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