United States
                              Environmental Protection
                              Agency
                      Solid Waste And
                      Emergency Response
                      (OS-220)
             Directive 9200.5-251 FS
             November 1989
                              Innovative  Technology
                              In-Srtu  Vitrification
TECHNOLOGY DESCRIPTION

    In-situ vitrification (ISV) can be used
to treat soils and sludges contaminated with
mixtures of various waste types (e.g., radio-
active, inorganic, and/or organic). The pro-
cess electrically melts the waste media, cre-
ating an extremely stable glass-like solid.
    A schematic  diagram of a typical ISV
treatment facility is shown in Figure 1.  Four
electrodes connected to a utility distribution
system or to an on-site diesel generator are
over the process area collects both organic
and inorganic gases, which are treated be-
fore being released into the atmosphere. An
off-gas treatment system is designed to
handle conditions at most sites. If necessary,
the treatment system may be modified to
meet specific site requirements. The off-gas
treatment may include any of the following
units:  a  wet scrubber system, a heat ex-
changer with a glycol cooling  system, a
heater, a filter, and/or an activated charcoal
assembly. The hood draws in large amounts
          Figure 1:  Schematic Diagram of a Typical In-SItu Vitrification
                             Treatment Facility
             To Treatment
 Note: adapted from Battelle Pacific Northeast Laboratories, for Booz. Allen & Hamilton Inc
inserted into the soil. Because soil typically
has low electrical conductivity, flaked graph-
ite and glass frit are deposited between elec-
trodes to provide a starter path for the elec-
trical current. As the current flows between
electrodes, the adjacent soil is  heated to
1600 - 2000°C, well above a typical soil's
melting temperature. The graphite starter
path eventually bums off and the current is
transferred to the now highly conductive
melted soil.
    Within the melt, organic contaminants
are vaporized and pyrolyzed (i.e., thermally
decomposed); the pyrolysis products rise to
the surface and combust in the presence of
oxygen.  Non-volatile inorganic elements
     Cisolved or incorporated into the melt.
     le metals may vaporize and rise to the
     e along with the pyrolysis products.
Table 1  lists the effectiveness of ISV on
general contaminant groups.
    A negatively pressurized hood placed
of outside air which helps to oxidize com-
bustible vapors and pyrolysis products. All
equipment involved with the ISV process,
including the off-gas treatment system, are
contained in  three mobile trailers.
    When the treatment is completed, the
power is shut off and the equipment (i.e.,
electrodes and hood) is moved to another
treatment area where the treatment process
is repeated. Following treatment, the sur-
face of the vitrified  area is covered with
clean soil, and the melt is allowed  to cool
slowly, producing an amorphous solid re-
sembling obsidian.  Several months are
required for the treated area to cool to ambi-
ent temperature; however, after four to five
days, the melt has cooled sufficiently for
equipment to be moved onto the treated area.
    The advantages of ISV include the
potential  ability  to destroy, remove,  or
immobilize all contaminant groups and to
reduce the volume of the waste/media being
treated. The need for off-gas collection and
treatment, however, is a disadvantage.

SITE  CHARACTERISTICS  AFFECTING
TREATMENT FEASIBILITY

    Generally, the acceptable levels for
treatment of contaminants in soil are 5 to 10
weight percent organics and 5 to 15 weight
percent inorganics. Due to the need to con-
sider several other factors (e.g., soil type) in
determining feasibility, treatability tests are
required.
    The  ISV process can be used to treat
saturated  soils; however, the water must be
evaporated first, requiring additional energy
and further expense. If the soil permeability
is high and the soils are  recharged by an
aquifer, a ground water diversion system
may need to be installed, adding additional
expense.
               Table 1
  Effectiveness of In-Situ Vitrification
  Treatment on General  Contaminant
      Groups for Soil and Sludge
Treatability Groups
Organic* . . •'•••
8
I
Halogenated volatlles
Halogenated semi-volatiles
Non-halogenated volatiles
Non-halogenaled semi-volatiles
PCBs
Pesticides
Dioxins/Furans
Organic cyanides
Organic corrosives
Volatile metals
Non-volatile metals
Asbestos
Radioactive materials
Inorganic corrosives
Inorganic cyanides
Oxidizers
Reducers
Effectiveness
Q
®
Q
Q
®
^^
^>
^>
O
0
^^
^>
•
O
^^
Q
Q
Demonstrated Effectiveness

Potential Effectiveness
                   No Expected Effectiveness  Q

                   Potentially Detrimental    X

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     The presence of significant amounts of buried metals (e.g.,
drums) may cause shorting between electrodes, therefore, the metal
concentration limit is 5 to 16 percent of the melt weight. Addition-
ally, metals cannot occupy more than 90 percent of the continuous
linear distance between electrodes. Table 2 lists those factors that
affect ISV feasibility.
                Gfoairaeteirllofllles &m& Itapsete atoni
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