Ever wondered why we don’t recycle more glass? Discarded glass comes from a variety of sources and collectively, bottles, containers and sheet glass can account for as much as 30% of municipal waste streams by weight. That is a lot of material, but only a fraction of the total is recycled at present. With the right information, and with the right equipment, recycled glass cullet can become an enormous resource with huge potential for reducing our dependence on virgin materials in a wide variety of products and processes. So why aren’t we recycling more glass?

Exploding the myth
There is no market for recycled glass. “Nonsense,” says Cynthia Andela, president and COO of Richfield Springs, NY based Andela Products, Ltd., manufacturers of glass breakers, pulverizers and recycling equipment. “There is some resistance in the business to handling and transporting discarded glass for recycling, so it is easier to claim there are no markets. That results in hauling contracts that often exclude recyclable glass, so a good portion of it winds up in our landfills. The truth is, crushed or pulverized glass can be used in many of the same applications as sand and gravel. For backfill, drainage, filtration, walking trails, parking lots, construction and even beach sand. The key is in working cooperatively with local producers of traditional aggregate. That’s when the real potential of recycled glass can be tapped,” she said.

How it’s done
In a traditional, dual-stream recycling program, the commingled containers are delivered to a Materials Recovery Facility or MRF. There, they are directed up a conveyor to a platform above where the glass is sorted manually by color. As glass items are pulled from the waste stream, they are directed off the main conveyor and into a chute or hopper that feeds a glass crusher stationed below. Glass crushers reduce recovered glass to crushed “cullet,” a form that is both safer and easier to handle for further recycling.

“A lot of crushers for dual-stream applications are designed to discharge ground cullet into a standard 55 gallon drum,” said Ron White, owner and general manager of C.S. Bell Company in Tiffin, OH. “The barrel sits on a pallet and is changed out when it is full for another one. In higher volume facilities, crushed glass sometimes accumulates in a pile under the crusher, or is carried away to another part of the facility by conveyor,” he added. To ensure the greatest value for crushed glass cullet, some installations use a separate crusher for each color – clear, brown, green, etc.

At the municipal level, there is a trend toward increased single-stream recycling. This is because it boosts participation by offering the convenience of not having to separate cans, plastics, glass and paper. When recyclables are delivered to a MRF, the sorting is performed there instead. The systems that separate the single-stream recyclables include a series of screens that break most of the glass. The mixed broken glass contains small pieces of plastics, metal and paper. If not recovered, the mixed glass would end up being part of the MRF residual and increase the costs associated with disposing of it. The good news is, technology is available to selectively reduce the mixed glass and remove it from plastics, metal and most paper.

Glass pulverizer systems, such as those provided by Andela Products, Ltd., feature a unique, flexible impactor system that can handle this dirty mix and produce fine sand and gravel sized glass aggregate without sharp edges. This material is often used by the local municipality and saves them the cost of buying aggregate for road construction projects. No longer a cost, but a valuable recycled material.

All recycling programs should include glass since it is a raw material that can replace sand or silica in the manufacture of new bottles or in the construction of raised bed septic systems, roads, beaches or a beautiful backyard landscape. The glass recycling program should consider both color sorting and crushing of glass along with pulverization of glass into aggregate. This will provide the MRF with multiple markets for the glass and avoids the cost of passing through and land filling broken glass.

How they work
Glass crushers provide size reduction and usually yield a glass cullet 2” in size and less. “It doesn’t matter if the glass is clean,” said Ron White. “Lids and labels are separated from the glass so the containers don’t have to be clean going in. The better systems today have no trouble extracting recyclable glass from any non-glass contaminants,” he said.

Glass pulverizer systems for the mixed glass from single-stream programs are complete systems with a surge feed hopper, pulverizer, screen and conveyor packaged as a stand-alone system or integrated into an existing MRF. The bottles and other recyclable glass enter the crusher through a hopper. Material then passes into the pulverizer/hammer mill where electric motors turn rotating flexible hammers that crush the glass but leave the non-glass items in their larger, original form.

The resultant crushed glass, exits the pulverizer through a discharge chute. Crushed glass is typically in the 3/8” minus size range with no sharp edges. Specific applications and sizes of crushed glass can be produced with the trommel screen as part of the system options. Non-glass contaminants such as paper and metal bits are separated from the glass aggregate and discharged into a separate container.

Breakers and pulverizers are available in a variety of sizes, and the right one for you depends on a number of factors. “To determine the best solution, the MRF operator needs to consider a number of issues,” said Cynthia Andela. “We always ask how the material is coming in. Is it mixed or sorted by color? Is it sorted by hand or through an automated process? How much volume by weight is being handled? And most importantly, what are the current costs associated with handling glass at the MRF? These are all factors to consider when sizing the right system for the job,” she observed.

For the MRF, glass recycling systems range in size from units designed for 2-3 tons per hour up to as large as 20 tons of glass per hour.

Options and maintenance
Most manufacturers offer a standard product, but options include such choices as larger motors, heavy-duty drive shafts and a variety of feed and discharge considerations to meet the needs of specific operations. Glass is an abrasive material, so the cost of parts that wear is a consideration that can equate to $1.00 to $3.00/ton in some cases.

With the burden of sorting recyclables shifting to the MRF, electronic control panels are becoming a more important option for operators that need to integrate their glass crushers and pulverizers with other equipment in the process.

Looking ahead
As the rate of glass recycling increases, glass crushers will play an increasingly more important role for MRF operators and processors everywhere. According to Andela Products, “Glass recycling has an exciting future. We’ve just begun to explore how this resource can pay off.”

If the glass that can be recovered from the recycling stream was substituted for aggregate (like limestone for example), a well-run high volume MRF has as much commercial value as a traditional limestone quarry. A MRF would have a continual supply of aggregate however, as apposed to the quarry that is mined and gone.

To put things in perspective, it is estimated that over 4,000 tons of recyclable glass is discarded in New York City alone - every week. That’s an annual resource pool of over 416,000,000 pounds of available raw material - from a single metropolitan area. On a national basis, there are hundreds of these “urban mines” representing an inexhaustible supply of recyclable glass. Through additional research, new applications for recycled glass are created and tested every year.

The markets are there. To boost the rate of glass recycling, MRF operators need to partner with private contractors and aggregate producers (or users) to get their raw material “out of the pit” and into the consumers of specialty aggregates.