Design Criteria for Water and Sanitation Agencies & PHED

Design Criteria for Water

and Sanitation Agencies &

PHED Punjab

The Urban Sector Planning and Management Services Unit (Pvt.) Ltd.

5th Floor, 503 Shaheen Complexes, Egerton Road, Lahore 042- 99205316-22 Fax.042-99205323

www.urbanunit.gov.pk, Email: [email protected]

http://www.urbanunit.gov.pk/

mailto:[email protected]

Water & Sanitation Agencies, Punjab Design Criteria

Disclaimer

DISCLAIMER

Design Criteria for the Water and Sanitation Authorities, Punjab has been revised and

updated by the Urban Sector Planning and Management Sector Unit (Pvt.) Ltd. Maximum

care and caution has been observed while developing this document.

No part of this document may be reproduced or transmitted in any form or by any means,

electronic or mechanical, including photocopying, recording or information storage and

retrieval system, without the express permission, in writing, by the Urban Unit.

The opinion expressed in the document are solely those of the authors and publishing them

does not in any way constitute endorsement of the opinion by the Urban Unit.

Reviewed By Dr. Nasir Javed

Technical Team Engr. Abid Hussainy, Sr. Specialist Water and Sanitation

Engr. Kashif Nadeem, Research Assistant

Engr. Rao Ali Raza, Research Analyst

Engr. Huma Anwar


Executive Summary

Preface

The Design Criteria for Water Supply (including Sewerage & Drainage) Schemes are already

in place. These criteria, which were approved by the Government of Punjab and notified in

1998, are currently being used for the design of all Public Health Engineering structures for

water supply, sewerage and drainage. The Water and Sanitation Agencies also follow this

Design Criteria with minor modifications suited to their requirements.

In 2008, the Design Criteria were also reviewed by the Punjab Devolved Social Services

Programme (PDSSP). No major changes were proposed; however, some amendments were

made and the resulting document is being selectively followed by the government

departments as a guideline.

It would be appropriate to develop suitable Design Criteria for the schemes to be taken up by

WASAs to meet the ground realities and the technological advancements. In pursuance of

this objective, a comparison of the notified criteria with the proposed criteria along with

justification of the proposals has been prepared for approval and adaptation by WASAs as per

their local conditions.

The design criteria has been reviewed based on past experience and the best solutions that

emerged during monitoring and evaluation of water supply and sewerage systems projects.


Table of Contents

Table of Contents

Preface ....................................................................................................................... 1

1 General Design Criteria of Water Network........................................................ 1

1.1 Project Design Horizon ........................................................................................... 1

1.2 Population Projections ............................................................................................ 2

1.3 Water Demand ......................................................................................................... 3

1.3.1 Domestic Water Consumption ..................................................................... 3

1.3.2 Industrial Water Consumption ..................................................................... 3

1.3.3 Variations in Water Demand ....................................................................... 4

1.4 Water Sources .......................................................................................................... 4

1.4.1 Purpose ......................................................................................................... 4

1.4.2 Key Principles .............................................................................................. 4

1.4.3 INVESTIGATIONS PRIOR TO DEFINING WATER SOURCES ........... 5

1.4.4 PRIORITY RANKING OF SOURCES....................................................... 6

1.5 Tubewells Design Criteria ...................................................................................... 6

2 Water Distribution and Storage ............................................................................. 8

2.1 Water Supply Design Criteria ................................................................................ 8

2.1.1 Terminal Pressure ........................................................................................ 8

2.1.2 Velocity Flow in Pipes ................................................................................. 9

2.1.3 Earth Cover over Pipes ................................................................................ 9

2.1.4 Public Stand Posts (PSPs) ............................................................................ 9

2.1.5 Minimum Size of Pipe ................................................................................. 9

2.1.6 Material of the Pipe ...................................................................................... 9

2.1.7 Service Connection .................................................................................... 10

2.1.8 Sluice Valves ............................................................................................. 10

2.1.9 Non-Retune Valves .................................................................................... 10

2.1.10 Air Relief Valve ......................................................................................... 10

2.1.11 Washout ..................................................................................................... 10

2.2 Storage Reservoirs ................................................................................................. 11

2.2.1 Overhead Reservoirs .................................................................................. 11

2.2.2 Groundwater Reservoir .............................................................................. 11

2.2.3 Water Metering .......................................................................................... 11

3 Potable Drinking Water Treatment .................................................................. 12


Table of Contents

3.1 Conventional Treatment ....................................................................................... 12

3.2 Ultrafiltration ......................................................................................................... 13

3.3 Activated Carbon Filter ........................................................................................ 15

3.4 Arsenic Removal .................................................................................................... 15

3.5 Fluoride Removal .................................................................................................. 16

3.6 Iron and Manganese Removal .............................................................................. 17

3.7 Nitrates Removal ................................................................................................... 18

3.8 Reverse Osmosis System ....................................................................................... 19

4 Sewerage System ............................................................................................. 21

4.1 Location of Disposal Works .................................................................................. 21

4.2 Design Period ......................................................................................................... 21

4.2.1 Master Plan ................................................................................................ 21

4.2.2 Land Acquisition ........................................................................................ 21

4.2.3 Civil Works Including Sewers ................................................................... 21

4.2.4 Pumping Mains .......................................................................................... 22

4.2.5 Pumping Station Civil Works .................................................................... 22

4.3 Design Flows .......................................................................................................... 22

4.3.1 Unit Flow Factor ........................................................................................ 22

4.3.2 In-Filtration ................................................................................................ 23

4.3.3 Peak Factor................................................................................................. 23

4.3.4 Maximum Dry Weather Flow .................................................................... 24

4.3.5 Industrial Wastewater Allowance .............................................................. 24

4.3.6 Storm water Allowance.............................................................................. 24

4.4 Shape of Sewer ....................................................................................................... 24

4.5 Velocity at Design Flow ......................................................................................... 25

4.6 Spacing of the Manholes ....................................................................................... 25

4.7 Minimum Size of Sewer ........................................................................................ 27

4.8 Earth Cover ............................................................................................................ 27

4.9 MANNING FACTOR OR COEFFICIENT OF ROUGHNESS ....................... 27

4.10 Bedding of Sewers ................................................................................................. 27

4.11 Class of Pipes ......................................................................................................... 28

4.12 Pipe Reinforcement ............................................................................................... 28

4.13 Slope of Sewer Line ............................................................................................... 28

4.14 Outfall Works ........................................................................................................ 28

4.15 Sewage Pump Selection ......................................................................................... 29


Table of Contents

4.16 Design Flow of Drainage ....................................................................................... 29

4.17 Pumping or Disposal Station ................................................................................ 30

5 Wastewater Treatment ..................................................................................... 32

5.1 Wastewater Characteristics .................................................................................. 32

5.2 Design Criteria ....................................................................................................... 32

5.2.1 Primary Screens ......................................................................................... 32

5.2.2 Inlet Chambers ........................................................................................... 33

5.2.3 Grit and Grease Removal ........................................................................... 35

5.2.4 Balancing Tanks......................................................................................... 36

5.2.5 Biological Treatment Stage ........................................................................ 37

5.3 Trickling Filter ...................................................................................................... 41

5.3.1 Design Requirements for Trickling filters ................................................. 42

5.3.2 Design Requirements for Sequencing Batch Reactor (SBR) System ........ 42

5.3.3 Design Parameters for the Secondary Clarifiers ........................................ 43

6 Miscellaneous ................................................................................................... 45

6.1 Preventive maintenance ........................................................................................ 45

6.1.1 Leakage DETECTION: ............................................................................. 45

6.1.2 Cleaning of pipes ....................................................................................... 45

6.1.3 Protection against pollution near sewers and drains .................................. 45


List of Tables

List of Tables

Table 1-1: Design horizon for water supply components .......................................................... 1

Table 1-2: Domestic water supply standards ............................................................................. 4

Table 2-1: Pipe material ............................................................................................................. 9

Table 2-2: Service Connection Standard ................................................................................. 10

Table 3-1: Design standards for slow sand filter ..................................................................... 12

Table 3-2: Design standards for rapid sand filter..................................................................... 12

Table 3-3: Design criteria of UF water treatment plants ......................................................... 13

Table 3-4: Design criteria of activated Carbon filters ............................................................. 15

Table 3-5: Design specifications for GHF ............................................................................... 15

Table 3-6: Design specifications for Activated Alumina ........................................................ 16

Table 3-7: Design specifications of activated Alumina absorbent for Fluoride removal ........ 17

Table 3-8: Design specifications of filter and oxidants for removal of Fe and Mn ................. 17

Table 3-9: Design criteria of ION Exchange resins for Nitrates removal ............................... 18

Table 3-10: Design Criteria for RO Plant ................................................................................ 19

Table 4-1: Unit flow factors for various sources ..................................................................... 22

Table 4-2: Infiltration Rate ...................................................................................................... 23

Table 4-3: Peaking factor wrt Population ................................................................................ 23

Table 4-4: Storm water Allowance .......................................................................................... 24

Table 4-5: Velocity and design flows ...................................................................................... 25

Table 4-6: Spacing of manholes in straight line ...................................................................... 26

Table 4-7:Design criteria for sewer above sub soil level ......................................................... 26

Table 4-8: Manning Coefficient of different materials ............................................................ 27

Table 4-9: Detention time ........................................................................................................ 28

Table 4-10: Run off coefficient for sandy soil ......................................................................... 29

Table 4-11: Run off coefficient for heavy soil ......................................................................... 30

Table 4-12: Run off coefficient for urban dwellings ............................................................... 30

Table 5-1: Characteristics of sewerage water .......................................................................... 32

Table 5-2: Design Criteria of primary Screens ........................................................................ 33

Table 5-3: Design Criteria of Inlet chamber ............................................................................ 33

Table 5-4: Design Criteria of secondary screens ..................................................................... 34


List of Tables

Table 5-5: Design Parameters for Grease Chambers ............................................................... 35

Table 5-6: Design Criteria for Grit Chambers ......................................................................... 35

Table 5-7 Design Parameters for Balancing Tanks ................................................................. 36

Table 5-8: Design Criteria of Conventional Activated Sludge (CAS) System ........................ 37

Table 5-9: Design Parameters for Sequencing Batch Reactors (SBR) System ....................... 38

Table 5-10: Specification of SBR reactor ................................................................................ 39

Table 5-11: Design Parameters for Extended Aeration System (Ea) ...................................... 40

Table 5-12: Organic loading parameters for EA wastewater treatment system ...................... 40

Table 5-13: Design parameters for secondary clarifiers .......................................................... 42

Table 5-14: Design parameters for secondary clarifiers .......................................................... 43

Table 5-15: Design guide for intermittent disinfection............................................................ 44


List of Acronyms

List of Acronyms

ADF Average Daily Flow ADWF average dry weather flow AC Alternating Current ASTM American Society for Testing Materials BOD Biological Oxygen Demand CAS Conventional Activated Sludge COD Chemical Oxygen Demand CU underflow concentration DO Dissolved Oxygen EA Extended Aeration EBCT Empty Bed Contact Time FRP Fiber Reinforced Plastic HRT Hydraulic Retention Time HDPE High density Polyethylene IT Information Technology IDEA Intermittent Decant Extended Aeration Lpcd Litres per capita per day LDA Lahore Development Authority MLSS Mixed liquor suspended solids NEQS National Environmental Quality Standards NTU Nephelometric Turbidity Unit OD Oxidation Ditch PHED Public Health Engineering Department PLC Programmable Logic Control PF Peaking Factor PVC Polyvinyl chloride PE Polyethylene PCGIP Punjab Cities Governance Improvement Project PCC Pre-stressed Concrete Cylinder PE Population Equivalent RCC Roller-compacted concrete RAS Return activated sludge SBR Sequencing Batch Reactor TDS Total Dissolved Solids TSS Total Suspended Solids TMA Tehsil Municipal Administration UPVC Un-plasticized polyvinyl chloride WWTP Waste Water Treatment Plant WASA Water and Sanitation Authority WAS Waste activated sludge


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General Design Criteria of Water Network

1 General Design Criteria of Water Network

1.1 Project Design Horizon

In a conventional manner, it is recommended to design water supply networks, trunk sewers,

water & wastewater treatment plants and interceptors for the projected peak flows expected

during 25 years period or for the saturation population of the area. Such long design periods will

make it possible to capture economies of scale in sewerage system especially. However, these

have to be balanced against the opportunity cost of capital, uncertainties in predicting future land

use patterns or direction of the growth of the city and high cost of maintain large sewers with low

flows. The use of shorter design periods avoids such problems and reduces the large capital

requirements, facilities financing, and enhances prospects of achieving greater coverage with a

given investment. With a shorter to medium design periods and construction by phase, starting

from upstream ends, the effects of errors in forecasting the population growth and their water

consumption can be minimized and corrected.

The design horizon for water supply components shall be as follows:

Table 1-1: Design horizon for water supply components

Water Supply Network Component Design Life

Tube Well 15 years

Pump Houses 15 years

Pumping Machinery 10 years

Treatment Works

Slow Sand Filter Plants

20 years (Repair or replacement of the pumping

sets might be necessary after 10 years of

operation).

Rapid Sand Filter plants 25 years (Repair or replacement of the pumping

sets might be necessary after 10 years of

operation).

Rising Mains 25 Years (for HDPE pipes). The size of rising

mains should be based on maximum day demand.

Distribution System

25 Years (for HDPE pipes). The capacities of

distribution system are to be based on peak hour

demand while tube wells and rising mains are to

be based on maximum day demands.


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1.2 Population Projections

The knowledge about the past populations and assumptions about future populations are

fundamental to the planning decisions. The projections are the estimates for the future dates.

They illustrate the plausible courses of future populations and are developed using normative

procedures comprised of mathematical models and analytical growth rates based on historical

data. The projected numbers are “best assessed” populations estimates based on published

government data comprising of most recent decennial census or the data available with the city

district government.

Additionally, the socio-economic models of population are more commonly used by the planners

for outline development plans/master plans, industrial development and IT service driven

development. The fact is that, none of the methods guarantees the exact precision of population

projections as the cities are dynamic entities and their development changes from time to time

and depending upon the master planning, city administration, policies, infrastructural creation

and socio-economic conditions.

The main objectives of the population projections are:

To forecast the projected population for the project horizon with interim target years

Analysis of the present and future populations using census data and published reports.

Analysis of the future trends of the population’s growth

Distribution of the population over the proposed water supply, sewerage network and

WWTP.

Estimated of wastewater generation using per capita water consumption patterns.

As per PHED Design Criteria 1998, the population projections are to be determined through

compound rate of growth method using following expression:

Pn = Po (1+r/100) n ……………………………….. (1.1)

Where,

Pn = Projected population by the end of nth year

Po = Population of base year, year of known population

r = Population growth rate per year to be taken from related District Census Reports.

n = No. of years, counted from base year i.e. design period


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1.3 Water Demand

When the proposed project is in a community with an existing community supply, the

community’s historic records provide the best estimate of water use. Conversion of total demand

to per capita demand (liters per capita per day, Lpcd) allows for the separation of population

growth from the growth in unit consumption. If the proposed project is to improve the water

quality, consideration should be given to the likelihood that unit demand will increase because of

the improved water quality. In the absence of existing data for the client community, nearby

communities with similar demographics are a good alternative source. When the demographics

differ in some particular aspect such as a higher or lower density of commercial facilities or a

major industrial component, adjustment in the total demand will be appropriate.

Firstly, the extent of sewerage, system pressure, water price, water loss, age of the community,

and availability of private wells also influence water consumption but to a lesser degree.

Secondly, the influence of industry is to increase average per capita water demand. Small rural

and suburban communities will use less water per person than industrialized communities.

The third most important factor in water use is whether individual consumers have water meters.

Meterage imposes a sense of responsibility not found in unmetered residences and businesses.

This sense of responsibility reduces per capita water consumption because customers repair leaks

and make more conservative water-use decisions almost regardless of price. Because water is so

inexpensive, price is not much of a factor. The rationale for the last factor is straightforward. Per

capita water use increases with an increased standard of living.

Following meterage closely is the aspect called system management. If the water distribution

system is well managed, per capita water consumption is less than if it is not well managed. Well

managed systems are those in which the managers know when and where leaks in the water main

occur and have them repaired promptly.

For a community supply system that includes a new treatment plant and a new distribution

system, water loss through leaks is not a major factor in estimating demand. For a new plant with

an existing old distribution system, water loss through leaks may be a major considerations.

1.3.1 Domestic Water Consumption

The standard for the determination of domestic water consumption is based on the population

slabs in Table1.2.

1.3.2 Industrial Water Consumption

For institutions such as hospitals, hostels, schools etc. an allowance @ 10 gallons per boarder and @ 5

gallons per day scholar is to be made.


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Table 1-2: Domestic water supply standards

Design Population Per Capita Consumption/day (inclusive of Non-Revenue Water (NRW) Above 1 lac

33 gallons (with 20%NRW) )sewerage facilities

Up to 3million 35 Gallon (with 20%NRW)

Up to 5 million 40 Gallon (with 20%NRW)

Above 5 million 45 Gallon (with 20%NRW)

Hospitals, Educational

Institutes, Govt.

Offices, Mosques &

Madrasa

As per actual no. of persons using particular building

The unit demand estimates are averages. Water consumption changes with the seasons, the days

of the week, and the hours of the day. Fluctuations are greater in small than in large

communities, and during short rather than long periods of time. The variation in demand is

normally reported as a factor of the average day.

1.3.3 Variations in Water Demand

The Following standers to be followed for computation of the short term variations:

A. Maximum day demand is to be taken as 1.5 times the average day demand

B. Peak hour demand to be taken as 1.5 times the maximum day demand

1.4 Water Sources

Water extracted from a source is referred to as raw water. The exploitable raw water

quantity during a definite time is denominated as the capacity of a source.

1.4.1 Purpose

In the context of public water supply design, the purpose of a raw water source is the reliable

delivery of water. A source is reliable if sufficient water is available every day of the year.

1.4.2 Key Principles

The following key principles apply:

Sources in proximity to the supply area shall prevail (economic consideration).

The source must ensure a reliable supply up to the design horizon.


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In case there is no single source providing the required amounts of water, a combination

of two or more sources has to be envisaged.

The use of the source shall not lead to conflicts with other water users (or at least only if

mitigation measures will be implemented prior to investing into source capping).

1.4.3 INVESTIGATIONS PRIOR TO DEFINING WATER SOURCES

The exploitation of a water source has to be conducted in a sustainable way. In particular, the

extracted water quantity must not exceed the quantity, which is recharged by the natural

hydro-geological or hydrological system. The admissible water quantity for exploitation

has to be identified for each specific source on the basis of hydro-geological and hydrological

investigations.

Thus, prior to identifying water sources to be used for a water supply system, investigations are

required. These should cover amongst others:

Identification of possible sources.

Collecting available information on sources (location, elevation, water quantity and

quality issues). This also includes the experiences of people living in the vicinity for a

longer period.

Assessing possible sources of pollution (potential or existing).

Assessing rates of usage of these sources (avoid overexploitation and conflicts with other

users).

Cultural aspects to be taken into account.

By carrying out these advance investigations, the number of potential sources is usually already

limited.

In case water quality and yields have not been monitored, but the source is identified as

potentially appropriate, it is recommended to carry out a survey for a period of at least one year

by measuring on a weekly basis the yield and on a monthly basis the water quality. The

minimum yield measured during this period, lowered by a climate change factor or by a

factor taking into account the rainfall of the year of measurement compared to a drought

year, will define the source capacity (Hydro geological assessments).

Prior to any design, the seasonal patterns of the source’s capacities shall be investigated

for a minimum period of one year. During this time, measurements of the source

capacity shall be conducted at appropriate intervals. Additional measurements are required

during heavy rainwater periods, floods and droughts. For groundwater, a hydro-geological


Page 6 of 55


investigation programme specifying the intervals and locations of measurement is necessary in

order to identify the seasonal pattern of source capacity.

In case only an intermediate yield was recognized, either the source must be omitted for supply

purposes or an alternative source has to be identified as a back-up solution for the period of low

or no-flow (this will not be feasible if the period of low flow or no-flow matches peak

demand periods. In this case, this specific source should immediately be taken out of the list of

potential water supply sources).

If two or more options for source tapping exist, a comparison of total costs shall contribute to the

decision of which option to choose. Generally, the least expensive option shall prevail.

1.4.4 PRIORITY RANKING OF SOURCES

The types of water sources usually feature different water qualities. Therefore, a water supply

design measure shall strive to exploit that source, which represents the best water

quality. The ranking of sources according to their quality level is as follows, beginning with the

best quality:

Spring

Ground water

Artificial basin

Lake

River

Rain water

For sweet water zones, groundwater is the source of choice. However, due to depleting aquifers,

surface water has become the ultimate choice. For brackish water zones, in case a canal or

distributaries available at a reasonable distance, skimming wells (shallow Tube wells) will be

installed along the bank and pumped to the community through a rising main after appropriate

treatment by chlorination or UF plant.

1.5 Tube wells Design Criteria

The Tube wells will be designed to meet Maximum day demand.

A. Entrance Velocity: The Entrance Velocity 0.05 ft / sec in the strainer is recommended

against the allowable value of 0.1 ft /sec to 0.2 ft / sec to check the entry of fine sand into

the screen. B. Opening Area of the Strainer: Opening area normally ranges from 10% to 12%, the

lower limit of 10% is recommended for design purposes.


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C. Slot Size: Slot size 1”x 1/30” is recommended for the screen. Shrouding shall be

provided.

D. House Pipe : The diameter of House Pipe will be based on the design discharge of tube

well

E. Sanitary Seal: To control and check the surface and ground contamination at shallow

depths sanitary seal consisting 1:2:4 plain cement concrete is recommended.

F. Shrouded Material: The shrouding material will be of pea gravels having size 1/8” to

3/8” and its thickness will be in the range of 3” to 6”, however the later one is preferred

and used.

G. Shrouding Pipes: Shrouding shall be done through 3” diameter P.V.C. Pipe or

equivalent. Suitable values of the parameters shall be carefully selected.

H. Delivery Pipes: Length of delivery pipe in pump house should be 6-9ft to have proper

installation of measuring instruments like portable Ultrasonic flow meter for energy audit

purpose. Pressure gauge should be installed on the delivery pipe for pressure head

measurements.


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Water Distribution and Storage

2 Water Distribution and Storage

2.1 Water Supply Design Criteria

Water distribution and storage are, in most instances, the most costly parts of a water supply

scheme. Hence savings in these areas through good design can often result in significant savings

for a whole project.

The elements of a water distribution and –storage system include some or all of the following:

Bulk water transmission systems;

Bulk-storage reservoirs;

Intermediate-storage reservoirs;

Distribution networks; and

Terminal consumer installations.

The water distribution system shall be designed, and pipe sizes shall be selected such that under

conditions of peak demand, the capacities at the fixture supply pipe outlets shall not be less than

the criteria provided. The minimum flow rate and flow pressure provided to fixtures and

appliances not listed here in design criteria shall be in accordance with the manufacturer’s

installation instructions.

2.1.1 Terminal Pressure

The minimum design nodal pressure are prescribed to discharge design flows onto the properties.

Generally, it is based on population served and type of area to be served (middle income, high

income, low income, high density, low density, single story, double story etc ).It is not

economical to maintain high pressure in the distribution network just to cater the needs of few

high rise buildings in the area. Moreover, the water leakage losses increase with the increase in

the terminal/system pressure in a water distribution system.

A) Keeping in view the trends of multistory building construction in urban residential areas it is

advisable to adopt at least 6 meters (0.6 bars) minimum terminal pressure and maximum

terminal pressure of 65 m (6.5 bars)

B) For rural residential areas, the existing standard of terminal pressure is 12 meter.


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2.1.2 Velocity Flow in Pipes

The following standards shall be adopted for the velocity of pipes:

Distribution mains 0.5 to 2 m/sec.

Rising mains 0.3 to 2 m/sec but for long rising mains, life cycle cost analysis will be done to

ensure most economical size of pipe

2.1.3 Earth Cover over Pipes

The minimum depth of cover for water distribution systems and sanitary force mains shall be 36

inches, measured from the top of the pipe to the established finished grade above the pipe.

However all road cuts are to be filled in with pit sand / river sand. During design, site layout of other

infrastructure (i.e. storm sewer, gravity sanitary sewer, etc) shall be considered in minimizing the

need to have deep pressure mains.

2.1.4 Public Stand Posts (PSPs)

The following standards to be adopted regarding PSPs:

PSPs should not be provided in urban areas and only be provided in the semi-urban areas/

peri-urban areas.

The location of the stand-posts shall be made in such a manner that it is at an

approximate distance of about 350 feet from the end consumers in the rural areas and

should be avoided in the semi urban areas as far as possible to reduce losses of water and

revenue.

Each stand-post shall serve about 200 persons.

PSP to be provided only after study of revenue collection data of concerned area.

2.1.5 Minimum Size of Pipe

The minimum size of the tertiary water pipe shall be taken as 3 inches.

2.1.6 Material of the Pipe

The pipe material to be used shall conform the standard given here below in Table Table 2-1.

Table 2-1: Pipe material

Material Standard

uPVC Class C Pipes BS: 3505:1986

PE Class C Pipes DIN 8074/8075

GRP Class C Pipes ASTM D-3517


Page 10 of 55


2.1.7 Service Connection

Following standards for service connection to be adopted.

Table 2-2: Service Connection Standard

Service Connection Buried G.I./ PE Pipe with Saddle Clamp & Ferrule

Domestic Service House Connection 1/2 inch

Commercial Connection 3/4 inch

2.1.8 Sluice Valves

Sluice valves will be located at main control points for balancing and regulating the flows. The

sluice valves shall be Cast Iron Flanged or non-rising stem.

2.1.9 Non-Return Valves

The Non-Return valve shall meet the following minimum standards:

Outside the delivery main of the Tubewells

In the rising main after every 1000 meters.

2.1.10 Air Release Valve

The Air relief valve shall meet the following minimum standards:

At the summits and

After 2000 meter intervals in straight reaches to facilities escape of trapped air

The material of the air relief valve shall be Cast Iron

2.1.11 Washout

Washout to be located at the lowest points to wash out all kinds of debris.


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2.2 Storage Reservoirs

2.2.1 Overhead Reservoirs

Overhead storage reservoirs should be provided for all water supply schemes. Capacity of

overhead reservoirs should be based on 1/6th of average day demand. Nearest standard size of

reservoir shall be used with a capacity min of 5,000 gals.

2.2.2 Groundwater Reservoir

When the length of the rising main is such that the loss of head is very high, intermediate

pumping stations comprising a storage tank and pumping machinery installed in a pump house

will be used. Capacity of ground water storage tank @ ¼th average daily demand will be

provided.

2.2.3 Water Metering

For ensuring sustainability of water supply schemes and for avoiding water wastage, 100%

metering will be done. The cost of water meters shall be recovered from the users in easy

installments.


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Potable Drinking Water Treatment

3 Potable Drinking Water Treatment

3.1 Conventional Treatment

Conventional Treatment Plant shall consist of an Intake Structure from canal or river,

Sedimentation Tank, Slow Sand filter(s), clear water tank and chlorination facility.

A) slow sand Filter

Table 3-1: Design standards for slow sand filter

Component Typical Standard

Raw water storage 50% of 21 days average water requirement

Rate of filtration 40 gallons per day per sft of sand area

Depth of filter sand 30 to 36 inches

Effective size of sand (d10) top of filter gravel to 1

feet

0.3 to 0.35 mm

1 to 2 feet 0.25 to 0.30 mm

Top layer 9 inches minimum 0.18 to 0.22 mm

Uniformity Co-efficient of sand (d 60/d 10) 2.5

Depth of water over the sand 3-4 feet

Velocity of water in under drainage system Not more than 0.75 feet/sec

B) Rapid Sand Filter

Table 3-2: Design standards for rapid sand filter


Flocculation Tank

Detention Time 20-30 Seconds

Velocity Gradient 20-75 L/s

Diffuser Wall

Velocity through the Diffuser Wall to prevent

floc break up 0.5 Ft/s

Sedimentation Tank

Detention Time 1.5-4.0 Hr

Overflow Rate 131-197 ft3/ft2/hr

Side Water Depth 10-16.5 Ft

Rapid Sand Gravity Filters

Type of Filters Constant Head

Filter Media Sand

Filtration Rate 16.4 – 49 ft3/ft2/hr


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Bed Depth 2 - 5.9 Ft

Uniformity Coefficient 1.3-1.7

Backwash Flow Rate media 10% of the settling velocity of the filter

Air Flow Rate 30-60 m3/m2/hr 36-72 m3/m2/hr

Minimum Filtration Cycle 24 Hr

Uniformity Coefficient 1.3-1.7

Backwash Flow Rate media 10% of the settling velocity of the filter

Air Flow Rate 30-60 m3/m2/hr 36-72 m3/m2/hr

Chemicals

Coagulants Alum & Lime

Disinfection Chlorine

3.2 Ultrafiltration

Design Criteria for various types of filter plants to be used, depending upon the type of

contamination as per water quality test results, will be as given in the table below:

Table 3-3: Design criteria of UF water treatment plants

Parameter Range of Typical values

Pretreatment

If turbidity is >1 NTU Coagulation, Flocculation & Sedimentation

Strainer or Cartridge / bag Filters of Rating 100-500 µm

Pre Filtration (Pressure Sand Filtration)

Filtration Rate 10.0 - 20 m/h

Backwash rate 40 -50 m / h

Backwashing Time Adjustable by PLC

Sand Effective Size 0.8 - 1.0 mm

UC 1.4 - 1.7

Depth 0.8 - 2.0 m

SG ≥ 2.63

Pre Filtration (Sand & Anthracite)

Filtration Rate 10 -25 m/h

40 -50 m / h

Backwash rate Adjustable by PLC

Backwashing Time Effective Size 0.45 - 0.65


Page 14 of 55


Parameter Range of Typical values

Sand UC 1.4 - 1.5

Depth 0.3 m

SG ≥ 2.63

Anthracite Coal Effective Size 0.9 -1.4

UC 1.4 - 1.5

Depth 0.45 m

SG ≥ 1.5 to 1.6

Vessel FRP

Activated Carbon Filtration Design Criteria separately presented

UF Membrane Filters

Membrane Type Hollow Fiber membrane with pore size 0.01 µm

Permeate flux (Pressurized) 30-170 L/m2 h

Transmembrane pressure (TMP) 15 - 100 psi

Area of membrane per module 8-70 m2per module

Modules per rack 2-300

Module dimensions

Diameter 100-300 mm

Length 1-6 m

Filter run duration 30-90 min

Backwash

Duration 1 - 5 min

Pressure 35-350 kPa

Flow rate 6 L/min/m2

Backwashing Time Adjustable by PLC

5 -180 d Time between chemical cleaning

Duration of Chemical Cleaning 1 - 6 h

Excess Membrane Capacity 25 % (To account for racks being off line for back

washing & /or maintenance / unanticipated change in

water quality)

Disinfection

Post Treatment

Bacteria Below Detection Level

Viruses Greater than 99.9999 Percent Rejection

Waste Disposal Into the sanitary sewerage system


Page 15 of 55


3.3 Activated Carbon Filter

The utilization of granu1ar- carbon filtration is a relatively simple and economical procedure. It

is possible to adopt existing plant filters for a combination filtration -adsorption unit process with

minimum alteration, by filling them with granular carbon.

Table 3-4: Design criteria of activated Carbon filters

Parameters Range of Typical Values

Filtration Rate 5 - 24 m/h

Empty Bed Contact Time 5 - 25 Minutes

Backwashing Rate 8 -38 m/h

Base Material Coconut shell, Wood, bituminous coal, lignite coal

Effective Size 0.8 -0.9 mm

Uniformity Coefficient ≤ 1.9

Washed Density 0.4 g/cm3

Iodine No 1050 mg/g (Min)

Surface Area 1000 m2/g

Vessel Material FRP

Replacement On depletion of the adsorption capacity

Waste Disposal In to the sanitary sewerage system

3.4 Arsenic Removal

A) The Design criteria for Granular Ferric Hydroxide (GHF) - absorbent iron based for

arsenic removal is as follows:

Table 3-5: Design specifications for GHF


Hydraulic Loading Rate 5 - 8 gpm /sft

Empty Bed Contact Time (EBCT) 5 -10 Min

Media Size 0.32 - 2.0 mm

Grain Density 1.59 g/cm3

Bulk Density 1.22 - 1.29 g/cm3


Page 16 of 55



Specific Surface Area 250 - 300 m2/g (Dry Weight

Backwashing / Regeneration NIL

Precondition

pH Value Range

Turbidity <0.3

PO-4 < 1 mg/l

Post Treatment None

Vessel Material Fiber Reinforced Plastics (FRP)

Process Control PLC / Digital

B) Activated Alumina (AA) absorbent for Arsenic Removal

Table 3-6: Design specifications for Activated Alumina


Hydraulic Loading Rate 5 - 8 gpm /sft

Empty Bed Contact Time (EBCT) 5 Min (Minimum)




Specific Surface Area 300 -350 m2/g (Dry Weight)

Backwashing 8 -9 gpm/ft2 for 50 % bed expansion

Regeneration NIL

Pretreatment

pH Value Range 5.5 - 6.0

Turbidity <0.3

Post Treatment pH adjustment

Vessel Material Fiber Reinforced Plastic (FRP)


3.5 Fluoride Removal

The specifications for Activated Alumina (AA) absorbent for Fluoride Removal shall be as

follows:


Page 17 of 55


Table 3-7: Design specifications of activated Alumina absorbent for Fluoride removal


Empty Bed Contact Time (EBCT) 5 Min (Minimum)

Fluoride Capacity of AA 6 -8 Kg /m3




Specific Surface Area 300 -350 m2/g (Dry Weight)

Bed Depth 0.9 - 1.85 m

Backwashing 8 -9 gpm/ft2 for 50 % bed expansion

Backwashing Time 10 -15 Minutes

Regeneration NIL

Pretreatment

pH Value Range 5 - 6.5 (with 5.5 at optimal)

Turbidity <0.3

Post Treatment pH adjustment

Vessel Material Fiber Reinforced Plastic (FRP)


3.6 Iron and Manganese Removal

Design Criteria for the removal of Iron & Manganese using strong Oxidizing agent (ClO2 or

MnO4) and subsequent Filtration through Green Sand Media.

Table 3-8: Design specifications of filter and oxidants for removal of Fe and Mn


Contact Time of Fe2+&Mn with ClO2 for

oxidation

5 & 20 Seconds

Contact Time with KMnO4 5 Min

Oxidants Requirement

Chlorine 0.64 mg /mg of Fe2+

ClO2 1.2 mg /mg of Fe2+

KMnO4 0.84 mg /mg of Fe2+

Filtration (Pressure Filters)


Page 18 of 55



Filtration Media Green Sand

Filtration Rate 240 - 480 m/d

Backwash Rate 480 -1200 m/d

Effective Green sand Media Size < 0.3 mm

Regeneration Periodic

Regenerate KMnO4 solution

Vessel Fiber Reinforced Plastics (FRP)

Note: Small concentrations of Fe2+ &Mn2+ can be removed through Ion Exchange Process

using SAC Resins – Sulphonated Polystyrene

Source: Water Treatment Principles & Design by MWH

3.7 Nitrates Removal

Design Criteria by using selective Ion Exchange Resins for Nitrates removal from water.

Table 3-9: Design criteria of ION Exchange resins for Nitrates removal


Hydraulic Loading Rate 400 - 800 m3/m2.d

Depth of Resin Bed >0.9 m

Backwash Rate 5 - 7 m3 / m3.h

Backwash Duration 5 - 20 min

Regenerated NaCl

Regenerated Dose 80 - 320 Kg of NaCl /m3 of Regenerated

pH Range 0 – 14

Resin Capacity 1.0 meq/l

Precondition

Turbidity < 5 NTU

TDS < 1000 mg/l

Treated water Quality Increased Chloride & Corrossivity

Post Treatment Usually None

Process Control PLC/ Digital


Page 19 of 55



Waste Characteristics Volumes of brine containing NO3 & excess NaCl

Waste Disposal Disposal into the sanitary sewerage system

3.8 Reverse Osmosis System

The RO plant shall be installed at places where water contains high concentrations of dissolved

solids. The Design Criteria of RO plants shall be as follows:

Table 3-10: Design Criteria for RO Plant


Pre Treatment Objectives

Turbidity < 1 NTU

Silt Density Index (SDI15) ≤5

pH 4.5 - 5.5

Pre Treatment

If turbidity is >1 NTU Coagulation, Flocculation & Sedimentation

Pressure Filtration Same as given in Ultrafiltration Design Criteria

Ultra-Filtration Same as given in Ultrafiltration Design Criteria

Cartridge Filter 100-500 µm

To controls Carbonate, Sulphates, Calcium

Fluoride and Silica Scaling

H2SO4 / HCl, SHMP, Organophosphates and

Polyacrelytes and other propriety compounds

(antiscalant dose to be decided in consultation with the

manufacturer and the degree of problem)

Microbial Fouling Control Chemical biocides and biocets

(Dose to be decided in consultation with the

manufacturer)

Iron and Manganese Fouling Control

H2SO4 / HCl, SHMP,

(Dose to be decided in consultation with the

manufacturer & degree of problem)

Reverse Osmosis

RO Membrane Type Spiral Wound Membrane


Page 20 of 55



Operating Pressure

Brackish Water (5000 mg/l TDS) 350 - 600 psi

Brackish Water (1000 mg/l TDS) 125- 300 psi

Packing density 164-1640 m2/m3

Flux 0.1-5 m3/m2 d

Recovery factor

Brackish Water (5000 mg/l TDS) 65 - 80 percent

Brackish Water (1000 mg/l TDS) 70 - 85 percent

Salt rejection 85-99 percent

Membrane Array Design

(Based on recovery)

One Stage ≤50 % Recovery

Second Stage >50 % but < 75 % Recovery

Third Stage < 90 % Recovery

Post Treatment

pH adjustment NaOH or NaHCO3 addition

CO2 stripping

H2S stripping

Corrosion inhibitor

Protection against future contamination Disinfection

Processed Water Characteristics Desired level of TDS in water

Waste (Concentrate) Disposal Controlled discharge in the sanitary sewerage system


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Sewerage System

4 Sewerage System

Sewerage systems (domestic wastewater treatment systems) or material alterations to sewerage

systems are required to be developed in accordance with design criteria. The design criteria set

minimum standards necessary for domestic wastewater treatment systems to function properly

and meet requirements for effluent quality. The criteria also contain certain safety standards.

The technical standards for sewerage system include the prescribed directions, requirements,

explanations, terms and provisions pertaining to the various features of the work to be done, or

manner and method of performance.

4.1 Location of Disposal Works

Following criteria to be followed for the location selection of the disposal works:

The waste water disposal station should be located at a place from where sullage water can be

safely economically and hygienically disposed of into a permanent and final disposal preferably

through some receiving natural water body.

The sewers will be generally designed as partially combined system allowing surcharging of the

system for some time depending upon the financial capability of the sponsoring agency.

Bypass arrangements at disposal station must be provided wherever possible in order to

meet emergencies and to avoid un-necessary pumping. For storm water disposal

additional storm well pump should be provided.

4.2 Design Period

4.2.1 Master Plan

Master plan with design horizon of 20 years should be prepared for the sewerage system but

implementation should take place in phases, according to the priority of work/area.

4.2.2 Land Acquisition

Land acquisition for STP, Pumping Stations, sewers etc. Since the land availability might be

difficult at the appropriate location at reasonable cost. It is proposed that the land shall be

acquired for at least 30 years. Especially for PPP mode. Sufficient area for the disposal station

should be acquired to accommodate future expansion for the next at least 40 years

4.2.3 Civil Works Including Sewers

The design period for civil works and sewers should be 25 years. There are a number of

considerations for selecting design period of sewers and allied civil work, which includes

expansion trends, economies of scale and financial position of the sponsoring / client

institutions. It has however been observed that sewers laid in various cities of the province for

the last more than 30 years are still functioning well. In view of the present economic condition

of the country it is advisable to use 25 years as design period for sewers and allied civil works.


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Sewerage System

4.2.4 Pumping Mains

Pumping mains shall be designed with a lifespan of at least 30 years. However, it is not

possible for pumping mains to work for 30 years without preventive and operational

maintenance. Repair or replacement of the pumping sets might be necessary after 10 years of

operation. The machinery needs continuous upkeep and maintenance, if properly maintained, it can last

for 20 years. For replacement purposes 15 years period is recommended.

4.2.5 Pumping Station Civil Works

Replacement of pumping station civil work is difficult and costly, therefore it is recommended to set

lifespan of pumping station for at least 30 years. However, it is not possible for pumping stations to

work for 15 years without preventive and operational maintenance. Repair or replacement of the

pumping sets might be necessary after 10 years of operation.

4.3 Design Flows

Wastewater flow quantities are necessarily lower than the quantity supplies/used because water

is lost through leakage/evaporation, garden watering, house cleaning etc. To determine the

expected amount of wastewater, it is important to keep records of pumping for each day and

fluctuations during the day. Reliance on estimates of water usage can lead to erroneous design

flows. Information should be obtained from the area under consideration. The design flow is

based on this returned quantity multiplied by a peaking factor which is inversely proportional

to the population size. All sewers will be designed on running full conditions with Manning’s

formula.

4.3.1 Unit Flow Factor

Unit flow factors are design parameter that are used to estimate design flows of sewerage

systems and sewerage treatment facilities. The unit flow factor is the average sewage flow

(average dry weather flow ADWF) contributed by the one unit of sewerage (person or

employee) per day.

Table 4-1: Unit flow factors for various sources

Waste water Source Water Requirements (lpcd) Sewerage flow(inclusive of 5%

infiltration ) lpcd

Residential 160(42 gpcd) 135

Commercial 47 40

Government institutions 47 40

Educational 47 40

The design flow is determined by summing the products of the number of the contributing

units of each source with appropriate unit flow factors. The unit flow factors for various

sources like residential, commercial, governmental, educational and religious can be adopted as

given in Table 4-1.

For the current scenario, sewage flow is to be adopted as 80% of the water consumption. Water

consumption has been taken as 35 gcpd/132 lpcd, so the sewage flow become 28 gpcd (i.e 80

% of water consumption).


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Sewerage System

4.3.2 In-Filtration

Following criteria shall be used for the computation of infiltration rates:

Table 4-2: Infiltration Rate

Sewer type Infiltration Rate

Sewerage above Sub-soil water level 350gpd/inch dia/mile

Sewer below Sub-soil water level 700gpd/inch dia/mile

4.3.3 Peak Factor

Peaking flows are the cumulative results of combinations of factors such as diurnal and

seasonal flow variations of flow components and characteristics responses of inflow and base

flows to the storm events. Peak flows can be determined by multiplying the average dry

weather flow (DWF) by the peaking factor (PF).

The maximum design flow is determined using Average Daily Flow (ADF) and the Harmon

Peaking Factor (HPF):

M = 1+ 14/ 4+P0.05 (4.1) Where, M = the Harmon Peaking Factor

p = population (in thousands)

The maximum design flow shall be the average daily flow times the peaking factor M.

The peak domestic sewage flow is calculated as:

Q(d) = Pq M/ 86.4 +lA (4.2)

Where:

Q (d) = Peak domestic sewage flow (including extraneous flow) in litres per second.

P = Design Population in thousands

q = Average daily per capita domestic flow in litres/capita/day

M = Peaking Factor (as derived from the Harmon Formula)

ℓ = Unit of peak extraneous flow in litres/hectare/second

A = Area in hectares

Population based peaking factors are to be used for hydraulic modelling purposes in the current

project. Population based peaking factors decrease with increasing populations. For cumulative

sewerage flow, the following criteria based on the population, have been used for the current

project.

Table 4-3: Peaking factor wrt Population

Population in thousand Peak Factor


Page 24 of 55

Sewerage System

Up to 5 4.50

5-10 4.00

10-25 3.50

25-50 3.00

50-100 2.50

More than 100 2.00

It is ratio of peak demand or peak flow over the maximum demand or flow.

4.3.4 Maximum Dry Weather Flow

Multiply the average daily flow by the peak factor to calculate the maximum dry weather flow.

4.3.5 Industrial Wastewater Allowance

Allowance should to be provided for industrial waste as per actual assessment of the treated

industrial waste according to the Environmental Quality Standards (NEQS).

4.3.6 Storm water Allowance

Proper arrangements for connecting storm water drainage appurtenances and sewerage system are to be adequately provided. The standard allowance criteria to be adopted is given

in Table 4-4.

4.4 Shape of Sewer

The shape of the sewers varies from circular, elliptical, egg shaped, semi elliptical to mouth

shaped the application of the respective kind will depend on site conditions and project

requirements.

Table 4-4: Storm water Allowance

Areas Storm water Allowance

For Rural area Nill

For Urban Areas Take 50% of peak flow as storm water

allowance in case of the Northern Zone;

and

Take 33% of peak flow as storm water

allowance in the Southern Zone.

Circular sewers are adopted when the flow of the sewers is nearly uniform, as these are

stronger, cheaper and structurally more stable than others. Oval or egg shaped sewers are

adopted best for situations where there is an intermittent flow of sewerage- that is, when the

flow varies considerably at different times. The reason for this is, at time when there is , but a

small quantity of sewage passing, the flow occupies the narrow bottom of the egg-shaped

sewer at a greater depth than it would be in a circular sewer of the same area of section. This

increase depth of the sewage causes it to flow with greater velocity, and thus renders the sewer

high hydraulic efficiency. However, they have become obsolete due to problems in laying,

instability at bottom and high precision required during laying.


Page 25 of 55

Sewerage System

Horizontal elliptical pipe is used with equivalent circular sizes with tongue and groove cement

mortar or mastic compound joint. The horizontal elliptical pipe is installed with the major axis

horizontal and is used for minimum cover situations or other conditions where vertical

clearance problems are encountered. It offers the hydraulic advantage of greater capacity for

the same depth of flow than other shapes of equivalent sectional area. Load under similar cover

conditions are similar to that of circular pipe with the same pan. Thus they are mostly used

under conditions of insufficient covers for laying of pipes. In ordre to ensure smooth flow for

carrying peak discharge by a hydraulically efficient system and leass prone to blockage, it is

proposed to have a circular pipes for sewerage collection netrwork

4.5 Velocity at Design Flow

It is proposed that minimum gradient to be adopted are such that to maintain a self-cleansing

velocity of 10 ft/sec at design peak flow in new sanitary sewer under the ultimate scenario

subject to minimum velocity of 2 ft/sec for peak flows at the current scenario. Hence, while

designing the sewers, it is proposed to maintain a desirable velocity under flowing full

condition is to be adopted as 2.5 ft. /sec. The maximum gradient to be adopted is such that the

maximum velocity should not exceed 2 ft. /sec when flowing half or full bore in order to

prevent scouring of sewers by erosive actions of suspended matter.

In case of construction of manholes for laterals, braches and sometimes even on the

intermediate sections, minimum velocity for the design flow is likely to be less that the self-

cleaning velocity. But manholes and sewers will be flushed out during peak flow period

carrying forward silt, which may get deposited during minimum flow period, especially during

night hours. Adopting lower values of velocities through lesser gradients will be helpful in

avoiding deep excavations. However, at certain sections, where undercrossing of deeper sub

drains and main drains as physical constraints, smaller sections of the sewer may be sloped at a

steeper gradient to minimize the number and height of the drops required invert levels. While

developing sewers, this point shall be given due consideration prior to the design of the sewers.

In case, where the above velocity criteria are not met, prescribes slope for different flows shall

be adopted.

Table 4-5: Velocity and design flows

Design Conditions Velocity

Desirable minimum 2.00 feet/second

In difficult situations 2.50 feet/second

Maximum in hilly areas 7 feet/second

4.6 Spacing of the Manholes

On sewers, which are to be cleaned manually, but cannot be entered for cleaning or inspection,

the optimum distance between the manholes may be 100-150 feet (for smaller dia. Sewers). In

Case of current scenario, a manhole spacing of 100 feet might be adopted for arterial sewers

which will be finalized in the final engineering design. Foe the sewers, which are to be cleaned

with mechanical devices, the spacing of the manholes will depend upon the type of the

equipment to be used for cleaning sewers. For diameter, less than 36 inches, spacing of

manholes adopted is 100- 300 ft. (30 -90 m) subjected to site accessibility and availability. The


Page 26 of 55

Sewerage System

spacing of the manholes above 300 ft to 500 ft may be allowed for sewers of diameters

45inches or above and which may further be increased upto 1000 ft for sewer of 72 inches

diameter subject to site accessibility.

A) Spacing of manholes in straight lines shall be as under:

Table 4-6: Spacing of manholes in straight line

Sewer Size Spacing Spacing

9 inches 50 feet

12 inches 100 feet

15 inches 150 feet

18 inches 200 feet

21-24 250 feet

27-42 300 feet

48-60 400 feet

Above 60 inches 500 feet

B) Where-ever drop is more than 3 ft, drop manhole should be constructed.

C) Sewer above Sub-soil water level shall be constructed as per following design criteria

Table 4-7:Design criteria for sewer above sub soil level

Size of Sewer (Inches) Depth (Feet) Manhole (Feet) Remarks

9–12 Up to 4 2’ x 2’ Masonry 1:3

9-21 4–7 4’ dia Cement mortar

24–30 8–20 5’ dia Up to 8 ft depth 9 inches

Masonry

33–42 8–20 6½’ dia From 8 ft to 15 ft depth

45–54 8–20 7½’ dia 13-½ to 9 inches

60 8–20 8’ dia Masonry

66 8–20 8’ dia From 15 ft to 20 ft,

72 8–20 9’ dia Depth, 18 to 13-½ inches

D) For manholes under sub soil water, core-wall and floor will be designed as per actual

depth of water encountered.

E) For depth more than 10 feet, RCC slab will be put at 7 feet from invert and then 4 feet

dia masonry will be constructed up to surface.


Page 27 of 55

Sewerage System

4.7 Minimum Size of Sewer

Although there are some agencies that allow new 6-inch sewers , a minimum sanitary sewer

pipe size of 9-inches is generally accepted as the industry standard and is the current proposed

Lahore WASA design criteria.Therefore, except for service lines (laterals), the minimum

acceptable gravity pipe diameter for all newly constructed pipelines shall be 9-inches.

4.8 Earth Cover

A 3.0 ft earth cover should be provided above crown of the sewer. However, in case of sewer laid under

road crossings, sand will be filled to provide cover instead of earth.

4.9 MANNING FACTOR OR COEFFICIENT OF ROUGHNESS

Manning's 'n' roughness coefficient is the friction factor utilized in the Manning's Equation for

gravity flow to describe the roughness of a particular pipe material or condition. There has

been much debate over the idea that the ‘n’ value of a pipe can change over time as the pipe

ages and a lime layer grows on the pipe wall. One side of the debate claims that the roughness

or ‘n’ value of this lime layer is the same whether the lime layer grows on a concrete wall, a

vitrified clay wall, or a plastic wall. The other side of this debate proposes that a different ‘n’

value should be used for different pipe materials, generally ranging from 0.008 for plastic pipe

to 0.016 for unlined concrete pipe with vitrified clay pipe between the two values. A Manning's

‘n’ design value of 0.013, the most widely accepted value in the industry, provides some

degree of conservatism if, in fact, there is a significant benefit to the smoother plastic pipe and

PVC-lined (T-lock) pipe walls.

Table 4-8: Manning Coefficient of different materials

Sewer Material Manning Coefficient

RCC

New Lines 0.013

Old lines 0.015

UPVC 0.009

PE 0.008-0.011

HDPE 0.012 - 0.024

4.10 Bedding of Sewers

A) Above sub-soil water level

For Sewers 9"-12" - Sand

For Sewers 15" dia - Crush stone and above ¼”-1” size

B) Below sub-soil water

Decision to be taken as per site conditions, PCC or RCC.

Outfall pumping stations are proposed to be designed to cater to the maximum

peak load plus a 33% stand by (33% of peak load). Capacity


Page 28 of 55

Sewerage System

Present average flow (if it is less than ½ of ultimate average) or ½ ultimate

average.

Present and ultimate peak flows. (Coarse screens with 2 inches mesh should be

installed on the screening chamber).

4.11 Class of Pipes

ASTM pipes class 11(C-76) as amended by PHED, for class-111 pipes, decision to be taken as per specific site conditions.

4.12 Pipe Reinforcement

As per BSS and ASTM specifications (as amended by PHED).

4.13 Slope of Sewer Line

Minimum gradient of sewers to attain velocities per section 4 above

4.14 Outfall Works

The capacity of pumps shall be such that combination for minimum average flow and

peak flow is possible.

Efficiency ≥70%

Motor P.F ≥ 0.89

Motor Efficiency≥ 85%

Motor should be installed with soft starter

Electrical Cable should be designed for 80% of load

Transformer should be design for 80% load

Pump minimum efficiency should be greater than 60%

Motor efficiency should be greater than 85%

Motor power factor should be greater than 0.89

There should be power Improvement capacitor to achieve 0.9-0.95

Rating of the motor should not be greater than pump rating by 25%

Standby arrangement should be made for 33 % of the peak flow.

For the design of collecting tanks (Wet Well) following detention times will be used.

Table 4-9: Detention time

Sewer Material Detention time (Minutes )

Population up to 25,000 10

25,000---50,000 5


Page 29 of 55

Sewerage System

50,000---100,000 4

100,000—200,000 3

Above 200,000 2

4.15 Sewage Pump Selection

The selection of sewage pumping units should be made keeping in the following

aspects/recommendations:-

Use of horizontal pumps in the depressed chamber should be avoided as far as

possible. Theses may be used for smaller discharges because the cordon shaft

pumps of smaller discharges may not be available.

Cordon shaft pumps may be used for greater discharge where the quality of

sewage is not good and the system is connected to surface drains as well.

All such pumps will be discharged for passing solids of 2-3 inches size. These

will be powered by AC electric connections.

4.16 Design Flow of Drainage

The capacity of storm water drainage is calculated according to Rational Method, which relates

the flow to the rainfall intensity, the tributary area, and a coefficient, which represents the

combined effects of ponding, percolation, and evaporation. This discharge is calculated as

follows:

Q = CIA

Where:

Q = Discharge in cusecs

C = Run Off Co-efficient

I = Rain fall intensity

A) Lawn, sandy soil

Table 4-10: Run off coefficient for sandy soil

Slope Run off coefficient

2% slope 0.05-0.10

2-7% slope 0.10-0.15

>7% slope 0.15-0.20

B) Lawn, Heavy soil


Page 30 of 55

Sewerage System

Table 4-11: Run off coefficient for heavy soil

Slope Run off coefficient

2% slope 0.13-0.17

2-7% slope 0.18-0.22

>7% slope 0.25-0.35

C) Urban and Suburban Area

Table 4-12: Run off coefficient for urban dwellings

Area Run off coefficient

Urban 0.50-0.70

Single Family area

Multi-units, detached 0.30-0.50

Multi-units, attached 0.40-0.60

Apartment Area 0.25-0.40

Sub-Urban 0.60-0.75

D) Industrial Area

Industry Type Run off coefficient

Light 0.50-0.70

Heavy 0.50-0.80

Parks, cemeteries 0.60-0.90

Playgrounds 0.10-0.25

Railroad yards 0.20-0.35

Unimproved areas 0.20-0.40

Heavy 0.50-0.80

4.17 Pumping or Disposal Station

Disposal station is normally provided under special circumstances in wastewater collection

networks. These may be (1) when a natural barrier like river, canal etc. comes in the sewer

route or (2) the depth of excavation increases to an extent that it becomes


Page 31 of 55

Sewerage System

uneconomical/impractical to provide the sewer at such a depth and thus the hydraulic grade

line is lifted by providing a Disposal Station.

The volume of the sump is computed based on the pumping capacity and the number of

starts/stops per hour. The maximum starts/stops occur when the inflow is half the outflow. The

volume is calculated using the following formula.

V = Q × T

Where;

V = volume of the sewerage to be lifted

Q = Pumping in cubic meter per hour

T = time between starts/stop in hours

The criteria to be adopted for the design of the disposal station is as follows:

A minimum of two submersible-type pumps or centrifugal pumps per station should be

furnished – one duty, one back-up. Peak design capacity should be available with the

largest pump out of service

The pump should be capable of developing the required total head at the rated capacity.

Pump should be suitable for single as well as parallel efficient operation at any point in

between the minimum and maximum system resistance.

The total head capacity curve of the pump should be continuously rising towards the

shut- off. The pump should deliver at least 125% of its rated capacity at 75% of the

specified total head.

Pump station inventory should consider the need to convey low flows effectively as

well as phasing considerations.

Either constant speed or variable frequency drive may be used for pump station drivers.

Electrical service infrastructure should be sized for ultimate requirements.

Emergency power should be provided on site.

Upstream sewer mains may not be considered part of available wet well storage

volume.


Page 32 of 55

Wastewater Treatment

5 Wastewater Treatment

As for as wastewater treatment is concerned, there is no existing treatment plant in Punjab

except a treatment plant at Faisalabad and an oxidation pond at Bahawalnagar. All other

wastewater treatment plants are in Karachi (Trickling Filters), Peshawar (Stabilization Ponds)

and Islamabad (Activated sludge). Almost all of them are abandoned or working at very low

capacity with very low efficiency.

However, there are no standards or any design criteria for the design of water treatment plants.

Most of them were constructed as either pilot projects or by the foreign consultants as per their

own design criteria. This is the first time that some kind of design criteria is being given for the

design of different treatment plants for wastewater.

5.1 Wastewater Characteristics

The characteristics of domestic wastewater (influent) and the corresponding desirable effluent

characteristics have been shown in Table The effluent characteristics have been considered

keeping in view the National Environmental Quality Standards (NEQS).

Table 5-1: Characteristics of sewerage water

Characteristics

Influent

Concentration

Effluent

Concentration

(NEQS)

Effluent

Concentration

(Horticulture

Purpose)

Biochemical Oxygen

Demand (BOD5)

Up to 250 mg/I 80 mg/l < 30 mg/l

Chemical Oxygen Demand

(COD) Up to 350 mg/I 150 mg/l < 80 mg/l

Total Suspended Solids

(TSS) Up to 300 mg/I 200 mg/l

< 80 mg/l

Design Temperature Ambient Ambient Ambient

Fats, Oil and Grease Up to 20 mg/I < 10 mg/l < 5 mg/l

5.2 Design Criteria

The criteria to be considered for the selection and the design of the wastewater treatment plant

is as follows:

5.2.1 Primary Screens

Upon reaching the sewage treatment plant, sewage flows through the primary screening facility

which is the first stage of treatment. The screens shall be provided upstream of all inlet pump

stations and shall be designed to protect downstream processes and equipment. The purposes of

primary screens are:


Page 33 of 55


To protect equipment from rags, wood and other debris

To reduce interference with in-plant flow and performance.

Design parameters for primary screen are summarized in Table below

Table 5-2: Design Criteria of primary Screens

Description Unit Design Criteria

Manually Raked Mechanically Raked

Maximum clear spacing mm 25 25

Slope to the vertical 300-450 150-450

Maximum approach velocity at the

feed channel

m/s 1.0 1.0

maximum flow through velocity at

the screen face

m/s 1.0 1.0

Minimum freeboard mm 150 150

Screening skip storage capacity day 7 7

Minimum channel width mm 500 500

Minimum channel depth mm 500 500

RC Staircase with riser detail 1 unit Anti-skid and non-

corrosive

Anti-skid and non-

corrosive

5.2.2 Inlet Chambers

Provision for inlet chamber before the primary screen channel is necessary for proper operation

and maintenance of the plant. A penstock shall be installed upstream to isolate the pump

station in the event of flooding in relation to the bypass and emergency overflow.

Table 5-3: Design Criteria of Inlet chamber

Description Unit Design Parameters

PE ≤50,000 PE > 50,000


Page 34 of 55


Number of pumps (all identical and

work sequentially)

4 (2 sets)

1 duty,

1 assist, per set

(100% standby)

6 (3 sets)

1 duty,

1 assist, per set

(50% standby)

Pumps design flow Each at 0.5 Q peak Each at .025 Q peak

Maximum retention time at Q ave min 30 30

Min pass through openings mm 75 75

Minimum suction and discharge

openings

mm 100 100

Pumping cycle (average flow

conditions)

Start/

hour

6 min

15 max

6 - 15

Lifting device* Mechanical and block Mechanical

Note: Motorized hoists shall be provided when the lifting weight exceeds 100 kg.

Table 5-4: Design Criteria of secondary screens


Manually Raked Mechanically Raked#

Maximum clear spacing mm 12 12

Slope to the vertical m/s 30 -45 15 - 45

Maximum approach velocity at the feed

channel

m/s 1.0 1.0

Maximum flow through velocity at the

screen face

m/s 1.0 1.0

Minimum freeboard mm 150 150

Screenings skip storage capacity day 7 7

Minimum channel width mm 500 500

Minimum channel depth

mm 500 500

RC Staircase with riser detail 1 unit Anti-skid and non-

corrosive

Anti-skid and non-

corrosive


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5.2.3 Grit and Grease Removal

This unit is important to minimize problems associated with grit and grease. Grit creates

problems to pumps and also sludge digestion and dewatering facilities. Grease creates

problems at the clarifier and is carried over in the final effluent.

In grit removal system, grit or discrete particles that have subsiding velocities or specific

gravities substantially greater than those of organic putrescible solids, e.g. eggshells, sands,

gravel are removed by gravitate settlement or centrifugal separation. Same principle apply to

oil and grease removal system, where free oil and grease globules lighter than water rise

through the liquid and skimmed from the top surface. The design parameters are summarized in

Table 5-5.

Table 5-5: Design Parameters for Grease Chambers


→50000 PE

Grease removal - Mechanical

Chamber type Aerated type

Minimum detention

time (Q peak)

min 3

Grit and grease storage period before off-site

disposal

day 7

Table 5-6: Design Criteria for Grit Chambers


>50000 PE

Grease removal - Mechanical

Chamber type - Aerated

Minimum detention

time (Q peak)

minute 3

Maximum gravity flow through

velocity

m/s 0.20

Maximum centrifugal flow through

velocity

m/s <1.0

Head loss (at partial flume) - -

Aeration requirement l/s/meter length of

tank

10.0

Chamber dimension:

Depth Width

Length Width

-

Manufacturer’s Specification


Page 36 of 55



>50000 PE

Estimated grit quantity m3/103 m3 of

sewage

0.03

Washing and dewatering of grit - Yes

5.2.4 Balancing Tanks

Balancing tanks are mandatory for all treatment processes that are not designed at peak flow.

The tanks are effective means of equalizing sewage flow. For extended aeration plants that are

designed with a retention time of more than 18 hours and clarifiers designed at peak flow, the

use of balancing tanks is not required. The purposes of balancing tanks are to:

Prevent flow variations entering secondary treatment processes.

Reduce hydraulic loading into secondary treatment processes.

Reduce potential overflows that may cause health hazard and pollution.

The design requirements for balancing tanks are:

All balancing tanks must be completely aerated and mixed.

Flow control shall by a non-mechanical constant flow device, such as an orifice, in

order to avoid double pumping. Allowance must be made for an emergency overflow.

Bypass and drain down facilities as well as suitable access for cleaning shall be

provided.

Table 5-7 Design Parameters for Balancing Tanks


Volume of tanks m3 1.5 hr detention at Q peak

Mixing power requirements W/m3 of sewage 5 at TWL


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Aeration m3 air/hour/

m3 sewage

1 m3 of air supply for every m3 of

sewage stored per hour at TWL

Overflow bypass to down stream

unit requirement

Yes

5.2.5 Biological Treatment Stage

Biological treatment is the heart of the sewage treatment process. It is the processes where the

dissolved and non- settle-able organic material remaining in the sewage are removed by living

organisms.

For reasons of long term whole life economics, ease of operation and maintenance, consistent

effluent standards and standardization, the following types of biological treatment processes

are recommended.

Suspended Growth System

Conventional Activated Sludge (CAS) System

Extended Aeration (EA)/Oxidation Ditch (OD) System

Sequencing Batch Reactor (SBR)/Intermittent Decant Extended Aeration (IDEA)

A) Conventional Activated Sludge (CAS) System

The design parameters to be considered while designing sewage wastewater treatment plant

based on conventional activated sludge system are as follows:

Table 5-8: Design Criteria of Conventional Activated Sludge (CAS) System


Organic loading

(depending on filter type)

Low rate

Intermediate rate

High rate

Kg BOD5/day/m3

0.08 – 0.15

0.15 – 0.5

0.5 – 2.0

Recirculation of flow to head of

plant Q recycle Q inflow

(to maintain wetting rate and

improve flow)

> 1.0

Acceptable media HDPE, PVC, stone, slag, coke,

etc. (random or standard

arrangement)

Hydraulic loading

Low rate

Intermediate rate

High rate

m3/day/m2

1 - 4

4 - 10

10 - 40

Sludge Yields

Low-rate filters

Intermediate filters

kg sludge 1 kg

BOD5 influent

0.5

0.6 - 0.8


Page 38 of 55



High-rate filters 1 .O

Minimum depth of media m 1.5

A) Design Parameters for Sequencing Batch Reactors (SBR) System

Sequencing Batch Reactors system is suspended activated sludge system. In this system,

sewage flows into one or more reactors where biological oxidation and clarification of sewage

take place within the same reactors sequentially on cyclical mode. There are five (5) basic

sequences in a cycle, namely:

Table 5-9: Design Parameters for Sequencing Batch Reactors (SBR) System


Primary Sedimentation System Must be provided

Minimum number of aeration

tanks

2

F/M ratio 0.25 – 0.50

Hydraulic retention time (HRT) hrs 6 J6 (for system where

only ammonia removal is

require)

Oxygen requirement (for BOD

and ammonia nitrogen removal)

KgO/kg substrate 2.0

Mixed liquor suspended solids

(MLSS)

mg/J. 1500-3000

Typical: 2500

Dissolved oxygen (DO) level in

tank

mg/.e 1.0

Aeration device rating Continuous, 24 hrs

Sludge yield Kg sludge produced/ kg

BOD consumed

0.8 – 1.0

Sludge age day 5 – 10

Waste activated sludge, QWAS m3/d Refer to equation below †

Return activated sludge flow,

QRAS

m3/d MLSS

𝐶 ∪ 𝑀𝐿𝑆𝑆𝑥 𝑄𝑎𝑣𝑔

Cu is underflow concentration

QRAS/ QINFLOW 0.75 – 1.0

Mixed liquor suspended solids

recirculation for de-nitrification

purpose

4 – 6 of Qavg

RAS pump rating hrs/day 24

Organic loading kg BOD kg MLSS 0.25 – 0.5


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Volumetric loading kg BOD /m3.d 0.3 – 0.6

Minimum mixing requirement W/ m3 20

Table 5-10: Specification of SBR reactor


Water depth m 3 – 5

Length: Width m 3:1

Max width of joined tank m < 30

Sludge Age = total solids in aeration tank

Excess sludge wasting/day+solid in effluent

𝑾𝑨𝑺 = 𝑽𝑻 𝒙 𝑴𝑳𝑺𝑺

∅ 𝒔𝒍𝒖𝒅𝒈𝒆− [𝑸𝒂𝒗𝒈 𝒙 𝑺𝑺 𝐞𝐟𝐟]

Where:

VT = Volume of reactor (m3)

MLSS = Mixed liquor suspended solids (kg/m3)

ᶿsludge = sludge age (days)

Qavg = average flow (m3/day)

SSeff = effluent suspended solids (kg/m3)

CU = underflow concentration (kg/m3)

B) Design Parameters for Extended Aeration System (EA)

The Extended Aeration process is similar to the Conventional Activated sludge process except

that it operates in the endogenous respiration phase of the growth curve, which requires a low

organic loading and long aeration time. The system produces high MLSS concentration, high

RAS pumping rate and low sludge wastage.

The advantage of having long hydraulic retention times is that it allows the plant to operate

effectively over widely varying flow and waste loadings. Secondary clarifiers must be designed

to the variations in hydraulic loadings and high MLSS concentrations associated with this

process.

EA plants shall be designed as either plug flow or completely mixed. Anoxic zone at the head

of the reactor must be provided for de-nitrification. The .anoxic zone must be mixed without

inducing dissolved oxygen

For Oxidation Ditches, the minimum velocity within the channel shall be sufficient to keep the

activated sludge in suspension. The minimum velocity within the channel shall not be less than

0.3 mis.


Page 40 of 55


Table 5-11: Design Parameters for Extended Aeration System (Ea)


Minimum number of aeration tanks 2

F/M ratio 0.05 – 0.1

Hydraulic retention time (HRT) hrs 18 - 24

Oxygen requirement (for BOD and

ammonia nitrogen removal)

KgO/kg

substrate

2.0

Mixed liquor suspended solids (MLSS) mg/ ℓ. 2500-5000

Typical: 3000

Dissolved oxygen (DO) level in tank mg/ ℓ 2.0

Sludge yield Kg sludge

produced/ kg

BOD5

consumed

0.4 (at 24 hrs HRT)

0.6 (at 18 hrs HRT)

Sludge age day >20

Waste activated sludge, QWAS m3/d Refer to equation †

Return activated sludge flow, QRAS m3/d MLSS

𝐶 ∪ 𝑀𝐿𝑆𝑆𝑥 𝑄𝑎𝑣𝑔

Cu is underflow concentration

RAS pump rating hrs/day 24

Recirculation ratio, QRAS/ QINFLOW 0.5 – 1.0

MLSS recycle ratio 4 – 6 times of Qavg

Volumetric loading kg BOD5 /m3.d 0.1– 0.4

Minimum mixing requirement W/ m3 20

Tank dimension

Water depth m 3 – 5

Length: Width ratio 3:1

Max width of joined tank m <60

Table 5-12: Organic loading parameters for EA wastewater treatment system



Page 41 of 55


Organic loading

(depending on filter type)

Low rate

Intermediate rate

High rate

kg BOD5

/day/m3

0.08 – 0.15

0.15 – 0.50

0.50 – 2.00

Recirculation of flow to head of plant

Qrecycle

QInflow

(to maintain wetting rate and improve

flow)

>1.0

Acceptable media HDPE, PVC, Stone, Slag,

Coke, etc.

(random or standard

arrangement)

Hydraulic Loading

Low rate

Intermediate rate

High rate

m3/day/m2

1 – 4

4 – 10

10 – 40

Sludge Yield

Low rate filters

Intermediate filters

High rate filters

Kg sludge/ kg

BOD5 influent

0.5

0.6 – 0.8

1.0

Minimum depth of media m 1.5

Note: Sludge Age = total solids in aeration tank

Excess sludge wasting/day+solid in effluent

𝑾𝑨𝑺 = 𝑽𝑻 𝒙 𝑴𝑳𝑺𝑺

∅ 𝒔𝒍𝒖𝒅𝒈𝒆− [𝑸𝒂𝒗𝒈 𝒙 𝑺𝑺 𝐞𝐟𝐟]

Where:

VT = Volume of reactor (m3)

MLSS = Mixed liquor suspended solids (kg/m3)

ᶿsludge = sludge age (days)

Qavg = average flow (m3/day)

SSeff = effluent suspended solids (kg/m3)

CU = underflow concentration (kg/m3)

Designer shall ensure that with 50% of blockage at the face of screen, sufficient freeboard is

provided to prevent the approach channel from overflowing washing and dewatering of

screenings shall be provided.

5.3 Trickling Filter

The Trickling Filter is an established biological treatment process removing 65 to 85% BOD5

and suspended solids. The process consists of a bed of highly permeable medium. An

overhead rotating distributor applies sewage to the media. The now trickles over and flows

downward 10 the under drain system.The media provides a large surface area to develop

biological slime growth which is also known as zoogleal film. The film contains living


Page 42 of 55


organisms that break down organic material in the sewage. Many variations of the Trickling

Filters have been constructed.

5.3.1 Design Requirements for Trickling filters

Secondary screens (< 6 mm) and flow balancing tanks to equalize the flow must be provided

before trickling filters. Provisions shall be available for even distribution to achieve complete

wetting of the filter media.

5.3.2 Design Requirements for Sequencing Batch Reactor (SBR) System

Sequencing Batch Reactors system is suspended activated sludge system. In this system,

sewage flows into one or more reactors where biological oxidation and clarification of sewage

take place within the same reactors sequentially on cyclical mode.

Table 5-13: Design parameters for secondary clarifiers

Parameter Unit Continuous Fill and

Intermittently

Decent

Intermittently Fill and

Intermittently Decent

No. of Reactors

Unit Minimum 2 Minimum 2

Hydraulic Retention

time at Qavg (at

average water level)

hr 18 – 24 18 – 24

F/M Ratio D 0.05 – 0.08 0.05 – 0.30

Sludge Yield Kg sludge/

kg BOD5

loud

0.75 – 0.85 0.75 – 1.10

MLSS (End of

decant)

mg/l 3000 - 4500 3000 – 4500

Cycle Time Hr 4 - 8 4 – 8

DO (Reactor)

DO (Effluent)

mg/l

mg/l

0 – 6.5

2.0

0 – 6.5

2.0

Oxygen Requirement 𝑘𝑔 𝑂2

𝑘𝑔 𝑆𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒

𝐶𝑦𝑐𝑙𝑒 𝑡𝑖𝑚𝑒

𝑎𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑡𝑖𝑚𝑒 𝑥

20𝑘𝑔 𝑂2

𝑘𝑔 𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒

𝐶𝑦𝑐𝑙𝑒 𝑡𝑖𝑚𝑒

𝑎𝑒𝑟𝑎𝑡𝑖𝑜𝑛 𝑡𝑖𝑚𝑒 𝑥

20𝑘𝑔 𝑂2

𝑘𝑔 𝑠𝑢𝑏𝑠𝑡𝑟𝑎𝑡𝑒

Decant time hrs ≥1.0 ≥1.0

Decant volume m Max 0.5 Max 1.0

Decanting device

loading rate

m3/m/hr ≤20 for decant draw-

down from TWL

≤20 for decant draw-down

from TWL

Minimum number of

decanter

2 nos. independent

decanter per tank

2 nos. independent decanter

per tank

Max. decanter length m 4.0 4.0

WAS kg sludge/d 𝑊𝐴𝑆

= 𝑇𝑜𝑡𝑎𝑙 𝑆𝑜𝑙𝑖𝑑𝑠 𝑖𝑛 𝑆𝑦𝑠𝑡𝑒𝑚

𝑆𝑙𝑢𝑑𝑔𝑒 𝑎𝑔𝑒

𝑊𝐴𝑆

= 𝑇𝑜𝑡𝑎𝑙 𝑆𝑜𝑙𝑖𝑑𝑠 𝑖𝑛 𝑆𝑦𝑠𝑡𝑒𝑚

𝑆𝑙𝑢𝑑𝑔𝑒 𝑎𝑔𝑒


Page 43 of 55


Fill volume m3

For continuous fill, length to width ratio shall be based on 3 :

Decanting device loading rate shall be based on Vm/decant time during decanting

RAS maybe necessary where length to width ratio poses dilution affect into the inlet.

5.3.3 Design Parameters for the Secondary Clarifiers

Following design shall be adopted for the design of the secondary clarifiers.

Table 5-14: Design parameters for secondary clarifiers


PE ≤ 5,000 PE > 5,000

Minimum number of tanks 2* 2

Tank configuration Square Circular Rectangular

Square Circular Rectangular

Minimum side water depth m 3** 3

Minimum hydraulic retention time (HRT) at Qpeak

hrs 2 2

Surface overflow rate at Qpeak m3/d/m2 ≤ 30 ≤ 30

Solids loading rate at Qpeak kg/d/ m2 <150 <150

Solids loading rate at Qavg kg/d/m2 <50 <50

Weir loading rate at Qpeak m3/d/m <180 <180

Return activated sludge (RAS) pumping rate

Continuous Continuous

Waste activated sludge (WAS) pumping rate

Continuous or batch

Continuous or batch

Sizing of Rectangular Tanks

Length: Width 3:1 or greater

Maximum side water depth m 3.0


Page 44 of 55


5.3.3.1 Intermittent Disinfection Following guidelines shall be used for the disinfection of the sewage water after the treatment.

Table 5-15: Design guide for intermittent disinfection

Type Design Criteria

Contact Tank

Contract Period 15 minutes at Qpeak

Maximum depth 3 m

Depth: width 2 : 1

Min no. of passes 4

Length: Width at each pass 6 : 1

Wetted Depth: Width < 2:1

Width: Depth 1:1 to 2.5:1

Sizing of Circular Tanks

Water depth, minimum m 3.0**

Floor slope wall 1:12


Page 45 of 55

Miscellaneous

6 Miscellaneous

6.1 Preventive maintenance

Preventive maintenance of water distribution system pipelines assures the twin objectives of

preserving the hygienic quality of water in the distribution mains and providing condition for

adequate flow through the pipe lines. Some of the main functions in the management of

preventive aspects in the maintenance of mains are assessment, detection and prevention of

wastages of water from pipe lines, maintaining the capacity of pipe line and cleaning of pipe

line.

6.1.1 Leakage DETECTION:

Leakage detection survey is confined only to the areas with heavy leakages as arrived at by the

waste assessment survey. The survey consists of:

Finding leaks in the pipes by visual determination of surface; and

Traversing the sub – zone in the night by sounding rod, or electronic leak locator for

pinpointing of leaks in pipes.

6.1.2 Cleaning of pipes

The necessity for systematic and periodic cleaning of pipelines is borne out by the fact that the

carrying capacity of the pipes gets reduced due to growth of slimes, incrustation deposits.

Flushing and swabbing of pipes, which are simple and inexpensive can go a long way in

maintaining the capacity.

The old cast iron and steel pipes which are cleaned can be protected from further incrustations

or corrosion by cement lining. Insertion of a plastic pipes has also practiced with success.

6.1.3 Protection against pollution near sewers and drains

A water main should be laid such that there is at least 3 m separation, horizontally from

existing or proposed drain or sewer line. If local conditions prevent this lateral separation of

water main may be laid closer to a storm or sanitary sewer, provided that the main is laid by

separate trench or on an undisturbed earth shelf located on one side of the sewer at such

elevation that the bottom of the water main is at least 0.5m above the top of the sewer.

In situations where water mains have to cross house sewer; storm drain, or sanitary sewer then

it should be laid at such an elevation that the bottom of the water main is 0.50 m above the top

of the drain or sewer with the joints as remote from the sewer as possible. This vertical

separation should be maintained for a distance of 3 m on both sides measured normal to the

sewer or drain it crosses.

Where conditions prevent the minimum vertical separation set forth above, or when it is

necessary for the water main to pass under a sewer or drain, the water main should be laid with

flanged cast iron pipe, with rubber gasket joints for a length on either side of the crossing to

satisfy the lateral separation of 3 m. A vertical separation of 0.50m between the bottom of the


Page 46 of 55

Miscellaneous

water main and the top of the sewer should be maintained with adequate support for the larger

sized sewer lines, to prevent them from settling on or breaking the water main. In making such

crossings, it is preferable to have the sewer also of casting flanged pipe with rubber gasket

joints and both the water and sewer mains pressure tested to assure water tightness before back

fillings.

Where a water main has already been laid and where a new sewer is to be laid, the above

aspects may also be taken into consideration and the water main may be realigned, when it is

not possible to lay the sewer consistent with the above recommendations.

Since water expands nearly about 10% in volume with an irresistible pressure, freezing solid

conditions should not be allowed in any pipe system to avoid interruption of service and

prevent damage to the pipes.

Documents

Design Criteria for Water and Sanitation Agencies & PHED