Process steps and innovations in glass recycling

Glass – a product of the modern age?

The production of glass is one of humanity’s oldest known high-temperature technologies, and its development impressively reflects the progress of ancient civilizations. As early as the 3rd millennium BCE, the first evidence of glass-like materials can be found in the Near East. Targeted glass production likely developed in Mesopotamia and Egypt. The earliest known glass objects – mostly small beads or inlays – date from around 1500 BCE.

The oldest glassworks dates back to the Bronze Age in Mesopotamia. The Romans valued glass’s neutral taste when used for drinking vessels – at that time, clay, wood, leather, and metal vessels were common. Glass in the form of glass beads was even a widespread form of currency.

In the Middle Ages, glass production in Europe increasingly shifted to forested regions, as large quantities of wood were needed both as fuel and for the extraction of potash. This so-called forest glass production resulted in characteristic, often slightly greenish glass, caused by iron impurities in the sand. Centers of this production were located, among other places, in Central Europe, such as in present-day Germany and Bohemia.

Another milestone was the development of Venetian glass on Murano beginning in the 13th century. Through improved raw material processing and refined melting techniques, it became possible to produce exceptionally clear, nearly colorless glass (“Cristallo”). At the same time, artistic forms of glasswork emerged, transforming glass into a significant commodity and luxury item.

Glass recycling

Glass was already being systematically recycled in ancient times. Archaeological finds show that in Ancient Egypt and especially in the Roman Empire, waste glass was specifically collected, crushed, and remelted. The reason was less ecological than economic: the production of primary glass was costly and energy-intensive, whereas shards could be melted down much more easily and at lower temperatures. In Roman times, a sort of two-tiered system even emerged: large primary workshops produced raw glass, while local workshops mixed waste glass with raw glass and processed it into new products.

Glass recycling is one of the most vivid and technically advanced examples of a functioning circular economy – in a sense, its “flagship material” in the field of inorganic materials.

Glass is considered one of the few raw materials that can be recycled an infinite number of times without any loss of quality. During the recycling process, the chemical structure of the glass remains unchanged, meaning it can be repeatedly processed into new glass products without compromising quality. The necessity of glass recycling stems from several closely interrelated factors. While primary raw materials such as quartz sand, soda, and lime are geologically available, their extraction involves significant disruption to ecosystems and high energy consumption. In particular, the energy-intensive melting process in glass furnaces –often at temperatures exceeding 1500 °C – makes glass production a significant source of CO₂ emissions. This is where recycling comes into play: The use of cullet significantly reduces energy requirements, shortens processing times, and cuts both direct and indirect emissions. Every increase in the proportion of cullet thus has a direct impact on the glass industry’s carbon footprint.

Recycling glass offers both environmental and economic benefits:

Primary raw materials for glass production include quartz sand, soda, lime, etc., as well as the effort and energy required for their extraction; 1 ton of cullet saves 1.2 t of primary raw materials.

Energy savings in the production of new glass products through the use of cullet – using 10 % cullet saves approximately 3 % energy. With an exemplary cullet usage rate of 70 % in container glass production, this results in a potential energy savings of more than 20 %.

Lower energy input reduces CO₂ emissions during the production of new glass (key figure: using 10 % cullet saves approx. 3.6 % CO2)

Glass can be recycled 100 % and would therefore not require landfill space.

Furthermore, the quality of the recycled material is becoming increasingly important. Modern glass products – such as those in the packaging sector, the flat glass industry, or high-tech applications – place high demands on purity, color fidelity, and chemical composition. Contaminants from ceramics, stones, porcelain, or heat-resistant glass, also known as glass-ceramics, can lead to production disruptions or scrap even in small quantities. As a result, the focus is shifting from mere “collection and melting” to high-precision processing methods.

Pressure on resources, energy, and emissions is forcing even established material cycles to be reevaluated – and hardly any material exemplifies the tension between tradition and innovation as much as glass. As a supposedly “perfectly” recyclable material, glass has been regarded for decades as a prime example of the circular economy. Yet this assumption falls short. Rising quality requirements, heterogeneous waste streams, new product designs, and stricter climate targets now present glass recycling with complex technical and systemic challenges. At the same time, state-of-the-art technology opens up new possibilities for making recycling loops significantly more efficient, cleaner, and more economical.

The state of the art in glass recycling today is characterized by a combination of mechanical processing, sensor-based sorting, and data-driven process optimization. After collection, waste glass shards undergo multi-stage cleaning processes: Initially, large foreign materials are removed from the material stream during mechanical pre-processing; metal separators remove valuable ferrous and non-ferrous metals; and air classifiers and screening technology separate lightweight materials and fine particles. Sensor-based sorting systems form the technological core. High-tech cameras detect foreign materials and miscolored items, which are then selectively ejected in real time via compressed-air nozzles. In particular, the detection of ceramics, stones, and porcelain (also known as KSP) and heat-resistant glass is considered a critical area of innovation.

AI-supported systems are also increasingly being used; these recognize patterns based on large datasets and adaptively optimize sorting processes. These systems not only enable higher purity of the recycled material but also offer solutions to previously unsolvable sorting tasks – a decisive advantage in light of increasing demands on product quality and efficiency.

At the same time, process integration continues to evolve: the use of operational data from processing plants, continuous monitoring, and predictive maintenance increase the efficiency and availability of the facilities. On the production side, improved melting technologies and hybrid furnaces (e.g., with electric support) enable even better utilization of recycled glass while simultaneously reducing emissions.

Glass recycling thus exemplifies the transformation from an established practice to a highly dynamic field of technology. The combination of regulatory pressure, technological innovation, and growing sustainability awareness creates the conditions for further exploiting the potential of this material cycle – while simultaneously adapting it to the requirements of a climate-neutral industry.

Process steps in waste glass processing

Every waste glass processing plant and its process steps are unique and tailored to specific requirements (volume, material origin and composition, particle size distribution, required final qualities, etc.). However, the process always begins with mechanical pre-processing to remove initial contaminants (non-glass materials) and optimally prepare the glass cullet for sorting. Pre-processing is crucial for achieving high final quality standards. The following section describes the individual process steps using the example of a flake processing plant from Binder+Co:

1. Material feeding and dosing ensure that, as far as possible, only glass and no large foreign materials enter the plant and the material is continuously fed into the system in the correct quantity.

2. The next step is the crushing of the waste glass. Whole bottles and large pieces are broken down into processable sizes. Attachments such as caps, seals, frames, etc., should be separated from the glass as much as possible to facilitate their later removal. As a result, the various materials should be as freely accessible as possible. For the crushing of container glass, for example, Binder+Co uses a crushing-screening drum developed in-house, which gently pre-crushes the glass while simultaneously removing non-crushable foreign materials from the material stream. Hard-to-crush glass fragments from the container glass are broken using a roll crusher developed by Binder+Co specifically for the glass industry. In the flat glass sector, pre-crushers – similar to shredders – and a downstream hammer crusher are typically used.

3. At this stage, the material stream is separated into different fractions. Cubic parts (such as corks) and foreign materials like cardboard, plastic bags are separated out by wind sifting. Through multiple screening stages, the material stream is further divided into coarse, medium, and fine fractions to enable more efficient processing. Additionally, very fine particles that cannot yet be sorted are screened out. The following machine types from Binder+Co are used in the classification process:

Bar screens for removing cubic parts or large contaminants

Long-part separators for separating more elongated parts such as ballpoint pens, cable ties, plastic cutlery, toothbrushes, window seals, etc.

BIVITEC screens for producing different particle sizes or screening out fine-particle fractions, especially when the material is still damp and sticks to machines and screen mats

4. In the next process step, magnetic material is removed at various points using overhead magnets. Non-magnetic metal parts (e.g., aluminum cans or window frames) are discharged via eddy current separators. All metallic “contaminants” are valuable byproducts for glass recycling facilities and are collected separately.

5. In addition to the metallic contaminants, the lightweight materials, organic matter, and dust must also be removed. Large and very small particles of paper, plastics (such as seals, PVB films), organic materials, etc., are typically removed using air separation systems like the BREEZER, targeted suction nozzles at dust removal stations, thereby cleaning the glass stream so as thoroughly as possible.

6. Between the individual process steps, the material must be transported and fed into the equipment. This is done using conveying units – for example, conveyor belts, vibrating conveyors, or material chutes. The goal is to transport the shards gently through the plant.

7. The material stream is dried to facilitate processing.This significantly reduces the surface moisture of the glass and the moisture content of organic materials, plastics, etc. This is done to the smallest extent possible in order to keep energy consumption low. In addition, the cullet is “polished,” which leads to improved sorting efficiency.

Binder+Co uses the DRYON fluidized-bed dryer for this purpose, which offers advantages in terms of gentle handling of the glass stream and low energy consumption.

8. A crucial step in the processing of waste glass is sensor-based sorting: In sensor-based or optical sorting machines, known as CLARITY, every single piece of the material stream is detected by one or more sensors, which evaluate and classify this image data within milliseconds using specialized software. The material stream is then sorted into two or three fractions via pneumatic valves – each individual particle are beeing removed into the designated chute. Different sensor technologies and lighting systems can be combined as needed, enabling the detection of a wide variety of contaminants in a single machine. Sorting machines in waste glass processing typically based on the transmitted light method: The used glass slides down a glass chute with a light source mounted on the back. Opposite the chute is the sensor that detects the transmitted light. A light source is located at the rear, with the sensor positioned opposite to receive the transmission signal. Glass is translucent, whereas contaminants such as ceramics are not. There are also applications where the lighting and sensor are positioned on the same side. Here, the particles‘ reflective properties are used for detection.

To process large volumes and different particle sizes, multiple sorting machines operate side by side or in series. Multi-stage sorting lines ensure higher product quality. The glass fragments are separated from impurities in a multi-stage process. In the so-called post-sorting stage, the waste fraction is subjected to a final sorting process, during which any remaining glass fragments are recovered.

In the sorting step, the following materials are separated from the cullet:

KSP (ceramics, stones, porcelain): Unlike glass, these are not transparent or have a different appearance from other non-transparent parts (e.g., bone, paper, wood, etc.).

Metals: Here, magnetic and non-magnetic metals are detected using induction sensors.

Plastics are detected using NIR-sensitive cameras and special infrared lighting. This allows even transparent plastics (Plexiglas) to be distinguished from valuable glass and sorted out.

Lead-containing glass (crystal glass): Can be detected easily, efficiently, and cost-effectively using UV-C light sources and UV-sensitive cameras, as lead fluoresces under UV light.

Heat-resistant glass and glass-ceramics: These can also be detected in the UV wavelength range. Here, the different structure of the specialty glass (crystalline structure) is used as a distinguishing feature.

Glass by color: Glass is usually separated into different colors depending on its task description (white, green, brown). Depending on the regional origin of the waste glass, there are significant variations in color distribution and color intensity.

9. Once the waste glass has gone through all these process steps, quality control takes place at the end. Due to the constantly increasing demands on product quality, continuous and fully automated quality control of the product streams is of the utmost importance. In-house analysis devices, such as the CLARITY QC system from Binder+Co – which is designed similarly to sensor-based sorting machines – constantly analyze product quality during plant operation, thereby providing real-time insights into the plant’s efficiency as well as whether the products can be produced and subsequently sold to the desired specifications and quality standards. In automatic analysis, it is important to continuously check large volumes for impurities or color defects. If the products are outside the specification, the plant can be shut down immediately or parameters optimized. The continuously generated report serves as proof of quality for the recycler and the glassworks. The end products of flake processing are:

White glass (flint or even super-flint, which is particularly pure, white glass)

Green glass (or mixed with brown) – in packaging glass

Brown glass (or mixed with green) – in packaging glass

Challenges and opportunities for waste glass processing plants

To reduce losses, as little glass as possible should be accidentally discharged along with other (contaminant) materials. This primarily involves improving the separation of glass from metal closures, as well as more efficient removal of labels from glass and the effective separation of glass from organic materials (paper clumps or cardboard).

In addition, the fine particles in the glass should be kept to a minimum. During transport from the collection point, during transfer, and in the processing plants, the shards shatter into smaller pieces, creating a fine fraction. The finest particle size fractions (smaller than 1 mm) are very difficult to process and clean. This results in a fine fraction of insufficient quality for use in the furnace. The development of increasingly thinner packaging glass is another factor contributing to a higher proportion of fine particles.

Sorting technology will also continue to evolve in the future. For example, improved sorting technologies should better detect glass with low transparency (e.g., bottle bottoms or dark glass) or glass with adhering labels and discharge them as good product. This will involve a combination of improvements to mechanical pre-processing and new technologies and approaches in sensor-based sorting.

Autonomous systems with early-detection systems for quality deviations or unplanned downtime can ensure maximum availability of plants and machinery as well as consistently high product quality. Support services, mostly digital – such as the processing of process and operational data – help mitigate the growing labor shortage. Support services – mostly digital, such as the processing of process and operational data – are in demand here.

Zero-Waste Processes – in addition to glass, ceramics or porcelain can also be produced as a clean fraction and kept in the cycle or used, for example, as an aggregate in the construction industry. Recovered metals are easily utilized in the metal recycling industry. The goal is to keep the fractions destined for landfill as low as possible – numerous legal requirements in the EU already ensure this. In many countries and regions, however, the necessary legal framework still needs to be established.

Special projects in glass recycling

1 Waste as a valuable source of energy and secondary raw materials: ENAGES’ Zero Waste strategy

In Niklasdorf/Styria, ENAGES GmbH demonstrates that waste is a valuable resource. Since 2004, ENAGES has operated one of Austria’s most modern thermal recovery plants. Each year, up to 140 000 t of residual materials are not only converted into electricity, steam, and district heating but also made available for recycling.

Through the use of efficient fluidized-bed combustion technology, the residual materials are completely incinerated in compliance with the highest environmental standards, releasing valuable, non-combustible raw materials. To feed these recyclable materials into the circular economy, a state-of-the-art recycling plant was built in 2023 in collaboration with Binder+Co.

Using innovative screening and sorting technology, as well as sensor-based systems, up to 20 different fractions can be recovered from the fluidized bed ash. These include, among others, ferrous and non-ferrous metals, glass, as well as ceramics, stone, and porcelain, which are made available to industry as secondary raw materials.

The recycling of metals and glass is particularly relevant here, as these can be reused almost indefinitely by smelters and glass producers. The ceramic and stone residues can be used in the concrete and cement industries. In this way, ENAGES also makes an important contribution to resource conservation and environmental protection following the energy recovery of waste. What used to be landfilled now flows back into the economic cycle.

ENAGES demonstrates how a comprehensive circular economy should be conceived, by utilizing waste both for energy and as an important source of raw materials.

2 New recycling plant for the brazilian company MASSFIX

As is generally the case in the South American waste management context, glass recycling in Brazil is also progressing slowly. By 2025, Brazil had achieved a recycling rate of 37 % for packaging glass waste from municipal and industrial collection. The logistical challenge is enormous.

Brazil is a country of continental proportions where collection infrastructure is completely lacking, the level of environmental education is low, separate collection is inefficient or nearly nonexistent, and there is a significant lack of public policies to promote the sector.

Promoting environmental awareness is an essential part of MASSFIX’s mission. Through lectures, workshops, campaigns, and initiatives in schools, companies, and communities, the Brazilian company disseminates information and inspires responsible action.

MASSFIX is a Brazilian company specializing in glass recycling with over 30 years of experience in recycling packaging glass, flat glass, laminated glass, and other specialty glass types.

Every year, MASSFIX collects and processes more than 200 000 t of waste glass (approximately 75 000 t of packaging glass, 83 000 t of flat glass, 43 000 t of laminated glass, and 1500 t of specialty glass).

MASSFIX pursues a holistic approach to glass recycling. For instance, the company has installed collection containers for waste glass in six states to increase collection rates, operates its own transportation logistics, and runs its own processing facilities that convert waste glass into a secondary raw material.

There are significant technical differences between the recycling of packaging glass – which, when sorted correctly, has a higher recycling rate – and flat glass, which requires more complex separation and decontamination processes. MASSFIX focuses here on developing highly productive processes and workflows that enable the company to increase recovery rates and the purity of the recycled material, thereby expanding the technical and economic viability of cullet in the circular economy.

To achieve these objectives, MASSFIX has chosen to collaborate with Binder+Co as a technology partner, solution provider, and supplier of high-tech machinery for the processing of cullet from various sources (container glass, flat glass).