Life cycle assessment and recycling

A life cycle assessment (LCA) adds up the environmental impact of a product from start to finish:

1. Extracting and processing raw materials (mining ore, drilling for oil, growing cotton).
2. Manufacturing and packaging.
3. Use and operation (the fuel a car burns, the electricity a fridge uses).
4. Disposal at the end of its life (landfill, burning, recycling).

Transport between stages counts too. At each stage an LCA looks at energy, water, resources used and waste or pollution made.

Energy, water and masses can be measured. How harmful a pollutant is has to be judged, so two groups can read the same data differently. A short or selective LCA can be used to back up a claim in an advert.

Add every stage before you compare. When one product is used many times, compare per use.

1. Glass bottle: 8.0 MJ to make, 0.6 MJ to wash and refill each use. Plastic bottle: 2.0 MJ, used once
2. each use of the glass bottle saves 2.0 − 0.6 = 1.4 MJ against a new plastic bottle
3. uses needed to pay back the 8.0 MJ = 8.0 ÷ 1.4 = 5.71
4. so from the 6th use onwards the glass bottle has used less energy in total

percentage lower = (higher total − lower total) ÷ higher total × 100

• Reduce: use less in the first place (thinner cans, longer-lasting goods).
• Reuse: use the object again as it is (washing and refilling glass bottles).
• Recycle: break the material down and make something new. Metals are melted and recast; glass is crushed and melted; scrap steel is added to iron from the blast furnace.

Recycling saves finite ores and usually energy, but collecting, sorting and transporting the waste use energy too, so include them.

1. Aluminium oxide Al₂O₃: Mr = 2 × 27 + 3 × 16 = 102
2. percentage of aluminium = 2 × 27 ÷ 102 × 100 = 52.9%
3. Recycling 10 tonnes of aluminium avoids 10 ÷ 0.529 = 18.9 tonnes of aluminium oxide
4. If the bauxite is 50% aluminium oxide, that is 18.9 ÷ 0.50 = 37.8 tonnes of bauxite not mined

Two aluminium atoms in Al₂O₃: using 27 instead of 2 × 27 halves the answer.