Transitions - Sustainable Design: The Science of Sustainability and Green Engineering - page 149

After identifying and characterizing the environmental problems, the next step
is to discover useful options. These options fall generally into three categories:
(1) operational changes, (2) materials changes, and (3) process modifications.
Operational changes might consist simply of better housekeeping: plugging up
leaks, eliminating spills, and so on. A better schedule for cleaning, and segregating
the water might similarly yield a large return on a minor investment. Also, as our
waste audit example demonstrates, less mass translates directly into less risk.
Materials changes often involve the substitution of one chemical for another
which is less toxic or requires less hazardous materials for cleanup. The use of
trivalent chromium (Cr 3 + ) for chrome plating instead of the much more toxic
hexavalent chrome has found favor, as has the use of water-soluble dyes and
paints. In some instances, ultraviolet radiation has been substituted for biocides
in cooling water, resulting in better-quality water and no waste cooling water
disposal problems. In one North Carolina textile plant, biocides have been used
in air washes to control algal growth. Periodic “blowdown” and cleaning fluids
had been discharged to the stream, but this discharge proved toxic to the stream
and the state of North Carolina revoked the plant's discharge permit. The town
would not accept the waste into its sewers, rightly arguing that this might have
serious adverse effects on its biological wastewater treatment operations. The
industry was about to shut down when it decided to try ultraviolet radiation
as a disinfectant in its air wash system. Happily, they found that the ultraviolet
radiation effectively disinfected the cooling water and that the biocide was no
longer needed. This not only eliminated the discharge but eliminated the use
of biocides all together, thus saving the company money. The payback was 1.77
years. 23 That is, in less than two years the conversion paid for itself, so that each
following year the profits were added to the company's bottom line.
Process modifications usually involve the greatest investments and can result in
the most rewards. For example, a countercurrent wash water use instead of a
once-through batch operation can significantly reduce the amount of wash water
needing treatment, but such a change requires pipes, valves, and a new process
protocol. In industries where materials are dipped into solutions, such as in metal
plating, the use of drag-out recovery tanks, an intermediate step, has resulted in
a savings in the plating solution and reduction in the waste generated.
Pollution prevention has the distinct advantage over stack controls that most
of the time a company not only eliminates or greatly reduces the release of haz-
ardous materials but also saves money. Such savings are in several forms, includ-
ing, of course, direct savings in processing costs, as in the ultraviolet disinfection
example above. The most obvious costs are those normally documented in com-
pany records, such as direct labor, raw materials, energy use, capital equipment,
site preparation, tie-ins, employee training, and regulatory recordkeeping (e.g.,
permits). 24 In addition, there are other savings, including those resulting from not
having to spend time on submitting compliance permits and suffering potential