Environmental Engineering Reference
In-Depth Information
E. Absorption
Absorption is widely used to remove gas-phase contaminants from indus-
trial waste streams. In such processes, contaminants are brought into contact
with water or chemically reactive liquid, slurry, or solid media. The process
is called scrubbing. Depending on the application, cleaning efficiencies for
target contaminants are on the order of 70 to 99%. The process has been
evaluated for use in controlling HCHO under laboratory conditions.
F. Room temperature catalysts
Low-temperature catalysts were developed by a U.S. company for use in
residential air cleaners. The room temperature catalyst, which included a
mixture of copper and palladium chlorides, was mixed with an equal quan-
tity of activated carbon in a thin-bed filter. Performance studies conducted
in a 1152 ft
3
(32.3 m
3
) room under static conditions indicated that this system
was capable of significantly reducing levels of O
3
, H
2
S, sulfur dioxide (SO
2
),
CO, and ammonia (NH
3
), and relatively ineffective in reducing concentra-
tions of nitric oxide (NO), nitrogen dioxide (NO
2
), and benzene. Its perfor-
mance under real-world conditions has not been reported.
G. Botanical air cleaning
Proposed by a NASA scientist, botanical air cleaning is a relatively novel
approach to removing vapor-phase contaminants from indoor air. Based on
this concept, air would be cleaned by the active uptake and metabolism of
contaminants by plant leaves. In initial static chamber studies, significant
reductions in HCHO and other VOCs were reported. Other studies indicated
this uptake was mostly associated with potting soil. Though uptake of var-
ious VOCs and other gases by plant materials can be shown in chamber
investigations, no studies have been conducted to demonstrate the efficacy
of plant use in indoor environments under real-world conditions. Because
absorption is passive and contaminant generation is dynamic, the use of
plants to control indoor air contaminants effectively is not probable. Never-
theless, it has caught the fancy of many Americans who have attempted to
use plants for air cleaning purposes.
H. Ozonation
Ozone is a powerful oxidizing substance produced by high-voltage systems
incidentally or for special purposes (e.g., water treatment). Ozone generators
are commonly used by contractors as an odor control measure in post-fire
rehabilitation of buildings. In the past two decades, a number of companies
have sold O
3
generators as air cleaning devices to homeowners, schools, and
a variety of building owners. The assumption has been made by manufac-
turers that O
3
generated in a space will react with aldehydes and other VOCs
