In the waste management hierarchy, which is most preferred and which is least preferred?

Incineration most, composting least

Which set of conditions suits aerobic composting?

C/N 25-30, moisture 50-60%, 55-65 degC, enough air

C/N 5, moisture 5%, 20 degC, no air

C/N 100, saturated moisture, 5 degC, no air

C/N 25-30, no air, 850-1100 degC

Why is incineration used mostly for medical and hazardous waste rather than general MSW in Nepal?

It needs high calorific, low-moisture waste, is costly and needs air pollution control

It produces compost as a by-product

What distinguishes a sanitary landfill from open dumping?

Waste is compacted in layers, covered daily with soil, with liner, leachate collection and gas vents

Practice · 8 marks

Solid waste management system and techniques

Short answer

Functional elements: generation, on-site storage, collection, transfer, treatment, disposal. Hierarchy: reduce, reuse, recycle, treatment, landfill. Composting: aerobic decomposition of organics, windrow/pit, C/N 25–30, 4–8 weeks. Incineration: 850–1100°C reduces volume ~90%, needs high calorific waste and emission control. Sanitary landfill: layered and compacted with daily soil cover, liner, leachate collection, gas vents.

Describe the functional elements of a municipal solid waste management system and explain composting, incineration and sanitary landfill as treatment and disposal techniques. Mention the waste management hierarchy.

Functional elements

Generation and source reduction (houses, markets, industries).
On-site handling and storage (bins, segregation at source).
Collection (door to door, community bins).
Transfer and transport (compactor trucks, transfer stations).
Processing and treatment (recycling, composting, incineration).
Final disposal (sanitary landfill).

Waste hierarchy (3R)

  Reduce  (most preferred)
    |
  Reuse
    |
  Recycle / recover
    |
  Treatment (compost, energy)
    |
  Landfill (least preferred)

Composting

Aerobic biological decomposition of organic waste by microorganisms into stable, humus-like compost. Methods: windrow, pit, aerated static pile and vermicomposting (using earthworms). Conditions: C/N 25-30, moisture 50-60%, temperature 55-65 $^\circ$ C, and enough air. Time: 4-8 weeks. The product is a soil conditioner. It suits the high organic fraction of waste in Nepal.

Incineration

Controlled burning of waste at 850-1100 $^\circ$ C to reduce volume by about 90% and mass by about 70%. The heat can generate steam or electricity. It needs waste of high calorific value and low moisture, and air pollution control (scrubbers, bag filters) for dioxins, fly ash and acid gases. It is costly, so it is used mostly for medical and hazardous waste.

Sanitary landfill

Engineered disposal of waste in layers, compacted and covered each day with soil (15 cm). Features: site selection (away from water sources), liner (clay/HDPE), leachate collection and treatment, gas vents (methane collection), final cap and monitoring. Leachate and methane are the main problems; the land can be reused after closure.

Other methods: open dumping (bad practice), pyrolysis, and biogas digestion of organic waste.

✓ Answer checked by Claude Opus 5.5 (high effort)

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