ebook water 123

Chapter 3 : Water Treatment

Objectives 1. Select the most effective
chemical.

2. Select the optimum dosage.

JAR TEST 3. Determine the value of a flocculant aid
Procedure and the proper dose.

1. Place an appropriate volume of water sample each of the jars (250 to 1000 mL samples may
1 be used, depending upon the size of the equipment being used). Start mixers and set for 100

r/min.

2 1. Add previously selected amounts of the chemical being evaluated. (Initial tests may use wide variations
in chemical volumes to determine the approximate range. This is then narrowed in subsequent tests.)

3 Continue mixing for 1 min.

51

Chapter 3 : Water Treatment

Problem

• Calculate the doses of alum and chlorine being streamed for each 500,000 liters of water in mg/L units based on the data obtained from a
water treatment plant.

• Calculate the quantity of alum and chlorine (in kg) needed in a day if the treatment plant operates in 24 hours. (1L = 4.5kg).

• A water treatment plant has 6 units of sedimentation tank to treat 200 million liters water per day. Calculate the dosage of alum (mg/L)
needed if the plant required 400 tones alum per year.

Raw water flow rate 95,000 L/hr
Alum flow rate 35 L/hr
Chlorine flow rate 20 L/hr
Strength of alum 5%
Strength of chlorine 0.5%

52

Chapter 3 : Water Treatment

The expansion of plant processes is paid Factors influence Location Avaibility of land cost of the land and taxes that
attention to. Space is made available for Selection of Factor will incurred on land and plant often dictate
adding capacity and for the addition of where a plant will be located once the supply is
processes. Treatment Plant Environmental identified. In many cases, a treatment facility can
Location Factor be at the point of supply, and where possible raw
Planning and water can gravitate to the plant from the reservoir
Environmental or the river.
Obstruction Factors
The examples of the impact from the treatment plant are:
Plant Design i) Effect of noise when operating the plant such as pump, generator or chemical tanks.
Factor ii) Dust impact during the construction
iii) Dangers of chlorine leakage during shipment
The process and instrumentation diagram and the detailed design iv) The smells of chemicals and sludge
criteria are developed by establishing v) Effect of sludge and wastewater from the plant to the river nearby
(1) the major process units and their size and place in the scheme of
53
design,
(2) the kind, amount and application points of chemicals reagent
and
(3) the monitoring and control of the processes and chemicals.

The three principal application for flow Chapter 3 : Water Treatment
measurement are establishing the flow rate
of the process and determining the liquid Power outages will undoubtedly occur for a
chemical and gas flow rates of various number of reasons, including damage to the
subordinates processes. power generation system or power supply
system as the result of accidents such as
Flow Standby earthquake, or even sabotage.
Power
Measurement Supply

Principle Design of
Plant Component

Level Piping
Measurement System

Level measurement is an essential item in plant Valve (1) raw water and finished waste
operation because the plant operator must be aware Selection distribution mains;
of the water level of all the process units, the levels of
chemical storage tank and silos, and the pressure of To be able to select an appropriate type of valve, all design engineers (2) plant yard piping that connects
water compressed air lines. must have a basic knowledge of the various types of commonly used the unit processes;
valves, the characteristic of the fluid that is to be regulated, and the
hydraulic characteristic of the piping system in which the valve is to be (3) plant utility, including the fire
installed. hydrant lines;

(4) chemical lines;
(5) sewer lines;
(6) miscellaneous pipings, such as

drainage and irrigation lines.

54

CHAPTER 4

WATER DISTRIBUTION
SYSTEM

55

Chapter 4 : Water Distribution System

Tank / pool Delivery pipe
pipes that carry treated water from
generally used to stabilize the treatment plants or from pump to the
supply on changing of the tank or from a tank to another tank.
demand.
Reticulation pipe
pipes that distribute treated
water to the supply areas.

Definition

Pipe connection Distribution pipe
- used for various pipes that distribute water to

Water meters reticulation pipes from the
complementary components services tank/pool, treatment
that are used to measure the
quantity of water has flowed Tape water / fire hydrant
taps to bring the water out of
through it. the supply system, especially for

fire fighting.

56

Dead End / Tree Chapter 4 : Water Distribution System
Grid Iron
Characteristics
Characteristics
This system is suitable for irregular developed towns or cities. In this system water flows in one From the mains water enters the branches at all Junctions in
either directions into submains of equal diameters. At any
direction only into submains and branches. The diameter of pipe decreases at every tree branch point in the line the pressure is balanced from two directions
because of interconnected network of pipes.
Advantages Disadvantages
Advantages
Circular / Ring Characteristics Distribution
Systems Disadvantages

Supply to the inner pipes is from the mains around the Radial Characteristics
boundary. It has the same advantages as the grid-Iron
system. Smaller diameter pipes are needed. The advantages This is a zoned system. Water is pumped to the
and disadvantages are same as that of grid-Iron system. distribution reservoirs and from the reservoirs it
flows by gravity to the tree system of pipes. The
Advantages pressure calculations are easy in this system.
Layout of roads need to be radial to eliminate
Disadvantages loss of head in bends. This is most economical
system also if combined pumping and gravity
flow is adopted.

57

Gravity System Methods Chapter 4 : Water Distribution System

When some ground sufficiently high above the city Pump System Dual System
area is available , this can be best utilized for
distribution system in maintaining pressure in water Constant pressure can be maintained in the This is also known as dual system. The pump is connected to the mains as
mains . system by direct pumping into mains. Rate of well as elevated reservoir. In the begining when demand is small the water
flow cannot be varied easily according to is stored in the elevated reservoir, but when demand increases the rate of
This method is also much suitable when the source demand unless number of pumps are pumping , the flow in the distribution system comes from the both the
of supply such as lake, river or impounding reservoir operated in addition to stand by ones. Supply pumping station as well as elevated reservoir.
is at sufficiently higher than city. can be effected during power failure and
breakdown of pumps. Hence diesel pumps As in this system water comes from two sources one from reservoir and
The water flows in the mains due to gravitational also in addition to electrical pumps as stand second from pumping station, it is called dual system.
forces. by to be maintained. During fires, the water
can be pumped in required quantity by the This system is more reliable and economical, because it requires uniform
stand by units. rate of pumping but meets low as well as maximum demand.

The water stored in the elevated reservoir meets the requirements of
demand during breakdown of pumps and for fire fighting.

58

Chapter 4 : Water Distribution System

Component Types

1. Casing: the impellor is enclosed in the casing, which is Pump
so designed that kinetic energy. Of the liquid is
converted into pressure energy before it leaves the Operation / maintenance
casing.
The function of pump is to left the water or any fluid to higher elevation or at
2. Delivery pipe higher pressure. Pumps are driven by electricity ,diesiel or steam power. They
3. Delivery valve are helpful in pumping water from the sources, that is from intake to the
4. Impeller treatment plant and from treatment plant to the distribution system or service
5. Prime mover reservoir . In homes also pumps are used to pump water to upper floors or to
6. Suction pipe store water in tanks over the buildings.
7. Strainer and foot valve
59

WHAT IS VALVE?

• Valve is a device that regulates, controls
• or directs the flow of a fluid by opening,
• closing, or partially obstructing fluid flow.
• A valve is a mechanical device that controls the flow and pressure of fluid within a system or Process.

• So basically, it controls flow & pressure.

Types of Valves Valves Functions

• In piping following types of So, the selection of valves is essential to Valve serve a various function within the piping system. Such as
valves are used depending the economics, as well as operation, of 1. Stopping and starting a fluid flow.
on the requirements. the process plants. 2. Throttling the fluid flow.
1. Globe Valve 3. Controlling the direction of a fluid flow.
• The cost of Valve in the 2. Gate Valve 4. Regulating a flow or pressure within the piping system.
piping system is up to 20 to 3. Check Valve 5. Relieve pressure or vacuum from the piping system and equipment.
30% of the overall piping 4. Plug valve 6. Pressure and vacuum relief valve safeguard the process system from overpressure
cost. 5. Ball Valve 7. and during vacuum condition.
6. Butterfly Valve
• And the cost of a given type 7. Needle Valve
and size of the valve can 8. Pinch Valve
vary 100%. 9. Pressure Relief Valve
10. Relief Valve
• It means that if you choose 11. Stop Valve
ball valve over butterfly
valve for the same function.
It can cost you more.

: Relief Valves Butterfly Valves Neddle Valves Ball Valves Plug Valves Check Valves Stop Valves

Gate Valves

Advantages and Disadvantages Pipe Material

Pipe Material Advantages Disadvantages Steel 1. No. of joining are less because these are 1. Maintenance cost is high
Cast Iron available in long lengths 2. The pipes are likely to be rusted by acidic or
1. Cost is moderate 1. Breakage of pipes are HDPE (High Density
2. The pipes are easy to join large Polyethylene) 2. The pipes are cheap in first cost alkaline water
3. The pipes are not subjected to 2. The carrying capacity of 3. The pipes are durable and strong enough to 3. The pipes require more time for repairs during
corrosion
4. The pipes are strong and durable these pipes decreases resist high internal water pressure breakdown and hence not suitable for
5. Service connections can be easily with the increase in life 4. The pipes are flexible to some extent and they distribution pipes
made of pipes. 4. The pipes may deform in shape under combined
6. Usual life is about 100 years 3. The pipes are not used can therefore laid on curves action of external forces
for pressure greater than 5. Transportation is easy because of light weight.
0.7 N/mm2
4. The pipes are heavier 1. Highly elastic 1. Difficult to connect
and uneconomical 2. Light 2. Need special equipment
beyond 1200 mm dia. 3. Strong on the impact 3. Higher cost
4. Very low internal friction 4. Necessary adjustments if connected to

other pipes.

Ductile Iron 1. Corrosion-resistant 1. Weight UPVC (Unplasticise 1. Light 1. Declined by ultraviolet (UV)
2. Strongly on the impact 2. High cost Polyvinyl Chloride) 2. Elastic 2. Easily leak
3. Corrosion-resistant 3. Expensive and dependent on petroleum
4. Low internal friction
prices

Asbestos Cement 1. Low cost 1. Weak in bending GRP (Glass Reinforced 1. Light 1. Easily damaged on impact
2. Easily leak when Plastic) 2. Corrosion-resistant 2. Very careful handling is required
2. Free from electrolysis 3. Low internal friction 3. Not suitable for high pressure
exposed to 4. Easily leak
3. Light excavation
machinery
4. Easy to handle - cut etc 3. Fragile
4. Leakage at the joints

62

The main function of the storage tank is :- Balancing tank Chapter 4 : Water Distribution System
1. to provide treated water storage
2. to minimize disruptions during the burst pipe. Balancing tank main function is to receive and Service tank
3. to provide treated water storage collect the treated water from treatment plants
4. to cope with the needs of the fluctuating. and then transfer it to a tank or some services Service reservoir serves to supply water to the reticulation system. Minimum
5. as a stress breaker tank where the level of differences range in tank. Balancing tank depends on the capacity of capacity service tanks and reserve pond in the distribution system should be equal
the treated water at treatment plants and to the reserve for one day. Storage per day is usually sufficient for the needs of fire
the supply area is divided into a zones. storage required to balance the inflows and prevention. Service reservoirs are provided in the water treatment distribution
6. to provide water storage for fire fighting purposes. The outflows from the reservoir. system for the following functions:
I. To equalize the variation in hourly demand of water by the consumers to a
amount of emergency storage needed to determine tank size. Water Storage Tank
uniform rate of supply from the source either by gravity or pumping,
Function II. To maintain the desired minimum residual pressure in the distribution

system,
III. To provide the required contact time for the disinfectant added in order to

achieve effective disinfection, and

General Components of a Storage Tank / Factors of tank 1. profit / life expectancy
Pool / Tank Pool material selection 2. strength of the structure
3. resistance to corrosion and abrasion (internal and

external)
4. the requirement of total load
5. location and environment

Types of Storage Reservoir

Types of Pool / Tank Construction Material Service reservoir

Reinforced Concrete In case the supply from the source is not
continuous for all the 24 hours and only
• Reinforced concrete pool is preferred because of low maintenance and life-saving use. Underground reservoir Balancing reservoir during certain duration by pumping for 12
• Can be constructed on land or elevated according to the pressure and site conditions. to 20 hours in a day and the water
The balancing reservoir has a single distribution is intermittent for certain
Pre-stress Concrete Underground reservoirs, also connection to serve as inlet as well as outlet. specified hours different from the pumping
• In Malaysia, the construction of tanks / ponds using pre-stress concrete only involves known as sumps serve as suction schedule, the supply from the source is
sources for pumps. These Balancing reservoir is also called floating stored in a storage reservoir and then
the construction on the land only and not for the construction of elevated tanks. reservoirs normally are built at the reservoir. Only one pipe is connected to the supplied to the consumers according to the
site of a supply source. It is reservoir, which will act as inlet as well as schedule.
Galvanized Pressed Steel (GPS) common to design a well pump outlet. In a water supply system with number Service Reservoir Has Separate Inlet And
• Pressed steel tanks are often used as a storage tank and can be built in a short time. station where number of well of service reservoirs one for each zone, they Outlet Connections.
• Rarely built on the ground and usually elevated and galvanized. pumps discharges to an onsite can be connected to a master balancing
reservoir. reservoir (MBR) so that the proper distribution
Fiber-Glass Reinforced Polyester (FRP) of water to each of the SRs can be achieved by
• FRP tanks are designed and constructed as a pressed-steel tank. It has an FRP panel supplying through independent feeder mains.

and can receive between 1 m3 to 2300 m3 of water

Steel Fussed with Glass ( SFG )
• This tank is designed with the same FRP and GPS panels from the ‘steel fussed with

glass’ material to produce a smooth, low friction, tough and waterproof.

Indirect measurement may consist three Non Revenue Water (NRW) could be due to leakage of Chapter 4 : Water Distribution System
leakage locations or partly, between the boundary in the distribution system or a pool of water, broken
the studied area. Measurements or estimates of pipes, overflowing water ponds, the use of fire 1. Pressure
water use components will be made without the fighting, water theft, damage to water meters; meter
leakage. Components of water use, other than reading is unperfected and wash system uses. The conversion or changes in pressure will change the rate of water
leakage are: - leakage through a leaking or broken pipes and faulty connections.
Indirect Definition Increased pressure in the system, even slightly, can cause an increase
i. metered usage, M Measurement of burst pipes in short-term.
ii. flow under recording, U Non Revenue
iii. Permitted use, but not metering as the Water (NRW) Factors That 2. Pressure Fluctuation
Influence
use of fire and movement of work for Leakage The pressure is always up and down in cycles may cause pipe failure.
maintenance purposes, D
iv. Use without leakage, I 3. Soil Movement

Formula to find the leaks value are: Leaks = The movement of land referred to here is a small movement that is
inflow-outflow - (M+U+D+I) caused by changes in soil moisture content.

Leakage Measuring Procedure 4. Rust In Pipe

Source of leakage is categorized in three areas: - Corrosion caused by chemical reactions that cause the movement of
i. Water pool electric current. Meanwhile, external corrosion is caused by differences
ii. Main pipe in soil water content along the pipe concerned.
iii. Distribution pipe
5. Quality of Material and Poor Work
From the study, leakage from the pool and the main pipe is small and if it exists, it can be easily detected. While, the distribution pipe leakage is high
and difficult to detect. Quality materials that do not meet the specifications and the work is
not monitored properly will cause the water supply system which has a
Water Pool Leakage high leakage rate.

To determine the rate of leakage from the pool of water, fall of water level in the pool is measured using the internal sensors (sensor depth) by closing 6. Soil Characteristic
all the out valves. First, the valves must be tested to ensure that it does not leak. Measurements will be made for 6 to 24 hours.
Some of soil is not affecting the pipe condition, but the Lias clay (Tanah
Leakage from Main Pipe liat Lias) or EPIC (alluvium) is very aggressive. 7.

Measurement rate of leakage in the main pipe is different the distribution pipe. This is because the main pipe does not involve a lot of connections. 7. Traffic Load
Before the leak test conducted, each connection valve between the two ends of the pipe need to be tested. Valves on both ends must be closed and
the water pipes installed in the first bypass valve. Water supply systems should be planted in the ground by a sufficient
depth. If it is planted at a less depth, vibration from traffic on it will
break the water supply pipe.

8. Pipe Age

Structural deterioration and exhaustion piping system will increase the
the pipe leaking.

64

Water distribution system pipes using
Hazen Williams formulation.

a. Delivery b. Distribution c. Dead-end Example 1
pipe size pipe size reticulation Dead-end system
One type of dead-end distribution system is proposed to supply water
pipe to a city such as in Figure 1 below. Using loss data and formulas
provided, estimate the size of the pipe for the AB and BC to the head by
Easily Pipe Design over 15.0 m.

Before the design of distribution system pipe sizes Data have been given :
can be implemented, pipe layout and all fixtures q = 175 litre/capita/day
required should be calculated in advance. The Q design = 3Q average
selection of plumbing system for a town or housing pressure = 15 m
scheme should take into account cost and distance AB = 700 m
effectiveness of the services. distance BC = 550 m
Formula Hazen- Wiliams Loss formula : (Hazen Williams)

Method of calculating the size of the pipe is HL = 1128 109  Q 1.85
divided into two, namely, to the dead-end and not d 4.87 100 
the dead-end system (grid, ring and radial).

where:  Q 1.85 where:
100  HL = head loss (m)
HL = head loss (m) HL = 1128 109 Q = flow rate (m3/hr)
Q = flow rate (m3/hr) d 4.87 d = pipe diameter (mm)
d = pipe diameter (mm)

Pipe References Total of Design flow Size Pipe Loss Surface level Hidraul Head user
population (m3/hr) estimated (m) Level (m)
Lenght (m)
(mm) Each 1000 metre (m) Actual A = 185.5 -168
(m) (m) =17.5 ≥ 15 m

175 7350 3 16.9 700 A = 185.5 Satisfied... OK
1000 B = 185.5 – 11.8 B = 173.7 -154
24 60 60 200 16.9 700 = 11.8 A = 168
= 44.7 litre/sec B = 154 = 173.7 = 19.7 ≥ 15 m
AB 7350 Satisfied... OK

= 160.8 m3/hr C = 166.1 – 146
= 20.1 ≥ 15 m
175 3100 3 13.8 550
1000 Satisfied... OK
BC 3100 24 60 60 150 13.8 550 = 7.6 C = 146 C = 173.7 – 7.6
= 18.8 litre/sec =166.1

= 67.6 m3/hr

Exercise 1
State the function of storage tank and balancing tank

Exercise 2

Explain briefly FOUR (4) classification of Non Revenue Water (NRW) cause. [CLO1] (10
marks)
___________________________________________________________________________
___________________________________________________________________________
______________________________________________________

Exercise 3

Water distribution network system can be divided into four types. Explain briefly different
TWO (2) type water distribution network system with the help of diagram.

CHAPTER 5

Sewerage
System

68

Combined Chapter 5 : Sewerage System

Combined system of
sewerage both sewage
discharge and the storm
runoff are collected and
conveyed through a
common collection system.

Sewerage System Partially

Separate system part of the storm water especially
collected from roofs and paved court yards of
separate system of the buildings is admitted in the same drain
sewerage there are two along with sewage from residences and
collection systems or pipe institutions, etc.
network;
1. for collecting 69

domestic sewage as
sanitary sewerage
system and
2. for collecting storm
water as storm water
drainage system.

• Advantages Advantages Disadvantages Chapter 5 : Sewerage System
Combined sewerage System
• In an area where rainfall is • Disadvantages
spread throughout a year, there
is no need of flushing of sewers, • Not suitable for the area with small
as self cleansing velocity will be period of rainfall in a year, because dry
developed due to more weather flow will be small due to which
quantity because of addition of self cleansing velocity may not develop
storm water. in sewers,resulting in silting.

• Only one set of pipe will be • Large flow is required to be treated at
required for house plumbing. sewage treatment plant before disposal,
hence resulting in higher capital and
• In congested areas it is easy to operating cost of the treatment plant.
lay only one pipe rather than
two pipes as required in other • When pumping is required this
systems. system is uneconomical.

• During rains overflowing of sewers will
spoil public hygiene.

Condition

Conventional gravity sewers are large networks of underground
pipes that convey blackwater, greywater and, in many cases,
stormwater from individual households to a (Semi-) Centralized
Treatment facility, using gravity (and pumps when necessary).

70

Chapter 5 : Sewerage System

• Advantages Advantages Disadvantages • Disadvantages

• As sewage flows in separate pipe, Separate sewerage System • Self cleansing velocity may not
hence the quantity to be treated at developed at certain locations in
sewage treatment plant is small, sewers and hence flushing of
resulting in economy of treatment. sewers may be required.

• This system may be less costly as • - This system requires laying two
only sanitary sewage is transported sets of pipe, which may be
in closed conduit and storm water difficult in congested area.
can be collected and conveyed
through open drains. • This system will require
maintenance of two sets of
• When pumping is required during pipelines and hence maintenance
disposal, this system is economical cost is more.
due to less flow.

Condition

Separate sewerage consists :
i- municipal wastewaters (blackwater from toilets, greywater
Ii - industrial wastewater)
Iii. surface run-off (rainwater and stormwater).
The separate collection prevent the overflow of sewer systems and treatment
stations during rainy periods and the mixing of the relatively little polluted surface
run-off with chemical and microbial pollutants from the municipal wastewater.

71

Chapter 5 : Sewerage System

• Advantages Disadvantages Disadvantages
Increased cost of pumping as
• Economical and reasonable size sewers are required.
compared to separate system at
• Work of house plumbing is reduced as rain water from treatment plants and intermediate
roofs, wastewater from bathrooms and kitchen, etc. are pumping station wherever
combined with discharge from water closets. required.

• Flushing of sewers may not be required as small In dry weather self-cleansing
portion of storm water is allowed to enter in sanitary velocity may not develop in the
sewage. sewers.

Advantages

Partially Combined or Separate System

Condition

The storm water from the other places is collected
separately using separate storm water conduits.

72

These types of sewer (Brick Sewers) are made - These types of sewer (steel sewers) are Chapter 5 : Sewerage System
at site and used for construction large size Impervious, light, resistant to high pressure, flexible,
sewer. suitable when;
Brick Sewers are very useful for construction - The sewage is carried under pressure
of storm sewer or combined sewer. - The sewage has to be carried across a river under
Nowadays brick sewers are replaced by water
concrete sewer. - The sewer has to cross under a railway track
Brick sewers get deformed and leakage may - They are generally used for outfall and trunk
take place. A lot of labour work is required. sewers

Brick Sewer Steel Sewers

Asbestos Cement (AC) Type of Sewer Pipe Cement Sewer i. PCC - for dia upto 60 cm Suitable for small
Sewer storm drains. Not durable .
ii. RCC - for dia > 60 cm They may be cast in
• Types of sewer like Asbestos Cast iron (CT) Sewer Plastic Sewers situ or precast, resistant to heavy loads,
Cement (AC) Sewers are corrosion and high pressure. These are very
manufactured from a mixture of Nowadays PVC sewers are used for heavy and difficult to transport.
cement and asbestos fiber. carrying sewage.
Plastic sewers are resistant to 73
• Asbestos Cement (AC) Sewers are corrosion.
suitable for carrying domestic - light in weight, smooth and can be
sanitary sewage. bent easily.
- having high co-efficient of thermal
• Asbestos cement sewer is best as expansion and cannot be used in
vertical pipe for carrying sullage These types of sewer are High strength and very hot areas.
from upper floors of multistory
buildings (in two pipe system of durability water tight. Cast Iron sewers can
plumbing). with stand high internal pressure and can

bear external load. Cast Iron sewers are

suitable for the following conditions.

- When the sewage is conveyed under high

pressure

- When the sewer line is subject to heavy

external load e.g. under railway line,

foundation wall etc, below highways

- When there is considerable difference in

temperature

Previous Chapter 5 : Sewerage System
experience
The value of the
Life expectancy coefficient of friction /

roughness

Resistance rustiness - Criteria for Pipe Selection The strength of
corrosion and abrasion pipe structural

inside and outside

Water sealing Facilities for get the
capabilities supply, delivery and

installation

Connection
method

74

Shallow Manholes Chapter 5 : Sewerage System

- Shallow manholes are the one A manhole is a masonry Deep
which are about 0.75 to 0.9m in or reinforced cement manholes
depth. concrete (R.C.C)
Deep manholes are those which
- They are constructed at the chamber constructed for are deeper than 1.5m.
start of a branch sewer. These providing access to the The size of such a manhole is
are also known as inspection sewer for the purposes larger at the bottom, which is
chambers. of inspection, testing, reduced at the top to reduce the
cleaning and removal of size of manhole cover.
Normal obstructions from the
75
Normal manholes are those which are about sewer line.
1.5m in depth.
- They are contrasted either in square (1mx1m)
or rectangular (0.8m x 1.2m) in cross-section.
- The section of such manholes is not changed
with depth. It is provided with heavy cover at its
top.

Chapter 5 : Sewerage System

Infiltration is groundwater that Infiltration in Groundwater can enter these cracks or
enters sanitary sewer systems Sewer Pipe leaks wherever sanitary sewer systems
through cracks and/or leaks in the lie beneath water tables or the soil
sanitary sewer pipes. above the sewer systems becomes
saturated.

Cracks or leaks in sanitary sewer pipes or
manholes may be caused by age related
deterioration, loose joints, poor design,
installation or maintenance errors,
damage or root infiltration.

76

Corrosion in Sewer
Pipe

77

Chapter 5 : Sewerage System

a. provide information on estimated costs for reviewing the Preliminary Zoning a. Distribution area, or zonation should be made in advance depending
reasonableness of a project investigation on the extent and condition of the surface areas, or housing schemes
where his sewer-channel system to be designed.
b. work granulation map must have at least aerial photographs
c. preliminary design is based on the estimated flow, contours of b. Construction of treatment plants will be over design if the area is too
large or the density is too low.
land, the road location or pipeline routes, and the position of
the sewage produced from the c. For areas where the population intensity are evenly distributed, it is
d. from this information, the estimated quantity of pipes of more economical, if the area is divided into several zones with high
different sizes can be made simultaneously with estimates of population density.
excavation, restoration of roads and sewer pipe components
which required. a. Sewer channel system should be
designed to meet current and
Design period future needs.

Sewage quantity Sewer Pipe Design Procedure b. The need to come means that the
estimation needs of the contemporary if not
Treatment plant too wide and not beyond the
a. The quantity of sewage is depend with the seasons, days and existing provisions.
hours. For example, the flow volume during the day would be Sewage is not entirely liquid, but
more than night, and this makes it difficult to determine the also contains some of the solid, c. time limit does not exceed 30
average daily flow rate and maximum flow rates. especially for combined sewer pipe years.
system. The velocity of sewage
b. Sewer must be designed so that they can carry a maximum flow in the sewer pipe must be Sewer layout
flow rate in flow ⅔ full for diameter more than 75cm, and the sufficient to ensure that no solids
flow of ½ full for sewers less than 75cm in diameter. The flow will settle out and create piles of a. The layout of the sewer pipe should be at the shortest
factor for this method : silt, resulting in clogged pipes. distance to the treatment plant so that infrastructure
a. 6 is used for all sewer which carries a flow rate of the costs can be minimized.
population less than 10,000 people
b. 4.5 for the culvert which carries the discharge b. Most of sewer pipeline route is parallel to the back door
population of more than 10,000 people of the terraced house, on the curb next to the main
channel, or on the front side of the road if no curb and
within individual lots for attached housing, with no road at
the back.

78

Chapter 5 : Sewerage System

How to calculate parameters for circular shape sewer

Formulas calculating the velocity

a) Chezy Formulas b. Manning Formulas

V = C mi V = 1 2 i

n m3

m = A/P = d/4

Where:

V = Flow velocity (m/s)

C = Chezy Constant

m = Hydraulic min depth (m)

i = Sewer slope
n – rougness coefficient

79

EXERCISE 1
Determine flow velocity in sewer channels of circular section
made from cast iron with a diameter of 25 cm and spread with a
slope of 1:35. n = 0.0013 and C = 45.50 Use the method below :
Chezy Formulas and Manning Formulas

EXERCISE 2

Calculate the flow velocity in sewer channels made of cast
iron with a diameter 25cm and spread over the slope 1:40,
C= 227. Assume the flow is full. n = 0.013

Example 1 :
Sewer pipe made of clay has 15cm diameter with a
manning coefficient, n = 0.014 and has grown into the
ground with a slope of 1:90.

1. Calculate the sewage velocity through it. Assume the
flow is full.
2. If the self-cleaning the pipe is 1.0 m/s, calculate the
slope of the sewer pipe.

V = 1 2 i

n m3

Solution

Example 2

A housing scheme consists of four rows of terraced houses where each line is there are
20 units in which the number of occupants per unit is about 6 people. By using the
Manning formula, calculate the required sewer diameters for this housing scheme by
making the assumption of flow in sewers are full. Then indicate whether the flow
velocity is appropriate or not.

Design criteria required are as follows
Culvert slope = 1:40
Water requirement per capita = 250 liters / person / day

Flow-rate factor: 6 for the population <10,000 people
4.5 for the population > 10,000 people

Self-cleaning velocity > 0.45 m / s

Roughness coefficient = 0.014





CHAPTER 6

Sewage
Treatment

86

2. Protect public Chapter 6 : Sewage Treatment
water supplies.
Effluent Standard

Parameter Standards
Unit
Temperature
pH Value AB
BOD5 at 20C
COD C 40 40 Effluent that is
discharged upstream of
Suspended Solids - 6.0-9.0 5.5-9.0 a water supply intake
should meet Standard
Mercury mg/l 20 50 A, while effluent that is
Cadmium discharged downstream
1. Protect mg/l 50 100 has to meet Standard B.
public health. Chromium, Hexavalent These standards are set
Purpose of Sewage 3. Protect mg/l 50 100 by the Environmental
Treatment aquatic life. Arsenic
Cyanide mg/l 0.005 0.05 Quality Act 1974.
Lead
mg/l 0.01 0.02
Chromium, Trivalent
mg/l 0.05 0.05
Copper
5. Protect 4. Preserve the best Manganese mg/l 0.05 0.10
adjacent lands. uses of the waters. Nickel mg/l 0.05 0.10
Tin mg/l 0.10 0.5
Zinc
Boron mg/l 0.20 1.0
Iron (Fe)
Phenol mg/l 0.20 1.0
Free Chlorine
Sulphide mg/l 0.20 1.0

Oil and Grease mg/l 0.20 1.0

mg/l 0.20 1.0

mg/l 1.0 1.0

mg/l 1.0 4.0

mg/l 1.0 5.0

mg/l 0.001 1.0

mg/l 1.0 2.0

mg/l 0.50 0.5

mg/l Not 10.0
Detectable

87

Chapter 6 : Sewage Treatment

colour

odor Tempertaure

Total Solid Substances Physical Turbidity

Nitrogen Compounds

Dissolved Gases Characteristics of Protozoa
Sewage
Chemical Oxygen Chemical Virus
Demand (COD) Biological

Biochemical Oxygen
Demand (BOD)

Algae

pH Alkalinity Bacteria Fungi

Phosphorus

Industrial and agricultural work involves the use of Surface waters are the natural water resources of Chapter 6 : Sewage Treatment
many different chemicals that can run-off into the Earth. They are found on the exterior of the
water and pollute it. Metals and solvents from Earth’s crust and include oceans, rivers and lakes Microorganisms that live in water feed on
industrial work can pollute rivers and lakes. These biodegradable substances. When too much
are poisonous to many forms of aquatic life and Surface water biodegradable material is added to water, the
may slow their development, make them infertile number of microorganisms increase and use up
or even result in death. Pesticides are used in the available oxygen. This is called oxygen
farming to control weeds, insects and fungi. depletion. When oxygen levels in the water are
depleted, relatively harmless
aerobic microorganisms die and anaerobic
microorganisms begin to thrive.

Oxygen depleting Humans often use aquifers as a means to
obtain drinking water, and build wells to access
Chemical Pollution in Water Groundwater it. When this water becomes polluted it is
called groundwater pollution. Groundwater
Suspended pollution is often caused by pesticide
matter contamination from the soil and it can infect
our drinking water and cause huge problems.

The suspended particles eventually settle and

cause thick silt at the bottom. This is harmful to

marine life that lives on the floor of rivers or

lakes. Biodegradable substances are often

suspended in water and can cause problems by

increasing the amount of anaerobic

microorganisms present. Toxic Nutrients

chemicals suspended in water can be harmful to Microbiology

the development and survival of aquatic life.

Microbiological water pollution is usually a natural form of water Nutrients are essential for plant growth and development.
pollution caused by microorganisms. Many types Many nutrients are found in wastewater and fertilizers, and
of microorganisms live in water and cause fish, land animals and these can cause excess weed and algae growth if large
humans to become ill. Microorganisms such as: Bacteria, Viruses concentrations end up in water. This can contaminate drinking
and Protozoa. Serious diseases such as cholera come from water and clog filters. This can be damaging to other aquatic
microorganisms that live in water. organisms as the algae use up the oxygen in the water, leaving
none for the surrounding marine life.

89

Chapter 6 : Sewage Treatment
90

Chapter 6 : Sewage Treatment

Sewage Treatment Processes

Purposes

1 Provides for the removal of large debris & heavy inorganic materials that could
Preliminary treatment damage plant equipment or would occupy treatment capacity without being
treated.

2 Removes settleable and floatable solids (may not be present in all treatment
Primary treatment plants).

3 Removes BOD and dissolved and colloidal suspended organic matter by
Secondary treatment biological action. Organics are converted to stable solids, carbon dioxide and
more organisms.
4
Advanced waste treatment Uses physical, chemical, and biological processes to remove additional BOD,
solids and nutrients (not present in all treatment plants).

5 Removes microorganisms to eliminate or reduce the possibility of disease when
Disinfection the flow is discharged.

6 Stabilizes the solids removed from wastewater during treatment, inactivates
Sludge treatment pathogenic organisms, and reduces the volume of the sludge by removing
water.

91

1 Chapter 6 : Sewage Treatment
Preliminary treatment
Processes Purposes
Screening
The purpose of screening is to remove large solids, such as rags, cans, rocks, branches,
Shredding leaves, roots9, e2tc., from the flow before the flow moves on to downstream processes.

Grit removal As an alternative to screening, shredding can be used to reduce solids to a size that can
enter the plant without causing mechanical problems or clogging.
Pre-aeration
The purpose of grit removal is to remove the heavy inorganic solids that could cause
Chemical addition excessive mechanical wear. Grit is heavier than inorganic solids and includes, sand, gravel,

clay, egg shells, coffee grounds, metal filings, seeds, and other similar materials.

to achieve and maintain an aerobic state (to freshen septic wastes), strip off hydrogen
sulfide (to reduce odors and corrosion), agitate solids (to release trapped gases and

improve solids separation and settling), and to reduce BOD.

to improve settling, reduce odors, neutralize acids or bases, reduce corrosion, reduce
BOD, improve solids and grease removal, reduce loading on the plant, add or remove

nutrients, add organisms, and aid subsequent downstream processes.

Chapter 6 : Sewage Treatment

The purpose of primary treatment (primary sedimentation or primary clarification) is to remove settleable organic and floatable solids. Normally,
each primary clarification unit can be expected to remove 90 to 95% settleable solids, 40 to 60% TSS, and 25 to 35% BOD. Sedimentation may be
used throughout the plant to remove settleable and floatable solids. It is used in primary treatment, secondary treatment, and advanced
wastewater treatment processes.

Purpose
2 Primary treatment

Process Overview

1. Primary treatment reduces the organic loading on downstream treatment processes by In primary sedimentation, wastewater enters a settling tank or basin. Velocity is reduced to
removing a large amount of settleable, suspended, and floatable materials. approximately 1 ft/min. Solids that are heavier than water settle to the bottom, while solids
2. Primary treatment reduces the velocity of the wastewater through a clarifier to that are lighter than water float to the top. Settled solids are removed as sludge and floating
approximately 1 to 2 ft/min, so that settling and floatation can take place. Slowing the flow solids are removed as scum. Wastewater leaves the sedimentation tank over an effluent weir
enhances removal of suspended solids in wastewater. and on to the next step in treatment. Detention time, temperature, tank design, and condition
3. Primary settling tanks remove floated grease and scum, remove the settled sludge solids, of the equipment control the efficiency of the process.
and collect them for pumped transfer to disposal or further treatment.

4. Clarifiers used may be rectangular or circular. In rectangular clarifiers, wastewater flowsfrom
one end to the other, and the settled sludge is moved to a hopper at the one end, either by
flights set on parallel chains or by a single bottom scraper set on a traveling bridge.

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Chapter 6 : Sewage Treatment

• In operation, wastewater is distributed evenly over the • The organisms aerobically decompose the solids producing more organisms and stable

surface of the trickling filter media. wastes, which either become part of the zoogleal slime or are discharged back into the
• As the wastewater flows over the surface of the media
wastewater flowing over the media.
the organisms in the slime remove the organic matter • The wastewater continues through the filter to the under drain system where it is collected
from the flow.
and carried out of the filter.
• At the same time air flows through the filter (bottom to the top or top to bottom depending on

temperature).
• Oxygen is transferred from the air to the wastewater and slime to maintain the aerobic

The surface of the disk is covered with a conditions.
biological slime similar to that on the • Periodically the slime on the media becomes too heavy and portions will be released.
• This material known as sloughing is carried out of the filter with the wastewater flow and is

removed in the settling tank following the filter.

media of a trickling filter. Trickling

RBC units are usually installed in a filter

concrete tank so that the surface of the

wastewater passing through the tank

almost reaches the shaft. Rotating Secondary treatment Oxidation pond
This means about 40% of the total Biological 3
surface area of the disks is always Contactor
submerged.
(RBC)
The shaft continually rotates at 1 to 2

rpm, and a layer of biological growth

2 to 4 mm thick is soon established Activate Additional settling of solids and biological treatment of organic matter in
on the wetted surface of each disk. d sludge the water occurs. Some of the feacal coliform in the water is also
The organisms in the slime assimilate removed.
(remove) organic matter from the Activated sludge refers to biological treatment processes that use a It also can provide additional clarification, BOD removal and disinfection.
wastewater for aerobic suspended growth of organisms to remove BOD and suspended solids. The oxidation pond is very similar in design to the stabilization pond.
decomposition.
The disk continues to rotate, leaving • Primary effluent (or plant influent) is mixed with return 94
the wastewater and moving through activated sludge to form mixed liquor.
the air.
• The mixed liquor is aerated for a specified length of time.
• During the aeration the activated sludge organisms use the

available organic matter as food producing stable solids and
more organisms.
• The suspended solids produced by the process and the
additional organisms become part of the activated sludge.
• The solids are then separated from the wastewater in the
settling tank.
• The solids are returned to the influent of the aeration tank
(return activated sludge).

Thickening is a first step to reduce sludge water Sludge dewatering is used to reduce Chapter 6 : Sewage Treatment
content. Sludge reaches 10 to 30 % dryness, and
can still be pumped. Note that the sludge volume by removing the water to
removal and pumping facilities and the method
of operation also affect the solids content. permit easy handling and After water treatment, additional treatments need to be
Various existing techniques are presented below. economical reuse or disposal. performed on sludge in order to:
Sludge thickening (or concentration) is a unit
process used to increase the solids content of Dewatering processes include sand i. reduce its water content,
the sludge by removing a portion of the liquid
Pre-treatment fraction. drying beds, vacuum filters, ii. stabilize its organic matter and reduce the
centrifuges, filter presses (belt and generation of odours
Pre-treatment consists of various physical and mechanical Thickening plate), and incineration.
operations, such as screening, sieving, blast cleaning, oil iii. reduce its pathogen load,
separation and fat extraction. Pre-treatment allows the iv. reduce its volume and global mass.

removal of voluminous items, sands and grease. Several treatments can be applied to sludge to achieve

Primary sludge Dewatering this. These are described in a following part of this report.
One of those transforms the sludge in a way that it is
Primary sludge is produced following primary treatment. This step consists of
physical or chemical treatments to remove matter in suspension (e.g. solids, Digestion considered as a new type of sludge usually referred to as
grease and scum). The most common physical treatment is sedimentation. “digested sludge”.
Sedimentation is the removal of suspended solids from liquids by gravitational
settling. Sedimentation is usually considered first because it is a simple and cost- Sludge Treatment

effective method. SLUDGE incinerators produce the maximum solids and moisture
reductions. The equipment required depend on
Secondary sludge
whether the unit is a multiple hearth or fluid bed
Secondary sludge is generated from the use of specially provided
decomposers to break down remaining organic materials in incinerator. Generally, the system will require a source

wastewater after primary treatment. The active agents in these Sludge Disposal Incineration of heat to reach ignition temperature, solids feed
systems are micro-organisms, mostly bacteria, which need the system and ash handling equipment. It is important to

available organic matter to grow. note that the system must also include all required

Mixed sludge equipment (e.g., scrubbers) to meet the air pollution

The primary and secondary sludge described Composting Ocean dumping control requirements. In operation, solids are pumped
above can be mixed together generating a type A few sewage works to the incinerator.

of sludge referred to as mixed sludge. compost sludge by the Dumping waste in the Spray Irrigation Landfill
process of ‘windrowing’. ocean, estuaries, or
Tertiary sludge The process generates inland lakes is regulated Spray irrigation is a landfills are the ultimate disposal location for
by emission standards modification of the system dried (dewatered) sludge, and this disposal
Tertiary sludge is generated when carrying out tertiary treatment. It is heat and a rise in for abating pollution of used in agriculture for method can be economically depending on the
an additional process to secondary treatment and is designed to temperature in the the oceans. The concept irrigating crops. However, the haul distance from the wastewater treatment
remove remaining unwanted nutrients (mainly nitrogen and composting material of an infinite ocean (a objective is the disposal of plant to the landfill. In considering the location,
phosphorus) through high performance bacterial or chemical causes pathogen mile and a half deep on liquid rather than providing design, operation and maintenance of sludge
processes. These treatments are necessary when a high level of destruction. The final the average around the moisture and nutrients to disposal lagoons and landfills, environmental
depollution is required. product may be suitable world) has given way to harvestable crops. After engineers must consider the sludge loading
the reality that the pretreatment and grease criteria, possible health effect through
for amenity use. ocean is a limited and removal, this system sprays groundwater pollution, the potential for heavy
valuable resource. wastewater through a sprinkler metal accumulation in the soil and groundwater,
system onto land that is the possibility of fertilizer nutrients like nitrogen 95
planted with special grasses. and phosphorus reaching the surface water, and

general nuisance developments.

Chapter 6 : Sewage Treatment

Septic tanks are prefabricated tanks that Septic tank Individual Imhoff Figure : Imhoff Tank
serve as a combined settling and Wastewater tank
skimming tank and as an unheated– Treatment Unit Source: http://www.sswm.info/category/implementation-tools/wastewater-
unmixed anaerobic digester. Septic tanks treatment/hardware/site-storage-and-treatments/imhoff-tank
provide long settling times (6 to 8 hours
or more), but do not separate The two-story or Imhoff tank is similar to a septic tank in
decomposing solids from the the removal of settleable solids and the anaerobic
wastewater flow. When the tank digestion of solids. The difference is that the two story
becomes full, solids will be discharged tank consists of a settling compartment where
with the flow. The process is suitable for sedimentation is accomplished, a lower compartment
small facilities (i.e., schools, motels, where settled solids and digestion takes place, and gas
homes, etc.), but due to the long vents. Solids removed from the wastewater by settling
detention times and lack of control, it is pass from the settling compartment into the digestion
not suitable for larger applications. compartment through a slot in the bottom of the settling
Septic Tank receives raw sewage, allow compartment. The design of the slot prevents solids from
it to settle, and pass the relatively clear returning to the settling compartment. Solids decompose
liquid to the adsorption field, which is anaerobically in the digestion section. Gases produced as a
the next stage of treatment. result of the solids decomposition are released through
the gas vents running along each side of the settling
compartment.

96

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