HAZARDOUS WASTE MANAGEMENT 455
Wet Air Oxidation Although not strictly incineration, wet
air oxidation is a related oxidation process. Usually air, and
sometimes oxygen, is introduced into a reactor where haz-
ardous material, or industrial waste, is slurried in water at
250° to 750°F.
Operating pressures are as high as 300 psig. Plants have
been built to treat wastes from the manufacture of polysulfite
rubber and other potentially hazardous materials. Emissions
are similar to those obtained in incineration, with the excep-
tion that there is liquid and gaseous separation. Careful eval-
uation of operating conditions and materials of destruction
are required.Pyrolysis Pyrolysis transforms hazardous organic materi-
als by thermal degradation or cracking, in the absence of an
oxidant, into gaseous components, liquid, and a solid resi-
due. It typically occurs under pressure and a temperature
above 800°F.
To date, the process has found limited commercial applica-
tion but continues to be one that will eventually be economically
attractive, the prime reason being the potential for recovery of
valuable starting materials. A great deal of experimentation has
been carried out both on municipal and industrial wastes. For
example, polyvinyl chloride can be thermally degraded to pro-
duce HCl and a variety of hydrocarbon monomers, including
ethylene, butylene, and propylene. This is a two-stage degrada-
tion process with the HCl coming off at relatively low tempera-
tures (400°C) and the hydrocarbon polymer chain breakdown
can be obtained with Polystyrene, with styrene as the main
product, and most other polymers. Experimental work carried
out in the early 1970s by the US Bureau of Mines, indicates
that steel-belted radial tires can be pyrolyzed to reclaim the
monomers, as well as gas and fuel oil.
Other target contaminant groups include SVOCs and
pesticides. The process is applicable for the treatment of
refinery, coal tar, and wood treating wastes and some soils
containing hydrocarbons.Disposal TechnologyLand Storage and Disposal Disposal of hazardous mate-
rials to the land remains the most common practice. It
is highly regulated and a practice which has been limited
because of public pressure and federal rules which require
the demonstration of alternate means of disposal. The design
of secure landfills for the acceptance of hazardous materials
must be such that ground waters, as well as local populations
are protected. The US Environmental Protection Agency has
implemented strict landfills. In practice all landfills accept-
ing hazardous wastes must insure that the wastes stored in
close proximity are compatible so that no violent reactions
occur should one or more waste leak.
Federal and State regulations prohibit the disposal of
liquids in landfills. Of equal importance to the disposal of
hazardous wastes, whether solid or semi-solid, is the assur-
ance that material will not leach away from the landfill or
impoundment. This assurance is provided by the use of“double-liners” with a leak detection system between the
liners, a leachate collection system for each cell, and a leach-
ate treatment system designed and operated for the facility.
In dilute form liquid wastes can be “landfarmed” where
microbial action will decompose the compounds over time.
This methodology has been utilized over many years for
hydrocarbons and has worked well. For highly toxic com-
pounds, such as chlorinated organics, it is less attractive even
though decomposition does occur. Land treatment of PCB
contaminated soils has been tested with some success.Stabilization The stabilization of hazardous materials prior
to land disposal is frequently practiced. Generally, the stabi-
lization is in the form of fixing the hazardous material with
a pozzolanic material, such as fly ash and lime, to produce a
solid, non-leachable product which is then placed in land dis-
posal facilities. Typically, this methodology is applicable to
inorganic materials. Most of the commercial processes claim
that they can handle materials with some organic matter.
Polymer and micro-encapsulation has also been uti-
lized but to a significantly lesser extent than the commer-
cially available process which utilize pozzolanic reactions.
Polymers which have been utilized include polyethylene,
polyvinylchloride and polyesters.
Grube^9 describes a study of effectiveness of a waste
solidification/stabilization process used in a field-scale
demonstration which includes collecting samples of treated
waste materials and performing laboratory tests. Data from
all extraction and leaching tests showed negligible release
of contaminants. Physical stability of the solidified material
was excellent.Remediation TechnologiesNatural Attenuation and Bioaugmentation The concept of
natural attenuation, or intrinsic bioremediation, has gained
a greater acceptance by the regulatory community as data
presented by the scientific community have demonstrated
the results of natural attenuation, and the costs and time
frames associated with traditional remedial methods.^1 This
approach is most appropriate for the dissolved phase ground-
water contamination plume. It is still necessary to remove or
remediate the source zone of an affected aquifer, after which
natural attenuation may be a reasonable approach to the dis-
solved phases.
Natural attenuation should not be considered “No
Action.” It requires a solid understanding of the contami-
nant, geologic and aquifer characteristics, and a defined plan
of action. The action involves demonstrating that the con-
taminants will breakdown, will not migrate beyond a speci-
fied perimeter, and will not impact potential receptors. It
may involve the stimulation of microorganisms with nutrients
or other chemicals that will enable or enhance their ability to1 Example of traditional remediation methods are ex-situ treatment of soil
and groundwater, such as soil excavation/disposal, groundwater pump-
and-treat using air stripping and granulated carbon polishing.C008_001_r03.indd 455C008_001_r03.indd 455 11/18/2005 10:28:44 AM11/18/2005 10:28:44 AM