Environmental Engineering

Total Marks= 50(Theory) + 50(Practical)
Final Paper = 30
Mid Exam. =10
Sessional Marks = 10
 Attendance = 05
 Class Test = 05
2

 Introduction to Environmental Engineering.
 What is Environment, What is Environmental Engineering & Science?.
 Duties of an Environmental Engineer and Branches of Environmental
Engineering.
 Terminologies used in Environmental Engineering.
 Environmental Segments, Environmental Pollution, Environmental Changes.
 Water Supply Engineering.
 Water Quality, Physical, Chemical Characteristics of water.
 Water Demands.
 Water Treatment Unit Processes/Operations.
 Sedimentation Theory, Design of Sedimentation Tanks.
 Filtration Theory, Types of Filters.
 Water Collection & Water Conveyance.
 Design of Water Treatment Plant.
 Water Distribution Networks.
 Water Quality Management.
 Environmental Legislation & Management.
3

1. Introduction to Environmental Engineering, L.Davis
2. Water Supply Engineering, S.K Garg
3. Environmental Pollution & Control, P.Aarne
4. Environmental Management, Dr.Biswaryo
4

• Living & Non-Living Components surrounding us is known as
Environment.
• Environment is consists of Air, Water & Land.
• Environment is a sum of social, economical, Biological, Physical &
Chemical factors which constitutes surrounding of the man, who is
both creator & modular of his environment.
6

What is difference between
Environmental Engineering &
Environmental Science?
• Environmental Engineering can be defined as
“ The application of Engineering Principles under
limits to the protection & enhancement of the
quality of the Environment and the protect and
enhance the public health & welfare”.
• Environmental Science can be defined as
“ Study of various Environmental issues (such as
issues of water pollution, Air pollution & Land
pollution), it does not include applications of
Engineering principles to protect quality of the
Environment.
7

• Environmental Engineer deals with the
structures, equipments, systems that are
designed to protect & enhance the quality
of the Environment and to protect &
enhance the public health & welfare.
• For example Environmental Engineer Plan,
Design, Construct, Operate and Maintain
the Water Treatment Plants to supply
pure water to the Public.
• Environmental Engineer also conduct an
EIA of various Engineering Projects & give
mitigation options.
8

Branches of Environmental Engineering
• Environmental Chemistry & Micro-biology.
• Drinking water Treatment, Distribution & Monitoring.
• Sewage & Industrial wastewater treatment, disposal and
water pollution control.
• Strom water drainage & Control.
• Solid & Hazardous waste management.
• Air & Noise Pollution & Control.
• Environmental Impact Assessment (EIA)
• Environmental quality modeling & monitoring.
– Environmental Monitoring Agencies in Pakistan EPA
(Environmental Protection Agency ) & PCIR (Pakistan Council of
Industrial Research) 9

• Following terms of Environment are most important and
we must know about these technical terms.
1. Ecology
2. Organisms
3. Species
4. Ecosystem
5. Micro Organism
6. Microbes
7. Pathogens
8. Biodiversity
10

1. Ecology: Ecology deals with the living & non-living components of
the environment in relation to their surrounding.
2. Organisms: Any living entity Animal or Plant which capable of
growth and reproduction are called organisms.
3. Species: A group of organisms having common attributes/quality
are called Species.
4. Ecosystem: A group of organisms interacting among themselves &
surrounding Environment forms an eco-system which includes both
living & non-living components of the Environment.
5. Micro Organism: Very small living entity see only with the help of
microscope is called micro-organisms.
6. Microbes: Micro Organisms are simply called microbes, all microbes
are not harmful for human health.
7. Pathogens: Harmful microbes which causes disease.
8. Biodiversity : The verity of life forms on earth & its process.
11

Environment is consists / composed of following 4 segments
1. Lithosphere.
2. Hydrosphere.
3. Biosphere.
4. Atmosphere.
12

• Pollution is defined as undesirable change in Physical,
Chemical & Biological characteristics of Water, Air or Soil,
that will harmfully affected the Human life and other
organisms.
13

1. Environment changes are carried by following two ways
1. Natural Changes
1. Natural Process
2. Natural Disasters (Earthquakes, Floods, Sea storms, Droughts
2. Anthropogenic Changes
1. Technology
2. Industrial Revolution
3. Transportation
4. Urbanization
5. Dam Construction
6. Intensive Agriculture implements
14

• Water is one of the most important material required to sustain life
& is considered as the source of human illness. It is rarely available
in nature because it has great tendency to dissolve various
substances in it while flowing on the surface of earth.
• The topic of water quality focuses on the presence of foreign
substances in it & their effect on human & other aquatic life.
• At present more than 85 chemicals are listed in US EPA drinking
water standards.
• Where as WHO listed over 100 chemicals in guide lines for drinking
water.
• In addition, the public need water that is soft, non-corrosive, free
from pathogens & suspended solids.
• Due to inferior quality of water millions of children die every year. In
the world under the age of 5years, due to water born diseases.
• Water quality for one purpose is not good / suitable for other
purpose.
16

• There are three parameters of water quality,
1. Physical Parameter.
2. Chemical Parameter.
3. Biological Parameter.
Impurities in water:
All type of water such as surface water, rain water & under ground
water contains various impurities because water has great tendency to
dissolve other substances in it. While flowing on surface of earth rain
water collects dust & gases from atmosphere. Surface water dissolve
sand, silt, suspended solids, organic matter, minerals & colloidal matter
while flowing on surface.
underground water mostly free from suspended solids, colloidal &
organic imparities but it contain various chemicals, minerals & salts. It
contain less impurities due to natural filtration action of underground
soil.
17

1. Color
2. Taste & Odor
3. Suspended Solids
4. Turbidity
5. Temperature
18

1. Color: color of water is due to presence of colloidal matter, decaying
vegetation.
scale of color from 0 to 70 units
Drinking water should not be more than 15 color units.
Normally mineral water available in market have 5 color unit.
19

2. Taste & Odor: Taste & odor of water is due to presence of decomposed organic
materials, minerals & salts of iron & Meneginies (Fe & Mn). Vegetation, chlorine,
algae etc.
odor is measured in “Threshold odor number”
pure drinking water is always Taste less & Odor less & also color less.
3. Suspended Solids (SS): SS in the water may be in the form of clay, silt, sand, silica &
Calcium carbonate or they may be in the form of organic matter oils, fats, grease. The
SS may easily be removed by sedimentation & Filtration.
4. Turbidity: it is caused by SS fine insoluble partials, silt, sand, clay & algae. Turbid water
does not allow passage of light which is either scattered or absorbed depending upon
the size & surface characteristic of partial. It also cause undesirable taste & odor to
water & affect the process of photosynthesis for algal growth in lakes & ponds.
Completely treated water has turbidity of less than 1 TU (Turbidity Unit).
Clear lake water has 25 TU where as muddy water has >100TU
Turbidity is measured by Jackson turbidity meter. A graduated rod is immersed in
surface water to obtain turbidity level.
20

5. Temperature: Solubility, Viscosity, Portability & Chemical reaction
are influenced by temperature. More quantities of chemicals get
dissolved at higher temperature but gases (D.O) are released.
water should not have higher temperature because due to that
aquatic life & plants are threatened/endangered.
Due to rise in temperature of lakes & Rivers, fishes may be die or
they have to migrate.
21

Many organic & inorganic chemicals affect water quality. In drinking
water these chemicals affects public health, where as in surface
water it affect to the aquatic life. Most important chemicals are,
1. Acidity, Alkalinity & pH
2. Hardness
3. Total Dissolved Solids (TDS)
4. Toxic Chemicals
5. Dissolved Oxygen (DO)
6. Fluorides
7. Chlorides
8. Sulfates
9. Nitrates
10. Phosphates
22

The presence & absence of living organisms in water can be one of
the most useful indicator of the quality of water.
The verity of species (Fishes) present in the lake be a sign of
unpolluted lake.
1. Micro-organisms
2. Bacteria
3. Algae
4. Protozoa
5. Viruses
24

Water requirement of any Town or City is determined by following
two factors,
1. Consumption per head per day or per capita demand.
2. Population
1. Per Capita Demand:
If “P” is population of the city or Town or Village and “Q” is the Total water
requirement in a year, then per capita demand is calculated by following
formula,
Per capita demand = Q/ (P*365) Liters or Gallons per day
25

• Various Type of Water Demands
1. Domestic Water Demand
2. Industrial Water Demand
3. Public Water Demand
4. Fire Water Demand
5. Losses & Wastages
S.No: Purpose Consumption Per
Capita Per day
01 Drinking 5 Liters
02 Cooking 5 Liters
03 Bathing 50 Liters
04 Washing 25 Liters
05 Washing utensils 15 Liters
06 Cleaning of House 10 Liters
07 Sewer flushing 25 Liters
Total Consumption/C/d 135.0
26

Water Supply Schemes
 Before a project of water supply for a particular locality is taken in
hand, a scheme is drawn out the different aspects of the whole
scheme are carefully viewed from different angles.
 Water supply schemes are prepared by the combination of field
observations and office work.
 Following are the points of importance in any water supply scheme:
 Financial aspect
 Population
 Quality of water
 Rate of consumption
 Sanitary survey of the area
 Sources of water supply
 Topography of the area
 Trends of town development
29

 Financial aspect: The data regarding the availability of funds for the
fulfillment of the water supply scheme should be obtained in the initial
stage of the scheme only. The scheme should then be adjusted in relation
to the funds available. Every step should be taken to make the scheme as
economical as possible.
 Population: From the available census of previous years, the present
population should be determined and it is general practice to make the
scheme to accommodate population after three or four decades. Failure
to provide for future expansion results in great hardship in future.
 Quality of Water: The more pure water (Source of supply) is, the less is
the cost of treatment. Hence, samples of available sources of water
should be taken and properly analyzed and the results of various tests
should be thoroughly studied to suggest an economical water supply
scheme.
 Rate of consumption: The demand of water depends on various uses
such as domestic, industrial, public etc. the rate of consumption per
capita should be decided by carefully considering all the possible uses.
This rate, when multiplied by the population, give the total quantity of
water required for the water supply scheme.
30

 Sanitary survey of the area: The sanitary of area surrounding the
available water sources should be carefully carried out. Such a survey
helps in estimating the possible pollution or contamination of water from
such sources.
 Sources of water supply: It is quite clear that the success of a water
supply scheme entirely depends on a good source of supply of water. The
source should be selected while keeping in view its adequacy, quality of
water and cheapness.
 Topography of the area: The topography map of the area to be served by
the scheme should be prepared and it should be suitable in relation to
low lying area, ridges, density of population, etc. The study is essential to
develop a simple & economical water supply scheme.
 Trends of town development: The trends of town development in future
should be predicted & properly adjusted in the water supply scheme.
Such trend may take various forms such as possibility of new industries,
public recreation, public institutions, residential blocks, etc.
31

Water Supply System
Professionals, working in Municipal Services or Public Health deptt: are
responsible for designing systems that provide a reliable and clean water
supply.
A water supply system begins at a water source.
Water is transported to a treatment facility where the water is treated to
ensure the supply is safe.
Once Treated, the water is transported to a storage facility (OHWT) where it is
stored for future demand.
32

Sources of Water
• Under ground water
• Surface water
• River
• Lakes
• Reservoirs
33

Water Storage
Treated water is pumped to a storage tank.
Storage tanks are often elevated.
A storage tank serves two purposes.
1.It stores the water until it is needed,
which reduces the peak demand on
the treatment facility.
2.Elevated water tanks create pressure
in the water distribution system.
Min: water pressure in distribution
line (1 psi = 2.31 feet of water)
34

Estimating Population
 The term population is used to indicate the total number of
human beings in a certain area at any particular time.
 The present population is obtained by referring to the statistics of
census records prepared by the local body.
 The water supply projects is not designed only for present
population. But it is made to accommodate the future population.
 The growth of population may be sharp, slow or even stationary
depending upon the factors contributing to the future
development of the locality such as coming up of new industries,
trade expansion, etc.
 The future period for which various services units of water supply
or sanitary engineering are designed is known as the period of
design.
 The period of design may varies from 20 to 40 years or even
upto 50 years. 35

The period of design for important
components of water supply Projects
S.No: Component Period of Design
In years
01 Clear water service reservoirs 15
02 Conveying pipes for raw water and clear water 30
03 Distribution system 30
04 Electrical Motors and pumps 15
05 Infiltration works 30
06 Storage reservoirs 50
07 Water treatment units 15
36

Population forecasts Methods:
(1) Arithmetical increase method:
In this method, the average increase of population for the last three or four
decades is worked out and then for each successive future decade, this
average is added. This method gives low results and it is to be adopted for
large cities which have practically reached their maximum development.
(2) Geometrical increase method:
In this method, it is assumed that the percentage increase in population
from decade to decade remain constant. From the available census record,
this percentage is fixed and then population of each future successive
decade is worked out. This fixation of percentage is case of developing
cities should be done carefully. Otherwise this method is likely to give high
results. This method gives better results for old cities which are not
undergoing future development.
(3) Incremental increase method: This method combines the above two
methods. The population of each successive future decade is first worked
out by the arithmetical increase method and to these values incremental
average per decade is added. It combines the advantages of both the
above methods and hence, it gives satisfactory results. 37

Problem No:01
The census record of a city show population as follows:
Present = 50000
Before one decade = 47100
Before two decade = 43500
Before three decade = 41000
Work out the population after one, two and three decade by using arithmetical
increase method.
Solution:
The average increase of population b/w successive decades up to present is
worked out as follows,
Present and first decade =50000-47100 =2900
first and 2nd decade =47100-43500 =3600
2nd and 3rd decade =43500-41000 =2500
TOTAL =9000
Average increase per decade = 9000/3 = 3000.
Population forecasting Example
38

The population after each successive future decade is obtained by adding
this average as follows:
Population after one decade = 50000+3000=53000
Population after two decade = 53000+3000=56000
Population after three decade = 56000+3000=59000
Answer
again work out the population by using Geometrical increase method.
Solution;
Present and 1st decade = (50000-47100) /47100 * 100 = 6.16
1st and 2nd decade = (47100-43500) /43500 * 100 = 8.28
2nd and 3rd decade = (43500-41000) /41000 * 100 = 6.10
TOTAL = 20.54
Average percentage = 20.54/3 =6.85 say 7
Population after one decade = 50000+ (50000*0.07)=53500
Population after two decade = 53500+(53500*0.07)=57245
Population after three decade = 57245+(57245*0.07)=61252
Answer
39

again work out previous problem by using incremental increase method.
Solution:
Increase in population
present and first decades = 2900
first and second decades = 3600
second and third decades = 2500
Incremental increase
2900-3600 = -700
3600-2500 = 1100
Net = + 400
average incremental increase = 400 / 2 = 200
average arithmetical increase as worked out in problem No:01 = 3000
arithmetic increase and this average incremental increase as follows:
Population after one decade = 50000 + 3000 + (1*200)= 53200
Population after two decades = 53200 + 3000 + (2*200)= 56600
Population after three decade = 56600 + 3000 + (3*200)= 60200
Answer
40

Problem No:02
The census record of a city show population as follows:
Present = 16000
Before one decade = 14500
Before two decade = 12000
Before three decade = 10000
Work out the population after one, two and three decade by using arithmetical
increase method and by using Geometrical increase method.
Solution:
The average increase of population b/w successive decades up to present is
worked out as follows,
Present and first decade =16000-14500 =1500
first and 2nd decade =14500-12000 =2500
2nd and 3rd decade =12000-10000 =2000
TOTAL =6000
Average increase per decade = 6000/3 = 2000.
41

this average as follows:
Population after one decade = 16000+2000=18000
Population after two decade = 18000+2000=20000
Population after three decade = 20000+2000=22000
Answer
again work out the population by using Geometrical increase method.
Solution;
Present and 1st decade = (16000-14500) /14500 * 100 = 10.34
1st and 2nd decade = (14500-12000) /12000 * 100 = 20.83
2nd and 3rd decade = (12000-10000) /10000 * 100 = 20.00
TOTAL = 51.17
Average percentage = 51.17/3 = 17
Population after one decade = 16000+ (16000*0.17)=18720
Population after two decade = 18720+(18720*0.17)=21902
Population after three decade = 21902+(21902*0.17)=25625
Answer
42

Population forecasts Methods:
(4) Graphical method:
In this method a curve is plotted between
Time & Decades on x-axis and population in
thousands on y-axis, the curve is then
extended carefully depending upon its
previous shape and population for the future
decade is determined from y-axis.
(5) Comparative method:
This method is based on assumptions that the
city under consideration may be developed as
similar cities have developed. In this case
similar three or four cities are taken which
have similar environment, similar culture,
similar population etc. after that graph are
plotted and are extended for next 30 or 40
years to estimate future population.
43

1. Domestic Water Demand:
In this case water is needed for drinking, bathing, washing, utensils & cleaning
of house & sewer flushing etc. domestic demand to be taken as 50% of Total
water requirement.
2. Industrial or commercial Water Demand:
It includes water for factories, hotels, markets etc. the consumption depends
upon the type of industries & the city where it is located. The percentage of
water required varies from 20 to 25 % of Total water requirement.
3. Public Water Demand:
In this case water is needed for colleges, schools, Hostels, public gardens,
picnic points, large hospitals, city community halls, jails etc. the percentage of
water requirement for this purpose to be taken as 10% of Total water
requirement.
4. Fire Water Demand:
It is very important for the municipal body to give adequate protection
against fire, during fire the demand of water is very high because large
quantity of water is required on urgent basis to control on the fire for this
purpose fire hydrant are provided on all street at some extant from where
water can be pumped at the rate of 950 to 1150 Liters / minute.
44

Following formulas are used to calculate fire demand.
4. Fire Water Demand:
I) Kuchling’s formula:
Q = 3182 √P
Where as
Q = Total water quantity (Liters/minute)
P = Population of the town in thousands
II) Free man’s Formula:
Q = 1136 [(P/5)+10]
II) National Board of Fire Formula:
Q = 4637 √P (1-0.01 √P )
Note:
about 1 to 5 L/C/d may be taken as fire demand. It depends on factors like
possibility of fire, nature of town habits of peoples etc.
4. Losses & Wastages:
About 10 to 15% of Total water requirement goes for losses & wastages due
to unauthorized connection & leakages. 45

– The total per capita average demand in Pakistan about 200 to 300
L/C/d, where as in USA it is about 500 to 700 L/C/d.
– In any community water demands varies, depending upon factors like
climate, duration of water supply, standard of living, drainage system.
– For example water consumption is more in morning time and evening
time it varies hourly, daily.
– Water demand more on Sunday due to leave while planning any water
supply scheme we have to calculate the average per capita demand &
depending on that the Total quantity of water is determined for the
Town, City, Village.
– It is important to note that mostly water supply schemes are designed
for the period of 15 to 30 years.
46

Stages in water treatment
1. Screening
2. Plain Sedimentation
3. Sedimentation with
coagulation
4. Flocculation
5. Filtration
6. Aeration
7. Disinfection
8. Softening
47

1. Screening:
The process of removing
large size particles such as
bushes of trees, dead
animals, fishes from the
water with the help of various
type of screens are called
screening.
Screens are installed at
different distances before
treatment plant.
48

2. Plain Sedimentation:
The process of retaining water in
large basin so that the
suspended particles may settle
down due to action of gravity is
called plain sedimentation.
3. Sedimentation with
Coagulation;
The process of adding certain
chemicals in the water to
remove fine particles & colloidal
particles with the help of floc
formation is called sedimentation
with coagulation.
Various chemicals which are
added in water are called
coagulants. The most popular
coagulant used widely is Alum. 49

4. Flocculation:
The process of formation of
flock is called flocculation.
In flocculation process fine &
colloidal particles are caught
by flock & the size of floc will
going to be increase & then
settle down by catching more
impurities.
5. Filtration:
The process of passing the
water through thick layer of
sand which acts as strainer is
called filtration.
50

6. Aeration:
The process of bringing water in
intimate contact with air in the
form of shower is called
Aeration.
7. Disinfection:
The process of killing bacteria
from water & to make it safe for
public health is called
disinfection.
In this method various chemicals
& gasses are used to kill the
bacteria present in water.
The most popular chemical used
for his purpose is Chlorine.
8. Softening:
The process of special treatment
for removing the dissolved
impurities from water is called
water softening. 51

Water Treatment Plant @ Jacobabad City
53

Group Assignment No:01
Max. Marks =05
Prepare a presentation on existing water supply system of your City/Town.
Presentation contents:
• Population of Town / City / Village.
• Map of Town / City / Village (From Google earth)
• Sources of water supply.(Surface water or underground water)
• Existing system of Treatment.(Current position)
• Quality of water supplied to public.
• Functional / Non-Functional of existing system.
• Your own recommendations for your Town / City / Village.
Present a Presentation in class on
following dates
Submit a hard copy of it.
54

Sedimentation
• Particles that will settle within a reasonable period of time can be removed in a
sedimentation basin (also called clarifier).
• Sedimentation usually rectangular or circular with either a radial or upward flow
pattern.
• Rectangular type basin, design can be divided into four zones: Intel, Settling,
Outlet and Sludge storage.
• The purpose of inlet zone is to evenly distribute the flow and suspended
particles across the cross section of the settling zone.
• Intel zone consists of a series of inlet pipes & baffles placed about 1m into the
tank and extending the full depth of the tank.
• The inlet velocities may never subside to the settling zone design velocity.
• The configuration & depth of sludge zone depends upon the method of cleaning,
the frequency of cleaning & quantity of sludge estimated to be produced.
• If the tank is long enough, storage depth can be provided by bottom slop, if not,
a sludge hopper is necessary at the inlet end.
• Mechanically cleaned basins may be equipped with a bottom scraper.
• A sludge hopper is designed with sides sloping with a vertical to Horizontal ratio
of 1.2:1 to 2:1 55

Zones of Sedimentation
(a) Horizontal flow clarifier (b) up-flow clarifier
(a) Horizontal flow clarifier (b) up-flow clarifier
Inlet Zone
It evenly distributes the flow and suspended
solids across the cross-section of the settling
zones. It covers approximately 25% of the tank
length.
Settling Zone
Where the actual settling of particles takes
place.
Sludge Collection Zone of Sludge
Configuration and depth of the sludge zone
depends on the method of cleaning and
quantity of sludge deposited. Well flocculated
solids, 75% settle in the 1/5th of the tank
length.
Outlet Zone
Removal of settled water without carrying
away any of the flocs. Should be designed to
avoid scouring by having either weirs or trough
(drain/channel).
56

(b) up-flow clarifier
57

Sedimentation
• Outlet zone is designed so as to remove the settled water from the basin without
carrying away any of the floc particles.
• A fundamental property of water is that the velocity of flowing water is proportional to
the flow rate divided by the area through which the water flows, that is, Vo= Q/A
• There are two important terms to understand in sedimentation zone design. The first is
the particle (floc) settling velocity Vs, the second is the velocity at which the tank is
designed to operate, called the overflow rate Vo.
• If Vs > Vo one would expect 100% particle removal.
• If Vs < Vo one would expect 0% particle removal.
• For design purpose, Vo is set at 50 to 70% for Vs for upflow clarifier.
• Hence an overflow rate is the same as a liquid velocity:
Vo = (Volume/Time) / Surface Area
Vo = (Depth*Surface Area) / Time * Surface Area = Depth / Time
Vo = h / t or Vo = Q/ As
• An Ideal Horizontal sedimentation tank is based upon three assumptions
1. Particles & Velocity vectors are evenly distributed across the tank cross section.
(This is the function of inlet zone).
2. The liquid moves as an ideal slug/hit down the length of the tank.
3. Any particle hitting the bottom of tank is removed. 58

Critical Settling Velocity and Overflow Rate
This figure shows that 50% of these particles (those below half the depth of
the tank) will be removed. That is they will hit the bottom of the tank
before being carried out because they only have settle one-half the tank
depth.
The percentage of particles removed P, with a settling velocity of Vs, in a
sedimentation tank designed with an overflow rate Vo is
P = Vs/Vo * 100
59

What percent of the particles will be removed?
A water treatment plant has a flow rate of 0.6 m3/sec. The settling basin at the
plant has an effective settling volume that is 20 m length, 3 m depth and 6 m wide.
Will particles that have a settling velocity of 0.003 m/sec be completely
removed? If not, what percent of the particles will be removed?
v0 = Q/A = 0.6 m3/sec / (20 m x 6 m) = 0.005 m/sec
Since V0 > Vs the settling velocity of the particle of interest,
they will not be completely removed.
The percent of particles which will be removed may be found using the
following formula:
Percent removed = (vs / v0) 100
Percent removed = (0.003/0.005) 100 = 60 %
60

Find out Detention time for a Sedimentation Tank
Problem No:01:
A Sedimentation Tank has a volume capacity of 20000 m3, if the
average flow rate entering the tank is 130 Million Liters/day.
What is the detention time ?
Data:
Volume (V) = 20000 m3
Flow rate (Q) = 130 ML/day
Solution:
As we know that
Q = V / T
T = V / Q
Detention Time (TD) = (20000 * 1000 ) Liters / 130000000 L/d
Detention Time (TD) = 0.15385 per day
Detention Time (TD) = 3.69 Hours
61

Sedimentation Tank Problems
(Previous paper 2012 of 09CE)
Problem:
Calculate the diameter and side water depth (SWD) of a sedimentation tank 20 ML/day. The
maximum surface over flow rate (SOR) 18m3/m2.day and detention period of 3hrs.
Data:
Depth =?
surface over flow rate (SOR) =18m3/m2.day
Flow rate (Q) = 20 ML/day = 20000 m3/day
Detention Time = 3hrs
Solution:
As we know that
Q = Volume / Detention time
V = Q * TD
= 20000 m3/day * (3/24)day = 2500 m3
As we know that Surface loading Vo= Q/As
As = Q/Vo = 20000 m3/day / 18m3/m2day = 1111.11 m2
Therefore Volume = surface area * depth
Depth = Volume / Surface area
Depth = 2500 m3 / 1111.11 m2
SWD = 2.25 m
Now find out the Diameter
D= (4*A/3.1415)0.5
D=37.6m
62

Sedimentation Tank Practice Problems
Assignment No:02
Max. Marks = 05
1. A Sedimentation Tank with a 50ft diameter and SWD of 9ft treat a flow
of 15000 gpd. What is the detention time ?
2. Compute the required volume of a sedimentation tank that provides
3hrs of detention time for a flow of 10 ML/d. if tank is 10m by 25m in
plan dimensions, how deep is the water in the tank.
3. A circular settling tank is to have a minimum detention time of 3 hrs and
a maximum overflow rate of 800gpd/ft2. Determine the required basin
diameter and SWD for a flow rate of 2mgd.
4. A rectangular settling tank is to have a minimum detention time of 3.5
hrs and a maximum surface loading of 25m/d. The tank length is to be
twice of its width. Determine the required tank dimensions, including
freeboard, for a flow of 5000 m3/day.
Note: submit your assignment earlier than 16th February 2016.
63

Coagulation & Flocculation
 Coagulation/flocculation is a process used to remove turbidity, color, and some
bacteria from water. In the flash mix chamber, chemicals are added to the
water and mixed violently for less than a minute. These coagulants consist of
primary coagulants and/or coagulant aids. Then, in the flocculation basin, the
water is gently stirred for 30 to 45 minutes to give the chemicals time to act
and to promote floc formation. The floc then settles out in the sedimentation
basin.
 We can define Coagulation as a method to alter the colloids so that they will be
able to approach and adhere to each other to form larger floc particles.
 In water treatment operations, the processes of coagulation and flocculation
are employed to separate suspended solids from water.
 Coagulation is the destabilization of colloids by neutralizing the forces that keep
them apart.
 Flocculation, is the action of polymers to form bridges between the flocs. and
bind the particles into large clumps.
 Once suspended particles are flocculated into larger particles, they can usually
be removed from the liquid by sedimentation.
64

Types of Coagulants
 Coagulant chemicals come in two main types - primary coagulants and
coagulant aids. Primary coagulants neutralize the electrical charges of
particles in the water which causes the particles to clump
together. Coagulant aids add density to slow-settling flocs and add
toughness to the flocs so that they will not break up during the mixing
and settling processes.
 Primary coagulants are always used in the coagulation/flocculation
process. Coagulant aids, in contrast, are not always required and are
generally used to reduce flocculation time.
 Chemically, coagulant chemicals are either metallic salts (such as alum)
or polymers. Polymers are man-made organic compounds made up of a
long chain of smaller molecules. Polymers can be
either cationic (positively charged), anionic (negatively charged),
or nonionic (neutrally charged.)
65

Chemical Name Chemical Formula Primary Coagulant Coagulant Aid
Aluminum sulfate (Alum) Al2(SO4)3 · 14 H2O X
Ferrous sulfate FeSO4 · 7 H2O X
Ferric sulfate Fe2(SO4)3 · 9 H2O X
Ferric chloride FeCl3 · 6 H2O X
Cationic polymer Various X X
Calcium hydroxide (Lime) Ca(OH)2 X* X
Calcium oxide
(Quicklime)
CaO X* X
Sodium aluminate Na2Al2O4 X* X
Bentonite Clay X
Calcium carbonate CaCO3 X
Sodium silicate Na2SiO3 X
Anionic polymer Various X
Nonionic polymer Various X
The common coagulant chemicals, which are used as primary coagulants or as coagulant aids.
66

Primary coagulants or as coagulant aids
Alum:
• There are a variety of primary coagulants which can be used in a water treatment
plant. One of the earliest, and still the most extensively used, is aluminum
sulfate, also known as alum. Alum can be bought in liquid form with a
concentration of 8.3%, or in dry form with a concentration of 17%. When alum is
added to water, it reacts with the water and results in positively charged ions.
Coagulant Aids
• Nearly all coagulant aids are very expensive, so care must be taken to use the
proper amount of these chemicals. In many cases, coagulant aids are not
required during the normal operation of the treatment plant, but are used during
emergency treatment of water which has not been adequately treated in the
flocculation and sedimentation basin. A couple of coagulant aids will be
considered below.
• Lime is a coagulant aid used to increase the alkalinity of the water. The increase
in alkalinity results in an increase in ions (electrically charged particles) in the
water, some of which are positively charged. These positively charged particles
attract the colloidal particles in the water, forming floc.
• Bentonite is a type of clay used as a weighting agent in water high in color and
low in turbidity and mineral content. This type of water usually would not form
floc large enough to settle out of the water. The bentonite joins with the small
floc, making the floc heavier and thus making it settle more quickly. 67

Mixing or Rapid Mixing
 Mixing, or Rapid mixing as it is called, is the process whereby the chemicals are
quickly and uniformly dispersed in the water.
 Ideally, the chemicals would be instantaneously dispersed throughout the
water.
 Rapid mixing is probably most important physical operation affecting coagulant
dose efficiency. The chemical reaction in coagulation is completed in less than
0.1 second, therefore, it is necessary that mixing be as instantaneous and
complete as possible.
 The treatment of water and wastewater the degree of mixing is measured by
the velocity gradient, G.
 The higher the G value, the more violent the mixing.
 The velocity gradient is a function of the power input into a unit volume of
water. It is given by G = ( P/µV)0.5
Where as;
G = Velocity gradient s-1
P = Power input, W
V = Volume of water in mixing tank, m3
µ = Dynamic viscosity, Pa.s or kg/m-s
68

Temperature
- t -
(oC)
Dynamic
Viscosity
- µ -
(Pa s, kg/m-s,
N s/m2) x 10-3
0 1.787
5 1.519
10 1.307
20 1.002
30 0.798
40 0.653
50 0.547
60 0.467
70 0.404
80 0.355
90 0.315
100 0.282
Mixing or Rapid Mixing
69

Flocculation
 While rapid mixing is the most important physical factor affecting coagulant
efficiency, flocculation is the most important factor affecting particle-removal
efficiency.
 Flocculation is the gentle mixing phase that follows the rapid dispersion of
coagulant by the flash mixing unit.
 The object of the flocculation is to bring the particles into contact so that they
will collide, stick together, and grow to size that will readily settle.
 Enough mixing must be provided to bring the floc into contact and keep the
floc from settling in the flocculation basin.
 Too much mixing will shear the floc particles.
 Therefore, the velocity gradient must be controlled.
 The flocculation basin should be divided into at least three compartments.
70

Types
 Flocculation can be provided by
either mechanical mixers or baffles.
General design criteria for a basic
rectangular flocculation tank:
 DT= 20-30 minutes at Qmax.
 Depth= 10ft to15fts
 G=30 s-1 average
Selection Criteria:
Selection of the flocculation process
should be based on the following
criteria:
- Treatment process: conventional,
direct, softening or sludge conditioning
- Raw water: turbidity, color, TDS
71

Design problem of Rapid Mixing
Problem:
The design flow for a Water Treatment Plant (WTP) is 1 MGD (3.785x103 m3/d). The
rapid mixing tank will have a mechanical mixer and the average alum dosage will be
30mg/L. The theoretical mean hydraulic detention time of the tank will be 1
minute. Determine the following:
a) the quantity of alum needed on a daily basis in kg/d,
b) the dimensions of the tank in meters for a tank with equal length, width, and
depth,
c) the power input required for a G of 900 sec-1 for a water temperature of 10 oC
express the answer in kW.
72

Filtration
 The water the leaving the sedimentation tank still contain floc particles. The settled
water turbidity is generally in the range from 1 to 10 TU with a typical value being
3TU. In order to reduce this this turbidity to 0.3TU, a filtration process is normally
used.
 Water filtration is a process for separation suspended or colloidal impurities from
water by passage through a porous medium, usually a bed of sand or other
medium.
 Water fills the pores (open spaces) b/w the sand particles, and the impurities are
left behind, either clogged in the open spaces or attached to the sand itself.
 There are several methods of classifying filters. One way is to classify them
according to the type of medium used, such as sand, coal (called anthracite), dual
media (coal plus sand), or mixed media (coal, sand and garnet).
 Another way to classify the filters is by allowable loading rate. Loading rate is the
flow rate of water applied per unit area of the filter. It is velocity of the water
approaching the face of the filter. V =Q/As
 Based on loading rate the filters are described as being slow sand filters, rapid sand
filters, or high-rate sand filters.
73

Slow sand Filters
Slow sand Filters:
 Slow sand filters were first introduced in the 1800s.
 The water is applied to the sand at a loading rate of 2.9 to 7.6 m3/m2.d.
 As the suspended or colloidal material is applied to the sand, the particles
being to collect in the top 75mm and to clog the pore spaces. As pores
become clogged, water will no longer pass through the sand and at this
point top layer of sand is scraped off, cleaned and replaced.
 Slow sand filters required large areas of the land and are operator intensive.
 Surface area of a slow sand filter may vary from 30 to 2000m2 or even
more.
74

Rapid Sand Filters
Rapid Sand Filters:
 In the early 1900s there was a need to install filtration system in large numbers in
order to prevent epidemics/infection/disease.
 Rapid sand filters were developed to meet this need. These filters have graded
(layered) sand within the bed.
 The sand grain size distribution is selected to optimize the passage of water while
minimizing the passage of particulate matter.
 Rapid sand filters are cleaned in place by forcing water backward through the sand.
This operation is called backwashing.
 The wash water flow rate is such that the sand is expanded and the filtered
particles are removed from the bed.
 After backwashing, the sand settle back into place. The larger particles settle first,
resulting in fine sand layer on top and coarse sand layer on the bottom.
 Rapid sand filters are the most common type of filters used in water treatment
today.
 Traditionally, rapid sand filters have been designed to operate at a loading rate of
120 m3/m2.d.
 The surface area of the filter tank (often called a filter box) is generally restricted in
size to about 100 m2.
75

Dual-media & Mono-media filters
Dual-media filters:
 In the war time era of the early 1940s, dual-media filters were developed.
 They are designed to utilize more of the filter depth for particle removal.
 In rapid sand filters, the finest sand is on top; hence, the smallest pore spaces are
also on the top. Therefore, most of the particles will clog in the top layer of the
filter. In order to use more of the filter depth for particles removal, it is necessary
to have the large particles on top of the small particles. This was accomplished by
placing a layer of coarse coal on top of the layer of fine sand.
 Coal has a lower specific gravity than sand, so, after backwash, it settle slower than
the sand and ends up on top.
 Dual-media filters are operated up to loading rate of 300 m3/m2.d.
Mono-media filters:
 In the mid 1980s, deep-bed Mono-media filters came into use.
 The filters are designed to achieve higher loading rates while at the same time
producing lower finishing water turbidities.
 The filters typically consist of 1.0-mm to 1.5-mm diameter anthracite about 1.5-m
to 2.5-m deep.
 Mono-media filters are operated up to loading rate of 800 m3/m2.d.
76

Backwashing of filters
Filters are employed to remove particles from liquids. Water treatment filters
that can be backwashed include rapid sand filters, pressure filters and granular
activated carbon (GAC) filters.
filters are backwashed according to the proprietary arrangement of pumps,
valves and filters associated with thedischarged without treatment to a sanitary
sewer system or is treated and recycled within the filtration system.
Spent backwash water is either plant
Backwashing of granular media filters involves
several steps. First, the filter is taken off line and
the water is drained to a level that is above the
surface of the filter bed. Next, compressed air is
pushed up through the filter material causing
the filter bed to expand breaking up the
compacted filter bed and forcing the
accumulated particles into suspension. After the
air scour cycle, clean backwash water is forced
upwards through the filter bed continuing the
filter bed expansion and carrying the particles in
suspension into backwash troughs suspended
above the filter surface. 78

Filter Design Problem
A city is to install rapid sand filters downstream of the clarifiers. The design loading
rate is selected to be 160 m3/(m2 d). The design capacity of the water works is 0.35
m3/s. The maximum surface area per filter is limited to 50 m2.
Design the number and size of filters and calculate the normal filtration rate.
Data:
Loading rate v = 160 m3/(m2 d)
Capacity Q = 0.35 m3/s or (0.35*60*60*24) m3/d
Max. As of filter = 50 m2.
79

Solved Problem of Filter Design
DATA:
Loading rate v = 160 m3/(m2 d)
Capacity Q = 0.35 m3/s or (0.35*60*60*24) m3/d
Max. As of filter= 50 m2.
Solution:
Step-1
Determine the Total As required = Q/v = 30240m3/d / 160 m3/(m2 d)
= 189 m2
Step-2
Determine the No: of filters (n) = 189/50 = 3.78
Select four number of filters
The surface area of each filter is (a) = 189 /4 = 47.25 m2
We can use 7m X 7m plan dimensions of the filter tank.
Step-3
if 7mX7m filter is installed, the normal filtration rate is;
v =Q/A = 30240/(4*49) = 154.28 m3/m2.day
80

What is Disinfection & Methods
of Disinfection
Disinfection refers to the reduction of pathogens (disease causing organisms)
Disinfection of water refers to the inactivation or destruction of undesirable
pathogenic organisms living in the water.
Disinfection of water started back in 500 BC with the boiling of water. Later
chlorination started in Europe (1880’s) and finally in the U.S. (1909).
Three general types of disinfection treatment are heat, radiation, and
chemical.
The heat method is to boil the water. This procedure is still used in cases of
emergency. The use of UV light to disinfect the water is radiation treatment.
This process disinfects when the UV light is passed through the water at close
proximity to the water. Only a small area of water can be treated by this
method, therefore is only used for small quantities of water.
chemical treatment is the most common form used to disinfect the water.
Chemicals will disrupt the life processes of an organism and it usually dies
before it can adjust. There are many different chemicals that can be used
depending on the situation and the targeted results. Many of the chemicals
have multiple purposes. Any of these different methods can be used to
disinfect water depending on how different treatment plants are equipped. 81

Chlorination
Chlorination is the most widely accepted and adopted method of
disinfection. It has been looked upon as the solution of problems and the
creator of others. Prior to chlorination, waterborne disease was a regular
occurrence. Throughout the 1800’s and 1900’s there was a high rate of
incidence of illness due to diseases like typhoid, dysentery and cholera. The
rate of illness and death due to these diseases dropped off with the
institution of chlorination.
Factors influencing disinfection by chlorination are: concentration of the
chlorine, contact time, temperature of the water, pH of the water, and how
many foreign substances there are in the water.
Chlorine gas can be added at different points in the water treatment
process, and each step has different effects.
Various forms in which Chlorine is used:
In the form of Liquid chlorine or Chlorine gas.
In the form of Hypo chlorides or bleaching powder.
In the form of Chloramines i-e Mixture of ammonia & Chlorine.
In the form of Chlorine dioxide.
82

Types of Chlorination
Pre-Chlorination: This means that chlorine is applied to raw water before other
treatments such as filtration, sedimentation.
Post-Chlorination: This means that chlorine is applied to treated water after
passing from filtration, sedimentation
Double-Chlorination: This means that water has been chlorinated twice. The Pre-
Chlorination & Post-Chlorination are generally used in double Chlorination.
Break Point Chlorination: This means that the extent (amount) of Chlorine added
to water. This represents such dose of chlorine beyond which any further addition
of chlorine will appear as free residual chlorine.
Super-Chlorination: it indicates the addition of excessive (too much) amount of
chlorine (i.e 5 – 15 mg/l) to water. This may be required in some special cases of
highly polluted water or during epidemics of water.
De-Chlorination: This means that removing of chlorine from water. This generally
required when super-chlorination has been practiced.
Free available-Chlorination: The sum of hypo chlorous acid, hypo chloride ions
and molecular chlorine existing in a sample of water is treated as free available
chlorine.
Chlorinator: The instrument used to applying chlorine to water is called
chlorinator.
83

Disinfection By-Products
Water is almost never pure H2O.
In rivers and reservoirs there is organic matter naturally floating in the water.
This natural organic matter (NOM) complicates simple reactions, allowing side
reactions to take place.
These side reactions form by-products other than the desired products of the
primary reaction.
The chlorine reacts on a secondary level with natural organic matter.
 A scientist in the Netherlands discovered Trihalomethanes (THMs) in 1974 .
THMs are a by-product of chlorine disinfection. Four of the common THMs are
Chloroform, Bromodichloromethane, Dibromochloromethane, and Bromoform.
The mechanism is not exactly known for the formation of THMs but the general
equation is as follows:
Free Chlorine + Precursors  THM’s + Other Halogenated
 (Humic Substances & Non-Halogenated
 & Bromide) By-products
These precursors come from sources like plants, algae and human activity.
85

Calculation of Chlorine dose
The actual dose of chlorine depends upon quality & quantity of water and the
level of impurities & bacteria present in water. This also depends upon the pH value
& Temperature of water.
The normal dosage of chlorine may vary b/w 0.3 to 1.1 mg/l, but chlorine dose is
increased in rainy seasons & in case of highly polluted water.
Following formula is used to calculate dose of Chlorine to treat water properly,
Kg /d=Q * C
Where as,
Kg/d = Amount of chlorine required in kg per day
Q = Average flow rate in ML/d (million liters / day)
C = Chlorine concentration mg/l
OR
lb /d=8.34*Q * C
Where as,
Kg/d = Amount of Chlorine required in pounds per day
Q = Average flow rate in mgd (million gallons / day)
C = Chlorine concentration mg/l
86

Calculation of Chlorine dose
Example:
A total of 15 kg of chlorine is used in 1 day to disinfect a volume of
50ML of water. What should be the Chlorine dose??
Data:
Kg of Chlorine per day = 15
Flow rate (Q) = 50 ML
Chlorine dose C = ??
As we know that,
Kg /d=Q * C
C = Kg/d / Q = 15kg/d/50*106 L
C =15*106 mg/d/50*106 L
C = 0.3 mg/l
87

Chlorine Dose: Demand and Residual
The chlorine dose required depends on two considerations: the chlorine
demand and the desired chlorine residual.
Dose (mg/L) = Demand (mg/L) + Residual (mg/L)
The chlorine demand is the amount of chlorine used in reacting with various
components of the water such as harmful organisms and other organic and inorganic
substances.
In other cases, however, such as at the end of the treatment process, it is desirable to
have an additional amount of chlorine in the water available for disinfection as it
travels through the distribution system. This additional chlorine is called the chlorine
residual.
Example Problem:
A water is tested and found to have a chlorine demand of 1.9 mg/L. If the desired
chlorine residual is 0.8 mg/L, what is the desired chlorine dose in mg/L?
Chlorine Dose = Chlorine Demand + Chlorine Residual
Chlorine Dose = 1.9 mg/L + 0.8 mg/L
Chlorine Dose = 2.7 mg/L
88

Chlorine Dose: previous paper Regular
examination 2010 of 07 Batch
Problem: The water is treated at treatment about 20,000m3/day, The chlorine usage is
6kg/day, the residual after 10 minutes contact time is 0.10mg/L. Calculate the dosage
in mg/L and chlorine demand of water.
Chlorine Dose
C = Kg/d / Q = 6kg/d/20,000m3/d
C = 6,000,000 mg/d/20,000,000 L/d
C = 0.3 mg/l
Chlorine Dose = Chlorine Demand + Chlorine Residual
Chlorine Dose - Chlorine Residual = Chlorine Demand
0.3 mg/L – 0.10 mg/L = Chlorine demand
Chlorine demand of water = 0.20 mg/L
89

Hardness of water
Hardness of water:
The presence of multivalent cations, most notably Calcium (Ca) &Magnesium (Mg)
ions, is referred as water Hardness.
Ground water special prone to excessive concentration of there ions. Hardness
causes two different problems, first, the reaction b/w hardness and soap produces a
sticky, gummy deposit called “soap curd” (the ring around the bathtub). Essentially all
home cleaning activities, from bathing and grooming to dishwashing and laundering,
are made more difficult with hard water.
When hard water is heated, calcium carbonate (CaCO3) and magnesium hydroxide
[Mg(OH)2] readily precipitate out of solution, forming a rocklike scale that clogs hot
water pipes and reduces the efficiency of water heaters, boilers etc. Pipe filled with
scale must ultimately be replaced, usually at great expense. Heating equipment that
has scaled up not only transmits heat less readily, thus increasing fuel costs, but also is
prone to failure at a much earlier time. For both of reasons, if hardness in not
controlled at the water treatment plant itself, many individuals and industrial facilities
find it worth the expense to provide their own water softening.
Hardness is defined as the concentration of all multivalent metallic cations in
solution. The principal ions causing hardness in natural water are calcium &
magnesium. Others, including iron (Fe), manganese (Mn), strontium (Sr), aluminum
(Al) may be present, though in much smaller quantities. 90

By Natural process: The Natural process by which water become hard, when rainwater
enters the topsoil, the respiration of micro organisms increases the CO2 contents of
water. The CO2 reacts with Water to form H2CO3.
What is Total Hardness (TH)
Total Hardness = Calcium (Ca) +Magnesium (Mg)
TH = Ca + Mg
Where as concentration of each are in consistent units mg/L as CaCO3.
The Total hardness is also broken down into two components
1. Carbonate Hardness
2. Non-Carbonate Hardness
TH= CH + NCH
Carbonate Hardness is defined as the amount of hardness equal to the total
hardness or the total alkalinity. CH = TH or Total alkalinity, whichever is less.
Non-Carbonate Hardness is defined as the total hardness in excess of the
alkalinity. It is called permanent hardness. It is not removed when water is
heated. NCH = TH - CH
Hardness range (mg/L CaCo3) Description
0 – 75 soft
75 – 100 Moderately hard
100 – 300 Hard
> 300 Very hard
91

Natural process by which water
become hard
CO2 + H2O  H2CO3
Subsoil
Limestone CaCO3(s) + H2CO3  Ca(HCO3)2
MgCO3(s) + H2CO3  Mg(HCO3)2
Precipitation
Topsoil
92

REMOVAL OF HARDNESS
A. FOR TEMPORARY HARDNESS:
1. Boiling
2. Addition of Lime
B. FOR PERMANENT HARDNESS:
1. Lime soda process
2. Zeolite process
3. Demineralization
93

LIME – SODA PROCESS
• In this process, lime and sodium carbonate or soda ash are used to remove
permanent hardness from water.
• The compounds calcium carbonate CaCO3 and magnesium hydroxide Mg (OH)2
are insoluble in water and they can, therefore, be arrested in the sedimentation
tank.
• The other compounds formed during the chemical reactions are soluble in water
and they do not impart the property of hardness to water.
• Lime often added as CaO, quick lime
– CaO + H20 --> Ca(OH)2
• Equipment required
– Feeding & Mixing apparatus
– Settling Tank
– Re-carbonation plant
– Filters
• Re-carbonation plant: it is necessary to remove calcium carbonate formed in this
process. Otherwise it will precipitate in sand filters and also cause incrustation in
pipes. For this reason, the water is allowed to pass through a re-carbonation plant
after it has passed through settling tank. In the settling tank, a dose of alum may be
given which will produce carbon dioxide. This carbon dioxide react with calcium
carbonate in this way,
CaCO3 + CO2 + H2O = Ca (HCO3)2
• Alternatively, the CO2 gas may be diffused into water in the re-carbonation plant.94

Zeolite process is also known as base-exchange or Ion exchange process.
The zeolites are compounds of aluminium, silica and soda.
The have excellent property of interchanging base.
They may be obtained from nature or may be prepared synthetically.
The natural zeolite is green in color and therefore known as green sand.
This is discovered in 1850s. J.T way, he succeeded in preparing base-
exchange materials.
In 1906 Gans and other German chemist applied this discovery and
prepared a synthetic known as “Permutit”
Zeolite process-Ion Exchange
95

Water Desalination
Obtaining reliable fresh water supplies
from challenging water sources
98

What is Desalination…?
Water, desalination is process of removing soluble salts from water to make
it suitable for drinking, irrigation, or industrial uses.
The principal methods used for desalination include distillation (or
evaporation), electro-dialysis, freezing, ion exchange, and reverse osmosis.

In distillation saltwater is heated in one container to make the water
evaporate, leaving the salt behind.
The desalinated vapor is then condensed to form water in a separate
container. Although, distillation has found limited application in water
supply because of the fuel costs involved in converting saltwater to vapor.
Representative of the early attempts in this direction were the solar
distillation methods employed (49 B.C.) by the legions of Julius Caesar for using
water from the Mediterranean sea.
Modern technological advances led to the development of more
efficient distillation units using solar energy; however, since these units have
small capacities, their utility is restricted.
99

Desalination Technologies
1. Thermal Desalination Processes
– Similar to the Earth’s natural water cycle
– Water is heated, evaporated and collected
– Produces clean water and brine
Example: Multi-Stage Flash Desalination
 Process uses multiple boiling chambers kept
at different atmospheric pressures
 Saltwater enters the system and is boiled and
evaporated in each chamber
 Process produces clean water and brine
100

Desalination Technologies
2. Membrane Desalination Processes
 Saltwater is forced through membrane sheets at high
pressures
 Membrane sheets are designed to catch salt ions
 Process produces clean water and brine
Example: Reverse Osmosis
 Saltwater is forced through a membrane
at 600 to 1000 psi
 Multiple layers of membranes remove as
many of the salt ions as possible
101

Desalination Plants around the World
Jabel Ali Desalination
Station in Dubai
 Capacity: 140 million
gallons per day
 Opened June 2010
DHA Desalination Plant
Owner: DHA COGEN LTD.
Capacity :03 MIGD
(million imperial gallons
of water per day)
REGISTRATION: 29th Jan 2003
102

What is Fluoridation?
 Fluoride is a naturally occurring mineral that is proven to
protect against tooth decay.
 Water fluoridation is the controlled addition of fluoride to
a public water supply to reduce tooth decay.
 Fluoridated water has fluoride at a level that is effective for
preventing cavities; this can occur naturally or by adding
fluoride.
 Almost all water contains some naturally occurring fluoride,
but usually at levels too low to prevent tooth decay.
 Fluoride helps to re-mineralize tooth surfaces and prevents
cavities from continuing to form. 103

What is De-fluoridation?
 De-fluoridation is needed when the naturally occurring
fluoride level exceeds recommended limits.
 The permissible limit of fluoride in drinking water in
Pakistan have been set up 1.5 ppm or mg/l
 A 1994 World Health Organization expert committee
suggested a level of fluoride from 0.5 to 1.0 mg/L ,
depending on climate conditions.
 Bottled water typically has unknown fluoride levels, and
some domestic water filters remove some or all fluoride
105

Methods of De-fluoridation?
 Activated carbons prepared from various materials can be used
as de-fluoridation.
 During lime soda process of water softening, fluorides are also
removed along with the removal of magnesium.
 The materials such as calcium phosphate, bone charcoal,
synthetic tri-calcium phosphate, etc may be added for removal
of excess fluoride content in water.
 Water may be allowed to pass through filter beds containing
fluoride retaining materials.
 Most of the above methods of de-fluoridation suffer from one
or the other disadvantage such as high initial cost, expensive
regeneration, poor fluoride removal capacity, etc
106

Health Hazards Linked to Fluoride
Over-Exposure
 As the number of studies into the toxic effects of fluoride has
increased, there is now support for a rather long list of
potential health problems related to fluoride accumulation in
your body.
 The following list contains the most commonly mentioned
health hazards and diseases associated with fluoride exposure:
 Lowers I.Q
 Brain damage
 Dental fluorosis (staining and pitting of teeth)
 Bone fractures
 Disrupts immune system
 Increases tumor and cancer rate
 Bone cancer
 Thyroid disease
107

Environmental Engineering

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Environmental Engineering