What this lesson teaches
I can evaluate the problems of urban solid waste and the strategies for managing it.
Syllabus 9173, Topic 3.1, 2. Sustainable Cities. Why is effective waste management important for progress towards sustainable urban development?
Make a guess
A city with patchy rubbish collection buys an expensive incinerator. Will it solve the waste problem?
- Yes, because burning waste makes it disappear.
- Yes, because incinerators remove the need to recycle.
- No, probably not, if waste never reaches the plant.
- No, because incinerators never make electricity.
Show the answer
No, probably not, if waste never reaches the plant.
A plant only treats what is collected. It also needs money, pollution controls and ash disposal, so the whole system must work.
A good waste system combines cutting waste, collecting it, recovering materials and safely treating what is left.
Prevention means less material becomes waste. Durable products, repair, refills and less packaging all help. Charging for rubbish can cut waste, but may hurt poor families or lead to illegal dumping if services are poor.
Collecting waste separately helps recover materials. Recycling needs clean inputs, processing plants and buyers. Food waste can be composted. It can also go through anaerobic digestion, where microbes break it down without oxygen and produce biogas. Informal waste pickers have useful skills; shutting them out can cut recovery. Contamination and poor operation reduce the value of these treatments.
Sort these
Where does each measure fit in a city's waste system?
Groups: Prevent waste, Recover materials, Treat what is left.
- Sending ash to a lined landfill such as Semakau
- Repair shops and refill stations
- Burning leftover waste in a waste-to-energy plant
- Collecting clean recyclables separately
- Digesting food waste to produce biogas
- Composting food waste
- Firms cutting the packaging on their goods
Show the answer
Prevent waste
- Repair shops and refill stations They keep products in use, so less material becomes waste in the first place.
- Firms cutting the packaging on their goods Using less packaging stops waste being created at all.
Recover materials
- Collecting clean recyclables separately Separate, clean collection lets materials be reprocessed instead of thrown away.
- Digesting food waste to produce biogas Microbes break waste down without oxygen and the gas is captured, recovering energy and material.
- Composting food waste Food scraps become compost, so their nutrients are recovered.
Treat what is left
- Sending ash to a lined landfill such as Semakau A lined landfill safely holds what remains after other options are used.
- Burning leftover waste in a waste-to-energy plant It shrinks waste that could not be avoided or recycled, though it leaves ash.
Leftover waste still needs safe treatment. Sanitary landfills are lined to control polluted liquid and gas, but use land and need long-term care. Incinerators shrink waste and can make electricity, but are costly, need pollution controls and leave ash. Burning materials that could be recycled also loses their value.
Singapore burns waste that is not recycled in waste-to-energy plants. Ash and waste that cannot be burned go to Semakau Landfill. This suits its lack of land, but it still needs to cut and recycle waste. A costly plant may not suit a city without reliable collection or funds. Judge the whole system, including maintenance, cost and who is included.
- Prevention
- Stop material becoming waste in the first place.
- Recovery
- Recycling, composting and anaerobic digestion.
- Singapore
- Waste-to-energy plants plus Semakau Landfill for ash.
Step by step
Start with prevention
Can the waste be avoided?
Fit the system
Waste type, money, collection, land and skills.
Check what remains
Ash, emissions, workers and households.
Real examples to use
Semakau Landfill, Singapore
Singapore's only landfill, built offshore, is expected to be full by about 2035. So Singapore burns most waste to reduce its volume and is pushing recycling and less packaging.
Tuas Nexus, Singapore
PUB and NEA are building the first plant in the world planned from the start to treat used water and solid waste on one site. Biogas from used water sludge and heat from burning waste make electricity, so the site makes more energy than it uses. Phases open from 2026.
Tokyo's 23 wards
Burning reduces Tokyo's combustible waste to about one-twentieth of its volume. The ash goes to landfill in Tokyo Bay, and the New Sea Surface site is the last landfill space there. So Tokyo sorts waste strictly to make that site last as long as possible.
Worked example: Same plant, different results
Two made-up cities buy similar equipment. One has reliable collection, trained staff and maintenance funds. The other has none of these. In the second city, better collection and operation may help more than another plant.
Watch out for this
Waste-to-energy makes landfills unnecessary.
Burning leaves ash, and some waste cannot be burned. Safe landfill is still needed.
Check your understanding
Why might an incinerator fail to solve a city's waste problem?
- Burning removes the waste entirely, so nothing is left for the city to manage.
- Incineration does little to reduce the volume of waste.
- Collection may be unreliable, and the plant needs money and ash disposal.
Show the answer
Collection may be unreliable, and the plant needs money and ash disposal.
Yes. The whole system must work, not just the plant.