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An Internship Report on
Chittagong Water Supply and Sewerage
Authority (CWASA)
Submitted by-
Quock San
MS Environmental Science
ID: 08208067
Session: 2011-12
Institute of Forestry and Environmental Sciences,
University of Chittagong (IFESCU)
Date: 10th March 2014
I
ACKNOWLEDGEMENT
At first, I express my profound gratitude to the God, the gracious and most munificent, who gives me
the energy and sound health to endure the rigor of this job.
We would like to express our profound sense of gratitude to Dr. Tapan Kumar Nath, Professor and
Acting Director, Institute of Forestry and Environmental Sciences, University of Chittagong
(IFESCU), provided us an opportunity to do our internship at Chittagong Water Supply and
Sewerage Authority (CWASA).
Utmost gratitude to The Chief Engineer Md. Abdul Karim Chowdhury of CWASA who accepted us as
an internee at their company and provided us an opportunity to enrich our technical competence as
well as increasing our managerial skillfulness regarding environmental aspects.
Then we would like express our sincerest gratitude to Secretary Md. Samsudduha, and Deputy-
Secretary Jahangir Alam Chowdhury, CWASA for their pleasant and benevolent cooperation.
We owe an immense debt of gratitude to Mr. Milan Kumar Chakraborty, Senior Chemist, Mohara
Water Treatment Plant (WTP), CWASA who helped us all the time by providing necessary
information whenever we need.
We want to express our sincere thanks to Executive Engineers of CWASA Md. Sarfaraj Akhter
(Mohara WTP), Md. Ariful Islam (MOD-2), Md. Mahbubul Alam (MOD-1), and Noor Mohammad
Abul Basher (Design Section) provided us a lot of information, suggestions and accompany us during
work under his supervision in their divisions.
We are thankful to Assistant Engineers of CWASA Mr. Sajib Barua (Mohara WTP), Mr. Soumit
Paul (Booster), Mr. S. M. Rabiul Hossain (MOD-2), Md. Abdur Rouf (MOD-1) for their kind
cooperation, assistance and providing important information in their divisions.
Then we would like to thank Sub-Assistant Engineer of CWASA Mr. Rafiqul Islam for his kind
support, assistance and accompany during our work in his divisions.
We are also indebted to all officials and staffs of CWASA for their cordial help and collaboration
during our work making life easier for us, which will be useful in our future career. We apologize if we
forgot to mention names of other personnel, but however, we are extremely grateful to every one
whatever he/she has offered us during our internship.
Author
10th March 2014
II
TABLE OF CONTENTS
ACKNOWLEDGEMENT I
TABLE OF CONTENTS II
LIST OF TABLES IV
LIST OF FIGURES IV
LIST OF ABBREVIATIONS V
CHAPTER ONE: INTRODUCTION
1.1 General overview 1
1.2 Summary of Existing Facilities of CWASA 2
CHAPTER TWO: MOHARA WATER TREATMENT PLANT
2.1 General information 3
2.2 Halda River 3
2.3 Main Components of Mohara Water Treatment Plant 4
2.4 Treatment process description 4
2.5 Treatment plant design data 7
2.6 Description of Process Unit 8
2.6.1 Intake and Raw Water Pump Station 9
2.6.2 Desilting Basin 9
2.6.3 Rapid Mixture 10
2.6.4 Clarifiers 10
2.6.5 Filters 10
2.6.6 Clear Well and High Lift Pump Station 10
2.6.7 Chemical Facilities 10
2.6.8 Sludge and Backwash Facilities 11
2.6.9 Power Supply and Generator 11
III
2.6.10 Laboratory 11
2.6.11 Plant Monitoring Arrangement 13
CHAPTER THREE: KALURGHAT IRP AND BOOSTER STATION
3.1 General information 15
3.2 Source and Treatment of Water in Kalurghat IRP 15
3.3 Treatment Procedure 16
3.4 Quality of Water 17
CHAPTER FOUR: MAINTENANCE, OPERATIONS AND DISTRIBUTION
(MOD)
4.1 General information 18
4.2 Coverage area: 18
4.3 Main activities: 18
CHAPTER FIVE: DESIGN DIVISION
5.1 Activities 19
CHAPTER SIX: CONCLUSION
6.1 Conclusion 21
IV
LIST OF TABLES
Table 2.1: Daily Water Analysis of Mohara WTP 12
Table 2.2: Weekly Water Analysis of Mohara WTP 12
Table 2.3: Monthly Water Analysis of Mohara WTP 12
Table 2.4: Water Quality of Mohara Water Treatment Plant 13
Table 3.1: Quality of water before and after treatment in Kalurghat Iron Removal
Plant (IRP).
17
LIST OF FIGURES
Figure 2.1: Process Flow Schematic of Mohara WTP 6
Figure 3.1: A Flow Chart of Kalurghat Iron Removal Plant and Booster Station 16
Figure 5.1: The activities of design division of CWASA 20
V
LIST OF ABBREVIATIONS
WASA Water Supply and Sewerage Authority
CWASA Chittagong Water Supply and Sewerage Authority
WTP Water Treatment Plant
Ctg Chittagong
KV Kilovolt
KVA Kilovolt Ampere
Km Kilometer
MGD Million gallons per day
NTU Nephelometric Turbidity Unit
MLD Million Liters Per day
imp gal Imperial gallon
sft Square feet
ft Foot
m Meter
mm Millimeter
gm Gram
I or L Liter
Mg/l Milligram/liter
kw Kilowatt
lbs Pounds
ml Million liters
d Day
gpd Gallons per day
gpm Gallons per minute
fph Feet per hour
mg Million gallons
mil Million
gal Gallon
kg Kilogram
hr Hour
hp Horse Power
IRP Iron Removal Plant
PC Personal Computer
LCD Lower Circuit Panel
MOD Maintenance, Operation and Distribution
WHO World Health Organization
DO Dissolve Oxygen
BOD Biological Oxygen Demand
COD Chemical Oxygen Demand
TDS Total Dissolve Solids
Coli. Coli form
BWDS Bangladesh Water Standards
VI
PDB Power Development Board
MIS Management Information System
Internship Report
Institute of Forestry and Environmental Sciences, University of Chittagong 1
CHAPTER ONE
INTRODUCTION
1.1 General overview
Chittagong is the second largest city of Bangladesh. A part from being the main centre of trade,
commerce and industrial activities is the life line of the economy for its sea port. Country's first
Export Processing Zone was established in this city. Over the last 3 decades, Chittagong has
grown at a great pace. This decade's remarkable phenomenon in the economy of the country is
unprecedented growth of garment industry in Chittagong. Development of industries has brought
rapid increase of population. Chittagong has witnessed major growth in population over the last
3 decades; mainly due to migration from the country-side. Since 1971, the population of the city
has grown from about 0.5 million to more than 3.0 million in 2007. The city area has also
expanded. The total area of Chittagong and sub-urban areas (including proposed Hathazari and
Sitakunda) is around 270 sq. km. This kind of growth presents tremendous challenges to the
utility authorities in providing utility services. Chittagong WASA, responsible for the water
supply of port city has taken up its all necessary steps to digitalize its overall operations. For easy
access of the respected consumers to the information and data regarding CWASA, an website
has been launched. Through this website a new dimension has been added in its communication
with the respected consumers. For better customer service, CWASA facilitated the consumers
with online billing system. For improved operations of CWASA, heartiest co-operation from the
respected consumers is highly expected. CWASA is striving hard to keep pace with the city
development.
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Institute of Forestry and Environmental Sciences, University of Chittagong 2
1.2 Summary of Existing Facilities of CWASA
Facility Quantity Capacity
Surface WTP 1 no. 90 MLD
Ground WTP 1 no. 68 MLD
Deep Wells 91 nos. 115 MLD
Pipeline 610km -
Reservoirs 14 46,142 ML
HL & Booster 4 & 3 -
Service Conn. 57,043 nos. -
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Institute of Forestry and Environmental Sciences, University of Chittagong 3
CHAPTER TWO
MOHARA WATER TREATMENT PLANT (WTP)
2.1 General information
The Mohara Water Treatment Plant is the part of the city of Chittagong Water Supply
and Sewerage Authority’s (CWASA).
Commissioning: Commissioned in December 1987.
Capacity: Its Capacity is 20 million gallon per day (MGD).
Source: River Halda at a point nearly half a mile upstream from its confluence with
the river Karnaphuli.
2.2 Halda River
Originates at the Badnatali Hill ranges in Ramgarh Upazila in the Ctg. Hill Tracts.
Flows through Fatickchari Upazila, Hathazari Upazila, Raozan Upazila and Kotwali
Thana, and falls into the Karnaphuli River.
81km long river has a very turbulent tributary.
The Dhurung River, which joins Purba Dahlai about 48.25 km downstream.
Navigable by big boats 25km into it (up to Nazirhat) and by small boats 16-24km
further (up to Narayanhat).
Halda is famous for breeding Pure Indian carp.
This is the only pure Indian carp breeding field of Bangladesh, perhaps in South Asia.
2.3 Main Components of Mohara Water Treatment Plant
Intake and Raw Water Pump Station
Desilting Basin
Rapid Mixer
Clarifier
Filter
Chlorine Contact Chamber and Clear Well
High Lift Pump Station
Chemical Facility
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Institute of Forestry and Environmental Sciences, University of Chittagong 4
Sludge and Backwash Facility
Power and Standby Generator
Laboratory
Plant Monitoring Arrangement
2.4 Treatment process description
The objectives of the Mohara water treatment plant are not only to provide safe water for
human consumption and appealing to consumers, but to bring the water quality within the
limit of the maximum allowable standards set by the World Health Organization (WHO).
The raw water for the Mohara Water Treatment Plant is taken from the Halda River. The
Halda River Water contains varying level of alkalinity (10-75 mg/l) and turbidity (15-350
NTU). These variations are a result of seasonal changes with the monsoon season causing the
higher turbidities, low alkalinities and high level of suspended solids. The overall treatment
process units include an intake structure with bar racks, pump station, raw water rising main,
desilting basins, rapid mixtures, clarifiers, filters, clear well, high-lift pump station, sludge
and backwash facilities, standby power generator, chemical building and facilities and
administration building. The intake structure and pump station are located on the west bank
of the Halda River. The intake structure contains five separate compartments, each with a
capacity of 45 ml/d (10 imp mgd). Hand raked bar screens is located in each compartment to
prevent the entry of coarse debris and floating material. Each compartment includes a pipe
that connects the intake structure to the raw water pump station. Provisions have been made
for five raw water pumps, but initially two duty pumps and one standby pump have been
provided. After the intake structures, the raw water are lifted by the raw water pumps to
either the desilting basins or directly to the rapid mix units. Two desilting basins are provided
to reduce heavy sediment loads to the clarifiers during the monsoon season, but may be
bypassed during the dry season. Provision is made to add alum to the water at the raw water
meter vault to aid in the settling of suspended solids in the desilting basin if necessary.
After desilting the next process steps are chemical injection, flash mixing and coagulation.
Mixing takes place in two upflow chambers in series by means of vertical turbine mixtures.
Chemicals added at this point include alum for coagulation, chlorine for aquatic growth
control and when necessary lime for pH adjustment. Chemically dosed water flows from the
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Institute of Forestry and Environmental Sciences, University of Chittagong 5
mixing chambers to a series of 24 upflow, inverted pyramid shaped, solid-contacts
clarification tanks. The hydraulic energy released at the bottom of the tank by the incoming
coagulated water results in a decreasing mixing action as the water rises up the diverging
tank and sludge blanket. Sludge is drawn off each clarifiers sludge blanket continuously by
fixed sludge conditioning or periodically by a draw off pipe for the sludge which settles to
the bottom and consolidates when the tank is taken out of service for cleaning.
Clarified water is separated from the sludge blanket and collected near the surface with
submerged orifice launders and flows by gravity to the filters. The filters are inflow splitting,
constant rate, variable head, self-backwashing, rapid unisized mono-media sand filters. The
filters operate until the rising water surface in the filter box reaches the maximum level at
which time the filter must be taken out of service and backwashed. Backwashing is
accomplished by stopping the inlet flow with a manually operated plug. Filtered water from
the operating filters flows back through the clogged filter to clean the media. The backwash
waste water flows over the central backwash water channel and out to waste.
Filtered water flows by gravity into the chlorine contact zone of the clear well, where
chlorine is added for disinfection. From the contact zone the water flows over a weir into the
clearwell. The weir ensures that filtered water has a 30- minute contact time after the addition
of chlorine and maintains a constant head available for filter backwashing. The clearwell is
divided into two halves to allow alternative cleaning.
The high lift pump station is next to the clearwell. Five (four duty one standby) constant-
speed, electric, vertical centrifugal pumps delivered the treated water to the Battali hill
reservoir.
Sludge comes from three sources: the desilting basins, the clarifiers and filter backwashing.
The sludge side streams will be returned to the Halda River downstream of the plant raw
water intake. Typically the river surface is low enough to allow silt, sludge and backwash
water to flow by gravity through a pipeline to discharge in the river. During times of
relatively high tides or river flooding, backed up water will close a check valve diverting
sludge and backwash water into the wet well of the sludge and backwash water pumping
facility, where they will be lifted enough to permit gravity flow to the river. Three duty pump
and one standby pump are provided at the sludge and backwash facility to handle the sludge
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Institute of Forestry and Environmental Sciences, University of Chittagong 6
and wash water from the clarifiers and the filters respectively. Silt and sludge is withdrawn
from the desilting basins by gravity when the river stage is low enough.
Figure 2.1: Process Flow Schematic of Mohara WTP
2.5 Treatment plant design data
Plant criteria for the Mohara Water Treatment Plant are listed as follows:
Design Data:
Capacity: 91 ml/day
Raw Water Pumps:
Number-duty/standby 2/1
Capacity-each 45/day (12.7 imp mgd)
FILTERS
(8)
ALUM
FLOW
METER
RAW WATER
PUMPS (3)
SLUDGE & BACK
WASH WATER
PUMPS (4)
CLEAR WELLHIGH LIFT
PUMPS (4)
FLOW
METER
LIME
Cl2
PROCESS FLOW SCHEMATIC
BYPASS
SLUDGE CHANNEL
SL
UD
GE
& B
AC
KW
AS
H C
HA
NN
EL
TO DISTRIBUTION
DESILTING
BASIN (2)
HALDA RIVER
INTAKE &
SCREEN
CLARIFIERS
(24)
Alum
Cl2Lime
RAPID MIX
CHAMBERS
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Institute of Forestry and Environmental Sciences, University of Chittagong 7
Power-each 110 kW (132 hp)
Desilting Basins:
Number 2
Overflow rate 0.18 mm/s (312imp gpd/sqft)
Detention time 120 minute
Flash Mixers:
Number 2
Detention time 10 s/chamber
Power-each 5.6 kW (7.5 hp)
Clarifiers:
Number 24
Type Upflow solids contact
Detention time 1.2 hours
Overflow rate 0.75 mm/s(1333imp gpd/sqft)
Minimum upflow velocity 0.75 mm/s (8.9 fph)
Filters:
Number 8
Area-each 22.3m2 (480 sq. ft.) each half 2.44m *9.1m (8 ft*30 ft)
Controls Influent-splitting Self-backwashing
Media type Unisized, mono media sand
Media size 0.85-1.2 mm
Media depth 1.22 m (4ft)
Loading 3.1 mm/s (3.8imp gpm/sq ft)
Backwash Rate 16.3 mm/s (20imp gpm /sq ft)
Clear well
Chlorine contact zone
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Volume 2.27 ml (500000 imp gal)
Detention time 30min at91 ml/d(20imp mgd)
Clearwell volume 11.4 ml (2.5 mil/imp gal)
Standby power generation:
Number 2
Type Diesel fuel
Size 1000 kW
High-lift Pumps:
Number-duty/standby 4/1
Capacity-each 22.5 ml/d (5imp mgd)
Power-each 350 kW (468 hp)
Sludge Backwash Facility Pumps:
Number-duty/standby 3/1
Capacity-each 645 L/S (2250 imp gpm)
Power-each 22.4KW (30 hp)
2.6 Description of Process Unit
2.6.1 Intake and Raw Water Pump Station
20 MGD with necessary provision & space for expansion up to 40 MGD.
Intake & Raw water pumping station constructed for 40 MGD capacity to meet future
requirement.
Since construction of Intake structure on the river bank is difficult & expensive.
2 Nos. duty & 3 Nos. Stand-by Raw Water Pumps of capacity 11 MGD & 132/160 KW
each.
2.6.2 Desilting Basin
Turbidity level varies from 20 NTU to 800NTU.
Provision for two desilting basins has been made.
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During monsoon river water first brought to the desilting basins. Turbidity reduced by
the settlement of mud, sludge etc.
In winter, water directly passes to the rapid mixing chamber through a by-pass system.
Desilting basins overflow rate 311gpd/sqft and detention time 120 minutes.
2.6.3 Rapid Mixture
Water from desilting basins/raw water pump station comes in the Rapid mix chamber.
Alum & lime is mixed with water.
Alum & lime are injected at the rapid mix chamber from the Chemical Building.
Two rapid mixtures of 7.5 hp each with detention time 10 second/chamber.
2.6.4 Clarifiers
24 Nos. hopper bottomed up-flow type clarifiers.
Water from rapid mix chamber come to the bottom of clarifier through 12" dia ductile
iron pipe from incoming channel.
Velocity of incoming water is reduced considerably when it comes to the top of the
clarifier.
Almost all the settle able materials settle down in the clarifiers and clean water are
collected to the filters.
Minimum flow velocity of 8.9 ft/hr with detention time 1.2 hrs & over flow rate 1333
gpd/sqft.
2.6.5 Filters
8 Nos. cells down flow conventional type rapid gravity filters.
Water from clarifier comes to the filter & passes through sand & gravel media.
All suspended materials & most of the bacteria are entrapped in filter media and clean
water is collected in the contact chamber for disinfections.
After disinfections collected in the clear well.
Each filter has an area of 480 sqft.
Filter media is sand monosized 0.85 -1.0 mm & 4' depth.
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The average loading 3.8gpm/sqft & back wash rate 20gpm/sqft.
Provision is kept for regular cleaning of filter media by back wash system.
Water from clear water channel of filter passes in a reverse direction from the bottom of
filter, cleaning the accumulated film of deposits.
To ensure top of the media adequately cleaned, an auxiliary fixed nozzle surface wash is
provided.
The back wash water passes to sludge tank & finally pumped out to river Halda.
2.6.6 Clear Well and High Lift Pump Station
Treated water from the filters is received in a 2.5 MG reservoir after disinfections in the
chlorine contact chamber.
Treated and disinfected water is pumped to the city by 4 Nos. pump duty and 1 no. stand-
by high lift pumps of capacity 3475 gpm and 320 KW each.
Chlorine contact time in the contact chamber is 30 minute at 20 mgd.
2.6.7 Chemical Facilities
Alum & lime are added to the water for aiding the flock formation & pH adjustment.
Provision is made to add alum to the water at the raw water venturi meter vault to aid in
the settling of suspended solids in the desilting basin during high turbidity.
Chlorine also injected to the water at rapid mixture and at contact chamber of clear well
for preventing any growth of algae & disinfections purpose.
Necessary storage, mixing & dosing of chlorine, alum and lime are done by pumps
centrally from the chemical building.
Re-circulation pumps of capacity 167 gpm re-circulate the alum solution within the alum
tank to promote the dissolution of lump alum to keep the alum solution mixed.
Hydrated lime is mixed by turbine impeller type mixture to make suspension of lime
slurry.
Alum & lime proportioning positive displacement diaphragm type pumps meter out the
correct Alum/lime dosage from the mixing tank.
The high capacity vacuum type chlorinators dose chlorine.
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2.6.8 Sludge and Backwash Facilities
Sludge that is collected at the bottom of clarifiers & desilting basins and back wash water
from filters is collected to sludge tank.
From where it is pumped out to the river Halda at a safe distance.
There are 4 pumps (with one standby) of each 2245 gpm at 13 ft and 30 hp capacities.
2.6.9 Power Supply and Generator
High lift pumps are operated at 3.3 KV.
Other pumps are operated at 0.415 KV.
Two 33 KV power supply from PDB directly from Madunaghat and Mohara Substation.
One stand-by diesel generator of 2500 KVA installed for use during any power failure.
2.6.10 Laboratory
The objective of the Mohara WTP is not only to provide water safe for human
consumption & appealing to consumers. But to bring the treated water quality within the
limits of the maximum allowable standards set by the World Health Organization
(WHO).
To this end laboratory in the plant is equipped with various sophisticated instruments for
regular testing of turbidity, pH, residual chlorine, alkalinity, hardness, TDS etc.
Depending on raw water quality the quantity of chemicals such as alum, lime and
chlorine are also determined through various tests.
Table 2.1 Daily Water Analysis of Mohara WTP
Sl. Parameter Unit
9.12.2009 10.12.2009
BWDS WHO
BWDS Raw
water
Treated
water
Raw
water
Treated
water
1 pH - 6.93~6.97 7.01~7.06 6.93~6.98 7.01-7.08 6.5-8.5 -
2 Turbidity NTU 60~100 0.8~0.98 60~100 0.8-0.99 10 5
3 T- Alkalinity mg/l 53~56 60~64 54~56 65-67 - -
4 Res. Chlorine mg/l . 0.61~0.69 - 0.59-0.68 0.2 -
5 Chloride mg/l 12~24 12~22 12~26 14~25 150-600 250
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Table 2.2 Weekly Water Analysis of Mohara WTP
Sl. Parameter Unit
9.12.2009 10.12.2009
BWDS WHO
BWDS Raw
water
Treated
water
Raw
water
Treated
water
1 T-Fe mg/l - 0.42 - 0.38 0.3-1 0.1-1
2 Mn. mg/l - 0.08 - 0.05 0.1 0.05-0.5
3 Coli. Bacteria Col/100
ml 2800 0 2250 0 0 0
4 TDS mg/l - 112 - 130 1000 1000
5 Ca Hardness mg/l - 25 - 31 - -
6 T-Hardness mg/l - 54 - 65 500 -
Table 2.3 Monthly Water Analysis of Mohara WTP
Sl. Parameter Unit
9.12.2009 10.12.2009
BWDS WHO
BWDS Raw
water
Treated
water
Raw
water
Treated
water
1 DO mg/l 7.8 7 8.2 7.8 6 -
2 BOD mg/l 1.1 1.01 2.2 0 0.2 -
3 COD mg/l 38 2 32 3 4 -
4 As mg/l - <0.004 - <0.003 0.05 0.01
5 Cd mg/l - <0.001 - 0.002 0.005 0.003
6 Cr mg/l - 0.002 - 0.003 0.05 0.05
7 Pb mg/l - 0 - 0 0.05 0.01
8 Zn mg/l - 0.12 - 0.2 5 3
9 CN mg/l - <0.02 - <0.01 0.1 0.07
10 F mg/l - 0.3 - 0.4 1 1.5
11 NH3-N (NH3) mg/l - 0.2 - 0.3 0.50 1.5
12 NO3-N (NO3) mg/l - 1.3 - 2.8 44 -
13 PO4 mg/l - 0.18 - 0.2 6 -
14 SO4 mg/l - 12 - 16 - 250
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2.6.11 Plant Monitoring Arrangement
PC monitoring system installed in the control room of main administrative building.
PC monitor LCD panel contains graphic display, plant alarm, and status indicators of
treatment plant process.
Plant intercoms paging systems for easy communication of the operation staffs within the
plant installed.
Table 2.4 Water Quality of Mohara Water Treatment Plant
No. Parameter Unit
Mohara Water Treatment Plant
Ba
ng
lad
esh
Sta
nd
ard
WH
O
Sta
nd
ard
Raw water
(Halda river)
Treated water
Min Max Min Max
1 Water temperature Degree
Centigrade 28 29 24 25 …… ……
2 Conductivity Micro
Siemens/cm …… …… 90 600 …… ……
3 pH NTU 6.4 7.2 6.9 7.4 6.5-8.5
4 Turbidity Mg/Liter 20 830 0.50 1.0 10 Max. 5 Max.
5 T-alkalinity Mg/Liter 34 70 35 70 …… ……
6 Calcium hardness Mg/Liter 22 28 24 30 …… ……
7 T hardness Mg/Liter 50 92 50 80 500 Max. 500 Max.
8 Ammonia-nitrogen Mg/Liter 0.2 0.4 0.2 0.4 0.5 Max. ……
9 Nitrate-nitrogen Mg/Liter 1.6 3.4 1.3 3.2 10 Max. 10 Max.
10 Phosphate Mg/Liter 0.30 0.61 0.18 1.2 6 Max. ……
11 Chloride Mg/Liter 4 200 4 200 600 Max. 250 Max.
12 Residual chlorine Mg/Liter …… …… 0.41 0.72 0.2 Min.
13 Sulphate Mg/Liter 13 28 156 20 400 Max. 400 Max.
14 Iron Mg/Liter 0.18 1.0 0.20 0.50 0.3-1.0 0.1-1.0
15 Manganese Mg/Liter …… …… 0.05 0.08 0.1 Max. 0.5 Max.
16 S.S. Mg/Liter 30 1000 1.0 3.0 10 Max. ……
17 TDS Mg/Liter …… …… 70 300 1000
Max. 1000 Max.
18 DO Mg/Liter 6.0 7.9 7.0 8.0 6 Min. ……
19 BOD Mg/Liter 0.9 1.2 …… 0.1 0.2 Max. ……
20 COD Mg/Liter 12 18 …… 2 4 Max. ……
21 Fecal bacteria Colonies /
100 ml 1800 2400 00 00 00 00
22 Arsenic Mg/Liter 0.001 0.004 0.001 0.004 0.05 Max. 0.01 Max.
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23 Cadmium Mg/Liter 0.001 0.003 0.003 0.005Max
.
0.005
Max.
24 Chromium Mg/Liter 0.004 0.009 0.008 0.05 Max. 0.05 Max.
25 Cupper Mg/Liter 0.4 0.7 0.06
26 Lead Mg/Liter 0.001 0.009 0.002 0.05 Max. 0.05 Max.
27 Mercury Mg/Liter 0 <0.001 <0.001 1 Max. 1 Max.
28 Zinc Mg/Liter 0.11 0.14 0.11 0.12 5.0 Max. 5.0 Max.
29 Cyanide Mg/Liter <0.02 …… <0.02 …… 0.1 Max. 0.1 Max.
30 Fluoride Mg/Liter 0.20 0.30 0.20 0.30 1.0 Max. 0.05 Max.
31 Trihelomethane Mg/Liter …… …… …… 0.037 …… 0.1 Max.
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CHAPTER THREE
KALURGHAT IRON REMOVAL PLANT (IRP) AND
BOOSTER STATION
3.1 General information
The second source of water of CWASA is extraction of ground water. There have more than 90
deep tube-wells in Chittagong city, by which CWASA extract ground water. The deep tube-wells
of Kalurghat region provide ground water with containing high concentration of Iron. Due to this
reason, CWASA treated this water before supply to the city dwellers. The production capacity of
Kalurghat Iron Removal Plant (IRP) is 64 MLD (Million Liter per Day) water. Now, water
supply from Kalurghat Iron Removal Plant (IRP) is 45 MLD. There have total 7 pumps which
are to create pressure in distribution line. For continuous electricity supply in this station, there
have a generator which able to supply 1750 KVA electricity during load-shedding.
3.2 Source and Treatment of Water in Kalurghat IRP
The source of water is ground water in Kalurghat Iron Removal Plant (IRP). Kalurghat Iron
Removal Plant (IRP) is treated water coming from 41 tube-wells. Among these tube-wells 39 is
in MOD-2 area and 2 in MOD-1 area. The main purpose of treatment of ground water in
Kalurghat IRP is removal of hardness of water. Hardness is the sum of all multivalent ions,
mainly calcium and magnesium. Water is considered to be hard if it contain 150 mg/l as calcium
carbonate (CaCO3) or more. Ground water also contains high concentration of carbon dioxide
(CO2). Lime is used to remove carbon dioxide (CO2) and hardness of water. Excess carbon
dioxide (CO2) concentration is reduced through aeration and also lowers lime requirements.
Calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2) compounds are able to
precipitate out of water. If non-carbonate hardness also needs to be removed from water, then
soda ash (Na2CO3) must be added to the water along with lime. Relevant chemical reaction is
given below:
Removal of Carbon dioxide (CO2):
CO2 + Ca (OH) 2 → CaCO3 ↓ + H2O
Lime
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Institute of Forestry and Environmental Sciences, University of Chittagong 16
Removal of Carbonate Hardness:
Ca (HCO3)2 + Ca (OH) 2 → CaCO3 ↓ + H2O
Calcium bicarbonate Calcium carbonate
Mg (HCO3)2 + Ca (OH) 2 → CaCO3↓ + MgCO3 + H2O
Magnesium bicarbonate Magnesium carbonate
MgCO3 + Ca (OH) 2 → CaCO3↓ + Mg (OH) 2↓
Magnesium hydroxide
3.3 Treatment Procedure
At first, extracted ground water comes to the aeration tower. There are two aeration towers. Then
water move to the sedimentation basin. Before coming sedimentation basin water mixes with
lime solution. There have two sedimentation basin, where calcium carbonate (CaCO3) and
magnesium hydroxide (Mg (OH) 2) compounds are precipitated. Then water is filtered by rapid
sand filter. There have 8 filters in Kalurghat IRP. The filtered water move to clear-well by
mixing with chlorine. Then from clear-well water move to distribution line by distribution pump.
The process is shown in a flow chart in below. (Figure: 3.1)
GROUND WATER FROM TUBE-WELL
AERATION TOWER
Lime Dosing
SEDIMENTATION BASIN
FILTERS
Chlorine Dosing
CLEAR WELL
DISTRIBUTION PUMP
TO MAIN TRANSMISSION LINE
Figure 3.1: A Flow Chart of Kalurghat Iron Removal Plant and Booster Station
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Institute of Forestry and Environmental Sciences, University of Chittagong 17
3.4 Quality of Water
Table 3.1: Quality of water before and after treatment in Kalurghat Iron Removal Plant
(IRP)
PH Fe
(mg/L)
T-Alkanity
(mg/L)
Cl2
(Mg/L)
T-
Hardness
(mg/L)
Residual
Cl2 (mg/L)
Before Filter 6.98 2.2 114 18
After Filter 7.11 1.4 118 18
Clear-well 7.21 0.72 128 20 80 0.58
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Institute of Forestry and Environmental Sciences, University of Chittagong 18
CHAPTER FOUR
MAINTENANCE, OPERATIONS AND DISTRIBUTION (MOD)
4.1 General information
This division of CWASA is responsible for the overall maintenance of water distribution in the
Chittagong city area. This division has two sections; these are MOD-1 and MOD-2.
4.2 Coverage area
MOD-1 operates the south-western part of Chittagong city from Dewanhat to Katgarh and
Katgarh to Salimpur. MOD-2 operates the north-eastern part of Chittagong city from Lalkhan
Bazar to Kalurghat, Kalurghat to Akbarshah including Chittagong Cantonment area.
4.3 Main activities:
The main responsibilities of MOD division are
Pipeline operation (such as pipe leakage mend, pipe set-up etc.)
Water distribution
Regular tube-well maintenance
Customer handling
Regeneration of tube-well.
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CHAPTER FIVE
DESIGN DIVISION
5.1 Activities
The main activity of Design Division of CWASA preserves documents of CWASA as built
drawing. These documents include pipeline design, distribution system map, treatment plant
design, tube-well distribution map, GIS data, MIS (Management Information System) Report
etc. MIS report is the total information of whole management of CWASA. This division also
arranges different training on their activity. The activity of design division of CWASA is given
in below chart (Figure No: 5.1)
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Institute of Forestry and Environmental Sciences, University of Chittagong 20
Design Division
Training M.I.S. (JICA) Bench Mark
(World Bank)
As Built
Drawing
G. I. S.
Non-Revenue
Water
Revenue Collection
Efficiency
Collection Period
No. of Permanent
Employee per %
Operating Ratio
Functioning Meter
of Installed Meter
Water Quality
Sample
Leakage Occurrence
Water Supply
Coverage
Average Tariff
Unit Production
Cost
Chief Revenue Officer
MOD-1
Accounts (M)
Mohara
Sales
Superintend Engineer
(MOD)
Secretariat
Computer Programmer
MOD-2
Accounts (Finance)
Construction Division-1
Sales
Construction Division-1
MOD-1
MOD-2
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CHAPTER SIX
CONCLUSION
5.1 Conclusion:
CWASA is one of the leading utility service provider government organizations in Bangladesh.
As a utility service Chittagong Water Supply and Sewerage Authority (CWASA) have great
contribution to development of Chittagong city. Despite of some sorts of limitation, they hardly
try to produce maximum quality water within their capacity to serve the citizens of Chittagong
city. I had the opportunity to work in this organization during my internship program. As a
student of Environmental Science, I have worked in engineering section of CWASA. During this
time I got an opportunity to observe the overall activities of CWASA specially treatment,
maintenance, operation, distribution and designing. As a utility service provider government
organization the overall management system of CWASA is well organized.