The term "solid wastes" is applied to garbage (food wastes), rubbish (paper, plastics, wood, metal, throw-away containers, glass), demolition products (bricks, masonry pipes), sewage treatment residue (sludge and solids from the domestic sewage), dead animals, manure and other discarded material. Solid waste should not contain night soil. The output of daily waste depends upon the dietary habits, life styles, living standards and the degree of urbanization and industrialization. The per capita daily solid waste produced ranges between 0.25 to 2.5 kg in different countries. In cities it is called ‘refuse’ and ‘litter’ in rural areas.
Solid waste is hazardous to health, if allowed to accumulate because it-
- decomposes and favors fly breeding
- attracts rodents and vermin
- Possibility of contamination of food through pathogens
- possibility of water and soil pollution
- unsightly appearance and nuisance from bad odours.
Sources of Refuse
- Street refuse
- Market refuse
- Stables litter
- Industrial refuse
- Domestic refuse – ash, rubbish, garbage
Storage of Refuse
- Storage at domestic level: storage can be envisaged in
- Galvanized steel dust bin with close fitting. Capacity depends upon the number of users and frequency of collection.
- Paper sack which itself is disposed off and replaced by a new sack.
- Public Bins: Public bins without cover cater for a larger number of people. In bigger municipalities, the bins are handled and emptied mechanically by lorries fitted with cranes.
Collection of Refuse
The method depends upon the funds and labour available.
- House to house collection – best method.
- People have to dump in nearest public bin.
- Disadvantage – refuse gets dispersed all along the street
- Thrown out in front and around the house.
- Requires sweepers to clean the streets and to collect the refuse from public bins.
The refuse is then transported to the place of ultimate disposal. Dead animals are directly transported to the place of disposal.
Environmental Hygiene Committee (1949) suggested the local bodies
- to arrange for collection of refuse from public bins and individual houses
- replace open refuse cart with enclosed vans.
Methods of Disposal
The choice of method of disposal depends on local factors such as cost and availability of land and labour.
he principal methods of refuse disposal are :-
- Controlled Tipping or Sanitary Land-fill
- Manure Pits
- Dumping: Refuse is dumped in low lying areas as a method of reclamation of land and as an easy method of disposal of dry refuse. As a result of bacterial action, refuse decreases considerably in volume and is converted gradually into humus. The drawbacks of open dumping are -
- exposed to flies and rodents,
- source of nuisance from the smell and unsightly appearance,
- loose refuse is dispersed by wind,
- drainage from dumps causes pollution of water and land.
A WHO Expert Committee (1967) condemned dumping as "a most insanitary method that creates public health hazards, a nuisance and a severe pollution of the environment. Dumping should be outlawed and replaced by sound procedures.
- Controlled tipping: In controlled tipping or sanitary landfill the material is placed in a trench or other prepared area, adequately compacted and covered with earth. The term ‘modified sanitary landfill’ has been applied to those operations where compaction and covering are accomplished once or twice a week. Three methods are used in this operation-the trench method, the ramp method and the area method.
- The trench method: A long trench is dugout and refuse is dumped, compacted and covered with excavated earth.
- The ramp method: sloppy area available is used to dump the waste. Some excavation is done to secure the covering material.
- The area method: land depressions are used for filling. The refuse is deposited, packed and consolidated in uniform layers and sealed to prevent infestation by flies and rodents and suppresses the nuisance of smell and dust.
Chemical, bacteriological and physical changes occur in buried refuse leading to complete decomposition of organic matter.
- Incineration or burning: It is a hygienic method of disposal in the absence of land. Most suitable for hospital and industrial refuse. A preliminary separation of dust or ash is needed which involves heavy expenditure.
- Composting: Composting is a combined disposal of refuse and night soil or sludge. It is a process of breakdown of organic matter under bacterial action, resulting in the formation of stable humus-like material called compost. This acts as rich manure to the soil. The principal by-products are carbon dioxide water and heat. The heat produced during composting amounts to 60ᵒC or higher, destroys eggs and larvae of flies, weed seeds and pathogenic agents. Methods of composting: Bangalore (Anaerobic) method, Mechanical (Aerobic) method
- Manure pits: Manure pit is the most suitable method for collection and disposal of refuse in rural areas. The garbage, cattle dung, straw and leaves should be dumped into the manure pits and covered with earth after each day's dumping. Two such pits will be needed, when one is closed, the other will be in use. The refuse gets converted into manure within 5 to 6 months and can be returned to the field.
- Burial: This method is suitable for small camps. A trench of 1.5 m wide and 2 m deep is excavated, and the refuse is dumped. It is covered with 20 to 30 cm of earth at the end of the day. When the level in the trench is 40 cm from ground, the trench is filled with earth and compacted. A new trench is dug out. The contents may be taken out after 4 to 6 months and used on the fields.
The problem of refuse disposal can be solved with people’s participation and education. Enforcement of laws may also be needed at times.
Economics and Finance
If refuse disposal is to be carried out efficiently, hygienically and economically heavy budget will be needed, whatever system of disposal is adopted.