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From Glass to Sand; The Benefits Abound
by Dan Eshelman

An assortment of bottles and jars of various shapes and colors cascaded from the bucket of a front-end loader into the opening of a large hopper.

A few seconds later, after a series of buttons were pushed to activate the machinery, shattered pieces of glass emerged from an outlet in the hopper and began an upward journey on a conveyor.

The material then entered an intricate assembly of crushers, separators and more conveyors, and within a matter of minutes was deposited - in the form of small granules - into a waiting storage bin.

The transformation of discarded glass into a substance resembling sand is now being performed at the Council Bluffs Recycling Center in Council Bluffs, Iowa with the introduction of new pulverizing equipment.

"This is a state-of-the-art machine," said Glen Ingham, supervisor in the Solid Waste Management Division of the Council Bluffs Department of Public Health. "It gives us the capability of converting waste items into a product with a lot of practical uses."

He noted that in the past, discarded glass had been difficult to recycle because bottles and jars often were contaminated with residues of their previous contents, and it was cost-prohibitive to bring some of the material to a condition where it was acceptable to glass remanufacturers.

With the pulverizer, the recycling center can now accept all types of glass - mirror, ceramic and plate glass, in addition to ordinary container glass.

"Since all these different kinds of glass can be mixed in the pulverizer, it reduces sorting time significantly," Ingham said. "We can take all colors of glass and can even accept drain tiles."

Because the machine can crush all categories of glass, it represents a major step forward in recycling items that at one time were routinely thrown away and ended up in landfills.

But the equipment provides another benefit.

By turning the glass into an aggregate, the pulverizer creates a reliable supply of raw material that the city can use in public works projects - thereby eliminating the need to purchase a comparable product from an outside vendor.

"Expenses can be lowered by using the crushed glass," Ingham said, noting that the material will become part of the "glassphalt" that will be put down on city streets during improvement projects scheduled this year.

After the glass is dumped into the first hopper of the machine, a vibrator starts the process of breaking up the material by bumping the pieces together.

On the first conveyor, a cross-belt magnet attracts and separates out any metal that may be mixed in with the glass. Another operation removes labels from the containers.

In the initial pulverizing unit, large steel tines churn the glass up, rotating the now-broken pieces and throwing them against each other to further shatter the material.

"There's a rapid whirling action in this unit, and that breaks the glass into even smaller pieces," Ingham said.

At this stage of the process, a special device separates any leftover garbage from the glass flow, and the material goes on another conveyer to the sanding unit. Extensive pulverizing is done by this equipment, which rotates and hammers the pieces into small chunks.

From here, the material goes by conveyor to a unit that rounds the edges of the glass granules - thus eliminating sharp points - and separates the material into two standard sizes. Pieces with diameters of three-eighths of an inch are used for seal coating work on streets, while pieces with diameters of one-eighth of an inch or less are used for sand.

Ingham said the material would be suitable for commercial landscapers and individual homeowners. He said that in some places in New Jersey, the pulverized glass is spread on beaches near the ocean.

At present, all the aggregate produced at the recycling center is scheduled to be used by the city's public works department. But Ingham said once the output capacity of the pulverizer has been increased, plans are to offer the material for sale to businesses and area residents.

By adding a sifting unit to the equipment, he said, "we'll be able to make sandblast grade material. There's a good market for this, so it would be a way to generate more revenue.

"The pulverized glass is also now being incorporated into septic systems of rural homes - a use that represents another viable market. "Studies have shown that water flows better through the glass granules," Ingham said.

Along with crushing bottles and jars brought in by consumers, the equipment will be in operation breaking up and converting ceramic drain tiles that are being replaced in the city with metal pipes.

The machine includes a vacuum system that catches and contains dust that may be a by-product of the crushing process. Particles are filtered, and then routed to a collection receptacle for later disposal.

—Reprinted with permission from Daily Nonpareil


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