GOVERNMENT COLLEGE OF ENGINEERING, KARAD

A Minor Project Report on,

“DESIGN OF SEWAGE TRETMENT PLANT FOR

KOLHAPUR CITY”

DEPARTMENT OF CIVIL ENGINEERING

ACADEMIC YEAR 2022 – 2023

B. TECH THIRD YEAR CIVIL ENGINEERING

Submitted by,
(21113275) ATHARV VIJAY DEORE
(21113277) PRASAD SANJAY LONISHTE
(21113178) DHANASHRI VITTHAL THOMBARE

(21113279) PAVAN LAHU PAWAR

(21113180) ANUSHKA MANSING PATIL

UNDER THE GUIDENCE OF

PROF. M.Y. JADHAV
1
 This is to certify that,
(21113275) ATHARV VIJAY DEORE
(21113277) PRASAD SANJAY LONISHTE
(21113178) DHANASHRI VITTHAL THOMBARE

(21113279) PAVAN LAHU PAWAR

(21113180) ANUSHKA MANSING PATIL

Studying in T.Y. B. Tech civil has successfully completed project

entitled

“DESIGN OF SEWAGE TRETMENT PLANT FOR KOLHAPUR

CITY”

Under guidance of Prof. M.Y. JADHAV during academic year 2022-2023

Prof. M.Y. JADHAV Prof. S.V. JOSHI

Guide & Asst. Professor Head of Department
Dept. of Applied Mechanics. Dept. of civil Engg.
GCE, Karad. GCE, Karad.

2
 ACKNOWLEDGEMENT

The success and final outcome of the project required a lot of guidance and
assistance from many people and we are extremely privileged to get this all along the
completion of our project. All that we have done is only due to such supervision and
assistance of our project guide Prof. M. Y. Jadhav and thank her for providing us an
opportunity to work on the project “DESIGN OF SEWAGE TRETMENT PLANT FOR
KOLHAPUR CITY” in Government College of Engineering, Karad. We are also thankful to
Prof. S. V. Joshi for giving us such an opportunity. We are very thankful to Dr. A. T. Pise,
Principal of Government College of Engineering, Karad for providing all the necessary
facilities to carry out project work. We take this opportunity to thank all our lecturers
who have directly or indirectly helped our project.

3
 ABSTRACT

Sewage treatment is a type of wastewater treatment which aims to remove

contaminants from sewage to produce an effluent that is suitable for discharge to the
surrounding environment or an intended reuse application, thereby preventing water
pollution from raw sewage discharges. Sewage contains wastewater from households
and businesses and possibly pre-treated industrial wastewater. In this study we are
focusing on the sewage treatment plant in the Kolhapur city. Currently the STP in the
Kolhapur city is fulfilling the requirements of the city but after few years due to increase
in population this treatment plant will get over flooded. To avoid excess burden on the
treatment plant we design a supplementary sewage treatment plant near to existing
sewage treatment plant. In this project we design supplementary sewage treatment
plant up to year 2035. Detailed design, approximate expenditure for its construction, 2d
drawing will be prepared. This treated water will be available for various activities which
indirectly reduces the water pollution in Kolhapur city.

4
 CONTENTS
SR. PARTICULARS PAGE
NO NO
I ACKNOWLEDGEMENT 3
II ABSTRACT 4

1 CHAPTER NO-1
(INTRODUCTION)

1.1 What is Sewage Treatment Plant? 10

1.2 Need of Sewage treatment plant 11
1.3 Advantages of STP 11
1.4 Disadvantages of STP 12
1.5 If STP not provided… 12
1.6 Existing sewage treatment plant in Kolhapur 13

2 CHAPTER NO- 2
(LITERATURE REVIEW)

2.1 Characteristics of waste water 16

2.1.1 Physical characteristics 16
2.1.2 Odour 16
2.1.3 Colour 16
2.1.4 Floatable matter 16
2.1.5 Temperature 16
2.1.2 Chemical characteristics 17
2.1.3 Biological characteristics 19
2.1.4 Constituents of sewage 20
2.1.5 Treatment process of sewage 21
2.1.6 Primary treatment of sewage 21
2.1.7 Secondary treatment of sewage 25

5
 CONTENTS

SR. PARTICULARS PAGE

NO NO
2.1.8 Tertiary treatment 30
2.1.9 Permissible limit of sewage disposal 31
3 CHAPTER NO-3
(DESIGN PROCEDURE)
3.1 Screening tank 33
3.2 Grit chamber 35
3.3 Primary settling tank 37
3.4 Aeration tank 38
3.5 clariflocculator 41
3.6 Sludge tank 43
3.7 Sludge thickener 44
3.8 Sludge digester 46
3.9 Sludge drying bed 50

4 CHAPTER NO - 4

(AUTO-CAD 2 D DRAWING) 51

5 CHAPTER NO – 5
(APPROXIMATE ESTIMATE OF STP) 52

6 CHAPTER NO – 6
(CONCLUSION) 54

7 References 55

6
 LIST OF FIGURES

FIG.NO PARTICULARS PAGE NO

1 Kasaba STP 14
2 Dudhali STP 14
3 Sewage sludge constituents 20
4 Treatment procedure of sewage 21
5 Primary treatment 21
6 Coarse screen 22
7 Grit chamber 23
8 Primary settling tank 24
9 Primary settling basin 24
10 Secondary treatment 25
11 Activated sludge process 25
12 Aeration tank 26
13 Diffused aerator plates 27
14 clariflocculator 27
15 Sludge digester 28
16 Sludge thickener 29
17 Sludge drying bed 29
18 Tertiary treatment 30
19 Permissible limit of sewage disposal 31

7
 Abbreviations

• STP – Sewage Treatment Plant

• PST – Primary Settling Tank
• ST1 – Screening Tank
• GC - Grit Chamber
• AT – Aeration Tank
• SST – Secondary Settling Tank
• ST2 – Sludge Tank
• ST3 – Sludge Thickener
• SD - Sludge Digester
• SDB – Sludge Drying Bed
• D – Diameter
• V – Volume
• A – Area
• MLD – Million-Liter Day
• MLSS – Mix Liquor Suspended Solids
• BOD - Biological Oxygen Demand
• COD – Chemical Oxygen Demand
• SVI - Sludge Volume Index
• PH – Potential of Hydrogen Ions
• RAS – Reverse activate sludge
• AST – Activated sludge treatment

8
 CHAPTER NO - 1

INTRODUCTION

9
1) Introduction

1.1) What is Sewage treatment plant?

As we all know, Sewage/Wastewater are essentially the water supply of the community
after it has been fouled by a variety of uses from the standpoint of sources of generation,
wastewater may be defined as a combination of the liquid (or water) carrying wastes removed
from residences, institutions, commercial and industrial establishments, together with such
groundwater, surface water and storm water as may be present.
Generally, the wastewater discharged from domestic premises like residences,
institutions and commercial establishments is termed as “Sewage/Community wastewater”. It
comprises of 99.9% water and 0.1% solids and is organic because it consists of carbon
compounds like human waste, paper, vegetable matter etc. Besides community
wastewater/sewage, there is industrial wastewater in the region. Many industrial wastes are
also organic in composition and can be treated chemically and/or by micro-organisms in the
same way as sewage.
Sewage treatment systems were introduced in cities after Louis Pasteur and other
scientists showed that sewage borne bacteria were responsible for many infectious diseases.
The early attempts, in the 1900s, at treating sewage usually consisted of acquiring large farms
and spreading the sewage over the land, where it decayed under the action of micro-organisms.
It was soon found that the land became 'sick'. Later attempts included the discharge of
wastewater directly into the water bodies, but it resulted in significant deterioration of the
water quality of such bodies. These attempts relied heavily on the self-cleansing capacities of
land and water bodies and it was soon realized that nature couldn’t act as an indefinite sink.
The construction of centralized sewage treatment plants began in the late 19th and early
20th centuries. Instead of discharging sewage directly into a nearby body of water, it was first
passed through a combination of physical, biological, and chemical processes that removed
some or most of the pollutants. Also beginning in the 1900s, new sewage-collection systems
were designed to separate storm water from domestic wastewater, so that treatment plants did
not become overloaded during periods of wet weather.

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 1.2) Need of Sewage Treatment Plant
The following points shows necessities of sewage treatment plant in environment such as:
i. The main goal of wastewater treatment facilities is to protect humans and the ecosystem
from harmful and toxic elements found in wastewater. Water treatment facilities were
designed to speed up the natural process of purifying water because the natural process is
overloaded.
ii. The overall aim of treating sewage is to produce an effluent that can be discharged to the
environment while causing as little water pollution as possible, or to produce an effluent that
can be reused in a useful manner. This is achieved by removing contaminants from the
sewage. It is a form of waste management.
iii. The purpose of a sewage treatment plant is to treat the wastewater as thoroughly as
practically possible – and, even though such plants can often deal with more waste than a
septic tank, they will still need emptying from time to time.

1.3) Advantages of Sewage treatment plant

The Advantages of sewage treatment plant are as follows:
i. Gone are the days when sewage was cleared manually by the workers. With the advent of the
latest technology, everything has gone exceptionally smoothly. A sewage treatment plant can
treat large amounts of sewage quickly, making it more time-efficient. Apart from this now,
wastewater is filtered so that it can be reused for other purposes.
ii. the sewage treatment plant occupies very little space, and hence it’s convenient for you to set
up at your big or a small store. They are compact and easy to transport.
iii. Sewage treatment plants do not have a complex structure for installation. They are
straightforward to install, have low plant operations. They can be installed even above the
ground and are very reliable.
iv. STP’s are eco-friendly. They reduce the risk to public health and the environment. It has a
well-proven technology to offer reliable performance at all times. The most significant
advantage of STP is that they preserve the natural environment against pollution at all times.
v. Reliable and unlikely to encounter problems with only regular maintenance.
vi. Sewage treatment plant Can be installed even on challenging or compact sites.

11
1.4) Disadvantages of Sewage treatment plant

There are some disadvantages of sewage treatment plant are follows:

i. The sewage treatment plant’s operating system requires an endless amount of electricity
to operate. In the absence, it can potentially stop working and even cause a few
problems.
ii. Though Sewage treatment plant are designed to be eco-friendly, some facilities still
leave an environmental impression when water is treated. Because the organic waste
treated needs to go somewhere, and sometimes it causes harm.
iii. A STP requires annual maintenance to check its proper functioning. If you fail to incur
maintenance costs at the end of the year or forget to maintain it, you probably have
missed out on something important.
iv. Design and installation of the system needs to be undertaken professionally.

1.5) If STP is not provided –

The overall aim of treating sewage is to produce an effluent that can be
discharged to the environment while causing as little water pollution as possible, or to
produce an effluent that can be reused in a useful manner. This is achieved by removing
contaminants from the sewage. It is a form of waste management.
The water treatment plants remove the chemicals, particulates, organic materials
as well as other debris from the water and treat the water resulting in clean and potable
water that can be used for cooking, cleaning, etc.
As an important municipal infrastructure, wastewater treatment plant plays a
significant role in reducing water environmental pollution caused by direct discharge of
wastewater. The environmental quality standard for surface water is not necessarily
consistent with the discharge standard for wastewater treatment plant.
If sewage treatment plant is not provided all waste water will accumulate. There
will be irritation of bad odour to human. There will be chances of spreading diseases
due to this sewage. & Indirectly human life will be in danger.

12
1.6) Existing sewage treatment plant in Kolhapur city

Presently Kolhapur Municipal corporation supplies around 120 MLD of water daily
to its citizen of which about 100 MLD of wastewater is generated in the city. This waste
water/sewage if this city is partially collected through underground drainage system at
Jayanti & Dudhali pumping station & also through nalla channels.

There are about 12 nallas in the city of which prominent ones are Jayanti nala&
Dudhali nalla. The Jayanti Nala carries majority flow of about 55 MLD is successfully
diverted to 76 MLD STP at Kasaba Bawada from October 2014.The Dudhali nalla having
17 MLD flows is diverted to Dudhali STP which is commissioned on 1/07/2012. Also,
Line bazar Nalla (5.5 MLD) is diverted Kasaba bawada STP on 27th November 2019 &
Bapat Camp Nalla (11.5 MLD) is diverted to Kasaba bawada STP on 04/12/2019 by
means of respective pumping station at these nalla. In this way by 04-12-2019 the total
quantity of wastewater flow diverted is around 93 MLD out of 100 MLD wastewater
generated.

The wastewater of other remaining 6 Nallas namely Lakshtirth, Rajhans,

Ramanmala, Dreamworld, Kasaba bawada & Vitbhatti nalla which combinedly
contributes around 10 MLD will be diverted newly constructed Sewage treatment plant
of Dudhali STP (4 MLD) & Kasaba Bawada (6 MLD) STP which is commissioned on
31/03/2020 under the AMRUT Yojna Scheme of central government. So, in this way by
31/03/2020 the total quantity of wastewater flow diverted to 4 STP is around 103 MLD
out of 100 MLD wastewater generated.

13
 Figure 1 Kasaba bawada (76 MLD)

Figure no 2 – Dudhali STP (17 MLD)

The current sewage generated in Kolhapur city is 100 MLD & Sewage treatment plant in
Dudhali & Kasaba bawada having 103 MLD capacity to treat sewage out of 100 MLD so current
STP’s will be overloaded for upcoming 2 years & exceed the capacity limit of current STP’s. For
overcome this problem we forecasting population for upcoming 15 years i.e., 2035. Hence for
increasing population around 30 MLD of sewage is generated. So, we design supplementary
sewage treatment plant in Kolhapur city to treat around 30 MLD of generated sewage.

14
CHAPTER NO - 2

LITERATURE REVIEW

15
2.1) Characteristics of waste water

2.2.1) Physical characteristics

Odour:
It depends on the substances which arouse human receptor cells on coming in contact with
them. Pure water doesn't produce odour or taste sensations. Thus, waste water which contains
toxic substances has pungent smell which makes it easy to distinguish. Odour is recognized
as a quality factor affecting acceptability of drinking water. The organic and inorganic
substance contributes to taste or odour. The ultimate odour testing device is the human nose.
The odour intensity is done by threshold odour test.

Colour:
Colour in water results from the presence of natural metallic ions such as Fe or Mg, humus
and peat materials, planktons and weeds. It is removed to make water suitable for general
and industrial applications.
After turbidity is removed the apparent Colour and that due to suspended matter is found out.
Tristimulus, Spectroscopic and Platinum cobalt method is used.

Floatable:
One important criterion for evaluating the possible effect of waste disposal into surface water
is the amount of floatable material in the waste. Two general types of floating matters are
found-
(I) Particulate matters like 'grease balls’
(ii) Liquid component capable of spreading as thin visible film over large areas.
It is important because it accumulates on the surface and may contain pathogenic bacteria
and viruses.

Temperature:
The normal temperature of sewage is generally slightly higher than the temperature of water.
The average temperature of sewage in India is 20°C.
The temperature has an effect on the biological activity of bacteria present in sewage.
Biological activities in sewage are higher at greater temperature.

16
2.2.2) Chemical Characteristics:
The sewage has the following chemical characteristics

1) Total Solids:
The sewage normally contains very small number of solids in relation to the huge quantity
of water. It only contains about 0.05 to 0.1% of total solid matters.
The solid matters present the sewage may be in any of the four forms:
• Suspended solids,
• Dissolved solids,
• Colloidal solids,
• Settleable solids,

It has been estimated that about 1000 kg of sewage contains about 0.45 kg of total solids, out
of which 0.225 kg is in solution, 0.112 kg is in suspension, and 0.112 kg is settleable.
Colloidal solids remain either in solution or in suspension.
Further, the solids in sewage comprise of both organic as well as inorganic solids. The
organic matter is about 45% of the total solids and the remaining about 55% is the inorganic
matter.
The total amount of solids presents in a given sewage can be determined by evaporating a
known volume of sewage sample and weighing the dry residue left. The quantity of
suspended solids can be determined by passing a known volume of sewage sample through
a glass-fiber filter apparatus and weighing the dry residue left.

2) pH Value
The pH value is defined as the logarithm of reciprocal of hydrogen ion Concentration present
in water. It is used to designate the acidity and alkalinity of Water.
Thus, pH value=-log [H+]
Nature of fresh sewage and treated sewage is alkaline and the septic sewage is Acidic in
nature. The pH value of fresh and treated sewage is generally more than 7 &the pH value of
septic sewage is less than 7. The pH value can measure quickly and Automatically with the
help of a potentiometer.

17
3) Chloride Content:
Chlorides are derived from the kitchen wastes, human excreta and industrial discharge. The
normal chloride content of domestic sewage is 120 mg/lit. High Chloride content of sewage
indicates the presence of industrial sewage or infiltration of sea water.
The chloride content can be measured by titrating the waste water with standard silver
Nitrate solution, using potassium chromate as indicator.

4) Nitrogen Content:
The presence of nitrogen in sewage indicates the presence of organic matter. It may occur
in one or more of the following forms:
a) Free ammonia
b) Albuminoid nitrogen
c) Nitrites
d) Nitrates

Presence of free ammonia indicates the very first stage of decomposition of Organic matter.
Albuminoid nitrogen indicates quantity of nitrogen present in sewage before the
decomposition of organic matter is started.
The nitrites indicate the presence of partly decomposed organic matter. Nitrates Indicate
the presence of fully oxidized organic matter.
The amount of free ammonia present in sewage can be easily measured by simply boiling
and measuring the ammonia gas. The amount of albuminoid nitrogen can be measured by
adding strong alkaline Solution of potassium permanganate to the already boiled sewage
sample and again Boling the same. The number of nitrites or nitrates present in sewage
sample can be measured by color matching methods.

5) Presence of fats, greases and oils:

These are derived in sewage from the discharges of animals, kitchens of hotels, Industries
etc. In order to determine the amount of fats, greases etc., a sample of Sewage is first
evaporated.
The residual solids left are then mixed with ether and the solution is then evaporated,
leaving behind the fat, grease as a residue.

18
2.2.3) Biological Characteristics:
The sewage contains the following bacteria and microorganisms-

1)Bacteria:

Bacteria are microscopic unicellular organisms. They may be following types: -

a) Pathogenic bacteria- These are responsible for all water borne diseases.
b) Non-pathogenic bacteria- These are harmless.
c) Aerobic bacteria- It helps the decomposition of sewage in oxidation ponds, lagoons etc.
d) Anaerobacteria- It helps the decomposition of sewage in septic tank, Cesspool etc.
e) Facultative bacteria- It has no function in sewage treatment.

2) Microorganisms:

The microorganism like algae, fungi and protozoa help the process of decomposition of
sewage by photosynthesis or by breaking the organic compounds.

3) Biochemical Oxygen Demand:

Biochemical Oxygen Demand (BOD, also called Biological Oxygen Demand) is the
amount of dissolved oxygen needed (i.e., demanded) by aerobic biological organisms to
break down organic material present in a given water sample at certain temperature over
a specific time period. The BOD value is most commonly expressed in milligrams of
oxygen consumed per liter of sample during 5 days of incubation at 20 °C and is often
used as a surrogate of the degree of organic pollution of water.
BOD can be used as a gauge of the effectiveness of wastewater treatment plants. It is
listed as a conventional pollutant in the U.S. Clean Water Act.

19
2.2.4) Constituents of Sewage
Sewage is a dilute mixture of various wastes from residential, commercial,
industrial and other public place. Before we can decide about line of its treatment and
disposal it is essential to know its composition, quality and characteristics.

Though the characteristics of sewage or wastewater depends upon the source of

its discharge, sewage is general contains organic matter, inorganic matter and living
organisms. The organic and inorganic matter may be in dissolved, suspended and
colloidal state. The inorganic and mineral matter may contain ash, cinder, sand, grit, mud
and other mineral salts.

The living organisms may be divided into plant life (such as algae, fungi etc.) and
animal life consisting of various types of micro-organisms such as protozoa, bacteria,
virus etc. The bacteria convert the complex organic constituents of sewage into simpler,
more stable, organic and mineral compounds. As mentioned above, the composition or
constituent of sewage waste water largely depends upon the source from which it is
founding domestic wastewater which may be classified as strong, medium and weak,
depending upon the concentration of these constituents. It should be noted that sewage
contains only a very small percentage of solids in relation to huge amount of water.
Liquid content of sewage is 99.9% while total amount of solids both suspend as well as
dissolved is only 0.1 percent.

Fig no-3
Sewage sludge constituents

20
2.2.5) Treatment Processes of Sewage

Fig no -4

2.2.6) Primary Treatment:

The primary treatment consists of the processes which remove those
constituents of the wastewater the presence of which would otherwise interfere with
subsequent treatment processes or mechanical equipment. Wastewater contains
varying quantities of floating and suspended Solids, some of considerable size. Primary
treatment processes remove floating materials (like dead bodies animals, pieces or
wood, papers, rags, metal containers, plastic rubber containers, grease etc.) and also
heavy settleable inorganic solids like grit, and fragments of masonry etc.

Fig no – 5

21
• Various units involved in primary treatment are:

✓ Screenings:
Screening is essential for removal of floating materials which are mainly sachets,
plastic sheet bits, leaves, fibers, rags, etc. Screen is used at first step in STP. A screen is
a device with openings generally of uniform size. The screening element may consist of
parallel bars, rods, gratings or wire mesh or perforated plates and the openings may be
of any shape, although generally they are contrived from circular or rectangular bars. It
is recommended that three sequential stages of screens shall be provided being coarse,
followed by medium and followed by fine screens.

There are three types of screens-

• Coarse screens – Coarse screens have a clear opening ranging from 6 to

150 mm (0.25 to 6 in). Coarse screen consists of parallel bars, rods or wires,
wire mesh or a perforated plate

• Fine screens – Fine screens have clear openings less than 6 mm. They
consisted of perforated plates, wire cloth, wedge wire elements that have
smaller openings.

• Microscreens – They are rotating drum screens which have a variable low
speed (up to 4 r/min), which is continuously backwashed operating in
gravity flow conditions. The filtering fabrics used should have openings
range from 10 to 35µm and fitted on the periphery of the drum

Fig no - 6

22
 ✓ Grit chamber
Grit removal is necessary to protect the moving mechanical equipment and pump
elements from abrasion and accompanying abnormal wear and tear. Removal of grit also
reduces the frequency of cleaning of digesters and settling tanks.
Grit in sewage consists of coarse particles of sand, ash and clinkers, egg shells, bone
chips and many inert materials inorganics in nature. Hence, it is possible to separate the
gritty material from organic solids by differential sedimentation in a grit chamber.

Fig no - 7

✓ Primary settling tank:

Primary settling tank is used to separate the suspended solids, which can settle
by gravity when the sewage is held in a tank. If these suspended solids are discharged
into water courses, they will result in sludge banks. The Primary Settlement or
sedimentation tanks are designed to reduce the velocity of the wastewater flow, allowing
heavier organic solids (called raw sludge) to settle. They are the first stage of treatment
after the removal of rags and grit in the inlet works. The primary settling tank is located
after screens and grit chambers and reduces the organic load on secondary treatment
units. It is used to remove
(i) Inorganic suspended solids or grit if it is not removed in grit chamber
described earlier
(ii) Organic and residual inorganic solids, free oil and grease and other
floating material
(iii) Chemical floc produced during chemical coagulation and
flocculation.
23
Primary Treatment objectives:

The fundamental goals of wastewater treatment are as follows:

1. To lessen the strength of sewage by 30 to 50 percent.
2. To reduce the number of settleable solids by 80 to 90 percent.
3. To lower BOD by 30 to 35 percent.
4. To prepare the sewage for subsequent treatment.

Fig no – 8

Fig no - 9

24
 2.2.7) Secondary Treatment

Fig no - 10

✓ Biological Treatment: Activated Sludge Process

In Activated Sludge process sewage containing organic matter is aerated in an
aeration basin in which micro-organisms metabolize the soluble and suspended organic
matter. Part of the organic matter is synthesized into new cells and part is oxidized to carbon
dioxide and water to derive energy. In activated sludge systems the new cells formed in the
reaction are removed from the liquid stream in the form of a flocculent sludge in clarifiers.
A part of this activated sludge is recycled to the aeration basin and the remaining form waste
or excess sludge.

Fig no - 11

25
 ▪ Activated Sludge Process Variables:
An ASP essentially consists of the following:

(i) Aeration tank containing microorganisms in suspension in which the

reaction takes place
(ii) Activated sludge recirculation system,

(iii) Excess sludge wasting and disposal facilities

(iv) Aeration systems to transfer oxygen and

(v) Secondary sedimentation tank to separate and thicken activated sludge.

✓ Aeration tank: (Diffused aeration)

In aeration tank diffused aeration process is take place. Diffused aeration
involves the introduction of compressed air into the sewage through submerged diffusers of
fine bubble or coarse bubble type. In the former, compressed air is released at or near the
bottom of the aeration tank through porous tubes or plates made of aluminum oxide or silicon
oxide grains cemented together in a ceramic matrix. In spite of such precautions, fine bubble
diffusers will require periodical cleaning. Air diffusers are generally placed along one side
of the aeration tank, helping to set up a spiral flow in the tank which improves mixing and
prevents the solids from settling.

Fig no - 12
26
 Fig no – 13

The above picture shows the aerator plates which aerate sewage in aerator tank

✓ Secondary Settling Tank: (clariflocculator)

Secondary settling assumes considerable importance in the activated sludge
process as the efficient separation of the biological sludge is necessary not only for ensuring
final effluent quality but also for return of adequate sludge to maintain the mixed liquor
suspended solids level in the aeration tank. The secondary settling tank of the activated
sludge process is particularly sensitive to fluctuations in flow rate and on this account, it is
recommended that the units be designed not only for average overflow rate but also for peak
overflow rates.

Fig no -14

27
 2.2.8) Treatment on sludge

✓ Sludge Tank:
The sludge to be created will depend on the suspended solids concentration in the
waste stream. The waste sludge is either discharged into the aeration tank or thickened in a
sludge thickening unit and digested directly, in extended aeration plants, the excess sludge is
taken to sludge digesters through which it is taken to sludge thickeners then it is proceed for
sludge drying beds or mechanical dewatering directly and the sludge filtrate discharged into
the effluent stream.

✓ Sludge Digester:
Sludge digestion is a biological process in which organic solids are decomposed
into stable substances. Digestion reduces the total mass of solids, destroys pathogens, and
makes it easier to dewater or dry the sludge. Digested sludge is inoffensive, having the
appearance and characteristics of a rich potting soil. In digester the dissolved matter is
converted by other bacteria into biogas, a mixture of carbon dioxide and methane. Methane is
combustible and is used as fuel as well as to generate electricity.

Fig no - 15

28
✓ Sludge Thickener:
Sludge Thickening is usually accomplished in a tank called a gravity thickener. A
thickener can reduce the total volume of sludge to less than half the original volume.
Thickening is usually done in sludge treatment because it is impractical to handle thin sludge,
slurry of solids suspended in water.

Fig no - 16

✓ Sludge Drying Bed:

Sludge-drying beds provide the simplest method of dewatering. Digested sludge
slurry is spread on an open bed of sand and allowed to remain until dry. Drying takes place
by a combination of evaporation and gravity drainage through the sand. This dried sludge is
later used as manure for farming.

Fig no - 17

29
2.2.9) Tertiary treatment:
Tertiary treatment is the final cleaning process that improves wastewater quality before
it is reused, recycled or discharged to the environment. The treatment removes
remaining inorganic compounds, and substances, such as the nitrogen and phosphorus.
Bacteria, viruses and parasites, which are harmful to public health, are also removed at this
stage.

Fig no - 18

✓ Chlorine contact tank (CCT):

The chlorine contact tank disinfects wastewater. Chlorine removes

microorganisms in treated wastewater including bacteria, viruses and
parasites such as Giardia and Cryptosporidium. The chlorinated water slowly winds
its way along the discharge tank, giving it time to react. Any remaining chlorine is
removed by adding sodium biosulphate just before it's discharged. Chlorine is removed
from the water since it can be harmful to water quality and aquatic life when in high
concentrations.

30
2.2.10) Permissible limits of sewage disposal –

Fig no - 19

31
CHAPTER NO - 3

DESIGN PROCEDURE

32
3.1) Screening tank

Sewage generation = 30 MLD

Assumptions-
• Assuming manual cleaning let us keep the bars at an inclination of 45° degree with
vertical.
• Let us use bars of size 15 mm X 50 mm with 15 mm facing flow.
• Let us keep clear spacing of 75 mm between the bars.
• Let us assume the desired velocity through the screen 0.8m/sec at peak flow.
30 X 106 X 103
∴ Maximum rate of flow =
24 𝑋 60 𝑋60

= 0.347 𝒎𝟑 /sec
maximum rate of flow
∴ Net area of screen = 𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦
0.347
=
0.8

= 0.434 𝒎𝟐
45
∴ Gross area = Net area ×
spacing
45
= 0.434 ×
75

= 0.26 𝒎𝟐
0.26
∴ Gross area of screen needed =
sin45°

= 0.368 𝒎𝟐
45
∴ Velocity flow above screen = velocity ×
spacing
45
= 0.8 ×
75
= 1.33 m/sec
Thus, we have V = 0.8 m/sec & v = 1.33 m/sec

33
 ∴ ℎ𝑙 = 0.0729 (𝑣 2 − 𝑉 2 )
= 0.0729 (1.332 − 0.82 )
= 0.0822 m
= 8.22 cm ~ 9 cm
This will be the head loss when the screen is clean. If, However, the screen is half clogged,
∴ V = 2 × 1.33 = 2.66 m/sec
∴ ℎ𝑙 = 0.0729 (𝑉 2 − 𝑣 2 )
= 0.0729 (2.662 − 0.82 )
=0.469 m
= 46.91 cm ~ 47 cm
Thus, we find that when the screen is clean (in the initial stage of operation), the head loss is
only 9 cm, while it shoots up to 47 cm when the screen is half clogged. Hence the bar screen should
be frequently cleaned, in order to keep the head loss within a desirable limit.
So, providing a depth of 0.3m.
0.368
∴ width of channel =
0.3

= 1.226 m ~ 1.3 m
0.347
∴ Velocity of flow in screen chamber =
0.3 × 1.3
= 0.89 m/sec
Which is greater than 0.42 m/sec with spacing of 30 mm
1.3
∴ No. of bars required =
0.03+0.01
= 33 bars
∴ Actual width of screens = 33 × 0.4 = 1.32 m
0.38
∴ Actual depth of sewage flow =
1.32
= 0.28 m ~ 0.3 m
Providing of free board of 0.5 m
∴ Actual depth of screens = 0.3 + 0.5
= 1.32 m ~ 1.4 m
Hence, Size of screen is screen is 1.4 m × 0.8m

34
3.2) Grit chamber

• Maximum flow: - 30 MLD

• Diameter of smallest grit particles to be removed: - 0.02 cm
• Specific gravity of particle: - 2.65
For grit particles, settling velocity is given by Hazen’s modified equation:
3𝑡+70
∴ 𝑣𝑠 = 60.6 (𝑆𝑠 − 1)
100
3 × 20+70
= 60.6 (2.65 − 1) 0.02 100
≈ 2.6 cm/sec
Again, critical velocity is given by the modified shield’s formula. Taking multiplying factor
as 4, we have
∴ 𝑣𝑐 = √𝑔 (𝑆𝑠 − 1)𝑑
= √981 (2.65 − 1)0.02
≈ 2.6 cm/sec
= 0.228 m/sec
∴ 𝑣ℎ = 𝑣𝑐 = 0.228 m/sec.
30 × 106 × 10−3
Now, Q = 30 MLD =
24 ×60 × 60

= 0.347 𝒎𝟑 /sec
Q
∴ cross sectional area, A =
𝑣𝑐
0.347
= 0.228

A = 1.52 𝒎𝟑

35
Providing a width of 1.3 m, liquid depth (H) required = 1.17 m.
Let us provide a free board of 0.3 m &
A space of 0.25 m for sludge accumulation.

∴ Total depth = 1.17 + 0.3 + 0.25

d = 1.72 m ~ 1.8 m

H 𝑣𝑠 2.6 1
Now, Ratio = = =
𝐿 𝑣𝑐 22.8 8.769

L = 8.769 H = 8.769 × 1.17

= 10.26 m

Let us make an allowance of 25% for inlet & outlet zone.

Hence total length = 1.25 × 10.26 = 12.83 m.
Keep length equal to 13 m.

Hence, Size of grit chamber is (13 m × 1.3 m × 1.8 m)

36
3.3) Primary Settling Tank
Assumptions-
• Assuming that 80% of water supplied to the city is converted into sewage.
• Let us assume a detention period of 2 hours.
• Let us assume an overflow rate of 30 𝑚3 /d /𝑚2 for average flow. (Value in between 25 –
35 𝑚3 /d /𝑚2 )
• Assume length is four times breadth.
30 × 103
∴ Capacity required = ×2
24

= 2500 𝒎𝟑
Again, for average flow,
30 × 103
∴ Surface area =
30

= 1000 𝒎𝟐
Capacity required
∴ Effective depth =
Surface area
2500
=
1000
= 2.5 m
∴ Again, ∴ B × L = 1000
Taking, L = 4B
∴ B × 4B = 1000
∴ 4B 2 = 1000

1000
∴ B= √
4

∴ B = 15.81 m ~ 16 m
∴ L = 4 × 16 = 64 m
Provide 4m for inlet& outlet arrangements.
∴ Total depth = 64 + 4 = 68 m.
Also, provide 1 m depth for sludge accumulation & 0.5 m as free board.
Hence, total depth = 1 + 0.5 + 2.5 = 4 m
∴ Hence, size of the primary settling tank will be (64 m × 16 m × 4 m)

37
3.4) Aeration tank
• Maximum flow: - 30 MLD
• Settle sewage BOD = 𝐿𝑎 = 200 mg/l
• Effluent BOD required = 15 mg/l
• For conventional process type, Take Mixed liquor suspended solids (MLSS) = 𝑥𝑡 = 3000
mg/l
• For conventional process type, F/M = 0.2
• Taking Sludge volume Index = SVI = 100

I. Average flow & process efficiency required

∴ Average flow = 30 MLD
200 − 15
∴ Efficiency required = × 100
200
= 92.5 %
II. Determination of volume of aeration tank
F 𝐹𝑜𝑜𝑑
∴M= = 0.2
𝑀𝑖𝑐𝑟𝑜−𝑜𝑟𝑔𝑎𝑛𝑖𝑠𝑚
F 𝑄 . 𝐿𝑎
∴M= 𝑉
( ) 𝑥𝑡
1000

30 × 200 × 1000
∴ 0.2 =
𝑉 × 3000

∴ V = 10000 𝒎𝟑
III. Check for hydraulic retention time
𝑉
∴ HRT = × 24
𝑄 × 1000
10000
= 30 × 1000 × 24

= 8 hours
(This is within the prescribed range of 4 to 8 hours)

38
IV. Check for volumetric loading
𝑄 . 𝐿𝑎
∴ Volume loading =
𝑉
30 × 200
= 10000
= 0.6 Kg BOD/𝒎𝟑
(This is within the prescribed range of 0.3 to 0.7)

V. Return Sludge ratio

Qr 𝑥𝑡
∴ = 6
Q (10 /𝑆𝑉𝐼 )− 𝑥𝑡
Qr 3000
∴ Q = 106
( )−3000
100

r = 0.429 = 𝟒𝟐. 𝟗%
(This is within the prescribed range of 25 to 50%)
VI. Tank dimensions
Let us adopt of 4.5 m & width of 5.4 m i.e. (1.2 × 4.5) = 5.4 m (width- depth ratio should
be between 1.2 – 2.2)
𝑉 10000
∴ Length of aeration tank = = = 411.52 m
𝐴 5.4 × 4.5
Provide a continuous channel with six baffles, so as to get seven sections, the length of
each section being 59 m (411.72/7 = 58.78 m) to give a total length of 59 × 7 = 413 m. Let
the thickness of each baffle wall be 0.25 m.
∴ Total width of aeration tank = (5.4 × 7) + (6 × 0.25)
= 39.3 m
Provide a free board of 0.5 m
Hence, overall inner dimensions of the tank are 59 m × 40 m × 4.5 m

VII. Check for horizontal velocity

30 X 103 (1+0.429) Qr
∴ Q + Qr = …………..( Q = 0.429)
24 × 60

= 29.77 𝐦𝟑 /𝐦𝐢𝐧
29.77
∴V= = 1.84 m/min Hence its ok.
3 × 5.4
39
VIII. Air requirement & arrangement of diffuser plates
∴ Air needed = 100 m3 /day per kg BOD removed.
100 (200 − 150) × 30
=
24 × 60

= 385.42 𝐦𝟑 /𝐦𝐢𝐧 ≈ 390 𝐦𝟑 /𝐦𝐢𝐧

Choose standard diffuser plates of 0.3 m × 0.3 m × 25 mm, passing 1.2 m3 of air/ min/ m2
with 0.3mm pores.

390
∴ No. of plates required =
0.3 × 0.3 × 1.2
= 3611.11 ~ 3615
Let’s us Providing 3615 plates.
A plate concentration of 30% extra provided in the first half of the tank care of
more frequent clogging of this zone.
3615
∴ No. of plates needed inthe first half = × 1.3 = 2349.75 ~ 2350
2
Let us provide clear distance between the plates of 0.9m to avoid interference
from the rising streams of bubbles.
Hence, c/c distance of rows plates = 0.9 + 0.3 = 1.2 m
413 206.5
∴ No. of rows in the first half length (of 206.5 m)= = = 172.0 rows
2 1.2
For first half, Provide 19 plates in a row of 2.1 m spacing c/c for 40m side & 19 plates
in a row of 1.55 m spacing c/c for 30 m side. Similarly, for second half Provide 17 plates in
a row of 2.35 m spacing c/c for 40m side & 17 plates in a row of 1.75 m spacing c/c for 30
m side.

IX. Check for minimum air availability

In second half, 2023 diffuser plates give air
= 2023 × 0.3 × 0.3 × 1.2 = 218.48 𝐦𝟑 /𝐦𝐢𝐧
218.48
∴ Air available per meter length of channel = = 1.06 m3 /min/m length.
206.5

This is more than prescribed value of 0.25 m3 /min/m length. Hence, satisfactory.

40
3.5) Clariflocculator or Secondary settling tank
• peak flow: - 30 MLD
• peak factor = 2.25
• Take surface loading rate of 20 m3 /d/m2 at average flow.
• Solids loading of 120 kg/d/m2 at average flow. (Take value is in between 100 to 150)
• Take MLSS = 3000 mg/l

30 × 103
∴ Average flow =
2.25

= 13.33 MLD = 13333.33 𝐦𝟑 /𝐝𝐚𝐲

∴ Surface loading rate of 20 m3 /d/m2 at average flow.
13333.33
∴ Surface area =
20

= 666.66 𝐦𝟐
∴ Check surface loading at peak flows,
30 × 103
∴ Surface area =
666.66

= 45 𝐦𝟑 /𝐝/𝐦𝟐
This is within the prescribed range of 40 to 50
∴ Solids loading of 120 kg/d/m2 at average flow.
13.33 × 106 × (3000 × 10−6 )
∴ Area required =
120

= 333.25 𝐦𝟐
Also, on the basis of solid loading of 250 kg/d/m2 at peak flow,
45 × 106 × (3000 × 10−6 )
∴ Area required =
250

= 540 𝐦𝟐

41
 Hence, adopt a surface area of 666.66 m2 which is highest of the three values. Adopting
a circular tank,

666.66 × 4
∴ Diameter = √
𝜋

= 29.13 m
~ 30 m

𝜋 × 302
∴ Actual area =
4
= 706.86 m2
∴ Actual Solids loading at average flow,
13.33 × 106 × (3000 × 10−6 )
∴ solid loading =
706.86

= 56.57 kg/day/m2 ~ 57 𝐤𝐠/𝐝𝐚𝐲/𝐦𝟐

Keep the depth of tank equal to 4m &, provide 0.5 m as free board.
∴ Total depth = 4 + 0.5
= 4.5 m
∴ Hence, size of the secondary settling tank will be diameter of 30 m with an overall depth
of 4.5 m.

42
3.6) Sludge tank
• peak flow: - 30 MLD
• Density of sludge = 350 Kg/m3
• Weight of sludge = sludge generate per day × MLSS
= 30 × 106 × 3000 × 10−6
= 90000 Kg/day
• Assume length is 1.5 times width

∴ Assume depth of tank = 5 m

90000
∴ volume of tank =
350

= 257.14 𝐦𝟑
257.14
∴ Area of tank =
5

= 51.428 𝐦𝟐
∴A=L×B
∴ 51.428 = 1.5 B × B ……...(L = 1.5B)
∴ 51.428 = 1.5 B 2

51.428
∴B=√
1.5

= 5.86 m ~ 6 m
∴ L = 1.5 × 6
∴ L=9m
∴ Hence, size of the sludge tank will be (9 m × 6 m × 5 m)

43
3.7) Sludge Thickener

• Population per capita = 2,08,500

• per capita settleable solids in primary sludge = 54 gm/day
• per capita settleable SS in activated sludge = 31 gm/day
• Total Suspended solids = 54 + 31 = 85 gm/day
• Specific gravity of wet mixed sludge = 𝑆𝑠𝑙 = 1.008
• Solid in combined sludge = 𝑃𝑠 = 3 %

∴ Weight of combined sludge = 85 × 10−3 × 2,08,500

𝑊𝑠 = 17722.5 kg/day

Recommended average surface loading = 40 kg/m2 /day

Hydraulic loading required = 25 𝑚3 /𝑚2 /𝑑𝑎𝑦
According to assumptions, the volume of wet sludge/day is given by,

𝑊𝑠
∴ 𝑉𝑠𝑙 =
𝑃𝑠 × 𝜌𝑤 × 𝑆𝑠𝑙
17722.5
∴ 𝑉𝑠𝑙 =
0.03 × 1000 × 1.008

= 586.06 𝑚3 /𝑑𝑎𝑦 ~ 590 𝐦𝟑 /𝐝𝐚𝐲

Ws
∴ Surface area needed =
Average surface loading
17722.5
= 40
= 443.06 𝒎𝟐

44
 ∴ Flow needed from giving a hydraulic loading of 25 𝑚3 /𝑚2 /𝑑𝑎𝑦
= 25 × 443.06 = 11076.5 𝐦𝟑 /𝐦𝟐 /𝐝𝐚𝐲

∴ Balance of 11076.5 – 590 = 10486.5 m3 /day is made available by blending with primary or
secondary effluent. & Let us provide a side water depth of 3 m.

Volume of tank
∴ Sludge detention period =
Volume of sludge

443.06 × 3
= × 24 = 54.06 ~ 𝟓𝟒. 𝟏 𝐡𝐨𝐮𝐫𝐬
590

This is more than 24 hours, & hence ok.

Let us provide a circular sludge blanket type thickener.

443.06 × 4
∴ Diameter = √
𝜋

= 23.75 m
~ 𝟐𝟒 𝐦

∴ Sludge blanket restricted to 1 m is adopted. & Expected solids in the thickened sludge = 6%

45
8) Sludge Digestor

• Population per capita = 2,08,500

• Specific gravity of minerals solids (which varies from 2.4 to 2.65) = 𝑆𝑓 = 2.5
• Specific gravity of volatile (organic) matters (which varies from 1.0 to 1.2) = 𝑆𝑣 = 1.0
• Weight of solids = 𝑊𝑠 = 100
• Assume average working temperature = 27.5℃, so Digestion period = 𝑇1 = 30 days
• Assume 60 days storage in monsoon = 𝑇2 = 60 days

I. Volume of mixed raw (undigested) primary plus activated sludge

58
∴ % of the volatile matter in raw mixed sludge = × 100
85
𝑊𝑓 = 68.24%
27
∴ % of the non − volatile (or fixed) matter sludge = × 100
85
𝑊𝑣 = 31.76%
∴ Specific gravity of dry solids in mixed raw sludge , 𝑆𝑑
𝑊𝑠 𝑊𝑓 𝑊𝑣
∴ = +
𝑆𝑑 𝑆𝑓 𝑆𝑣

100 68.24 31.76

∴ = +
𝑆𝑑 1 2.5

∴ 𝑆𝑑 = 1.235
Taking percentage solids as 4%, specific gravity of wet sludge (mixed primary plus
activated sludge) is,
100 % of moisture % of solids
∴ = +
𝑆𝑠𝑙 Specific gravity of water 𝑆𝑑

46
 100 96 4
∴ = +
𝑆𝑠𝑙 1 1.235

∴ 𝑆𝑠𝑙 = 1.0077 ~ 1.008

∴ Volume of mixed sludge , 𝑉𝑠𝑙
𝑊𝑠
∴ 𝑉𝑠𝑙 =
𝑃𝑠 × 𝜌𝑤 × 𝑆𝑠𝑙
17722.5
∴ 𝑉𝑠𝑙 =
0.03 × 1000 × 1.008

= 586.06 𝑚3 /𝑑𝑎𝑦 ~ 590 𝐦𝟑 /𝐝𝐚𝐲

II. Volume of mixed digested primary plus activated sludge.

20
∴ % of the volatile matter in raw mixed sludge = × 100 = 35.09%
57
37
∴ % of the non − volatile (or fixed) matter sludge = × 100
57
𝑊𝑣 = 64.91%
∴ Specific gravity of dry solids in mixed raw sludge , 𝑆𝑑 ′
𝑊𝑠 𝑊𝑓 𝑊𝑣
∴ = +
𝑆𝑑 ′ 𝑆𝑓 𝑆𝑣

100 35.09 64.91

∴ = +
𝑆𝑑 ′ 1 2.5

∴ 𝑆𝑑 ′ = 1.638
Taking percentage solids digested sludge as 7%, specific gravity of wet digested sludge
is,
100 % of moisture % of solids
∴ = +
𝑆𝑠𝑙 ′ Specific gravity of water 𝑆𝑑
100 93 7
∴ = +
𝑆𝑠𝑙 ′ 1 1.638

∴ 𝑆𝑠𝑙 ′= 1.028

47
 ∴ Volume of digested mixed sludge , 𝑉𝑠𝑙 ′
𝑊𝑠
∴ 𝑉𝑠𝑙 ′ =
𝑃𝑠 × 𝜌𝑤 × 𝑆𝑠𝑙 ′

57 × 10−3 × 208500
∴ 𝑉𝑠𝑙 ′ =
0.07 × 1000 × 1.028

= 165.15 𝒎𝟑 /𝒅𝒂𝒚

III. Volume of digester

Assume a parabolic reduction of volume, the capacity (or volume) of the digester is,
2
∴ V = [𝑉𝑠𝑙 − (𝑉𝑠𝑙 − 𝑉𝑠𝑙 ′ )] 𝑇1 + 𝑉𝑠𝑙 ′ 𝑇1
3
2
= [590 − 3 (590 − 161.15 )] 30 + (161.15 × 60)

V = 19112 𝒎𝟑
Volume of digestor 19112
∴ population
=
208500

= 0.09 𝐦𝟑 /𝐜𝐚𝐩𝐢𝐭𝐚
(This is within 0.08 to 0.15 m3 /capita of combined sludge)

IV. Loading Factor

∴ Total loading of volatile solids = 58 × 10−3 × 208500
= 12093 kg/day
12093
∴ volatile solids loading factor =
19112

= 0.63 kg/day/𝐦𝟑
(This is within prescribes range of 0.3 to 0.75 kg/day/m3 ) Hence is ok.

48
 V. Dimension of Digester
Assume that for cylindrical digester the average gas production is at 0.9 m3 /kg of
volatile matter destroyed.
∴ Volatile matter destroyed during digestion of combines sludge = 38 gm/capital.
∴ Total Volatile matter destroyed = 38 × 10−3 × 208500
= 7923 kg
∴ Gas produced = 7923 × 0.9 = 7130.7 𝐦𝟑

It is recommended that in order to avoid foaming, the optimum diameter or depth is

calculated such that twice the average rate of gas production, the value of 9 m3 /m2 of tank area
is not exceeded.
Hence, minimum area of digester required (to avoid foaming)
2 × 7130.7
= = 1584.6 𝐦𝟐
9
Volume of digester
∴ Depth of digester =
Surface area of digester
19112
= = 12.06 m ~ 12.5 m
1584.6
But the depth should not exceed 9 m. Hence 2 digesters are proposed.
1
∴ Volume of each tank = × 19112
2

= 9556 𝐦𝟑
∴ Adopting depth of 8m in each tank,
9556 × 4
∴ Diameter of each tank = √ 𝜋×8

Diameter = 38.99 m ~ 39 m
Provide a free board of 0.6m
∴ Hence, adopt 2 numbers of digestion tanks, each of 39 m diameter & height of 8.6 m

49
3.9) Sludge Drying Bed
• Total solid remaining in digested sludge (combines primary & activated) = 57
gm/capita/day
• Adopt dry solids loading of 100 kg/𝑚2 /year (take value is between 80 to 120 kg/𝑚2 /year)

∴ Daily solids = 57 × 10−3 × 2,08,500

= 11884.5 Kg/day
11884.5 × 365
∴ Area of bed needed = 100

= 43378.4 𝒎𝟐
43378.4
∴ Check for capita area = 208500

= 𝟎. 𝟐𝟎𝟖 𝐦𝟐
(This is within recommended range of 0.175 to 0.25)
Let us adopt 8 m wide × 40 m long beds with single point discharge & a bed
slope of 0.5%.
43378.4
∴ No of beds = 8 × 40

= 135.5 ~ 136 beds

Assuming 2 months of rainy season in a year & 3 weeks for drying & one week
for preparation & repair of bed, number of cycles per year
(12−2) 4
= = 10
4

Assuming 7 % solids & a specific gravity pf 1.025, the volume of digested sludge
is given by:
𝑊𝑠
∴ 𝑉𝑠𝑙 = 𝑃
𝑠 × 𝜌𝑤 × 𝑆𝑠𝑙

11884.5
= = 165.63 𝐦𝟑 /𝐝𝐚𝐲
0.07 × 1000 × 1.025
165.63 × 365
∴ Depth of application of sludge =
136 × 8 × 40 × 10
= 0.139 m
= 13.9 cm ~ 14 cm
∴ Hence, size of the sludge drying bed will be 8 m × 40 m of 136 beds with depth of 14 cm.
50
CHAPTER NO - 4

2 D DRAWING OF STP

51
CHAPTER NO - 5

ESTIMATE

52
CHAPTER NO - 6

CONCLUSION

53
 CONCLUSION

The current sewage generated in Kolhapur city is 100 MLD & Sewage treatment plant in
Dudhali & Kasaba bawada having 103 MLD capacity to treat sewage out of 100 MLD so
current STP’s will be overloaded for upcoming 2 years & exceed the capacity limit of current
STP’s. For overcome this problem we forecasting population for upcoming 15 years i.e., 2035.
Hence for increasing population around 30 MLD of sewage is generated. So, we design
supplementary sewage treatment plant in Kolhapur city to treat around 30 MLD of generated
sewage.
The approximate estimated amount of supplementary plant is RS. 12,15,49,200. We have
also draft auto cad drawing for the treatment plant which gives detailed information about
various components of the sewage treatment plant. Methane gas is produced from Sludge which
is removed from wastewater in a sludge digester having approx. quantity of 7100 cubic meter.
After production of gas this sludge is proceed to sludge drying bed where dewatering of sludge
takes place and the dewatered sludge is used as fertilizer for agricultural purpose. The treated
water is further used for various purposes like gardening, washing purpose, industrial use etc.
This sewage treatment plant will help to improve the quality of water and it will ultimately
improve life of the people in Kolhapur city and also it will contribute to smooth flow of
environment cycle.

54
 REFERENCES

1) Design of Sewage Treatment Plant with Experimental Investigations by P. B. Narandiran ,

radhamani, manikkumar from international journal of research and technology

2) Analysis and design of sewage treatment plant by rajnandini published on 2 November 2019

4) Case study on sewage treatment plant, Delawas (Jaipur) by rahul shrama, PriteshAgrawal volume
7 published on 2017

5) Upgrading of sewage treatment plant by sustainable and cost-effective separate treatment of

industrial waste water by willie Driessen published on 2010

5)Comparative case study of sewage treatment plant between Jaipur and Delhi STP published on 6
June 2020 by dipanshu dixit and manaswee Varma volume 8

6) A study on sewage treatment and disposal in Delhi by Shreya gupta and S.K. singh published on
15 June 2018 volume 6

7) https://openjicareport.jica.go.jp/pdf/12112884_08.pdf

8)https://www.academia.edu/6078256/DESIGN_OF_PRIMARY_SEWAGE_TREATMENT_PLAT

9) https://www.humanitarianlibrary.org/sites/default/files/2019/05/AWWT.pdf

55