This document discusses various sewer appurtenances including manholes, drop manholes, gully pits, intercepting traps, septic tanks, soak pits, and holding tanks. Manholes provide access for inspection and cleaning of sewers. Drop manholes are used when a branch sewer enters a manhole at a higher level to prevent splashing. Gully pits trap solid waste before it enters drainage systems. Intercepting traps disconnect house drains from sewers to prevent gas/bacteria entry. Septic tanks facilitate anaerobic digestion of sewage. Soak pits allow septic tank effluent to seep into soil. Holding tanks temporarily store effluent before pumping to treatment.

1. Sewer
appurtenances
Presented By
Gayathry Satheesan

2. Sewer appurtenances
 Sewer appurtenances are those structures and devices
of a sewerage system which are constructed at suitable
intervals along a sewer line to assist in the efficient
operation and maintenance of the system.

3. 1. Inlets
2. Catch Basins or Catch Pits
3. Clean-Outs
4. Manholes
5. Drop Manholes
6. Lamp-Holes
7. Flushing Devices
8. Grease and Oil Traps
9. Inverted Siphons
10. Storm Water Regulators.
Important Sewer Appurtenances:

4. Manhole
 A manhole is one approach for inspection and cleaning of sewer.
 These are constructed on sewers at all junctions; change of direction,
gradient, or at intervals of 50 to 150 m depending on the size of the
sewers.
 Lateral connections of service lines with the main sewer are also done
at the manholes.
 Being structurally stronger, the sections of the manholes are generally
circular.

5.  The top of the manholes are provided with C.I. covers of heavy
duty or medium duty or light duty, according to the location of
the manholes.

6. Drop Manhole
 When a branch sewer enters a manhole at a level more than 500-600
mm above the main sewer, the sewage is brought down into the
sewer through a pipe and carried down from the branch sewer to the
bottom of the manhole.
 The sewage is not allowed to drop directly into the manhole from a
height as it would otherwise splash in the manhole causing unwanted
deposits and due to dropping from a height heat would be generated
accelerating decomposition of the sludge in the manhole which, is
not desired.
 Provision of drop manhole reduces the length of the pipe and cost of
excavation.

7. Gully Pit/Trap
 Provision of gully trap is essential in the house drainage system to cut off
the house from the direct communication with the drain, the barrier
being caused by the water seal of the trap which should be at least 75
mm.
 It is provided for reception of waste water from the sinks, baths, basins,
rain water and surface water and pouring into the drainage system.
 These are provided with C.I. grating on top to deliver the waste water
into the gully and exclude the coarser materials

8. Intercepting Trap/Master Trap
 It is also called disconnecting trap. It disconnects the house
drains from the street sewer and is placed in a small chamber
between the lower end of the house drain and the street sewer
with the primary object of preventing the foul gas and
pathogenic bacteria of the public sewer from entering the
house.
 They have a deeper seal not less than 100 mm and have a
‘cleaning eye’ for periodic cleaning of any obstruction.

9. Septic Tank
 Septic tank is horizontal, continuous flow, one storey
sedimentation tank of masonry or concrete through which sewage
is allowed to flow slowly permitting suspended matter to settle at
the bottom, where it is retained until anaerobic decomposition is
established resulting in the change of some of the suspended
organic matter into liquid and gaseous substances and reduction in
the quantity of sludge to be deposited.
 The septic tanks are usually built underground.

10.  The anaerobic bacteria flourish in absence of free oxygen and due
to warmth and those conditions are created in a septic tank.
 The heavier matter settles at the bottom and the lighter matter
forms a layer called ‘scum’ on the top.
 The tanks are made air and water tight.
 The inlet and outlet pipes are bent downwards and their open ends
are kept midway in the water, and the centre of the outlet pipe is
kept generally 50-75 mm below the centre of the inlet pipe.

11.  As a precaution against the disturbance of the scum as well as
sludge, vertical partition wall is built having opening at the lower
portion.
 If the septic tank is long, a second baffle wall may be provided. In
a septic tank the rate of flow of effluent is desired to be equal to
the rate of flow of the influent at all times.

12. Soak Pit/Well
 These are masonry wells of required diameter and about 3,000
mm in depth from the ground level.
 The well is built in dry brickwork for allowing water from the
well to seep in the soil, top 1.0 m being with cement mortar.
 The well is filled up with over-burnt brickbats or cinder.
 The top of the well is covered by R.C.C. slab with a manhole.

13.  The effluent from the septic tank is diverted into the well
through S.W. pipes which trickles through the brickbat filling.
 After a lapse of period when the brickbats are saturated, it seeps
in the soil through the dry brickwork.
 The soak wells require periodic cleaning when the filled
materials are saturated and clogged and the well does not
function properly; the filled materials are taken out through the
manhole, cleaned and dried.

14.  The well wall is then repaired, if found damaged.
 It is then filled again with dry fills as before for normal
function .

15. Cost-Effective Sanitation System
 The health statuses of low-income communities in the rural and
semi-urban areas who cannot afford conventional sanitation
system need some cost-effective alternative system.
 The conventional system of sanitation is capital intensive and in-
house water facility is a pre-requisite for its proper functioning.
 Both of these feature call for alternative cost-effective sanitation
system.

16.  Ventilated Improved Pit latrines and Pour Flush latrine are the
alternatives which can cater the need of the low-income
communities in rural and semi-urban areas.

17. Holding Tank
 These are underground masonry, preferably R.C.C. tanks, where
effluent is collected.
 The tanks are required to be water-tight. The effluent from a
definite area is collected through a sewerage system.
 The effluent is not allowed to be digested in the tank, but is
pumped into an effluent carrying tanker and thrown in a sewerage
system for final disposal or is carried to a sewage treatment plant
or is disposed of to an area meant for the purpose.

18.  This is definitely a safe method as it leaves very little scope for
pollution or contamination; but it requires a considerable size of
holding tank and a whole set of machineries for lifting the effluent
from the underground tank to the tanker and transport to the
disposal site.
 The size of the holding tank becomes quite big as all the volume
of the effluent is to be collected in the tank.

19.  The entire quantity of the effluent shall have to be transported
from the holding tank to the disposal site.
 Prompt and stable lifting and transport arrangement is required as
the effluent is not allowed to be digested in the tank.

20. Sewage Disposal System
 There are various technologies available for sewage treatment and
disposal.
 The technologies are more or less used in consideration of the
nature and pollution level of the sewage.
i. Activated Sludge Process (ASP),
ii. Trickling Filter (TF),
iii. Waste Stabilization Ponds (WSP)

21. iv. Areated Lagoon (AL) and Oxidation ditch.
 ASP and TF are conventional sewage treatment plants and are
associated with highly complex unit processes and operations,
involving high coats; but have comparative less impact on
environment and require less land area.
 WSP, if properly designed and maintained, are the simplest and
least expensive wastewater treatment technology requiring no
external energy and mechanical equipment.

22.  It is very simple and easy to operate, requiring practically no
technical crew.
 WSP achieve higher efficiency in destroying pathogenic organisms
and ova of intestinal parasites. However, WSP require large land
area.
 Areated Lagoon (AL) — This system require some mechanical
equipment and external power, but much less in comparison to ASP
and TP.

23.  The system requires comparatively less land than WSP.
 Selection of a system should be made after assessing impact on
environment, taking into consideration of land requirement, cost of
installation, pollution control, aesthetic aspect and health protection
of different technologies — WSP is considered to be the best, then
comes AL, ASP and TF.
 However, compromise may have to be made when sufficient land is
not available for WSP technology.

24.  The conventional sewage disposal system is by traditional methods
adopted in the sewage treatment plant and is considered to be the best
as it has less chance of contamination and pollution.
 But the systems require elaborate network for collection of sewage
by gravitation or lift pump and then disposal after sewage digestion
and treatment involving large capital outlay and recurring
expenditure for maintenance and operation of the treatment and
disposal plant.

25.  Moreover, in segregated and isolated areas, introduction of
conventional system may not be possible.
 In such cases, any of the alternative systems stated can be adopted in
consideration of the necessity and site condition.

26. Inspection Pit or Chamber
 This is a miniature form of manhole provided in house drainage
system in order to open out the house drainage pipes and to inspect
the condition of the flow, cleaning the obstructions, if any, in the
drain and providing branch connections with the main line or the
house drain.
 This is also provided at every change of direction, or gradient or at
every 30 m intervals or at the point where the vertical soil pipe joins
the house drain

27. Shape of Sewer
 The cross-section of the sewer depends upon efficiency of flow
desired, structural stability, convenience in maintenance and
operation, resistance to internal and external pressure and resistance
to corrosion.
 Usually, circular sections are used; but circular sections are not very
effective in combined system.

28.  The flow in the dry weather condition becomes negligible compared
to the combined flow during rainy season, causing deposition of
solids for low velocity of the flow.
 But when semi-elliptical and U-shaped sewers are used, the cross-
section also goes reducing with the discharge and velocity is not
much altered.
 But such shapes are costlier in construction and, due to narrow base;
distribution of pressure is on a smaller area.

29.  Also, if proper shape is not provided, self- cleansing velocity will not
be obtained, which is essential for efficient functioning of the sewer.

30.  Generating proper velocity for smooth flow in sewer is an important
design criteria.
 Large quantities of organic and inorganic solids are carried with the
sewage.
 The solids remain floating with the velocity of the flow. At lower
velocity, stagnation condition approaches which results in deposition
of the solids on the sewer invert and, thereby, causing obstruction of
the flow and, ultimately, complete chokage of the sewer.
Self-Cleansing Velocity

31.  This state of affair is taken care of by prompt cleaning of the sewer or
by generating increased velocity of the flow which will not allow
deposition of solids. Such velocity is termed self-cleansing velocity.
 This again depends upon the scouring action of the flowing sewage
and the material used for the sewer conduit.
 The self-cleansing velocity required for transport of the solid
particles varies between 4.5 cm/sec minimum to 9.0. cm/sec.
maximum.

32. Ventilation Shaft
 The putrescent organic material in sewer decomposes while it is on
the way to its point of disposal and produces foul smell and
corrosive and explosive mixture of gases in the sewer lines.
 The gases act upon the sewers, reduce their life and carrying
capacity and may cause fatal accidents to the maintenance crew on
duty.
 Ventilating shaft is provided and it is connected with the sewer for
release of the gases.

33. Sewer Joints
 A good sewer joint should satisfy that it is economical, easier to construct,
water-tight, resistant to penetration of tree roots, resistant to sewage gases and
acids, flexible, non-absorbent and durable.
 The various types of joints used in sewage lines are:
a. Bandage joint
b.Spigot and socket,
c. Collar joint and
d. Flush joint.

34. Thank you