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.
