Odors and Malodors:
Removal, Destruction and Modification
OSCAR BUD LAUREN, Consultant
Photonic Environmental Corporation
Chicago, Illinois 60636
INTRODUCTION
Removal
Hydrogen sulfide is a highly toxic substance and it possesses one of the most powerful
and objectional malodors. A newly developed process for the removal of H,S, mercaptan
and other sulfur bearing pollutants from waste treatment facilities is presented.
Destruction
The destruction of viruses and bacteria associated with causes of malodor is
accomplished with unique and effective applications of advanced germicidal technology.
Modification
State of the Art of Odor Modification explains the complexities of odors and
malodors. Techniques of abatement procedures is outlined.
REMOVAL OF MALODORS
The rapid industrialization of the world has made the removal of hydrogen sulfide —
mostly an unwanted by-product — one of the major pollution problems of industrial
society. At the start of the century hydrogen sulfide emissions were largely confined to
active volcanoes, sulfur spas and occasional rotten eggs. Since then, on one hand, the
quantities of hydrogen sulfide involved have increased to an unprecedented degree, and, on
the other hand, pollution by hydrogen sulfide of air and water is now of great concern and
has led to stringent regulations as to permitted emission levels.
Major sources of hydrogen sulfide emissions currently include: natural gas processing;
petroleum refining, coal in uses such as coking, metallurgical processes which often start
from sulfidic ores; the Kraft paper industry which converts some of its main reactant,
sodium sulfide, into hydrogen sulfide; various chemical processes that form by-product
hydrogen sulfide, such as in the sulfuretting of fats with sulfur or the production of viscose
where carbon disulfide is partly hydrolyzed to hydrogen sulfide and C02; sewage treatment
under anaerobic conditions.
Hydrogen sulfide is a highly toxic substance and it possesses one of the most powerful
and unpleasant malodors. The American Conference of Industrial Hygienistsin 1970 set an
upper limit of 10 ppm in air as the level safe for 8 hours exposure. The level is mainly based
on the onset of eye-irritation (conjunctivitis). The common harm for hydrogen sulfide in the
atmosphere derives from odor pollution. The Arthur D. Little study of Odor Thresholds
gives two values for hydrogen sulfide: 0.00047 and 0.0047 ppm, ascribing the difference of
one order of magnitude to "impurities." Rhodia's own Recognition Threshold of 0.0003
ppm was determined by an expert panel in their odor chambers. The extraordinary
"covering power" of this odorant can be visualized by stating that 1 ton hydrogen sulfide
released into the atmosphere and diluted to 0.001 ppm(l ppb) requires 3 x 10" cubic feet of
air. If it formed a layer lOOfeet high on the ground it would cover about 10,000 square miles.
While a trace of hydrogen sulfide is indispensible for the good aroma of a cup of coffee, one
ton could blanket a state the size of Massachusetts or New Jersey to produce a noticeable
malodor. This hypothetical condition fortunately never occurs, the hydrogen sulfide does
not stop 100 feet above ground level and it does not stay stationary and it gradually gets
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