Mains Sewage Systems.
Name: Padraig McMahon
Module: Building services
Definitions.
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Surface water
Run-off of rain water from roofs and any paved surfaces around
the building.
Soil water
Water containing excreted material i.e from W.C. pans
Waste water
Used water from waste appliances i.e sink, bath etc. This
includes washing machines and dish washers.
Foul water
Any water contaminated by soil water or waste water
Definitions.
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Ventilation
To prevent the water seal from being broken by pressures or
suction and to allow the release of gases
Sewage
Mixture of foul and surface water which needs to be removed
from the building
Sewer
Form of drain which collects foul water/sewage from a number
of drains.
Definitions.
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Traps
All points of discharge into a drainage system should be fitted
with a water seal to prevent foul air leaking into the building all
traps not part of a removable appliance should be removable or
fitted with a cleaning eye.
Drain
A below ground pipe or closed channel where water flows by
gravity
Sewerage
A network of sewers that disposes of sewage from a
community, town or city.
Effluent/sewage disposal.
Domestic sewage consists of human wastes, paper and vegetable
matter. This is organic waste because it is made of compounds
of carbon and can be broken down by micro organisms.
Sewerage is a system of under ground pipes used to collect and
carry sewage either to a treatment unit i.e. septic tank or a a
public/ main sewer. The concept of sewage is to pipe waste
mater both solid and liquid away from the building, to allow for
safe treatment and return to the water table.
Types of Waste disposal.
Main types of waste disposal
There are two main types of waste disposal available in Ireland,
septic tanks and sewage systems which under EU law must now
incorporate a treatment works.
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Septic tanks
Septic tanks are mainly used in one off housing in rural areas.
this is the typical system used in the country side.
Sewerage
Sewage systems are used mainly in built up areas such as
villages, towns and cities and is necessary to have a large
number of houses to make such a system viable.
Public Drainage Schemes.
Types of drainage systems.
There are 2 main types of Public drainage schemes, separate
drainage system or combined drainage system.
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Separate drainage system.
Surface water is kept separate from foul water by means of two
separate pipe lines. Surface water remains clean and needs no
treatment.
Higher cost to install but cheaper to run as their is less material
entering the treatment works.
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Combined drainage system
Foul and surface water are mixed and the system uses one large
pipe.
their is a danger especially with heavy rain fall the treatment
plant can get over loaded, plus the previously clean water needs
to be cleaned again at extra cost.
Sewage treatment Plants.
Typical Treatment Processes.
The following are the typical processes involved in sewage
treatment.
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Preliminary treatment (1)
This is done to remove large solids and grit to prevent
blockages further down the line. A system of sedimentation,
mesh filters or equipment such as vortex separators can be
used to do this.
Primary treatment (2)
This uses a system of sedimentation tanks, were the water is
stagnant enough to allow fine sediments to fall out of
suspension by gravity.
Treatment Processes.
Other materials such as oil and grease can form a scum on the
surface of the water and this can be scraped off. These forms of
treatment the bod measurement by up to 40% and suspended
solids by 70%.
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Secondary treatment
This involves exposing the settled sewage to bio chemical
reactions under aerobic conditions. Purified water is then moved
to secondary settlement tanks. The most common methods
used for this are biological filtration and activated sludge.
Treatment Processes.
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Biological filtration
the waste water is trickled through a bed of inert material on
which a bio mass of micro organisms develops and aeration
occurs naturally.
Activated Sludge
Mechanical agitators are used to aerate the mixture and to
encourage the growth of new biomass.
In both cases the bacteria created are able to grow multiply and
purify the sewage, and are later removed in sediment tanks.
Treatment Processes.
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Tertiary treatment
This third stage is used if the effluent has still not reached a
suitable quality. Their are three main methods used to resolve
this 1. Lagoon settlement
2. Irrigation on to land
3. Filtration using sand or gravel.
Sludge treatment
Sludge has two main components, liquid effluent and sludge
solids. Effluent is easily treated but the sludge can cost up to
50% of overall costs to dispose of. It can be incinerated, spread
on the land or placed in land fill.
Natural Rain Water cycle.
The natural rain water cycle will also further purify the water and
remove any remaining waste material.
Pipe Laying and Connections
to Sewer Lines.
Typical aboveground System.
This is an example of
above ground typical
drainage pipes
showing waste and
foul water pipes. Note
the vent and the
gradient on the pipes.
These are all linked to
the sewer system.
Underground Pipe Work.
Layout
1) The lay out should be kept a s simple as possible with
changes in gradient and direction kept to a minimum.
2) Access should be provided only were necessary and
connections should always be made obliquely to the direction
of the flow.
3) The system should be ventilated by a flow of air and
should be at the end of each main drain and to any branch
longer than 6 meters
Underground Pipe Work.
4) Pipes should be laid at an even gradient and any change in
this should have an access point.
5) Pipes should be laid in a straight line and were small bends
occur access should be provided
6) When laying pipes near or under building and in unstable
ground special considerations should be made to allow for
settlement
7)pipes should be bedded in sand, clay or cement were
appropriate.
Simple pipe Layout.
Two simple systems showing combined and separate systems
Combined sewers
Separate sewers
Pipe Laying.
This diagram shows how sight rails
in conjunction with a boning rod
are used to insure an even
gradient while laying out the
trenches.
Bedding for Rigid Pipes.
Bedding for rigid
Pipes.
key
Small stones, sand
and clay.
10 mm Aggregate
with a compaction
factor of 0.2.
•This must be well
compacted and this type
of bedding is necessary
when connecting to a
mains sewer as it is a
rigid pipe.
Bedding of Flexible Pipes.
Bedding for flexible piping
key
Small stones
sand and clay.
Granular fill.
10 mm aggregate
with a compaction
faction of 0.2
•This type of fill is used
mostly around foul water
pipes and general drainage.
General Pipe Materials.
The following are the main types of pipes used in
underground gravity feed systems
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Rigid pipes
Fibber cement
Vitrified clay
Concrete
Flexible pipes
uPVC
uPVC is the most commonly used as it comes in a wide variety of
shapes is easily joined and cut and has a wide variety of fittings.
Jointing of Pipes.
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All joints should be appropriate to the material being used.
To minimise the effects of differential settlement pipes should
have flexible joints and be allowed room for movement were
ever possible
All joints should remain sealed under test conditions and normal
working conditions and their working life.
Nothing in the pipes, their fittings e.t.c should obstruct the flow
of materials and all joints should run obliquely to the direction
of flow.
Joining to a Mains Sewer.
Note the shape of the saddle. The main sewer is cut to
allow the round sleeve to inter and it is then bedded in
mortar to insure a good seal.
Samples of available Fittings.
Samples of Piping.
Plain gulley
Waste water reducer
External gulley
Tapered joint
with flexible
hosing
Samples of Piping.
Connection to a
Toilet. Note the
Allowance for settlement
around the pipe
Man hole junction.
Note the cut section
pipes. This hole will
have a concrete base
uPVC junction box.
Quick and easy to
Install and will be
sat on a concrete
base
Samples of Man Holes.
Precast man hole
with cut section
Pipes.
Close up of a
similar precast man
hole with flexible
pipes.
Precast man
hole used to
change
gradients.
Jointing methods Available.
Joining of Piping.
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Piping must be jointed securely but still allow for flexibility and
settlement.
Pipe work should be tested before it is back filled, using either
smoke, water or air under pressure.
Pipe should be knocked together using waste timber to insure
no damage to the edges.
Different joints are used in different situations but uPVC is the
most common, using simple sleeve joints or rubber seals.
Pipe jointing.
This is an example of a pipe joining to another pipe. Note the
way the branched section is running obliquely to the other
pipe to insure the continued flow of waste material.
Types of Joints.
Access Junctions and Man
Holes.
Clearance of Blockages.
There are four main types of access to remove blockages.
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Roding eyes
These provide access to any pipe in accessible from the trap.
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Access fittings
Small chambers on the pipe but do not have an open chamber.
 Inspection chambers
shallow chambers which allow access for working at ground
level.
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Manholes
Large chambers with working space at drain level.
All covers should be easy to remove and of a suitable strength.
They should be air tight were necessary and secure in position.
Regulations on Access fittings.
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Access fittings
Depth to
invert.
0.6
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A.J
0.6
Internal size
length & width
150 x 100
300 x 100
300 x300
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Shaft
2.7
900 x 840
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Man hole
2.7
1200X750
1200 x 840
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Inspection chamber 1.0
450 x 450
Connection.
Connecting to Main Sewers.
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When connecting to a mains sewer one must make the
necessary applications when applying for planning permission in
individual cases.
In housing estates the builder is responsible for making the
necessary connection.
In both cases their is a fee, which varies from county to county
and permission must be sought before digging for a sewer and
the necessary research should be carried out in relation to
under ground wires e.t.c.
The end