SEWER

APPURTENANCES BUILDING SERVICES - I

SONAKSHI BHATTACHARJEE | 114AR0024 | FIFTH SEMESTER, B.ARCH | P&A | NIT ROURKELA

SEW

ER A

PP

UR

TEN

AN

CES

1

ACKNOWLEDGEMENT

I am very thankful to Prof. N. Saha for her constant

support and valuable guidance. I am also thankful to my

friends for valuable suggestions for the preparation of my

report.

Ms. Sonakshi Bhattacharjee

114Ar0024

SEW

ER A

PP

UR

TEN

AN

CES

2

INTRODUCTION

In order to make the process of construction easy and to have efficient

working and maintenance, the sewer system requires various additional

other structures. These are called as sewer appurtenances. Sewer

systems require various types of appurtenances for their proper

functioning and maintenances because if simply sewers are laid, the

sewage cannot flow in it continuously longer time. After some time, it will

be choked up and will require cleaning of sewers.

If sewerage system will not be maintained properly, silt, ashes, fats, oils

and greasy matters etc. will choke the sewer line. Therefore for the

operation and proper maintenance of sewerage system various devices

are essential, which would be in accessible to the general public.

SEW

ER A

PP

UR

TEN

AN

CES

3

MANHOLE

At every change of alignment, gradient or diameter of the sewer,

manholes are constructed for giving access into the sewer for inspection,

cleaning, repairs and maintenance. Manholes are masonry or RCC

chambers which are constructed on the top of sewer. This are fitted with

suitable cast iron covers at their top.

The essential components are:

1. A working chamber – for necessary examination and cleaning in an easy manner.

a. Minimum internal sizes are i. For depth of 0.8m or less – 0.75m X 0.75m (Shallow

manholes) ii. For depth of 0.8m and 2.1 m – 1.2m X 0.9m (Normal

manhole) iii. For depth more than 2.1m – circular chambers of 1.4m

diameter or rectangular chamber of 1.2m X 0.9m (Deep manhole)

2. An access shaft – a. For providing access to the working chamber. b. Formed by corbelling the working chamber on three sides at

top. c. Minimum internal dimensions of the shaft - 0.5m X 0.5m

3. A strong cover on the top flush with the road level – a. Made of cast iron or RCC

i. Cast iron cover - Placed in the cast iron frame fixed at the top of access shaft. Weights vary from 51 kg to 255 kg depending on the type of traffic on the road.

ii. RCC cover – Precast cover is placed on the top of manhole opening. Provided with flush with the road level and have a size so that a man can easily enter in the chamber. Minimum size is 50cm diameter.

The bottom of the manhole is usually made of concrete slightly sloped at

the top towards the open channels, which are in continuation of the

SEW

ER A

PP

UR

TEN

AN

CES

4

sewer line. Top surface of the concrete is called benching and the man

stands on it top during cleaning and inspection of the sewer lines.

Circular shaped manholes are more stable and stronger though it is

difficult to construct. The circular manhole should be at least 180cm high

and 120 cm in diameter or it may be 90 X 120cm in plan (longer dimension

should be along the flow).

I.S.I have recommended – maximum distance between

Manhole to manhole – 30m

Manhole to gully chamber - 6m (maximum)

If 2 or more sewers join at the same level in a manhole, the branch

channels should be given a smooth curve to meet the main channel. If the

inlet and outlet pipes are of different diameters, the crown of both the

pipes should be placed at the same level and the necessary slope should

be provided in the invert of the main channel.

The types of manholes are –

1) Straight through Manholes -This is the simplest type of manhole, which is built on a straight run of sewer with no side junctions. Where there is change in the size of sewer, the soffit or crown level of the two sewers should be the same, except where special conditions require otherwise.

2) Junction Manholes- This type of manholes are constructed at every junction of two or more sewers, and on the curved portion of the sewers, with curved portion situated within the manhole. This type of manholes can be constructed with the shape other than rectangular to suit the curve requirement and achieve economy. The soffit of the smaller sewer at junction should not be lower than that of the larger sewer. The gradient of the smaller sewer may be made steeper from the previous manhole to reduce the difference of invert at the point of junction to a convenient amount.

3) Side entrance Manholes-In large sewers where it is difficult to obtain direct vertical access to the sewer from the top ground level due to obstructions such as, other pipe lines like water, gas, etc., the access shaft should be constructed in the nearest convenient position off the

SEW

ER A

PP

UR

TEN

AN

CES

5

line of sewer, and connected to the manhole chamber by a lateral passage. The floor of the side entrance passage which should fall at about 1 in 30 towards the sewer should enter the chamber not lower than the soffit level of the sewer. In large sewers necessary steps or a ladder (with safety chain or removable handrail) should be provided to reach the benching from the side entrance above

4) Scraper (service) type manhole- All sewers above 450 mm in diameter should have one manhole at intervals of 110 to 120 m of scraper type. This manhole should have clear opening of 1.2 m x 0.9 m at the top to facilitate lowering of buckets.

5) Flushing Manholes- In flat ground for branch sewers, when it is not possible to obtain self-cleansing velocity at all flows, due to very little flow, it is necessary to incorporate flushing device. This is achieved by making grooves at intervals of 45 to 50 m in the main drains in which wooden planks are inserted and water is allowed to head up. When the planks are removed, the water will rush with high velocity facilitating cleaning of the sewers. Alternatively, flushing can be carried out by using water from overhead water tank through pipes and flushing hydrants or through fire hydrants or tankers and hose. Flushing manholes are provided at the head of the sewers. Sufficient velocity shall be imparted in the sewer to wash away the deposited solids. In case of heavy choking in sewers, care should be exercised to ensure that there is no possibility of back flow of sewage into the water supply mains.

SEW

ER A

PP

UR

TEN

AN

CES

6

DROP MANHOLE

When it is uneconomical or impracticable to arrange the connection

within 60cm of the invert of the sewer and manhole, then a vertical shaft

is constructed outside the manhole chamber through which the sewage

of branch sewer is allowed to enter the manhole.

If the difference in level between the branch sewer and main sewer is

within 60cm and there is sufficient roof within the working chamber, the

connecting pipe may be directly brought through the manhole wall by

providing a ramp in the benching. Such manhole which drop the level of

invert of the incoming sewer ,by providing a vertical shaft , are called drop

manholes, the main purpose being to avoid the splashing of sewage on

the an working and on the masonry work.

The branch sewer line is connected to the manhole in such a way that it

can be cleaned and rodded when necessary. For inspection of the

incoming sewage and cleaning of vertical shaft, the vertical shaft is taken

upto the ground level.

SEW

ER A

PP

UR

TEN

AN

CES

7

LAMPHOLE

In narrow lanes, change of gradient and slight curves where space is

insufficient for the construction of manholes, a vertical shaft of 20-30cm

diameter is connected to the sewer by a T-bend. These small size

openings are covered by a cast iron or RCC cover flush with the road level

at the top.

While inspecting a lamp is lowered in the vertical shaft and is seen from

the manholes on either sides to find that sewer is clean or obstructed.

The lampholes are provided at places when the regular manholes are

placed at longer intervals. Mostly local authorities do not recommend

lamp holes in the sewer lines.

SEW

ER A

PP

UR

TEN

AN

CES

8

OIL AND GREASE TRAPS

The sewage from hotels, restaurants, kitchen and industries contains

grease, oils and fats, which if not removed before it enters the sewers,

will stick to the interior surface of the sewer conduit and will become hard

and cause obstruction in the movement of the sewage. To check them

grease traps are required, which are placed in the pipe connecting the

kitchen with sewer line. Sewage from garages and service stations

contains sand, mud, oils and grease which should also be removed before

the sewage enters sewer line. Combined silt and oils trap are used at such

places. Such traps also prevent gasoline from entering the sewer and

causing explosion hazard. These traps should be regularly cleaned for

their proper functioning.

SEW

ER A

PP

UR

TEN

AN

CES

9

CATCH BASINS

These are small masonry chambers (75-90cm in diameter and 75- 90cm

deep) which are constructed below the street inlets to prevent the flow

of grit, sand or debris in the sewer lines. When storm water enters these

basins, the grit, sand etc. settle in the bed and the storm water free from

all these enters the sewers. The outlet pipe of catch basin is fixed about

60cm above the bottom. The outlet pipe is provided with a trap to

prevent the escape of odours from the sewers to catch the catch basins.

Catch pits should be provided –

i. When the sewers are laid at very small gradients, and the velocity

of flow is less than self – cleaning velocity.

ii. When the drains are passing along the water bound macadam road

or in sandy area, and the market (where lots of refuse is dropped

in the drains).

The catch basins collect the solids from the storm water. The solid need

to be frequently removed to avoid blocking of the passage which results

in flooding during monsoons. If roads are in good condition (well-paved),

catch pits may not be used and street inlets can be directly connected

with the sewer.

SEW

ER A

PP

UR

TEN

AN

CES

10

CLEANOUT

A clean out is an inclined pipe which is connected to the underground

sewer. The other end of the clean out pipe is brought up to ground level

& cover is placed at ground level. A clean out is generally provided at the

upper ends of lateral sewers in place of manholes.

The working of a clean out is simple. The cover is taken out and the water

is forced through clean out pipe to the lateral sewers to remove the

obstacles in the sewer lines. If the obstructions are large enough, a

flexible rod may be inserted through the clean out pipe and pushed

backward and forwarded to remove such obstacles.

SEW

ER A

PP

UR

TEN

AN

CES

11

SEWER VENTILATORS

Various gases are produced in the sewers due to decomposition of

organic materials of sewage. These gases are foul in nature, cause harm

to human health and corrode the sewers reducing their life. The gases so

produced are highly explosive and in high concentration may cause fatal

accidents to the maintenance people on duty due to their explosive and

poisonous characters.

Due to the above difficulties, ventilation is provided to the sewers lines at

every 80-100 meters which will provide fresh air to the workers working

in the manholes. It may be of RCC or cast iron 15 to 23 cm in diameter

with a cowl provided at the top. The ventilating shaft is generally

connected to the manholes by 15 cm in diameter pipe. In open areas, the

manhole covers may provide with vent pipes, but in crowed areas they

should be air tight and connected with ventilating shaft. In modern, well

designed sewerage system, there is no need to provide ventilation on

such elaborate scale considered necessary in the past especially with the

present day to omit intercepting traps in house connections. The

ventilating columns are not necessary where intercepting traps are not

provided. It is necessary however to make provision for the escape of air

to take care of the demands of full flow and also to keep the sewage as

fresh as possible especially in outfall sewers. In storm water this can be

done by providing ventilating manhole covers.

SEW

ER A

PP

UR

TEN

AN

CES

12

STORM WATER INLET/GULLIES/STREET INLET

An inlet is an opening through which storm water and surface wash

flowing along the streets are admitted and conveyed to the storm water

sewer by means of pipe.

The inlets are located or placed by the sides of roads at a distance of about

30 to 60 m. The inlets are so located that the storm water is collected in

a short period and there is no flooding or accumulation of huge quantity

of storm water on the roads. The inlets are connected to nearby manholes

by pipe line. The clear opening should not be more than 25mm. The dia.

of connecting pipe to street to main street sewer should not be less than

200mm. The inlet leads the storm water directly to the sewer and hence,

its design should be made in such a way that the least opportunity is given

for the storm water to stop. The openings of inlet therefore should be of

such pattern that the chances of clogging are brought down to minimum

possible extent. The objects that are cause most of the troubles at the

openings of an inlet are sticks, waste papers, leaves etc. the cleanliness

of footpaths and streets is therefore most essential for the successful and

efficient functioning of inlets.

There are 3 types of inlets –

1) Curb Inlet: These are vertical opening in the road curbs through which storm water flow enters the storm water drains. These are preferred where heavy traffic is anticipated.

2) Gutter Inlets: These are horizontal openings in the gutter which is covered by one or more grating through which storm water is admitted.

3) Combined Inlets: In this, the curb and gutter inlet both are provided to act as a single unit. The gutter inlet is normally placed right in front of the curb inlets.

SEW

ER A

PP

UR

TEN

AN

CES

13

STORM WATER REGULATOR/OVERFLOW DEVICES

The structures constructed to divert part of sewage in case of combined

sewers are known as the storm water regulators and they come into

operation when discharge exceed certain value.

The main object of providing a storm water regulator is to divert the

excess storm water to natural stream or river. The excess sewage will be

mainly composed of storm water and it will therefore be not foul in

nature. It will further result in the decrease in load on the treatment units

or pumping stations.

The following are the three types of storm water regulators-

1) Leaping weir- The term leaping weir is used to indicate the gap or opening in the invert of a combined sewer. The intercepting sewer runs at right angles to the combined sewers. When the discharge is small, the sewage falls directly into the intercepting sewer through the opening. But when a discharge exceeds a certain limit, the excess sewage laps or jumps across the weir and it is carried to natural stream or river. The leaping weir has no moving parts. A grating may be provided at the gap level to prevent the entry of small stones, debris etc. into the intercepting sewer.

2) Overflow weir - In this type of arrangement, the excess sewage is allowed to overflow in the channel made in the manhole. When the quantity of sewage exceeds the capacity of the combined sewer, it overflows and falls into the channels and it is conveyed to the storm water sewer. In order to prevent the escape of floating matter from

SEW

ER A

PP

UR

TEN

AN

CES

14

the combined sewer channel, the adjustable plates, are sometimes provided.

3) Siphon spillway - This arrangement of diverting excess sewage from the combined sewer is the most effective because of following-

a. It works on the principle of siphon action and it operates automatically.

b. The rise of sewage in combined sewer is thus controlled in a better way.

c. It is automatic in functioning and this is the most effective in all other methods.

d. This arrangement has no moving parts and thus low maintenance. However it is likely to be clogged due to narrow passages.

SEW

ER A

PP

UR

TEN

AN

CES

15

INVERTED SIPHON

An inverted siphon is a sewer section which is constructed lower than the

adjacent sewer sections and which runs full under gravity with pressure

greater than the atmosphere. To ensure the self-cleansing velocities for

wide variations in flow the two or more pipes not less than dia. 200mm

are provided so that up to the average flow the pipe is used and when the

flow exceeds the average the balance flow is taken by second or

subsequent pipes. The siphon should not have any sharp bends as it

should be cleaned by self-cleansing velocity (It is necessary to have the

self-cleansing velocity 1.0m/s for minimum flow to avoid the deposition

in the line).

Inlet and outlet chamber- The inlet and outlet chambers should allow the

sufficient room for entry and maintenance of siphon. The outlet chamber

is so designed so that to prevent the backflow of sewage into the pipes

which are not used at a time of minimum flow.As the inverted siphon is

pipe under pressure, a difference in the level at the inlet and outlet is the

head under which the siphon operates. This head should be sufficient to

cover the entry, exit and frictional losses in the pipes.

In the multiple pipe siphon, the inlet should be such that the pipes come into action successively as the flow increases. This may be achieved by providing lateral weirs with heights kept in accordance with the depth of flow at which one or more siphon pipes functions.

In two pipe siphon, the first pipe should take 1.25 to 1.5 times the average flow and second should take the balance of the flow.

The main purpose of

installation of inverted

siphons is to carry the sewer

line below obstructions such

as ground depression,

streams, rivers, railway etc.

SEW

ER A

PP

UR

TEN

AN

CES

16

FLUSHING TANKS

A flushing tank is a device or an arrangement which is made to hold and

then to through water into the sewer for the purpose of flushing it where

it is not possible to obtain self-cleansing velocities due to flatness of

gradient especially at the top ends of branch sewers which receive very

little flow.

It is essential that some form of flushing device be incorporated in the

system. This can be done by making grooves at intervals of 45 to 50 m in

main drains in which wooden planks are inserted and water allowed to

head up and which will rush on with great velocity when planks are

removed. Alternately, an overhead tank is built from which a connections

are made through pipes and flushing hydrants to rush water to the

sewers. The flushing can be conveniently accomplished by the use of a

fire hydrant or tanker & hose. The flushing manholes are provided, they

are located generally at the head of the sewers. Sufficient velocity shall

be imparted in the sewer to wash away the deposited solids.

There are two types-

1. Hand operated flushing tank. | 2. Automatic flushing tank.

The automatic systems which are operated by mechanical units get often

corroded by the sewer gases and do not generally functions satisfactory

and hence not recommended. In case of hard blockage in sewers, care

should be taken to ensure that there is no possibility of backflow of

sewage into the water supply mains. The water required for the working

of flushing tanks are untreated. There is no need of treated water.

SEW

ER A

PP

UR

TEN

AN

CES

17

VALVES, FLAP GATES AND FLOOD GATES

Control of the flow in sewers can be regulated by means of automatic

mechanical regulators. These are actuated by the water level in the sump

interconnected to the sewers. These regulators involve moving parts

which are actuated by the varying depths of flow in the sewers. They

required periodic maintenances and inspection.

Flap gates or backwater gates are installed at or near sewer outlets to

prevent backflow of water during the or at high stages in the receiving

stream. Such gates should be designed so that the flap should open at a

very small head differential. With a properly operated flap gate it is

possible to continue to pump a quantity equivalent to the sanitary sewage

flow from the combined sewer to the treatment plant even though flood

conditions prevail in the stream at the sewer outlet. Many flap or back

water gates are rectangular and may consist of wooden plank. Circular or

rectangular metallic gates are commercially available. Flat gates may be

of various metals or alloys as require. Flap gates are usually hinged by a

link type arrangement that makes it possible for the gate shutter to get

seated more firmly. Hinge pins, linkage and links should be of corrosion

resistance material. The maintenance of the flap gates requires regular

inspection and removal of debris from the pipe and outlet chamber.

Lubrication of hinge pins and cleaning also it requires.

SEW

ER A

PP

UR

TEN

AN

CES

18

SEPTIC TANK

A septic tank is a watertight tank which is designed to slow down the

movement of raw sewage and wastes passing through so that solids can

separate or settle and be broken down by liquefaction and anaerobic

bacterial action. It does not purify the sewage, eliminate odours or

destroy all solid matter. It conditions the sewage so that it can be

disposed off to a surface leaching system or to an artificial sand filter

without prematurely clogging the system.

The effluent, although clarified to some extent, will still contain

considerable amount of dissolved and suspended putrescible organic

solids and viable pathogens, and therefore the disposal of the effluent

merits careful consideration. Because of the unsatisfactory quality of the

effluent and also difficulty of providing a proper disposal system for the

effluent, septic tanks are recommended only for small communities and

institutions whose contributory population does not exceed 300. For

larger communities, provision of septic tanks should be avoided as far as

possible. For the septic tanks to function satisfactorily, a fairly adequate

water supply is a pre-requisite. Wastes containing detergents and

disinfectants are not suited for treatment in septic tanks as they adversely

affect the anaerobic decomposition.

Usually rectangular tanks with 2 to 4 aspect ratio . Minimum width is 750

mm, minimum depth is 1000 mm and minimum capacity is 1000 L. HRT is

24 to 48 hours for average daily flow. Septic tank is compartmentalized

(has two or more compartments) when size is >2000L. 1st chamber is

twice the size of the second chamber. The two chambers are connected

by 100-150 mm size openings at 300 mm below the top water level.

Inlets- Inlet introduces raw sewage into the septic tank without disturbing the settled sludge and the floating scum . One or more T shaped dip pipes of diameter larger than the incoming sewer with top limb rising above scum layer and bottom limb extending about 300 mm below the water level are used as the inlets. In case of larger septic tanks (>1200 mm width), submerged bends are used as inlets. A small

SEW

ER A

PP

UR

TEN

AN

CES

19

benched chamber with invert level 58 mm above the top water level receives sewage and delivers into the submerged bends at the bottom. The submerged bend opens into the tank at >75mm below the water level – invert level of the bend is 300-325 mm below the water level. A baffle extending 150 mm below the invert level of the inlet and 150 mm above the water level is provided at 150 mm distance from the inlet end

Outlets - Outlet withdraws the sub-surface clarified sewage from the septic tank without disturbing the settled sludge and the floating scum and while maintaining constant water level within the tank. A T- shaped dip pipe with top limb rising above scum layer and bottom limb extending to 1/3rd of the liquid depth below the liquid level is used as the outlet. Invert level of the outlet is 50 mm below that of the inlet. In case of larger septic tanks (>1200 mm width), a weir outlet extending full width is used as the outlet. Outlet is protected by a scum board extending by 150 mm above the weir and by 1/3rd liquid depth to the surface water level. A deflector protruding by 150 mm is provided at 150 mm below the scum board base. Submerged bends are used as inlets.

SEW

ER A

PP

UR

TEN

AN

CES

20

REFERENCES

1. Water supply and sanitary engineering by G.S. Birdie ,1996 , Dhanpat rai & sons

2. Water supply and sanitary engineering by- Rangwala ,2015 , Charotar &sons publication

3. Manual on sewerage and sewage treatment. Second edition

4. National building code , 2005

5. Indian standards