From Glass to Sand; The Benefits Abound
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
"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
With the pulverizer, the recycling center can now accept
all types of glass - mirror, ceramic and plate glass, in addition to ordinary
"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
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
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
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