It may seem more environmentally economical to send glass to be re-melted than create completely new glass and dump the old containers, but the glass may need to meet certain standards to be accepted by a smelter.
Auckland glass smelter OI, for example, rejects contaminated glass or consignments containing too much broken glass.
However, there are still recycling options for unwanted glass. Central Otago District Council waste minimisation officer Sophie Mander said the most common alternative option was to use it for roading as a "gravel substitute".
A spokesperson for Fulton Hogan said the company took glass from recycling centres in Wanaka and Queenstown and the sorting plant in Frankton. It crushed the glass at a facility near Cromwell and used the resulting product as a roading aggregate.
Crushed glass could also be used in building foundations. This was done by Blackhead Quarries in Dunedin, and was believed to store heat better than gravel.
Mike Olsen, of Earnscleugh, with some funding from the Glass Packaging Forum, built a crusher and had it installed at Wastebusters in June 2009.
He hoped it would be able to crush all the glass coming through the depot and start eating through the glass mountain, but this proved impossible.
However, Mr Olsen is developing a translucent paving system for surfacing paths that contains crushed and tumbled plate glass.
In Cromwell, owner and operator of Naked Waste Rory Alexander imported a portable crusher that can crush up to 10,000 bottles an hour. Small-scale crushing operations that could be used locally were a great alternative to shipping used glass to Auckland, he said.
After crushing the glass, Mr Alexander sifts it into various sizes. The finest product looked and felt "just like sand and is child-safe".
Bigger particles can be used for sand-blasting or decorative purposes.
