3.13 Recycling and Recovery of Waste



3.13 Recycling and Recovery of Waste

Recycling consumes less energy, and therefore produces less CO2, than extracting and processing raw materials. In 2008, the amount recycled in the UK saved the same amount of CO2 (18 million tonnes) as taking five million cars off the road, even with only 31 per cent of household waste being recycled or composted. Recycling also reduces the need for extracting (mining, quarrying and logging), refining and processing raw materials, all of which cause substantial air and water pollution.

(Source Open University [see reference 8])
Above text sourced from The Open University under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence

Recycling of Metals

In the UK, consumers discard 84% of all cans, which means the overall rate of aluminium waste, after counting for production losses is 88%. As the cost of energy rises, so does the cost of production of metals. As a result the value of scrap metal increases. This has led to an increase in metal being sold for scrap, and in UK specifically, an increase in theft of metals for scrap, such as lead being stolen from church roofs or copper cables being stolen from the side of railways. The energy cost of recycling metal is much less than producing it from ore, and it is easier to separate ferrous metal from the waste stream as magnets can be used.

Recycling of Plastic

Plastic has a high recyclability, however different types of plastic cannot be mixed and additives and fillers added during the manufacturing process tend to degrade the plastics. As a result, plastic is easy to recycle in the factory, but once in the waste stream very difficult to separate.

The following is a talk about successful recycling of plastic in the USA


There are 4 levels of plastic recycling:

  • Primarydirectly re-extruded, possible only where a pure waste stream exists in the factory
  • SecondaryA mechanical process where waste plastic is ground into small chips or powder, washed and dried and converted to resin for re-use. Contaminants reduce the quality of recycled plastic
  • TertiaryInvolves pyrolysis (burning without oxygen). This chemically breaks down plastic into feedstock. Technically feasible but energy and financial cost is high
  • QuaternaryPlastic is burnt for heat as energy recovery. If this process is completed efficiently a very small amount of volatile organiccompounds will be released. This could be considered a better step than land fill, as at least energy is recovered from the process.

(Source Sustainable Materials With Both Eyes Open [see reference 2])
Above text sourced with permission from Sustainable Materials With Both Eyes Open. This book is available free to view online

Many cities have incinerators, which burn waste and recovery the heat gained from the process for district heating systems and electricity production. This is sometimes considered a source of renewable energy, but it is a questionable term as generally the waste products were not manufactured with renewable resources. The efficiency of the burn process is paramount, as the emissions from an incinerator can be toxic.

As resources become scarce and energy costs and therefore manufacturing costs become high, the cost benefits of recycling will increase and more recycling will occur. Currently though, recycling rates are quite low compared to the amount of waste produced.

Engineers can mitigate against these issues by designing products with a higher recyclability. This can be done by avoiding mixing different materials where possible, as they will have to be separated before recycling. In the case of plastics, reducing the scale and variety of plastics on the market would increase recycling rate too.