by Charnele Andrews, Sheridan College and John Nicholson, M.Sc., P.Eng
Glass is made by supercooling a hot liquid mixture of sand and soda ash until it is rigid. With supercooling the material does not crystalize, but keeps the same structure as the liquid. This also allows for the material to be formed into various structures. Glass waste generated from municipalities is typically from glass products such as bottles/containers and glassware.
Glass is 100% recyclable and can be recycled endlessly without loss in quality or purity. The challenge with recycling glass is two-fold. The cost of making glass from sand and soda ash is relatively cheap and the cost of recycling glass is relatively expensive, especially when different colored glass needs to be separated.
Another challenge with glass recycling is contamination. Glass containers for food and beverages are 100% recyclable, but not with other types of glass. Other kinds of glass, like windows, ovenware, Pyrex, crystal, etc. are manufactured through a different process. If these materials are introduced into the glass container manufacturing process, they can cause production problems and defective containers. As such, recycling glass into cullet is generally what glass recyclers focus on.
A recent survey conducted by the U.S. Northeast Recycling Council (NERC) demonstrates the challenge of glass recycling. Of the waste glass collected, 54% of it was sent to secondary processors for cleaning in 2017. The second most common destination of the waste glass was landfill as alternative daily cover (23.5%), followed by landfilling (14.7%0 and uses in aggregate applications (7.8%).
Within the more recent years, there has been more effort in the recovery of postconsumer glass waste. Recycling facilities aid in the sorting and processing of municipal recyclables like glass. Glass can either be recycled in recycling bins, in some retail locations or at community waste glass drop – off locations.
Typically waste glass in recycling facilities is sorted by colour and crushed to a size less than 50 mm. Coloured glass, referred to as cullet can be used to manufacture new glass containers. This however is not used very frequently due to the contamination issues mentioned earlier.
Recycled waste glass when crushed to sizes similar to that of natural sand has properties of an aggregate material. This aggregate glass material can be used in pipe bedding and the sub surfaces of roads and parking areas.
Recycled glass used to make balls
NexCycle, an Ontario-based company has been recycling glass for 15 years. The company collects both post-consumer and post- industrial scarp waste. Optical sorting technology is used to sort the glass by colour and purity. The glass is then processed into cullet, which can be sold to glass manufacturing industries as raw material. NexCycle claims to be the largest supplier of cullet to the glass container/bottle industry in Canada. The company also sells cullet to fiberglass manufacturers, the glass bead industry. Ground glass produced by Nexcyle is sold to the abrasive industry.
The Regional Municipality of Niagara in Ontario is looking into creating a new market for recycled glass. With funding assistance from the Community Improvement Fund, the Municipality will undertake a project that will look into the use of processed recycled glassware in the formation of bio-soil. The processed glassware would be a replacement for the 85% sand component of the bio-soil. Glass is a resource in which its granular size can be controlled and easily reproduced. Bio-soil already is used in many places around the Niagara region, including parking lot islands, parks and storm water planters.
