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
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.
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.
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.
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.