Tips for High-Quality Cullet

Contamination from non-container glass, metal, gravel, and dirt can occur when glass containers are set out for recycling, during collection and processing, or in transit. Unwanted items in cullet:

• Decrease the value of recovered glass.
• Increase recycling costs.
• Slow container production.
• Reduce glass quality.
• Damage glass manufacturing equipment.

To improve markets—and revenue—for recovered glass:

• Step up quality control to weed out contamination.
• Retain glass size during collection and processing.
• Set up recycling contract incentives with a shared revenue component.
• Use new, high-tech equipment, such as optical sorting.
• Add restaurant, bar, and hotel recycling to expand clean glass recovery.

1. Step up quality control.

• Know market specifications—Understand the buyer’s specifications and acceptance policies, ability to remove contaminants (including metals), transportation preference (truckload or rail car), and “furnace ready” requirements.
• Conduct inspections—Before adding newly-collected glass to stored recyclables and during loading for shipment, inspect for quality. Also check the truck bed and the tarp used to cover the load for any residue from a previous haul.
• Protect stored cullet—If stored outdoors, place cullet on a concrete pad—not on the ground or asphalt—to avoid contamination from dirt or gravel during loading. Cover cullet during cold or wet weather.
• Keep cullet separated by color—When storing multiple loads of colored cullet, keep cullet separated to avoid intermingling of colors.

2. Retaining glass size during collection and processing.

• Avoid crushing cullet—Glass containers naturally break with handling, a trade off for economic transport. Crushing cullet, however, will not add to its value.
• Reduce compaction—Experiment with reducing the compaction ratio in the collection trucks. Although this may shorten collection routes a bit, it will also reduce breakage and color mixing, improving the value of the recovered glass.

3. Provide contract incentives to recycling service providers.

When developing a contract with the recycling service provider, create shared revenue or limits to encourage low residual and contamination rates. This will support more glass being marketed to the highest value end-market—container glass.

It may be useful in a contract to prescribe the type of end-markets acceptable for the recovered glass, or exclude marketing as aggregate. Some cities include contract language to help ensure recyclables are not disposed of or used as daily landfill cover.

What’s the advantage? The recovered glass will yield more revenue, with fewer residuals to dispose of. It will also help to close the loop—returning container glass back into new containers.

4. Implement new systems or technologies.

Employ or pilot test new procedures and equipment to improve the quality and amount of glass recovered for recycling:

• Automated sorting—These processing technologies can reduce overall costs and increase quality. Optical sorting, which uses air classifiers and jet streams tied to ultraviolet beams to sort crushed glass by color, and ceramic detection technology are available at both materials recovery facilities (MRFs) and glass processing plants across the U.S. Automated equipment in most beneficiation plants is also available to separate nonferrous metals, such as bottleneck rings, from cullet.
• Efficient transportation—Transporting cullet to locations where it can be recycled may result in prohibitively high costs. To respond, the glass container industry works with communities to explore ways to make transporting cullet less costly, such as backhauling or shipping by rail.
• Materials exchange—Glass container plants across the country have different color specifications. To alleviate surplus and shortages, some companies participate in a swapping program, exchanging cullet they do not need for a color they can use. List of state waste exchanges.
• Cooperative marketing—For smaller communities, pooling the glass each city collects, or materials consolidation, and then marketing it together may help to secure a higher value end use for the cullet and save costs.

5. Add commercial collection routes

A commercial collection route for bars, restaurants, and other businesses that generate high-value recyclables provides for increased glass recycling with fewer collection stops. More on bar/restaurant recycling.