Waste Materials and Their Effective Management
Senior 1 · Chemistry
Waste Materials and Their Effective Management
Lesson 3 of 5
25 min
On the northern edge of Kigali, in Nduba Sector, a hill is growing that is made not of rock but of the city's rubbish. Lorries arrive all day. People living nearby complain of the smell, of flies, and of dirty water running from the site into their fields. What exactly makes badly managed waste so dangerous, and what can go wrong at a landfill?
Table 3.1: Hazards of badly managed waste
| Hazard | How it happens | Example |
|---|---|---|
| Disease | rotting waste feeds flies and rats; rainwater in discarded containers and tyres breeds mosquitoes | diarrhoea and typhoid spread by flies; malaria |
| Water pollution | rain soaks through waste and dissolves chemicals and metals, forming leachate that seeps into groundwater and streams | a well near a dump becomes unsafe |
| Air pollution | burning waste, especially plastics, gives off smoke, soot and poisonous gases; rotting waste gives off methane and bad smells | choking smoke from burning rubbish heaps |
| Fire and explosion | methane from buried waste is flammable and can collect in pockets | fires that smoulder inside dumps for weeks |
| Floods | plastic bottles and litter block drainage channels | streets flooded after heavy rain |
| Harm to animals | cattle and goats swallow plastic; animals are trapped in litter | a cow with plastic in its stomach |
| Poisoned soil | heavy metals from batteries and e-waste leak into the ground | lead and cadmium around a dumped battery |
| Injury | broken glass, needles, and collapsing waste heaps | the Kiteezi landfill collapse (below) |
Definition
Leachate: the polluted liquid formed when water drains through waste, dissolving and carrying away substances from it, such as salts, acids and heavy metals. Example: the dark, smelly liquid that runs out from the bottom of a rubbish heap after rain.
Inside a large heap, food and other organic waste is buried where air cannot reach it. Bacteria that live without oxygen break it down anaerobically, producing a mixture of methane and carbon dioxide called landfill gas. For glucose:
Methane is flammable, and a mixture of methane and air can explode:
It is also a greenhouse gas many times more powerful than carbon dioxide. Burning plastics is no answer: PVC gives off hydrogen chloride, and burning plastics in general produce soot and dioxins, which are poisonous even in tiny amounts.
Figure 3.1: An open dump compared with a sanitary landfill.
Definition
Sanitary landfill: an engineered site where waste is buried in layers in a pit lined with clay and plastic, covered with soil every day, with pipes that collect the leachate for treatment and the landfill gas for burning or use as fuel. An open dump has none of these protections.
Nduba is Kigali's landfill, in Nduba Sector, Gasabo District. It opened in May 2012 after the old Nyanza landfill in Kicukiro was closed. It started on 15 hectares and was later enlarged, so that the total area is now 52.6 hectares. It is managed by WASAC through private operators. In April 2024 a committee of Rwanda's Parliament reported serious problems: workers without proper protective equipment, waste water flowing from the site into surrounding communities, waste not being processed into fertiliser as planned, and about 394 residents still living inside the buffer zone that should separate the site from homes. The government said it was seeking funds for a new, modern site. (KT Press, 30 April 2024.)
Worked example
Problem. The Nduba site covers 52.6 hectares. (a) Convert this to square metres (). (b) A football pitch is about 0.714 hectares. About how many pitches would fit on the site? (c) By how many hectares has it grown since it started at 15 hectares?
Solution.
Answer: , about 74 football pitches, 37.6 ha more than at the start. Every tonne that is composted or recycled instead is space the city does not have to find.
Kiteezi is the main dump for Kampala, Uganda's capital. It was reported to have reached its capacity in 2012 but kept receiving waste. On the morning of 9 August 2024, during a heavy rainstorm, the unstable mountain of garbage slid downhill onto homes, gardens and people. By 16 August, 35 deaths had been confirmed. A waste heap is not solid ground: rain makes it heavier and slippery, and it can fail like a landslide.
Worked example
Problem. Balance the equation for the anaerobic breakdown of glucose in a landfill: .
Solution.
Answer: landfill gas is roughly half methane and half carbon dioxide, which is why it can burn.
Warning
Stay safe around waste. Do not play on or search through rubbish heaps: they hide broken glass, needles and poisonous chemicals, they can catch fire, and they can collapse. Never burn plastic, tyres, batteries or e-waste. If you find a needle, do not touch it; tell an adult.
Tip
Waste harms through "the four Ws": Water (leachate), Wind (smoke and gases), Wildlife and people (disease, injury), and Wasted resources.
TED-Ed: What really happens to the plastic you throw away (4 min). Follow the three bottles and note which journey ends in a landfill.
Practice
Sources and credits
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
