One morning this past June, I was relaxing on my patio, when
I observed a robin hovering momentarily above the grass in my backyard. Its
fluttering wings were forcing the air beneath to wave the lush green grass. The
air in motion (the simplest definition of "wind") generated by the
robin was in the range of what meteorologists call the "microscale."

The air movement (or lack of it) on this scale is critical
to the dispersal of obnoxious odors. Of course, water treatment plant owners
and operators don't depend on avian aerobics to disperse their objectionable
fumes, but air-in-motion in the smallest, middle ("mesoscale"), or
even the largest ("macroscale") range can send malodor molecules to
undesirable destinations.

The effort of birds notwithstanding, the wind typically
originates from the fact that "warm air rises." This fundamental
principle of meteorology begins to explain most atmospheric circulations from
turbulence to the jet streams. But, regardless of whether the wind is thermally
or mechanically produced, once generated, its path is diverted by a wide variety
of obstructions.

The path air takes across a landscape is similar to the path
water takes across terrain. Water will flow into and along gullies and move in
sheets across impervious open fields. So too the wind. Air will generally
follow the twists and turns of the land, especially when speeds are slow. And,
air will flow rather straight-forwardly across flat, open fields.

If obstructions exist, the air can take some tortuous paths.

For example, if buildings are present, the air will go
around the walls and over the roof. A cavity can form in the lee of the
building. Such cavities can produce high concentrations of fumes as the air
becomes trapped and stagnant.

Malodor malady and tips for its cure

So what does this all mean to the water-treatment plant
owner and operator? Sometimes wind and water can be a bad combination. Plant
operators know that under certain weather conditions their plant can become an
unwelcome neighbor. If winds carry malodors from the operation to nearby
residents, neighbors may perceive more than foul odors.

They could perceive their property values dropping. And
more, local residents are likely to equate odorous emissions with chemicals
harmful to their health. These
perceptions could spell a community relations, legal, and regulatory compliance
nightmare for the plant.

Odor-minimization practices can reduce your facility's
chance of emitting offensive odors beyond its borders. These practices include:

* Material
Substitution/Reformulation--replace odorous chemicals with less odorous ones;

* Good
Housekeeping--train employees in beneficial operating practices like spill and
leak prevention, proper material handling, and preventive maintenance; and

* Equipment
Redesign--replace or renovate old, inefficient equipment that lets malodors
escape.

To reduce the likelihood of malodors impacting employees and
surrounding neighborhoods, if possible, locate your odoriferous sources:

* Away from building air intakes;

* At or near the center of your property; and

* At a stack/vent release height sufficient to disperse
emissions above building aerodynamic cavities and wakes. This height is roughly
two times the lesser of the height or crosswind width of the largest nearby
building.

If odor controls are needed, a variety of methods can be
applied, such as:

* Thermal oxidation;

* Absorption;

* Adsorption;

* Condensation; and

* Biofiltration.

Chemical characteristics and concentration of the offensive
molecules and budgetary and engineering constraints will help guide the decision
on which method will meet your malodor challenge.

More quickly than a bird in flight, the winds can carry
offensive odors from your water-treatment plant to your neighbors, fowling
(oops. . .fouling) your good-neighbor image. But, by implementing odor-minimization
techniques, careful siting and construction of potential odor-producing
sources, and the use, when necessary, of odor controls, your plant can
successfully minimize malodors and keep its good-neighbor status.