CE 271: Building Services I: Plumbing
CE 271
Building Services I
Course Teacher: Dr. Rowshan Mamtaz
• 2 Credits (2 hrs/wk)
• Course Content:
Introduction to plumbing, water requirements,
water sources;
Water supply and distribution in buildings;
Sewage and sewer system, building sewer and
drainage system, sewage disposal;
Plumbing of multi-storeyed buildings;
Rural sanitation programmes in Bangladesh
Objectives of the Course
• Reference Books:
– Plumbing Practices by Syed Azizul Haq
– Elements of Environmental Engineering by K.N.
Duggal
– Sewerage Engineering & Environmental Sanitation
by M.A. Aziz
– Environmental Technologies in Architecture by
Bertram Y Kinzey and Howard M Sharp
On completion of this course the students will
be able to:
• know the system of water supply and
wastewater discharge in a building
• understand the plumbing system of single and
multistorey buildings
• know the rural sanitation system of
Bangladesh
What is Plumbing?
Plumbing System
• The word Plumbing comes from the Latin word
“Plum” means lead as pipes were once made
from lead
• It is the art and science of creating and
maintaining sanitary conditions in building used
by humans.
• It is the art and science of installing, repairingand
servicing the pipes, fixtures, appurtenances
necessary for bringing in water supply and
removing liquid and water borne wastes.
• Refers to a system of pipes and fixtures installed
in a building for the distribution of potablewater
and the removal of water borne wastes
• Includes all potable water supply and distribution
pipes; all plumbing fixtures and traps; all sanitary
and storm drainage system; vent pipes, roof
drains, leaders, downspouts; all building drains
and sewers including their respective joints and
connections, devices, receptacles and
appurtenances within the property; water linesin
the premises; potable, tap, hot and chilled water
pipes etc.
Plumbing System
Plumbing system
• Two main components of a building’s
plumbing system:
– Water supply
– Sanitary drainage
Supply pipe
Fixtures
Drainage
pipe
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History of Plumbing
History of Plumbing
• Copper pipes used in water supply was first
discovered in ancient palace ruins in Indus
valley which is about 5500 years old.
• Around 2500 years BC, Egyptians used copper
pipes in their irrigation and sewerage system
• Romans were (500 BC – 450 AD) very
advanced in the field of water supply and
sanitation. They built Aquaduct to convey
water from source to houses. Bath houses is
another mentionable example.
History of Plumbing
• In 1500 AD, a type of water closet was
developed
• Septic tank was introduced in mid 1800’s.
• Modern sewerage system had begun
operating in London in 1860.
History of Plumbing
Indus Valley Drainage System
Water Fountain at Al-Hamra Palace,
Granada
Roman Bath House
History of Plumbing
Roman Lead Pipe
Al Jeba at Granada
Water Supply System in a building
• Water source
Water Supply System in a building
• Water sources
– Public system with water main
– Private well
– Harvesting rainwater
Water Cycle
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Water Supply
• House water connection
Water requirements in a bldg
• Water quality
• Water quantity
Water supply requirements
• Adequate quantity
• Adequate pressure
Water requirements for domestic use
• Socio economic status
• Type of habitants
• Population
• Public facilities
House water connection
• Water main --- supply pipe installed and
maintained by a public entity and on a public
property
• Water service pipe --- from the water main to
the building supply pipe
• Water meter --- measures the amount of
water transported through the service pipe
• Valve --- a fitting used to control water flow
(next to the meter)
• Water Quality
– wholesome/potable water
– should satisfy Drinking water quality standard of
Bangladesh (ECR 1997) and WHO Standard
Water requirements
• Water Demand --- is the rate of flow usually
expressed in gallons per minute (gpm) or litre
per second (lps), furnished by a water supply
system to various type of plumbing fixtures
and water outlets under normal conditions.
Q = p xq
• Socio Economic group (BNBC 2012)
– High Income: monthly income > 1 lacTk
– Middle Income: monthly income > 30,000 – 1 lac
– Low Income: monthly < 20,000
• Type of Habitants/Population(BNBC 2012)
– City corporation areas, big cities: Population> 0.5
million
– Small district towns, Upazillas, urban growth
centres: Population> 0.1 million
– Village areas: Population < 0.5 million
Building Occupancy Classification
– According to BNBC 2012, Building Occupancy is
classified as follows:
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Population estimation
• Actual number of
occupants
• Assume average family
size
• For office bldg
occupancy allow 80 -100
sft of floor space per
person (BNBC 2012)
depending on the type
of occupancy
Water requirements for fire fighting
Direct Supply
Water Supply system in a building
• Direct supply
• Overhead tank supply
• Underground overhead tank supply
• Direct pumping system
Overhead Tank Supply
Water Distribution System in Building
• Up Feed System
• Down Feed System
Underground & Overhead Tank Supply
Design of water supply in Building
• Principles governing the design
– Absolutely no risk of contamination – no cross
connection, no back flow.
– Water supply and drainage pipe should not be laid
very close to each other
– Enough protection for pipe damage
– Adequate pressure should be maintained
Building Drainage System
• A drainage system is a system of piping that
conveys sewage and storm water or other
liquid wastes to an adequate and approved
means of disposal.
– The objective of installing sanitary drainage
system in a building is to provideefficient sanitary
disposal of human excreta, ablutionary
wastewater, laundry and kitchen wastewater etc.
from the fixtures to the public sewer.
Building Drainage system: Terminology and
definition
• Sewage is the liquid waste of a community. The
constituencies are i) domestic wastes (Black
water)which includes human excreta as well as
discharges from kitchens, baths, lavatories etc. from
public/private buildings ii) industrial wastes from
manufacturing processes iii) rainwater from houses,
roads etc.
• Sludge is the solid and semi-solid portion of the
sewage.
• Sullage is the liquid discharges from kitchens, wash
basins and excludes discharges from water closets
and urinals. Sullage is also known as Grey water.
Terms and definition
• Stack is the vertical main of a system of soil, waste or
vent piping.
• Soil stack/pipe is any pipe which conveys the discharge
of water closets or fixtures having similar functions
with or without the discharge from other fixtures to
the building drain or building sewer.
• Waste stack/pipe is a pipe which carries liquid wastes
free from fecal matter.
• Vent stack/pipe is a pipe or system installed to provide
air flow to or from a drainage system or to provide a
circulation of air within such system to protect trap
seals from siphonage and back pressure
• Relief vent is a vent the primary function of which is to
provide circulation of air between drainage and vent
system
Building Drainage System
• Principles governing design of Building Drainage system
– All pipes are to be effectively sized and sloped for effective
and quick removal of foul gases
– The passage of gases, odour and vermin from the sewer
into the building must be prevented by providing a water
seal trap.
– The drainage pipes should be sufficiently strong and
durable to withstand any corrosive action of liquid waste.
They should also be airtight and gas tight
– The pipe joints should be strong and should prevent any
leakage
– The entire network of pipe should have means for cleaning
and removing obstruction
– Any possibility of air locks, siphonage, undue deposits and
obstruction should be prevented
– Piping should be fully ventilated to allow for the removal
of foul gases
Terms and definition
• Sewer is a pipe or conduit, generally closed but temporarily
not flowing full, for carrying sewage.
• Building drain is the part of the lowest piping of a drainage
system which receives the discharge from soil, waste and
other drainage pipes inside the walls of the building and
conveys it to the building sewer beginning 3 ft outside the
building
• House sewer is a pipe conveying the discharge from the
building drain and conveys it to a public sewer, individual
sewage disposal system or other point of disposal.
• Grades of Horizontal House Sewer Drainage pipes should
have a minimum slope of ¼ inch per ft toward the point of
disposal. Where this is not practicable due to depth of a
street sewer or the arrangement of the structural features,
pipes 4 inch or larger dia may have a slope of not less than
1/8 inch per ft should be provided.
Terms and definition
• Back flow is the flow of water or other liquids,
mixtures or substances into the distributing pipes
of a potable supply of water from anysources.
• Back pressure is due to air pressure in drainage
pipes being greater than atmospheric pressure,
with the result that air or wastes from drainage
pipes are forced up through the traps.
• Backflow preventer is a device or means to
prevent back flow in the potable watersupply
• Flushing cistern is a cistern with a discharge
arrangement for flushing water closet, urinals etc.
Traps
• Traps are fittings placed in drainage pipes, which prevent the
passage of foul air or gases through drains, waste or soil pipes and
thus prevent their entry into the interior of the houses or
buildings. This is possible because traps are equipped with water
seals having a minimum depth of 25 mm.
Trap Seal is the maximum vertical depth of
liquid that a trap will retain, measured between
the crown weir and the top of the dip of the trap
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Trap
• Quality of a good trap:
– Non absorbent having water seal at all times
– Smooth
– Provided with suitable access for cleaning
Type of Trap: Floor Trap
• Floor trap is used to admit sullage from the
floor of rooms, bathroom, kitchen into the
sullage pipe.
Types of Traps
• According to shape
• According to use
– P Trap exits into the wall behind
the sink
– Q Trap is used in toilet under
WC
– Floor trap
– Gully Trap
– Intercepting Trap
– S Trap is used in siphonage pipe
Type of Trap: Gully Trap
• A gully trap is provided outside the building before
connecting to external sewerage line. It also collects
waste water from the kitchen sink, wash basins, baths
and wash area. It has deep water seal of minimum 50
mm depth and it also prevents entry of bugs and
insects from sewer line to waste water pipes.
Type of Trap: Intercepting Trap
• This trap is provided at the last manhole of
building sewerage to prevent entry of foul gases
from public sewer to building sewer. It has a deepwater seal of 100 mm
Loss of Trap Seal
Loss of trap Seal
• Cause
– Evaporation
– Capillary action
– Leakage
– Compression
– Induced siphonage
– Back siphonage
• Effect
– If a trap seal loss, smell from the sanitary appliances
enter into the building.
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Loss of Trap Seal
Planning Toilet System
– Toilets should be grouped in an orderly manner
– Allow easy and direct connections from fixtures to vertical
stacks or manholes
– Outlet pipes from WC or floor traps should not be buried in
sunken floors.
– They should run exposed or laid at the ceiling of the lower
floors except the ground floor
– Allow easy repair and maintenance without breaking the
walls
Pipes in Sunken Slab
• Sunken floors are necessary
for installation of Indian
type squatting WC
• Alternatively the floor can
be raised by as much as 40 0
mm requiring at least two
steps which may be
inconvenient for old, infirm
and the children
• It is good to avoid traps in
sunken slabs and install
them exposed in the ceilin g
of the lower floor to avoid
structural and water
proofing problems
• Pipes and fittings
– Pipes should be straight, smooth, uniform, easy to cut and
join
– Pipe fittings must have the same diameter as that of the
main pipe
– All branches, bends and connections should be rounded
and smooth at junctions
• Roles of Atmospheric pressure
– Vent pipes expel foul air and odours into the atmosphere
and draws air when required and thus keep the drainage
system in a state of equilibrium
– Self-siphonage: when fixtures about 2 – 2.5m away from
the stack of manhole are flushed, they induce a negative
pressure in the pipe preceding the flow. This occurs in
horizontal connections, vertical stacks or when large
volumes of water are discharged in a fixture or trap, which
is known as Self-siphonage.
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• Anti Siphonage pipe (ASP): when fixtures are connected one or top
of other as in tall buildings, high rate of flow from WCs from upper
floors may induce negative pressure and induce siphonage when the
flow passes the fixtures in lower floors resulting in loss of trap seal.
This can be prevented by connecting the crown of a trap to a
separate stack which terminates at roof level. Traps of all floors are
connected to this pipe. This stack is called Anti Siphonage pipe. It
provides access to atmospheric air eliminating the possibility of
generating negative pressure thereby maintaining hydraulic
equilibrium in the system.
• Induced siphonage: The negative pressure in the pipe immediately
after a connection from the trap will induce contents to be forced
down into the pipe due to higher atmospheric pressure above the
trap. This is a siphonic action caused by the air pressure imbalance
in the system unsealing the trap. It is known as induced siphonage.
This condition can be eliminated by connecting the crown of traps
to a separate vertical stack known as Anti Siphonage Pipe (ASP). It
provides access to atmospheric pressure preventing the above
conditions.
• Elements:
Building Drainage System: Soil and Waste
Pipe System above grounds
• Two Pipe System
• One Pipe System
• Single Stack system
• Partially ventilated Single Stack system
Two Pipe system
– Soil pipe
– Waste pipe
– Vent Pipe
Advantages of Two pipe system:
– Ensures segregation of the foul sewage from waste water
– No danger of back flow of sewage into waste fittings in
case of blockage of soil pipe
– Separate waste stack permits arrest of solids from kitchen
in gulley traps thus preventing from entering the sewer
– Reduce waste load for septic tank where there is no public
sewer
Two pipe system
• Disadvantages
– Difficult to install in high rise buildings where the
vertical stacks terminate in a service floor or in the
ceiling of a basement
– Long external horizontal runs are required to
reach external walls and lines connected to the
sewer. Provision of gulley trap becomes difficult
– Requires more space
– Costly system
– Installation of more pipes needs more joints. So
probability of leakage through joints increases
One Pipe System
Soil and waste
Fittings are discharged
Into a common stack with
Addition of trap ventilation
pipes.
One pipe system
• Advantages
– Now widely used in modern multistoried building
– High quality of pipes, fittings and installation
techniques ensures reduction of blockage
problem
– Requires lesser space in pipe shafts andducts
• Disadvantages
– Costlier than single stack system
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Single stack system
• All fixtures discharge
directly into a
common stack known
as Single stack.
• Should not be
installed in buildings
more than six stories
Single stack system
• Advantages of single stack system
– Simplicity in lay out, design, plumbing of the sanitary
fixtures
– Improved external appearances
– More compact system
• Disadvantages
– Air and waste from drainage pipes may be forced up
through traps by back pressure due to blockage or bad
design
– Water in the seal may be evaporated in dry season or
in absence of flushing for a long time
– Self siphonage due to sudden discharge from
appliance sucking away its own trap seal, due to
discharge of another appliance in the system.
Partially ventilated single stack system
Flushing Cistern
• Improved form of
single stack system
• Traps of WC are
separately
ventilated by relief
vent pipe.
• Sullage fixtures are
not connected to
the vent pipe.
• Less costly
Flushing Cistern
• Flushing cistern is installed to flush WCand
Urinal.
• It is made of cast iron, glazed earthen ware or
vitreous china or plastic.
• For Indian WC, cistern are made of cast ironand
fixed at a ht of about 1.75 m above the pan.
• For European WC, cisterns are made of vitreous
china or plastic and are fixed at about 30 cm from
top of the WC.
Provision for disabled people
WC Stall for disabled person (BNBC,2012)
Building Drainage: Connection from vertical stacks
Provision for Ambulant Disabled Person
WC Stall for ambulant disabled person (BNBC,2012
• All fixtures and pipes from vertical stacks must
be connected to building sewer
• In two pipe system waste stacks are
terminated and discharged over a gulley trap.
Soil pipes and waste pipes are connected to
the building sewer separately
• Soil and waste pipe in one pipe system and
single stack are connected directly to the
building sewer.
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Manhole
Manhole is a masonry chamber constructed at
suitable interval along sewer line.
Manholes
• Functions
– Serve as junctions to join one or more sewer lines
– Offer means of access to inspect and clear lines of
any accumulation or stoppages that may occur
• Locations of manholes
– At every grade
– At each junction in direction of sewer
– At every junction of two or more sewer
Pipes for Drainage
• The following points should be kept in view:
Pipes for drainage
• Following sizes of drainage pipes are commonly employed:
– All soil, waste and vent stacks may be conveniently
grouped in shafts or ducts of sufficient capacity. This is to
perform repair work and inspection.
– Pipes should be adequately protected during the
construction of building by housing sleeves or pipes in
suitable positions in walls or floors through which pipes
have to be laid.
– Pipes which not embedded should run clear of the wall
with a minimum clearance of 5 cm.
– Waste pipes should be separated from the house drain by
means of gully trap to prevent entry of foul air or gas,
vermin etc. into the building
– Soil, waste and vent stacks should be vertically carried
above the top of the building and should be suitably
covered on top by copper or galvanized iron wire domes to
prevent nesting of birds or inadvertent falling in of objects
inside the pipe
Rainwater Drainage System
• Amount and rate of rainfall or Rainfall
Intensity (I)
Rainwater drainage system
• According to US Plumbing code, 180 sft of roof area is
equivalent to one fixture unit (FU) when the rate of rainfall is
4 inch/hr. (Book Aziz)
• One 4 inch dia pipe can take care of 4 Fixture unit (1 FU = 7.5
gpm = 1 cfm)
• Area of catchment (A)
• Runoff coefficient (C)
Problem # Determine the number of rainwater pipe for a roof
area of 5184 sft. The intensity of rainfall is 4 inch/hr
Q = CIA
Sol: Amount of rain water = [5184X (4/12)]/60
= 28.8 cfm =29 FU
No. of 4 inch dia pipe reqd. to drain
out rainwater = 29/4 = 7.25 = 8
Sizing of Drainage Pipes
On site Sewage Disposal system: Septic Tank
• Building drains and sewers
• Horizontal Branches and Drains
• Size and lengths of vents
• Size of vertical leaders
• Size of gutters
• A septic tank is a buried, watertight receptacle
designed and constructed to receive
wastewater from a home.
• Its purposes are to separate the solids from
liquids, to provide limited digestion of organic
matter, to store solids and to allow the
clarified liquid to discharge for further
treatment and disposal.
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Septic Tank
• Processes in a Septic tank
– Separation of suspended solids
– Digestion of sludge and scum
– Stabilization of the liquids
– Growth of micro organisms
Processes in a septic tank
1. Separation of suspended solids and scum: Results in
Processes in a septic tank
the formation of
– A sludge layer at the bottom
– A floating layer of scum at the top
– A relatively clear layer of liquid in the middle
2. Digestion/decomposition of sludge and scum:
anaerobic bacteria decomposes organic matter in
sludge and scum and produces volatile acids,
methane
The formation of gases in the sludge layer causes
irregular floatation of sludge flocs that settle after
the release of gas at the surface
3. Stabilization of liquid:
Organic materialsin the liquid are also stabilized by
anaerobic decomposition
Processes in a septic tank
4. Growth of Micro organism
A large variety of microorganisms grow, reproduce and die
during biodegradation processes in the tank. Most of them
are separated out (by settling) with solids. However a large
number of microorganisms (bacteria, viruses, protozoa,
helminthis) survive the processes in the tank and remain in
the effluent, the sludge and scum.
Different Zones of a Septic Tank
• Design of a septic tank
– Scum storage zone
– Sedimentation zone
– Sludge digestion zone
– Digested sludge storage zone
Rural sanitation programs in
Bangladesh
• Sanitation may be defined as the science and
practice of effecting healthful and hygienic
conditions and involves the study and use of
hygienic measures such as
– Safe reliable water supply
– Proper drainage of wastewater
– Proper disposal of human waste
– Proper disposal of solid waste
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• Objectives
– To improve public health
– To minimize environmental pollution
Sanitation scenario in Bangladesh
• Relatively low priority over the last decades
compared to other development sectors
• Technological innovations are slow in fulfilling
the various needs of the people and in facing
the growing socio-economic and
hydrogeological challenges
Low Cost Rural Sanitation Technologies in
Bangladesh
• National sanitation coverage
43%
• Urban sanitation coverage
61%
• Rural sanitation coverage
41%
• Coverage by simple pit latrines 30%
• Pit latrine
• Ventilated Improved Pit latrine
• Pour flush latrine
• Twin Pit Pour flush latrine
• Unhygienic hanging latrine users
– Rural
– Urban slums
38%
86%
Pit latrine
• Simplest of all on-site disposal system
• Consists of a pit with a platform having a
defecation hole
• Excreta fall into the pit through squat hole
Pit latrine
• General design consideration
– The pit should be as large as possible, however it
should not be more than 1.5m wide, otherwise
construction cover slab will be more expensive
– soils with permeability below 2.5 mm/hr are
unsuitable for pit latrines, as the liquid fraction of
excreta is unable to infiltrate into soil
– Pits in unstable soils should be fully lined,
otherwise the pit will collapse and the
superstructure may fall into it
– Safe distance between pit and tube wells or any
other water bodies should be at least 10.0m
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Design of Pit latrine
• Effective Pit volume
V = C x P xN
Where,
V = Effective volume of the pit
C = Solids accumulation rate
P = Number of persons will beusing
the latrine and
N = Design life in years
Pit Latrine
• Effective Pit volume: V = (πd2/4)h
Where
d = diameter of pit
h = effective depth of pit
Maximum dia, d = 1.5 m
Total depth = Effective depth, h + free space 0.5m
For dry pits, C varies from 0.03 to 0.06 m3/person/yr and for
wet pits, C varies from 0.02 to 0.04 m3/person/yr.
Design of Pit Latrine
• Local Authority in a village is offering pre-cast
concrete rings of 1.0 m diameter and 0.3 m depth
and concrete slab to cover it at a subsidized price.
Design a pit latrine for a family of 7 with maximum
design life. The soil is unconsolidated, loose and the
groundwater table is 5.0 m below ground surface
Solution#
Considering groundwater table, max. permissible depth
of pit = (5-2) = 3.0 m
Considering manual excavation, max. practical depth of
pit = 6 ring = 6x0.3 m = 1.8m
Pit latrine
• Advantages
– Least costly and structurally safer
– Easy construction and maintenance
– Free from the risk of fallinga child into it and
suitable for children
– Prevents hookworm transmission
Design of Pit latrine
Hence, total design depth of pit, H = 1.8 m
Total no. of rings = 1.8/ 0.3 = 6
Effective depth of pit = 1.8 m - 0.5 m = 1.3m
Effective volume of pit, V = (πd2/4)h
= (πx(1.0m)2 /4) x 1.3 m
= 1.021m3
Now V = CPN = 0.06 x 7 x N = 1.021
N = 2.4 yrs
Pour Flush Latrine
• Improvement to the pit latrine with a water seal.
• Water seal is a u pipe filled with water, attached
below the squatting pan that prevents passage of
flies and odors.
• Disadvantages
– Flies lay their eggs in feces within poorly built
latrines and causing the risk of spreading diseases
from fecal pathogens
Twin Pit Pour Flush Latrine
• Consists of a squatting pan, two pits and a Yjunction
• At least 20 mm water seal to prevent passage of gas
and insects from pits
Design consideration of a Pour Flush Latrine
• Shape of pits can be circular, square or rectangular
• Minimum water requirements is 1.5 – 2.0 litre for flushing the
toilets
• For ease of emptying and avoiding groundwater pollution, pit
should not exceed 1.8 m in depth.
• Pits may be lined with burnt clay, concrete, brick masonry or even
bamboo
• The inlet into the pit should be at least 0.5 m above the highest
groundwater level
• A 0.5 m free space should be kept above the inlet
• Bottom of pit should be undisturbed and unsealed
• Safe distance between pit and tube wells should be at least 10.0 m
• Permeability of surrounding soil is an important factor
• Distance between two pits for twin pit latrines should be at least
equal to the effective depth of pits
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Pour flush latrine
Design of Pour Flush Latrine
• For single pit pour flush latrine
Effective volume V = VS + Vi
VS = C x P x N
Where,
Vi = (πd2/4)h
The side wall area reqd. for infiltration A i= Q/I
Where Q = Wastewater flow, l/d and I = Infiltration
rate
Ht of the side wall area h = Ai / πd
Vi = Ai d/4
Vi = Q d/4I
Pour Flush Latrine
• Disadvantages
– Water must be available throughout theyear
– Water seal may be clogged if garbage is thrown
into
– Construction is difficult and expensive in areas
with high groundwater and shallow soil overlying
hard rock
– Risk of polluting nearby water sources
– Construction and maintenance of twin pit pour
flush latrine is relatively difficult
• Advantages
– Less expensive compared to conventional systems
(sewerage systems)
– Offers hygienic solution for excreta disposal
– Requires low volume of water (1-3 l/flush)
– Can be upgraded to connect to a sewer or septic tank
system
– Eliminates odor, insect, flies breeding
– Safe for children
– Easy construction & maintenance
– Twin pit can serve as a permanent structure because of its
pits are used alternately
– Potential for resource recovery using the sludge as soil
conditioner
Small Bore Sewerage (SBS)
System
• Major elements of SBS System
– Septic tanks
– Small bore sewer reticulation
– Treatment plant
Design of Septic Tank
• Design a septic tank for a household of 8 family members. The water use
is 200 l/p/d and temperature is ≥25 0C. The liquid detention time is 1 day,
sludge accumulation rate is 40 l/p/yr and desludging frequency is 3 years.
Sol# Volume of Septic Tank, V = Vs + Vl = NSP + twQP
Given data: P = 8
N = 3 years
q = 200l/p/d
tw = 1 day
Sludge accumulation rate, S = 40 l/p/yr
V = 3x40x8 + 1x90% of qx8 = 960 + 1x0.9x200x8 = 2400 l =2.4 m 3
Assume Depth of Septic Tank, D = 1.5 m
For a two chambered septic tank, V = LxWxD
V = 1.5x(2W+W)xW
2.4 = 4.5 W2, W = 0.73 m, L= 2w+w= 3x0.73= 2.19 m
Freeboard 0.3 m, Total Depth = 1.5 + 0.3 = 1.8 m
Dimension of the tank: 2.19m x 0.73m x 1.8m
Design of Septic Tank
Design of Septic Tank
• A 10 person household discharges about 200 l/p of wastewater/day. The
owner chooses to treat only black water in a septic tank. Design the
septic tank using the follwing data: liquid detention time is 1 day, sludge
accumulation rate is 40 l/p/yr and desludging frequency is 3 years.
Sol# Volume of Septic Tank, V = Vs + Vl = NSP + twQP
Given data: P = 10
N = 5 years
Q = 35% of 200 = 70 l/p/d
tw = 1 day
Sludge accumulation rate, S = 40 l/p/yr
V = 5x40x10 + 1x70x8 = 2000 + 560 = 2560 l =2.56 m 3
Assume Depth of Septic Tank, D = 1.5 m
For a two chambered septic tank, V = LxWxD
V = 1.5x(2W+W)xW
2.4 = 4.5 W2, W = 0.75 m, L= 2W+W= 3x0.75= 2.25 m
Freeboard 0.3 m, Total Depth = 1.5 + 0.3 = 1.8 m
Dimension of the tank: 2.25m x 0.75m x 1.8m
Typical Two Chambered Septic Tank
• According to BNBC, septic tank shall have a
minimum liquid capacity of 2000 litre,
minimum width 1 m and minimum liquid
depth 1 m. The length of septic tank shall be
at least twice its width and shall not be more
than 4 times of its width.
• The maximum size of septic tank shall be
limited to the number of users not exceeding
300 persons for residential building and 1000
persons for others.
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Design of Water Distribution system in a building
Septic Tank Design
• Wastewater flow is 60-70% of water
consumption
• In absence of data, WW flow: 120 lpcd for
Cities, 50 lpcd for district town and 20 lpcd for
thanas and rural areas
Design of Pump
Design of Underground Tank
• Calculate total daily demand for the building
• Water is stored in underground water reservoir with extra
one day reserve for emergency requirements
• Capacity of UGWR(V) = 2 x Total daily demand of water
(m3)
• UGWR is usually provided below stair case. So the surface
area (A) of the tank depends on the area available below
stair case
• Water depth in tank H1= V/A
• Use a thumb rule - 10:1
• Total height = H1 + Free board (6 -12 inch)
Design of Riser
• Total length of riser (L)
= total building ht (10 ft per floor) + 10’ from UGWR + OH tank
inlet height above top roof
• Total Frictional head HL
= (hL * L)/100 + 8 psi required pressure at the O/H tank + 5
psi minor loss due to bends
•
Frictional Head = HL *144 /62.2 (ft)
• Total Head, H = Static head + Velocity head + Friction head
Pump capacity = HQ/(3960 E).
Assume E = 60-65%
Design of Riser
• Total amount of water carried by the riser
each time of pumping to OH tank
= total daily demand (gpd) /
pumping frequency
• Assume velocity = 8-10 fps
• Using Nomograph, determine pipe size
(d) and head loss (hL) (psi/100 ft)
Design of Rooftop Tank
Design of Water supply pipes in a Building
• Required volume for water storage,
V = Daily water requirement (V1)+ Water for fire-fighting (V2)
•Assume 1 hr pumping twice daily,
V1 = Total Daily Demand (m3)/2
At least 30 mins for fire-fighting water should be stored in the
tank, so
V2 = fire-fighting rate (m3/min) * 30 min (For Light-hazard
building-I, Fire-fighting water flow rate: 1000 l/min)
Therefore capacity of the tank = V1 + V2
• Total tank height = water depth + freeboard (10” - 12’’)
To provide sufficient pressure, the bottom of the tank
must be elevated sufficiently above the top floor
water fixtures.
15
Sizing of Water Distribution Pipes in a Building
Sizing of Water Distribution Pipes in a Building
• The design of water supply pipe to the fixtures is
based on:
a) the number and kind of fixtures installed;
b) the fixture unit flow rate; and
c) the probable simultaneous use of these
fixtures.
• The fixture units for different sanitary
appliances or groups of appliances are given in
the following Table (BNBC, 2012)
Sizing of Water Supply Pipe: Hunter Curve
Sizing of Water Supply Pipes in a Building
Steps:
• Compute demand weight i.e., total fixture unit value
(wsfu) of different fixtures
• Calculate Peak Water Demand using Hunter Curve
• Determine equivalent length (sum of pipe length,
bends and branch length)
• Pressure at fixture: Maximum 50 psi and minimum8
psi
• Check with average available pressure drop
Design of Pipes
Design of Drainage Pipes
• Drainage Fixture Unit (DFU): A relative measure
of the drain wastewater flow or load by various
plumbing fixtures into the drainage system.
• According to Uniform Plumbing Code UPC 2006,
The drainage fixture-unit value for a particular
fixture depends on its volume rate of drainage
discharge, on the time duration of a single
drainage operation and on the average time
between successive operations.
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25-Sep-22
17
DFU
Type of Fixtures
DFU Value as Load Factors
Flush Tank WC (One bathroom group consisting of
WC, WB, BATH TUB and shower stall)
3
Design of Drainage system in a building
Flush Valve WC (One bathroom group consisting
of WC, WB, BATH TUB and shower stall)
6
1. Design
Bathtub
2
Bidet
2
Combination sink and tray
Drinking fountain
2
0.5
Floor trap
1
KS
2
WB
2
Shower stall
2
Urinal
4
WC Water Tank
3
WC flush valve
6
“Two pipe drainage system “.
2. Determination
size of soil pipes/ waste pipes:
To estimate the total load weight (DFU) carried by a soil or waste
pipe, the relative load weight for different kinds of fixtures use Table
8.6.14.
Table 8.6.15 provides an approximate rating of those fixtures not
listed in Table 8.6.14
The maximum number of fixture units that may be connected to a given
size of building sewer, building drain, horizontal branch or vertical
soil or waste stack should be as provided in Tables 8.6.16 and
8.6.17.
Using the load factor unit as obtained in step-1, calculate size of
horizontal branches or vertical soil or waste stack(s) from Table8.6.16
Max. number of fixtures that can be connected to
branches and stacks
Design of Drainage system in a building
Reference of septic tank
• https://www.slideshare.net/VikasVerma16/se
ptic-tank-10112405
• https://www.slideshare.net/jshrikant/septictank-45759365
• http://web.sahra.arizona.edu/education2/wrt
t/lecs/Poe_SepticSysBasics_2.pdf
• http://www2.myoops.org/twocw/jhsph/cours
es/TropicalEnvironmentalHealth/PDFs/Lecture
2.ppt
18