Good Odor Control Makes Good Neighbors

No, this isn't a flashback to those personal hygiene lectures you had to endure in your high school gym class. We're talking about unpleasant odors several orders of magnitude of raunchiness beyond your worst beat-up sneakers.

Odor control is becoming a bigger issue with wastewater and drinking water treatment plants, certain industrial facilities like paper mills, food processors, landfills and confined animal feeding operations (CAFOs) as they increasingly locate near developed areas. These types of facilities frequently generate strong smells emanating from certain compounds - such as ammonia, hydrogen sulfide (H2S), mercaptans, skatole and amines. Such odors can cause community complaints and create unpleasant working conditions for the facilities' employees. In many communities, wastewater treatment plants and landfills have been rejected because of the citizens' concern about potential odors. These fears are understandable since offensive odors can take their toll on residents in many ways: psychological stress, reduced appetite for food, negative impacts on real property values; and inhibition on capital investment in the impacted neighborhoods.

Just as beauty is said to be in the eye of the beholder, objectionable odors can often be in the nose of the smeller. A person raised as a child on a family-owned cattle ranch or hog farm may be less easily offended by odors wafting from a nearby wastewater treatment plant than a person raised in a sanitized suburb. Current trends show a move from sampling-based regulations to community involvement in determining acceptable standards for controlling offensive odors in populated areas.

To deal with the subjectivity often related to individuals' reactions to strong odors, scientists use a variety of methods to characterize and measure them, such as conducting odor surveys, odor panel testing and using equipment like olfactometers and H2S meters. As pointed out in Metcalf & Eddy's standard industry work, Wastewater Engineering, four independent factors are required for the complete characterization of an odor: intensity, character, hedonics (the odor's relative pleasantness or unpleasantness) and intensity.

Another method of measuring the impact of facilities' odors on nearby neighborhoods can involve the use of air dispersion modeling to track prevailing wind patterns that can carry offensive odors downwind from facilities.

After a facility's odor problems have been analyzed and measured, the next step is to determine the best method for tackling such odors. Odor control technologies can be divided into three main methods. Physical methods include adsorption on to beds of activated carbon or compost, masking agents, containment with covers, dilution with odor-free air, oxygen injection and combustion. Biological technologies consist of trickling filters and special biological towers. Chemical methods include chemical oxidation and chemical scrubbers. The benefits from odor control are improved community relations, public health and employee working conditions.

Biogas systems are an example of a new successful approach to controlling odors at large animal feeding operations, which usually manage manure as liquids and slurries. These systems consist of anaerobic digesters that are covered containers designed to hold decomposing manure under warm, oxygen-free conditions that promote the growth of naturally-occurring bacteria. These bacteria digest the manure, producing methane and an effluent the farmers can use in place of untreated manure. Besides reducing offensive odors, these systems also recover methane gas - a potent greenhouse gas. The recovered methane is then used as an energy source.

This approach is being promoted by The AgSTAR Program, which is a joint effort of the U.S. Environmental Protection Agency, the U.S. Department of Agriculture and the U.S. Department of Energy. For more information about this project, go to

Another recent development in this area is the Water Environment Research Foundation's (WERF) current project that involves the assessment of municipal and industrial odor sources and control technologies from collection systems through final use. In addition to the $200,000 from WERF, the project team, which includes 18 wastewater agencies, is providing an additional $1 million in funding. This two-year study includes an exhaustive global literature search, a project workshop, preparation of an assessment and research agenda, development and implementation of recommended field testing protocols and preparation of the study's final report.

The project will mainly focus on municipal and industrial wastewater treatment odor sources and odor control technologies. This focus encompasses wastewater unit processes at treatment facilities, including basic processes, solids-handling facilities, combustion sources and collection systems. The team will review and assess industrial odor control for possible application at municipal wastewater odor sources. Industrial sources to be surveyed include industrial wastewater treatment facilities, agricultural and animal products industries, chemical manufacturers, refineries and pulp and paper mills. To learn more about this project, check out WERF's Web site at or call 703.684.2470.

In the coming years, as our U.S. population continues to boom, more of these facilities will be right under our noses. Consequently, it's important that they master the basics of olfactory etiquette so they'll be a welcomed part of our neighborhoods.

This article originally appeared in the May 2001 issue of Environmental Protection, Vol. 12, No. 5, p. 6.

This article originally appeared in the 05/01/2001 issue of Environmental Protection.