Methods of excreta disposal

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Methods of Excreta Disposal

Source: Park's Textbook of Preventive and Social Medicine

Public Health Importance

Human excreta is a major source of infection and environmental pollution. Improper disposal leads to:

Soil and water pollution
Contamination of food
Fly propagation

Diseases resulting from improper excreta disposal include typhoid and paratyphoid fever, dysenteries, diarrhoeas, cholera, hookworm disease, ascariasis, viral hepatitis, and other intestinal infections.

How Disease Spreads from Excreta - The F-Diagram

Faeces transmit disease through five routes: Fingers, Flies, Fluid (water), Soil, and Food - all ultimately reaching a new host. The "sanitation barrier" (a sanitary latrine + disposal pit) interrupts this cycle.

Classification of Methods

EXCRETA DISPOSAL METHODS
├── I.  Unsewered Areas
│   ├── 1. Service Type (Conservancy System)
│   ├── 2. Non-service Type (Sanitary Latrines)
│   └── 3. Latrines for Camps / Temporary Use
└── II. Sewered Areas
    └── Water-Carriage System + Sewage Treatment

I. Excreta Disposal in Unsewered Areas

1. Service Type - Conservancy System

Nightsoil is collected from bucket/pail latrines by human agency and transported in "nightsoil carts" for final disposal by:

Composting
Burial in shallow trenches

Drawbacks: Nightsoil exposed to flies; risk of water and soil pollution; dignity concerns for workers; prone to collapse if sanitation staff strike. The Environmental Hygiene Committee (1949) recommended replacing service latrines with sanitary latrines.

2. Non-Service Type (Sanitary Latrines)

A sanitary latrine must meet four criteria:

Must not contaminate ground or surface water
Must not pollute the soil
Must not be accessible to flies, rodents, or animals
Must not create nuisance from odour or unsightly appearance

(a) Bore Hole Latrine

Circular hole 30-40 cm diameter, dug 4-8 m deep (commonly 6 m) using a special auger
Concrete squatting plate placed on top
Serves a family of 5-6 for over a year
When contents reach within 50 cm of the ground, hole is sealed with earth and a new one is dug
Nightsoil undergoes purification by anaerobic digestion
Merits: No sweeper needed; dark pit unsuitable for fly breeding; no water pollution if >15 m from water source
Demerits: Fills rapidly; requires special auger; difficult in high subsoil water or sandy soils; not recommended today - superseded by better designs

(b) Dug Well / Pit Latrine

Circular pit ~75 cm diameter, 3-3.5 m deep
Improved over the bore hole latrine; first introduced in Singur, West Bengal (1949-50)
Lined with pottery rings in sandy soil
Fitted with a concrete squatting plate

(c) Water-Seal Type Latrines

These use a water seal (a bent pipe/trap holding water) to prevent odour and fly access. Three main types:

Type	Features
PRAI Type	Pour-flush; uses a pan and trap with water seal
RCA Type	Rural Community Architecture; detailed specifications for pan, trap, squatting plate; water seal depth 2 cm (3/4 in.); most widely recommended in India
Sulabh Shauchalaya	Twin pit pour-flush; popular low-cost model for rural India

Key components of the RCA latrine:

Location: Minimum 15 m (50 ft) from any water supply, at lower elevation
Squatting plate: Cement concrete, 90 cm square, 5 cm thick, sloped toward pan
Pan: 42.5 cm long, with smooth finish
Trap: 7.5 cm diameter bent pipe providing the water seal

(d) Septic Tank

A two-stage purification system:

Anaerobic digestion (inside the tank) - sludge is reduced in volume and stabilized; methane gas is released
Aerobic oxidation (outside, in sub-soil) - effluent percolates through perforated/open-jointed pipes in trenches 90 cm deep; aerobic soil bacteria oxidize organic matter into nitrates, CO2, and water

Maintenance: Desludge at least once a year; avoid phenol/soap water (kills tank bacteria); seed new tanks with ripe sludge.

(e) Aqua Privy

Functions like a septic tank but simpler
A water-tight chamber filled with water; a drop pipe from the latrine floor dips into the water
Capacity: ~1 cubic metre for a small family (lasts 6+ years)
Nightsoil undergoes anaerobic digestion
Effluent treated by sub-soil irrigation; vent pipe required for gas escape
Can also be designed for public use

3. Latrines for Camps and Temporary Use

Type	Use
Shallow trench latrine	Very temporary; soil thrown over each use
Deep trench latrine	For longer camps; deeper pit, more capacity
Pit latrine	Standard temporary installation
Bore hole latrine	Temporary/semi-permanent family use

II. Excreta Disposal in Sewered Areas - Water-Carriage System

Sewage flows from household fittings (water closets, urinals, wash basins) through house drains (10 cm diameter) into trunk sewers (minimum 22.5 cm, up to 2-3 m diameter), maintained at "self-cleansing velocity" of 2-3 feet/second.

Sewage Treatment

a. Primary Treatment

Screening - Metal screens (bars 5 cm apart) remove large floating objects (wood, rags, dead animals); screenings disposed of by burial/trenching
Grit Chamber - Removes heavy solids (sand, gravel); 10-20 m long; constant velocity ~1 ft/sec; detention 30 sec to 1 min
Primary Sedimentation Tank - Large rectangular tank; sewage flows at 1-2 ft/min for 6-8 hours; 50-70% of solids settle; 30-40% reduction in coliform organisms; sludge mechanically removed and undergoes anaerobic digestion

b. Secondary Treatment

Trickling Filter (Percolating Filter) - Effluent sprayed over a bed of stones; aerobic bacteria on the stone surface oxidize organic matter
Activated Sludge Process - Effluent aerated in tanks; microorganisms in suspended sludge oxidize organic matter; highly efficient

c. Other Methods of Final Disposal

Method	Description
Sea outfall	Treated sewage discharged into deep sea via outfall pipes; must discharge at depth to prevent washback
River outfall	Sewage must be purified before discharge; degree depends on the river's dilution and self-purification capacity
Sewage farming (land treatment/broad irrigation)	Applied to porous land after grit removal and screening; 1 acre treats sewage of 100-300 persons; suitable crops include fodder grass, potatoes, plantain; NOT suitable: sugarcane, tomato, cucumber, onion, coriander
Oxidation pond (waste stabilization pond)	Shallow open pool 1-1.5 m deep; depends on algae + bacteria + sunlight; algae provide O2 for bacteria; bacteria oxidize organic matter releasing CO2 for algae - a mutually beneficial cycle; cheap and effective

Summary Table

Method	Setting	Mechanism	Best For
Conservancy system	Rural/unsewered	Manual collection + composting/burial	Being phased out
Bore hole latrine	Rural, family	Anaerobic digestion	Hookworm campaigns historically
Pit/dug well latrine	Rural	Anaerobic digestion	Family use
Water-seal latrine (RCA/Sulabh)	Rural/peri-urban	Water seal + anaerobic pit	India's standard rural sanitation
Septic tank	Peri-urban	Anaerobic + aerobic	Individual homes/institutions without sewers
Aqua privy	Rural/peri-urban	Anaerobic digestion	Public/community use
Trench latrines	Camps/disasters	Simple burial	Emergency sanitation
Water-carriage + treatment plant	Urban/sewered	Primary + secondary treatment	Urban municipalities
Oxidation pond	Semi-urban	Biological (algae + bacteria)	Low-cost sewage treatment
Sewage farming	Peri-urban	Land treatment	Where porous land available

Park's Textbook of Preventive and Social Medicine, Chapter on Environmental Health - Excreta Disposal (pp. 860-868)

Methods of waste disposal

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Methods of Waste (Refuse) Disposal

Source: Park's Textbook of Preventive and Social Medicine

What is Solid Waste / Refuse?

The term solid waste includes:

Garbage - food wastes (ferments quickly, needs rapid removal)
Rubbish - paper, plastics, wood, metal, glass, throw-away containers
Demolition products - bricks, masonry, pipes
Sewage treatment residue - sludge, coarse screenings
Dead animals, manure, and other discarded material

Per capita daily solid waste output ranges from 0.25 to 2.5 kg depending on dietary habits, lifestyle, and degree of urbanization.

Sources of Refuse

Source	Contents
Street refuse	Leaves, straw, paper, animal droppings, litter
Market refuse	Large proportion of putrid vegetable and animal matter
Stable litter	Animal droppings, leftover animal feeds
Industrial refuse	Wide variety - from inert materials (calcium carbonate) to toxic/explosive compounds
Domestic refuse	Ash (cooking/heating residue), rubbish, and garbage

Health Hazards of Improper Solid Waste Disposal

Accumulated refuse is a health hazard because it:

Decomposes and favours fly breeding
Attracts rodents and vermin
Allows pathogens to be conveyed back to food via flies and dust
Causes water and soil pollution from drainage
Creates nuisance from bad odour and unsightly appearance

There is a direct correlation between improper solid waste disposal and the incidence of vector-borne diseases.

Storage and Collection

Storage: Refuse should be stored in galvanized steel dustbins with close-fitting covers while awaiting collection. The bin capacity depends on the number of users and frequency of collection.

Collection methods:

House-to-house collection - most satisfactory; refuse collected directly from homes
Community bins / depots - people bring refuse to a common collection point
Refuse is then transported in refuse collection vehicles (including modern "dustless refuse collectors" with totally enclosed bodies) to the place of final disposal
Dead animals are transported directly to the place of disposal

Methods of Disposal

No single method is equally suitable in all circumstances. The choice is governed by local factors such as cost, availability of land and labour.

(a) Dumping

Refuse is dumped in low-lying areas, partly for land reclamation and partly as an easy method of disposal of dry refuse. Through bacterial action, refuse decreases in volume and converts to humus.

Example: Kolkata disposes of refuse by dumping; the reclaimed land is leased for cultivation.

Drawbacks:

Refuse exposed to flies and rodents
Source of nuisance - smell and unsightly appearance
Wind disperses loose refuse
Drainage pollutes surface and groundwater

A WHO Expert Committee (1967) condemned open dumping as "a most insanitary method that creates public health hazards, a nuisance, and severe pollution of the environment" and called for it to be outlawed.

(b) Controlled Tipping (Sanitary Landfill)

The most satisfactory method where suitable land is available. Differs from open dumping in that refuse is placed in a prepared area, adequately compacted, and covered with earth at the end of each working day.

Three operational methods:

Method	Best For	Details
Trench method	Level ground	Trench 2-3 m deep, 4-12 m wide; refuse compacted and covered with excavated earth; 1 acre/year needed for 10,000 population at 2 m fill depth
Ramp method	Moderately sloping terrain	Some excavation done to secure covering material
Area method	Filling depressions, quarries, clay pits	Refuse deposited in layers 2-2.5 m deep; each layer sealed with mud cover ≥30 cm thick to prevent flies, rodents, and odours

Key facts:

Temperature rises to over 60°C within 7 days, killing all pathogens and hastening decomposition
Takes 2-3 weeks to cool down
4-6 months for complete decomposition of organic matter into an innocuous mass
Refuse should never be tipped into water (causes odour nuisance from decomposition)
Mechanization by bulldozers has greatly improved this method

(c) Incineration

Refuse is burnt in purpose-built incinerators at high temperatures, reducing it to inert ash.

Advantages:

Complete destruction of pathogens
Large volume reduction
No fly or rodent problem
Can be done at or near the source
The heat generated can be used for energy (heat recovery)

Disadvantages:

High capital and running costs
Not suitable for wet/high-moisture refuse
Risk of air pollution from smoke/fumes if not properly managed

(d) Composting

Composting is a method of combined disposal of refuse and nightsoil or sludge. It is a process whereby organic matter breaks down under bacterial action, resulting in the production of a stable, humus-like material called compost which has value as a soil conditioner and fertilizer.

Process:

Organic refuse is mixed with nightsoil or sewage sludge
Bacterial decomposition (aerobic) generates heat, kills pathogens
End product is dark, odourless, humus-like compost

Advantages:

Produces a useful by-product (manure/compost)
Hygienic - pathogen destruction by heat
Suitable for rural India where organic waste predominates
Reduces waste volume significantly

(e) Manure Pits

A method practiced in rural areas, particularly in India. Refuse is collected in pits where it undergoes anaerobic decomposition to form manure. The resulting manure is used as agricultural fertilizer.

Simple and low-cost
Produces useful agricultural by-product
More suitable for rural settings where land is available

(f) Burial

Refuse is buried directly in the ground. This is a simple method used for small quantities, at the household or camp level. Decomposition takes place underground. It is especially useful for:

Camp/emergency sanitation
Disposal of small amounts of hazardous or infectious material

Comparison of Methods

Method	Cost	Land Needed	Health Safety	Best Setting	By-product
Open Dumping	Very low	Large	Poor (condemned)	Nowhere	Humus (long term)
Controlled Tipping	Low-moderate	Moderate	Good	Urban/peri-urban	Reclaimed land
Incineration	High	Small	Excellent	Urban	Ash, heat
Composting	Low	Moderate	Good	Rural/peri-urban	Compost/manure
Manure Pits	Very low	Small	Moderate	Rural	Manure
Burial	Very low	Small	Moderate	Camps/emergency	Nil

Special Considerations

Public Education

Refuse disposal cannot be solved without public education. People have little interest in cleanliness outside their homes. Health education via pamphlets, newspapers, broadcasting, and films is needed, alongside police enforcement of laws.

Economics and Finance

Efficient, hygienic refuse disposal requires heavy capital outlay. In highly industrialized countries, up to 20% of municipal budgets are spent on collection and disposal of solid wastes.

International Cooperation

ISWA (International Solid Wastes and Public Cleansing Association) was formed in 1970
A WHO International Reference Centre in Switzerland collects, evaluates, and disseminates information on waste disposal practices and fosters research

Park's Textbook of Preventive and Social Medicine - Disposal of Wastes (pp. 855-858)

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