Introduction to Environmental Sanitation

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”.


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)



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



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)



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


Cholera

Typhoid

Personal

Domestic

Water

Crops

3. Geohelminthiases Latent

Very persistence

Unable to multiply

Very high infectivity


Hookworm

Ascariasis

Domestic

Field

Crops

4. Excreta-related

insect vector diseases

Infections 1-3

transmitted

mechanically by flies

and cockroaches

Water



“Fecal-Oral” Transmission Route of Diseases

Water

Hands

Insects/

Flies

Soil

Milk

Food

Vegetables

New

HostExcreta




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).



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.


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


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


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).


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.



(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



(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


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).



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).


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.


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


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


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.



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.




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.




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.


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


What are the criteria for an acceptable

sanitation options?

Basis for Assessing Rural Sanitation Options


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


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


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


Simple or “Home-Made” Pit Latrines

Figure: Conventional Pit Latrines


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.)


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.)


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.


Figure: Ventilated Improved Pit (VIP) Latrines


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


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.



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


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)


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


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


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.


Prevention of Groundwater Pollution:

Thumb Rule

Figure: Groundwater Pollution from Pit Latrines (after Dahi, 1996)


10 m

2.0 m

Typical “Pit” Construction


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”


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


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


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.)


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


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.)


Disposal of Septic Tank Effluents


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


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


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


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

Introduction to Environmental Sanitation

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