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Encyclopedia of Physical Science and Technology EN012I-591 July 26, 2001 15:54
596 Pollution Prevention from Chemical Processes
or products could serve the same function and (2) adding
large volumes of nitrogen gas because of the use of air as
an oxygen source, heat sink, diluent, or conveying gas.
3. Segregate and reuse. Avoid combining waste
streams together without giving consideration to the im-
pact on toxicity or the cost of treatment. For example, it
may make sense to segregate a low-volume, high-toxicity
wastewaterstreamfromseveralhigh-volume,low-toxicity
wastewater streams. Examine each waste stream at the
source and determine which ones are candidates for reuse
in the process or can be transformed or reclassified as a
valuable coproduct.
4. Recycle. A large number of manufacturing facilities,
especially chemical plants, have internal recycle streams
FIGURE 4 Context of pollution prevention within all possible pro- that are considered part of the process. In this case, re-
cess changes. cycle refers to the external recycle of materials, such as
polyester film and bottles, Tyvek envelopes, paper, and
spent solvents.
defines the hierarchy shown in Fig. 5 as environment man-
5. Recover energy value in waste. This step is a last
agement options. Industry defines as pollution prevention
step to attain any value from the waste. Examples include
the upper five levels, from minimize generation to recover
burning spent organic liquids, gaseous streams containing
energy value in waste. The European Community, on the
volatile organic compounds, and hydrogen gas for the fuel
other hand, includes the entire hierarchy (levels 1–7) in its
value. The reality is that often the value of energy and re-
definition of pollution prevention, as is done in this article.
sources required to make the original compounds is much
Adefinition of each tier in the pollution prevention hi-
greater than that which can be recovered by burning the
erarchy is given below:
waste streams for the fuel value.
6. Treat for discharge. This involves lowering the toxi-
1. Minimize generation. Reduce to a minimum the
city, turbidity, global warming potential, pathogen con-
formation of nonsaleable by-products in chemical reac-
tent, etc., of the waste stream before discharging it to
tion steps and waste constituents, such as tars, fines, etc.,
the environment. Examples include biological wastewa-
in all chemical and physical separation steps.
ter treatment, carbon adsorption, filtration, and chemical
2. Minimize introduction. Minimize the addition of
oxidation.
materials to the process that pass through the system unre-
7. Safe disposal. Waste streams are rendered com-
acted or that are transformed to make waste. This implies
pletely harmless or safe so that they do not adversely
minimizing the introduction of materials that are not es-
impact the environment. In this article, we define this as
sential ingredients in making the final product. Examples
total conversion of waste constituents to carbon dioxide,
of introducing nonessential ingredients include (1) using
water, and nontoxic minerals. An example is subsequent
waterasasolventwhenoneofthereactants,intermediates,
treatment of a wastewater treatment plant effluent in a pri-
vate wetlands. So-called “secure landfills” would not fall
within this category unless the waste is totally encapsu-
lated in granite.
In this article, we will focus on the upper three tiers of the
pollution prevention hierarchy; that is, minimize genera-
tion, minimize introduction, and segregate and reuse. This
is where the real opportunity exists for reducing waste and
emissions while also improving the business bottom line.
V. DRIVERS FOR POLLUTION PREVENTION
Since the early 1960s, the number of federal environmen-
FIGURE 5 Pollution prevention hierarchy. tal laws and regulations has been increasing at a rate three