introduction to environmental sanitation
TRANSCRIPT
Environmental Engineering II
Zaki Uddin Ahmad
Lecturer
Department of Civil Engineering
University of Information Technology and Sciences
Topics to be Covered:
Classification of Wastes
Definition of Sanitation
Relationship between Sanitation and Health/ Disease
Classification of Sanitation System
Introduction to
Environmental Sanitation
Towards a Sustainable World
Classification of Wastes
Human Waste or Human Excreta: refers to only human feces and
urine. Also known as “night soil” when collected without dilution in
large volumes of water.
Municipal Sewage/ Wastewater: Liquid waste conveyed by sewer
and may include domestic and industrial discharge as well as storm
water, groundwater infiltration and inflow.
Domestic/ Sanitary Sewage: Liquid waste which originates in
sanitary conveniences, e.g. water closets, urinals, baths, sinks, etc.
of dwellings, commercial facilities and institutions in a community.
Sometimes it is also referred to as “Sanitary Sewage”.
Black Water: Wastewater containing human waste (fecal matter,
urine), i.e., toilet wastewater. It contains pathogens and must be
treated before releasing into environment.Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Classification of Wastes (Contd.)
Sullage/ Greywater: Water coming from domestic equipment other than
toilets (e.g., bathtubs, showers, sinks, washing machines). It is often
separated from “Black water” to reduce the amount of water that gets
heavily polluted. Separation of blackwater and greywater nowadays
happens with all ecological/ smart buildings. Greywater could be reused for
different purposes (other than potable use) after primary treatment.
Industrial Waste: Liquid discharges from spent water in different industrial
processes such as manufacturing and food processing.
Storm Water: Surface runoff immediately and after rainfall, which enters
sewers through inlets. Storm water is usually not very polluted, and could
be carried through open drains/ channels and disposed of in rivers/
streams/ small channels.
Solid Waste: Includes all materials which are normally solid and discarded
as useless or unwanted.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation (Definition)
“Sanitation” may be defined as the science and practice of affecting
healthful and hygienic conditions, and involves the study and use
of hygienic measures, such as:
Safe and reliable water supply
Proper disposal of all “human waste”
Proper drainage of wastewater
Prompt removal of all refuse (solid waste)
WHO includes food sanitation, rainwater drainage, solid waste
disposal and atmospheric pollution under sanitation.
However, the term “sanitation” commonly refers to disposal of
“human waste/ wastewater”.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation & Disease (Contd.)
• Proper sanitation can control many “human waste/ excreta”
related diseases.
• Important to have clear understanding of such diseases and their
transmission routes.
• Excreta-related diseases are caused by disease producing micro-
organisms, called pathogens that are excreted by people already
infected with disease.
• Common diseases cause by pathogens include:
Bacteria: Cholera, Bacillary dysentery, typhoid, and para-typhoid.
Viruses: Hepatitis, Poliomyelitis, Diarrhea
Protozoa: Amebic dysentery, Giardiasis
Helminths: Schistosomiasis (bilharzia or snail fever)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation & Disease (Contd.)
Classification of Excreta-Related Diseases:
(1) Excreted Infections (Direct Transmission of Pathogens):
Cholera, Typhoid (also insect vector)
Infected Excreta New InfectionsDirect Transmission
Infected Excreta New Infections
(2) Vector Transmitted Diseases: Schistosomiasis
Vector
Insects (Flies, Mosquitoes);
Cockroach; Rat; Animals
(Cow, Pig); Snail
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation & Disease (Contd.)
Transmission of Excreted Pathogens depends on
Excreted Load (Number of pathogens excreted in the environment
is termed as “excreted load”)
Changes in number of pathogens in the Environment
Changes in number of pathogens during environmental transmission
are governed by three key properties:
Latency (i.e., how long it takes for the pathogens to become
ineffective)
Persistence (i.e., how long pathogens survive in the environment)
Multiplication (i.e., ability of pathogens to multiply)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation & Disease (Contd.)
Category Transmission Features Examples of
infection
Transmission
Focus
1. Non-Bacterial Fecal-
Oral
Diseases
Non-latent
High infectivity
Low to medium persistence
Unable to multiply
No intermediate host
Hepatitis A & E
Diarrhea
Giardiasis
Personal
Domestic
2. Bacterial Fecal-Oral
Diseases
Non-latent
Medium to low infectivity
Medium to high persistence
Able to multiply
No intermediate host
Cholera
Typhoid
Personal
Domestic
Water
Crops
3. Geohelminthiases Latent
Very persistence
Unable to multiply
Very high infectivity
No intermediate host
Hookworm
Ascariasis
Domestic
Field
Crops
4. Excreta-related
insect vector diseases
Infections 1-3
transmitted
mechanically by flies
and cockroaches
Water
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation & Disease (Contd.)
“Fecal-Oral” Transmission Route of Diseases
Water
Hands
Insects/
Flies
Soil
Milk
Food
Vegetables
New
HostExcreta
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation & Disease (Contd.)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Figure: Disease Transmission and Sanitation
Sanitation & Disease (Contd.)Interrelationship among Water, Sanitation, Hygiene Education and Health
The importance of health education in
improving health has been clearly
demonstrated in water supply and
sanitation situation of Bangladesh.
Despite tremendous success in improving
access to safe water (over 90% coverage
of rural population) during the International
Drinking Water Supply and Sanitation,
IDWSS decade (1981-1990), water and
excreta related diseases remained the
major cause of mortality and morbidity in
Bangladesh (Rashid and Rahman, 1994).
The infant mortality rate came down by
only 12 from 122 to 110 for every thousand
live births in 1990. The reasons identified
were low sanitation coverage and overall
absence of health education and hygienic
promotion.
Figure: Interrelationship among Water,
Sanitation, Hygiene Education and Health
(Source: Veenstra S., 1994).
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation & Disease (Contd.)
Important issues for controlling excreta-related diseases:
• Sanitation is clearly the most important intervention required for
the control of excreta related diseases.
• Also important is improved personal, domestic and peri-domestic
hygiene, through improved water supplies and improved housing.
• Animal excreta control and effective sullage and solid waste
disposal must also be addressed to control all excreta related
diseases.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation: Commonly Used Terms
Total Sanitation: Refers to total sanitary condition for healthy living.
Therefore includes:
• Hygiene latrine facilities;
• Proper management of solid waste; and
• Proper disposal of household wastewater
100% Sanitation: At the very last, the term 100% sanitation includes
all of the following:
• No open defecation;
• Hygiene latrine available to all;
• Use of hygienic latrines by all;
• Proper maintenance of latrine for continual use; and
• Improved hygienic practice
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Definition of Sanitation System
A sanitation system involves all arrangements necessary to store,
collect, process and deliver human waste or other forms of waste
back to nature in a safe manner. Sanitation system with respect to
human waste management may be considered to have the following
functions:
Excretion and storage
Collection and Transportation
Process/ Treatment
Disposal/ Recycle
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Classification of Sanitation System
(1) On site Sanitation System: When the wastes are collected, treated and
disposed of at or close to the point of generation.
Example: Pit latrines (rural), septic tank system (urban).
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Figure: Conventional Simple Pit Latrine
Classification of Sanitation System (Contd.)
(1) On site Sanitation System (Contd.):
Basic Principle:
•Liquid infiltrates into the soil (infiltration capacity of soil and location of ground
water table are important issues).
•Solids are retained (confined) and anaerobically digested. Solids have to be
removed periodically, or a new pit has to be dug at regular intervals.
Features:
•Designed to dispose of human waste only.
•Wastewater from other sources (kitchen, washing, bathing) has to disposed
separately.
•Suitable for sparsely settled rural areas with low population density, and low water
consumption.
•Not feasible in areas with: (a) high population density (b) high water consumption
(c) low infiltration capacity of soil (d) high groundwater table.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Classification of Sanitation System (Contd.)
(2) Off-Site Sanitation System: When the wastes are collected and transported to
somewhere else for treatment disposal.
Example: Conventional Sewerage System; Small-Bore Sewerage System (SBS);
Bucket Latrines.
Treatment Plant
Public Sewer
Network
House
Connection
Disposal
Property Line
Figure: Conventional Sewerage System
River/ Stream
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Classification of Sanitation System (Contd.)
(2) Off-Site Sanitation System (Contd.):
Basic Principle:
• Basic elements of off-site sanitation system include collection, transportation,
treatment, disposal and/ or reuse.
•The waste is collected either through house sewers or manually using buckets or
vaults, transported either by sewer system, cart or truck to a suitable distant place
where it is treated prior to disposal or reuse.
Features:
•Collection and transportation of waste through a sewer reticulation system requires
that the waste be diluted by water.
•Hence piped water supply is essential where this system is to be applied.
•Most satisfactory system of waste disposal, provided sufficient funds are available
for its construction and maintenance.
•Because of high cost, preferable to introduce gradually; where possible existing
sanitation system (e.g., septic tank system) should be upgraded and improved (e.g.,
SBS system utilizing existing septic system). In this system, the costs can be
significantly reduced because of smaller sewer size and lower gradients.Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Classification of Sanitation System (Contd.)
Sanitation system may be further classified into:
(a) Dry Sanitation System: No water is used for the dilution of waste. Applied in
areas with no piped water supply.
Example: Pit latrines (rural, on-site), Bucket Latrines (Urban, off-site).
(b) Wet Sanitation System: Waste is diluted with flushes of water (to carry it away
from the point of generation).
Example: Septic Tank System (on-site), Conventional Sewerage System (off-site).
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Classification of Sanitation System (Contd.)
Sanitation system may be further classified into:
(i) Permeable System: Allows infiltration of liquid portion of waste into the soil,
causing potential pollution of groundwater.
Example: Pit latrines.
(ii) Confined System: Does not allow infiltration of liquid portion of waste into the
soil.
Example: Septic tank (not septic tank system, which also includes a soakage pit).
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Suitability of Sanitation System
Most important factor affecting suitability of sanitation system:
Level of Water Supply:
Pit latrines would not be appropriate with piped water supply
Water borne system (e.g., conventional sewerage system) is not feasible with
bucket carried or hand pump water supply
Population Density
On site system are more appropriate for low density rural settings, and low
density urban areas
Off-site systems are suitable for high density urban centers.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Figure: Various Sanitation systems based on water consumption level and population density
(Source: Veenstra et. Al., 1997).
Suitability of Sanitation System (Contd.)
Appropriate sanitation system based on level of water supply
and population density
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Sanitation System in Bangladesh
Rural areas (without piped water supply):
Pit latrines
Pour-flush latrines
Hanging latrines/ open defecation (still practiced)
Urban Areas:
Septic tank system
Conventional/ water borne sewerage system (only in Dhaka, coverage ranges
from 7 to 20%)
Direct connection to storm sewer line (with or without septic tank) and storm
drains
Slum/ low income areas: Pit latrines/ Hanging latrines/ Open defecation
Decentralized wastewater treatment system (DWATS): pilot scale application in
some slums
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Important Factors Need to be Considered for
Sanitation System in Bangladesh
Housing Density
Single pit latrines are suitable for use in rural areas and low density urban areas
up to about 300 people per hectare.
Some other local factors such as average household size, housing design, plot
layout, plot area have such large influence.
Water Supply Service Level
In water where water use is low (less than 30 lpcd) and where water has to be
hand carried from public stand points, tubewells, or communal wells, pit latrines,
either single pit or alternating twin pit, are technically feasible.
Difficulties associated with pit latrines
Digging pits in loose and unconsolidated soil (e.g., sand or fine grained
alluvium) is difficult and the lining must not prevent the seepage of faecal liquids
out of the pit into the surrounding soil.
Pit latrines are vulnerable in areas which are subjected to annual flooding or
where water table rises during monsoon. Flooding undermines the durability of
latrines and contributes to the contamination of the surrounding water bodies.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Important Factors Need to be Considered for
Sanitation System in Bangladesh (Contd.)
Difficulties associated with pit latrines (Contd.)
Construction of pit latrines becomes both difficult and expensive in rocky
ground. Householders wishing to build pits in rocky areas might need assistance
from the local public works department for digging with mechanical devise.
Operation and Maintenance
For all latrines cleanliness is of the utmost importance. Squatting slabs easily
become fouled in such communities where people are previously accustomed to
open defecation. Fouled pit latrines become a focus of disease transmission
and may create health hazard.
Garbage thrown into the pan blocks the latrine.
Sometimes the build up latrines are very shallow and they get filled up very
soon, which induces the people of household to go back to open defecation to
avoid the inconveniences of frequent cleaning or changing pits.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Important Factors Need to be Considered for
Sanitation System in Bangladesh (Contd.)
Soil Permeability
Soils with permeability below 2.5 mm per hour are unsuitable for pit latrines, as
the liquid fraction excreta is unable to infiltrate into the soil, thereby leading to
overflow of the pits.
Infiltration capacity is also greatly reduced where the water table is high, e.g., in
the coastal zone of Bangladesh.
Groundwater Pollution
The deposition of excreta in pits may pollute water sources, particularly wells,
tubewells, pond etc. The danger of pollution increases if the pit is dug down to
the water table or to fissured rock or weathered rock.
Bacteria will not penetrate more than 1-2 m in most unsaturated soil, but they
have been known to travel over 100 m in gravel below water table and in rock
fissures.
There should be at least 2 m of soil depth between bottom of the pit and the
water table surface to avoid any risk of faecal contamination of groundwater.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Important Factors Need to be Considered for
Sanitation System in Bangladesh (Contd.)
Groundwater Pollution (Contd.)
As a general guide, users are required to locate pits at least 10 m from
tubewells or other water sources to avoid potential pollution.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Topics to be Covered:
Typical sanitation options in rural/ low income areas
Hygiene latrine (definition)
Rural Sanitation Technologies (Pit latrine/ Pour Flush latrines)
Septic Tank System
Public and Communal Sanitation
On-Site Human Waste Management:
Technological Options
Different types of sanitation options are in use in rural and low-
income urban areas, not all of which are hygienic.
A wide range of on-site sanitation technologies exist that are low
cost and can be selected for use in different hydrological, socio-
economic, and cultural conditions.
Basis for Assessing Rural Sanitation Options
Typical Sanitation Options: Rural/ Urban Slum
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Typical Sanitation Options: Rural/ Urban Slum
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Typical Sanitation Options: Rural/ Urban Slum
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Typical Sanitation Options: Rural/ Urban Slum
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
What are the criteria for an acceptable
sanitation options?
Basis for Assessing Rural Sanitation Options
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
A “hygienic latrine” is defined as a sanitation facility which effectively
breaks the cycle of disease transmission. A hygienic latrine would
include all of the following:
1. Confinement of waste (feces),
2. Sealing of the passage between the squat hole and the pit to
effectively block pathways for flies and other insect vectors,
thereby breaking the cycle of disease transmission, and
3. Venting out of foul gases generated in the pit through a properly
positioned vent pipe to keep latrine odor free and encourage its
continual use.
Hygiene Latrine
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
The most fundamental health objectives of sanitation must be
achieved through proper design, installation, and use of a sanitary
or hygiene latrine.
There is no universal design of a sanitary/ hygiene latrine that
could be used for all socio-economic and hydro-geologic
conditions.
Therefore, a wide range of sanitary/ hygienic latrine technologies
should be available to suit different conditions.
Most technological options are:
Pit latrines
Pour flush latrines (often both types are referred to as “pit
latrines”)
Hygiene or Sanitary Latrine
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
A pit is simply a hole in the ground that receives human waste. Urine and other
liquids soak into the ground and solid materials are retained and decomposed
in the pit.
All forms of pit latrines are not fully sanitary/ hygienic. With slight modifications
in design and with some interventions, conventional pit latrines could be
improved to be hygienic.
The major types of pit latrines are:
Simple or Home-made Pit Latrines
Ventilated Improved Pit (VIP) Latrines
Reed Odorless Earth Closet
Pit Latrines
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Simple or “Home-Made” Pit Latrines
Figure: Conventional Pit Latrines
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
A manually dug/ bored hole
A seat or squatting slab
A superstructure
Preferred option when water
availability is limited
Note: When “flushing water” is
available, “pour flush” latrines
are preferred options.
Simple or “Home-Made” Pit Latrines (Contd.)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
The simplest “home-made” latrine is built by digging a small hole and placing a
platform (concrete, bamboo) on it.
One can use a concrete squatting slab and a ring for an improved version.
This option, though not fully sanitary, is sometimes promoted to discourage
open defecation.
Types of simple pit latrine:
Direct pit latrines: When excreta fall directly into a pit underneath the user
Offset pit latrine: When excreta pass through a short pipe or a channel to a pit
few meters away
Partly offset pit latrine: when part of the pit is under the shelter and part is
outside, where removable cover allows the contents to be taken out.
Simple or “Home-Made” Pit Latrines (Contd.)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Advantages Least costly ;
Easily constructed and maintained ;
Structurally safe and therefore free from the risk of children falling into it;
Prevent hookworm transmission ;
Offer a better solution than open defecation and unhygienic hanging latrines.
Disadvantages Flies lay their eggs in faeces within poorly built latrines. Increase in the fly
population increases spread of diseases caused by the faecal pathogens they
carry;
Odor nuisance;
Improper pit construction may led to pit collapse.
Ventilated Improved Pit (VIP) Latrines
Figure: Ventilated Improved Pit (VIP) Latrines
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
The pit (single pit or alternating twin pit)
Cover slab, usually of reinforced
concrete slab, containing two holes-the
squat hole and the other for the vent
pipe
A superstructure for privacy and
protection from rain and sun
The vent pipe and fly screen which keep
the latrine from flies, mosquitoes, and
unpleasant odors.
Figure: Alternating Twin-Pit (VIP) Latrines
Alternating Twin-Pit VIP Latrines
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Two separate pits, with the
superstructure located centrally over
the off-set pits.
The slab covering the pits has two
squat holes, one over each pit.
Can use permanent structure.
Ventilated Improved Pit (VIP) Latrines
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
General
Overcome disadvantages of simple pit latrines (e.g., fly and mosquito
problems, odor nuisance)
Single Pit VIP
Suitable, specially where mechanical pit emptying is possible
Twin Pit VIP
One pit is used at a time. When one pit is full (1-3 years), it is closed and the
second is put into service.
When the second pit becomes full, the contents of the first are removed and put
back into the service. The cycle continues.
VIP Latrines: Advantages and Disadvantages
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Advantages
Controls odor and insects to a large extent
Relatively low-cost, easily constructed and maintained
Twin pits offer long term solution
Minimum health risk
Minimum water requirement
Disadvantages
Absence of seal between squat hole and pit prevents it from becoming a
“sanitary/ hygienic latrine”.
Potential for groundwater pollution
Difficulty of construction in rocky and high water table areas
Figure: Reed Odorless Earth Closet (ROEC)
Reed Odorless Earth Closet (ROEC)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
A variation of VIP latrine
Pit fully “off-set” from superstructure,
and connected to squatting slab with a
“curved chute”
Connected with vent pipe to control
odor and insect nuisance
It is claimed that the chute, in
conjunction with the ventilation stack,
encourages vigorous air circulation
down the latrine, thereby removing
odors and discouraging flies. This type
of latrine is common in Southern
Africa.
ROEC: Advantages and Disadvantages
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Advantages
Controls odor and insects to a large extent
ROEC pit can be made larger, as the superstructure is fully off-set, which
ensure a longer life
Pit can be easily emptied without disturbing superstructure; hence can be a
permanent facility
Structurally more stable
Aesthetically more acceptable as the excreta cannot be seen
Disadvantages
The ROEC chute easily becomes fouled with excreta, thereby providing a
possible site for fly breeding and odor nuisance;
The chute has to be regularly cleaned with a long handled brush or a small
amount of water.
VIP/ROEC: Odor and Fly Control
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Odor Control
Wind blowing across the top of the vent
pipe creates circulation of air
Unpleasant odor from pit are thus
sucked up through the vent pipe,
leaving the toilet odor free
Fly Control
Fly enter the pit via squat hole (to lay
egg)
On their way out, they instinctively fly
towards the light
If the latrine door is closed and the
latrine is dark inside, only light they can
see is at the top of vent pipe.
Since the vent pipe is provided with fly-
screen, flies are unable to escape and
eventually die.
General Design Considerations of “Pits”
Pit should be as large as possible, but the diameter should not exceed 1.5
m. Otherwise the cover slab become too expensive.
There should be at least 2 m of soil depth between bottom of the pit and the
water table surface to avoid any risk of faecal contamination of groundwater.
As a general guide, users are required to locate pits at least 10 m from
tubewells or other water sources to avoid potential pollution.
Soils with permeability below 2.5 mm per hour are unsuitable for pit latrines,
as the liquid fraction excreta is unable to infiltrate into the soil, thereby
leading to overflow of the pits.
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Prevention of Groundwater Pollution:
Thumb Rule
Figure: Groundwater Pollution from Pit Latrines (after Dahi, 1996)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
10 m
2.0 m
Typical “Pit” Construction
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Liquid infiltration only
through the bottom
Perforated Concrete Rings would
increase pit life by 4-5 times (Not
Common in Bangladesh)
Liquid infiltration
Typical Pit in loose/ unconsolidated soil
Typical Pit in relatively stale soil
Typical Dimension of Each Ring:
Diameter: ~ 3 feet/ 1 m
Height: 1 feet/ 0.3 m
Wall Thickness: 1.25 to 1.50 inch
Depth of Pit:
5 to 6 ring (i.e., 1.5 to 1.8 m) are most common (manually dug pit)
Design of “Pit” for “Pit Latrines”
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
0.5 m
Effective Pit
Volume
Design of “Vent Pipe/System”
Material
PVC, UPVC, GI, Brick (Choice depends on durability, availability, cost, ease of
construction)
Height/ Position
500 mm higher than roof
500 mm above highest point in roof (sloping roof)
Internal Diameter
A ventilation rate of 20 m3/hr (depends on roughness of pipe, length, head loss
through fly screen, wind direction etc.)
Recommended size:
PVC: 150 mm diameter
Brick: 230 mm square
Others: 230 mm diameter
Specifications for Fly Screen:
Purpose: To prevent passage of mosquito, flies
Size: Aperture ≤ 1.2 mm × 1.5 mm
Material: Corrosion resistant, able to withstand intense rainfall, high temperature,
sunlight, preferably steelZaki Uddin Ahmad, Lecturer, Department of CE, UITS
Operation and Maintenance of Pit Latrines
Important operational aspects include the following:
Regular cleaning of the squatting slab with some water and a little disinfectant if
available. In case of ROEC, the chute has to be cleaned regularly.
For “simple pit latrine”, a light fitting lid may be placed on the squatting hole after
every use to ensure insect and odor control.
In case of ROEC/VIP latrines, the squat hole should never be covered to ensure
continuous airflow; rather the door of latrine should be kept closed for keeping
inside dark.
Some water should be always available in or near the latrine for cleaning.
Ash or sawdust can be sprinkled occasionally in the pit to reduce smell and
insect breeding.
Non-biodegradable material like stones, glass, plastics, rags etc. should not be
thrown into the pit as they reduce the effective volume of the pit.Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Septic Tank System
Figure: Components of a Septic System
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
A septic tank is a buried water tight
receptacle designed and constructed
to receive wastewater from home, to
separate the solids from liquid, to
provide limited digestion of organic
matter, to store solids, and to allow
the clarified liquid to discharge for
further treatment and disposal
(Polprasert et. Al., 1982).
Settleable solids and partially
decomposed sludge settle to the
bottom of the tank and gradually build
up.
A scum of light weight material
including fats and greases rises to the
top.
The partially treated effluent is allowed
to flow through an outlet structure
below the floating scum layer.
Processes in the Septic Tank System
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
A septic tank is simply a sedimentation basin with no external or internal moving parts or
added chemicals, the natural processes that take place within the tank are complex, and
interact with each other.
Most important processes that take place within the tank are separation of suspended
solids, digestion of sludge and scum, stabilization of the liquids, and growth of micro-
organisms.
Separation of suspended solids is a mechanical process which results in the formation of
three distinct layer in the septic tank-a layer of sludge at the bottom, a floating layer of
scum on the top and a relatively clear layer of liquid in the middle.
Anaerobic bacteria degrade the organic matter in the sludge as well as in the scum and
as a result of this bacterial action, volatile acids are formed at the first instance and
eventually are converted mostly to water, carbon dioxide and methane.
Processes in the Septic Tank System (Contd.)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Organic materials in the liquid are also stabilized by anaerobic bacteria, which break
down complex substances into simpler ones in a process similar to the one that take
place in the sludge layer.
A large variety of micro-organisms grow, reproduce and die during the biodegradation
processes that take place in the tank.
Although there is an overall decrease in the number of micro-organisms, a large
number of Bacteria, Viruses, Protozoa and Helminths survive in the tank and remains
active in the effluent, sludge and scum.
Design Procedure
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
The septic tank design is based on the
Brazilian septic tank code, which takes a
more rational approach to design than
others. In this approach, the tank is
considered to be made up of four zone,
each of which serves a different function:
Scum storage zone
Sedimentation zone
Sludge digestion zone
Digested sludge storage zoneFigure: Functional Zone in a Septic System
Design Procedure (Contd.)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Design Procedure (Contd.)
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Disposal of Septic Tank Effluents
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Soakage Pits These are deep excavations used for
sub-surface disposal of septic tank
effluents. Absorption pits are
recommended as an alternative when
absorption field/ trenches are not
practicable and where the top soil is
under laid with porous soil or fine gravel.
The capacity of an absorption pit can be
calculated on the basis of percolation
tests to be made at the disposal site.
Soakage pits or soakaways are mostly
used in Bangladesh. Typically soakage
pits can be 2 to 3.5 m in diameter and 3
to 6 m deep depending on the amount of
wastewater flow and infiltration capacity
of soil.
Figure: Typical Soakage Pit
Problem on Septic Tank
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Design a septic tank to serve a household of ten persons who produce 90 lpcd of
wastewater. The tank is to be desludged every three years. If the soil is sandy loam with
a long term infiltration rate of about 30 l/m2 day, design a soakage pit for the disposal of
effluent from the septic tank.
Assignment
Design a septic tank system for a family of 10 persons with a desludging interval of 5
years. The average wastewater flow is 15 liters per capita per day. Also design the soak
pit for the disposal of the septic tank effluent. The soil is silty with a long term infiltration
rate of 20 l/m2-day.
Communal Sanitation System
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
A communal sanitation system consists of a number of squatting facilities with a common disposal
system.
Communal sanitation system facilities are provided where sewerage systems are not feasible both
technically and economically, and where on-site individual sanitation systems are not possible due to
house density and ground conditions.
It is important to be noted that there is a common distinction between communal sanitation facilities
and public toilet facilities.
Communal facilities are built outside household plots in communities and used by people for their
daily needs when at home. Public toilet facilities are built in or near market places, commercial areas,
city centers and other public places and are intended for people who are away from their homes.
Communal sanitation facilities should be provided with a piped or tubewell water supply sufficient for
flushing, anal cleansing, hand washing and if available, for shower and laundry facilities.
Figure: Typical Communal Sanitation Facility
Communal Sanitation System: Advantages and Disadvantages
Zaki Uddin Ahmad, Lecturer, Department of CE, UITS
Advantages
This option is suitable for densely populated slum area where individual on site system is
technically and economically unfeasible.
Total cost of communal sanitation facilities can be shared by the users
If connected to a biogas plant, communal sanitation facilities may provide significant
amount of energy required for cooking and lighting.
Disadvantages
Lack of commitment by individual users to keep the communal facilities clean and
operating properly
Lack of privacy particularly for women
Difficult to use at night and in bad weather, specially for children, the sick and the elderly
Communal sanitation facilities cannot be upgraded to individual household sanitation
facilities