This document provides information about the design of a sewage treatment plant for Bhagalpur municipality in India. It discusses the various components and processes involved in sewage treatment, including preliminary treatment like screening and grit removal, primary treatment using sedimentation, secondary treatment using activated sludge or rotating biological contactors, and tertiary treatment options like filtration, lagooning, and disinfection. It also provides design criteria for the sewage treatment plant including a 30-year design period and effluent quality standards.

1. SEWAGE TREATMENT PLANT
THIS PROJECT SUBMITTED IN PARTIAL FULFILLMENT
OF THE REQUIREMENT FOR THE DEGREE OF
BACHELOR OF TECHNOLOGY in Civil Engineering
Submitted By
RITWIZ KUMAR 15101119002
Gmail-ritwizaa100@gmail.com
DEPARTMENT OF CIVIL ENGINEERING
ADWAITA MISSION INSTITUTE OF
TECHNOLOGY, SHIVDHAM BANKA

2. ACKNOWLEDGEMENT
My heart quivers with the thrill for offering gratitude to those
individualswho helped me in completion of the project. The most idyllic
point of presenting a thesis is the opportunity to thank those who have
contributed to it.
Unfortunately, the list of acknowledging no matter how extensive is
always incomplete and inadequate. Indeed, this page of mention shall
never be able to touch the horizon of generousness of those who tendered
their help to me. First of all, I would like to express my gratitude and
obligations to Nitish sir, for her kindness in allowing me for introducing
the present topic and for her inspiring direction, constructive judgment
and valuable propositions throughout this project work. Next, I would
like to thank Ramish Rajasir for his relentless helpwithoutany complain.
I am sincerely thankful to him for his effort in improving my contents of
this project.
I am also thankful to Govind Raja Sir (Head of the Department of CIVIL)
for assigning me this interesting project and for his valuable suggestions
and boosts at various stages of the work. A combination of this nature
could never have been attempted without reference to and inspiration
from the works ofothers whose details are mentioned inreference section.
I acknowledge my indebtedness to all of them.
Lastbut not least, my sincere thanks to all my friends whohave patiently
extended all sorts of help for achieving this undertaking.
Raghunandan Das Prabhakar KumarSingh
2015101003 2015101047
Adwaita Mission Institute of Technology Shivdham
Bounsi, Banka (Bihar)

3. ABSTRACT
Bhagalpur municipality has been upgraded with corporation status. The
steady incremental in the city pollution resultin increase in domestic
sewage generation. Butstill now treatmentplant. So, it is required to
construct a sewage plantwith sufficient capacity to increase the sewage.
The Project deals with the design of sewage treatmentplantand it
majour component such as screening, chamber, grit chamber, skimming
tank, sedimentation tank, secondaryclarifier, active sludge tank and
sludge drying beds.
The project covers the 342 sq.km of Bhagalpur municipalcorporation of
next 30 years and its increasepopulation. Bhagalpur city, the head
quarter of Bhagalpur districtis a distance of 230 km at north west of
Patna and 370 km south west of Ranchi.
By the execution of project, the entire sewage of the city can be treated
effectively and efficiently.

4. INTRODUCTION
Sewage treatmentis the process of removing ofcontaminants from waste
water and household sewage, both runoff and domestic.it include
physical, chemical and biological process to remove physical, chemical
and biological contaminants .itobjective is to produce to treated influent
and solid waste sludge suitable for discharging or reuse back into the
environment. This material is often inadvertently contaminated with
many toxic and organicand inorganiccompounds.
Sewage implies the collecting of wastewater from occupied areas
and conveying them to some point of disposal. The liquid wastes will
require treatment before they are discharged into the water body or
otherwisedisposed of without endangeringthe public health or causing
offensive conditions.
As the cities have grown, the more primitive method of
excreta disposal has gain place to the water-carried sewerage system.
even in the small cities the greater safety of sewerage, its convenience,
and freedom from nuisance have caused it to be adopted wherever
finances permit.
DEFINITONS
Sewerage is the artof collecting, treating and finally disposing of
the sewage
Sewage is liquid, consist of any one or a mixture of liquid waste
origins from urinals, bath room, kitchens of a dwelling, commercial
building or institutional building.
Storm sewage is a liquid following in sewer during of following
a period of rain fall and resulting there from.
A partially separate sewer system is the sewerage system in which the
domesticsewage is carried with the storm water in rain season.

5. Activated sludge is the active biologicalfloc produce in activated sludge
plants, largely composed saprotrophic bacteria, protozone flora and
range of other filter feeding species.
Mixed Liquor Suspended Solid (MLSS)is the amount of
suspended solid in the mixed of raw water and activated sludge.
Return Active Sludge (RAS)is the activated sludge exerted from
the system and mixed with raw water to form the mixed liquor.
Waste Activated sludge (WAS)is exceed activated sludge thatis
exerted from the system to be directed to sludge treatment.
Sludge age is the average residence time ofbiologicalsolid in the
system.itcan be defined as the averagelifespan of bacteria in the system.
Overflow rate /Surface loadingis the discharge per unitof plan
area. This parameter is the design factor in designingthe settling tanks.
Food to micro-organism ratio is the ratio between daily BOD
load applied to Aerator system and total microbialmass in the system.
Objectives of the study:
The principal objective of waste water treatment is generally to allow
human and industrial effluents to be disposed of without danger to
human health or unacceptable damage to the natural environment. An
environmentally-safe fluid waste stream is produced. No danger to
human health or unacceptable damage to the natural environment is
expected. Sewage includes household waste liquid from toilets, baths,
showers, kitchens, sinks and so forth that is disposed of via sewers.
Sewage alsoincludes liquid waste from industry and commerce.
The following physical characteristics were studied:
i. Odour
ii. Taste
iii. Colour
iv. Floatables
v. Turbidity
The following chemical characteristics were studied:
i. Total Iron

6. ii. Copper
iii. Zinc iv. Potassium
v. Lead
vi. Aluminum
For determination ofinorganicnon-metallicconstituents, we determined
the:
i. Alkalinity
ii. Acidity
iii. Chloride iv. Residual Chlorine
v. Sulphate
vi. Ph. of the sample
vii. Biochemical Oxygen Demand
viii. Dissolved Oxygen
1.3 Literature Review:
Physicalcharacteristic of waste water:
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 acceptabilityof drinkingwater.
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
Taste: The sense of taste result mainly from chemical stimulation of
sensory nerve endings in tongue. Fundamental sensations oftaste are, by
convention more than by research evidence, salt, sweet, bitter, and sour.
The rating involves the following steps: a) dilution series including
random blanks is prepared b) initial tasting of about half the sample by
taking water into mouth and holding it for several seconds and
discharging itwithoutswallowing.c)Forming an initial judgmenton the

7. rating scale d) a final rating made for the sample e) rinsing mouth with
taste and odour free water f) resting.
Colour: Colour in water results from the presence ofnatural metallicions
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, Spectroscopicand Platinum cobaltmethod is used.
Total solids: It refers to matters suspended or dissolved in water and
waste water. Solids affect the water or effluent quality adversely in a
number of ways. Water with highly dissolved solids are not palatable
and may cause physiologicalreaction in transientconsumer.
A limit of 500 mg dissolved solids/L is desirable for drinking waters.
Evaporation method is used to separate total solids and their weight is
found out.
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
pathogenicbacteria and viruses.
Turbidity: Clarity of water is importantin producing products destined
for human consumption and in many manufacturing uses. It is caused
by suspended matter such as clay, silt, finely divided organic and
inorganic matter, soluble collared organic compounds. Turbidity is an
expression of the optical property that causes light to be scattered and
absorbed rather than transmitted in straight lines through the sample.
The standard method for determination of turbidity has been based on
the Jackson candle turbidimeter and Nephelometer.

8. Chemicalcharacteristic of waste water:
Chemical characteristics of water state the presence of metals their
treatment, the determination of inorganic non-metallic constituents and
the determination of organic constituents. Here goes a brief description
of all the experiments we have performed.
Biologicalcharacteristic of waste water:
Water quality has a key role in deciding the abundance, species
composition, stability, productivity and physiological condition of
indigenous populations of aquatic communities. Their existence is an
expression of the quality of the water. Biological methods used for
evaluating water quality include the collection, counting and
identification of aquatic organisms. Most microorganisms known to
microbiologists can be found in domestic wastewater like Bacteria,
Protozoa, Viruses, and Algae.
Planktons, Periphyton, Macro-python, Macro-invertebrates, Fish,
Amphibiansand Aquaticreptiles are the bioticgroup of interdependent
organisms. Wastewater contains vast quantities of bacteria and other
organisms. Aerobic bacteria break down organic matter in the presence
of available oxygen. Anaerobic bacteria disintegrate organic matter
which is shut off from free oxygen, such as in the interior of a mass of
faces or a dead body. The products of anaerobicdecomposition have an
extremely nauseatingodour. Matter in which this condition exists is said
to be septic. A multitude of the bacteria in wastewater are coliform
bacteria: those found in the digestive tract of normal humans. It is these
comparatively few pathogenic organisms that pose the greatest public
health hazard. Waste waterwhich is notproperly treatedmayeventually
find its way into a community water source and spread waterborne
diseases.
TREATMENT OF SEWAGE

9. The treatmentof sewage consists of many complex functions. The degree
of treatmentdepends upon the characteristics ofraw inletsewage as well
as the required effluent characteristics.
Treatmentprocess processes often classified as:
i. Preliminarytreatment
ii. Primary treatment
iii.Secondary treatment
iv.Tertiarytreatment
PRELIMINARY TREATMENT
Preliminary treatment consists solely in separating the floating
materials like free branches, papers, pieces of rags, wood, etc. and
heavy settable inorganicsolid. It helps in removal of oil a greases and
reduces the BOD by 15% to 30%. The process under these are:
 Screening - to remove floating papers, rags, clothes.
 Gritchamber - to remove gritand sand.
 Skimmingtank - to remove oils and greases.
PRIMARY TREATMENT
Removaloflarge objects from influentsewage
In primary treatment,the influent sewage water is strained to remove all
large objects that are deposited in the sewer system, such as rags, sticks,
tampons, cans, fruit, etc. This is most commonly done with a manual or
automated mechanically raked bar screen. The raking action of a
mechanical barscreen is typicallypaced according tothe accumulation on
the bar screens and/or flow rate. The bar screen is used because large
solids can damage or clog the equipment used later in the sewage
treatmentplant. The solids are collected in a dumpster and later disposed
in a landfill.
Sedimentation

10. Many plants have a sedimentation stage where the sewage is allowed to
pass slowly through large tanks, commonly called "primary clarifiers" or
"primary sedimentation tanks." The tanks are large enough that sludge
can settle and floating material such as grease and oils can rise to the
surface and be skimmed off. The main purpose of the primary
clarification stage is to produce both a generallyhomogeneous liquid
capable of being treated biologicallyand a sludge that can be separately
treated or processed.
SECONDARY TREATMENT
Secondarytreatment is designed tosubstantiallydegrade the biological
content of the sewage such as are derived from human waste, food
waste, soaps and detergent. The majority of municipal plants treatthe
settled sewage liquor using aerobicbiological processes. For this to be
effective, the biota require both oxygen and a substrate on which to live.
There are a number of ways in which this is done. In all these methods,
the bacteria and protozoa consume biodegradable soluble organic
contaminants (e.g. sugars, fats, organicshort-chain carbon molecules,
etc.) and bind much of the less soluble fractions into floc. Secondary
treatmentsystems are classified as fixed film or suspended growth.
Fixed-film treatmentprocess including tricklingfilter and rotating
biologicalcontactors where the biomass grows on media and the sewage
passes over its surface. In suspended growthsystems—such as
activated sludge—the biomass is well mixed with the sewage and can be
operated in a smaller space than fixed-film systems thattreat the same
amount of water.

11. Activated sludge
In general, activatedsludge plants encompass a variety of mechanisms
and processes that use dissolved oxygen topromote the growth of
biologicalfloc that substantially removes organicmaterial.
The process traps particulate materialand can, under ideal conditions,
convert ammonia to nitrite and nitrate and ultimately to nitrogen gas.
Secondary sedimentation
The final step in the secondary treatmentstage is to settle out the
biologicalfloc or filter material and produce sewage water containing
very low levels of organicmaterial and suspended matter.
Rotating biological contactors
Rotating biological contactors (RBCs)are mechanicalsecondary treatment
systems, which are robust and capable of withstandingsurges in organic
load. RBCs were first installed in Germany in 1960 and have since been
developed and refined into a reliable operating unit. The rotating disks
support the growth of bacteria and micro-organisms present in the
sewage, which breakdown and stabilize organicpollutants.

12. Tertiary treatment
The purpose of tertiary treatmentis to provide a final treatmentstage to
raisethe effluent quality before it is dischargedto the receiving
environment(sea, river, lake, ground, etc.). More than one tertiary
treatmentprocess may be used at any treatmentplant. If disinfection is
practiced, it is always the final process. It is also called "effluent
polishing."
Filtration
Sand filtration removes much of the residual suspended matter.
Filtration over activated carbon removes residualtoxins.
Lagooning
Lagooning provides settlementand further biological improvement
through storage in large man-made ponds or lagoons. These lagoons are
highly aerobicand colonization by native macrophytes,especiallyreeds,
is often encouraged. Small filter feeding invertebrates such
as Daphnia and species of Rotiferal greatlyassistin treatmentby
removing fine particulates.

13. Disinfection
The purpose of disinfection in the treatmentof wastewater is to
substantially reduce the number of microorganisms in the water to be
dischargedback intothe environment. The effectiveness of disinfection
depends on the quality of the water being treated (e.g., cloudiness, pH,
etc.), the type of disinfection being used, the disinfectantdosage
(concentration and time), and other environmentalvariables.Cloudy
water will be treated less successfully since solid matter can shield
organisms, especially from ultravioletlightor if contact times are low.
DESIGN PERIOD
A sewerage scheme involves the layingof underground sewer pipes and
construction of costly treatmentunits, which cannot be replaced or
increased in their capacities easily and conveniently ata latter date .in
order to avoid such complications, the future expansion of the city and
consequent increasein the sewage quantity should be forecast to serve
the community satisfactorilyfor a reasonable year.The future period for
which the provision is made in designing the capacities of various
components of the sewerage is known as the period. This sewage
treatmentplant is design for 30 years.
PARAMETERS RAW SEWAGE OF
BGP.Corp.*
EFFLUENT
(expacted)**
pH 6.4 5.5-9.0
BOD 300 mg/l <=20 mg/l
COD 600 mg/l <=250 mg/l
Oil $ Grease 50 mg/l <=5 mg/l
Total Suspended Soil 600 mg/l <=30 mg/l
Nitrogen 61mg/l <=5 mg/l
Ammonia Nitrogen 50 mg/l <=50 mg/l

14. Total Phosphorus
(as PS40)
5 gm/l <=5 gm/l
Total Coli form 100000MPN/ml <=1000 no/100 ml
*- Raw sewage characteristics, tested in environmental laboratory
with Technical division , Bhagalpur corporation.
**- Expected effluent characteristics according the design.
GEOMETRIC INCEASE METHAD
Year Population Increase in
population
Increase rate %
1991 253225
2001 340349 87124 34.4%
2011 410210 69861 20.5%
2021 472300 62092 15.14%
r1 = (100/253225)87124=34.4
r2 = (100/340349)69861=20.5
r3 = (100/410210)62092=15.14
r = (34.4 x 20.5 x 15.14)^1/3 =22.02
Population after 3 decay
P3 = 472300(1+(22.02/100)^3
P3 = 857836approx.
At design the period of 30 years the forecast population of the
Bhagalpur city is 857836.

15. CALCULATION OF SEWAGE GENERATION
Ultimate design period = 30 years
Forecasted population at 2050 = 857836
Per Capita Water Supply =135 lpcd
Ave. Water supply per Day =857836 x 135
=115807860
=116000000
=116 MLD
Average sewage generation per day = 80% of supplied water
= 0.8 x 116
=92.8 MLD
In cumec,
Avg. sewage generation per day =92.8 x 1061000 x 24 x 60 x 60
Avg. discharge = 0.308 cumec
Max. discharge = 3 x avg. discharge
= 3 x 0.308
=0.924 cumec

16. SEWAGE TREATMENT PROCESS
Sewage contain various type ofimpurities anddisease bacteria. This
sewage is disposed of by dilution or on land after collection and
conveyance. If the sewage is directly disposed of, it will be acted
upon the natural force, which will convertitintoharmful substance.
The natural source of purification cannot purify any amount of
sewage within specified time. ifthe quantity ofsewageis more, then
receiving water is more, then receiving water will become polluted
or the land will become sewage sick. Under the circumstances it
become essential to do some treatmentof the sewage, so that it can
accepted by the land or receiving water withoutany objection.
OBJECT OF TREATMET
Sewage treatment is the process of removing contaminants from
municipal wastewater, containing mainly household sewage plus
some industrial wastewater. Physical, chemical, and biological
processes are used to remove contaminants and produce treated
wastewater (or treated effluent) that is safe enough for release into
the environment. A by-product of sewage treatment is a semi-solid
waste or slurry, called sewage sludge. The sludge has to undergo
further treatment before being suitable for disposal or application
to land.

17. DEGREE OF TREATMENT
The degree of treatment will mostly be decided by regulatory
agencies and the extent to which the final product of treatment is to
be utilized. The regulatory bodies might have laid down standard
for thee influent or might specify the condition under which the
effluent must be discharge into the natural stream. The method of
treatment adopted should not only meet the requirement of the
regulatory bodies, but also result in the maximum use of the end
product with economy.
DESIGN PERIOD
The treatment plant normally designed to meet the requirement
over a 30 years period after it completion. The time lag between
design and completion should not normally exceed 2 to 3 years.
Care should be taken the plant is not considerablyunder loaded in
the initial stages, particularlythe sedimentation tank.
LAYOUT OF TREATMENT PLANT
The following point should be kept in mind while giving layout of
any sewage treatmentplant.
 All the plant should be located in the order of sequence, so
that sewage from one process should be directly go to the
process.
 If possible, all the plantshould be located at such elevation
that sewage can flow one plant into next under its force of
gravity only.
 All the treatment unit should be arranged in such a way
that minimum area is required itwill alsoensure economy
in its cost.
 Sufficient area should be occupied for future extension.
 Staff quarter and office also should be provided near the
treatment plant, so that the operators can watch the plant
easily.

18.  The site of treatment should be very neat and give very
good appearance.
 Bypass and overflow weir should be provided tocut out of
operation any unit when required.
FLOW DIGRAM OF SEWAGE TREATMENT PLANT
RECEIVING CHEMBER
Receiving chamber is the structure to receive the raw sewage
collected through Under Ground Sewage System from the city.it is
a rectangular shape tank constructed at entrance the sewage
treatment treatment plant. The main sewer pipe is directly
connected with this tank.

19. DESIGN
Design flow = 0.924 cumec
Detention Time = 60 sec
Volume required = flow x detention time
= 0.924 x 60
Vreq= 55.44 m³
Provide, depth = 3m
Area = 55.443
= 18.48 m²
Length: Breadth = 2:1
L x B = 2B x B = 2B² = 18.48
B = 3m
L = 6.2m
CHECK:
Volume designed = 6.2 x 3 x 3
Vdes = 55.8 m²
Vreq = 55.44 m³
Vdes > Vreq
Receiving chamber is designed for the size of
6.2m x 3m x 3m (SWD) + 0.5 (FB)

20. SCREENING
Screening is the first unit operation used at wastewater treatment
plants (WWTPs). Screening removes objects such as rags, paper,
plastics, and metals topreventdamage and clogging ofdownstream
equipment, piping, and appurtenances.
Coarse Screens
Coarse screens remove large solids, rags, and debris from
wastewater, andtypically have openings of6 mm (0.25 in)or larger.
Types of coarsescreens include mechanicallyand manuallycleaned
bar screens, including trash racks.
Fine Screens
Fine screens are typically used to remove material that may create
operation and maintenance problems in downstream processes,
particularly in systems that lack primary treatment. Typical
opening sizes for fine screens are 1.5 to 6 mm (0.06 to 0.25 in). Very
fine screens with openings of 0.2 to 1.5 mm (0.01 to 0.06 in) placed

21. after coarse or fine screens can reduce suspended solids to levels
near those achieved by primaryclarification.
DESIGN OF COARSE SCREEN:
Peak discharge of sewage = 0.924 m³/s
Assume the velocity of average flow is notallowed toexceed 0.8 m/s
The net area screen opening required = 0.92408
= 1.16 m²
Clear opening between bars = 30 mm =0.03 m
Size of the Bar = 75 mm x 10 mm
Assume width of the channel = 1 m
The screen bars as placed at 60º to the horizontal.
Velocity through screen at peak flow = 1.6 m/s
Clear area = 1.161 x 6 sin60
= 0.837 m²
No. of clear openings = 0.8370x 03
=28 Nos
Width of the channel = (28 x 30) +(29 x 30)
=1130mm = 1.13 m
Provide width of channel = 1.2 m
Coarse screen channel is designed for the size of
1.2 m X 0.7 m(SWD) +0.5 m(FB)

22. GRIT CHAMBER
Grit removal basins are the sedimentation basins placed in front of fine
screen to remove the inorganic particles having of 2.65 such as sand,
gravel, grit, egg shells and other non-putrescible materials that may clog
channels or damage pumps due to abrasion and to prevent their
accumulation in sludge digesters. the grits chamber is designed to scour
the lighter organicparticles while the heaviergritparticles remain settled
Here the horizontal flow type grit chamber is designed to give a
horizontal straight-line flow flow velocity, which is kept constant over
varyingdischarge
DESIGN
Peak flow of sewage =0.924m³/s
Assume average detention period =180s
Aerated volume =0.924x 180
= 168 m³
In order to drain the channel periodically for routine cleaning and
maintenance two chambers are used.
Therefore, volume of one aerated chamber = 1682 m³

23. = 84 m³
Assumed depth of 3m and Width to depth ratio2:1
Width of the channel = 2 x 3
= 6 m
Length of the channel = 843 x 6
= 4.7 m
Increase the length about 20% to account of inlet and outlet
Provide length =4.7m x 1.2m
=5.7 m
Gritchamber is designed for the size of 5.7m x 6m x 3m
SKIMMING TANK
A skimming tank is a chamber so arranged thatthe floating matter like
oil, fat, greaseetc., 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.

24. It is mostly present in the industrialsewage. In ordinary sanitary
sewage, its amountis usually too small.
DESIGN
The surface area required for the tank A = 6.22 x (10-3)x qVr m²
Where, q = rate of flow sewage in m³
Vr = minimum rising velocity pf the oily material to be
removed in m/min
q =0.924x 60 x 60 x 24
=79833.6m³/day
Vr = 0.25 m/min
=0.25 x 60 x 24
=360 m/day
A =6.22 x (10-3)x 79833.6360
A = 1.37 m² = 1.5 m² approx.
Provide the depth of the skimming tank is 3 m
The length breadth ratiois 1.5:1
Therefore L = 1.5 B
L x B =1.5 B²
Therefore B =1m
L =1.5 m
Skimmingtank is designedfor the size of1.5m X 1mX 3m + 0.5m(FB)

25. PRIMARY SEDIMENTATION TANK
In this step, the settleable solid are removed by gravitational settling
under quiescent conditions. The sludge formed at the bottom of the tank
is removed as under flow either by vacuum suction or by raking it to a
discharge pointat the bottom of the tank for withdrawal. The clear liquid
produced is known as the overflow and itshould contain noreadilysettle-
able matter.

26. The sedimentation operation in waste treatment applications may be
carried out in rectangular horizontalflow, circular radial flow or vertical
flow basis. Fig. shows the three main types of arrangements.

27. DESIGN
Max. quantity sewage = 92.8 MLD
Surface loading = 40 m³/m²/day
Detention period = 1 hrs
Volume of sewage = 26.560X 124
=1110 m³ approx.
Provide effective depth = 2.5 m
Surface area = 444 m²
Surface Area the tank = Total flow surface loading
=664 m²
Dia of tank = 664 x 4л =29.2 approx.
Primary sedimentation tank is designed for the dimension of
29.2 m(dia)X 2.5m (depth) +0.5 (FB)

28. SECONDARY SEDIMENTATION TANK
A sedimentarytank constructed next to the aeration tank is the
secondary sedimentation. this tank will be as the primary sedimentation
tank with certain
Modifications as no floating materialsare here, provisions for the
removal floatage are not needed.
The surface area for the secondary sedimentation tank for the
removal of scum, floatage are not needs
The surface area for the secondary sedimentation
tank is designed for both overflow rate basis and solids and solid
loading rate basis, the larger value is adopted.

29. DESIGN
NO. OF secondary clarified = 1
Average flow =110000 m³/day
Recirculated flow = 53%
= 14070m³/day
Total inflow = 110000+14070
=
Provide hydraulicdetonation period = 2 hrs
Volume the tank =40630 x 224
= 3386.4m³
Assume liquid depth = 3.5 m
Area = 3386.43 x .5
= 967.54m²
surface loading rate of averageflow =25 m³/m²/day
surface area provide = 1062.4m²
Dia =1062.4 x л
= 37 m approx.
I. CHECK FOR WEIR LOADING:
Average flow =100000m³/day
Wear loading = 100000x 37л
176.13m³/day/m
It is lesser than 185 m³/day/m. Hence it is OK.
II. CHECK FOR SOLIDS LOADING:
Recirculated flow = 14070 m³/day
Average flow = 110000m³/day
MLSS in the tank = 3000 mg/l
Total solid in flow = (110000+14070)X 3 =372210kg/day

30. Solid loading = 125.98kg/day
It is lie between 100-150kg/m²/day
Hence it is OK.
Provided secondary sedimentation as 37m(dia)X 3.5m(depth)+ 0.5m
Hopper slope shall be 1 in 12.
STABILIZATION TANK
Total return flow =14070 m³/day
=9.771 X 15
= 146.6 m³
Provide depth as 3m, width as 5 m
Therefore, length is =9.8m
Wet well dimension as 9.8m X 5m X 3m + 0.5 m (FB)
Dry well dimension as 9.8m X 9.8m
2 No. of pump house of each of 14.07 MLD capacity in the well are
provided.
SLUDGE DRYING BED
Sludge drying beds are provided to allow surplus sludge that is
withdrawn from the process to dry for easier handling. Sludge
drying relies on an underground drainage system as well as sunshine.
Liquid from the underdrainsshould be returned to the sewage treatment
process for further treatment.
A sludge dryingbed is a common method utilized to dewater sludge via
filtration and evaporation. Perforated pipes situated at the bottom of
the bed are used to drain seepage water or filtrate. A reduction of about
35% or less in moisture content is expected after drying.

31. DESIGN
Sludge applied to dryingbed atthe rate of 100kg/MLD
Sludge applied =300kg/day
Specific gravity = 1.015
Solid content = 2%
Volume of sludge =14.778m³/day
Number of cycle in one year =36510
=37 cycle
Period of each cycle =10 days
Spreadinga layer of 0.3m per cycle,
Area of bed required = 500m²
Provide 5 nos. of bed =100 m²
5 bed of dimension 12.5m X 8m are designed.
SEWAGE DISPOSAL
When a liquid sludge is produced, further treatmentmay be required to
make it suitable for final disposal. Sludges are typicallythickened
and/or dewateredto reduce the volumes transported off-site for
disposal. Processes for reducing water content include lagooning in
drying beds to produce a cake that can be applied to land or
incinerated; pressing, where sludge is mechanicallyfiltered,often
through cloth screens to produce a firm cake; and centrifugation where
the sludge is thickened by centrifugallyseparatingthe solid and liquid.
Sludges can be disposed of by liquid injection to land or by disposal in a
landfill.
There is no process which completely eliminates the need to dispose of
treated sewage sludge.
The disposal of treated effluent into land or water body is sewage
disposal. This can be of two method –

32.  Dilution – disposal on water bodies.
 Effluent irrigation – disposal on land.
DILUTION:
The disposal of effluent by discharging it into water courses such as
streams, rivers or large body of water such as lake, sea is called dilution.
IFFLUENT IRRIGATION:
when the effluent is spread on the surface of land It is effluent irrigation.
The water of sewage percolates on the ground and the suspended solid
remain on the surface of ground. The remaining organicsuspended solid
are partially acted upon by the bacteria and are partially oxidised by
exposure to atmosphericaction of heat, lightand air.
SI no. Characteristics Tolerance limitas per IS
: 3307-1986
Effluent of the
plant
1 pH 5.5-9.0 5.5-9.0
2 BOD 100 mg/l <=20 mg/l
3 suspended solid 200 mg/l <=30 mg/l
4 Oil and Grease 10 mg/l <=5 mg/l
5 Chlorides 600 mg/l <=400 mg/l
6 Sulphate 1000 mg/l <=250 mg/l
Compression between IS: 3307-1986 and expected effluent’s
characteristics.
The effluent to be disposed and Land Effluent Irrigation method and it is
done by constructing Ridge and Furrow in the disposal land. Here the
land is first ploughed up to 45cm, then lived and divided into plots and
sub-plots. Then each sub-plot is enclosed by small dykes. Now ridge and
furrows are formed in each sub-plot. The sewage is allowed to flow in
furrows, whereas crop are grown on ridge. After an interval of 8-10 days
the sewage can be be again applied depending on the crop.

33. SALIENT DETAILS OF PROJECT
S No. ATTIBUTE DATA
1 PROJECT Sewage treatmentplantfor BGP
municipal corporation
2 Sewage type Partially Separate Sewerage
System
3 Population Census
1991 253225
2001 340349
2011 410210
2018 462101
2021 472308
4 Method of Forecasting Incremental Increase Method
5 Design Population
Base year-2031 576301
Intermediate-2041 703202
Ultimate year-2051 858047
6 Per Capita water supply 135LPCD
7 Existing Sewerage
System
Nil

34. CONCLUSION
A successful technical project involves integration ofvarious field. This is
an attempt to combine several aspects of environmental, biological,
chemical and CIVIL Engineering.
Since, In Bhagalpur Municipal Corporation there is notreatmentplantfor
sewage, itis necessary to construct a sewage treatmentplant. The plantis
designed perfectly to meet the future expansion to the next 30 yeas in
accordance with Indian Codal provisions. This project consists the design
of the complete component of the Sewage Treatmentplantfrom receiving
chamber, screening chamber grit chamber, Skimming Tank, secondary
tank, secondary clarifier, Active Sludge Tank for the sewage.