Design of Primary Sewage Plant

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RESEARCH TITLE

DESIGN OF PRIMARY SEWAGE TREATMENT PLANT FOR SHIATS

ALLAHABAD

BY

Er. ANURAG SINGH

B.Tech

SHIATS ALLAHABAD

M.TECH

BIT MESRA


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TABLE OF CONTENTS

Chapter Title Page No.

ACKNOWLEDGEMENT I

ABSTRACT II

LIST OF FIGURE III

LIST OF TABLE IV

LIST OF ABBRAVITIONS V

LIST OF SYMOLS VI

I INTRODUCTION

Sewage 2

Waste Water Volume in India 2

Need of Domestic Sewage Treatment 3

Benefits of Sewage Treatment Plant 3

Waste Water Reuse in India 4Objective of the Study 4

II REVIEW AND LITERATURE 510III MATTERIALS AND MATHODS

3.1 Climate 11

3.2 Sewage 11

3.3 Treatment of Sewage 12

3.3.1 Preliminary Treatment 12

3.3.2 Primary Treatment 12

3.3.3 Secondary Treatment 13

3.3.4 Tertiary Treatment 133.4 Sewage treatment process 15

3.5 Degree of Treatment 15

3.6 Design Period 15

3.7 Estimation of sewage volume 16

3.8 Location of Treatment Plant 18

3.9 Layout of Treatment Plant 18

3.10 Point Consideration in Design 19

3.11 Design of Receiving Chamber 21

3.12 Screening 23

3.12.1 Design of Coarse Screen 243.13 Design of Grit Chamber 25

3.14 Design of Skimming Tank 26

3.15 Design of Primary Sedimentation Tank 27

3.16 High Rate Trickling Filter 28

3.16.1 Estimation of BOD in raw sewage 29

3.16.2 Filter area 29

3.16.3 Design of rotary distribution 31

3.16.4 Design of arms 31


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3.17 Activated Sludge Process 31

3.18 Contact Stabilation Method 32

3.19 Design of Aeration Tank 32

3.20.1 Check for Aeration Period/HRT 34

3.20.2 Check for volumetric Loading 34

3.20.3 Check for Return sludge Ratio 343.20.4 Check for SRT 35

3.21 Capacity of pump 35

3.22 Dry bed 36

3.23 Sewer pipe line 37

3.23.1 Forces acting on sewer pipe line 37

3.23.2 Criteria for selecting the material of sewer pipe 37

3.23.3 Operation and maintenance of sewer 39

IV RESULT AND DISCUSSION

4.1 Calculation of Sewage Generation 424.2 Receiving Chamber 45

4.3 Coarse Screen 47

4.4 Grit Chamber 49

4.5 Skimming Tank 51

4.6 rimary Sedimentation tank 52

4.7 High Rate Trickling Filter 55

4.8 Aeration Tank 57

4.9 Sludge Drying Beds 59

4.1 Sewer Pipe 61

V SUMMARY AND CONCLUSION 63REFERENCE 6466APPENDIX 67 -84


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ABSTRACT

A study was conducted for the primary treatment and management of sewage generated in

SHIATS hostels and residential area and a sewage treatment plant was designed. The total

sewage generated in one day was estimated 3.6ML considering the projected population

hostels and residential for the next 30 years. The various components of primary sewage

treatment plant viz. screening chamber, grit chamber, skimming tank, sedimentation tank,

active sludge tank and sludge drying bed were designed considering the various standards

and permissible limits of treated sewage water. It was concluded from the study that in next

30 years the predicted population will be 23,000 and estimated sewage will be 3.6 MLD.

The receiving chamber of dimension 4m x 2m x 1.5m, the coarse screen of dimension 0.6m

x 5.3m, Grit chamber of dimension 5.2m x 3m x 1.3m, Primary sedimentation tank with

diameter of 7m and depth 2.5m, trickling filter of diameter 15.5m and depth 2m, aeration

tank of dimensions15m x 8m x 4m and sludge dry bed of dimensions 12.5m x 8m will

effectively treat the sewage water at primary stage keeping the sewage quality within the

permissible limits.

It was recommeneded that the treated water will be supplied for irrigating the crops on

Research Farm and the remaining sludge after treatment will be used as manure on Farm.

The use of treated water will reduce the ground water use and additionally the treated sludge

will be very useful for increasing the fertility of soil.


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LIST OF FIGURES

Fig. No. Title Page no.

3.1 Flow chart of processes of sewage treatment plant 17

3.2 Layout of sewage treatment plant 22

4.1 Receiving chamber 46

4.2 Corse screen 48

4.3 Grit chamber 50

4.4 Skimming tank 52

4.5 Sedimentation tank 54

4.6 Trickling filter 56

4.7 Aeration tank 58

4.8 Sludge drying bed 60

4.9 Layout and designing of primary sewage treatment plant 62


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LIST OF TABLES

Table No. Title Page No

3.1Climatologically Data of AllahabadDistrict

14

3.2Chemical Quality of Raw Sewage andStandard

20

3.3Non - scouring Limiting Velocities in

Sewer and Drains

40

3.4 Manhole Spacing as per IS 1742196040

3.5

Internal Dimension for Manhole Chamber

as per

IS 17421960

41

4.1 Detail result of primary sewage treatment plant43

4.2 Details of receiving chamber45

4.3 Details of coarse screen 47

4.4 Details of grit chamber 49

4.5 Details of skimming tank 51

4.6 Details of primary sedimentation tank53

4.7 Details of trickling filter55

4.8 Details of aeration tank57

4.9 Details of sludge drying bed 59

4.10 Details of sewer pipe line6


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LIST OF ABBREVIATIONS

BOD Biochemical oxygen demand

DO dissolved oxygen

Fig Figure

e.g Example gratia. For example

etc. Etcetera

et.al et. Alibi and other

l/h/d liter head per day

COD Chemical oxygen demand

MLD million liter per day

MLSS Mixed liquor suspended solids

HRT hydraulic retention time

SRT Solids Retention Time

NPK nitrogen phosphorus potassium

H.P Horse power
http://en.wikipedia.org/wiki/Chemical_oxygen_demandhttp://en.wikipedia.org/wiki/Chemical_oxygen_demandhttp://en.wikipedia.org/wiki/Chemical_oxygen_demand


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LIST OF SYMBOLS

% Percentage or per hundred

C Degree Celsius

mm MeterCm Centimeter

mm Milli meter

Hrs Hours

Vs velocity of critical particle

Q Flow rate

A Area

Kinematic viscosity

Ss Sp. Gravity of a particle

Dp Dia. of a critical particleV Volume

d Depth

H Head loss

Va Aerated volume of chamber

L Length

W Width

D Diameter

Efficiency

BOD at inlet

BOD at outletXt MLSS

T HRT

Sludge recirculation rate

C SRT


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CHAPTER - I

INTRODUCTION

More than two billion people worldwide lives in regions facing water scarcity. Water scarcity

already affects every continent and more than 40 percent of the people on our planet. By

2025, 1.8 billion people will be living in countries or regions with absolute water scarcity,

and two-thirds of the worlds population could be living under water stressed conditions.

Global water use has been growing at more than twice the rate of population growth in the

last century. About 1.1 billion people do not have access to adequate water to meet their most

basic needs. Around 1.2 billion people, or almost one-fifth of the worlds population, live in

areas of physical water scarcity, and 500 million people are approaching this situation (FAO,

2003)

Agriculture is the number-one user of water worldwide, accounting for about 69% of all

freshwater withdrawn from lakes, rivers and aquifers. The daily drinking water requirement

per person is 2-4 liters, but it takes 2000 to 5000 liters of water to produce one persons daily

food.

Indias demand for water is growing at an alarming rate. India is surrounded by water bodies

on the three sides, yet we face water shortage every year. The per capita water availability inIndia was 3450cu.m in 1951. By 2025 the annual per capita availability of water is expected

to rise drastically from the current 1800cu.m per person to 1200 1500 cu.m. The quality of

available water is also fast deteriorating, over extraction of ground water has led to salt water

intrusion into coastal aquifer. It has also resulted into presence of excessive fluoride, iron,

arsenic and salinity in water affecting about 44 million people in India. Groundwater is

facing an equally serious threat from contamination by industrial effluent and fecal matter as

well as pesticides and fertilizers from runoff. Unless priority is given quickly to creating an

infrastructure to assure availability of water, there may be no water to meet agricultural,

domestic and industrial needs of a population that has tripled in 50 years to one billion.

Sewage treatment is the process of removing contaminants from wastewater and household

sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological

processes to remove physical, chemical and biological contaminants. Its objective is to

produce a treated effluent and a solid waste or sludge suitable for discharge or reuse back


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into the environment. This material is often inadvertently contaminated with many toxic

organic and inorganic compounds.

Sewage implies the collecting of wastewaters 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 otherwise disposed of without endangering the public health or

causing offensive conditions.

Sewage

Sewage is a dilute mixture of the various types of wastes from the residential, public and

industrial places.

The sewage pollutant causes undesirable changes and it affects the land, water and air or the

environment as a whole. In the modern living the heavy industrialization and increase of

population increased the rate of water pollution. Therefore, the need of water pollution

control has drawn the attention of the concerned department. The characteristics and

composition of sewage mainly depend on this source. The main Source of water pollution is

industrial wastes coming from the industrial area and big industries contain grease, oil

chemical, highly odorous substances, explosives, etc. The main industries which contribute

to the Indian rivers pollution are oil and soap, pulp-paper, sugar and distilleries, chemical,

textile, steel mills, pharmaceuticals, tanneries, oil refineries and various other miscellaneousindustries. The other source is domestic sewage which also contains oils, human excreta,

decomposed kitchen wastes, soapy water etc.

Wastewater Volumes in India

Urban areas in India generated about 5 billion liters a day (bld) of wastewater in 1947 which has

Increased to about 30 bld in 1997 (Winrock International, India 2007). According to the Central

Pollution Control Board (CPCB), 16 bld of wastewater is generated from Class-1 cities

(population >100,000), and 1.6 bld from Class-2 cities (population 50,000-100,000). Of the

45,000 km length of Indian rivers, 6,000 km have a bio-oxygen demand above 3 mg/l, making

the water unfit for drinking (CPCB 1998). An estimated 80% of wastewater generated by

developing countries, especially China and India, is used for irrigation (WinrockInternational

India 2007). In India, where wastewater is mainly used in agriculture, a policy framework

covering the issues associated with this practice is lacking. Strauss and Blumenthal (1990)


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estimated that 73,000 ha were irrigated with wastewater in India. However, Buechler and

Mekala (2003: 939) estimated that even just along the Musi River that runs through Hyderabad

city in Andhra Pradesh State, and the canals and tanks off this river approximately 40,000 ha of

land were irrigated with urban and industrial wastewater diluted with fresh river water

especially during the monsoon season. Untreated wastewater from domestic, hospital and

industrial areas pollute rivers and other natural water bodies. More than 80% (only 4,000

Million Liters per Day [MLD] out of 17,600 MLD wastewater generated in India is treated) of

wastewater generated is discharged into naturalwater bodies without any treatment due to lack

of infrastructure and resources for treatment(Winrock International India 2007).

Farmers have customary rights to any water that flows through the river and it should be the

responsibility of the irrigation and water authorities to maintain the quality of this water to

ensure the sustainable use of this water. The interviews held with farmers along Musi River in

Hyderabad clearly highlight that the wastewater quality is very poor and has adverse impacts on

the health of farmers and reduces soil productivity over time, not to mention the high water

tables and groundwater contamination in these areas. The Water Act covers industrial effluent

standards, but ignores the domestic and municipal effluents even though they constitute 90% of

Indias wastewater volumes (Sawhney 2004).

Need and Benefit of Domestic Sewage TreatmentSewage treatment, or domestic wastewater treatment, is the process of removing

contaminants fromwastewater and household sewage,bothrunoff (effluents)and domestic.

It includes physical, chemical, and biological processes to remove all the pathogens, that it

may not pollute the receiving water and make than unsafe for use, to reduce the volume of

sewage sludge, so that it can be easily disposed off.

The cost of reclaimed water exceeds that of potable water in many regions of the world,

where afresh water supply is plentiful. However, reclaimed water is usually sold to citizens

at a cheaper rate to encourage its use. As fresh water supplies become limited from

distribution costs, increased population demands, or climate change reducing sources, the

cost ratios will evolve also.

Using reclaimed water for non-potable uses saves potable water for drinking, since less

potable water will be used for non-potable uses.
http://en.wikipedia.org/wiki/Contaminantshttp://en.wikipedia.org/wiki/Wastewaterhttp://en.wikipedia.org/wiki/Sewagehttp://en.wikipedia.org/wiki/Surface_runoffhttp://en.wikipedia.org/wiki/Effluentshttp://en.wikipedia.org/wiki/Potable_waterhttp://en.wikipedia.org/wiki/Fresh_waterhttp://en.wikipedia.org/wiki/Fresh_waterhttp://en.wikipedia.org/wiki/Potable_waterhttp://en.wikipedia.org/wiki/Effluentshttp://en.wikipedia.org/wiki/Surface_runoffhttp://en.wikipedia.org/wiki/Sewagehttp://en.wikipedia.org/wiki/Wastewaterhttp://en.wikipedia.org/wiki/Contaminants


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It sometimes contains higher levels of nutrients such as nitrogen, phosphorus and oxygen

which may somewhat helpfertilize garden and agricultural plants when used for irrigation.

Wastewater Reuse in India

In India, since wastewater is mainly untreated, it is used in the agricultural sector where the

risks are considerably lower to using it in households or industry. It is mainly used for

irrigation of Cereals, Vegetables, Flowers, Avenue trees and parks, Fodder crops,

Aquaculture and Agro forestry.

Considering the above facts the present study has been planned with the following objectives

Objective of the study

1.

To estimate the volume of sewage water generated during the different periods from

SHIATS hostels and residential area.

2.

To estimate the volume of sewage water to be generated during the next 30 years from

SHIATS hostels and residential area.

3. To design the primary sewage treatment units for the estimated sewage discharge.
http://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Phosphorushttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Fertilizerhttp://en.wikipedia.org/wiki/Fertilizerhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Phosphorushttp://en.wikipedia.org/wiki/Nitrogen


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CHAPTERII

REVIEW OF LITERATURE

Jillies and Kushwaha (1990) reported that liquid digested sludge can be used as soil

amendment to provide low cost fertilizer and improve tilth. Dried digested sewage sludge

was mixed with soil in test plot near Saskatoon, Canada at application rate of 75 tones

sludge/hectare. The plots were irrigated with decent water from the sludge drying bed.

Tripathi and Dwivedi (1990) reported that the effect of irrigation with raw urban sewage

effluents mixes with industrial effluents, treated sewage effluents and tubewell water potato

yield anand plant and soil heavy metal content was content was studied in a field experiment

at benaras hindu university, Varanasi. Very low concentrations of heavy metals were

observed in rubbers from the raw sewage irrigation treatment, although Cu, Zn, Fe in soil

increased.

Korentajer (1990) reported the application of sewage sludge on agricultural land may

provide an economical way to dispose of the increasing amount of sludge application may be

limited by its potential health.

Hundal and Sandhu (1992) reported that soil sample at varying distance along the sewage

from three tyres of field sewage waste water irrigated and tube well irrigated were collected

and analyzed for total and DTPA extractable toxic metal content.

Maiti et al. (1992)reported that the sewage effluent and sludge of Calcutta city was made to

assess their manorial values. Sewage were natural to slightly alkaline in reaction andcontained high level basic tons, particularly in winter, bicarbonate and chloride Ions were at

toxic levels. Although sewage effluents and slugged were rich in nutrient the toxicity levels.

Welch et al. (1992)reported the zinc movement in sludge treated soils as influenced by soil

properties water quality and soil moisture level.


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Hundal et al (1993)reported that the surface soil samples were collected from field along a

sewage drains which were irrigated with sewage effluents sewage effluents plus tube well

water or tube well water and their chemical properties were investigated. Zinc and copper

contents increased 3 and 8 times respectively in the sewage effluents treated soils reaching

toxic levels to plants.

Azad (1995)reported that the fate of Fe in sewage wastewater irrigated soil was investigated

in Punjab India. Total Fe content of normally irrigated soil ranges from 1.4-3.2% in the 0-15

cm layer with mean value of 2.03% in soils receiving sewage wastewater total Fe ranges

from 2.2-4.1% with an average value 2.78% which was 36.9% higher than in normal soils.

Mathan (1995) reported that the study conducted in a sewage farm of the Maduraei

Corporation in India to compare the effect of sewage effluent properties. The soil was sandy

loam and had been irrigated for 10-15 years. Soil irrigated by canal fed well water had the

highest bulk density.

Kuba et al. (1997)examined the role of denitrifying phosphorus removing bacteria (DPB) in

wastewater treatment plants using batch tests with activated sludge from two plants in the

Netherlands. DPBs appeared to be of little importance in one plant, but contributed

substantially to P removal in the other

Singh and Varloo (1997)studied the accumulation and bioavailability of metals in semi arid

soil irrigated with the sewage effluent, the sewage had slightly lower pH but higher organic

carbon as compared to those receiving irrigation with tube well water.

Antil et al. (1998) reported that the raw sewer water sample was collected from various

sewer disposal sites in Haryana India where these waste water are directly used for irrigating

the crops. The chemical composition of sewer water varied from site to site. The

physicochemical properties DTPA extractable and total macro and micronutrients and toxic

the composition metals icons(CD,Ni) varies according to composition of the sewer water.

Wiger and Hamedi (1999) reported that accumulation and mobility heavy metals in soils

irrigated with sewage effluent in Haryana India.


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Bednared and Tkaczy (1999)reported that the influence of treated municipal on occurrence

of soluble form of phosphorous potassium and magnesium in peat muck soil. Municipal

sewage did not change in reaction and value of hydrolytic acidity. Treated municipal sewage

caused contents of soluble potassium in upper layer (0-20) of soil.

Joshi and Pathak(2000) reported that the effect of sewage assessing the effect if sewage

application on sewage application on soil properties identified the problem.

Song et al. (2002) using thermodynamics, modeled the effects of P and Ca concentration,

pH, temperature, and ionic strength on theoretical removal.

Tchobanoglous et al (2003)Chemical precipitation has long been used for P removal. The

chemicals most often employed are compounds of calcium, aluminum, and iron.

Bradford et al. (2003) In the villages near Hubli-Dharwad in Karnataka, the main

wastewater irrigated agroforestry land uses are orchards and agrosilviculture which consists

of spatially mixed treecrop combinations.

Zeng et al. (2004)High phosphate removal (> 95% in 10 min, batch system) was obtained

from a 33 mg/L P solution, but direct applicability to wastewater treatment (lower

concentrations, possible interferences) was not investigated. The gas concretes removal

efficiency can be regenerated at low pH, with the resulting concentrated phosphate solution

potentially a source of recycled phosphate. Similarly, iron oxide tailings were found to be

effective for phosphorus removal from both pure solutions and liquid hog manure

Chattopadhyay (2004)The East Calcutta sewage fisheries are the largest single wastewater

use system in aquaculture in the world. The wetland ecosystem of Kolkata supports 100,000

direct stakeholders and 5,100 ha of cultivation. Annually, it provides direct employment for

about 70,000 people, produces 128,000 quintals of paddy, 69,000 quintals of fish and 7.3

quintals of vegetables.


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Neethling et al. (2005) examined the factors that influence the reliability of EBPR in full-

scale plants. They concluded that P concentrations 25:1) is one requirement for reliable high removal efficiencies. This might be achieved by

BOD augmentation through fermentation or addition of a fermentable substrate. Control of

recycle streams is also necessary, so that they do not bring too much P back to the EBPR

process. They also concluded that while GAOs can be problematic, their presence does not

preclude good P removal.

Mekala (2006) In Hyderabad, along the Musi River about 10,000 ha of land is irrigated with

wastewater to cultivate Para grass, a kind of fodder grass.

Randall (2006)discussed the use of carbon augmentation in EBPR. Short chain volatile fatty

acids (VFAs), particularly acetic and propionic acids, are most desirable. Some carbon

sources, such as some sugars and alcohols, may lead to production of GAOs, bulking, or

excessive exocellular polymer production. VFAs may be generated in the sewer system, arise

from industrial discharges, be added directly, or be generated on-site. For many plants, on-

site generation in the anaerobic zone may be sufficient. Alternatively, fermentation of the

primary sludge, primary effluent, or some of the activated sludge might be practiced. In the

PhoStrip process, fermentation also occurs in the stripping tank.

Reardon (2006) reported on several plants achieving


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Neethling and Gu, (2006)Chemical addition points include prior to primary settling, during

secondary treatment, or as part of a tertiary treatment process.

Neethling and Gu, (2006) the process is more complex than predicted by laboratory pure

chemical experiments, and that formation of and sorption to carbonates or hydroxides are

important factors. In fact, full-scale systems may perform better than the 0.05 mg/L limit

predicted.

Strom, (2006)Use of alum after secondary treatment can be predicted to produce much less

sludge, but the increase could still be problematic.

Moller (2006) reported on an iron reactive filtration system achieving


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present as soluble organic or inorganic P. In particular, anaerobic conditions are likely to

release soluble P from EBPR sludge and iron precipitates (ferrous phosphate is much more

soluble than ferric phosphate). Any released P may then be returned to the main wastewater

treatment process in high concentrations through recycle side streams, thus requiring removal

a second time. Non-continuous processes may also lead to variable loadings from side

streams.


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CHAPTERIII

MATERIALS AND METHODS

This chapter deals with design of primary sewage treatment plant for staff residential area

and hostels of SHIATS, Allahabad. The district Allahabad is located at 2557 North and

8241 East altitudes. The altitude of the place above mean sea level is 93.0 m. The detail

description of the study area is given below.

3.1 ClimateThe mean of monthly maximum temperature varies from 23.6C (January) to 2.3C (may),

and the mean monthly temperature in the range between 8.7C January and 28.5C June.

The normal annual total rainfall is 1,017.7 mm. August is the month with maximum

precipitation (307.6mm), followed closely by July 300.1mm. The period from June to

September accounts for about 87% of the total rainfall. Winter rains occur mostly during the

months of January and February and account for about 1.6% of total rainfall. The details of

climatilogical data of Allahabad is given in Table No. 3.1.

3.2 Sewage

Sewage treatment is the process of removing contaminants from wastewater and household

sewage, both runoff (effluents) and domestic. It includes physical, chemical, and biological

processes to remove physical, chemical and biological contaminants. Its objective is to

produce a treated effluent and a solid waste or sludge suitable for discharge or reuse back

into the environment. This material is often inadvertently contaminated with many toxic

organic and inorganic compounds. Sewage implies the collecting of wastewaters 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 otherwise disposed of without

endangering the public health or causing offensive conditions.


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Sewerage is the art of collecting, treating and finally disposing of the sewage. Sewage is

liquid, consists of any one or a mixture of liquid waste origins from urinals, latrines, bath

rooms, kitchens of a dwelling, commercial building or institutional buildings.

Storm sewage is a liquid flowing in sewer during or following a period of rainfall and

resulting there from.

A Separate Sewer System is the sewerage system in which the domestic sewage is not carried

with the storm water in the rain season.

3.3 Treatment of Sewage

The treatment of sewage consists of many complex functions. The degree of treatment

depends upon the characteristics of the raw inlet sewage as well as the required effluent

characteristics.

Treatment processes are often classified as:

(i) Preliminary treatment

(ii) Primary treatment

(iii) Secondary treatment

(iv) Tertiary treatment.

3.3.1 Preliminary TreatmentPreliminary treatment consists solely in separating the floating materials like tree branches,

papers, pieces of rags, wood etc. and heavy settable inorganic solids. It helps in removal of

oils and greases and reduces the BOD by 15% to 30%. The processes under this are-

Screeningto remove floating papers, rags, clothes.

Grit chamberto remove grit and sand.

Skimming tankto remove oils and greases.

3.3.2 Primary Treatment

Primary treatment consists in removing large suspended organic solids. It is usually

accomplished by sedimentation in settling basins. The liquid effluent from the primary


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treatment often contains a large amount of suspended organic material and has a high BOD

(about 60% of original).

3.3.3 Secondary Treatment

Here the effluent from primary treatment is treated through biological decomposition of

organic matter carried out either aerobic or anaerobic conditions.

Aerobic Biological Units

(i)

Filters ( intermittent sand filters, trickling filters)

(ii)

Activated Sludge Plant (feed of active sludge, secondary settling tank and aeration

tank)

(iii)

Oxidation ponds and Aerated lagoons.

Anaerobic Biological Units

(i) Anaerobic lagoons

(ii) Septic tanks

(iii)

Imhoff tanks.

The effluent from the secondary treatment contains a little BOD (5% to 10% of original) andmay contain several milligrams per liter of DO.

3.3.4 Tertiary Treatment

The purpose of tertiary treatment is to provide a final treatment stage to raise the effluent

quality before it is discharged to the receiving environment (sea, river, lake, ground, etc.).

More than one tertiary treatment process may be used at any treatment plant. If disinfection is

practiced, it is always the final process. It is also known as "effluent polishing". The flow

chart of sewage treatment plant is given in Fig.3.1 and 3.2.


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Table 3.1 Climatological data of Allahabad District

Month Avg. Min

Temp in

Allahabad,India (C)

Avg Max

Temp in

Allahabad,India (C)

Allahabad

Average

Temperature(C)

Average

Precipitation/

Rainfall(mm)

Wet

Days

(>0.1mm)

Average

Sunlight

Hours/Day

Relative

Humidity

(%)

January 9 24 16.5 20 3 8.1 67

February 12 27 19.5 22 3 9.2 51

March 17 33 25 14 2 8.9 35.0

April 23 39 31 5 1 9.9 24

May 27 42 35 8 2 10.0 27

June 29 40 35 102 8 7.2 47

July 27 34 31 275 19 5.2 76

August 26 32 29 333 21 4.9 81

September 25 33 29 195 13 6.9 77

October 20 33 27 40 5 8.9 61

November 13 29 21 7 1 9.3 55

December 9 25 17 6 1 8.9 63


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3.4 Sewage Treatment Process

Sewage contains various types of impurities and disease bacteria. This sewage is disposed of

by dilution or on land after its collection and conveyance. If the sewage is directly disposed

of, it will be acted upon the natural forces, which will convert it into harmful substances. The

natural forces of purification cannot purify any amount of sewage within specified time. If

the quantity of sewage is more, then receiving water will become polluted or the land will

become sewage sick. Under such circumstances it becomes essential to do some treatment of

the sewage, so that it can be accepted by the land or receiving water without any objection.

These treatment processes will directly depend on the types of impurities present in the

sewage and the standard up to which treatment is required.

3.5 Degree of Treatment

The degree of treatment will mostly be decided by regulatory agencies and the extent to

which the final product of treatment are to be utilized. The regulatory bodies might have laid

down standard for the effluent or might specify the condition under which the effluent must

be discharged 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.

3.6 Design Period

A sewerage scheme involves the laying of underground sewer pipes and construction of

costly treatment units, which cannot be replaced or increased in their capacities easily or

conveniently at a later date. In order to avoid such complications, the future expansions of

the hostels and residential area, consequent increase in the sewage quantity should be

forecasted to serve the community satisfactorily for 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 design period. This sewage treatment plant is designed for 30 years.

The treatment plant is normally designed to meet the requirement over a 30 year period after

it completion. The time lag between the design and completion should not normally exceed

2-3 years. Care should be taken that the plant is not considerably under loaded in the initial

stages, particularly the sedimentation tank. The ultimate design period should be 30 years


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and to that extent sufficient accommodation should be provided for all the units necessary to

cater to the need of ultimate population. In some cases, it may be necessary to combine a

number of sewage systems with a common sewage treatment plant.

3.7 Estimation of Sewage volume

Present population

Hostels =1800

Residential area = 700

Population by the year 2042 considered for design

Hostels = 20,000 head

Residential area =3,000 head

Total Population predicted by the year 2042 = 23,000

Ultimate design period = 30 years

Water supply per capita

hostels = 180 l/h/d

Residential area = 250 l/h/d

Sewage generation per day = 80% of supplied water

Total amount of sewage = sewage produced in hostels + sewage produces in

residential area


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Inlet from sewer

Fig 3.1Flow Chart of Processes of Sewage Treatment Plant

Screening

Grit removal

Primary

sedimentation

Biological

treatment

Tertiary

treatment

Discharge to

receiving

Temporary

storm water

storage

Large solids, rags,

plastics

Grit, stones,

sand

Primary

sludge

Secondary

sludge

Tertiary

sludge


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3.8 Location of Treatment Plant

The treatment plant should be located as near to the point of disposal as possible. If the

sewage as to be disposed finally in to the river, the plant should be located near the river

bank. Care should be taken while locating the site that it should be on the downstream side of

the city and sufficiently away from water intake works. If finally the sewage as to be applied

on land, the treatment plant should be located near the land at such a place from where the

treated sewage can directly flow under gravitational forces toward the disposal point. The

plant should not be much far away from the town to reduce the length of the sewer line. On

the other hand the site should not be close to the town, that it may cause difficulties in the

expansion of town and may pollute the general atmosphere by smell and fly nuisance.

3.9 Layout of Treatment Plant

The following point should be kept in mind while giving layout of any sewage treatment

plant:

All the plant should be located in the order of sequence, so that sewage from one

process should directly go to other process.

If possible all the plant should be located at such elevation that sewage can flow from

one plant into next under its force of gravity only.

All the treatment units should be arranged in such a way that minimum area is

required it will also ensure 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

operators can watch the plant easily.

The site of treatment plant should be very neat and give very good appearance.

Bypass and overflow weir should be provided to cut out of operation any unit when

required.

All channels, conduits should be laid in such a way as to obtain flexibility, convenience and

economy in the operation.


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Returned activated sludge

Dried sludge

Disposal+

3.2 Layout of sewage treatment plan

GRIT CHAMBER SKIMMING

TANK

PRIMARY SETTING

TANK

AERATION TANK

FINAL SETTINGTANK

SLUDGE

DISGESTION

TANK

TRICKLING

FILTER


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3.10 Design consederations

Following points are considered during the design of sewage treatment unit:

The design period should be taken between 25 to 30 years.

The design should not be done on the hourly sewage flow basis, but the average

domestic flow basis.

Instead of providing one big unit for each treatment more than two numbers small

units should provided, which will provide in operation as well as no stoppage during

maintenance and repair of the plant.

Overflow weirs and the bypasses should be provided to cut the particular operation if

desired.

Self cleaning velocity should develop at every place and stage.

The design of the treatment units should be economical; easy in maintenance should

offer flexibility in operation.


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Table 3.2. Chemical Quality of raw and standard sewage

Parameters Raw Sewage Effluent (Expected)

pH 6.4 5.5 - 9.0

BOD 200 mg/l 20 mg/l

COD 600 mg/l 250 mg/l

oil and grease 50 mg/l 5 mg/l

total suspended solids 600 mg/l 30 mg/l

Nitrogen 61 mg/l 5 mg/l

ammonia nitrogen 50 mg/l 50 mg/l

total phosphorous 5 mg/l 5 mg/l

total coli form 100000 MPN/ml 1000 no / 100 ml


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3.11 Design of Receiving Chamber

Receiving chamber is the structure to receive the raw sewage collected through Under

Ground Sewage System. It is a rectangular shape tank constructed at the entrance of the

sewage treatment plant. The main sewer pipe is directly connected with this tank.

Design flow = 0.126 cumec

Setting velocity of a critical particle(Vs)

.. (3.1)

Where

Q = flow rate ,m3

A = area of surface of tank,m2

As per the Stock law

Vs = (Ss-1) dp .... (3.2)

Where -

VsSettling velocity (m/s)

kinematic viscosity of waterSssp. Gravity of a particledpdia. of a critical particle (m)

Volume of receiving chamber (V)

V = flow x detention time ....(3.3)


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Area of receiving chamber (A)

. ..(3.4)

Where -

A = area,m

2

V = volume ,m3

d = depth,m

Length and Breadth ratio of receiving chamber

Length: Breadth = 2 : 1

3.12 Screening

Screening is the very first operation carried out at a sewage treatment plant and consists of passing

the raw sewage through different types of screens so as to trap and remove the floating matter such

as tree leaves, paper, gravel, timber pieces, rags, fibre, tampons, cans, and kitchen refuse etc.

Purpose Of Screening:

Screening is essential in sewage treatment for removal of materials which would otherwise damage

the plant, interfere with the satisfactory operation of treatment unit or equipment.

To protect the pumps and other equipments from the possible damages due to floating

matter.

To remove the major floating matters from the raw sewage in a simple manner before it

reaches into the complex high energy required process.

Coarse Screens: The coarse screens essentially consist of steel bars or flat placed 30 to 60

inclination to the horizontal. The opening between bars are 50mm or above. These racks are

placed in the screen chamber provided in the way of sewer line. The width of the rack channel

should be sufficient so that self cleaning velocity should be available and a bypass channel should

be provided to prevent the overtopping. The bypass channel is provided with vertical bar screen.

A well drained trough is provided to store the impurities while cleaning the rack. These racks are

cleaned mechanically.


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3.12.1 Design of Coarse Screen

Assume the velocity at average flow is not allowed to exceed 0.8 m/s

The net area screen opening required (A)

..(3.5)

Clear opening between bars = 20 mm = 0.02m

Size of the bars = 75 mm x 10 mm

Assume width of the channel = 0.5m

The screen bars are placed at 60 to the horizontal.

Clear area

(3.6)

No of clear openings

.(3.7)

Head loss

Head loss through the screen

H=0.0729( ) . (3.8)

Where

H = head lossV = velocity through the screen when opening get half clogged.

V = velocity through the screen

When the screen openings get half clogged then the velocity through the screen

V = allowed velocity x 2


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3.13 Design of Grit Chamber with aeration

Grit removal basins are the sedimentation basins placed in front of the fine screen to remove the

inorganic particles having specific gravity 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 grit chamber is designed to scour the lighter organic

particles while the heavier grit particles remain settled.

Here the horizontal flow type grit chamber is designed to give a horizontal straight line flow

velocity, which is kept constant over varying discharge.

Peak flow of sewage = 0.126 /s

Assume average detention period = 180s

Volume of chamber

Volume = Peak flow x Detention period (3.9)

In order to drain the channel periodically for routine cleaning and maintenance two chambers are

used.

Therefore

Volume of one chamber

..(3.10)

Where

V = Volume of one chamber,m3

Va = Volume of chamber, m3

Depth of 1m and width to depth ratio 2:1

Length of channel

.(3.11)

Where

L = length of chamber ,m


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d = depth of chamber,m

W = width of chamber,m

Increase the length by about 30% to account for inlet and outlet

3.14 Design of Skimming Tank

Skimming tanks are the tanks removing oils and grease from the sewage constructed before the

sedimentation tanks. Municipal raw sewage contains oils, fats, waxes, soaps, fatty acids etc. The

greasy and oily matter may form unsightly and odorous scum on the surface of settling tanks or

may interfere with the activated sludge process.

In skimming tank air is blown along with chlorine gas by air diffuser placed at the bottom of the

tank. The rising air tends to coagulate and solidify the grease and cause it to rise to the top of the

tank whereas chlorine destroys the protective colloidal effect of protein, which holds the grease in

emulsified form. The greasy materials are collected from the top of the tank and the collected are

skimmed of by specially designed mechanical equipments.

Surface Area of the Tank

A = 6.22 x x q / Vr (3.12)

Where

q = rate of flow sewage in / day

Vr = minimum rising velocity of the oily material to be removed in m/min

Provide the depth of the skimming tank is 0.5m

The length breadth ratio is 1.5 : 1

3.15 Design of Primary Sedimentation Tank

Primary sedimentation tank is the settling tank constructed next to skimming tank to remove the orga

solids which are too heavy to be removed i.e. the particles having lesser size of 0.2 mm and spec


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gravity of 2.65. The designed tank is circular type which makes settling by allowing radial fl

Generally carbon steel is used for fabrication with epoxy lining on the inside and epoxy coating on

outside. Built on the concept of inclined plate clarification was used which clarifiers use gravity

conjunction with the projected settling area so as to effect a fairly high percentage of removal

suspended solids as 60 to 65% of the suspended solids and 30 to 35% of the BOD from the sewage.

Max. discharge (Q) of sewage was estimated considering the present population of the hostels and

residential area of the university including the prediction of future population

Surface loading

.(3.13)

Where

Q = DischargeA = surface area of tank,m

2

Settling Velocity

Vs = (Ss-1) dp ..(3.14)

Where

VsSettling velocity ,mkinematic viscosity of water

Sssp. Gravity of a particledpdia. of a critical particle ,m

Diameter of the tank (D) was calculated by the formula

D = ..3.15

Surface area of tank(A) was calculated by the formula

.(3.16)


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Where -

V = volume of tank ,m3

d = depth of tank (m)

Depth of Tank (d) was calculated by the formula

..(3.17)

3.16 Design of High Rate Trickling Filter

The improved form of conventional filters known as high rate trickling filters are now almostuniversally adopted for treatment to sewage. These filters consist of tanks of coarser filtering

media, over which the sewage is allowed to sprinkle or trickle down, by means of spray nozzles or

rotary distributors. The percolating sewage is collected at the bottom of the tank through a well

designed under drainage system. Trickling filter tanks are generally constructed above the

ground. They may either be rectangular or more generally circular. The circular filter tanks are

provided with rotary distributors having a number of distributing arms (generally four arms are

used).

The rate of revolutions varies from 2 RPM for small distributors to less than RPM for large

distributors. The distributing arms should remain about 15 to 20 cm above the top surface of the

filtering media in the tank.

Data regarding the discharge of sewage passing through the filter was used for the design of

high rate trickling filters with the assumption that the BOD concentration in raw sewage should be

200 mg / l .

3.16.1 Estimation of BOD in Raw sewage

The BOD present in the raw sewage was estimated using the formula with the assumption that the

percentage of BOD removed in primary tank is within the 30%

BOD = Total quantity of sewage x BOD concentration in sewage (3.18)


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The BOD left in the sewage, Total BOD and BOD removed by the filter was estimated using the

following formulas with assumption that the concentration of final effluent BOD is within the 20

mg per lit per day

BOD Left = Total BOD x 0.7 .(3.19)

Total BOD Left = total quantity of sewage x desire BOD concentration (3.20)

BOD removed by the filter = BOD left in the sewage entering per day - Total BOD left in the

effluent per day .(3.21)

3.16.2 Filter area (A)

Filter area (A) was calculated by the formula

.(3.22)

Where

A = filter area,m2

Efficiency of the filter ()

= .....(3.23)

Volume of the Filter (V)

..(3.24)

Where -

Y = total BOD in kg.

F = recirculation factor


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Recirculation factor (F)

F = .(3.25)

where-

Surface area of the tickling filter

(3.26)

Diameter (d) of circular tickling filter was calculated by the formula

(3.27)

3.16.1 Design of Rotary Distribution

The rotary distributer of tickling filter was designed by the assumption of the velocity at central

column of the distributor is within 2 m/s.

The diameter of central column (D) was calculated by the formula

(3.28)

Velocity (V) at central column was calculated by the formula

(3.29)

3.16.2 Design of Arms

In design of spray type rotary reaction distributor n 4 arms were considered.

Discharge per arms (Q) was calculated by the formula


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.. (3.30)

Length of arms was calculated by the formula

.(3.31)

3.17 Activated Sludge Process

The activated sludge process is an aerobic, biological sewage treatment system to treat the settled

sewage consist a variety of mechanisms and processes that use dissolved oxygen to promote the

growth of biological floc that substantially removes organic material. The essential units of the

process are an aeration tank, a secondary settling tank, a sludge return line from the secondary

settling tank to the aeration tank and an excess sludge waste line.

Atmospheric air is bubbled through primary treated sewage combined with organisms to develop a

biological floc which reduces the organic content of the sewage. The Mixed Liquor, the

combination of raw sewage and biological mass is formed. In activated sludge plant, once the

effluent from the primary clarifier get sufficient treatment, the excess mixed liquor is discharged

into settling tanks and the treated supernatant is run off to undergo further treatment. Part of the

settled sludge called Return Activated Sludge (R.A.S.) is returned to the head of the aeration

system to re-seed the new sewage entering the tank. Excess sludge which eventually accumulates

beyond R.A.S known Waste Activated Sludge (W.A.S.) is removed from the treatment process to

keep the ratio of biomass to food supplied (F:M) ratio. W.A.S is further treated by digestion under

anaerobic conditions.

3.18 Contact Stabilization

Microorganisms consume organics in the contact tank.

Effluent from primary clarifier flows into the contact tank where it is aerated and mixed

with bacteria.

Soluble materials pass through bacterial cell walls, while insoluble materials stick to the

outside.


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3.19 Design of Aeration Tank

Aeration tank is the mixing and diffusing structure in the activated sludge plant. These are

rectangular in shape having the dimensions ranging 3 to 4.5m deep, 4 to 6m wide and 20 to 200m

length. Air is introduced continuously to the tank. Combined Aeration type aerators having the

diffused air aeration as well as mechanical aeration together in a single unit are used in the project.

The Dorroco model is designed as it gives higher efficiency and occupies less space. This results in

higher efficiency and lesser detention period and lesser amount of compressed air.

Estimation of BOD at inlet

The BOD at inlet was estimated using the formula with the assumption that the percentage of BOD

removed in grit chamber is within the 20%.

BOD at inlet ( ) was calculated by the formula

= flow velocity x BOD ..(3.32)

BOD removed in activated plant was calculated by the formula

BOD removed in activated plant = -

Where

= BOD at outlet

Efficiency (E) of plant was calculated by the formula

x 100 ..(3.33)

F/M ratio was calculated by the formula

F/M ratio = . (3.34)


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Volume (V) of aeration tank was calculated by the formula

V = .. (3.35)

Where

Xt = Mixed liquor suspended solids (MLSS)

3.20 Cross checking of the design parameters against the permissible limits

3.20.1Aeration Period/ Hydraulic retention time (HRT)

Since the permissible limit of aeration period is between 3 6 hr, so if the designed period is

within this limit the design is acceptable.

Hydraulic retention time (t) was calculated by the formula

t = V x 24 Q .(3.36)

3.20.2 Volumetric Loading

Since the permissible limit of volumetric loading is between 1.02.0, so if the designed period is


Volumetric loading was calculated by the formula

Volumetric loading = .(3.37)

3.20.3 Return Sedge Ratio

Since the permissible limit of return sedge ratio is between 0.5 1.0, so if the designed period is


Return active sludge ( ) was calculated by the formula


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= ..... (3.38)

Where

SVI = Sludge Volume Index (it is ranging between 50150 ml / gm)

3.20.4 Sludge Retention Time(SRT)

Since the permissible limit of sludge retention time is between 58 day, so if the designed period

is within this limit the design is acceptable.

SRT( )was calculated by the formula

..(3.39)

Where

= constant for municipal sewage with respect to MLSS, 0.5

= constant for municipal sewage, 0.06

3.21 Capacity of Pump

Pump capacity for aeration process was estimated by the formula with the assumption that the

oxygen transfer rate by aerator in standard condition is 1.41 kg. / HP /hr, and the efficiency of

aerators at field condition in percentage are 90%.

Oxygen transfer capacity aerators at field conditions calculated by the formula

Oxygen transfer capacity aerators at field conditions = 0.9 x oxygen transfer capacity

. (3.34)

Oxygen to be applied in each tank was calculated by the formula

Oxygen to be applied in each tank = oxygen requirement x BOD removed in each tank x peak

oxygen demand .(3.35)


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Pump capacity was calculated by the formula

HP of aerators required = .(3.36)

3.22 Design of Sludge Drying Beds

Drying of the digested sludge on open beds of land is sludge drying and such open beds of land are

known as sludge drying beds. The digested sludge from digestion tank contains a lot of water. So it

is necessary to dry up or dewater the digested sludge before it disposed of dumping.

The sewage sludge is brought and spread over the top of drying beds to a depth of 20 to 30 cm,

through distribution troughs. A portion of the moisture drains through the bed while most of it gets

evaporated to the atmosphere. In hot countries like India it takes 6 to 12 days to dry. After the

period the sludge cakes are removed with spades and they are used as manure as it contains 2 to3% of NPK.

Sludge drying beds are open beds of land 45 to 60 cm deep, 30 to 45 cm thick graded layers of

gravel or crushed stone varying in size from 15cm at bottom and 1.25 cm at top. Open jointed

under drain pipes of 15 cm diameter are laid below the gravel layers. Large beds are portioned by

concrete walls, and a pipe header from the digesters with gated openings allows application of

sludge independently to each cell. Seepage collected in the under-drains is returned to the plant

wet well for treatment with the raw wastewater. Volume of sludge, number of cycle, Volume of

sludge per cycleand required bed area were calculated using the following formulas

Volume of sludge

Volume of sludge = (3.37)

Number of cycle each year

Number of cycle each year was calculated by the formula with the assumption that the drying

period is 8 days for sewage drying bed in Allahabad district.

Number of cycle in one year = ..(3.38)


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Volume of sludge per cycle

Volume of sludge per cycle = volume of sludge x period of each cycle

Required bed area

Required bed Area = .(3.39)

3.23 Design of Sewer pipe line

A Sewer consists of collection of sewage water from the source, carrying it or transporting it to the

treatment plant and finally distributing the treated water among the use. Separate sewer system is

used for transporting the sewage material.

A Separate Sewer System is the sewerage system in which the domestic sewage is not carried with

the storm water in the rain season. Shape of sewer design was considered.

3.23.1 Forces Acting on Sewer pipe line

The following forces are acting on the sewer pipe line

1.

Internal pressure of sewage

2.Pressure due to external loads

3.Temperature stresses

4.Flexural stresses

3.23.2 Criteria for selecting the Material of Sewer pipe line

For selecting the material for sewer pipe the following points were considered.

1. Resistance to corrosion

2. Resistance to abrasion

3.Strength and durability

4. Light weigh

5. Imperviousness

6. The economy and cost


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7. Hydraulically efficient

Discharge through sewer pipe linewas calculated by the formula

Q = A x V (3.40)

Cross - Section Area of sewer pipe line was calculated by the formula

or (3.41)

Where r is the radius of sewer, m

Cross-section area of pipe was calculated considering the pipes are running half full and by using

the following formula

A = .(3.42)

Wetted perimeter (P) of pipe

P = .(3.43)

Flow velocity in sewers pipe line and drainpipe line

V = 0.85 C (Hazen-William's formula) . (3.44)

Where

V= velocity, m/s;R = hydraulic radius, m;

S= slope,C= Hazen-William's coefficient,

(Manning's formula) (3.45)

Where:V= velocity, m/s;

R = hydraulic radius, m;S= slope

n = Manning's coefficient


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= (Darcy-Weisbach formula)(3.46)

where= head loss

L = length of sewer ,mU = flow velocity ,m/sD = diameter of sewer ,m

F = darcyweisbach coefficient

Self cleaning velocity ( ) of sewage fluid was calculated by the formula

= . kd(G - 1) .(3.47)

Wheren= Manning's coefficient

r= radius of sewerk= dimensional constant

d= effective diameter of sewerG = specific gravity of sewage particle

3.23.3 Operation and Maintenance of Sewers

1.

A sewer system is subject to a variety of operational problems, Depending on the wastewater

flow characteristics, surrounding soils condition, and quality of construction, the pipeline can

suffer from clogging, scouring, corrosion, collapse, and, ultimately, the system's deterioration.

The collection system is designed to serve for a specific useful life. To incumbent of the City

provided following adequate operation and maintenance structure and machineries are

Manholes, Drop manholes, Lamp holes, Cleanouts, Street inlets(gullies), Catch basins,

Flushing tanks, Grease and oil traps, Inverted siphons, Storm regulators to maximize the

benefit throughout its designed useful life.


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Table 3.3 Recommendations of National Buildings Organization (N.B.O.) on Nonscouring

Limiting Velocities in Sewers and Drains

Table 3.4 Manhole spacing as per IS 1742 1960

S. NO Sewer Material Limiting Velocity in m/sec

1Vitrufied Tiles and

Glazed Bricks4.5 - 5.5

2 Cast Iron Sewers 3.5 - 4.5

3Stone Ware

Sewers3.0 - 4.0

4Cement Concrete

Sewers2.5 - 3.0

5Ordinary Brick -

Lined Sewers1.5 - 2.5

6 Earthen Channels 0.6 - 1.2

Size of the Sewer

Recommended Spacing of

Manholes on Straight Reaches of

Sewer Line as per IS 1740 - 1962

Dia. up to 0.3 m 45 m





Dia greater than 1.5m 300 m


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Table 3.5 Minimum internal dimensions for Manhole Chamber as per IS 1742 1960

S. No. Depth Min. Size Specified

1 0.8 m or less 0.75 m x 0.75m

2 0.8 and 2.1 m 1.2 m x 0.9m

3 > 2.1 m

Circular chambers with

min. dia. of 1.4 m; or

rectangular chambers

with min dimensions of

1.2 m x 0.9 m

Min. wall thickness

up to

(a) 1.5 m depth 20 cm

(b) > 1.5 m depth 30 cm


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CHAPTERIV

RESULT AND DISCUSSION

This chapter deals with the various results on design of primary sewage treatment plant for staff

residential area and hostels of SHIATS, Allahabad. The detail descriptions of the results are given

as under.

Estimation of Sewage volume

For the estimation of sewage water volume used for design of primary sewage treatment plant the

present population of SHIATS hostel and residential area was estimated. The present population

was found 2500 for estimation of the population after 30 years the future planning of SHAITS

hostel expansion plan was considered and it was assumed that by the year 2042, the population of

the students in the hostel will be 20,000 and the residents in residential area will be 3000, all

together the 23,000 was estimated. The design discharge was estimated as described in Article 3.7

and the results are given in Table 4.1. The table value shows that the design period was considered

30 years and by the year 2042 the population will be 23000 adults including the Hostels and

Residential area of SHIATS. While calculation of sewage water generation it was assumed that theaverage sewage produced by an adult is 180 lit. /day and hence the total sewage water volume

generated through design population was estimated 3.6 MLD.


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Table 4.1 details of the design parameters of the primary sewage treatment plant

S.No. Design parameter Value

1 Design period 30 years

2 Estimated population by the year 2042 23000 adults

3 Water supply per capita

In hostels = 180 l/h/d In Residential area = 250 l/h/d

4 Total Volume of sewage water

estimated from the population ofSHIATS hotels and residential area

( MLD)

3.6

5 Average discharge 0.042 Cumec

6 Maximum discharge 0.126Cumces

7 Dimensions of Receiving chamber Length4mWidth2mDepth1mFree board0.3 m

8 Dimension of Corse screen Width0.2 mDepth0.6mFree board0.3m

9 Dimension of Grit chamber Length5.2mWidth3m

Depth1.5m10 Dimension of Skimming tank Length0.532mWidth0.355mDepth1mFree board0.3m

11 Dimension of Primary sedimentationtank

Diameter7mDepth2mFree board0.5m

12 Dimension of Trickling filter Diameter15.5mDepth2.5m

13 Dimension of Aeration tank Length - 15m

Width8mDepth4m14 Dimension of Sludge drying bed Length12.5m

Width8mDepth1.7m


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4.2 Receiving Chamber

For the design of receiving chamber of the primary sewage treatment plant the influent volume has

been estimated as 0.126 cumec with an assumed detention period of 60 sec and 1m depth .The

planned cross-section of the designed chamber is given in Fig 4.1. The detention period for

receiving chamber was calculated 60 seconds. The volume of sewage water required at receiving

chamber was estimated 0.864 m3. The ratio of depth and width is taken as 2:1. The design

dimensions of receiving chamber to carry the required volume was calculated width of the

chamber is 2m, length of the chamber 4 m and the depth was 1m with total cross-section area of

7.86 m2. A free board of 0.3 m was provided for the safety purpose to avoid the overflow.

Table No. 4.2 Details of receiving chamber for primary sewage treatment plant

S.No. Design parameter Value

1 Average flow in receiving chamber 0.126cumec

2 Detention time 60 sec

3 Required volume of receiving chamber 0.864

4 Surface area of the receiving chamber 7.86

5 Depth of receiving chamber 1 m

6 Length of receiving chamber 4 m

7 Width of receiving chamber 2 m


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Fig. No.4.1 Design dimensions of receiving Chamber


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4.3 Coarse Screen

For the designing of Coarse Screen, no. of opening of coarse screen was estimated as the formula given in

article 3.12 and accordingly the width and depth of channel to carry the sewage discharge paring through

the design coarse screen was estimated 0.5 m and 0.6 m respectively,0.3 m free board was proceed for

safety factor. The coarse screen is made of steel bares at 60 inclination to horizontal with 15 mm opening

between the bars. The steel bares size 75mm x 10 mm was recommended for the coarse screen. The

maximum allowable velocity was considered 0.18 m/sec for the average sewage flow through the coarse

screen .The detailed result are and the head losses occurring due to the coarse screen and sewage

movement through the channel was also estimated and given in Table 4.3.

Table No. 4.3 Details of coarse screen for primary sewage treatment plant

S. No. Design parameter Value

1 Pick flow through core screen 0.126 /s

2 Velocity through the screen 0.8 m / sec

3 Clear opening area 0.115

4 Clear opening between bars 0.02 m

5 No. of clear opening in Coarse Screen 4

6 Width of channel for coarse screen 0.6 m

7 Depth of channel for coarse screen 0.5 m

8 Head loss through the screen 0.013 m

9 Head loss when screen openings get halfclogged

0.15m


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Fig. No. 4.2 Design of core screen


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4.4 Grit Chamber

For the design of Grit Chamber to carry the sewage passing through the coarse screen the

dimension of the grit chamber was designed as discussed on article 3.13 and result are shown in

Table 4.3.The specific gravity of sewage water screened through coarse screen was assumed 2.65

and the detention period was considered 180 sec respectively for design of grit chamber. It was

also suggested that in order to the maintain the grit chamber efficient, periodically two chamber

should be used.The detailed result of the dimension of grit chamber and the Aerated volume of grit

chamber was also estimated and given in Table 4.3

Table No. 4.4 Detail of grit chamber for primary sewage treatment plant


1 Peck flow of sewage in grit chamber 0.126 /s

2 Detention period 180 sec.

3 Aerated volume of one grit chamber 11.35

4 Depth of grit chamber 1.5 m

5 Width of grit chamber 3 m

6 Length of grit chamber 5.2 m


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Fig. No. 4.3 Design of grit chamber


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4.5 Skimming Tank

For the designing of the Skimming tank, the estimation of the area of tank, discharge and

dimension of the tank is given in the Article 3.14 and the result are shown in the table 4.5. The

depth of the skimming tank was assumed as 1m and the length to the breadth ratio was taken as

1.5: 1.

Table No. 4.5 details of skimming tank for primary sewage treatment plant


1 Peak flow of sewage in skimming tank 10886.4 / day

2 Area of skimming tank 0.189

3 Width of skimming tank 0.355 m4 Length of skimming tank 0.532 m

5 Depth of skimming tank 1.3 m


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Fig. No. 4.4 Design of skimming chamber


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4.6 Primary Sedimentation Tank

For the designing of the Primary sedimentation tank estimation of the dimension of tank, volume

of sewage, and surface area of tank as given in the Article 3.15 and the result are shown in Table

4.6. The tank provided a fairly high percentage of removal of suspended solids as 65% of the

suspended solids and 35% of the BOD from the sewage. The detention period was assumed as 2

hrs and the depth was assumed as 2 m. 0.5 m free board was provided for the safety purpose to

avoid the over flow.

Table No. 4.6 Details of primary sedimentation tank for primary sewage treatment plant

S. No Design parameter Value

1 Quantity of sewage 3.6 MLD

2 Volume of sewage 75

3 Detention period 2 hr

4 Surface area of primary sedimentation tank 37.5

5 Depth of primary sedimentation tank 2.5 m

6 Diameter of primary sedimentation tank 7 m


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Fig. No. 4.5 Design of primary sedimentation tank


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4.7 High Rate Trickling Filter

For Design of High Rate Trickling Filter the estimation of total BOD present in the raw sewage,

diameter of the trickling filter and the central column, Efficiency of the filter have been done as

given in the Article no 3.16 and the result is shown in the Table no 4.7 . The concentration of BOD

in raw sewage was assumed as 200 mg/l and the percentage removal in primary tank was assumed

as 30% and the final BOD concentration in effluent was estimated as 20 mg/l.

Table No. 4.7 details of trickling filter for primary sewage treatment plant


1 Quantity of sewage flowing into the filter 3.6 MLD

2 BOD left in the sewage entering per day in

filter unit

504 kg.

3 Total BOD left in the effluent per day 83 kg

4 BOD removed by the filter 432 kg

5 Efficiency of the filter 85.7%

6 Surface area 1850

7 Filter depth 2.5 m

8 Dia. of trickling filter 15.5 m

9 Diameter of central column 0.22m

10 Arms length 7 m


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Fig. No, 3.6 Design of trickling filter


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4.8 Aeration Tank

For the designing of Aeration tank the estimation of efficiency in the activated plant, dimension of

the tank, volume of aeration tank, BOD of inlet, BOD of outlet was done as given in the Article no

3.19 and the result are shown in Table 4.8. The F/M ratio was assumed as 0.4. The liquid depth of

the tank as 4 m and the width to depth ratio was assumed as 2:1.

Table No. 4.8 Details of aeration tank for primary sewage treatment plant


1 Average volume flow in aeration tank 3600

2 BOD in inlet( ) 160 mg/l

3 BOD at outlet( ) 20 mg / l

4 BOD removed in activated plant 140 mg / l

5 F/M ratio 0.4

6 Required Volume of the tank 480

7 Depth of aeration tank 4 m

8 Length of aeration tank 15 m

9 Width of aeration tank 8 m


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Fig. No. 4.7 Design of Aeration tank


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4.9 Sludge Drying Beds

For the designing of the Sludge Drying Bed, estimation of volume of sludge, no of cycle per year

and dimension of beds was done as given in Article no 3.22 and the result are shown in Table no

4.9. The number of dry have been taken as 5. The solid content present in the sludge was assumedas 2% and the drying period of the sludge was assumed to be done in 8 days.

Table No. 4.9 details of sludge drying bed for primary sewage treatment plant


1 Sludge applied to the dry bed 300 kg /day

2 Specific gravity 1.015

3 Volume of sludge 14.778 / day

4 Number of cycle in one year 46

5 Drying Period of each cycle 8 day

6 Area of bed required 492.6

7 No of dry bed 5

8 Area of each bed 100

9 Depth of Spreading layer per cycle 0.3 m

10 Length of dry bed 12.5 m

11 Width of dry bed 8m


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Fig. No. 4.8 Design of drying bed


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4.10 Sewer Pipe Line

For the designing of a Sewer pipe, estimation of the dia. of pipe, self cleaning velocity and slope of

the sewage pipe was done as given in the Article no 3.23 and the result are shown in Table no 4.10.

The shape of the pipe was taken as circular and R.C.C was used as the material for sewer pipe

building. The limiting velocity of sewage in the sewer pipeline was taken between 2.5 to 3.0

m / sec according to the N.B.O.

Table No. 4.10 Details of sewer pipe line for primary sewage treatment plant


1 Self cleaning velocity in sewer pipe line 0.9 m/sec

2 Diameter of sewer pipe line 0.5 m

3 Slope of pipe line 1 in 556


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CHAPTERV

SUMMARY AND CONCLUSION

In the present study a scheme for the primary treatment and management of sewage generated in

SHIATS hostels and residential area has been developed. The total sewage generated in one day is

3.6ML. The scheme is proposed to be constructed at SHIATS Crop Research Farm near NH-27.

The treated water will be supplied for irrigating the crops on Research Farm and the remaining

sludge after treatment will be used as manure on Farm. The use of treated water will reduce the

ground water use and additionally the treated sludge will be very useful for increasing the fertility

of soil. Important units of the scheme have been designed for a specific case are:-

1. The design of primary sewage treatment is for the predicted population of 23,000 and

estimated sewage of 3.6 MLD.

2. The dimension of receiving chamber is 4m x 2m x 1.5m.

3.

The dimension of screen is 0.6m x 5.3m

4.

The dimension of grit chamber with aeration is 5.2m x 3m x 1.3m

5. The dimension of the primary sedimentation tank is diameter of 7m and depth 2.5m

6. The dimension of the trickling filter is diameter of 15.5m and depth 2m

7.

The dimension of the aeration tank is 15m x 8m x 4m

8. The dimension of sludge dry bed is 12.5m x 8m

9.

The construction of the primary sewage treatment plant will prevent the direct disposal of

sewage in Yamuna river and the use of treated water will reduce the surface water and

ground water contamination.


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REFERENCE

Azad, A.S. (1995) . Design of primary sewage treatment plant. Madras Agricultural Journal1994, 81:5, pp 272273;

Besnarek, W. and Tkaczyk , P. (1999) folia Waste water treatment and disposalagricultural journal 2001, pp 5072;

Bose, P. and Reckhow, D. A. (2007).Effect of Ozonation on Natural Matter Removal by Alum

Coagulation. Water Research, 41: 1516-1524.

Caroline Snyder (2005). "The Dirty Work of Promoting "Recycling" of Americas SewageSludge".International Journal of Occupational and Environmental Health 11: 415427.

Cha, J., and A. M. Cupples. (2009)"Detection of the antimicrobials triclocarban and triclosan in

agricultural soils following land application of municipal biosolids." Water Research 43: 2522-30.

Cha, J., and A. M. Cupples. (2010) "Triclocarban and triclosan biodegradation at fieldconcentrations and the resulting leaching potentials in three agricultural soils." Chemosphere 81:

494-9.

Diouf, Jacques , Journal of FAO,2003 Q&A with FAO Director-General.

Environmental Health Perspectives. February (2004) Journal A High-Level DisinfectionStandard for Land Applying Sewage Sludges (Biosolids)"..

Birdie, G.S and J.S. Birdie (1997) .Water supply and sanitary engineering. Published by Rai &

dhanpat Ed. PP 50 -120;

Harrison EZ, Oakes SR (2002). A Journal of Environmental and Occupational Health Policy 12(4): 387408 "Investigation of Alleged Health Incidents Associated with Land Application ofSewage Sludges

Horenstein, B., Hernandez, G., Rasberry, G., Crosse, J. (1990) Successful dewateringexperience at Hyperion wastewater treatment plant, Water Science and Technology, v. 22, p. 183-191

International Journal of Environment and Pollution 11 (1): 136. (1999)."Land application ofsewage sludges: an appraisal of the US regulations".

Jones, Lepp, T. and Stevens, R. (2007) Pharmaceuticals and personal care products inbiosolids/sewage sludge: the interface between analytical chemistry and regulation, Analytical &Bioanalytical Chemistry, v. 387, p. 11731183

Kumar, A., Saroj, D. P., Tare, V. and Bose, P. (2006). Treatment of Distillery Spent-Wash by

Ozonation and Biodegradation: Significance of pH Reduction and Inorganic Carbon RemovalPrior to Ozonation. Water Environment Research. 78(9): 994-1004.
http://www.sludgefacts.org/IJOEH_1104_Snyder.pdfhttp://www.sludgefacts.org/IJOEH_1104_Snyder.pdfhttp://ehp.niehs.nih.gov/members/2003/6207/6207.pdfhttp://ehp.niehs.nih.gov/members/2003/6207/6207.pdfhttp://ehp.niehs.nih.gov/members/2003/6207/6207.pdfhttp://ehp.niehs.nih.gov/members/2003/6207/6207.pdfhttp://www.sludgefacts.org/IJOEH_1104_Snyder.pdfhttp://www.sludgefacts.org/IJOEH_1104_Snyder.pdfhttp://www.sludgefacts.org/IJOEH_1104_Snyder.pdf


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McBride M. (2003).Toxic metals in sewage sludge-amended soils: has promotion of beneficialuse discounted the risks

Garg, S.K. (2006 ) .Sewage disposal and air pollution engineering. TMH publishing Ed by laxmi

publication, PP 219300;

Srivastava, S., Bose, P., and Tare, V. (2006). Enhancement of COD and Color Removal ofDistillery Spent-Wash by Ozonation. Water Environment Research. 78(4): 409-420.

Tare, V., Bose, P. and Gupta, S. K. (2003) . Suggestions for a Modified Approach towards

Implementation and Assessment of Ganga Action Plan and Other Similar River Action Plans inIndia. Water Quality Research Journal, Canada, 38: 607-626.

Tare, V., Gupta, S. and Bose, P. (2003).Case Studies on Biological Treatment of Tannery

Effluents in India. Journal of Air and Waste Management Association, 53: 976-982.

Tare, V., Yadav, A.V.S and Bose, P. (2003). Analysis of Photosynthetic Activity in the Most

Polluted Stretch of River Ganga. Water Research, 37: 67-77.

Turek et al. (2005).Removal of Heavy Metals from Sewage Sludge Used as Soil Fertilizer

Wu, C., A. L. Spongberg, J. D. Witter, M. Fang, and K. P. Czajkowski. (2010) "Uptake of

pharmaceutical and personal care products by soybean plants from soils applied with biosolids andirrigated with contaminated water." Environmental Science & Technology 44: 6157-6161.".
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W75-48V7VBX-1&_user=5781704&_coverDate=10%2F31%2F2003&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_rerunOrigin=scholar.google&_acct=C000016587&_version=1&_urlVersion=0&_userid=5781704&md5=c83232dc86f783980ea66b97c8c75f02&searchtype=ahttp://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W75-48V7VBX-1&_user=5781704&_coverDate=10%2F31%2F2003&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_rerunOrigin=scholar.google&_acct=C000016587&_version=1&_urlVersion=0&_userid=5781704&md5=c83232dc86f783980ea66b97c8c75f02&searchtype=ahttp://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W75-48V7VBX-1&_user=5781704&_coverDate=10%2F31%2F2003&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_rerunOrigin=scholar.google&_acct=C000016587&_version=1&_urlVersion=0&_userid=5781704&md5=c83232dc86f783980ea66b97c8c75f02&searchtype=ahttp://www.ingentaconnect.com/content/tandf/bssc/2005/00000014/00000001/art00005http://www.ingentaconnect.com/content/tandf/bssc/2005/00000014/00000001/art00005http://www.ingentaconnect.com/content/tandf/bssc/2005/00000014/00000001/art00005http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W75-48V7VBX-1&_user=5781704&_coverDate=10%2F31%2F2003&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_rerunOrigin=scholar.google&_acct=C000016587&_version=1&_urlVersion=0&_userid=5781704&md5=c83232dc86f783980ea66b97c8c75f02&searchtype=ahttp://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6W75-48V7VBX-1&_user=5781704&_coverDate=10%2F31%2F2003&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_rerunOrigin=scholar.google&_acct=C000016587&_version=1&_urlVersion=0&_userid=5781704&md5=c83232dc86f783980ea66b97c8c75f02&searchtype=a


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APPENDIX

Calculation for design of primary sewage treatment plant

Calculation of Sewage Generation

Total present population-Hostels = 20,000 person

Residential area =3,000 personWater supply per capita -

hostels = 180 l/h/dResidential area = 250 l/h/d

Sewage generation per day = 80% of supplied waterPer capita sewage waterHostels = 150 l/h/dResidential area = 200 l/h/d

Total sewage generation per day

Hostels150 x 20,000 = 3000000 l/dResidential area200 x 3000 = 600000 l/dTotal amount of sewage3000000 + 6000000 = 3600000 = 3.6 MLDIn cumec,Average discharge = 0.042 cumec

Maximam discharge = 3 x avg. discharge= 3 x 0.042

= 0.126cumces

Design of Receiving Chamber

Design flow = 0.126 cumecDetention time = 60 sec

Volume required = 0.126 x 60

Vrqd = 7.56

Provide depth = 1 m

Area = 7.56

Take ratio of length : breadth = 2 : 1

L x B = 2B x B = 2 = 7.56= 3.78

B = 1.94 mSay 2m

L = 3.88 mSay 4m

Cross Checking of the designed parameter


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Volume designed = 4m x 2m x 1m

Vdes = 8

Vrqd = 7.56

Vdes > Vrqd

Design of Coarse Screen

Peak discharge of sewage flow = 0.126 /s

Assume the velocity at average flow is not allowed to exceed 0.8 m/sThe net area screen opening required = 0.126 / 0.8

= 0.16

Clear opening between bars = 20 mm = 0.02m

Size of the bars = 75 mm x 10 mmAssume width of the channel = 0.5m

The screen bars are placed at 60 to the horizontal.Velocity through screen at peak flow = 1.6m/s

Clear area = 0.16 / 1.6 x sin 60= 0.115

No of clear openings = 0.115 / 0.03= 3.83 = 4 Nos.

Width of channel = (4 x 30) + (5 x 10)= 170mm = 0.17m

Provided width of the channel = 0.2mDepth of channel = 0.115 / 0.2

= 0.57m

Design of Grit Chamber

Peak flow of sewage = 0.126 /s

Assume average detention period = 180sAerated volume = 0.126 x 180

=22.68 = 22.7

In order to drain the channel periodically for routine cleaning and maintenance two chambers are

used.

Therefore volume of one aerated chamber = 22.7/ 2

= 11.35

Assume depth of 1.5m and width to depth ratio 2:1

Width of channel = 1.5x 2= 3 m

Length of channel = 11.35 / 3= 3.78 m

Say 4mIncrease the length by about 30% to account for inlet and outlet Provided length = 4+1.2 = 5.2 m


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Design of Skimming Tank

The surface area required for the tank A = 6.22 x x q / Vr

q = 0.126 x 60 x 60 x 24

= 10886.4 / day

Vr = 0.25 m / min= 0.25 x 60 x 24

= 360 m / day

A = 6.22 x x 10886.4 / 360

= 0.189

Provide the depth of the skimming tank is 1m

The length breadth ratio is 1.5: 1L = 1.5B

A = 1.5

0.189 = 1.5

B = 0.355 mL = 0.532 m

Design of Primary Sedimentation Tank

Max. Quantity sewage = 3.6 MLD

Surface loading = Q /

= 20,000 / / day

Detention period = 2hr

Volume of sewage =

= 75

Provide effective depth = 2mSurface area = volume / depth

= 75 / 2

=37.5

Diameter of the tank

= 37.5

6.91msay 7mPrimary sedimentation tank is designed for the dimension of 7m dia and 2m depth with free board

of 0.5m extra depth.

Design of High Rate Trickling Filter

Quantity of sewage flowing into the filter per day = 3.6 MLDBOD concentration in raw sewage = 200 mg / l


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Total BOD present in raw sewage = 3.6x 200= 720 kg.

BOD remove in primary tank = 30%BOD left in the sewage entering per day in filter unit = 720 x 0.7

= 504 kg.BOD concentration desires in final effluent = 20 mg / l

Total BOD left in the effluent per day = 3.6 x 20= 72 kg

BOD removed by the filter = 50472= 432 kg

Efficiency of the filter = (BOD removed / total BOD) x 100

= x100 = 85.7%

For Computing the volume of filter used equation -

=

Where = 85.7%

Y = total BOD in kg. Recirculation factor

F = recirculation factor

F =

Here

F =1.89

So

Design of Primary Sewage Plant

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