United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
'•¥
Research and Development
EPA-600/S2-81-193 Oct. 1981
Project Summary
Options for Resource
Recovery and Disposal of
Scrap Tires: Volume I.
Patricia L Deese, James F. Hudson, Richard C. Innes, and Douglas
Funkhouser
This report presents a review of the
environmental, technological, and
economic problems associated with
the management of the approximately
200 million tires that are discarded in
the United States each year. The
report analyzes trends and problems
associated with tire retreading, col-
lection, and shredding; rubberized
asphalt; and tires as a fuel supplement
(tire derived fuel or TDF). The eco-
nomics of tire collection, rubberized
asphalt, and tire derived fuel are
analyzed in depth. Various incentive
options are examined briefly, from
which the authors chose the product
charge of 4.46/kilo (2C/pound) as
offering several advantages over the
others for resolving the scrap tire
problem.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory. Cincin-
nati. OH. to announce key findings of
the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Each year approximately 200 million
automobile and 40 million truck tires
are removed from service (a total of
some 4 million tons), most of which
enter landfills for final disposal. Although
various new resource recovery options
(mainly energy recovery) for the use of
these tires have appeared at least
superficially attractive, the economics
of these processes have permitted only
a very slow growth in their utilization.
Traditional industries for the reuse of
these scrapped tires, rubber reclaiming,
tire splitting, and retreading have all
experienced zero to negative growth in
recent years, with the result that an
increasing proportion of these tires are
placed in landfills.
A number of impacts associated with
this situation tend to make the costs of
managing waste tires higher than the
minimum necessary. Tires are nearly
wholely produced from petroleum
derivatives. Since a large percentage of
this petroleum is imported, this causes
an obvious negative impact on the
nation's balance of payments, especially
in a world of cartelized oil prices.
Further, these tires displace volume in
landfills that in many communities is
increasingly scarce in supply, raising
disposal cost. This is a problem primarily
in densely populated areas where the
distribution of scrap tires closely
parallels the population density. Re-
ducing the size of the tires by splitting or
shredding to save landfill volume is
costly. Charges imposed to cover the
cost of shredding creates an incentive
for tires to be illegally dumped or
littered, causing negative aesthetic
impacts.
There are health impacts also, prin-
cipally the greater risk of fire and
disease from stockpiled and/or littered
tires. Tires have been implicated in
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V
mosquito borne encephalitis cases in at
least one community.
The causes of the scrap tire problem
are to be found in the interplay of
technological and economic factors. On
the technical side, a lack of simple
processes to reclaim high quality rubber
and/or constituent materials such as
carbon black from used tires means that
such products, if obtained, are costly
and not competitive with virgin mater-
ials, although the recent rise in virgin
feedstock prices should begin to reduce
the cost differential. Technical diffi-
culties that American companies en-
countered earlier with the construction
of steel-belted radial tires have made
them virtually unretreadable, probably
leading to a higher rate tire scrappage
than would have otherwise occurred.
This problem now seems to have been
resolved.
Technical Options for
Tire Reuse
Currently, there are four technologies
in various stages of use and develop-
ment that lead to reuse of scrap tires in
some form and may lead to greater
future use. These technologies are
shredding, retreading, rubberized as-
phalt, and energy recovery.
Shredding
Shredding is a fairly well developed
technology and is an intermediate
processing step for disposal, rubberized
asphalt, and energy recovery.
Retreading
Currently, approximately 13 million
truck and 31 million auto tires are
retreaded annually. The figure for
passenger auto tires has been declining
throughout the decade of the seventies,
and stood, for example, at 36 million in
1974. The state of the art is such that
well-made retreaded tires are produced
with relative ease but the variable
performance observed is because of the
many small retread shops that do not
have the proper equipment for good
retreading and/or seek to avoid the cost
of producing high quality retreads.
Also, it is true that the shift to radials
is having a significant negative impact
on the rate of retreading. In 1978, for
example, the retread rate for bias-belted
tires produced in 1976 was 38%; for
radials, 6%. Unless American tire
manufacturers can solve the technical
problems of construction that have
made their radial tires unretreadable,
and unless retreaders get the equipment
in place to retread these radials, there
will be a significant further decline in
retread rates, leading to a substantial
increase in the number of tires dis-
charged for disposal.
Rubberized Asphalt
Adding rubber to asphalt is an old
concept, although using scrap tires as
the source of the rubber component in
the mixture has received serious
attention in only the last 10 to 15 years.
There are two very similar processes in
use, both developed in Phoenix, Arizona.
Essentially, the process consists of
adding crumb rubber (derived from a
rubber reclaiming process) to hot
asphalt in an asphalt distributor truck,
spraying it on the road surface, and
covering it with stones ("chips"). The
anticipated benefits in road applications
(potentially the largest use for the
material) are two: (1) prevention or
retardation of the rate at which cracks
reflect through new asphalt courses
overlaid on older and failing pavements,
and (2) as a waterproof membrane (for
use on bridge decks, for example). The
most effective use may be in preventing
pavement failure resulting from ex-
pansive soils such as clays that stimu-
late "alligatoring," so named because of
the dense and interconnected nature of
the cracks.
The effectiveness of rubberized
interlayers in two other major types of
pavement failure, lateral and transversal
cracking, is more problematical. Lateral
cracking stems from weather caused
expansion and shrinking of concrete
pavements. Transversal cracking comes
from pavement and/or base failure,
often caused or exacerbated by excessive
weights of vehicles.
Rubberized seal costs are about 70%
($0.45/ydz) more costly than the con-
ventional nonrubberized treatments.
Table 1 shows the discounted payback
periods implied by various combinations
of discount rates and cost savings on a
square yard basis. As yet, no good
information exists on what the savings
are. For example, the stress-relievin
interlayer (placed between the
pavement surface and a new, thicker
overlay or finish course), some prelim-
inary evidence indicates an annual
maintenance cost savings of $0.26/yd2.
These savings suggest a discounted
payback of 4 to 5 years at rates of
discount of 6 to 10 percent.
Another important use of rubberized
asphalt is in crack and joint sealing
compounds. Preliminary evidence sug-
gests that the rubberized sealer is
technically superior to conventional
sealers (which often fail in less than a
year) and the cost premium is only 30%.
Thus, the likelihood of the cost effec-
tiveness of the material is high, although
again, the answer to this question of
cost effectiveness is not known with
precision.
Energy Recovery
Essentially, two basic technologies
are being considered by a number of
firms as methods of recovering the
energy content of tires—direct com-
bustion and pyrolysis. Both normally
require shredded tires as feedstock.
Neither of these technologies, in the
various forms in which they appear, are
much beyond experimental or pilot
stages, and many have not reached the
pilot stage. For the most part, the
processes are not yet profitable.
Direct combustion techniques take
tires (whole or shredded) and burned
them singly or mixed with other fuels
(especially coal) typically for steam
production. There is no comprehensive
information on the air pollution impacts
of burning tires, but past experiences
suggest that proper feed rates and
standard emissions control equipment
will be able to deal with tire related
residuals.
Large scale combustion of tires
depends on an adequate supply of tires
for the process. As such, the supply is
sensitive to the cost of collection,
especially transportation costs, and to
prices to be paid (positive or negative)
Table 1. Discounted Payback Periods for an Asphalt-Rubber Seal Coat (years)
Discount
Rate
(%)
6
10
15
20
25
Annual Maintenance Savings (C/yde)
.10
6
7
8
13
>50
.15
4
4
5
5
7
.20
3
3
3
4
4
.25
2
2
3
3
3
.30
2
2
2
2
3
.40
2
2
2
2
2
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for delivery of tires to a facility.
Processing costs do not seem to be an
important consideration, at least for
plants of 30 tons/day or more. The
study of a hypothetical facility in New
England suggests that the process
would be profitable if as few as 6
percent of tires in New England were
collected and delivered to the plant.
Currently, there are still no important
- facilities for shredding or otherwise
processing tires for energy recovery.
The cost of collection and the insuf-
ficiently high prices of alternative fuels
do not seem to make energy recovery
from tires economical at present.
Pyrolysis of whole or shredded tires
has and still attracts the attention of
many chemical engineers. Such com-
panies as Firestone*, Goodyear, Tosco,
and others have made substantial
investments in the past trying to recover
fuel oil, carbon black, and gases from
pyrolized tires. Typically, carbon black, a
major ingredient in tires, is of insuf-
ficient quality to make it competitive
without further processing. Again,
economics is the hurdle that remains to
be surmounted before energy recovery
from tires becomes profitable.
Public Policy Options and
Recommendations**
The full report briefly reviews the
advantages and disadvantages of alter-
native public policies dealing with the
scrap tire problem. These include
landfill regulations, tire size standards,
tire maintenance, and such economic
incentives as disposal charges and
product charges. The authors recom-
mend adopting a product charge, with
the revenue distributed to qualified
disposers to cover the costs of proper
disposal.
The full report was submitted in
fulfillment of Contract No. 68-03-2735
by Urban Systems Research and
Engineering, Inc., under sponsorship of
the U.S. Environmental Protection
Agency.
Patricia L Deese, James F. Hudson, Richard C. Innes. and Douglas Funkhouser
are with Urban Systems Research and Engineering, Inc., Cambridge, MA
02138.
Haynes C. Goddard is the EPA Project Officer (see below).
The complete report, entitled "Options for Resource Recovery and Disposal of
Scrap Tires: Volume I," (Order No. PB 82-107 491; Cost: $14.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
•fy US GOVERNMENT PRINTING OFFICE, 1981 — 559-017/7392
.'Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use.
""Although this report has been reviewed by the
Municipal Environmental Research Laboratory,
and approved for publication, this approval does
not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Pro-
tection Agency.
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