Pain in the Glass

Some adopters of single-stream recycling have discovered that glass can reduce the efficacy of their programs. As a result, they are looking for ways to remove glass from their systems.

Some, like the Pierce County Department of Public Works and Utilities in Washington state, have forbidden residents to put glass into their recycling bins. Others, such as Norcal Waste Systems in San Francisco and Casella FCR, a wholly owned recycling subsidiary of Rutland, Vt.-based Casella Waste Systems, have found effective ways to remove glass by installing relatively new sorting technology at their material recovery facilities (MRFs).

A 2003 report by Conservatree, a San Francisco-based non-profit research and consulting organization specializing in environmentally friendly paper, recommends removing glass from single-stream collection programs. Glass fragments, shards and even whole containers pose a “severe problem” for paper mills, the report says.

The report cites four major problems that arise when glass contaminates recycled paper feed stocks:

  • Glass pieces damage equipment gears, bearings and gasket seals at sorting facilities. They clog screens. They also function like sandpaper to wear down equipment parts.

  • Single-stream recycling collection reduces collection workers' risks, but pushes safety problems up the line to the mills.

  • Glass sometimes gets all the way through the system and into finished products, thereby creating hazards for consumers.

  • Finished products contaminated with glass may erode public confidence in recycled products.

Glass contamination has made it more difficult for recycling plants to market their materials. The upshot is that single-stream recycling won't deliver on its promise until communities figure out how to deal with the problems created by including glass in the collection mix.

Curbside Recycling

Communities across the United States have been carrying out curbside recycling programs since the middle of the 1970s. Over the years, collection has grown more and more sophisticated. “We've seen an evolution from collecting newspapers only using wire bins attached under garbage trucks to collecting glass, cans and newspaper in separate compartments,” says Chaz Miller, director of state programs for the Washington-based Environmental Industries Association.

Each change was an attempt to control the cost of recycling collection programs. But as recycling programs grew and added multiple streams, costs increased. “Looking for ways to collect more efficiently, the industry realized that costs were higher on the collection side than on the processing side,” Miller says.

That realization paved the way for single-stream, commingled recycling collection programs to enable communities to reduce collection costs, thus lowering the overall cost of the recycling system. The lower single-stream collection costs come from the use of automated trucks, which make it possible to cut labor and worker's compensation costs. Single stream also makes recycling easier for residents who on average recycle 25 percent more materials in such a system.

According to Miller, estimates suggest that as many as 10,000 communities in the United States have adopted curbside recycling programs. Of those, about one-third have converted to single-stream operations.

Unfinished Conversions

But there has been a hitch. The glass portion of a single-stream recycling program is creating problems on the material processing side of the equation. “Some early single-stream facilities were simply old MRFs that had been retrofitted,” says Kate Krebbs, executive director of the Washington-based National Recycling Coalition. “These facilities were designed to deal with large quantities of material, not to process and ship high-quality commodities. At that point, the responsibility to clean up bales of recycling materials fell on the manufacturers, not the MRFs.”

Single-stream collection proponents never intended to push the responsibility for cleaning up materials off on manufacturers. Their interest was to reduce costs within their closed recycling system.

A single-stream conversion isn't finished until new MRF processing equipment restores the outgoing materials to the uncontaminated state that prevailed during the days of dual-stream recycling. “You have to add new sorting equipment and new hand sorting concepts to the recycling center,” says Robert Reed, spokesman for Norcal Waste Systems.

At Norcal's 200,000-square-foot Recycle Central plant in San Francisco, for example, single-stream recycling materials pour through the front door, while 16 types of clean, marketable commodities flow out the back door. Among them are flint, amber and green glass sorted and ready to return to the production line at a glass mill. The plant also ships uncontaminated mixed paper, several grades of newspaper, cardboard and card stock.

When trucks carrying commingled materials arrive at Recycle Central, they dump their loads on the tipping floor. Sorting begins as the material goes up a conveyor and across an initial sort deck where cardboard is removed by hand and sent down a chute into a baler. Sorters also remove plastic garbage bags and other materials.

Next on the line comes a key technological addition related to single-stream collections: the material flows across a spinning disk screen. Designed with hundreds of vertical spinning disks positioned in rows, the screen tosses large light materials like paper up so that they stay atop the disks and move upward.

Smaller and heavier materials like glass bottles, glass fragments, cans and plastic tumble downward. To insure that the paper is separated from everything else, the remaining paper passes through another disk sorting line that shakes fragments of glass, metal and other materials off and sends them down onto another conveyor below.

Hand sorters pick the mixed paper according to prices in the current market. If one kind of paper is selling particularly well, sorters focus on that grade. Recycle Central conveyors using magnets and then eddy currents remove metal and aluminum containers, leaving plastic and glass. On the next line, workers pick off the plastic.

All along the line, conveyors underneath the main line catch small pieces that fall through, including broken pieces of glass. Little if any plastic gets through. A magnet pulls off the metal, and the broken glass goes into a mixed aggregate bunker that is sold for use as road base. “Finally, two sorters at the end of the line separate glass bottles by color,” Reed says. “They throw the bottles into bunkers so that they break. Then it goes to the glass plant. It could be back on the shelf with a beverage in it within six weeks.”

Single-Stream Glass

There are different ways to deal with the problem of glass. Casella FCR separates glass on the sorting lines of its 24 MRFs with spinning vertical disk conveyors similar to those used at Norcal's Recycle Central.

“It is true that there weren't good processing systems in place to handle the change from dual to single-stream collections,” says Sean Duffy, a regional vice president with Casella and president of FCR. “As a result, glass has contaminated paper. In the last five years or so, technology has begun to catch up. Today's sorting systems make much better quality fiber product than older systems. Better quality products are always more saleable.”

Duffy goes on to say that recycled glass has one primary use and a couple of alternative uses. For Duffy, the ideal use is as a container material. Alternative uses include daily cover at a landfill, a drainage management material similar to stone aggregate and a fiberglass feedstock.

During Casella's single-stream recycling processing, a lot of glass breaks and ends up in a pit of mixed glass fragments usually shipped off for low-cost alternative uses. “We're working on something else,” Duffy says. “We've invested in a company called Green Mountain Glass (GMG) that markets a patented [chemical] technology that de-colorizes mixed cullet glass and then re-colorizes it.”

FCR's idea is to market the GMG colorizing system along with mixed cullet to glass manufacturers, who are familiar with the chemicals used in the process because they are the same chemicals now used to colorize amber and green glass, Duffy says. The difference is that the GMG process has standardized a method to de-colorize and then re-colorize green and amber glass in the molten stage, thus making it possible to produce new glass from mixed cullet without sorting.

Just Saying No to Glass

What if residents demand single-stream collection but refuse to pay for processing equipment that will eliminate glass contamination of commodities? The Solid Waste Division of the Department of Public Works and Utilities in Pierce County, Wash., faced this problem 18 months ago.

When curbside recycling began in Pierce County in 1990, the goal was to collect 40 pounds per month per household, says Sally Sharrard, senior planner with the Solid Waste Division. After reaching the goal, residents began to slack off.

During planning aimed at updating the county's solid waste management plan, a residents' advisory committee called for a single-stream recycling system. “Residents had seen that Tacoma had gone to a single-cart system with an extra small bin for glass,” Sharrard says. “Seattle had also gone to a single-stream program.”

Additional research found that Pierce County's recycling processors did not have the equipment to process commingled materials containing glass. Nor could the facilities afford the technology required without substantially raising rates charged to residents.

Conversations with towns and cities in the county indicated that while they would like to see the recycling program changed, residents did not want their costs to rise more than $2 per month.

“We asked haulers to calculate their costs to change over,” Sharrard continues. “When the estimates came in, the only way we could keep the price hike under $2 per month was to eliminate glass.”

Sharrard presented the results in a series of public meetings in cities and towns across the county. The consensus of several dozen meetings was to hold the cost increase below $2 by removing glass from the recycling stream.

Pierce County did what its residents wanted and set up a single-stream system that held the cost hike below $2 per month by eliminating glass from the recycling stream and beefing up an existing network of drop-off facilities.

But residents won't want to make special trips to drop off glass forever, and haulers wouldn't want to allocate trucks just for glass for very long. Sooner or later, the county's processors will have to buy the equipment and add a line that sorts out the glass.

Mike Fickes is a Westminster, Md.-based contributing writer.