Page 439 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology EN012I-591 July 26, 2001 15:54

Pollution Prevention from Chemical Processes 605

XI. WASTE STREAM AND B. Process Analysis
PROCESS ANALYSES
In the manufacturing facility in Fig. 2 all of the materials
added to or removed from the process are valuable to the
Properly defining and subdividing the problem ultimately
business. Therefore, to help frame the problem for a real
leads to the best pollution prevention solutions. The goal
manufacturing facility, a process analysis should be com-
is to frame the problem such that the pertinent questions
pleted.
arise. When the right questions are asked, the more fea-
For either a new or existing process, the following steps
sible and practical solutions for pollution prevention be-
are taken:
come obvious. Analyzing the manufacturing process in
this manner before and during the brainstorming ses-
1. List all raw materials reacting to saleable products,
sion will often result in an improved process that ap-
any intermediates, and all salable products. This is
proaches an absolute minimum in waste generation and
“list 1.”
emissions.
2. List all other materials in the process, such as
nonsaleable by-products, solvents, water, air,
A. Waste Stream Analysis nitrogen, acids, bases, and so on. This is “list 2.”
3. For each compound in list 2, ask “How can I use a
The best pollution prevention options cannot be imple-
material from List 1 to do the same function of the
mented unless these are identified. To uncover the best
compound in list 2?” or “How can I modify the
options, each waste stream analysis should follow four
process to eliminate the need for the material in
steps:
list 2?”
1. List all components in the waste stream, along 4. For those materials in list 2 that are the result of
with any key parameters. For instance, for a wastewa- producing nonsaleable products (i.e., waste
ter stream these could be water, organic compounds, in- by-products), ask “How can the chemistry or process
be modified to minimize or eliminate the wastes (for
organic compounds (both dissolved and suspended), pH,
example, 100% reaction selectivity to a desired
etc.
product)?”
2. Identify the compounds triggering the concern, for
example, compounds regulated under the Resource Con-
servation and Recovery Act (RCRA), hazardous air pol- Analyzing the process in these ways and then apply-
lutants (HAPs), and carcinogenic compounds. Determine ing fundamental engineering and chemistry practices will
the sources of these compounds within the process. Then often result in a technology plan for driving toward a min-
develop pollution prevention options to minimize or elim- imum waste generation process. Other key ingredients for
inate the generation of these compounds. a successful pollution prevention program are a proven
3. Identify the highest volume materials (often these methodology and the ingenuity of a savvy group of peo-
are diluents, such as water, air, a carrier gas, or a sol- ple to generate the options.
vent) because these materials or diluents often con-
trol the investment and operating costs associated with
end-of-pipe treatment of the waste streams. Deter- XII. WHEN SHOULD ONE DO
mine the sources of these diluents within the process. POLLUTION PREVENTION?
Then develop pollution prevention options to reduce the
volume. The continuum depicted in Fig. 11 shows the relative mer-
4. If the compounds identified in step 2 are success- its of when a pollution prevention program should be im-
fully minimized or eliminated, identify the next set of plemented. The decision of how far to move toward the
compounds that has a large impact on investment and op- lowest waste and emissions design will depend on a num-
erating cost (or both) in end-of-pipe treatment. For ex- ber of factors including corporate and business environ-
ample, if the aqueous waste stream was originally a haz- mental goals, regulatory pressures, economics, the ma-
ardous waste and was incinerated, eliminating the haz- turity of the process, and product life. It is safe to say,
ardous compound(s) may permit the stream to be sent to “the earlier, the better.” If one can make changes during
the wastewater treatment facility. However, this may over- the R&D stage of the process or product life cycle, then
load the biochemical oxygen demand (BOD) capacity of one has the best opportunity to make significant reduc-
the existing wastewater treatment facility. If so, it may be tions in waste generation at the source. However, as one
necessary to identify options to reduce organic load in the moves down the continuum from R&D through process
aqueous waste stream. design and engineering and post-startup operation, one’s