Creating Circularity Through Glass Recycling and Reuse  

Photo courtesy of NGA

Glass has important sustainability attributes, is infinitely recyclable, and can be adapted and reused in building applications.

Glass is being asked to do more in terms of performance, aesthetics, and now, reducing the cost of carbon on our environment. Both glass recycling and circular building design can aid in these efforts.

“Glass is a super material,” explains Sophie Pennetier, founder of Digne, an academic-industry work collaborative. “It’s super inert, it’s super transparent, it’s as strong as steel in compression, and it’s as elastic as aluminum. It’s a very versatile material.” Additionally, glass has important sustainability attributes. It is infinitely recyclable. And it can be adapted and reused in building applications.

Buildings generate nearly 40% of global carbon dioxide emissions, according to Architecture 2030. The embodied carbon of building materials, referring to the CO₂ used to manufacture those materials, accounts for 11% of those emissions.

Recently, legislation and updates to building standards and certifications, as well as requirements from architectural firms, are demanding greater material transparency regarding the embodied carbon of products, including life cycle assessments and the creation of environmental product declarations, which account for the CO₂ emissions used to create building products. Despite greater regulatory interest in reducing embodied carbon, incentives for glass recycling and circularity remain complex in North America.

The Glass Recycling Supply Chain

Photo courtesy of NGA

The float glass process recycles virtually all the glass waste, called cullet, from the in-plant production melting and cutting processes.

Pre-Consumer Cullet: Cullet generated within the same float glass plant can be reintroduced to the original process. While some float manufacturers also have agreements with glass fabricators to return glass cut-offs—created during the glass fabrication process, which can be used as part of the float manufacturing process—pre-consumer, internally-produced cullet is the most ideal kind to reuse in the float manufacturing process.

Using glass cullet in the float production process reduces carbon emissions because fewer raw materials are being used, and the flat glass can be formed at a lower temperature. According to Glass for Europe, recycling 1,000 tons of cullet can result in a savings of approximately 600 tons of CO₂ emissions, lowering the embodied carbon of the float glass.

Pre-consumer cullet does not qualify as recycled content for green building initiatives such as LEED Building Certification.

Post-Manufacturing Glass Waste: Float glass manufacturers typically do not recycle post-consumer or pre-consumer recycled cullet from glass fabricators or other sources primarily due to glass composition differences and possible contamination.

Recyclers, sometimes called municipal/mixed/material recycling facilities or MRFs, typically accept glass from a broad spectrum of suppliers and industries beyond just flat glass fabricators, such as glass bottles and containers, automotive, solar, appliance, and electronics. Knowledge of how to leverage value across many different end markets is needed.

Where Does Recycled Glass Go, And What Are the Benefits of Recycling?

Glass is infinitely recyclable, and post-installation or post-consumer glass can potentially be made into many new products. In addition to being recycled back into architectural glass, cullet and glass waste, as well as glass cut-offs, can be used to make many products of reduced quality, including the following:

• Fiberglass: High levels of recycled glass are in fiberglass insulation products. Recycled glass accounts for 40% of the raw materials in residential fiberglass insulation. Energy savings is a primary benefit of using recycled glass because it reduces the costs associated with manufacturing. According to the North American Insulation Manufacturers Association (NAIMA), the industry uses over 3.2 billion pounds of crushed glass annually.
• Highway Glass Bead: Clear, low–iron, and tinted glass are used in the production of small glass beads, which are added to highway paint to create a reflective surface. The glass beads are sprayed on top of paint. The average amount of glass beads needed for one mile (1.6 kilometers) of a continuous strip of paint is more than 102 pounds (46 kg).
• Abrasives: Crushed glass can be used as an abrasive. Glass is crushed, separated by mesh size, and then sold to blasting distributors and contractors who use it to clean and prepare metal surfaces for painting.
• Terrazzo Countertops and Flooring: Some terrazzo countertops and flooring are produced using 100% recycled decorative glass as one of the primary materials. Terrazzo countertop and flooring manufacturers often mix crushed mirror with their glass aggregate for these applications. These markets are regional, prefer clear glass, and tend to use small quantities.
• Other Usage and Applications: Recycled glass products serve many other purposes. Recycled glass is used as abrasive material to place in grinding wheels or into matches, as flux in metal foundries, and as specialized fillers. Some companies use recycled glass as decorative glass aggregate for use in landscaping or fire pit glass. The glass aggregate may be further processed to form mosaic patterns.

Benefits of Returning Recycled Glass to a Glass Manufacturing Process

Glass recycling has major implications and benefits, for reducing or eliminating the environmental costs of mining raw materials, reducing the embodied carbon of glass manufacturing, and even for job creation.

Reduced Freight and Mined Minerals: Using cullet reduces the need to mine virgin materials out of the ground. Typically, it takes approximately 1,200 tons of batch to make 1,000 tons of glass. Glass manufacturers lose approximately 17% of the weight of the batch through the conversion of oxide batch materials. By using more cullet, the total weight of shipped incoming raw materials can also be reduced, lowering the environmental impact of trucking. Reductions in scope 1 emissions—or emissions created directly from onsite industrial processes—can be realized, as well as reduced landfill rates.

According to the Glass Packaging Institute, “over a ton of natural resources are conserved for every ton of glass recycled, including 1,300 pounds of sand, 410 pounds of soda ash, 380 pounds of limestone, and 160 pounds of feldspar.” Recycled glass can substitute up to 95% of raw materials.

Energy Savings: Energy costs drop about 2-3% for every 10% of cullet used in the manufacturing.

Increased Throughput: When demand is high, cullet can be used to achieve higher furnace pull rates. Although this benefit forfeits energy and furnace life savings, the bottom line is favorable to meet end market demand most efficiently.

Extend Furnace Life: Including cullet in the manufacturing mix makes it less corrosive and lowers the melting temperature (from 2,800°F to 2,600°F), prolonging furnace life.

Lowers Emissions: According to a Glass Processing Institute container plant study, a relative 10% increase in cullet reduces particulates by 8%, nitrogen oxide by 4%, and sulfur oxide by 10%. For every 10% of cullet used in glass manufacturing, energy consumption is reduced by 2.5% and CO₂ emissions by 5%. Considering the environmental impact of cullet usage, for every 10% of cullet used in glass manufacturing, energy consumption is reduced by 2.5% and CO₂ emissions by 5%.

Supports Jobs: Recycling 1,000 tons of glass creates slightly over 8 jobs.

Promotional Value: Glass recycling is a closed-loop system, creating no additional waste or by-products. The value of cullet recycling is a platform for building brand equity in the industry and local communities.

Challenges to Recycling in North America

Photo courtesy of Resource Recovery

Large container with broken flat glass pieces destined for recycling

There are multiple markets and geographies when it comes to glass recycling. The Glass Packaging Institute has conducted extensive studies around cullet recycling rates and the differences between the U.S. and European markets. Glass for Europe has also conducted studies around the European flat glass industry and understanding a path forward. Close the Glass Loop is an exhaustive study about the glass packaging industry in Europe as well. These studies can be referenced and used to build a greater understanding of today’s markets, current global recycling rates, existing infrastructure, and key differences across the globe.

With a thorough understanding of the issues around a more advanced glass recycling infrastructure, there are some indicators that can help paint a picture of where U.S. recycling is right now.

• The U.S. residential recycling rate (of all recyclable materials) is approximately 33%, whereas many European countries have achieved approximately 90%. In 2021, the average EU collection rate for glass packaging was 80.1%.
• Only 40% of glass put into single-stream recycling gets recycled. The other 60% is landfilled, deemed contaminated or low quality, and sent to landfill or downcycled to fiberglass, road aggregate, or other products.
• Legislation around multi-stream waste management often drives recycling rates.
• Geography and freight rates often impact economic viability.
• New technologies exist to drive recycling of laminated and low-iron crystalline PV glass, though this is still rare.

According to glass industry leaders, demand for glass waste is increasing. Still, many challenges remain in establishing a glass recycling infrastructure. Here are a few of those challenges.

Challenges related to cullet and quality:

• Contaminants in recycled material can jeopardize manufacturing. Contaminants in recycled glass, such as aluminum, nickel, ceramics, and other metals, could compromise the float bath equipment and negatively impact the quality of new glass, leading to issues like downtime and increased equipment maintenance if extreme care is not taken. While aluminum and nickel are two of the most concerning elements, all types of contamination can cause serious damage to a glass furnace and the glass products produced from an architectural float. Aluminum doesn’t fully combine and absorb into the glass melt, but floats on the surface of the molten glass, rapidly volatilizing and causing millions of bubbles. The only way to eliminate this contaminant is to go in and remove the volatile material floating on the surface. This is an extremely complicated procedure given the design and nature of the float glass manufacturing process. A single aluminum can could easily cause over $250,000 in unusable product. Additionally, nickel has an extremely dangerous state when formed as nickel sulfide (NiS), as it can lead to spontaneous or unexplained breakage in tempered glass. The only way to avoid nickel sulfide is to eliminate the use of nickel or nickel-containing materials in all portions of the supply chain. This would mean eliminating not only nickel as a raw material but also avoiding certain types of stainless steel in the transportation, conveyance, weighing, and melting operations.
• Quality impacts can undermine CO₂ savings. According to Glass for Europe, recycling 1 ton (1000 kg) of cullet can result in a savings of approximately 318 kg of CO₂ emissions. However, quality impacts from the use of the processed and recycled cullet can offset these savings. Depending on the draw rate, cullet usage, and quality impact of potential savings, these savings could be offset by the demand for additional glass production. The expected CO₂ savings achieved from the use of cullet can be wiped out with a single quality upset that would require additional production time to make similar volumes of material. Poorly executed and vetted projects could increase the CO₂ needed to make a fixed volume of a product. For this reason, adequate risk-mitigation steps should be implemented. The potential benefits and risks versus the potential gains of CO₂ should be carefully considered before using cullet as a means to improve sustainability.
• Some cullet cannot be used in float glass manufacture. Many types of cullet, such as flint bottle cullet and low-iron crystalline silica PV glass, are currently unusable in the flat glass industry because of the compatibility issues around batch composition, forming process variants, and potential process contamination.
• No ASTM or industry-wide standard yet exists for cullet grading and composition. As a result, particular care should be taken to work closely with the cullet processor selected for supply. Low-iron glass also requires mostly low-iron cullet for reuse, so separating cullet by colors can sometimes have a significant impact on potential outcomes of cullet waste streams.
• Additional testing may be required for recycled glass. Glass that has a higher potential for nickel sulfide inclusions may require additional processing by downstream processors. For instance, tempered glass may be subjected to heat-soak testing as per NGA Glass Technical Paper FB56-18 Heat Soak Testing of Tempered Glass for Architectural Glass Applications. Though this testing is not required for all tempered glass, some process streams may require this testing for certain applications, depending on the risk tolerance of spontaneous breakage, and there is additional energy and cost associated with this testing.
• Challenges related to recycling infrastructure:
• Glass manufacturers may not be aware that glass waste or cullet has value. Beyond technical concerns for the realities of glass recycling, another major barrier to the recycling of glass remains awareness. Many glass industry members may not be aware that the cullet they produce has a potential market value. Kyle Sword, R&D director, North America of NSG/Pilkington, says that many glass fabricators or glass industry companies are still not aware that cullet’s value has changed in the past two decades, and that minor changes to their operations to separate cullet from contaminants could yield high-quality cullet that has value.
• Shipping distances to recycling facilities are long, and landfill costs are relatively low in many areas of the United States. When it comes to recycling, says Sword, many of the incentives, such as higher gas prices and higher landfill prices in Europe, don’t always exist in North America. “The reality is, natural gas [which can be used to manufacture new glass] is pretty cheap in North America compared to elsewhere in the world, landfill costs are pretty cheap compared to elsewhere in the world, and shipping distances are pretty long as compared to elsewhere in the world,” he explains.
• Recovery of post-demolition glass remains challenging. Already installed glass that is removed from buildings for retrofit or demolition could be an opportunity for glass recycling. But the logistics and financial cost can be prohibitive, says Austin Beaupré, national supply manager, Resource Recovery, a glass recycler with locations across the U.S. “When it comes to demoing a building, logistics is everything,” he says, from determining who will break down the windows, put them in scrap, transport them and potentially separate glass from other building materials. “It just comes down to a numbers game of figuring out what to do with all of that,” he says.

Infinite Recycled Technologies does retrofit and post-demolition recycling and has found some resistance from demolition crews to the extra work that’s required to recycle glass. “A lot of them don’t take into consideration that as we take that glass for them, we’re doing the hauling, we’re providing the containers, and we’re recycling it,” says Patrick Elmore, president of business development, laminated glass recycling for Infinite Recycled Technologies. “They’re saving on the costs of hauling. They’re saving on the container. They’re saving on the landfill costs, which are astronomical in New York, so we’re saving them a lot of money.”

• Lack of recycling infrastructure leads to low collection and can mitigate benefits. Glass recycling should be a part of decarbonization efforts, but a lack of recycling facilities can mitigate those effects in many ways. “Recycling glass is awesome, but if we have to bring a diesel truck and then drive it 200 miles to recycle the glass, it could offset the [carbon] impact,” says Beaupré.

Collaborating To Expand Recycling

Photo courtesy of NOIC

Participants in the Glass Recycling Blitz, an initiative helmed by the Northwest Ohio Innovation Consortium to encourage local glass recycling in the Northwest Ohio region.

The recycled glass markets are interdependent among many different industries—infrastructure around transportation, cullet processing, cullet storage, and local waste management facilities like MRFs can all have significant impacts on results. Collaborating regionally, and across different sectors of the glass industry, will be key to creating infrastructure in the U.S.

Glass Fabricators Can Work with Local Facilities to Recycle Glass Waste

Glass fabricators should establish a working relationship with their nearest glass recycling company in order to lower freight costs and drive the highest value. Recyclers typically accept glass from a broad spectrum of suppliers and industries beyond just glass fabricators, such as automotive, solar, appliance, and electronics. Therefore, knowledge of the glass fabricator and its recycling company on how to leverage value across many different end markets is needed.

Most glass scrap generated by an architectural glass fabricator can be recycled if attention is given to avoiding cross-contamination. Laminated glass is potentially a valuable part of the value stream of recycled glass when the interlayer is separated from the laminate. Prior to shipment, fabricators should work with their recycler to define the best way to segregate their scrap to ensure positive value and acceptability. Finding and communicating with a local, knowledgeable glass recycler helps ensure a successful recycling program.

Ways To Improve the Quality of Cullet

The cullet waste stream from all areas has a potential market value. These streams have often been considered an issue of waste management, but the economics and value creation from the reuse of cullet are dynamic. Post-consumer glass is a local, domestic raw material of growing importance for multiple industries.

Some basic manufacturing process changes can dramatically increase the value of scrap cullet. As described above, aluminum and nickel are particularly risky contaminant materials, so keeping waste streams clean and avoiding contamination can be worth the costs incurred by manufacturers to cleanly separate materials. Key methods could include the following:

• Separate glass from other waste streams, including glass broken as a result of heat-soak testing, a process used by glass fabricators to identify potential contaminants in tempered glass.
• Separate cullet storage from metal storage and processing.
• Avoid nickel-containing storage bins and racks.
• Implement robust training programs for all site employees and stakeholders (simple things like minor floor sweepings can contaminate entire batches of waste cullet).
• Look to efficient supply routes and freight methodology that reduce the transport of cullet from source to processor.
• Separate different types of cullet. IGUs, laminates, and painted glass may all have different routes to market, so it will be important to work with a local cullet processor.
• Understand contamination potential from storage locations and exposure.

As new technologies and additional infrastructure become available, process efficiencies, availability, and costs will change. Glass fabricators can work with a network of cullet processors, end users, and other industries to better understand specifications, available processing, and market needs for cullet quality.

Understanding the freight implication of and impact on the company’s own fleet can also play a significant role in the feasibility of increased recycling. Empty return hauling and shared freight can often impact the economics of a freight situation significantly. Collapsible or returnable cullet bins, mobile cullet processing centers, and partner relationships can all impact the viability and value of the cullet supply.

Industry Collaboration Will Be Key to Expanding Recycling Infrastructure

As already stated, the recycled glass markets are interdependent across many different industries. Collaborating with other people in this space to identify and share resources, results, and paths forward can often lead to better results for all involved.

As an example, Glass for Europe is in the process of evaluating the entire value chain for glass recycling for flat glass in Europe and looking for ways to drive success. Similar collaborative efforts are underway in the U.S., and organizations are often looking at grants and other incentive programs to help.

One of the collaborative initiatives currently underway in the U.S. started at Ace Glass, whose founder, Courtney Little, also founded a recycling business, Epic Glass Recycling, in 2018. Epic Glass Recycling aims to divert glass from landfills, reduce greenhouse gas emissions, decrease litter, and create jobs. The organization provides glass collection services for residents and businesses and has established drop-off locations to capture glass that would otherwise end up in the landfill. In addition, it performs recycling services to support community and corporate events. Ace Glass Aggregates then processes this collected glass in its recycling facility, converting recycled glass into a lightweight foam aggregate material using an environmentally friendly manufacturing process.

At the time of Epic Glass’s founding in 2018, the state of Arkansas, where the businesses are based, was collecting about 4 million pounds of glass per year. After Little began his efforts at glass collection, that amount grew to 30 million-plus pounds of glass in 2024. He says his goal is that his recycling efforts and local partnerships continue increasing the amount of recycled glass, and that the next step in infrastructure is to work with others to identify gaps in regional recycling.

“Let’s get together and talk about where there are some [regional] holes in the U.S. that are not collecting glass, or [about] what fabricators don’t have an outlet for recycling,” he says. “And let’s find a regional person that can help take that and increase the value of the glass so that it incentivizes a company or a community to collect it and recycle.”

The Northwest Ohio Innovation Consortium, a nonprofit comprised of global industry companies, including Owens Corning, NSG/Pilkington, and Libbey, is another example of industry collaboration. The NOIC, designed to encourage innovation across industry partnerships, aims to help the region of Northwest Ohio better strategically plan for greater recycling infrastructure, NSG/Pilkington’s Kyle Sword says. By having a broader view of the glass and cullet available in the region, as well analyzing the capacity for cullet production and who can buy and sell it regionally, they can make both the financial and sustainability case for glass recycling, he says, which can then be replicated in other parts of the country.

Beaupré adds that shared infrastructure for local recyclers, who may be competitors, may be needed to increase the volume of recycling possible. “We’ve worked with some competitors, and we’ve talked about having shared [material] dumping, sort of shared facilities, where we can work together,” he says. “And if I had to guess, that’s probably where we’ll end up, these companies working together, and then having the locations that we need.”

Infinite Recycled Technologies is also working to ensure that architects are aware and ready to support architectural glass recycling before it’s even installed. Elmore says the company worked with the architectural firm Gensler and top contractors to create a specification sheet for glass recycling. This would control the life cycle of the glass, he says. “So now, when the architects are spec-ing new buildings, then they have that language in there already that glass, whether it’s going to be retrofit or if the building is going to be demolished, the glass needs to be recycled,” he says.

Why Local Glass Recycling Matters

Glass recycling in the regions participating in the blitz has faced challenges similar to other parts of the country, in that glass recycling collection may be inconsistent between different areas. “We’re really trying to help people understand that they can recycle glass in this region,” Kirian emphasizes. To that end, the initiative is also testing out new recycling collection points around the area to aid in that process. Kirian says the NOIC is looking to “build connections” towards a larger goal of increasing recycling rates and collection for the area’s local Municipal Recycling Facilities. Kirian says the NOIC is “really hopeful for driving the recycled content volume up in our region, getting it back to industry faster, and helping them utilize it better … and also just helping people feel more engaged in this region.”

Next Steps In Making Greater Recycling Possible

After the success of this event, the NOIC is planning a series of follow-up blitz events through project partners over the next year to continually quantify and analyze the economic feasibility of collection points around Northwest Ohio.

Consumer education also remains a throughline in the NOIC’s efforts to raise recycling rates. Partnering with the Glass Manufacturers Industry Council, the NOIC plans to provide content for glass education tool kits that can be used to educate K-12 students about glass and the importance of recycling. “You tell students, and they tell their parents,” Kirian says.

Beyond recycling, the NOIC is also investigating the use of AI to optimize furnace control and energy efficiency, in addition to partnering with the University of Toledo and Bowling Green State University to expand research, including in the solar glass space.

In creating new recycling infrastructure and connections that strengthen local industry, the NOIC is also looking to ensure workforce development and talent retention in the area. Kirian has said that the region has historically seen a “brain drain” and that this type of initiative could help reverse that. “We have so much great expertise here. We want to help people build their careers here, build out careers for their kids. We’re trying to really perpetuate that.”

Exploring The Horizon of Circularity and Reuse

While recycling is one type of reuse, it’s not the only consideration for circularity. Pennetier is encouraging the glass industry to take a long view of decarbonization and reuse, and to consider not just the next iteration of a product but what its whole lifecycle could be.

Pennetier does not feel that a distinction between upcycling or downcycling of material is as important as keeping the material out of the landfill. “I think trying to keep [the material] roughly around the same application is going to be better, [but you have to consider] are you limiting its future recycling potential?” Ultimately, these differences between upcycling and downcycling can be “a potential distraction from what we can do to divert it from landfill,” she says.

Beyond finding new methods of use and reuse for glass, Pennetier also sees potential for expanding online material databases for secondhand construction materials, like Rheaply. Users would be able to search for both new and lightly used products, the latter of which could be certified. “It’s like going to a car dealership for their knowledge. You buy from them because they have the knowledge, not necessarily because they made a new thing for you,” she explains.

Creating A Quality Protocol For Post-Consumer Glass

Using quality control scanning technology, the researchers in Pennetier’s study on post-consumer glass worked to create a quality protocol that would potentially allow those dismounting glass systems to evaluate post-consumer glass for the purpose of reinstalling it elsewhere in the built environment. The study investigated three aspects that could relate to post-consumer glass strength, including:

• The effect of surface quality on the glass performance.
• How the position of the face of the glass—facing the cavity or the external environment—affected the quality of glass.
• The appropriate test method for post-consumer glass.

Overall, the researchers’ findings suggest that post-consumer glass can be reused in a new IGU, contingent on the glass having good surface quality.

Potential Expansions to Other Glass Types

While this particular study reviewed clear annealed glass, in an interview with researcher Marco Zaccaria, a researcher in the R&D center of AGC Glass Europe, he said that there’s potential to create a quality protocol for other glass types as well. Zaccaria says he’s aware of other experiments in the industry looking to reuse laminated and tempered glass in different ways. “I think every glass type has pros and cons in reuse,” he said. And reuse can look many different ways—for example, some in the industry are interested in reusing laminated glass as separate glass lites, and others interested in reusing the laminated glass unit itself, he says.

Given that there is such variation, and glass reuse is still at an exploratory phase, he says that the valuation and reuse of further glass types should be project-specific. “That way people are exploring reusing actual existing building materials, and the challenges that coexist with those specific building projects—those challenges are all different and will pose their own specific challenges for reuse,” he explains.

The Waste Hierarchy and the Challenges for Glass Reuse

Within the study, the researchers cite the environmental incentives to reduce contributions to global warming, and cite the “waste hierarchy triangle,” often presented as an inverted pyramid with the most preferred options for waste management and disposal at the top, and the least preferred at the bottom. In this paradigm, reuse can be considered more ideal than recycling, because the glass does not have to be remelted. 

A potential horizon for glass reuse 

could be that so much architectural glass is harvested that a float plant could be turned off without affecting glass market needs, according to the study’s researchers.

While possible, Zaccaria says that the amount of glass dismounting and glass system disassembly that would need to happen for that to become a reality would be “huge.” “We would have to have cranes all around dismounting glass in order to feed that system,” he says.

The biggest challenge to glass reuse, from his perspective, remains the harvesting or “dismounting” of glass systems from the built environment, including from a safety perspective. “Glass is a brittle material and it’s very sharp when it’s broken. Clearly you don’t want to create unsafe conditions for the people involved with this assembly [and dismounting process],” he says. To that end, he recommends that manufacturers think towards a “design for dismounting” paradigm, designing systems in such a way that they would be safe to dismount from the installation when the time comes.

Norah Dick is the Editor of Glass Magazine, an official publication of the National Glass Association.