HAZARDOUS WASTE MANAGEMENT 453
ton or greater fee, may make processing for recycling and/or
reuse the best practice. In the present context, we are defining
recycling as internal to the plant, and reuse as external to the
plant. This is not a legal definition which defines recycling as
essentially both internal and external, but it is helpful in this
discussion.
Internal recycling will require, in general, high efficiency
separation and potential additional processing. Thus, if a sol-
vent is being recycled, impurities such as water, by-products,
and other contaminants must be removed. Depending on the
volumes involved, this may be done internally to the process
or externally on a batch basis.
Reuse involves “selling” the waste to a recycle and
reclaimer. The reclaimer then treats the waste streams and
recovers value from them. The cleaned-up streams are then
his products for sale.
From a regulatory, liability perspective, there are advan-
tages to reuse as the liability for the waste ends when it is
successfully delivered to the reclaimer. Because he pro-
cesses the material, he then assumes responsibility for the
products and wastes that are generated. If the material is
internally recycled, then the recycler, that is the plant, main-
tains responsibility for any wastes that are generated as a
result of the recycling operation.
In some cases, it may be desirable to dispose of wastes
directly to the user. This is particularly true when there are
large quantities involved and a beneficial arrangement can be
worked out directly. Waste exchanges have been organized
to promote this type of industrial activity. Detailed discus-
sions of their mode of operation can be obtained directly
from the exchanges.Waste Minimization The alternative scenario develop-
ment will be not only site, but substance specific. Two basic
approaches to hazardous waste management are:1) In-process modifications
2) End-of-pipe modificationsEach will have advantages and disadvantages that are pro-
cesses, substance, and site specific.
In-process alternatives include changing process con-
ditions, changing feedstocks, modifying the process form
in some cases, or if necessary eliminating that process and
product line.
In-process modification is generally expensive and must
be considered on a case-by-case basis. There are some poten-
tial process modifications that should be considered to mini-
mize the production of toxic materials as by-products. These
include minimization of recycling so side-reaction products
do not build up and become significant contributors to the
pollution load of a bleed stream. For example, waste must
be purged regularly in the chlorination of phenols to avoid
the build-up of dioxin. It may also be desirable to optimize
the pressure of by-products. For example, phenol is produced
and found in condensate water when steam-cracking naphtha
to produce ethylene unless pressures and temperatures are
kept relatively low.It may be desirable to change feedstocks in order to elim-
inate the production of hazardous by-products. For example,
cracking ethane instead of naphtha will yield a relatively
pure product stream.
Hydrazine, a high energy fuel, was originally produced
in a process where dimethylnitrosamine was an intermediate.
A very small portion of that nitrosamine ended up in a waste
stream from an aqueous/hydrocarbon separation. This waste
stream proved to be difficult, if not impossible, to dispose of.
A new direct process not involving the intermediate has been
substituted with the results that there are no noxious wastes
or by-products.
In the ultimate situation, production of a product may
be abandoned because either the product or a resulting
by-product poses an economic hazard which the corpo-
ration is not willing to underwrite. These include cases
where extensive testing to meet TSCA (Toxic Substances
Control Act) was required. They include the withdrawal of
pre-manufacturing notice applications for some phthalate
ester processes. However, production of certain herbicides
and pesticides was discontinued because a by-product or
contaminant was dioxin.Treatment/Destruction TechnologyChemical Treatment/Detoxification Where hazardous mate-
rials can be detoxified by chemical reaction, there the mol-
ecule will be altered from one that is hazardous to one or
more that are non-hazardous, or at least significantly less
hazardous. For example, chlorinated hydrocarbons can be
hydro-dechlorinated. The resulting products are either HCl
or chlorine gas and nonchlorinated hydrocarbons. A number
of these processes are being developed for the detoxification
of PCB (polychlorinated biphenols) and are being demon-
strated as low concentrations of PCB’s in mineral oil. The
end products, if concentrated enough, can be useful as feed-
stocks or the hydrocarbons may be used as fuel.
Cyanide can be detoxified using any number of chemi-
cal reactions. These include a reaction with chlorine gas to
produce carbonate and chlorine salt. Cyanide can also be
converted to cyanate using chlorine gas. In addition, ozone
can be utilized to break up the carbon-nitrogen bond and
produce CO 2 and nitrogen.
Hexavalent chromium is a toxic material. It can be
reduced to trivalent chromium which is considerably less
hazardous and can be precipitated in a stable form for reuse
or disposal as a non-hazardous material. Chromium reduc-
tion can be carried out in the presence of sulfur dioxide to
produce chromium sulfate and water. Similar chemistry is
utilized to remove mercury from caustic chlorine electroly-
sis cell effluent, utilizing sodium borohydride.
Lead, in its soluble form, is also a particularly difficult
material. Lead can be stabilized to a high insoluble form
using sulfur compounds or sulfate compounds, thus remov-
ing the hazardous material from the waste stream.
Acids and bases can most readily be converted to non-
hazardous materials by neutralizing them with appropriateC008_001_r03.indd 453C008_001_r03.indd 453 11/18/2005 10:28:44 AM11/18/2005 10:28:44 AM