Controlling odorous emissions has always been
difficult for sewage treatment facilities, particularly for those near
residential areas. But as nearby populations increase and pump
stations transfer more wastewater solids to the plants, odor control
is becoming a bigger challenge. Treatment facilities traditionally
have used activated carbon adsorbers to clean the air. Now, a new type
of activated carbon, catalytic/adsorptive carbon, controls odors
better and costs less.
The principle sources of odor in wastewater operations are septic
wastewater containing hydrogen sulfide (H2S) and other
odorous compounds in the plant's pipelines; industrial wastes
discharged to the sewage collection system; unwashed grit; scum on
primary settling tanks; organically overloaded biological treatment
processes; solids thickening tanks; waste-gas burning operations in
which lower than optimum temperatures are used; chemical mixing
operations; solids incinerators; and digested solids in drying beds or
solids holding basins.
Odors from these sources vary in degree and intensity depending on the
amount of anaerobic decomposition present. Hydrogen sulfide, the most
prevalent source of all odors, often is accompanied by mercaptans,
indole, skatole, amines, fatty acids and other volatile organic
compounds (VOCs). Odor-control systems typically focus on
H2S because of its low odor threshold (0.47 ppb),
predominance as an odorous agent, and ease of analytical
detection.
Authors: Gary Van Stone and Daniel Brooks,
Calgon Carbon Corporation, Pittsburgh, Pennsylvania,
USA.
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