Turning Waste Glass into Sustainable Fertilizer

As the world’s second-most consumed resource after water, sand supplied essential material for concrete, glass production, insulation, water filtration, and landscaping. Yet, at a staggering 50 billion metric tons consumed annually, sand disappeared faster than nature could replenish it.

With only 21 percent of the world’s glass recycled, Andela Products saw an opportunity to address sand shortages by transforming waste glass into “glass sand.” Sharing the same size, shape, and texture as sand, pulverized waste glass offered a promising alternative to sand shortages. Teaming up with Cornell University materials science and engineering graduate student Ryan Greene, Andela Products ventured further, exploring glass sand as a potential fertilizer. Together, they crafted a process that turned waste glass into nutrient-rich silica pellets—creating a sustainable, sand-like fertilizer ready to enrich soils and reduce waste.

“Through growth study research, we found plants need the silica in the glass, using it to build sturdy stalks, especially in nightshade varieties like tomatoes. If the glass could carry and release additional nutrients gradually, we’d achieve double benefits. One major issue with fertilizers is that they often wash away too quickly, ending up in streams and eventually the ocean, causing environmental problems. Our goal was to transform waste material into a beneficial resource,” explained Cyndy Andela, President and CEO of Andela Products.

Glass sand into fertilizer

Traditional fertilizer pellets relied on plastic binders to stay intact, releasing microplastics and contaminating soil and water sources. The research team addressed this issue by developing a method that used pulverized glass to carry fertilizer salts, binding sand glass into pellets without adding microplastics or additional chemicals. Initially, they explored an ion exchange process to infuse plant nutrients into the glass sand at room temperature. “The idea was that the sand glass would release nutrients gradually,” explained Ryan Greene, a materials science and engineering graduate from Cornell University. 

After initial testing, researchers discovered minimal nutrient infusion with room-temperature ion exchange but noticed that as the high-salinity bath dried, salts in the solution precipitated onto the glass particles, binding them into agglomerates that could release the fertilizer salts gradually. Through trial and error, the team fine-tuned the formula and mechanical processing, producing pellets that dissolved over time in soil, while remaining stable enough for shipping. 

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To test the sand glass fertilizer prototype, researchers submerged pellets in water, observing that in about 8-9 hours they dissolve completely. For comparison, the same amount of fertilizer in its pure salt form was found to dissolve in around 10 minutes. Greene explained, “In moist soil, these pellets would likely provide sustained fertilization for a week or two. But if we applied the same amount of fertilizer as plain salt, it would dissolve in about 10 minutes. The sand particles essentially act as a shield for precipitates within the pellets. First, the outer layers of salt are exposed to moisture and begin to dissolve, which then breaks the pellet apart and exposes more of the core over time.”

Setting up a facility for pulverizing waste glass, mixing it with fertilizer salts in large water baths, and pressing it into pellets would require a capital investment. However, once operational, the facility could run with minimal expenses due to the low energy demands and the abundance of waste glass as raw material.

Pulverizing glass

Andela Products’ glass pulverizing systems transform waste glass into a sand-like texture ideal for multiple applications. “We don’t use traditional grinding; instead of a cheese grater, our process functions more like a blender and colander,” explained Andela. “The glass gets small and rounded like sand, while trash, labels, caps, and similar items stay larger. We then dump the mixture into an integrated screen to separate the sand from the trash.”

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Soda-lime glass dominated roughly 90 percent of the glass market, fueling the production of both flat glass for windows and container glass for bottles, light bulbs, and drinking glasses. Manufacturers crafted this versatile glass by melting a blend of silica (silicon dioxide), soda (sodium oxide), lime (calcium oxide), magnesium oxide, and aluminum oxide in a furnace heated to approximately 1,675 °C (3,047 °F). For float glass, they poured the molten mixture into a bath of molten tin, allowing it to float and cool into a flat, smooth sheet. For container glass, they combined air and pressure to shape specific parts in molds, like the neck, and inflated the glass, balloon-like, to form the bottle. 

Fresh synthesizing

While glass-based fertilizers gained popularity, most manufacturers synthesized them from new glass rather than recycled material. They typically melted a blend of raw materials, such as silica, soda, and lime, adding fertilizers like nitrogen, phosphorus, and potassium, then processed this glass into sand. However, creating new glass requires significant energy, failing to address the millions of tons of waste glass piling up in landfills. The Andela Products team sought a sustainable solution by converting waste glass into usable fertilizer with minimal energy.

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Recycling waste glass into fertilizer tackled several challenges: reducing landfill waste, lowering the energy demands of creating new glass fertilizers, and eliminating plastic and chemical binders. These sand glass pellets also provided a soil additive for infertile regions. By repurposing glass back into sand, the project helped replenish beaches, support agriculture, and control erosion, promoting self-sustainability and enabling local food growth.

The collaboration between Andela Products and Cornell researchers repurposed discarded glass into nutrient-rich silica pellets, offering an eco-friendly alternative to conventional fertilizers that enriched soils and reduced pollution. These innovations marked a step toward a circular economy, where waste materials drive lasting benefits for ecosystems and global sustainability.

Nicole Imeson is an engineer and writer in Calgary, Alberta.