Odor control

Refuse-handlers and many industries release unpleasant odors into the air which can travel for miles. Odors inside factories can also make it difficult for people to work, and pollutants can impart a strong odor to water.

Odors can be released from chemicals , chemical reactions, fires, or rotting material. The air carries odor-producing gas molecules, and they are detected by breathing or sniffing. The molecules stimulate receptor cells in the nose, which in turn send nerve impulses to the brain where they are processed into information about the odor.

Research is being performed to quantify and characterize odors. Tests such as sniff chromatography , emission rate measurement, and hedonics are being used in an effort to develop a better definition of what offensive odors are.

Scientists have found that the perception of odors is highly subjective. What one person might not like, another person might not be able to smell at all, and what people define as an offensive odor depends on age and sex, as well as other characteristics.

One method of controlling unpleasant smells is deodorizers. Deodorizers either disguise offensive odors with an agreeable smell or destroy them. Some deodorizers do this by chemically changing odor-producing particles while others merely remove them from the air. Disinfectants, such as formaldehyde, can kill bacteria, fungi or molds that create odors. Odors can also be removed through ventilation systems. The air can be "scrubbed" by forcing it through liquid or through filters containing such materials as charcoal, methods which trap and remove odor-producing particles from the air. Factories can also employ a process known as "re-odorization," which works on the principle that there are seven basic odor types: camphoraceous, mint, floral, musky, ethereal, putrid, and pungent. The process is based on the theory that different combinations of these odor types produce different smells, and re-odorization releases chemicals into the air to combine with the regular factory odors and generate a more pleasant smell.

Aeration is one method of removing objectionable odors from water. The surface of the water is mixed with air and the oxygen oxidizes various materials that would otherwise turn the water foul. Aeration can be accomplished by running the water over steps or spraying the water through nozzles. Trickling the water over trays of coke also helps eliminate offensive odors, and adding activated charcoal can have the same effect.

Even though science has shown that the perception of odors is subjective, many people are offended by them. It is often considered a quality-of-life issue, and politicians have been strongly influenced by their constituencies. Nuisance regulations have been passed in many states and municipalities, and though they often vary, their attempts to distinguish between acceptable and unacceptable odors are often vague and difficult to apply. Proving that odors interfere with the quality of life is not only subjective but nearly impossible. Refuse-handlers and factories are perhaps the most adversely affected; they often receive heavy fines for odors, although there is no proven method for eliminating them. Many believe a more concrete system of regulations is needed, but science has not been able to provide the basis on which to build one.

See also Noise pollution; Pollution control

[Nikola Vrtis ]

RESOURCES

BOOKS

Bowker, P. G. Odor and Corrosion Control in Sanitary Sewerage Systems and Treatment Plants. New York: Hemisphere, 1989.

Hesketh, H. E. Odor Control Including Hazardous-Toxic Odors. Lancaster, PA: Technomic, 1988.

Kreis, R. D. Control of Animal Production Odors: The State-of-the-Art. Ada, OK: U.S. Environmental Protection Agency, 1978.

PERIODICALS

Hunt, P., and K. Hauck. "Raising a Stink Over Composting Odors." American City and County 105 (December 1990): 64–65.