Life Cycle Assessment

Is it best to use cups made of paper, polymer foam, or ceramic? Which ones cause the least environmental damage? Paper, of course, comes from wood, and wood is a natural renewable resource. On the other hand, foam cups are made of polystyrene, which is obtained from crude oil, a nonrenewable resource. Does this mean a paper cup is [Page 1048]more environmentally friendly than a foam cup? However, even though paper is from a renewable source, many harmful chemicals are emitted during its manufacture. Do the advantages of renewability outweigh the harm from emissions? Life Cycle Assessment (LCA) aims to answer questions such as these and can be useful for making technological choices.

LCA evaluates the environmental impact of a product throughout its life cycle starting from raw material extraction, going through product manufacture, use, recycle, and disposal. The life cycle of a paper cup would thus include cutting down the trees to obtain wood chips, transporting them to paper mills where they are converted to paper cups, transportation of cups to the market, sale of cups to consumers, and use by consumers. The cycle would end when the cups are reused, recycled, or discarded.

A typical LCA of a product consists of four steps: goal and scope definition, inventory analysis, impact assessment, and improvement analysis. The first step consists of specifying the purpose of the life cycle study and in simple cases means comparing the environmental burden of two products with similar uses. Scope definition implies identifying and specifying the important processes to be included in the life cycle of a product.

For the second step, inventory data are collected for each of the processes in the life cycle. Input data typically includes material and energy consumption data, while output data includes the emissions of various substances. There can be a variety of emissions during the entire life cycle, such as carbon dioxide, sulfur dioxide, methane, or benzene. These have different impacts on human health and ecosystem quality.

Impact assessment, the third step, aims at understanding the quantitative magnitude and significance of the potential environmental effects of all these emissions in different impact categories. For example, carbon dioxide and methane can cause global warming; sulfur dioxide and benzene can affect human health. This is the step in life cycle assessment where the results are used to draw conclusions and make recommendations for improving the environmental performance of a product.

Returning to the example of the paper, plastic, and ceramic mugs, it turns out that each of these three cups has a dark side. A ceramic mug is made from clay, which is relatively clean; it can also be used multiple times, which reduces waste. These properties make it attractive. But is it better than a paper or plastic cup?

Wood, the original source material of paper, is supposedly green, but during the transformation of wood to paper, steam is needed to heat the wood, machines are used to grind the wood fiber, and vacuum pumps and dryers are essential to remove the water from the pulp. All of these consume energy. Additionally, many inorganic chemicals—chlorine, sodium hydroxide, sodium chlorate, sulfuric acid, sulfur dioxide, and calcium hydroxide—are used during the pulping and bleaching phases. Also, although paper is biodegradable, it releases methane during its degradation, which contributes to global warming.

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