Glass recycling

Glass recycling is the process of collecting, processing, and re-manufacturing waste glass into new products. Glass is ideal for recycling because it is not degraded by normal use. Scrap glass material, known as cullet, is used in glass manufacturing to reduce the consumption of energy and new raw materials. There are two types of cullet:

  • Internal cullet comprises waste glass generated by glass production processes themselves, including quality control rejects, material from production transitions (such as colour or specification changes), and manufacturing offcuts.
  • External cullet consists of post-industrial and post-consumer waste glass collected through organised recycling programmes.

External cullet requires more extensive processing and quality control because of potential contamination from consumer use and collection processes.

Prior to recycling, glass waste must be purified and cleaned of contamination. Then, depending on the intended use and local processing capabilities, it might also have to be separated into different sizes and colours. Many recyclers collect different colours of glass separately, because glass tends to retain its colour after recycling; collection points often have separate bins for clear (flint), brown (amber) and green waste glass. Separation by colour at the collection point may not be required if the glass re-processor uses optical sorting equipment.

Heat-resistant glass, such as borosilicate glass (including Pyrex), must not enter the glass recycling stream, because even a small piece will alter the viscosity of the fluid in the furnace at remelt.

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