CHAPTER:9 (7 to 8 marks) (2 hrs)
Disposal of Solid Waste
Prepared by: Er. Sachin yadav
Contents:
9.1. Types and characteristics of solid waste.
9.2. Composition of solid waste.
9.3. Methods of solid waste collection.
9.4. Disposal of solid waste by dumping, incineration, composting and sanitary landfill.
9.1. Types and characteristics of solid waste
Based upon the types of solid wastes, they are classified as follows:
i) Municipal wastes
→ It includes garbage, rubbish (combustible and non combustible waste), ashes, demolition wastes, etc.
a) Garbage
→ It includes all putrescible(decay) organic wastes from kitchen.
→ It also includes animal dung, leaves of trees, etc.
→ It decomposes quickly, resulting foul odour and the breeding of flies and mosquitoes.
→ It weighs form 450 to 900 kg/m³.
b) Rubbish
→ It includes combustible wastes (paper, plastics, wood) and non-combustible wastes (glass, tin cans)
→ It weighs form 50 to 400 kg/m³.
c) Ashes and residues
→ It includes residues of burning of wood, coal, etc.
→ It is incombustible and composed of fine powdery materials.
→ It weighs from 700 to 850 kg/m³.
d) Demolition and construction wastes
→ It includes wastes from demolished building and construction structures.
→ It comprises stones, bricks, dirt, plaster, etc.
ii) Industrial wastes
→ It includes rubbish, ashes and construction wastes. It can be recycled and recovered.
(iii) Hazardous wastes
→ It is corrosive, reactive and toxic in nature.
→ It posses threat for plant and animal life.
Depending on characteristics of constituents of solid wastes, they are classified as follows:
i) Organic wastes
→ It includes food wastes, grass, animal excreta, etc. It produces highly unwanted odour.
ii) Inorganic wastes
→ It includes rubbish, ashes and construction wastes. Hazardous wastes fall in this category.
Depending upon source, they are classified as:
i) House refuse
→ It includes wastes produced form housekeeping activities. It comprises food wastes, ashes, rubbish, plastic,
etc.
ii) Street refuse
→ It includes wastes produced form streets. Street sweeping, catch basin debris, etc. fall in this category.
iii) Trade refuse
→ It includes wastes produced from factories, hotels and business centres. It includes food wastes, industrial
and other wastes.
9.2. Composition of solid waste
i) Quantity of garbage in solid wastes depends upon food available culture, living standard, etc.
ii) According to survey, organic wastes produced are about 55% and inorganic wastes are about 45%.
iii) In Nepal, average household waste generation rate is 0.25 kg/person/day.
9.3. Methods of solid waste collection.
Solid wastes are collected in the following ways:
i) It is collected in individual houses in small containers.
ii) Public dustbins may also be used.
iii) Hand carts of 0.5 m³ capacity is also suitable.
Transportation of collected wastes to the disposal site is achieved by the following vehicular means:
1) Auto-rickshaws
→ Capacity varies from 0.5 to 0.75 tonnes.
→ Suitable for areas where heavy vehicles cannot go.
2) Trailers
→ Capacity varies from 2 to 3 tonnes.
→ Unloading is done by hydraulically operated jack.
3) Trucks
→ Capacity varies from 5 to 10 tonnes.
→ Generally, of tilting-tipping type.
9.4. Disposal of solid waste by dumping, incineration, composting and sanitary landfill.
Or
SOLID WASTE DISPOSAL METHOD
1. Dumping.
→ It is the open throwing of refuse to fill up the low lying areas.
→ Simple and economic method of disposal.
→ It does not produce foul smell.
2. Sanitary Landfill
→ It is an alternative to landfill to solve the problem of leaching and odour nuisance.
→ They are lined with impermeable materials like plastics and clay.
→ The solid waste is compacted by mechanical means and covered well by earth work to all exposed surfaces.
→ Final cover is provided of soil and geo membrane after completion of filling in landfill.
Advantages
→ Minimized environment risk.
→ Reduced risk from leachate and gas.
Disadvantage
→ It is a longer sitting process.
→ Cost and site preparation time is large.
3. Incineration
→ It is the most modern and hygienic method of disposal of solid wastes.
Following phenomena takes place in this method
a) The incinerator consists of furnace provided with grating and chimney
b) Charging doors are provided for feeding the refuse and ash formed is removed through ash door
c) Furnaces may be circular, rotary kiln, multi-cell or even rectangular
d) To reduce load on furnace, inert materials like earth, broken glass, etc. are separated out
Following points should be carefully observed
a) The charging of refuse should be rapid and continuous
b) Each batch of refuse should be well mixed
c) Minimum temperature in combustion chamber should be around 670°C
Advantages
a) Complete destruction of pathogens and insects.
b) No dust nuisance or odour trouble.
c) Clinkers produced may be used for road construction.
Disadvantages
a) Initial expenditure required is large.
b) Improper handling leads to air pollution.
c) Residues from burning of solid wastes requires further disposal.
d) High chimneys are required for safe disposal of smoke.
4. Composting.
→ It is a method applied for putrescible organic matter that can be decomposed aerobically/anaerobically by
biochemical process.
→ Beneficial in agricultural economy.
• There are three methods of composting
- Composting by trenching
- Open window composting
- Mechanical composting
a) Composting by trenching
b) Open window composting c) Mechanical composting:
Advantages
→ It converts available biomass into compost and provides economic returns.
→ It saves cost of transportation and disposal.
→ This method consumes less energy than other methods like incineration.
→ There is possibility of community participation
→ The wastes also get recycled.
Disadvantage
→ High operation costs.
→ There is need of waste segregation into degradable and non-degradable.
→ Some wastes may not be suitable for composting due to significant quantities of paper, plastic, etc
