What is In Situ Vitrification?
In Situ Vitrification is a new technology developed for a
new nastier breed of contaminants and pollutants. "In
Situ" means to work in place.
"Vitrification" is the process to make glass out of
something. The relevant meaning of "In Situ
Vitrification" in respect to soil and groundwater pollution
is to turn the soil containing the pollutant into a large block
of glass. The pollutant can then be left in place forever
encased inside of the glass. A normal site undergoing in
Situ Vitrification looks like the following.
Diagram
drawn by Edward Behm.
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The Process of In Situ
Vitrification.
The first part of the procedure for using In Situ Vitrification
is determining the type of pollutants in the ground. After
the determination of what type of pollutant is involved the
decision to use in situ vitrification can be made. In Situ
Vitrification utilizes 4 large graphite electrodes that are
inserted into the ground in a square pattern. The
Vitrification depth is limited by the length of the graphite
electrodes and the availability of power. As the electrodes
are driven into the ground, powerful generators or a direct line
to a city power grid are activated. The electricity arcs
from one electrode to another. As the electricity passes
through the soil great heat is produced. This heat reduces
the soil into a molten form. As the ground liquefies the
electrodes move deeper, increasing the amount of molten
soil. When the graphite electrodes have reached the maximum
possible depth the electricity is shut off and the electrodes are
disconnected from the system. As the molten soil solidifies
into glass the graphite electrodes become entombed. The
temperatures achieved by In Situ Vitrification have reached
temperatures ranging from 1,600 to 1,800 degrees Celcius.
Individual blocks of glass have been formed as large as 1,400
tons and depths exceeding 20-ft have been achieved. Adjacent
processes can fuse the vitrified blocks together to form a single
contiguous monolith.
The pollutants react in various ways to this remediation
technique. Organic pollutants are pyrolyzed and are
generally reduced into gasses. The gasses rise to the
surface where they are collected by a gas hood over the affected
site. The gases are then transported to an off-gas
treatment center. This is a treatment system for the
rendering volatile or dangerous gasses from the vitrification
process inert. The inorganic pollutants or heavy metals are
encased in the glass formed by the vitrification process.
Radioactive materials are also encased in the glass and the glass
formed by the soil also helps to limit the radiation
leakage. During the molten phase of the process
almost all of the void spaces in the soil are removed and
therefore there is a volume reduction of 20-50%. This
results in a very dense block of glass.
drawn
by Edward Behm
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The Advantages of In Situ
Vitrification.
There are many advantages to In Situ Vitrification over other
conventional remediation techniques.
Value of In Situ
Vitrification to Soil and Groundwater Remediation.
The Insitu vtrification process can have several advantages over
other remediation processes or the removing of the pollutant in
question. Below is a list of these advantages:
Send comments or suggestions to:
Student Authors:
Matthew Gross (mgross@vt.edu)
Editor in charge of HTML format and Text Editor
Edward Behm (ebehm@vt.edu)
Graphics Artist
Dan Quesenberry (dquesenb@vt.edu) Text
Editor
Dan Vipperman (dvipperm@vt.edu) Text Editor
Faculty Advisor: Dr. Persuad (npers@vt.edu)
Copyright © 1998 Daniel Gallagher (dang@vt.edu)
Last Modified: June 7, 1998
