Ikelic - Alliance Digital Repository

COAL
Cofiring MGP Wastes In Utility Boilers
One possibility is to cofire tar-contaminated soil
with coal In utility boilers. However, only non-
hazardous solid wastes can be cofired in in
dustrial boilers without extensive regulatory per
mits. Thus this option can be considered only for
tar-contaminated material determined to be nonhazardous
upon excavation from an MGP site or
for excavated material that can be rendered nonhazardous
on-site within a 90-day accumulation
period (as required by United States Environmen
tal Protection Agency regulations).
According to previous research by EPRI and test
ing by individual utilities, a high benzene con
centration is the primary reason that MGP site
remediation wastes exhibit a hazardous charac
teristic in TCLP (Toxicity Characteristic Leaching
Procedure) testing. Tarry MGP wastes seldom
fail TCLP testing for any other parameter. If ex
cavated MGP material can be managed on-site
to reduce its TCLP benzene concentration, then
the material is a candidate for cofiring in a utility
or similar boiler.
In one EPRI-sponsored study,
coal and tar were
mixed in various proportions, and the mixtures
were analyzed for total benzene and TCLP ben
zene. It was found that a mixture containing
4.45 percent tar would have a 97.5 percent proba
bility of being found non-hazardous in TCLP test
ing.
Chemical Extraction Methods
Removal of subsurface tars at or near residual
saturation by injection and recovery of aqueous
solutions of surfactants or solvents to enhance
solubilization of constituents may be possible,
but could be performed only at sites where the
flow and recovery of the solutions can be control
led with confidence. Moreover, it is clear from
bench-scale experiments that large concentra
tions of solvent or surfactant would be required
to achieve substantial recoveries of tar mass by
dissolution. Fairly large doses of surfactant are
required to promote enhanced solubility of PAH
compounds In the presence of soil because of
sorption of surfactant on the soil. In the
presence of an organic liquid phase, partitioning
of the surfactant to the organic liquid could oc
cur, possibly resulting in even higher required sur
factant doses.
MGP-REM Process
IGT has developed and demonstrated a remedia
tion technology, known as the MGP-REM
process,
which is based on the enhancement
and acceleration of indigenous biological activity
and the application of chemical treatment. The
chemical treatment uses hydrogen peroxide and
iron salt (Fenton's reagent) to oxidize
polynuclear aromatic hydrocarbons, making
them more amenable to biological treatment.
The MGP-REM process is faster and achieves a
significantly higher degree of cleanup
than the
conventional biological process alone.
Moreover, it costs no more than conventional
bioremediation and is considerably less expen
sive than incineration. IGT successfully field
tested the technology in the landfarming mode
from 1991 to 1993 and in the soil-slurry mode in
1993-1994. In situ field tests are expected to
start in 1995.
IGT and its commercial partners operated a pilot-
scale bioslurry reactor system based on the
MGP-REM process at an MGP site in New Jer
sey.
Figure 1 depicts the pilot-scale bioslurry reactor
system.
The treatment process starts with the excavation
of the soil, which is screened before being mixed
with water in the attrition scrubber. Slurry from
the attrition scrubber is then pumped to the
respective reactors for either biological or chemi
cal treatment. After treatment, the slurry is
pumped to a thickener where the water is
removed. The water is stored for reuse, and the
thickened solids are made available for backfill at
the site.
THE SYNTHETIC FUELS REPORT, JANUARY 1995