Solid waste practice questions.

Wells sunk into a capped landfill collect the gas produced as buried food and paper decompose without oxygen. The gas of greatest climate concern in that mixture is

• carbon dioxide
• methane
• nitrous oxide
• sulfur dioxide

Answer: methane

Anaerobic decomposition produces roughly equal proportions of methane and carbon dioxide, but methane traps far more outgoing longwave radiation per molecule. That is why engineered sites capture the gas and burn it rather than vent it.

A closed landfill is fitted with wells that collect the gas produced by the waste and burn it in a generator. In the pollution management model this belongs to

• the level that controls the release of the pollutant
• the level that changes the human activity producing the waste
• the level that cleans up and restores the damage already done
• no level of the model, because energy is being recovered

Answer: the level that controls the release of the pollutant

The second level of the model intervenes between the activity and the environment by capturing the pollutant as it is released. Changing what households discard would be the first level, and remediating contaminated land would be the third.

A city replaces landfilling with mass-burn incineration and reports that the volume of waste falls by about 90 %. Which consequence must it still plan for?

• Recycling rates rise automatically because the waste is sorted first
• Bottom ash and fly ash still require disposal
• The mass needing disposal falls by the same 90 % as the volume
• Waste generated per person falls sharply within a year

Answer: Bottom ash and fly ash still require disposal

Incineration reduces volume and recovers energy but does not make matter disappear: the residue is roughly a quarter of the original mass, and the fly ash captured from the flue gases is a concentrated hazardous stream that needs secure landfill.

Electronic waste exported from high-income countries is often dismantled by hand and by open burning to recover metals. The chief hazard to the people doing that work is

• exposure to lead, mercury and dioxins from the dismantling
• physical injury from the weight of the discarded appliances
• loss of income once the exported material runs out
• noise from the machinery used to shred the circuit boards

Answer: exposure to lead, mercury and dioxins from the dismantling

Circuit boards, screens and cables hold heavy metals and brominated flame retardants, and burning the plastic off to reach the copper produces dioxins. The value in the material is real, which is why the trade exists; the problem is that the recovery is done without the containment and protective equipment that make it safe.

Under an extended producer responsibility scheme, a manufacturer pays for the collection and treatment of its products once consumers discard them. The intended effect is that

• consumers pay less attention to how a product is disposed of
• the design of the product begins to reflect the cost of disposal
• local authorities take over responsibility for the safety of products
• the product becomes cheaper to buy at the point of sale

Answer: the design of the product begins to reflect the cost of disposal

Moving the disposal cost onto the party that chooses the materials and the design gives that party a reason to make the product easier to dismantle, repair and recycle. This is the internalising of a cost that would otherwise be borne by the municipality, which is why the instrument sits at the first level of the pollution management model rather than the third.

Mass-burn incineration produces two ash streams. The fly ash captured from the flue gases must be handled as hazardous waste, because it

• is much greater in volume than the original waste stream
• remains hot enough to ignite for several months after it is captured
• concentrates the heavy metals and dioxins removed from the gas
• cannot be landfilled anywhere under international agreements

Answer: concentrates the heavy metals and dioxins removed from the gas

Cleaning the flue gases does not destroy the contaminants; it moves them into a small mass of very concentrated ash. The bottom ash is far less contaminated and can often be used in construction, so a claim that incineration reduces waste by ninety per cent has to say what happened to the remaining tenth.