A Project Report on

DESIGN AND MODELLING OF STP

Submitted in
fulfilment of the requirements for the degree of
BACHELOR OF TECHNOLOGY
in
Civil Engineering
by
Abhishek Moond (19ESKCE005)
Akanksha Foujdar (19ESKCE011)
Arvind Kumawat (19ESKCE022)
Atiba Qureshi (19ESKCE026)

Under the supervision of

Sitaram Saini
Assistant professor Department of Civil engineering

DEPARTMENT OF CIVIL ENGINEERING

SWAMI KESHVANAND INSTITUTE OF TECHNOLOGY
MANAGEMENT &
GRAMOTHAN, JAIPUR-302012
June 2023
 SWAMI KESHVANAND INSTITUTE OF
TECHNOLOGY , MANGEMENT & GRAMOTHAN ,
JAIPUR, INDIA-302017

CERTIFICATE

This is to certify that the project work entitled “DESIGN AND MODELLING
OF STP” which is being submitted by Abhishek Moond (19ESKCE005) ,
Akanksha Foujdar (19ESKCE011) , Arvind Kumawat (19ESKCE022)
and Atiba Qureshi (19ESKCE026) in partial fulfillment for the award of the
degree of Bachelor of Technology in Civil Engineering, SKIT, J aipur is a
bonafide work carried out under my supervision.

Sitaram Saini

Assistant professor

Department of Civil Engineering

SKIT, Jaipur.
 SWAMI KESHVANAND INSTITUTE OF TECHNOLOGY
MANGEMENT & GRAMOTHAN , JAIPUR, INDIA-302017

CANDIDATE’S DECLARATION

We hereby certify that the work which is being presented in the report “DESIGN AND
MODELLING OF STP”, in partial fulfillment of the requirements for the award of the
Degree of Bachelor of Technology and submitted in the Department of Civil Engineering of
the Swami Keshvanand Institute of Technology Mangement & Gramothan, Jaipur is an
authentic record of our own work carried out during a period from September 2022 to May
2023 under the supervision of Sitaram Saini , Assistant Professor , Department of Civil
Engineering, SKIT, Jaipur.

Abhishek Moond (19ESKCE005)

Akanksha Foujdar (19ESKCE011)
Arvind Kumawat (19ESKCE022)
Atiba Qureshi (19ESKCE026)
 ACKNOWLEDGEMENT

It gives us a great sense of pleasure to present the report of the B.Tech. Project undertaken
during B.Tech. Final Year. We owe special debate of gratitude to Sitaram Saini , our project
guide and Associate Professor of Civil Department in SKIT college for his constant support
and guidance throughout the course of our work. His sincerity, thoroughness and perseverance
have been a constant source of inspiration for us. It only his cognizant efforts that our endeavor
have seen light of the day.
We also take the opportunity to acknowledge the contribution of DK Sharma , Head of
Department of Civil Engineering, SKIT college for his support and guidance during the
development of the project.
We also do not like to miss the opportunity to acknowledge the contribution of all faculty
members of the department for their kind assistance and cooperation during the development
of our project. Last but not the least, we acknowledge our friends for their contribution in the
completion of the project.

Abhishek Moond (19ESKCE005)

Akanksha Foujdar (19ESKCE011)
Arvind Kumawat (19ESKCE022)
Atiba Qureshi (19ESKCE026)
 ABSTRACT

A sewage treatment plant is quite necessary to receive the domestic and commercial waste and
removes the materials which pose harm for general public. Its objective is to produce an
environmentally-safe fluid waste stream (or treated effluent) and a solid waste (or treated
sludge) suitable for disposal or reuse (usually as farm fertilizer). The main purpose of the
Sewage treatment process is to remove the various constituents of the polluting load: solids,
organic carbon, nutrients, inorganic salts, metals, pathogens, etc. Effective wastewater
collection and treatment are of great importance from the standpoint of both; environmental
and public health. Sewage/Wastewater treatment operations are done by various methods in
order to reduce its water and organic content, and the ultimate goal of wastewater management
is the protection of the environment in a manner commensurate with public health and
socioeconomic concerns. In this article, Sewage/Wastewater treatment techniques, factors
affecting selection and design of Sewage/Wastewater systems are discussed briefly.
A study on domestic waste water characterization has been performed followed by the design
Of sewage treatment plant .
In this project we have made a working model of sewage treatment plant showing all the units
of treatment including a canal in which water is carried from institutions , residential building
, commercial buildings etc . We have also prepared a poster showing the flow chart of all the
units of sewage treatment plant .
Along with all this things we have designed 6 units of treatment unit which includes screening
, grit chamber , skimming tank , primary sedimentation tank , aeration tank and secondary
clarifier . We have proposed a designing of these units to the SKIT college for their reference
and future use . As we all know population is increasing day by day so we have toodify our
present STP according to the needs of of future populations .
We have tested the raw sewage taken from the SKIT plant and check their pH , turbidity ,
BOD , total solids and then further cross check with as per the permissible limit .
Prepared a preliminary layout of the model . Also visited few STP’s located in Jaipur for the
analysis of working method and gathered a lot of knowledge from their .
At the last the main aim of paper is to use the treated water in a way; which does not harm
human and environment along with consideration of mentality of society.
 TABLE OF CONTENT
SR. NO. CONTENT PAGE NO
1. Chapter-1 Introduction 1
1.1 Objectives of the Study 2
1.2 Types of Wastewater Treatment Plant 2
1.2.1 Sewage wastewater 3
1.2.2 Industrial wastewater 3
1.3 Sources of Water Pollution 3
1.4 Sewage characteristics 4
1.5 Principal pollutants 5
1.5.1 Organic material 5
1.5.2 Suspended solids 5
1.5.3 Plant nutrients 5
1.5.4 Microbes 6
1.6 Sewerage systems 6
1.6.1 Combined systems 6
1.6.2 Separate systems 6
1.7 Problems related to wastewater 7
2. Chapter-2 Literature Review 8
3. Chapter-3 Origins of Wastewater 9
3.1 Wastewater constituents 10
3.2 Wastewater quality indicators 11
3.3 Sewage disposal 12
3.4 Effects on biology 13
4. Chapter-4 Characteristics of wastewater 14
4.1 Physical characteristics 14
4.1.1 Odour 14
4.1.2 Colour 14
4.1.3 Floatables 14
4.1.4 Temperature 14
4.2 Chemical characteristics 15
4.2.1 Total solids 15
4.2.2 pH value 15
4.2.3 Chloride content 16
4.2.4 Nitrogen content 16
4.2.5 Presence of fats , grease and oils 16
4.3 Biological characteristics 17
4.3.1 Bacteria 17
4.3.2 Microorganisms 17
4.3.3 Biochemical oxygen demand 18
5. Chapter-5 Processes involved in Sewage Treatment 19
5.1 Preliminary Treatment 19
v
 5.1.1 Screening 19
5.1.1.1 Fine Screen 20
5.1.1.2 Coarse Screen 20
5.1.2 Grit Chamber 21
5.1.3 Skimming Tank 22
5.1.4 Primary Sedimentation Tank 23
5.2 Secondary (or Biological) Treatment 23
5.2.1 Secondary Sedimentation Tank 24
5.2.2 Aeration Tank 24
5.2.3 Activated Sludge Process 25
5.3 Final Treatment 28
5.3.1 The final or advanced Treatment 28
5.3.2 Disinfection Chamber 28
5.3.3 Distribution Chamber 28
5.4 Final Disposal of Sludge 28
6. Chapter-6 Designing proposal for STP plant at SKIT College 30
6.1 Design of Screening 30
6.2 Design of Grit Chamber 31
6.3 Design of Skimming Tank 33
6.4 Design of Primary Sedimentation Tank 34
6.5 Design of Aeration Tank 35
6.6 Design of Secondary Clarifier 36
7. Chapter-7 About Sewage Treatment Plant at SKIT 38
7.1 Introduction 38
7.2 Working 38
7.2.1 Inlet Section 38
7.2.2 Screening 38
7.2.3 Aeration 39
7.2.4 Sedimentation 39
7.2.5 Sludge Tank 39
7.2.6 Pump House 40
7.3 Tests conducted on Wastewater 40
7.3.1 Measurement of Ph 40
7.3.2 Measurement of Turbidity 41
7.3.3 Measurement of Total Solids 41
7.3.4 Measurement of BOD 42
8. Chapter-8 Miscellaneous technique of Disposing Sludge 43
8.1 Disposal of MSW(refuse) by shredding and 43
pulverization
8.2 Disposal of MSW (refuse) by Composting 43
8.3 Disposal of MSW (refuse) by Incineration and 43
Pyrolysis
9. Chapter-9 Results and Discussions 44
10. Chapter-10 Scope for Future 45

vi
 LIST OF FIGURE

Specification of Figure Page No

Fig. no. 5.1.1.1 20
Fig. no. 5.1.1.2 20
Fig. no. 5.1.2 22
Fig. no. 5.1.3 23
Fig. no. 5.2.1 24
Fig. no. 5.2.2 25
Fig. no. 5.2.3 26
Fig. no. 5.4 29
Fig. no. 6.1 31
Fig. no. 6.2 32
Fig. no. 6.3 33
Fig. no. 6.4 34
Fig. no. 6.5 36
Fig. no. 6.6 37
Fig. no. 7.2.1 38
Fig. no. 7.2.2 38
Fig. no. 7.2.3 39
Fig. no. 7.2.4 39
Fig. no. 7.2.5 39
Fig. no. 7.2.6 40

vii
 LIST OF TABLES

Specification of Table Page No

Table 4.2 17
Table 7.3.1 40
Table 7.3.2 41
Table 7.3.3 41
Table 7.3.4 42

viii
 CHAPTERS

Chapter – 1 Introduction
Chapter – 2 Literature Review
Chapter – 3 Origin of Wastewater
Chapter – 4 Characteristics of Wastewater
Chapter – 5 Process involved in Sewage Treatment
Chapter – 6 Designing proposal for STP plant at SKIT College
Chapter – 7 About Sewage Treatment Plant at SKIT
Chapter – 8 Miscellaneous techniques of disposing digested Sludge
Chapter – 9 Results and Discussions
Chapter – 10 Scope for Future

ix
 INTRODUCTION Chapter-1

Water treatment is a process that improves the quality of water. It is used for drinking,
industrial water supply, irrigation, river flow maintenance. Water treatment
removes containments and undesirable components, or reduces their concentration so that
the water is useable in day to day life. Water is the most crucial compound for life on Earth,
and having drinkable water is a key worldwide concern for the twenty-first century. All living
things require clean, uncontaminated water as a basic requirement. Water covers more
than 71 percent of the earth’s surface, but only around 1% of it is drinkable according
to
international standards due to various contaminations. Waste water discharge from
industries, agricultural pollution, municipal waste water, environmental and global changes
is the main sources of water contamination.
Pollution in its broadest sense includes all changes that curtail natural utility and exert
deleterious effect on life. The crisis triggered by the rapidly growing population and
industrialization with the resultant degradation of the environment causes a grave threat to the
quality of life. Degradation of water quality is the unfavorable alteration of the physical,
chemical and biological properties of water that prevents domestic, commercial, industrial,
agricultural, recreational and other beneficial uses of water. Sewage and sewage effluents are
the major sources of water pollution. Sewage is mainly composed of human fecal material,
domestic wastes including wash-water and industrial wastes. The growing environmental
pollution needs for decontaminating wastewater result in the study of characterization of waste
water, especially domestic sewage.Water treatment is a process that improves the quality
of water. It is used for drinking, industrial water supply, irrigation, river flow
maintenance. Water treatment removes containments and undesirable components, or
reduces their concentration so that the water is useable in day to day life. Water is the most
crucial compound for life on Earth, and having drinkable water is a key worldwide concern
for the twenty-first century. All living things require clean, uncontaminated water as a
basic requirement. Water covers more than 71 percent of the earth’s surface, but only
around 1% of it is drinkable according to international standards due to various
contaminations. Waste water discharge from industries, agricultural pollution, municipal
waste water, environmental and global changes is the main sources of water contamination.

1
Sewage Treatment Plant is a facility designed to receive the waste from domestic, commercial
and industrial sources and to remove materials that damage water quality and compromise
public health and safety when discharged into water receiving systems. It includes physical,
chemical, and biological processes to remove various contaminants depending on its
constituents. Using advanced technology it is now possible to re-use sewage effluent for
drinking water.
The present study comprises the study on quality of domestic waste water and industrial waste
water (mixed sewage) .The study includes characterization tests for pH value, acidity,
alkalinity, chloride, turbidity & BOD etc. Depending upon the values of these parameters,
calculations are done for designing the different units of a 0.3 MLD Sewage Treatment Plant
and a preliminary layout is prepared for the same .

1.1 Objectives of the study:

The objective Of municipal and industrial waste water treatment is to extract pollutants,
remove toxicants, neutralize coarse particles, kill pathogens so that quality of discharged water
is improved to reach the permissible level of water to be discharged into water bodies or for
agricultural land.

Treatment of water thus aims at reduction of BOD, COD, total solids, nitrogen content etc. of
receiving water bodies and prevention of bio-magnification of toxic substances in food chain.
The effluents to be disposed of without danger to human health or unacceptable damage to the
natural environment.

The objective of this project can be summarized as-

Physical, chemical and biological characterization of waste water.

Comparison with the prescribed standard
Design of the sewage treatment plant.

1.2 Types of Wastewater Treatment Plant

Wastewater is the water that originates from water used in domestic, agricultural, industrial as
well as medical or transport activities. Basically, wastewater can be divided into two:

2
1.2.1 Sewage Water : Sewage water is wastewater from people living in a community. It is
the water released from households after use for various purposes like washing dishes,
laundry, and flushing the toilet, thus the name wastewater. The used water moves from
the houses through pipes installed during plumbing. The sewage water then moves into
sewers, either constructed by the house owner, or into a sewer facility set up by the
municipality. Mostly, sewage water consists of grey water and black water. Grey water
is the waste water from washing either from bathing, dishes or laundry. Black water is
the waste water from toilets. It is characterized by debris such as paper wrappings,
sanitary products, soap residues, and dirt due to the chemical composition of the
various waste materials. Plus, sewage water has a foul smell. The concern is that
it due to overpopulation in urban areas without proper planning, it has resulted
in Sewage pollution, which poses a threat not only to the environment but also
to human health. It also affects biodiversity, aquatic life, agriculture, and is a major
contributor to eutrophication and an increase in Biological Oxygen Demand (BOD).

1.2.2 Industrial wastewater : Industrial wastewater is not just a by-product of oil and gas
or mining and chemical manufacturing companies, but also a by-product of food
and beverage processing industries, essential in the making of the clothes on your back,
the shoes on your feet, the computer at your fingertips, and the car your drive. To
comply with existing laws, any organic and inorganic pollutants to water used
in industrial production must be managed. Organic matter, metals, and the like
found in the wastewater must be removed before the water can be safely
discharged back to land, into bodies of water, or reused in plant operations.

1.3 Sources of Water Pollution

Water pollutants may originate from
1. Point sources
2. Dispersed sources.
A point-source pollutant is one that reaches water from a single pipeline or channel,
such as a sewage discharge or outfall pipe.

3
 Dispersed sources are broad, unconfined areas from which pollutants enter a body of
water. Surface runoff from farms, for example, is a dispersed source of pollution,
carrying animal wastes, fertilizers, pesticides, and silt into nearby streams. Urban storm
water drainage, which may carry sand and other gritty materials, petroleum residues
from automobiles, and road deicing chemicals, is also considered a dispersed source
because of the many locations at which it enters local streams or lakes.

Point-source pollutants are easier to control than dispersed-source pollutants, since

they flow to a single location where treatment processes can remove them from the water.
Such control is not usually possible over pollutants from dispersed sources, which cause a
large part of the overall water pollution problem. Dispersed-source water pollution
is best reduced by enforcing proper land-use plans and development standards.
Understand global warming as a factor in the decline of dissolved oxygen in the ocean.
1.4 Sewage characteristics :
There are three types of wastewater, or sewage :
1. Domestic sewage
2. Industrial sewage
3. Storm sewage.
Domestic sewage carries used water from houses and apartments; it is also called sanitary
sewage. Industrial sewage is used water from manufacturing or chemical processes. Storm
sewage, or storm water, is runoff from precipitation that is collected in a system of pipes or
open channels.
Domestic sewage is slightly more than 99.9 percent water by weight. The rest, less than 0.1
percent, contains a wide variety of dissolved and suspended impurities. Although amounting
to a very small fraction of the sewage by weight, the nature of these impurities and
the large volumes of sewage in which they are carried make disposal of domestic wastewater
a significant technical problem. The principal impurities are putrescible organic materials and
plant nutrients, but domestic sewage is also very likely to contain disease-causing microbes.
Industrial wastewater usually contains specific and readily identifiable chemical compounds,
depending on the nature of the industrial process. Storm sewage carries organic materials,
suspended and dissolved solids, and other substances picked up as it travels over the
ground.

4
1.5 Principal pollutants
1.5.1 Organic material
The amount of putrescible organic material in sewage is indicated by the biochemical
oxygen demand, or BOD; the more organic material there is in the sewage, the higher the
BOD, which is the amount of oxygen required by microorganisms to decompose the
organic substances in sewage. It is among the most important parameters for the
design and operation of sewage treatment plants. Industrial sewage may have BOD levels
many times that of domestic sewage. The BOD of storm sewage is of particular concern
when it is mixed with domestic sewage in combined sewerage systems . Dissolved oxygen
is an important water quality factor for lakes and rivers. The higher the concentration
of dissolved oxygen, the better the water quality. When sewage enters a lake or stream,
decomposition of the organic materials begins. Oxygen is consumed as
microorganisms use it in their metabolism. This can quickly deplete the available oxygen
in the water. When the dissolved oxygen levels drop too low, trout and other aquatic
species soon perish. In fact, if the oxygen level drops to zero, the water will
become septic. Decomposition of organic compounds without oxygen causes the
undesirable odours usually associated with septic or putrid conditions.
1.5.2 Suspended solids
Another important characteristic of sewage is suspended solids. The volume of sludge
produced in a treatment plant is directly related to the total suspended solids present
in the sewage. Industrial and storm sewage may contain higher concentrations of
suspended solids than domestic sewage. The extent to which a treatment plant
removes suspended solids, as well as BOD, determines the efficiency of the treatment
process.
1.5.3 Plant nutrients
Domestic sewage contains compounds of nitrogen and phosphorus, two elements that are
basic nutrients essential for the growth of plants. In lakes, excessive amounts of
nitrates and phosphates can cause the rapid growth of algae. Algal blooms, often caused
by sewage discharges, accelerate the natural aging of lakes in a process called
eutrophication .

5
1.5.4 Microbes
Domestic sewage contains many millions of microorganisms per gallon. Most are
coliform bacteria from the human intestinal tract, and domestic sewage is also likely to
carry other microbes. Coliforms are used as indicators of sewage pollution. A high
coliform count usually indicates recent sewage pollution.

1.6 Sewerage systems

A sewerage system, or wastewater collection system, is a network of pipes, pumping
stations, and appurtenances that convey sewage from its points of origin to a point of
treatment and disposal.
1.6.1 Combined systems : Systems that carry a mixture of both domestic sewage and
storm sewage are called combined sewers. Combined sewers typically consist of
large-diameter pipes or tunnels, because of the large volumes of storm water that
must be carried during wet-weather periods. They are very common in older cities
but are no longer designed and built as part of new sewerage facilities. Because
wastewater treatment plants cannot handle large volumes of storm water, sewage
must bypass the treatment plants during wet weather and be discharged directly
into the receiving water. These combined sewer overflows, containing untreated
domestic sewage, cause recurring water pollution problems and are very troublesome
sources of pollution. In some large cities the combined sewer overflow problem has
been reduced by diverting the first flush of combined sewage into a large basin
or underground tunnel. After temporary storage, it can be treated by settling and
disinfection before being discharged into a receiving body of water, or it can be
treated in a nearby wastewater treatment plant at a rate that will not overload the
facility.

1.6.2 Separate systems : New wastewater collection facilities are designed as separate
systems, carrying either domestic sewage or storm sewage but not both. Storm
sewers usually carry surface runoff to a point of disposal in a stream or river. Small
detention basins may be built as part of the system, storing storm water temporarily
and reducing the magnitude of the peak flow rate. Sanitary sewers, on the other hand,
carry domestic wastewater to a sewage treatment plant. Pre-treated industrial

6
 wastewater may be allowed into municipal sanitary sewerage systems, but storm
water is excluded. Storm sewers are usually built with sections of reinforced
concrete pipe. Corrugated metal pipes may be used in some cases. The pipelines
are usually located to allow downhill gravity flow to a nearby stream or to a
detention basin. They usually are not less than 200 mm (8 inches) in diameter and carry
sewage by gravity into larger submains, or collector sewers. Interceptors are
usually built with precast sections of reinforced concrete pipe, up to 5 metres (15
feet) in diameter. Other materials used for sanitary sewers include vitrified clay,
asbestos cement, plastic, steel, or ductile iron.

1.7 Problems related to Wastewater

1. Decreasing of drinking water day by day.
2. Odour Issues in the Sewage Treatment Plant in India.
3. Harm aquatic and marine life.
4. Water Related Disease Like (Dengue, Malaria, Yellow Fever Etc.)

7
 LITERATURE REVIEW Chapter -2

PUSPALATHA ET.AL (2016) REVIEWED ON DESIGN APPROACH FOR

SEWAGE TREATMENT PLANT. A CASE STUDY OF SRIKAKULAM
GREATER MUNICIPALITY.
The present study involves the analysis of parameters like BOD, raw sewage, effluent. The
construction of sewage treatment plant will prevent the direct disposal of sewage in
nagavali river and the use of treated water will reduce the surface water and
contaminated ground water.
Pramod sambhaji patil et.al. (2016) studied on design of sewage treatment plant for
Dhule city.
Some treatment units are designed like screens, grit chamber, storage tank, settling tank,
aeration tank and skimming tank. The effluent can also be used for artificial recharge of
ground water, flushing, foam control, fire protection, lawn sprinkling.
Murthy polasa et.al (2014) reviewed about design of sewage treatment plant for gated
community.
In this project three types of treatment unit operations are conducted. Like physical,
chemical and biological processes. By increasing the detention time of sewage in each
treatment unit increases the efficiency of removal unwanted impurities.
Chakar Bhushan et al. (2017) reviewed about design of sewage treatment plant for
Lohegaon village, Pune.
This project studied that social and environmental pollution issue due to sewage is disposed
in some part of village and directly sewage drain in open land. It is used for recharging sub
surface water level at Lohegaon and used for irrigation purpose.
M. Aswathy et al. (2017) studied on analysis and design of sewage treatment plant of
apartment in Chennai.
This project is studied that domestic and commercial waste and removes the material with
possess harm from generated public. To produce an environmental sewage fluid waste stream
and solid waste suitable from disposal of use.
S. Ramya et al. (2015) reviewed on design of sewage treatment plant and characteristics
of sewage.
The growing environmental pollution need for decontaminating water results in the
study of characterization of waste water
especially domestic sewage. The waste water leads to developing and implementing new
treatment techniques to control nitrogen
and other priority pollutants.
Sequential batch reactor (SBR) Lin et al. (2004), investigate the municipal sewage
wastewater treatment by chemical coagulation and sequencing batch reactor (SBR)
methods with an aim to elevating water quality to meet the standards required for
agricultural irrigation. Both the conventional and modified SBR methods are considered. The
conventional SBR technology is a batch process based on a single activated sludge treatment
reactor.

8
 ORIGINS OF WASTE WATER Chapter -3

Sewage is created by residential, institutional, and commercial and industrial establishments

and includes household waste liquid from toilets, baths, showers, kitchens, sinks and
so forth that is disposed of via sewers. In many areas, sewage also includes liquid waste from
industry and commerce. The separation and draining of household waste into Greywater
and Black water is becoming more common in the developed world, with Greywater being
permitted to be used for watering plants or recycled for flushing toilets. Most sewage also
includes some surface water from roofs or hard-standing areas and may include storm
water runoff. Sewerage systems capable of handling storm water are known as combined
systems or combined sewers. Such systems are usually avoided now since they complicate
and thereby reduce the efficiency of sewage treatment plants owing to their seasonality.
The wide variability in flow, affected by precipitation, also leads to a need to construct much
larger, more expensive, treatment facilities than would otherwise be required. In addition,
heavy storms that contribute greater excess flow than the treatment plant can handle may
overwhelm the sewage treatment system, causing a spill or overflow. Modern sewer
developments tend to be provided with separate storm drain systems for rainwater. As
rainfall travels over roofs and the ground, it may pick up various contaminants including soil
particles and other sediment, heavy metals, organic compounds, animal waste, and oil and
grease. (See urban runoff.) Some jurisdictions require storm water to receive some level of
treatment before being discharged directly into waterways. Examples of treatment
processes used for storm water include retention basins, wetlands, and buried vaults with
various kinds of media filters, and vortex separators (to remove coarse solids). Sanitary
sewers are typically much smaller than storm sewers, and they are not designed to
transport storm water. In areas with basements, backups of raw sewage can occur if
excessive storm water is allowed into a sanitary sewer system. Wastewater or sewage can
come from :
• Human waste (faces, used toilet paper or wipes, urine, or other bodily fluids), also known
as Black water, usually from lavatories.
• Cesspit leakage.
• Septic tank discharge.
• Sewage treatment plant discharge.

9
• Washing water (personal, clothes, floors, dishes, etc.), also known as Greywater or
sullage.
• Rainfall collected on roofs, yards, hard-standings, etc. (generally clean with traces of oils
and fuel); Groundwater infiltrated into sewage.
• Surplus manufactured liquids from domestic sources (drinks, cooking oil, pesticides,
lubricating oil, paint, cleaning liquids, etc.).
• Urban rainfall runoff from roads, car parks, roofs, sidewalks, or pavements (contains oils,
animal faces, litter, fuel or rubber residues, metals from vehicle exhausts, etc.).
• Seawater ingress (high volumes of salt and micro-biota).
• Direct ingress of river water (high volumes of micro-biota).
• Direct ingress of manmade liquids (illegal disposal of pesticides, used oils, etc.).
• Highway drainage (oil, de-icing agents, rubber residues). Storm drains (almost anything,
including cars, shopping trolleys, trees, cattle, etc.).
• Black water (surface water contaminated by sewage).
• Industrial waste.
• Industrial site drainage (silt, sand, alkali, oil, chemical residues).
• Industrial cooling waters (biocides, heat, slimes, silt).
• Industrial process waters.
• Organic or bio-degradable waste, including waste from abattoirs, creameries, and ice cream
manufacture.
• Organic or non bio-degradable/difficult-to-treat waste (pharmaceutical or pesticide
manufacturing).
• Extreme pH waste (from acid/alkali manufacturing, metal plating).
• Toxic waste (metal plating, cyanide production, pesticide manufacturing, etc.)
• Solids and Emulsions (paper manufacturing, foodstuffs, lubricating and hydraulic oil
manufacturing, etc.).
• Agricultural drainage, direct and diffuse.
3.1 Wastewater Constituents
The composition of wastewater varies widely. This is a partial list of what it may contain:
• Water (> 95%) which is often added during flushing to carry waste down a drain
• Pathogens such as bacteria, viruses, prion and parasitic worms
• Non-pathogenic bacteria (> 100,000 / ml for sewage)

10
• Organic particles such as faces, hairs, food, vomit, paper fibres, plant material, humus,
etc.
• Soluble organic material such as urea, fruit sugars, soluble proteins, drugs,
pharmaceuticals, etc.
• Inorganic particles such as sand, grit, metal particles, ceramics, etc. Soluble inorganic
material such as ammonia, road-salt, seasalt, cyanide, hydrogen sulphide, thio-cyanides,
thio-sulfate, etc.
• Animals such as protozoa, insects, arthropods, small fish, etc.
• Macro-solids such as sanitary napkins, nappies/diapers, condoms, needles, children's toys,
dead animals or plants, etc.
• Gases such as hydrogen sulphide, carbon dioxide, methane, etc.
• Emulsions such as paints, adhesives, mayonnaise, hair colorants, emulsified oils, etc.
• Toxins such as pesticides, poisons, herbicides, etc.
3.2 Waste Water Quality Indicators
Any oxidizable material present in a natural waterway or in an industrial wastewater will be
oxidized both by biochemical (bacterial) or chemical processes. The result is that the oxygen
content of the water will be decreased. Basically, the reaction for biochemical oxidation may
be written as: Oxidizable material + bacteria + nutrient + O2 → CO2 + H2O +
oxidized inorganic such as NO3 or SO4
Oxygen consumption by reducing chemicals such as sulphides and nitrites is typified
as follows:
S -- + 2 O2 → SO4-
NO2 - + ½ O2 → NO3-
Since all natural waterways contain bacteria and nutrients, almost any waste compounds
introduced into such waterways will initiate biochemical reactions (such as shown above).
Those biochemical reactions create what is measured in the laboratory as the Biochemical
oxygen demand (BOD). Such chemicals are also liable to be broken down using strong
oxidizing agents and these chemical reactions create what is measured in the laboratory as the
Chemical oxygen demand (COD). Both the BOD and COD tests are a measure of the
relative oxygen depletion effect of a waste contaminant. Both have been widely adopted
as a measure of pollution effect. The BOD test measures the oxygen demand of biodegradable
pollutants whereas the COD test measures the oxygen demand of oxidizable pollutants. The

11
so-called 5-day BOD measures the amount of oxygen consumed by biochemical oxidation of
waste contaminants in a 5-day period. The total amount of oxygen consumed when the
biochemical reaction is allowed to proceed to completion is called the Ultimate BOD.
The Ultimate BOD is very time consuming, so the 5-day BOD has almost universally been
adopted as a measure of relative pollution effect. There are also many different COD tests
of which the 4-hour COD is probably the most common. There is no generalized correlation
between the 5-day BOD and the ultimate BOD. Similarly there is no generalized correlation
between BOD and COD. It is possible to develop such correlations for specific waste
contaminants in a specific waste water stream but such correlations cannot be generalized
for use with any other waste contaminants or waste water streams. This is because the
composition of any waste water stream is different. As an example and effluent consisting of
a solution of simple sugars that might discharge from a confectionery factory is likely to
have organic components that degrade very quickly. In such a case the 5 day BOD and
the ultimate BOD would be very similar i.e. there would be very little organic material
left after 5 days. . However a final effluent of a sewage treatment works serving a
large industrialized area might have a discharge where the ultimate BOD was much greater
than the 5 day BOD because much of the easily degraded material would have been
removed in the sewage treatment process and many industrial processes discharge difficult
to degrade organic molecules. The laboratory test procedures for the determining the above
oxygen demands are detailed in many standard texts. American versions include the "Standard
Methods for the Examination of Water and Wastewater".

3.3 Sewage Disposal

In some urban areas, sewage is carried separately in sanitary sewers and runoff from streets
is carried in storm drains. Access to either of these is typically through a manhole. During
high precipitation periods a sanitary sewer overflow can occur, causing potential public
health and ecological damage Sewage may drain directly into major watersheds with
minimal or no treatment. When untreated, sewage can have serious impacts on the quality of
an environment and on the health of people. Pathogens can cause a variety of illnesses. Some
chemicals pose risks even at very low concentrations and can remain a threat for long periods
of time because of bioaccumulation in animal or human tissue.

12
3.4 Effects on Biology : Sewage treatment plants can have multiple effects on nutrient levels
in the water that the treated sewage flows into. These effects on nutrients can have large effects
on the biological life in the water in contact with the effluent. Treatment ponds can include
any of the following: • Oxidation ponds, which are aerobic bodies of water usually 1- 2 meters
in depth that receive effluent from sedimentation tanks or other forms of primary treatment.
• Polishing ponds are similar to oxidation ponds but receive effluent from an oxidation pond
or from a plant with an extended mechanical treatment.
• Raw sewage lagoons or sewage lagoons are aerobic ponds where sewage is added with no
primary treatment other than coarse screening.
• Anaerobic lagoons are heavily loaded ponds.
• Sludge lagoons are aerobic ponds, usually 2-5 meters in depth, which receive an
aerobically digested primary sludge, or activated secondary sludge under water.

Phosphorous limitation is a possible result from sewage treatment and results in flagellate-
dominated plankton, particularly in summer and fall. At the same time a different study
found high nutrient concentrations linked to sewage effluents. High nutrient concentration
leads to high chlorophyll a concentrations, which is a proxy for primary production in marine
environments. High primary production means high phytoplankton populations and most
likely high zooplankton populations because zooplankton feed on phytoplankton.
However, effluent released into marine systems also leads to greater population
instability. A study done in Britain found that the quality of effluent affected the plank
tonic life in the water in direct contact with the wastewater effluent. Turbid, low-quality
effluents either did not contain ciliated protozoa or contained only a few species in small
numbers. On the other hand, high-quality effluents contained a wide variety of ciliated
protozoa in large numbers. Due to these findings, it seems unlikely that any particular
component of the industrial effluent has, by itself, any harmful effects on the protozoan
populations of activated sludge plants. The plank tonic trend of high populations close
to input of treated sewage is contrasted by the bacterial trend. In a study of Aeromonas spp.
in increasing distance from a wastewater source, greater change in seasonal cycles was
found the furthest from the effluent. This trend is so strong that the furthest location
studied actually had an inversion of the Aeromonas spp. cycle in comparison to that
of fecal coliforms.

13
 CHARACTERISTICS OF WASTE WATER Chapter-4

4.1 PHYSICAL CHARACTERISTICS

The sewage has the following physical characteristics:-

4.1.1 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 tasting device is the human nose. The odour
intensity is done by threshold odour test.
4.1.2 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.
4.1.3 Floatables:
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.
4.1.4 Temperature:
The normal temperature of sewage is generally slightly higher than the temperature of water.
The average temperature of sewage in India is 20℃.
The temperature has an effect on the biological activity of bacteria present in sewage.
Biological activities in sewage are higher at greater temperature.
Temperature also affects the solubility of gases in sewage. In addition, temperature also affects
the viscosity of sewage, which in turn affects the sedimentation process in its treatment.

14
4.2 CHEMICAL CHARACTERISTICS:-
The sewage has the following chemical characteristics:-

4.2.1 Total Solids:-

The sewage normally contains very small amount 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 present 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.

4.2.2 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.
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 measured quickly and automatically with the help of
a potentiometer.

15
4.2.3 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 measured by titrating the waste water with standard silver nitrate
solution, using potassium chromate as indicator.

4.2.4 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:

• Free ammonia
• Albuminoid nitrogen
• Nitrites
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 boiling the same. The
amount of nitrites or nitrates present in sewage sample can be measured by color matching
methods.
4.2.5 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.

16
Effluent discharged standards for Sewage Treatment Plant :
Parameter Existing general effluent Standards for new STP’s
Standards (CPCB) (CPCB)

BOD , mg/L 30 Not more than 10

Total suspended solid , mg/L 100 Not more than 20

COD , mg/L 250 Not more than 50

Ph 5.5-9 6.5-9.0
Total nitrogen , mg/L 100 Not more than 10
Faecal Coliforms MPN/100 Not specified Less than 100
mL

Table – 4.2

4.3 BIOLOGICAL CHARACTERISTICS:-

The sewage contains the following bacteria and microorganisms
4.3.1 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
d) Anaerobic bacteria - It helps the decomposition Of sewage in septic tank, cesspool etc.
e) Facultative bacteria - It has no function in sewage treatment.

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

17
4.3.3 Biochemical Oxygen Demand:
Biochemical Oxygen Demand (1301), 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
litre of sample during 5 days of incubation at 20 oc 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.

BOD is similar in function to chemical oxygen demand (COD), in that both measure the
amount of organic compounds in water. However, COD is less specific, since it measures
everything that can be chemically oxidized, rather than just levels Of biodegradable organic
matter

18
 PROCESS INVOLVED IN SEWAGE TREATMENT Chapter -5

Sewage can be treated close to where it is created, a decentralized system, (in septic tanks,
bio-filters or aerobic treatment systems), or be collected and transported via a network of pipes
and pump stations to a municipal treatment plant, a centralized system, (see sewerage
and pipes and infrastructure). Sewage collection and treatment is typically subject to local,
state and federal regulations and standards. Industrial sources of wastewater often require
specialized treatment processes (see Industrial wastewater treatment)
Sewage can be treated in different ways .Treatment process are often classified as:-
(i) Preliminary treatment
(ii) Secondary (or Biological ) treatment
(iii) Final treatment

5.1 PRELIMINARY TREATMENT :

Preliminary treatment consists solely in separating the floating materials (like dead animals,
tree branches, papers, pieces of rags, wood, etc.), and also the heavy settleable inorganic solids.
It also helps in removing the oils and greases, etc. from the sewage. This treatment reduces
the BOD of the wastewater, by about 15 to 30%. The process used are screening for removing
floating papers, rags, clothes, etc., Grit chambers or Detritus tanks for removing grit and sand.,
and skimming tanks for removing oils and greases .

5.1.1 SCREENING
Wastewater Screening is the first unit operation in all wastewater treatment plants. Screen is
the device used to retain solids found in the influent wastewater to the treatment plant such as
rags, paper, plastics etc . The main purpose of screening is to remove solid materials that could:
• Cause damage to other process equipment.
• Cause reduction in efficiency of the whole system
• Contaminate waterways
Some modern wastewater treatment plants use both coarse screens and fine screens.
Types of Screens:-
a) Fine screens
b) Coarse screens

19
5.1.1.1 Fine Screen
Fine screens are mechanically cleaned screens using perforated plates, woven wire cloths, or
very closely spaced bars with clear openings of less than 20 mm, less than 6 mm typical.
Commonly these are available in the opening size ranging from 0.035 to 6 mm. Fine screens
are used for pretreatment of industrial wastewaters and are not suitable for sewage due to
clogging problems, but can be used after coarse screening. Fine screens are also used to
remove solids from primary emuent to reduce clogging problem of trickling filters.

Fig.- 5.1.1.1

5.1.1.2 Coarse Screen:-

It is used primarily as protective device and hence used as first treatment unit. Common type
of these screens are bar racks (or bar screen), coarse woven-wire screens, and comminutors.
Bar screens are used ahead of the pumps and grit removal facility. This screen can be manually
cleaned or mechanically cleaned. Manually cleaned screens are used in small treatment plants.
Clear spacing between the bars in these screens may be in the range of 15 mm to 40 mm.

Fig.- 5.1.1.2

20
5.1.2 GRIT CHAMBER
Grit chamber is the second unit operation used in primary treatment of wastewater and it is
intended to remove suspended inorganic particles such as sandy and gritty matter from the
wastewater. This is usually limited to municipal wastewater and generally not required for
industrial effluent treatment plant, except some industrial wastewaters which may have grit.
The grit chamber is used to remove grit, consisting of sand, gravel, cinder, or other heavy
solids materials that have specific gravity much higher than those of the organic solids in
wastewater. Grit chambers are provided to protect moving mechanical equipment from
abrasion and abnormal wear, avoid deposition in pipelines, channels, and conduits; and to
reduce frequency Of digester cleaning.
Separate removal of suspended inorganic solids in grit chamber and suspended organic solids
in primary sedimentation tank is necessary due to different nature and mode of disposal of
these solids. Grit can be disposed Off after washing remove higher size organic matter settled
along With grit particles; whereas, the suspended solids settled in primary sedimentation tank,
being organic matter, requires further treatment before disposal .

Their functions are:

• To protect mechanical equipment’s used in the wastewater treatment plant from
abrasion. To prevent heavy deposits in pipelines and channels
• To reduce the frequency of digester cleaning.
• To reduce maintenance cost in high-speed centrifuges which needs almost all grit
particles to be removed. It is also inevitable to reduce grit load for the safe operation of heat
exchangers and pressure diaphragm pumps

Principle of Working of Grit Chamber

Grit chambers are nothing but like sedimentation tanks, designed to separate the intended
heavier inorganic materials (specific gravity about 2.65) and to pass forward the lighter
organic materials. Hence, the flow velocity should neither be too low as to cause the settling
of lighter organic matter, nor should it be too high as not to cause the settlement of the silt and
grit present in the sewage. This velocity is called "differential sedimentation and differential
scouring velocity". The scouring velocity determines the optimum flow through velocity.

21
 Fig.- 5.1.2

5.1.3 SKIMMING TANKS

A skimming tank is a chamber so arranged that the floating matter like oil, fat, grease etc.,
rise and remain on the surface of the waste water (Sewage) until removed, while the liquid
flows out continuously under partitions or baffles.
It is necessary to remove the floating matter from sewage otherwise it may appear in the form
of unsightly scum on the surface of the settling tanks or interfere with the activated sludge
process of sewage treatment. It is mostly present in the industrial sewage.
In ordinary sanitary sewage, its amount is usually too small. The chamber is a long trough
shaped structure divided up into two or three lateral compartments by vertical baffle walls
having slots for a short distance below the sewage surface and permitting oil and grease to
escape into stilling compartments.
The rise of floating matter is brought about the blowing air into the sewage from diffusers
placed in the bottom. Sewage enters the tank from one end, now'S longitudinally and leaves
out through a narrow inclined duct. A theoretical detention period of 3 minutes is enough. The
floating matter can be either hand or mechanically removed.
Grease traps are in reality small skimming tanks designed with submerged inlet and bottom
outlet .The traps must have sufficient capacity to permit the sewage to cool and grease to
separate. Frequent cleaning through removable covers is essential for satisfactory operation.
Grease traps are commonly employed in case of industries, garages, hotels and hospitals.

22
 Fig.- 5.1.3
5.1.4 PRIMARY SEDIMENTATION TANK
The primary sedimentation process is basically a physical process utilizing gravitational
forces. Settleable and suspended solids, which are the major components of sludge and are
heavier than water, settle out of the sewage along with any grit carryover from the head
works. Scum, which is lighter than water, floats to the surface and is removed by skimming.
Approximately 60 to 65 percent of the suspended solids will be removed by gravitational
forces as part of primary sedimentation.

5.2 SECONDARY (OR BIOLOGICAL ) TREATMENT

Secondary treatment involves further treatment of the effluent, coming from the primary
sedimentation tank. This is generally accomplished through biological decomposition of
organic matter, which can be carried out either under aerobic or anaerobic conditions. In these
biological units, bacteria will decompose the fine organic matter, to produce clearer effluent.
The treatment reactors, in which the organic matter is decomposed (oxidized) by aerobic
bacteria are known as aerobic biological units; and may consist of Filters (intermittent sand
filters as well as trickling filters), Aeration tanks, with the feed of recycled activated sludge
(i.e. the sludge, which is settled in secondary sedimentation tank, receiving effluents from the
aeration tank). Oxidation ponds and Aerated lagoons. Since all these aerobic units, generally
make use of primary settled sewage, they are easily classified as secondary units.

23
5.2.1 SECONDARY SEDIMENTATION TANKS
The Secondary Sedimentation Tanks are circular tanks equipped with rotating mechanical
sludge and scum collectors. Appurtenant systems include spray systems for moving
scum and for odour control, and pumps for draining tanks. Sedimentation Tank No. 1 is 75
feet in diameter with side water depth of 9 feet. Sedimentation Tank No. 2, is located just
south of Sedimentation Tank No. 1, is 65 feet in diameter with a side water depth of
12 feet. The walls of both tanks extend above the predicted 100 year flood-stage elevation. A
flap gate in each tank’s wall allows floodwater inflow so the structure will not become
buoyant and prevents wastewater outflow. The effluent from the Aeration Structure
enters each tank through the bottom, rises up through the centre column, and then is
distributed into the sedimentation zone. Settled sludge is removed through collecting
pipes located on the submerged collecting rake arms and by means of hydraulic differential
flows to the sludge collection chamber near the top of the centre column.

Fig.- 5.2.1
5.2.2 AERATION TANK
Aeration is the process by which air is circulated through , mixed with or dissolved in a liquid
or substance .
Aeration brings water and air in close contact in order to remove dissolved gases and to oxidize
dissolved metals , including iron , hydrogen sulfide and volatile organic chemicals (VOC’s) .
This process is typically the first major process at drinking water treatment plant , and occurs
in the secondary treatment processes of activated sludge treatment in wastewater treatment
plants . An evenly distributed oxygen supply in an aeration system is essential to effective
wastewater treatment for fostering microbial growth .

24
The efficiency of aeration depends on the amount of surface contact between air and water .
This is primarily controlled by the size of the water drop or air bubble . Aeration brings water
and air in close contact by exposing drops or thin sheets of water to the air or by introducing
small bubbles of air and letting them rise through the water . Dissolved gases are then removed
from the solution and allowed to escape into the surrounding air .
In municipal and industrial wastewater treatment, aeration is part of the secondary treatment
process. The activated sludge process is the most common option in secondary treatment
Aeration is an activated sludge process, promoting microbial growth in the wastewater. The
microbes then feed on organic material, forming flocks which easily settle out. Once settled
in a separate settling tank, bacteria forming the "activated sludge" flocks are continually
recirculated back to the aeration basin, increasing decomposition rates.
In industrial use, the most common method of aeration is water-fall aeration, through the use
of spray nozzles. There is also the air diffusion method of aeration, in which air is diffused
into a receiving vessel containing counter-current flowing water.
Aeration is used in liquids, soils and foods to improve quality and reduce contamination. The
process is used to oxidize soluble iron and manganese to insoluble precipitates. Aeration can
also reduce ammonia and hydrogen sulfide and is ideal for bacteria control. When it comes to
industrial water conditioning, the major objective of aeration is to remove carbon dioxide .

Fig.- 5.2.2

5.2.3 ACTIVATED SLUDGE PROCESS

The activated sludge process is a type of wastewater treatment process for treating sewage.
The general arrangement of an activated sludge process for removing carbonaceous pollution
includes the following items: An aeration tank where air (or oxygen) is injected in the mixed
liquor. This is followed by a settling tank (usually referred to as "final clarifier" or "secondary

25
settling tank") to allow the biological flocs (the sludge blanket) to settle, thus separating the
biological sludge from the clear treated water.
The general arrangement of an activated sludge process for removing carbonaceous pollution
includes the following items:
• Aeration tank where air (or oxygen) is injected in the mixed liquor.
• Settling tank (usually referred to as "final clarifier" or "secondary settling tank") to
allow the biological noes (the sludge blanket) to settle, thus separating the biological
sludge from the clear treated water.
Treatment of nitrogenous matter or phosphate involves additional steps where the mixed
liquor is left in anoxic condition (meaning that there is no residual dissolved oxygen).

Fig.- 5.2.3
Sludge production
Activated sludge is also the name given to the active biological material produced by activated
sludge plants. Excess sludge is called "surplus activated sludge" or "waste activated sludge"
and is removed from the treatment process to keep the ratio of biomass to food supplied in the
wastewater in balance. This sewage sludge is usually mixed with primary sludge from the
primary clarifiers and undergoes further sludge treatment for example by anaerobic digestion,
followed by thickening, dewatering, composting and land application.
The amount of sewage sludge produced from the activated sludge process is directly
proportional to the amount of wastewater treated. The total sludge production consists of the
sum of primary sludge from the primary sedimentation tanks as well as waste activated sludge
from the bioreactors. The activated sludge process produces about 70—100 kg/ML of waste

26
activated sludge (that is kg of dry solids produced per ML of wastewater treated; one mega
litre (ML) is 103 A value of 80 kg/ML is regarded as being typical. In addition, about 1 10—
170 kg/ML Of primary sludge is produced in the primary sedimentation tanks which most -
but not all - of the activated sludge process configurations use. I
A variant of the activated sludge process is the Nereda process where aerobic granular sludge
is developed by applying specific process conditions that favour slow growing organisms.
Sludge Digestion Process
The residue that accumulates in sewage treatment plants is called sludge (or bio solids).
Sewage sludge is the solid, semisolid, or slurry residual material that is produced as a by-
product of wastewater treatment processes. This residue is commonly classified as primary
and secondary sludge. Primary sludge is generated from chemical precipitation,
sedimentation, and other primary processes, whereas secondary sludge is the activated waste
biomass resulting from biological treatments. Some sewage plants also receive sewage or
septic tank solids from household on-site wastewater treatment systems. Quite onen the sludge
is combined together for further treatment and disposal.
Treatment and disposal of sewage sludge are major factors in the design and operation of all
wastewater treatment plants. Two basic goals of treating sludge before final disposal are to
reduce its volume and to stabilize the organic materials. Stabilized sludge does not have an
offensive odour and can be handled without causing a nuisance or health hazard. Smaller
sludge volume reduces the costs Of pumping and storage.
Sludge digestion may also take place is, in the presence of oxygen. The sludge is vigorously
aerated in an open tank for about 20 days. Although aerobic systems are easier to operate than
anaerobic systems, they usually cost more to operate because of the power needed for aeration.
Aerobic digestion is Often combined With small extended aeration or contact stabilization
systems.
Aerobic and conventional anaerobic digestion convert about half of the organic sludge solids
to liquids and gases. Thermal hydrolysis followed by anaerobic digestion can convert some
60 to 70 percent of the solid matter to liquids and gases. Not only is the volume Of solids
produced smaller than in conventional digestion, but the greater production Of biogas can
make some wastewater treatment plants self-sufficient in energy.

27
5.3 FINAL TREATMENT
5.3.1 The Final or Advanced Treatment
This treatment is sometimes called tertiary treatment, and consists in removing the organic
load left after the secondary treatment, and particularly to kill the pathogenic bacteria. This
treatment, which is normally carried out by chlorination, is generally not carried out for
disposal of sewage in water, but is carried out, while using the river stream for collecting
water for re-use or for water supplies. It may, however, sometimes be adopted, when the
outfall of sewage is very near to the water intake of some nearby to

5.3.2 Disinfection Chamber

Wastewater disinfection takes place after primary, secondary and sometimes tertiary
wastewater treatment. It is typically a final step to remove organisms from the treated
water before the effluent is released back into the water system. Disinfection prevents the
spread of waterborne diseases by reducing microbes and bacterial numbers to a regulated level.
A variety of physical and chemical methods are used to disinfect wastewater prior to
it being released into natural waterways. Historically, the chemical agent of choice for
municipal wastewater treatment has been chlorine, due to its disinfecting properties and
low cost. However, the rising cost of chlorine and concerns that low chlorine concentrations
can still be toxic to fish and other wildlife, has given rise to more physical methods
of wastewater disinfection being adopted such as ozonation or ultraviolet (UV) light

5.3.3 Distribution Chamber

The distribution sampling chamber is used to direct the outflow from a wastewater tank to a
percolation pipe network allowing treated water to percolate back into the ground. This
chamber is used to take periodic water samples so the performance of the wastewater tank can
be regularly tested .

5.4 FINAL DISPOSAL OF SLUDGE

All the sewage sludge produced at a treatment plant must be disposed of ultimately. Treatment
processes such as have been described may reduce its volume or so change its character as to
facilitate its disposal, but still leave a residue which in most cases must be removed from the

28
plant site. Like the liquid effluent from the treatment plant, there are two broad methods for
the disposal of sludge —
(l ) Disposal in water
(2) Disposal on land
This applies regardless of whether or not the sludge is treated to facilitate or permit the selected
method or disposal.
Disposal in Water:-
This is an economical but not common method because it is contingent on the availability of
bodies of water adequate to permit it. At some seacoast cities, sludge either raw or digested is
pumped to barges and carried to sea to be dumped in deep water far enough off shore to provide
huge dilution factors and prevent any ill effects along shore.
Disposal on land:-
Use of sludge for fill is confined almost entirely to digested sludge which can be exposed to
the atmosphere without creating serious or widespread odor nuisances. The sludge should be
well digested without any appreciable amount of raw or undigested mixed with it. It is
applicable, however, only where low waste areas are available on the plant site or within
reasonable piping distance. They are frequently used to supplement inadequate drying bed
facilities.

Fig.- 5.4

29
 DESIGNING PROPOSAL FOR STP PLANT IN SKIT COLLEGE
Chapter 6
6.1 DESIGN OF SCREENING
Maximum Flow = 0.30 MLD
= 0.0030 cumec
Velocity of flow (0.6m/sec-0.9m/sec) = 0.8 m/sec
Hence . Net submerged area of screen openings = maximum flow/velocity of flow
= 0.0030/0.8 = 0.0044 sqm
Gross vertical area required = net submerged area*Sin60
=0.0044*sin 60 = 0.0038 sqm
Providing a depth of 0.003 m
Width of channel = Gross vertical area / depth
= 0.0038/0.003 = 1.2700 m
The velocity of flow in screen chamber = Maximum flow/(Providing depth*Width of channel)
= 0.0030/(0.003*1.27) = 0.92 m/sec
Shape of bars : MS Bars
Size of bars : 10*50 mm2
Clear spacing : 30 mm (6-40mm for medium screens)
No. of bars required = 32 bars
Actual width of screen = No of bar*(clear spacing + dia. of bar)
= 1.28 m
Actual depth of sewage flow = Gross vertical area/Actual width of screen
= 0.0038/1.28 = 0.003m
Providing free board = 0.0050 m
Total depth of screen = 0.0080 m
Size of screen = 1.28*0.0080 m

30
 Fig.- 6.1

6.2 DESIGN OF GRIT CHAMBER

To prevent scouring of already deposited particles the magnitude of “v” should not exceed
critical horizontal velocity Vc .
The critical velocity , Vc , can be given by the following equation (Rao and Dutta , 2007)
8𝑔
Vc = √ β(Gs − 1) d
𝑓

Where ,
β = constant
= 0.04 for unigranular sand
= 0.06 for non uniform sticky material
f = darcy weisbach friction factor = 0.03 for gritty matter
g = gravitational acceleration
Gs = specific gravity of the particle to be removed (2.65 for sand)
d = diameter of the particle
(8∗9.81∗0.06∗(2.65−1)∗0.2)
Vc = √ = 0.228 m/sec
(0.03∗1000)

The grit chambers are designed to remove the smallest particle of size 0.2 mm with specific
gravity around 2.65. For these particles, using above expression the critical velocity comes
out to be Vc = 0.228m/sec

31
Keeping horizontal velocity 0.2m/s (<0.228m/s) to prevent scouring and detention time 60 sec
(vary from 40-60s)
To lower the velocity, hydraulic structures like Sutro weir and Parshal flume should be
provided.

Length of grit chamber = velocity of flow x detention time

= 12.00 m
Volume of grit chamber = discharge x detention time
0.2100 sqm
Cross section area of flow = volume of grit chamber/length

= 0.0175 sqm

Providing width of grit chamber = 3.00000 m

Depth of grit chamber = 0.0058 m

Now assuming Grit Generation (0.05 m 3 per 1000 m3 of sewage) = 0.05 m3

Grit storage provided for average flow = 8.00 hr

Storage Volume required = 0.01 m 3

Grit storage depth = 0.29m

Providing free board = 0.50 m

Total depth of Grit chamber = 0.79 m

Size of Grit Chamber = 12.00*3.00*0.79 m

Fig.- 6.2

32
6.3 DESIGN OF SKIMMING TANK

Detention time = 3 to 5 minutes

Compressed air required = 300 to 600 m 3

𝑞
Surface area required = A=0.00622
𝑉𝑟

Where ,

Q = Rate of flow of sewage in m/day

Vr = minimum rising velocity of greasy material to be removed in m/minute = 0.25 m/minute

Surface area required = 7.46 sqm

Side of tank = 3.00 m

Actual area of tank = 3.00*3.00 m

Fig.- 6.3

33
6.4 DESIGN OF PRIMARY SEDIMENTATION TANK

Continuous flow tank is to be provided

Detention time (1-2hrs) = 2.00 hr

Quantity of sewage treated = 25 m 3

Assuming that the low velocity through the tank = 0.30 m/minute

The length of tank required = Velocity of flow * Detention time

= 36.00 m

Cross section area of the tank required = capacity of the tank/length of the tank

= 1.00 sqm

Assuming that the water depth in the tank = 5.50 m

Width of the tank required = Area of cross section/Depth = 0.18 m

Since the tank is provided with mechanical cleaning arrangement , no space at bottom is
required for sludge zone .

Providing free board = 0.50 m

Overall depth of the tank = 6.00 m

Rectangular sedimentation tank = 36.00*0.18*6.00 m

Fig.- 6.4

34
6.5 DESIGN OF AERATION TANK

BOD of sewage aeration tank = 189.00 mg/L

BOD left in the effluent = 25.00 mg/L

BOD removed in activated plant = 86.77%

BOD upto 85%-92% conventional aeration process adopted

Volume of the aeration tank can be designed by assuming a suitable value of MLSS and θc (or
F/M ratio)

MLSS (between 1500-3000 mg/L) = 2500.00 mg/L

F/M ratio (between 0.3 to 0.4 ) = 0.30 YO XT

𝐹 𝑄 𝑌
= 𝑋
𝑀 𝑉 𝑋
V = 75.60 m3

Adopt an aeration tank of Liquid Depth = 5.00 m

Width of tank = 20.00 m

Length of tank = V/B*D = 0.76 m

Provide two aeration tanks , each of lengths = 0.38 m

Check for volumetric loading (0.4-0.7) = Q*YO/V = 0.75

OK

Check for Return Sludge Ratio = QR/Q

Assuming SVI (50-150 ml/gm) = 100.00 ml/gm

Check for Return Sludge Ratio(0.25-0.5) = 0.33ml/gm

OK

35
As all the parameters of design are coming in range , Hence design is OK

Providing free board = 0.50 m

Aeration Tank = 0.38*20.00*5.50 m

Fig.- 6.5

6.6 DESIGN OF SECONDARY CLARIFIER

No. of secondary clarifier = 1.0 no
Average flow = 300.00 m 3 /day
Recirculated flow (assuming 50%) = 150.00 m 3 /day
Total inflow = 450.00 m3 /day
Volume of tank = 37.5 m 3
Assume liquid depth = 0.05 m
Area (=volume/depth) = 750.00 m 2
Surface loading rate of average flow (25-35 m3/m/hr)
Surface area to be provided = 10.00 m 2

36
Taking area whichever is higher = 750.00 m 2
Dia of circular tank (d) = 30.90 m
Check for weir loading
Average flow = 300.00 m 3/day
Recirculated flow (assuming 50%) = 150.00 m 3/day
MLSS in tank = 25.00 mg/l
Total solid in inflow = 11.25 kg/day
Solid loading = 1.1250 kg/day/m
Providing freeboard = 0.005 m
Overall depth = 0.055 m

Fig.- 6.6

37
 ABOUT SEWAGE TREATMENT PLANT AT SKIT Chapter-7
7.1 INTRODUCTION :
A STP can be express as the factory , which prevents the environment from waste produced
by human beings . When the waste produced is beyond the limit of environment to decompose
, STP is only the solution . The STP reduces the waste produces manure and energy and helps
us to keep our rivers , ponds clean .
The STP is working of all the wastewater of the SKIT College . And the treated water is used
for the irrigation purpose in the entire college .
7.2 WORKING :
7.2.1 Inlet Section – The STP consist of inlet section . The raw sewage of the entire college
first collects here and then further gets treated step by step .

Fig.- 7.2.1
7.2.2 Screening – After commencement of water in inlet section it is screened through bar
screen inclined at an angle of 45 degree .

Fig.- 7.2.2

38
7.2.3 Aeration – Aeration is provided by fine bubble diffusers installed in groups at the tank's
bottom. Bio-mass growth on the biomedia aids in the break - down of contaminant which
results in clean water.

Fig.- 7.2.3
7.2.4 Sedimentation - sedimentation tank, also called settling tank or clarifier, component of a
modern system of water supply or wastewater treatment . A sedimentation tank allows
suspended particles to settle out of water or wastewater as it flows slowly through the tank,
thereby providing some degree of purification.

Fig.- 7.2.4
7.2.5 Sludge Tank - Sludge tanks are essential equipment. They act as a holding area for sludge
before it receives further treatment and disposal. After the sludge finally leaves the tank, it
is dewatered through a sludge press and hauled away in this area .

Fig.- 7.2.5
39
7.2.6 Pump House – This is the pump house built on STP at SKIT college from where
everything is getting controlled .

Fig.- 7.2.6
7.3 TESTS CONDUCTED ON WASTEWATER :
7.3.1 Measurment of pH :-
The negative logarithm of concentration of hydrogen ion gives the pH of a sample. pH varies
from 6-8 in waste water sample, due to hydrolysis of salts of bases and acids. Carbon dioxide,
Hydrogen Sulphide and Ammonia which are dissolved affect pH value of water.

Instrument – pH meter (an electrical device that determines the acidity or basicity Of aqueous
solutions)

Procedure - To use a pH meter, the pH electrode is first calibrated with standard buffer
solutions with known pH values. To make a pH measurement, the electrode is immersed into
the sample solution until a steady reading is reached. The electrode is then rinsed after each
sample and stored in a storage solution after all the measurements have been completed.

Calculations –
Sample 1 7.1
Sample 2 7.3
Sample 3 7.0
RESULT 7.13
Table-7.3.1
The resultant pH of the Raw sewage is – 7.13

40
7.3.2 Measurement of Turbidity
Turbidity refers to the cloudiness of water caused by tiny particles or suspended solids. These
particles are so small that they are invisible to the naked eye. Turbidity is technically described
as the measure of clarity in water. Turbidity in wastewater treatment describes the clarity or
haziness of a wastewater sample.
Calculations -
Sample 1 65
Sample 2 63
Sample 3 70
RESULT 66
Table-7.3.2
The resultant turbidity of the Raw sewage is – 66
7.3.3 Measurement for Total Solids:
Principle : The sample is evaporated in a weighed dish on a steam-bath and is dried to a
constant mass in an oven either at 103-105℃ or 179-181℃ . Total residue is calculated from
increase in mass .ln general, by evaporating and drying water samples at 179-181℃ values are
obtained which conform more closely to those obtained by summation of individually
determined mineral salts.
The apparatus used are:

• Evaporating Dish
• Drying Oven
• Desiccator
• Analytical Balance
The total amount of solids present 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 . The difference between the total solids and
the suspend solids represents dissolved solids plus colloidal.

Sample RAW (mg)

TS SS DS
Sample 1 569 38 531
Sample 2 934 272 662
Sample 3 470 132 338
RESULT 657 147 510
Table-7.3.3

41
7.3.4 Measurement for BOD:
Principle : The biochemical oxygen demand (BOD) test is based mainly on the classification
of biological activity of a substance. A procedure measures the dissolved oxygen consumed
by micro-organisms while capable of taking and oxidizing the organic matter under aerobic
conditions. The standard test condition lets in incubating the sample in an air tight bottle, in
dark at a required temperature for specific time.
The apparatus used are:

• Incubation Bottle
• Air incubator

i) Incubation Bottles : The bottle has capacity of 300 ml. It has narrow neck with
even mouth and has ground glass stoppers. New bottles are cleaned with 5 N hydrochloric
acid or sulphuric acid and rinsed with distilled water. In normal use, bottles once used for
Winkler's procedure should only be rinsed with tap water followed by distilled water.
During incubation water is added to the flared mouth of the bottle time to time, to ensure
proper sealing.

ii) Air Incubator: Air incubation with thermostatically controlled 270C +- 1℃. Light
is avoided to prevent possibility of photosynthetic production of oxygen.

Procedure : After taking water in incubation bottles, 4 gm of NaOH is kept at the neck of the
bottle. A magnetic stirrer is retained inside the bottle. The magnetic stirrer continuously
revolves inside the bottle. Special caps attached with an electronic meter keep the bottle air
tight. The instrument directly records BOD reading at every 24 hour. The bottles are preserved
in the incubators for days as per need of study. The same procedure follows for BOD 3 days
and BOD 5 days.

SAMPLE RAW mg/L

Sample 1 144
Sample 2 226
Sample 3 186
RESULT 185.3
Table-7.3.4
The resultant BOD of the sample is 185.3 mg/L
Observations : As the results of raw sewage we have obtained the values and compared from
their permissible values . Hence , further treatment of raw sewage is required before its disposal
into surface streams .

42
MISCELLANEOUS TECHNIQUE OF DISPOSING SLUDGE Chapter - 8

8.1 Disposal of MSW (Refuse) by Shredding and Pulverisation:-

The size and volume reduction of municipal solid waste MSW) is the physical processes of
actions of cutting and tearing, whereas, pulverisation refers to the action of crushing &
grinding . They help in reducing overall volume of the original MSW, by as much 40%. The
shredding and pulverising not only helps in reducing the volume of MSW but also changing
the physical character of the waste, which becomes odourless and unattractive to the
insects.The pulverised refuse, though contains fertilizing elements like potash, phosphorus,
and nitrogenous materials, yet cannot be suitably used as manure. It has, therefore, to be further
disposed of either by filling in trenches, or is digested in open windrows or closed digesters.

8.2 Disposal Of MSW (Refuse) by Composting:-.

Composting of refuse is a biological method of decomposing solid wastes. This decomposition
can be either under aerobic conditions, or under anaerobic conditions, or under both. The final
end product, is a manure, called the compost or humus, which is in great demand in European
countries as fertilizer for farms. Basically composting is considered to be an aerobic process,
because it involves piling up of refuse and its regular training, either manually or by
mechanical devices, so as to ensure supply of oxygen during its decomposition by bacteria,
fungi and other microorganisms.

8.3 Disposal Of MSW (Refuse) by Incineration and Pyrolvsis:-

Burning of refuse at high temperatures in incinerators, is quite a sanitary method of refuse
disposal where the collected refuse calorific value, and is, hence quite suitable to burning
Normally, however, only the combustible matter, such as garbage and dead animals are burnt,
and the incombustible matter like broken glass, chinaware, metals, etc. are either left unburnt
or are separated out for recycling and reuse, before buming the solid wastes. The left out ashes
and clinkers from the incinerators along with the non recycled incombustible materials may,
however, measure as much as 10 to 25% of the original waste, which in any case, shall have
to be disposed of either by sanitary land filling, or in some other productive manner.

43
 RESULTS AND DISCUSSIONS Chapter-9
After following the designing procedure , the size of different treatment units required are as
follows –
Size of screen – 1.28m x 0.0080m
Size of grit chamber – 12.00m x 3.00m x 0.79m
Size of skimming tank – 3.00m x 3.00m
Size of primary sedimentation tank – 36.00m x 0.18m x 6.00m
Size of aeration tank – 0.38m x 20.00m x 5.50m
Size of secondary clarifier – Diameter : 31m
Depth : 0.055m

As these parameters are coming within specified range .

Hence , the design is OKAY

LAYOUT OF SEWAGE TREATMENT PLANT

44
 SCOPE FOR FUTURE Chapter - 10

As per future perspective of this project, the characteristics of different units designed in this
project can be compared with alternate treatments units and their treatment efficiencies are
calculated for designing the STP.
For example — We choose activated sludge process in secondary treatment, but any other
treatment processes like trickling filters, aerated lagoons, RBCs can also be taken as secondary
treatment unit and are designed. The design values & other parameters related to it are
compared and the graphs are plotted accordingly. The best alternative should be selected as
the final one.

45
 REFERENCES

1. Manual on water supply and treatment, C.P.H.E.E.O., Ministry of Urban Devlopment;

Government Of New Delhi.

2. Manual on Sewerage and Sewage Treatment, C.P.H.E.E.O., Ministry of Urban

Devlopment; Government of India,New Delhi.

3. Jayshree Dhote, Sangita Ingole (2012); Review on Wastewater Treatment

Technologies Published in International Journal of Engineering Research and
Technology. pp. 2-5.

4. SciTech Encyclopaedia (2007) http:/ftv.vw.answer.com/topic/sewagetreatment 5)

A.K. Jain; Environmental Enginnering, Khanna Publishing House.

5. SK. Garg; Water supply and Sewage Disposal Engineering Vol 1&2, Khanna
Publications

46