- Practice · 6 marks
Physical and chemical characteristics of solid waste
Short answer
Physical: composition (organic, paper, plastics) guides treatment; density (loose 100–300, compacted 400–700 kg/m³) sizes bins; moisture (20–60%) affects calorific value; particle size determines shredder design. Chemical: proximate (moisture, volatile, ash) and ultimate (C,H,O,N,S) analyses predict combustion; calorific value 3000–4500 kJ/kg decides incineration feasibility; C/N 25–30 for composting; hazardous constituents affect safety.
Explain the physical and chemical characteristics of municipal solid waste and state why each is important in the management of solid waste.
Municipal solid waste (MSW) is the solid waste generated by households, markets, offices, institutions and streets. Its characteristics decide the methods of collection, treatment and disposal.
Physical characteristics
| Property | Meaning | Importance |
|---|---|---|
| Composition | Percentage of food/organic, paper, plastics, glass, metal, textile, inert | Selection of recycling, composting or incineration; developing countries have 50-70% organic waste |
| Density | Mass per unit volume (loose 100-300; compacted 400-700 kg/m) | Design of bins, vehicles, landfill volume |
| Moisture content | Water in the waste, typically 20-60% | Affects heating value, composting and leachate |
| Particle size | Size distribution | Design of shredders, separators |
| Generation rate | kg/person/day, depends on income and season | Planning of services |
Chemical characteristics
- Proximate analysis: moisture, volatile matter, fixed carbon and ash. Indicates how well the waste burns and how much ash must be disposed of.
- Ultimate analysis: percentage of C, H, O, N, S and ash; used to compute the energy value, the air requirement and the gases formed in incineration.
- Calorific (heating) value: energy per kg, about 3000-4500 kJ/kg for MSW in developing countries (higher in developed countries). Incineration needs at least about 6000-7000 kJ/kg, or an auxiliary fuel.
- C/N ratio: best 25-30:1 for composting.
- pH, lipids, carbohydrates, proteins, fusing point of ash (clinkering): relate to biodegradability and furnace operation.
- Hazardous constituents: heavy metals and toxic chemicals that affect compost quality and leachate toxicity.
Sampling is carried out by quartering, and sorting the sample gives the composition by weight.
✓ Answer checked by Claude Opus 5.5 (high effort)
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