About recycling rates & product lifetime in the circular economy.

Prof. Dr Walter Stahel is one of the founding fathers of the circular economy, and the core science behind it. In a lecture he held at KTH in March 2021, Stahel presented very convincingly why we should not only focus on high recycling rates, but first and foremost on products with long lifetime.
Circular

Let’s follow his reasoning, step by step

A soft drink can, made of a mixture of aluminium alloys, has an average lifetime of 3 weeks: in other words, 3 weeks have passed between the production of the can, its filling in the drink factory, its delivery to a retail point, its consumption, and finally its disposal in a recycling bin.

 

Let us assume that I have freshly produced 100 kg of aluminium cans, today. My question is for how long will this material remain in-use, circulating in the economy?

 

In a simple model, this depends on 2 parameters: the lifetime of my product (3 weeks) and the recycling rate of my society. Recycling rate means here how much spent aluminium is re-used for making new aluminium cans. Let’s assume this rate is 70%. Losses can occur for various reasons such as improper collection, but also technical limitations during recycling.

 

  • At time 0, I have freshly put on the market 100 kg of aluminium cans.

 

  • After 3 weeks, I have collected and recycled 70% of my 100 kg, which is 70 kg. The remaining 30 kg are lost and disposed in landfills.

 

  • After 6 weeks, I have again collected and recycled 70% of the 70 kg I had left. So 49 kg remain in the economy, and 21 kg more are sent to landfill.

 

  • And the story repeats itself every 3 weeks until we’ve lost all the initial material…

 

The general equation is therefore yt=y0 x rt/p : where y is the amount of material in-use at time t, r is the recycling rate, and p is the lifetime of my products. For the mathematics nerds: note that the product lifetime is in an inverse power relation. Let’s look at this equation graphically:

Material Still In Use

The figure above shows how much material remains after a couple of years, for different recycling rates. It is clear: with a recycling rate of 50% or even 70%, in less than half a year all the aluminium has been landfilled. With 90% recycling, it takes just 3 years before all is lost. Even when reaching rather “challenging” recycling rates of 95%, most of the material is lost in just a couple of years.

 

This means that despite very high recycling rates, we still need to mine virgin materials, at a high pace, to cope with the short product lifetime.  

 

Now, let us see what happens if we instead increase the lifetime of the product, from 3 weeks to 81 weeks. Increasing the product life may mean that we implement a re-use scheme. Stahel explained for instance that re-usable glass bottles perform on average 27 cycles (of 3 weeks each, that is 81 weeks in total) before being sent for recycling.

Material Still In Use2

In the figure above, we show the same blue curves as before (3-week product lifetime), and orange curves with an 81-week product lifetime. We still need lots of virgin material, but it already looks slightly better: while all the material was lost to landfills quite rapidly in the first case; now with a 90% recycling rate and an 81-week lifetime, we still have 50% of the material in-use after 10 years!

Conclusion

What we have illustrated above with aluminium cans and glass bottles applies to any material product. Thus any business aiming for circularity should focus on long-lived products designed to be easily and efficiently recycled.

 

To conclude, let’s quote Prof. Dr Stahel:

 

“Efficiency in the circular economy must be measured in yearly statistics of maintained stocks, not in waste collection rates” (delusively called recycling rates)

 

“The circular economy is silent, invisible, local, and thus ecologic – it requires little publicity, no global distribution infrastructure. In contrast the industrial linear economy is noisy and visible, relying on containers ports, logistic centres, and transport infrastructure.”

 

“Circular economy in one word is: ‘caring’, caring for the materials and resources we have”.

 

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Note on waste management statistics in the European Union:

 

  • As Stahel recalls, in the past 3 decades, the EU statistics used the terminology “recycling rates” to in fact measure “collection rates” of potentially recyclable fractions. This never really mean that “materials collected in recycling bins” would actually be used in the production of new products. It just meant that it would be “sent for recycling”, most often abroad, with very little transparency on the final fate of the recycled material.
  • This terminology however changed in 2020. Now the EU is collecting information on the quantities of material sent to a given recycling process(2) (e.g. pulping plant for paper, glass furnaces, metal furnaces, and palletisation, extrusion or moulding for plastics).

 

Sources:

 

(1) Prof. Dr Stahel’s full lecture is available on YouTube: https://www.youtube.com/watch?v=--kdHePj0y4

(2)  "Commission Implementing Decision (EU) 2019/665 of 17 April 2019 amending Decision 2005/270/EC establishing the formats relating to the database system pursuant to European Parliament and Council Directive 94/62/EC on packaging and packaging waste" https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=celex:32019D0665.