61    UTILIZATION OF WASTE TIRE RUBBER AS AN
ANAEROBIC FIXED-FILM SUPPORT MEDIA
Charles C. Ross, Director of Engineering
Environmental Treatment Systems, Inc.
Atlanta, Georgia 30377
John A. Pierson, Research Engineer
Georgia Tech Research Institute
Atlanta, Georgia 30332
INTRODUCTION
In a series of laboratory- and pilot-scale research studies by Georgia Tech,1"4 anaerobic packed-bed
(fixed-film) reactors (APBRs) were studied to demonstrate the feasibility of utilizing high-rate anaerobic treatment of poultry processing wastewaters as a replacement for more traditional physical/
chemical pretreatment technologies such as dissolved air flotation. At loading rates above 5.2 kg
COD/m3-day and retention times under 10 hours, laboratory reactors utilizing ceramic berl saddles as
a packing media were able to continuously provide BOD5, TSS and FOG removal efficiencies exceeding 80%, and effluent contaminant concentrations below levels typically required for discharge to a
municipal sewer without surcharges.
Initial capital cost was identified as a major impediment to the economic viability of a packed-bed
anaerobic process in this pretreatment application.5 Capital costs for a high-rate anaerobic system
traditionally are higher than comparable physical/chemical or aerobic pretreatment systems. The
packing media in an upflow anaerobic process enhances biomass attachment and entrapment, flow
distribution, and biomass settling. The polypropylene or polyethylene packing media (random pack
or modular) typically used in these systems usually range in installed cost from $3 to $10 per cubic foot
and is estimated to account for 33% of the total reactor cost or 15% of the total APBR system cost.
Reducing the packing media cost of an APBR while maintaining comparable treatment performance can be accomplished by using less media or reducing the unit cost by replacing the commercial
plastic media with a low-cost alternative. For example, bench-scale research determined that a half-
packed upflow anaerobic reactor provided the same treatment performance as a fully-packed reactor
in the treatment of a furfural byproduct wastewater.6 Many others have attempted to identify low-
cost alternatives to commercially available plastic media in anaerobic packed-bed or fixed-film processes including clay shards, mussel shells and coral.7
In this study, waste automobile tires were identified as a potential source of packing media for an
anaerobic packed-bed process. There are over 240 million tires discarded annually in the United States
alone8 with only 30% reused within the tire industry or as an alternate source for fuel, asphalt, or
other materials. In some states, the waste tire market is driven by a surcharge ($l-$2 per tire) for tire
brokers to handle disposal.9 Typically these tires can be chopped or shredded for less than $0.10 per
tire with a resulting bulk volume of roughly one cubic foot per tire. In this form, chopped or shredded
tires could be used as an inexpensive packing media for APBR and hybrid anaerobic processes.
Besides lower cost, the porous tire surface would appear to be more conducive to biofilm attachment;
moreover, the exposed steel belts from shredded steel belted tires could serve as a source of iron to the
process.
While waste tires have the potential to be a low-cost and effective alternative to commercially
available random pack or modular media, there was concern over the potential of contaminants
leaching from a tire media bed over time. Field and lab studies conducted on chipped tires used as a
roadway sub-grade support10 indicated the possibility of metals and polynuclear aromatic hydrocarbons (PAHs) leaching from a tire bed under certain pH conditions. Barium, Cd, Cr, Pb, Se, and Zn
were found to leach in concentrations exceeding Recommended Allowable Limits for drinking water
at pH levels below 5.0. PAHs were found to leach at higher concentrations at pH levels exceeding 8.0.
49th Purdue Industrial Waste Conference Proceedings, 1994 Lewis Publishers, Chelsea, Michigan 48118. Printed in
U.S.A.
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