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Municipal Solid Waste Management


Municipal Solid Waste: Mixture of solid & semi-solid waste originated due to different activities in the residential & commercial establishments. Solid waste is classified as 

  • Industrial
  • Domestic
  • Hazardous – waste that possess substantial danger immediately or over a period of time. Ex- Radioactive substance, flammable waste etc.

DOMESTIC WASTE (REFUSE)

  • Garbage – Biodegradable (450-900 kg/m3)
  • Ashes – Non-combustible (700-900 kg/m3)
  • Rubbish – Non-biodegradable (50-400 kg/m3)

If various materials in the waste are having different densities, the overall bulk density is calculated as follows –

Methods of Disposal

  1. Open Dumping
  2. Sanitary Land Filling
  3. Composting
  4. Incineration & Pyrolysis
  5. Shredding & Pulverization
  6. Barging into the sea

 1.OPEN DUMPING

  • Very simple method in which the solid wastes collected from the city are dumped in low lying area located far off from the city.
  • Not an eco-friendly method.
  • Results in contamination of environment.
  • Highly unacceptable method as it gives unsightly nuisances, obnoxious odour & is a breeding place for mosquitoes & flies.
2.SANITARY LANDFILL

  • Refuse is carried and dumped in low lying areas under an engineered operation designed & operated in an environmentally sound manner so as to not cause any public nuisance or hazard to public health.
  • The refuse is dumped & compacted in layers  of about 1m thickness & after the day’s work, it is covered with good earth of 15 cm thickness.
  • The cover is called daily cover.
  • Sealants are used on the surface of earth before dumping so as to prevent leaching of impurities.
  • Sealants used can be bitumen, asphalt, butyl chloride, vinyl chloride, bentonite slurry (drilling mud)
  • DDT & insecticides are spread over the daily cover to prevent mosquito and fly breeding.
Advantage: 
  • No costly plant required
  • Low lying waterlogged areas & quarry pits can be put to better use
  • No residues or byproducts left. Hence, further disposal not required
Disadvantage:
  • Continuous evolution of foul gases.
  • Leachate (impure water percolating through the soil) is formed which may pollute the ground water.
  • Low lying areas may not be easily available.
3.COMPOSTING
  • Composting is biological disposal (segregating at source itself) of refuse in which decomposition can be carried out aerobically or anaerobically.
  • The end product of composting is termed as compost or manure or humus.
  • Composting is ecologically most acceptable method.
  • If composting is carried out aerobically, it is called INDORE PROCESS.
  • Aerobic process is completed within 2-3 months, mixing being done either manually or mechanically.
  • If the mixing is carried out anaerobically, it is called BANGALORE PROCESS.
  • Anaerobic process is completed within 5-6 months in which the refuse is kept in closed trenches
  • In composting, the optimum conditions are attained when Carbon/Nitrogen ratio is between 30-50.
  • A ratio much higher than this will slow down the decomposition by oxidizing the excess carbon to CO2.
  • If the ratio is lower than 30, composting will be inhibited due to low-energy supply and nitrogen will be lost both by leaching and volatilization as ammonia.


Note – In Composting, Vermi-compost is the end product of the breakdown of organic matter by an earthworm.

4.INCINERATION & PYROLYSIS

  • Best method for disposal of plastic & rubber
  • In these methods, disposal of refuse is carried out by burning it at high temperature
  • If burning is done in the presence of oxygen, it is termed as Incineration
  • If burning is done in limited or no supply of oxygen, it is termed as Pyrolysis.
  • This method is adopted for refuse having high calorific value
  • Costliest method, heavy power consumption
5.SHREDDING AND PULVERIZATION

  • These methods reduce the nuisance of refuse before disposal
  • Pulverization is based on grinding action. It is done by MACERATORS
  • Shredding is based upon cutting or tearing action. It is done by COMMINUTORS
6.BARGING INTO THE SEA

  • Disposal of refuse into sea can be done if it is disposed far off from the shore (15 to 20 km) below the water surface level (3-5 m) during the time of low tides.
Note – Biomagnification is the accumulation of toxic substances when they enter a food chain. Ex- DDT & other pesticides etc.

CLASSIFICATION OF PLASTIC








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