What is solid waste management | Solid waste management methods

What is solid waste management?

The management of waste materials coming out from animals, humans, and organic raw materials like plant leaves, fruit, etc to the place where it needs to be disposed of in a safe manner without spreading any disease or bad smell is known as solid waste management.

  • Due to an increase in population and urbanization, solid wastes are produced in large quantities in cities/towns alongside liquid wastes.
  • They are present in dry form, hence called dry refuse.
What-solid-waste-management
What-solid-waste-management

Classification of solid wastes

Based on the types of solid wastes, they are classified as follows:

1) Municipal wastes

It includes garbage, rubbish, ashes, demolition wastes, etc.

2) Garbage

  • It includes all putrescible organic wastes from the kitchen.
  • It also includes animal dung, leaves of trees, etc.
  • It decomposes quickly, resulting in the foul odor and the breeding of flies and mosquitoes.
  • It weighs from 450 to 900 kg/m³.

3) Rubbish

  • It includes combustible wastes ( paper, plastics, wood ) and non-combustible wastes ( glass, tin cans )
  • It weighs from 50 to 400 kg/m³.

4) Ashes and residues

  • It includes residues of the burning of wood, coal, coke, etc.
  • It is incombustible and composed of fine powdery materials.
  • It weighs from 700 to 850 kg/m³.

5) Demolition and construction wastes

  • It includes wastes from demolished buildings and construction structures.
  • It comprises stones, bricks, dirt, plaster, etc.

6) Industrial wastes

It includes rubbish, ashes and construction wastes. It can be recycled and recovered.

7) Hazardous wastes

It is ignitable, corrosive, reactive and toxic in nature. It posses a threat to plant and animal life.

Depending on the characteristic of constituents of solid wastes, they are classified as follows:

8) Organic wastes

It includes food wastes, grass, animal excreta, etc. It produces a highly unwanted odor.

9) Inorganic wastes

It includes rubbish, ashes and construction wastes. Hazardous wastes fall into this category.

Depending upon the source, they are classified as:

1) House refuse

It includes wastes produces from housekeeping activities. It comprises food wastes, ashes, rubbish, plastic, etc.

2) Street refuse

It includes wastes produced from streets. Streets sweeping, catch basin debris, etc. fall in this category.

3) Trade refuse

It includes wastes produced from factories, hotels and business centers. It includes food wastes, industrial and other wastes.

Quantity of solid wastes

  1. Quantity of garbage in solid wastes depends upon food available, culture, living standard, etc.
  2. According to the survey, organic wastes produced are about 55% and inorganic wastes are about 45%.
  3. In Nepal, the average household waste generation rate is 0.25 kg/person/day.

Collection  and transportation of solid wastes

Solid waste is collected in the following ways:

  1. It is collected in individual houses in small containers.
  2. Public dustbins may also be used.
  3. Hand carts of 0.5 to 0.75 m³ capacity are also suitable.

Transportation of collected wastes to the disposal site is achieved by the following vehicular means:

a) Auto-rickshaws

  • Capacity varies from 0.5 to 0.75 tonnes.
  • Suitable for areas where heavy vehicles cannot go.

b) Trailers

  • Capacity varies from 2 to 3 tonnes.
  • Unloading is done by a hydraulically operated jack.

c) Trucks

  • Capacity varies from 5 to 10 tonnes.
  • Generally, of tilting-tipping type.

Solid wastes disposal methods

d) Pulverization

  • In this method, dry refuse is pulverized to powder form without a change in chemical composition.
  • The powdered product can be used as manure.

Advantages

  • Site appearance is improved.
  • Reduction in transport cost due to an increase in the density of dry refuse.
  • Uniform settlement of dampers material with no voids

Disadvantages

It is a costlier process.

e) Land filling

  • It is a method applied in urban areas where a large amount of waste is generated and has to be dumped in a commonplace.
  • For this, a pit is dug and a layer of soil is scattered on top of the waste and compressed each day.
  • After full landfill, the Area is covered with a thick layer of mud and the site can be developed as a park.
  • Sometimes, contamination of groundwater and soil through landfill occurs, known as leaching.

f) Dumping

  • It is the open throwing of refuse to fill up the low lying areas.
  • A simple and economical method of disposal.
  • It does not produce a foul smell.

g) Composting

  • It is a method applied for putrescible organic matter that can be decomposed aerobically/anaerobically by the biochemical process.
  • Beneficial in the agricultural economy.

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Methods of composting

1) Composting by trenching

  • Trenches 3 to 12 m long, 2 to 3 m wide and 1 to 21 m deep are excavated.
  • Trenches are filled with dry refuse in a 15 cm layer.
  • 10 cm thick good layer earth is placed above 0.3 m ground level.
  • Biological action destroys organic matter in refuse.
  • Heat is generated and the temperature reaches up to 75⁰C.
  • Refuse is stabilized in 4-6 months period and forms humus which has manure value.
  • Stabilized mass is sieved through 12.5 mm sieve and sold as manure.

2) Mechanical Composting

  • It is applied in cities where a large area is not available.
  • Here, compost mass i9s stabilized by using a mechanical device.

Following process occurs in this method:

  • Reception of refuse
  • Segregation
  • Shredding and pulverization
  • Stabilization
  • Marketing the humus

3) Open window composting

  • In this method, mineral matter like dust, stone, etc. are removed from refuse.
  • Refuse is dumped in the form of piles.
  • Heat is generated by biological action which causes riser of temperature up to 75⁰C.
  • Piles are now cooled to avoid anaerobic reactions.
  • The process is carried out for 4 to 6 weeks.
  • After a drop in temperature, compost can be used.

4) Incineration

  • It is the most modern and hygienic method of disposal of solid wastes.
  • It is used in conjunction with the landfilling method.

Following phenomena are taking place in this method:

  1. The incinerator consists of furnace provided with grating and chimney.
  2. Charging doors are provided for feeding the refuse and ash formed is removed through ash door.
  3. Furnaces may be circular, rotary kiln, multi-cell or even rectangular.
  4. To reduce the load on the furnace, inert materials like earth, broken glass, etc. are separated out.

Advantages of solid waste management

  • The sites appeared clean and attractive.
  • The environment looks fresh.
  • It can be recycled to get a new model of usable products like toys.
  • It prevents the pollution of water resources.
  • It prevents from blocking of water of the irrigational structure like a canal, drain, etc.

Disadvantages of solid waste management

  • It is expensive to manage solid waste as it requires transportation, labor charge as well as pots to collect solid waste.
  • It consumes space of the cities as solid waste collecter pots.
  • It is time-consuming for the safe disposal of solid waste management.

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