Life cycle assessment and recycling

Chemistry · Using resources. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

A life cycle assessment (LCA) measures the effect a product has on the environment over its whole life. It looks at four stages: getting and processing the raw materials, manufacturing and packaging, use during its lifetime, and disposal at the end, with transport at every stage.

Some things are easy to measure, such as the water, energy and resources used and the waste produced. The harm done by pollutants is harder to give a number to, so it needs a value judgement. This means an LCA is not purely objective.

We can use fewer resources if we reuse products and recycle materials. This saves raw materials and energy and makes less waste.

Rules to remember

LCA stages: raw materials, manufacturing and packaging, use and operation, disposal; include transport and distribution at each stage.
To compare two products fairly, work out the impact per use, not just the impact of making one item.
A shortened or selective LCA can leave out stages, so it can be misused to support advertising claims.
Reuse: the object is used again as it is, e.g. a glass bottle is washed and refilled.
Recycle: the material is processed into something new, e.g. glass is crushed and melted, metals are melted and recast.
Recycling metals uses less energy than extracting them from ores, saves limited ore, and reduces mining and waste.
Adding scrap steel to iron from the blast furnace reduces the amount of iron ore that must be extracted.

Common mistake

Students compare only the energy needed to make each product. Always check how many times each one is used and what happens to it at the end of its life.

Worked example

A glass bottle needs 8.0 MJ of energy to make. It is used 20 times and each wash uses 0.2 MJ. A plastic bottle needs 1.5 MJ to make and is used once. Which uses less energy per use?

Washing energy for the glass bottle = 20 × 0.2 = 4.0 MJ.
Total for the glass bottle = 8.0 + 4.0 = 12.0 MJ, so energy per use = 12.0 ÷ 20 = 0.60 MJ.
The plastic bottle is used once, so its energy per use = 1.5 MJ.

Answer: The glass bottle, at 0.60 MJ per use compared with 1.5 MJ for the plastic bottle.

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