Glass recycling is the processing of waste glass into usable products.[1] Glass that is crushed or imploded and ready to be remelted is called cullet.[2] There are two types of cullet: internal and external. Internal cullet is composed of defective products detected and rejected by a quality control process during the industrial process of glass manufacturing, transition phases of product changes (such as thickness and color changes) and production offcuts. External cullet is waste glass that has been collected or reprocessed with the purpose of recycling. External cullet (which can be pre- or post-consumer) is classified as waste. The word "cullet", when used in the context of end-of-waste, will always refer to external cullet.
To be recycled, glass waste needs to be purified and cleaned of contamination. Then, depending on the end use and local processing capabilities, it might also have to be separated into different sizes and colours. Many recyclers collect different colors of glass separately since glass tends to retain its color after recycling. The most common colours used for consumer containers are clear (flint) glass, green glass, and brown (amber) glass. Glass is ideal for recycling since none of the material is degraded by normal use.
Many collection points have separate bins for clear (flint), green and brown (amber). Glass re-processors intending to make new glass containers require separation by color. If the recycled glass is not going to be made into more glass, or if the glass re-processor uses newer optical sorting equipment, separation by color at the collection point may not be required. Heat-resistant glass, such as Pyrex or borosilicate glass, must not be part of the glass recycling stream, because even a small piece of such material will alter the viscosity of the fluid in the furnace at remelt.[3]
To be able to use external cullet in production, any contaminants should be removed as much as possible. Typical contaminations are:
Manpower or machinery can be used in different stages of purification. Since they melt at higher temperatures than glass, separation of inorganics, the removal of heat resistant glass and lead glass is critical. In the modern recycling facilities, dryer systems and optical sorting machines are used. The input material should be sized and cleaned for the highest efficiency in automatic sorting. More than one free fall or conveyor belt sorter can be used, depending on the requirements of the process. Different colors can be sorted by optical sorting machines.
Glass bottles and jars are infinitely recyclable.[4] The use of recycled glass in manufacturing conserves raw materials and reduces energy consumption.[5] Because the chemical energy required to melt the raw materials has already been expended, the use of cullet can significantly reduce energy consumption compared with manufacturing new glass from silica (SiO2), soda ash (Na2CO3), and calcium carbonate (CaCO3). Soda lime glass from virgin raw materials theoretically requires approximately 2.671 GJ/tonne compared to 1.886 GJ/tonne to melt 100% glass cullet. As a general rule, every 10% increase in cullet usage results in an energy savings of 2–3% in the melting process, with a theoretical maximum potential of 30% energy saving.[6] Every metric ton (1,000 kg) of waste glass recycled into new items saves 315kg (694lb) of carbon dioxide from being released into the atmosphere during the manufacture of new glass.[7] But recycling glass does not avoid the remelting process, which accounts for 75% of the energy consumption during production.[8]
The use of the recycled glass as aggregate in concrete has become popular, with large-scale research on that application being carried out at Columbia University in New York. Recycled glass greatly enhances the aesthetic appeal of the concrete. Recent research has shown that concrete made with recycled glass aggregates have better long-term strength and better thermal insulation, due to the thermal properties of the glass aggregates.[9] Glass which is not recycled, but crushed, reduces the volume of waste sent to landfill.[10] [3] Waste glass may also be kept out of landfill by using it for roadbed aggregate.[5]
Glass aggregate, a mix of colors crushed to a small size, is substituted for pea gravel or crushed rock in many construction and utility projects, saving municipalities, such as the City of Tumwater, Washington Public Works, thousands of dollars (depending on the size of the project). Glass aggregate is not sharp to handle. In many cases, the state Department of Transportation has specifications for use, size and percentage of quantity for use. Common applications are as pipe bedding—placed around sewer, storm water or drinking water pipes, to transfer weight from the surface and protect the pipe. Another common use is as fill to bring the level of a concrete floor even with a foundation. Foam glass gravel provides a lighter aggregate with other useful properties.
Other uses for recycled glass include:
Mixed waste streams may be collected from materials recovery facilities or mechanical biological treatment systems. Some facilities can sort mixed waste streams into different colours using electro-optical sorting units.
The alternative markets for recycled glass waste include the construction sector (using glass waste for road pavement construction, as an aggregate in asphalt, pipe bedding material, drainage or filler aggregate), the production of cement and concrete (using glass waste as aggregate),[12] [13] [14] as partial replacement to cement,[15] [16] [17] partial replacement for cement and aggregate in the same mixture or raw material for cement production, as well as decorative aggregate,[18] abrasives,[19] or filtration media.[20]
Three different samples of recycled glass with different gradation curves produced from residential and industrial waste glass streams in Victoria were studied in this research to investigate their usage as a construction material in geotechnical applications. The Fine Recycled Glass (FRG) and Medium Recycled Glass (MRG) were classified as well-graded (SW-SM), while Coarse Recycled Glass (CRG) was poorly graded (GP) according to the Unified Soil Classification System (USCS). The specific gravity of recycled glass was approximately 10% lower than that of natural aggregate. MRG exhibited higher maximum dry unit weight and lower optimum water content compared to FRG. LA abrasion tests showed FRG and MRG to have abrasion resistance similar to construction and demolition material, while CRG had higher abrasion values. Post-compaction analysis indicated stability for FRG and MRG, but CRG displayed poor compaction behavior due to particle shape and moisture absorption issues. CBR and direct shear tests revealed MRG's superior shear resistance and slightly higher internal friction angle compared to FRG. Consolidated drained triaxial shear tests confirmed these findings, suggesting FRG and MRG behave similarly to natural sand and gravel mixtures in geotechnical applications. Hydraulic conductivity tests demonstrated medium permeability and good drainage characteristics for FRG and MRG. Compliance with EPA Victoria requirements for fill material was also confirmed. Overall, the study supports using recycled glass in various geotechnical engineering applications.[21]
Polymer concrete, a material commonly used in industrial flooring, uses polymers, typically resins, to replace lime-type cements as a binder. Researchers have found that grounded recycled glass can be used as a substitute for sand when making polymer concrete.[22] According to research, using recycled glass instead of sand produces a high strength, water-resistant material suitable for industrial flooring and infrastructure drainage, particularly in areas subject to heavy traffic such as service stations, forklift operating areas and airports.
Despite all the improvement in the waste and recovery processes, challenges include:
| +Container glass collection | Country | 2021[24] |
|---|---|---|
 | 87% | |
 | 114% | |
 | 78% | |
 | 59% | |
 | 52% | |
 | 81% | |
 | 88% | |
 | 78% | |
 | 91% | |
 | 82% | |
 | 84% | |
 | 36% | |
 | 38% | |
 | 85% | |
 | 84% | |
 | 85% | |
 | 70% | |
 | 63% | |
 | 99% | |
 | 63% | |
 | 87% | |
 | 90% | |
 | 73% | |
 | 54% | |
 | 64% | |
 | 74% | |
 | 98% | |
 | 73% | |
 | 88% | |
 | 95% | |
 | 74% | |
| 80% |
In 2004, Germany recycled 2.116 million tons of glass. Reusable glass or plastic (PET) bottles are available for many drinks, especially beer and carbonated water as well as soft drinks (Mehrwegflaschen). The deposit per bottle (Pfand) is €0.08-€0.15, compared to €0.25 for recyclable but not reusable plastic bottles. There is no deposit for glass bottles which do not get refilled.
Non-deposit bottles are collected in three colours: white, green and brown.
In 2021, India recycled 78.6 million tons of glass. Many drinks are packaged in reusable glass and plastic (PET) bottles, especially beer and carbonated water. Recycled waste glass has many uses such as cement and paint additives as well as remanufacturing into glass tiles.
Specially, Indian recycling companies (Faizal Ahamed & Co, AMB Traders, Abubakkar Sons and JBA Groups in Tamil Nadu, India) collect 5 million tons of glass for recycling per month.
Non-deposit bottles are typically collected in three colors: clear, green and brown.
The first bottle bank for non-deposit bottles (glasbak) was installed in Zeist in 1972. Glass is collected in three colours: white, green and brown.[25] There is a deposit for refillable beer bottles when returned to supermarkets.[26]
Glass collection points, known as bottle banks are very common near shopping centres, at civic amenity sites and in local neighborhoods in the United Kingdom. The first bottle bank was introduced by Stanley Race CBE, then president of the Glass Manufacturers' Federation and Ron England in Barnsley on 6 June 1977.[27] Development work was done by the DoE at Warren Spring Laboratory, Stevenage, (now AERA at Harwell) and Nazeing Glass Works, Broxbourne to prove if a usable glass product could be made from over 90% recycled glass. It was found necessary to use magnets to remove unwanted metal closures in the mixture.
Bottle banks commonly stand beside collection points for other recyclable waste like paper, metals and plastics. Local, municipal waste collectors usually have one central point for all types of waste in which large glass containers are located.
In 2007 there were over 50,000 bottle banks in the United Kingdom, and 752,000 tons of glass was being recycled annually.[28]
Approximately 45% glass waste gets recycled each year.[29]
Rates of recycling and methods of waste collection vary substantially across the United States because laws are written on the state or local level and large municipalities often have their own unique systems. Many cities do curbside recycling, meaning they collect household recyclable waste on a weekly or bi-weekly basis that residents set out in special containers in front of their homes and transported to a materials recovery facility. This is typically single-stream recycling, which creates an impure product and partly explains why, as of 2019, the US has a recycling rate of around 33% versus 90% in some European countries.[30] European countries have requirements for minimum recycled glass content, and more widespread deposit-return systems that provide more uniform material streams.[31] The lower population density and long distances in much of the United States, and the cost of shipping heavy glass also mean that recycling is not inherently economical in places where there are no nearby buyers.
Apartment dwellers usually use shared containers that may be collected by the city or by private recycling companies which can have their own recycling rules. In some cases, glass is specifically separated into its own container because broken glass is a hazard to the people who later manually sort the co-mingled recyclables. Sorted recyclables are later sold to companies to be used in the manufacture of new products.
In 1971, the state of Oregon passed a law requiring buyers of carbonated beverages (such as beer and soda) to pay five cents per container (increased to ten cents in April 2017) as a deposit which would be refunded to anyone who returned the container for recycling. This law has since been copied in nine other states including New York and California. The abbreviations of states with deposit laws are printed on all qualifying bottles and cans. In states with these container deposit laws, most supermarkets automate the deposit refund process by providing machines which will count containers as they are inserted and then print credit vouchers that can be redeemed at the store for the number of containers returned. Small glass bottles (mostly beer) are broken, one-by-one, inside these deposit refund machines as the bottles are inserted. A large, wheeled hopper (very roughly 1.5 m by 1.5 m by 0.5 m) inside the machine collects the broken glass until it can be emptied by an employee. Nationwide bottle refunds recover 80% of glass containers that require a deposit.[5]
Major companies in the space include Strategic Materials, which purchases post-consumer glass for 47 facilities across the country.[32] Strategic Materials has worked to correct misconceptions about glass recycling.[33] Glass manufacturers such as Owens-Illinois ultimately include recycled glass in their product. The Glass Recycling Coalition is a group of companies and stakeholders working to improve glass recycling.[34]
In 2019, many Australian cities after decades of poor planning and minimum investment are winding back their glass recycling programmes in favour of plastic usage.[35]
For many years, there was only one state in Australia with a return deposit scheme on glass containers. Other states had unsuccessfully tried to lobby for glass deposit schemes.[36] More recently this situation has changed dramatically, with the original scheme in South Australia now joined by legislated container deposit schemes in New South Wales,[37] Queensland,[38] Australian Capital Territory,[39] and the Northern Territory, with schemes planned in Western Australia (2020), Tasmania (2022) and Victoria (2023).
South Africa has an efficient returnable bottle system which includes beer, spirit and liquor bottles. Bottles and jars manufactured in South Africa contain at least 40% recycled glass.[40]
Life Cycle Analysis (LCA) is an important tool for ecological evaluation of products or processes. LCA is an internationally accepted standard (ISO 14040 & ISO 14044) and scientific tool that is used to quantify the environmental performance attributable to the different life stages of our products, including upstream stages such as raw material production and energy supply. Results are benchmarked based on LCA indicators with the final aim of identifying operational efficiencies and optimising product design while providing a higher level of environmental transparency.[41] The life-cycle of glass starts from extraction of raw materials, to distribution, use by final consumers to disposal/landfilling. In light of saving the economy and the environment, researchers are working to eliminate the linearity of this lifecycle to have a circular/closed loop life cycle where extraction of raw materials and landfilling after final consumption will be eliminated.[41] Glass takes up to millions of years to decompose in the environment and even more in landfill. Fortunately, glass is 100% recyclable, making it a sustainable resource for producing new forms of packaging without relying on raw materials. The problem now is that only 70% of glasses are being collected for recycling in the EU (30% in the US) (which is already good, but can be better). Its recyclability can hence be improved by improving its collection rate all around the world. The only way we can increase collection rate is to enlighten every single consumer of glass to properly dispose and speak up against improper disposal of this glass.
The Cradle-to-Cradle analysis is an approach which evaluates a product's overall sustainability across its entire life cycle. It expands the definition of design quality to include positive effects on economic, ecological and social health. The Cradle to cradle analysis of glass showed that the most impactful phase of a glass lifecycle is at its raw materials usage. Hence, why the sustainability of this product is focused on eliminating this stage of production by recycling used glasses to make secondary raw materials.[42]
International Organization for Standardization (ISO) is a non-governmental institution (established under the aegis of the UN) bridging public and private sectors. ISO is an international standard setter for “business, government and society,” through its pursuit of voluntary standards. These standards range from those dealing with size, clarity, and weights measures to the systems businesses ought to put in place to enhance customer satisfaction. Its work thus has an intimate impact on daily life by shaping and molding the way in which commerce is conducted, the operating procedures of business, and the way in which consumers engage with markets.[43] Some of this standard setting was the result of government and business agreement on product development; others were the consequence of commercial battles fought out over the most appropriate format. The organization boasts having developed more than 17,000 international standards in its 60-year history and claims that it is engaged in producing an additional 1,100 standards each year.[43] ISO are usually put in consideration in lifecycle assessment of products.
The ISO 81.040 contains the international standards for glass. It's divided in four chapters.
Other related ISO:
