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Issues Of The Environment: The Challenges Of Recycling Glass


Glass is one of many materials that can and should be recycled.  In this week's "Issues of the Environment," WEMU's David Fair talks with Ypsilanti Department of Public Services director Ronald Akers about why glass is no longer allowed as part of the city's curbside recycling program and how residents can make sure the glass still gets recycled. 


  • The Glass Manufacturing Industry Council (GMIC), a nonprofit trade association, says that recycling glass reduces waste sent to the landfill, and using recycled glass “cullet” in the manufacturing of new glass is significantly more energy efficient and reduces greenhouse gas emissions.  Still, each year, Americans throw out about 10 million metric tons of glass, and almost all of it goes to a landfill.  Only about one-third of U.S. glass is recycled.  
  • In August of 2019, Ypsilanti city officials announced that glass would no longer accept glass as part of curbside recycling.  The Western Washtenaw Recycling Authority sorts recyclables for Ypsilanti (also western Washtenaw County, Chelsea, and Dexter), using a single-stream collection approach, where all recyclable materials are placed in the same bin and sorted later at the recycling facility. 
  • Single-stream recycling is less expensive than multistream recycling, where residents sort and place different types of recyclables in different bins, but Chemistry and Engineering Magazine reports, “40% of glass from single-stream collection ends up being recycled into new products, compared with about 90% of glass from multistream systems.”
  • The glass recycling market is far less volatile than the plastic, paper, and electronic waste recycling markets, and there are plenty of facilities that process recycled glass into new materials.  The challenge lies in getting the glass to these plants in the quality and condition that is actually usable.  Reuters reported, “With the potential to lower environmental pollution from waste disposal and in inefficient manufacturing of glass containers, the recycled glass market is poised for an anticipated 7.6% growth rate from 2018 to 2025.”
  • Ypsilanti Department of Public Services Director Ron Akers says that glass recycling ended because, in the single-stream process, there was no guarantee that glass would be recycled.  He says that residents can take glass (as well as milk cartons, juice boxes, and motor oil, which the city of Ypsilanti also dropped from the curbside recycling program) to the Recycle Ann Arbor drop-off station on Ellsworth Road.  The $3 entrance fee for standard cars can be waived for Ypsilanti residents by picking up a pass at the City Clerk’s office, or requesting one online.  The Western Washtenaw Recycling Authority also offers glass recycling at eight drop-off locations in the county. 

Challenges with Recycling Glass

Americans dispose of some 10 million metric tons of glass annually.  Most of it ends up in the trash.  Only about one-third gets recycled.  That’s not because of some intrinsic materials or chemical property that makes glass difficult to recycle.  “Glass is 100% recyclable,” says Robert Weisenburger Lipetz, executive director of the Glass Manufacturing Industry Council (GMIC), a nonprofit trade association.  “It has an unlimited life and can be melted and recycled endlessly to make new glass products with no loss in quality,” he adds.

And the US’s roughly 33% glass-recycling rate, which pales compared with the 90% recycling rate in Switzerland, Germany, and other European countries, is not the result of a lack of technical know-how.  “Recycled glass is nearly always part of the recipe for making new glass,” says Joseph J. Cattaneo, executive director of the Glass Packaging Institute (GPI), a trade association representing the North American glass-container industry.  The glass industry regularly mixes cullet—a granular material made by crushing bottles and jars usually collected from recycling programs—with sand, limestone, and other raw materials to produce the molten glass needed to manufacture new bottles and jars.

Manufacturers agree that using cullet benefits glassmakers, the environment, and consumers.  And national surveys show that Americans overwhelmingly favor glass recycling and deem it to be important.  Yet as the percentage of glass recycled in Spain and the UK, for example, has doubled and tripled in the past 25 years, respectively, the numbers in the US have barely budged.

The US glass-recycling shortfall comes down to the interplay between the quality and availability of cullet and the economics of making glass, he explains.  And, he says, the recycling rate discrepancies between the US and other countries result mainly from differences in government policy and consumer education and habits.  By understanding these hurdles to glass recycling, GMIC, GPI, and other industry groups hope to boost the rate in the US.

Cullet’s Many Benefits

When studying glass recycling, the first thing that becomes clear is that cullet is extremely useful.  It provides many benefits to glass manufacturing.

First, cullet allows glass manufacturers to reduce their need for raw materials.  The key ingredients used in glassmaking are sand (mainly silica, SiO2), sodium carbonate (also known as soda ash, Na2CO3), and limestone (CaCO3).  One kilogram of cullet replaces 1.2 kg of raw materials, according to James V. Nordmeyer, vice president of global sustainability at Owens-Illinois, a major manufacturer of glass bottles and containers.

Cullet also helps manufacturers save on energy costs.  For every 10% of cullet included in the glassmaking feed mixture, the energy needed to keep the furnace at temperatures high enough to generate molten glass falls by nearly 3%, Rue says.  Running furnaces at lower temperatures extends furnace lives and reduces operating costs and, as a result, the price of the final glass products.

According to Pennsylvania State University’s John C. Mauro, adding cullet to the feed mixture also improves the quality of glass products. Mauro is a materials scientist and glass specialist who spent nearly 20 years at the glassmaker Corning.  He explains that melting cullet doesn’t release carbon dioxide or other gases that can form unwanted trapped bubbles in the glass.  Also, using cullet limits the deposition of crystals of unmelted starting materials, as well as the formation of streaks and optical imperfections due to incomplete mixing of those materials.

Finally, cullet has a significant environmental benefit.  Adding the material to the mix reduces greenhouse gas emissions during manufacturing, Nordmeyer points out.  When the carbonates from limestone melt with the other materials, they release CO2.  Using 10% cullet in the manufacturing feed lowers emissions of CO2by roughly 5%.  Basically, for every 6 metric tons of cullet used in manufacturing, glassmakers can cut 1 metric ton of CO2 emissions.

The Problems with U.S. Recycling: Single-stream is cost effective, but less sustainable

Despite cullet’s long list of benefits, glassmakers are limited by what recycled material is available to them at a manageable cost.  Getting cullet in a clean, furnace-ready form generally requires a lot of processing. And depending on how the US recycles, that processing is done relatively inefficiently compared with what happens in Europe.

US municipalities manage residential recycling primarily via single-stream curbside collection.  Single-stream means residents use their recycling bins to comingle glass with aluminum and steel cans, various types of plastic, newsprint, junk mail, cardboard, and other paper products.

People also tend to throw in a lot of things that shouldn’t go in the bin, such as plastic bags, batteries, light bulbs, soiled food containers, used napkins, and what Nordmeyer and others call “wish-cycling” materials.  One example is a popular single-serve coffee-brewing product that features a plastic cup and foil lid.  Well-meaning people think since those components can be recycled, they’re justified in tossing the whole thing—dirty filter, wet coffee grounds, and all—into a recycling bin.

Garbage, like those products, contaminates all the recyclables in the bin, Nordmeyer says.  “You have to sort through all the trash to get to the material that manufacturers want and are willing to pay for.”  That sorting happens via a combined manual-plus-automated multistep process at a materials recovery facility.  About 400 such facilities operate in the US, according to Rue.

To start the sorting process, front-end loaders dump huge piles of single-stream recyclables onto conveyor belts.  Trained operators manually remove scrap metal, textiles, hoses, and other materials that never belonged in the recycling bin and can damage sorting equipment.  Next, automated separators called star screens, together with powerful air jets, remove cardboard and paper, while magnets pull out iron-containing materials. After several more separation steps, a device known as a glass-breaking screen removes most of the glass from the single-stream load so it can be sent to cullet suppliers, who clean it and make it furnace ready for glass manufacturers.

Multistream recycling, which is a far less common approach in the US, is simpler on the processing end.  In these programs, consumers separate glass from other recyclables, depositing them in glass-only collection bins.  This type of collection requires a high level of consumer education and is considerably more expensive than single-stream collection.  But glass from multistream collection is much cleaner than what comes out of the single-stream supply.  Multistream glass typically bypasses materials recovery facilities and goes directly to cullet processors.  Because of the difference in the quality of glass from the two streams, just 40% of glass from single-stream collection ends up being recycled into new products, compared with about 90% of glass from multistream systems.

So one key factor that stands in the way of the US glass industry’s ability to boost recycling numbers is the limited availability of satisfactory cullet produced via single-stream processing.  “Large quantities of high-quality cullet are essential to further increase the recycled content in our products,” says Frank O’Brien-Bernini, vice president and chief sustainability officer for Owens Corning, a major fiberglass manufacturer.

Compared with multistream recycling, “single stream is an inherently inefficient and expensive recycling method,” Lipetz says.  But most municipalities in the US stick with single stream because the collection costs are lower than those with multistream systems.  To switch to multistream systems, these municipalities would need to introduce taxes or fees to meet the higher collection and handling costs.  And most municipalities are reluctant to do so. 

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— David Fair is the WEMU News Director and host of Morning Edition on WEMU.  You can contact David at734.487.3363, on twitter @DavidFairWEMU, or email him at dfair@emich.edu

Contact David: dfair@emich.edu
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