Quality Parameters of Water

The Properties that ascertain qualities of raw water are termed as Quality
Parameters.
1. Suspended solids are those which remain floating in water. (>100nm)
2. Dissolved solids are these which dissolve in waste water. (< 1 nm)
3. Colloidal solids are those which have particle size in between dissolved and
suspended. (1-100nm)
4. Settleable solids are that portion of solid matter which settles out if the waste
water is allowed to remain undisturbed for 2 hours.
1. Physical Water Quality Parameters
i. Suspended Solids
It is measured by filter the water sample and weight of residue obtained is
calculated. (Gravimetric technique)
For Suspended solids, as per Environmental Protection Agency, the
maximum permissible limit is 30mg/L for drinking water.
ii. Turbidity
Measure of extent to which light is either absorbed or scattered by
suspended matter in water.
It is objectionable because: Measure of turbidity is done
by:
• Aesthetically displeasing
• It provides absorption sites for chemical • Turbidity rod
and biological agents thereby reducing • Jackson's turbidimeter
the efficiency of further treatment • Bayli's Turbidity meter
• They may also be biologically active • Nephelometer
which may result in causing various
diseases
• In Natural water bodies(rivers, ponds..) Q. Turbidity in water is due to
turbidity interferes with light penetration a)Algae
and hence with photosynthesis reactions
b)Fungi
c) Organic Salts
d) Colloidal Particles

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A. Turbidity rod
• Graduations are encrypted on
rod in ppm (1mg/L=1ppm)
• As depth of insertion
increases, reading decreases
• Turbidity which 1 mg of Silica
produces in 1 litre of distilled
water is taken as 1 STU unit

Q. Which test is used to measure Q. On which scale turbidity is

the resistance to passage of light measured?
through water? a) Platinum scale
a) Turbidity test b) Silica cobalt scale
b) Temperature test c) Silica Platinum scale
c) Colour Test d) Standard Silica Scale
d) Permissible Test

B. Jackson's Turbidity meter

• Level of water is increased till
image of flame disappears
• This method is used only when
turbidity is greater than 25ppm
• This method is not used for
drinking water

C. Bayli's Turbidity meter and • Acceptable limit for turbidity is

Nephelometer 1 mg/L or 1 NTU

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 Turbidity less than 1ppm can also • Permissible limit for turbidity
be measured, So most widely used is 5 mg/L or 5 NTU
for domestic supplies • Cause for rejection is 5 mg/L
• UNIT in Nephelometer is NTU or 5 NTU
(Nephelometer Turbidity Unit)
OR Formazine turbidity unit
(FTU)

COLOUR
• Colour is produced by suspended matter • Colour is measured by
and dissolved matter TINTOMETER (apparatus
• True Colour → Dissolved Solids name) and Nessler tube
• Apparent colour→ Suspended Solids used
• Why is colour objectionable? •
• Iron Oxide gives Reddish colour • Result is expressed in True
• Manganese oxide gives brown/Black Colour Units (TCU) or
colour Hazen Unit
• Humic acid gives yellowish brown colour
• Certain colour causing compounds react
with chlorine and form carcinogenic
(cancer causing compounds) • AL = 5 TCU
• • CFR = 15 TCU
Q. Tintometer is used for
a) Colour
b)Odour
c) Hardness
d) Temperature

Taste and Odour

• Caused by Chemicals and • Taste and odour are measured by

dissolved gases like H₂S, methane, instrument known as Osmoscope
etc industrial liquids, ammonia, • Intensity of taste and odour is
etc. measure in Threshold Odour
• Taste and odour are objectionable Number (TON)

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 because of carcinogenic nature

A B
TON
NOTE: GOI recommends TON A.L A
-- 1 • A= volume of odorous water in ml
CFR -- 3 • B= volume of odour free water
required to produce a mixture in
which odour is hardly detectable

Q 12.5 mL sample of treated waste water required 187.5 mL of odour

free distilled water to reduce the odour to a level that is just
perceptible. What is the Threshold Odour Number (TON) for the waste
water sample?
(a) 0.07 (b) 0.07
(c) 15 (d) 16

Temperature
• Temperature affects chemical and biological reactions
• For water supply, it should be between 10 to 20°C and greater than 25°C is
objectionable
Chemical Parameters
i. Dissolved solids iv. Hardness vii. Phosphorous
ii. Ph v. Chloride content viii. Fluorides
iii. Alkalinity vi. Nitrogen Content ix. Metals

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i. Dissolved solids ii. pH

It can also be measured by gravimetric • It indicates acidity or

technique. basicity of the water.
• Acidic water impact
corrosion in pipes.
One more method is to measure the
• Basic water impact
dissolved solid is by knowing the
incrustation in pipes.
electrical conductivity of water
• pH = -log[H+], where [H+] is
in moles/Litre
Acceptance Limit as 500mg/L • AL = 6.5-8.5

Cause for rejection as 2000 mg/L

pH can be measure by colored

indicators like methyl orange
Working range of methyl orange is 3.1
and
to 4.4
phenolphthalein

Working range of
Phenolphthalein is 8.6 to 10.3

Q. The product of H+ ions and OH ions Q. What is the most common
in a strong Alkali is source of acidity in water?
a) 0 b)1 a) Oxygen
c)101 d)1014 b)Sulphuric acid
c) Carbon dioxide
Q. pH of sea water varies from d) Nitrogen
a) 6.5 to 7.5 b)8.2 to 9.3
c) 6.2 to 7.1 d) 7.5 to 8.4

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Alkalinity
• Quantity of ions that will neutralize • For Alkalinity Measurement
H+ ions 0.02 N H2SO4 is used in
titration.
• Alkalinity is due to CO32-, HCO3-1, OH
-, HS-, HPO4-, etc. • 1 ml of acid i.e.0.002N H2SO4
given 1 mg/L value of Alkalinity
• CO32- + H+ HCO3-1
expressed as CaCO3.
• HCO3-1 + H+ H2CO3
• TITRANT (0.02 N H2SO4)
• INDICATOR (methyl orange
• Major constituents of Alkalinity: and phenolphthalein)
1. CO3-2 (carbonate alkanity)
2. HCO3-1(Bicarbonate alkalinity)
3. OH- (caustic alkalinity)

Q. Alkalinity in water is expressed as Q. Which Chemical indicator

mg/L in terms of turns water into pink colour if
the pH is more than 8.3 ?
a) Calcium Carbonate
a) Bromothymol b)
b) Magnesium Carbonate
Murexide
c) Sodium Carbonate
c) Phenolphthalein
d) Sodium Bicarbonate d) Methyl Orange

Q. Q. The major portion of alkalinity in

natural waters is caused by
a) Hydroxide carbonate and
Bicarbonate
b) Hydroxide, phosphate and Bicarbonate
c) Silicate, ammonia and bicarbonate
d) Hydroxide, ammonia and Bicarbonate

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Hardness

• Hardness is the concentration of • Hardness can be of two types:

multivalent metallic cations 1.Carbonate Hardness (Temporary
present in water. Hardness may hardness) (carbonates and
be induced due to Ca2+, Mg2+, bicarbonates of multivalent ions)
AL3+, Fe2+, etc
2. Non Carbonate Hardness
• Major constituent are Ca2+, Mg2+. (Permanent Hardness) (chlorides,
• The ability of water to destroy the Sulphates, nitrates, etc of multivalent
surfactant property of soap. ions)
• Hardness due to chlorides,
sulphates, nitrates, etc of all the
multivalent metallic cations is
known as Non Carbonate
Hardness.
• It is also called as Permanent
Hardness because it can not be
removed by simple boiling or
addition of Special Techniques are
used for its removal which are
known as Softening Techniques

• Hardness of water is determined IMPACTS OF HARDNESS

by titrating water sample against • 1. It leads to increased consumption
0.01 M EDTA (Ethylene di amine of soap due to lesser formation of
tetra acetic acid) solution, also lather or foam
called as Versanate solution, • 2. Hardness in water leads to
using EBT (Erio-chrome black T) corrosion and incrustation
• Initially EBT forms red colour • 3. Hard water makes food tasteless
and titration changes colour to • 4. Magnesium Hardness due to
Sulphate (MgSO4) induces
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 blue LAXATIVE effect in the water, hence
its concentration should be limited
to 30 mg/L
Q. Standard EDTA solution is used Q. The presence of Calcium and
to determine the Magnesium chloride in water causes
a) Hardness in water a) Softening
b) Turbidity in water b) Bad taste
c) Dissolved oxygen in water c) Hardness
d) Residual Chlorine in water d) Turbidity

Q. The Hardness caused by Q. Q. When the calcium carbonate

sulphates, chlorides and nitrates hardness varies from 0-55 mg/l then
of calcium or magnesium is the water is called
termed as (a) Soft water
a) Pseudo Hardness (b) Medium hard.
b) Permanent Hardness (c) Hard water
c) Alkaline Hardness (d) Very hard water
d) Temporary Hardness

Q. A soft water would have • The Hardness is expressed as CaCO3

hardness (in mg/l): equivalent of Calcium and
(a) > 180 Magnesium present in water

(b) 60-150
(c) 150-180
(d) < 60

Hardness as CaCO3 in mg/L Degree of Hardness

0-55 Soft Water
56-100 Slightly Hard
101-200 Moderately Hard
201-500 Very Hard

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Q. If the hardness of water is greater Q. If total hardness and
than its total alkalinity, the carbonate alkalinity of a water sample are
hardness will be equal to 200mg/l as CaCO3 and 260mg/l
as CaCO3 respectively, what are
a) Total Alkalinity
the values of carbonate
b) Total Hardness hardness and non carbonate
c) Total hardness - Total Alkalinity hardness?

d) Non carbonate Hardness a) 200 mg/l and zero

b) Zero and 60mg/l

• Acceptable limit of hardness = 200 c) Zero and 200mg/l

mg/L as CaCO3 d) 60mg/l and zero
• Cause for rejection = 600 mg/L
• For domestic supply it should be
between 75-150mg/L

Chloride Content
Excess of chloride water is termed as • Acceptable limit = 250 mg/L
Brackish Water and it indicates
• Cause for rejection = 1000
pollution of water.
mg/L

Measured by titration

Titrant – silver nitrate

Indicator – potassium chromate

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Q. Excessive fluoride Q. Cavities in teeth are caused if
concentration in drinking water fluoride concentration is less than
causes problems related with (mg/L)
a) Bones and joint stiffness a) 1.5 b) 1
b) Kidney Function c) 0.5 d) 0.25
c) Heart Disease
d) Dysentry Q. Maximum permissible limit of
fluorine in domestic water supply
is ?
a) 0. 3 ppm b) 0.05 ppm
c) 03 ppm d) 1.5 ppm

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Metals
1. Metal Acceptance Cause for Comments
Limit Rejection
1 Iron and Causes color
Manganese problem
Iron 0.1 mg/L 1 mg/L
Manganese 0.05 mg/L 0.05 mg/L
2 Copper 0.05 mg/L 1.5 mg/L Large quantities
affects lungs and
respiratory organs
3 Sulphate 100 mg/L 400 mg/L
4 Zinc 5 mg/L 15mg/L Zinc is called
nutrient of life
5 Arsenic 0.01mg/L 0.05 mg/L Causes acute
toxicity to humans
6 Cyanide 0.05 mg/L 0.05 mg/L cyanide renders the
body incapable of
carrying oxygen
7 Mercury 0.001 mg/L 0.001 mg/L Mercury is toxic to
all forms of life. It
should not be
greater than 0.001
mg/L

Q. The phenolic compounds in Q. The permissible limit of Arsenic

public water should not be more in drinking water as per the
than guidelines of WHO is
a) 0.1 ppm b) 0.01 ppm a) 0.01 ppm b) 0.01 ppb
c) 0.001 ppm d) 0.0001 ppm c) 0.05 ppm d) 0.05 ppb

Q. The acceptable limits of total Q. As per Indian Standard (IS

dissolved salts for drinking water 10500 : 2012) iron in drinking
is water should not exceed
a) 250 b) 500 a) 0.5 mg/L b) 0.4 mg/L
c) 1000 d) 1500 c) 0.3 mg/L d) 0.2 mg/L
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 Q. If lead is present in water, it
causes
a) Alkalinity
b) Colour change
c) Turbidity
d) None of the above (becomes
toxic)

Nitrogen Content
• Presence of Nitrogen represent presence of organic matter.
• Nitrogen occurs in following forms:

Free Ammonia (NH3): Organic Ammonia (Albuminoid) :

indicates recent Pollution quantity of oxygen before
decomposition of organic matter
has started
AL = 0.15 mg/L
AL = 0.30 mg/L
CFR= 0.30 mg/L
CFR= 0.45 mg/L

Nitrite (NO₂): Nitrate (NO3):

indicates partly decomposed indicates fully oxidized organic
condition matter, it can also indicate old
pollution
AL=0 (toxic in nature, so not
acceptable) AL = 45 mg/L
CFR= 45 mg/L

Q. Q. Nitrates more than 45 mg/L in Nitrate is not harmful because it is

water lead to a diseases called fully oxidized and can not react
a) Gastroenteritis further, but too much of nitrate
affects infants because it causes
b) Mottled teeth
Blue Baby Disease or
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 c) Polio Methemoglobinemia
d) Mathemoglobinemia

Biological Parameters
• Most important organisms are pathogens because they are capable of
transmitting diseases, ex (bacteria, virus, protozoa, helminth, etc.)
• Coliforms: harmless aerobic lactose fermenters organisms
• E-coli (Escherichia-coli)

Biological Water Quality Parameters

The most important organisms are pathogens because they are
capable of transmitting diseases like bacteria, virus, protozoa, helminth, etc.
Pathogenic Bacteria can be tested and counted in Lab but with great
difficulty. The usual routine test are generally conducted to detect and count
the presence of Coliforms, which in themselves are harmless Aerobic Lactose
Fermenter Organisms but their presence or absence indicates the
presence and absence of Pathogenic Bacteria.
Coliform called "E-Colli [Eschrichia-Coli]" is found to be present in all
living organisms. Also, these bacteria live much longer than any other
bacteria. Hence, if E-Coli is absent, pathogenic bacteria will also be absent
Following are the tests for Coliforms:
1. Membrane Filter Technique:
• In this test, water sample is passed through
sterile membrane over which all microorganisms
are retained. This membrane is brought in
contact with nutrient rich medium called M-
Endo Medium.
• After Incubating (sufficient conditions to continue
a reaction) at 35°C, for 24 hours, the number of
colonies of coliforms are counted which are
further related to Colonies of Pathogens

2. Most Probable Number (MPN test)

• MPN test is Multiple Tube Fermentation Test in which we mix water samples
with different dilution ratio and lactose broth acts as nutrient for Coliform

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• The samples are incubated at 35°C ± 2°C and for 24 hours and after
incubation these are tested for the presence of acids and Carbon Dioxide
• Then we refer to Standard Tables corresponding to the result observed, This
is called MPN
• MPN represents Microbial Density which is most likely to be present in
100ml of water sample

Coliform Index
Coliform Index is reciprocal of Smallest Quantity of the sample that gives
positive Coliform Test.
Coliform Index Test and MPN tests are used now a days.

Q. The coliform organism in 100 Q. Match List-l (Parameters) with

ml of drinking water should not be List-II (Units) and select the
more than correct answer using the code
given below lists:
a) 1000 b) 450
1. List-I List -II
c) 250 d) 1
A. Turbidity 1. ΤΟΝ
B. Pathogen 2. TCU
C. Odour 3. JTU
D. Colour 4.
Codes:
a 2 1 4 3
b 3 1 4 2
c 2 4 1 3
d 3 4 1 2

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 Wastewater and Its Quality:
1. Introduction to Wastewater/Sewage
Wastewater is the mixture of liquid and liquid
waste. It is any water that has been adversely
affected in quality due to human activities. It is
generated from communities due to different
activities.
It includes:
• Domestic wastewater (from households, toilets, sinks, showers).
• Industrial wastewater (from factories,
manufacturing, chemical plants).
• Agricultural runoff (pesticides, fertilizers,
livestock waste).
• Storm water (rainwater mixed with pollutants
from streets).

SANITARY SEWAGE: It is the sewage obtained from the residential

buildings & industrial effluents establishments.

2. Characteristics of Wastewater (Quality Parameters)

Wastewater quality is assessed based on physical, chemical, and
biological properties.
A. Physical Characteristics

Parameter Description Impact

Indicates contamination (grey, Aesthetic issues, possible

Color
black, brown). toxins.

Caused by organic decay (H₂S,

Odor Nuisance, health hazard.
ammonia).

Cloudiness due to suspended Blocks sunlight, harms

Turbidity
solids. aquatic life.

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Parameter Description Impact

Affects oxygen levels and Thermal pollution harms

Temperature
microbial activity. ecosystems.

Dissolved oxygen (DO)

• Respiration of aerobic microorganisms
• The dissolved oxygen in fresh waste water depends upon temperature.
It the temp of sewage is more, DO content will be less.
• For survival of fish, 4ppm (4mg/L) DO is required
• DO content of waste water is found out by Winkler's method

Chemical Oxygen Demand (COD)

• COD is used to measure the content of Biodegradable as well as Non
biodegradable organic matter
• The oxygen equivalent of organic matter that can be oxidized is
measured by using a strong oxidizing agent in an acidic medium
(K2Cr2O7). This COD test is also called as Dichromate Test
• COD - BOD = non biodegradable organic matter

Theoretical Oxygen Demand (ThOD)

• Amount of oxygen required to oxidize the quantity of all organic
matter
• ThOD> COD > BOD

Q. What is theoretical oxygen demand of 300mg/L glucose solution?

a) 300 mg/L b) 320 mg/L
c) 350 mg/L d) 400 mg/L

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Biochemical reactions in Waste Water
• The aerobic and anaerobic are the two basic forms of Biological
stabilization reaction whose occurrence is dependent upon the
availability or non-availability of oxygen.
• Aerobic Reactions taken place in the presence of free oxygen and
produce Stable inorganic end products with relatively low energy
content.
• Anaerobic reactions occur in the absence of free oxygen.
• Anaerobic reactions are slow and do not remove the organic content
completely.
Biochemical reactions in Waste Water
• Bacteria are primary decomposers of organic material
• Bacteria require energy and material for growth and reproduction
• Energy for bacteria is derived from biological oxidation or reduction of
organic or inorganic compounds
• Material is derived from organic or inorganic compounds. Bacteria are
classified according to the energy source

Various Types of Bacteria

1. AUTOTROPS: They derive both energy and material from inorganic
substances.
2. HETEROTROPHS: They derive both energy & material from organic
substances
3. PHOTOTROPS: They utilize sunlight as energy source and inorganic
substances as material source
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4. FACULTATIVE HETROTROPS: They are capable of functioning both
in the presence and in the absence of oxygen to oxidize organic matter.
5. AEROBIC HETROTROPS: They utilize organics in the presence of
oxygen.
6. ANAEROBIC HETROTROPS: They utilize organics in the absence of
oxygen.
Biochemical Oxygen Demand (BOD)
• BOD is used as a measure of the quantity of oxygen required for
oxidation of Biodegradable organic matter present in water sample by
aerobic bio chemical reactions.
• BOD of water during 5 days at 20° c is taken as standard BOD and
is approx., equal to 68% of ultimate BOD
• The BOD is determined by diluting a known volume of a sample of
waste water with a known volume of Aerated water and then
calculating DO of the diluted sample.
• The diluted sample is then incubated at 20° c for 5 days the DO at the
end of 5 days is again calculated.
• The difference between initial DO and final DO will indicate the oxygen
consumed
• BOD = (DOi – Dof)  D.F

volumeof dilutedsomple
Dilution factor DF
volumeof undilutedsample taken
Q. If initial DO = 5mg / L final DO = 2mg / L
5ml of sample is mixed to form 100 ml of diluted sample. Find BOD. 5ml of sample is
mixed with 95ml of aerated water
100
Ans. BOD (5 2)
5
BOD = 60mg / L

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 • The first Demand occurs
due to oxidation of
organic matter and is
called Carbonaceous
demand or First stage
demand.

• The later demand occurs

due to biological
oxidation of Ammonia
and is called Nitrogenous
demand or II stage
demand

Population Equivalent
• It indicates strength of industrial waste water for estimating the
treatment required at the municipal treatment plant
• Average BOD of domestic sewage is 80g/capita/day

total BOD5 of the industry in kg / day

Population equivalent
0.08 kg / day
TREATMENT OF WATER

UNIT OPERATIONS AND UNIT PROCESSES

• Unit Operations are the application of Physical forces. In this, no
other external forces are required.
• Example: Screening, aeration, sedimentation, etc.
• Unit processes are the types of treatment in which removal of
contaminants is brought about by the addition of chemicals or by
microbial activities.
1. Preliminary Treatment: 2. Primary Treatment:

• It is also called as One • It includes all the treatment units

Degree treatment when of preliminary system and

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 used along with primary Primary Sedimentation tank.
sedimentation tank. Note: Primary Sedimentation Tank
is also called as Primary Clarifier.
• It removes floating • Purpose of Primary Treatment is
materials and large to remove suspended solid
inorganic particles of waste materials from incoming waste
water water.

• It comprises of screens • It does not remove the colloidal

(screen chamber), grit and dissolved organic content of
chamber, skimming tank waste water.
and oil and grease traps

• Large Debris are removed by

3. Secondary Treatment Screens.
System or Two Degree
Treatment System:
• Inorganic solids are removed in
• After primary treatment, its
Grit chambers
waste water is further
treated for the removal of
Colloidal and Soluble • Organic solids are removed in
organic matter present in Sedimentation tank
waste water. This is called
• Disposal of inorganic Matter is
as Secondary Treatment
convenient because it does not
System.
decompose but disposal of
• It consists of biological organic material is difficult
conversion of organics into because if it is disposed
biomass (bacteria) that can untreated, it will create nuisance
be subsequently removed
by sedimentation in • Hence it is desired that inorganic
Secondary Sedimentation and organic matters are removed
Tank. in two separate units
• Contact between
microorganisms and the • Primary Sedimentation Tank
organic matter is optimised removes 60-70% of suspended
by suspending the biomass organic matter.
or by passing waste water
over a film of biomass
4. Tertiary Treatment System:
attached to solid surfaces

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 • The most common biomass • Tertiary Treatment involves
system is the Activated further clarification and
Sludge Process disinfection
• In India tertiary treatment is
generally not done except in case
of epidemics some other
emergency conditions

Screening
• Purpose: Removes large
debris (leaves, plastic, sticks).
• Process: Water passes
through metal or mesh
screens.
• Used in: Pre-treatment for
municipal and industrial
plants.

Screen Clear Spacing

Coarse 45o to 60 > 50 mm
Medium 20-50 mm
Fine < 20

Grit Chamber: NOTE:

• They are located before pumps
to prevent clogging, damage to Detritus Tank:
the pumps.
• Removal of grit reduces the
frequency of cleaning of other It is similar to grit chamber, the only
units difference is that Detritus Tank is
meant for removing more finer
• They are provided in the form particles as compared to Grit
of channels of long length and Chamber
smaller cross sectional area.

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 Skimming Tanks

• These are used for removal of

Oils and Grease, soaps, etc
• Skimming Tanks are provide
before sedimentation tanks

2. Aeration
• To remove gases like H₂S and CO₂
• Aeration adds oxygen to water to carry out the oxidation of undesirable
substances like organic matter and oils
• Aeration also removes phenols, humic acids from water
Fe3++ + O2  Fe (OH)3 (ppt) + H+(Acidity)
Mn2++ + O2 MnO2 (ppt)

Methods of Aeration
A. Spray Nozzle Method B. Cascade Aerator
• Most efficient method • Efficiency is about 40%
• Pressurized water is used to
increase surface area of water

C. Spray Tower Method D. Diffused air Method

• Best method to remove iron, • It has highest operational cost
manganese and CO₂

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Q. Aeration of water is done to remove
a) Turbidity b) Colour
c) Hardness d) Dissolved gases(H2S, CO2)

3. Sedimentation
• Sedimentation is a natural process by which solids with higher density than
the fluid in which they are suspended, settles under the action of gravity
• Sedimentation tank is used to remove suspended solids
• According to Stoke's law
g(G s 1)d 2
Vt
18v
v=kinematic viscosity (m²/sec)
Gs = specific gravity of particle
d=dia of particle

Sedimentation Tank is of two types

Q. Q. The quantity of water flowing Q. Q. Particles to be removed

per hour per unit horizontal area continuous flow water
is called _____ sedimentation tank should have
a) Detention time settling velocity
b) Flowing through period a) More than surface loading of the
c) Displacement time tank
d) Overflow rate b) Less than the surface loading of
the tank
c) Equal to horizontal velocity
d) None of the above

Q. Q. Which one of the following is

most important criteria for
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 removal of discrete particles in the
design of continuous flow
rectangular tank?
a) Depth of the tank

b) Length of the tank

c) Surface over flow rate
d) Temperature of water to be treated

4. Coagulation:
The efficiency of sedimentation is very less when water contains very fine
suspended solids. Hence to improve efficiency, coagulation is done along
with sedimentation.

Coagulation is process in which certain chemicals known as Coagulants are

added in the water so as to neutralize the charges over the particles so that
the particles can come together to increase efficiency.
A certain minimum amount of Energy is required for this process, known as
Threshold Energy which is provided in the coagulation process by inducing
rapid mixing in the water Entire process of Coagulation is carried out in
three
steps:
A. Coagulation-Fast mixing
B. Flocculation-slow mixing
C. Sedimentation

Different types of Coagulants used are:

A. Alum Al2(SO4)3.18H20
B. Copperas FeSO4.7H2O
C. Chlorinated Copperas Fe2(SO4)3. FeCl3
D. Sodium Aluminate Na2Al2O4

Q. Why Alum is preferred over other coagulants?

a) It is easy to dewater the sludge formed
b) It imparts corrosiveness to water
c) It reduces taste and odor in addition to turbidity
d) The time required for floc formation is less
Q. Alum is a coagulant found to be most effective when pH range of water
is about
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 a) 2 to 4 b) 4 to 6
c) 6 to 8 d) 8 to 10
Q. The alum when added as a coagulant in water
a) Does not require alkalinity in water for flocculation
b) Does not affect pH value of water
c) Increases pH value of water
d) Decreases pH value of water
Q. Filter alum, used as coagulant is
a) Ferrous sulphate b) Chlorinated Copperas
c) Sodium Aluminate d) Aluminium Sulphate

5. Flocculation:
• In Flocculation, neutralized, suspended particles are provided with sufficient
contact time so as to combine and grow in size and get finally removed in
the sedimentation process.
• In order to promote the contact between neutralized particle so as to form
bigger sized flocs, slow mixing is done

• Flocculation depends on:

1. Turbidity: More turbidity, more will be flocculation

2. Type and dose of Coagulant: iron coagulant will form heavy flocs in less time
3. Temporal mean velocity gradient (G)

6. Filtration:
• Filtration is most often used as limiting step to remove the flocs and finer
unsedimented particles through beds of granular materials
• Filtration also removes suspended organic matter, microorganisms and
dissolved minerals from the water

• Two types of Filters are used

1. Gravity Filters 2. Pressure Filter

1. Gravity Filters
These are the types of filter in which head is required by water to pass
through filter medium. This head is provided by height of water itself over
the filter medium.
These are of two types:
A. Slow sand Filters
B. Rapid Sand Filters
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2. Pressure Filters
These are the types of filter in which head required by water to pass through
filter medium is provided artificially by the application of pressure over the
water

Theory of Filtration
1. Mechanical Straining
Impurities greater than the size of filter are strained over the filter
2. Sedimentation
Turbulence is removed from water during filtration hence suspended
particles tend to settle over sand partilces
3. Biological changes
• Organic matter  Algae Oxygen  Oxidation of organic matter
• This dirty layer of bacteria, algae, organic matter is called as Schmutzdecke
layer
• More the thickness of schmutzdecke layer, more will be the biological
efficiency of filter
4. Electrolytic Changes
• Impurities and filter media particles carry opposite charge and hence
neutralization of charge occurs in water
7. Disinfection:
• Disinfection may be defined as the process of destruction of harmful
microorganisms either by physical process or chemical process.
• Physical- Boiling, UV treatment, etc.
• Chemical- Chlorination, treatment by Bromine, lodine, Ozone, potassium
permanganate, etc.

Q. The ozonation in drinking water helps to remove

a) Colloidal particles b) Hardness
c) Flocs d) Micro organisms
Q. At lower pH, the contact period required for chlorination is
a) Lower b) Higher
c) Same d) None of the above

CHLORINATION

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At pH < 5, chlorine does not react with water and remain as Free chlorine
HOCI, OCI- and Cl₂ are combinely called as Free Chlorine
HOCl is most destructive
pH of water during chlorination should be between 5 to 7

Chlorine immediately reacts with ammonia present in water to form

chloramines. Chloramines are combined form of Chlorine and are less
effective than freely available chlorine. But chloramines are stable and
remain in water for a long duration. In the usual chlorine treatment, in
which pH is kept between 5 to 7, dichloramine is predominately present.
The dose of Chlorine should be sufficient so as to leave 0.2 mg/L of chlorine
after 10 minutes of contact period. This dose is called Chlorine demand of
water.
NH3 + HOCl → NH2Cl + H2O
NH2Cl + HOCl → NHCl2 + H2O
NHCl2 + HOCl → NCl3 + H2O

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Q. The following residual chlorine compounds are formed during
chlorination of water :
1. NH2Cl
2. NHCl2
3. HOCI
4. OCl-
The correct sequence of formation of these residual chlorine compounds is
a) 2, 1, 3, 4 b) 1, 2, 4, 3
c) 1, 2, 3, 4 d) 2, 1, 4, 3

Forms in which Chlorine is added are:

A. As free chlorine
B. Bleaching powder or Hypochlorite (CaOCl2)
C. Chloramines
D. Chlorine dioxide (CIO₂)

Effective in Disinfection: CIO₂ >HOCI>Chloramines>Ocl-

Q. The treatment of water with bleaching powder is known as
a) Prechlorination b) Superchlorination
c) Dechlorination d) Hypochlorination
Q. Which of the following chemical compounds can be used for
dichlorination of water?
a) Carbon dioxide b) Bleaching powder
c) Sulphur dioxide d) Chloramines
Q. Chlorine demand of water is equal to
a) Applied chlorine
b) Residual Chlorine
c) Sum of applied and residual chlorine
d) Difference of applied and residual chlorine

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Types of Chlorination

A. Plane Chlorination
• Only chlorine treatment and no other treatment. It helps to remove bacteria
and colour from water and it also controls the growth of algae

B. Pre Chlorination
• Chlorine is added before raw water enters sedimentation tanks. It helps in
reducing the number of coagulants and to improve coagulation

C. Super Chlorination
• The application of chlorine to water beyond the stage of breakpoint is known
as super chlorination. It is most commonly added at the end of filtration. It
is adopted whenever there is a breakout of water borne diseases.

D. Post chlorination
• This is the standard form of chlorination in which chlorine is added to water
as it leaves filters and before it enters the distribution system. The residual
chlorine present in water is useful for its protection against contamination
in the distribution system. Residual = 0.1 to 0.2 mg/l

Q. Which of the following process includes chlorination of water above the

break point ?
a) Plain Chlorination b) Dechlorination
c) Excess Chlorination d) Super Chlorination
Q. Residual chlorine in water is determined by
a) lodine starch method b) Orthotolidine method
c) Both a) and b) d) None

Testing of Chlorine Residue

A. Orthotolidene Test
B. DPD Test (DiEthylParaphenyleneDiamene)
C. Starch lodide Test
D. Chlorotex Test

Various dechlorinating agents are:

a) Sodium thiosulphate
b) Activated carbon
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 c) Sulphur dioxide

Q. A rural water supply scheme serves a population of 10,000 at the rate

of 50 litres per capita per day. For the chlorine dose of 2ppm, the
required amount of bleaching powder with 20% available chlorine will
be -
a) 0.5kg b) 5kg
c) 10kg d) 15kg
Q. A water treatment plant treats 5000 cubic metres of water per day. If it
consumes 20 kg chlorine per day, then the chlorine dosage would be
a) 10 mg/L b) 04 mg/L
c) 0.4 mg/L d) 0.25 mg/L

Q. The Water Prevention and Control of Pollution act was implemented by

Indian Parliament in the year
a) 1972 b) 1974
c) 1986 d) 1994

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