chlorination:
• The process of application of chlorine beyond the formation of break point.
• This treatment is necessary when there is an epidemic due to some water borne diseases.
• But in this treatment, much residual clorine in water may appear- which is unpleasant to
the consumers.
• To neutralize the residual chlorine, “dechlorination” should be done.
Dechlorination:
• The process of removal excess residual chlorine from water.
• The residual chlorine should not be removed completely.
• But some amount of chlorine about 0.25 to 0.50 ppm should remain in water so that it
may not be polluted in the distribution system.
“Chemicals used for dechlorination”:
Sulphur di oxide, Sodium sulphite, Activated carbon, Potassium permanganate.

Water Softening
Sulphate is a naturally occurring ion found in almost all kinds of water bodies. It is an important
anion imparting hardness to the water.
Removal of Temporary Hardness:
• By Boiling: ---For Domestic Purpose only
When water is boiling for a long time, the chemical reactions takes place as given below.
Mg(HCO3)2 →MgCO3+CO2+H2O
Ca(HCO3)2→CaCO3+CO2+ H2O
Thus the magnesium and Calcium carbonates are formed in water which are insoluble in water
and they settle down at the bottom of the tank when the water is cooled gradually.
* By adding Lime:
When Lime is added to water,
Mg(HCO3)2 + Ca(OH)2 →CaCO3+Mg(OH2)+ H2O
Ca(HCO3)2 + Ca(OH)2 →2CaCO3+ 2H2O
After reaction, the “calcium carbonate” and “magnesium hydroxide” are formed.
They are insoluble in water and settle down at the bottom of the tank.
Removal of Permanent Hardness
• Lime soda Process
• Zeolite Process
• Demineralization Process
1. Lime-Soda Process:
Lime+ Soda →Solution is made. “Solution” is stored in Lime-Soda tank. This
solution will be added to water by which the permanent hardness of water will be
removed.
Advantages
Disadvantages

pH increases
Destroys harmful bacteria
Removes ’iron’ and ‘manganese’
Reduces the dose of coagulants
Large volume of sludge
2. Zeolite Process: Zeolite—a compound of aluminium, silica and soda.
“Natural Zeolite”- Green in colour – Green sand
“Artificial Zeolite” – permutit – synthetic hydrated silicate of aluminum and sodium. The
raw materials for artificial Zeolite include: felspar, kaolin clay, Soda.
Zeolite process
2. Demineralization: (suitable for Industrial purpose)
Hard water →bed of carbonaceous matter (resin) having ‘Hydrogen ions’ as base. Here
“Hydrogen ions” are exchanged to “metallic ions”. So, this process is also called deionization
process.
Parameter Permissible (according to Standard Agencies, like WHO, BIS etc)

Water Quality standard for Drinking water (WHO)
Source: Frontiers in Science, 2013, 3(3): 89-95

3 steps for computing WQI…..
Relative Weight of Chemical Parameters

Water quality classification based on WQI value