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Odor testing seems mysterious and odor data mythical to most practitioners in the waste water industry. For years engineers and treatment plant operators have relied on “odor experts” to interpret odor testing results.

“Olfactomatics” is a specialty field of environmental mathematics that contains several unique concepts and laws for the calculations related to olfactometry (odor testing). Misunderstanding these concepts leads to incorrect representation of odor testing data and, worse yet, sometimes leaves important questions left unanswered.

Some most frequently asked questions of odor testing:

What is an “odor unit”?

Where does the result come from?

How accurate is the result?

What is the standard deviation of an odor number?

Are these two numbers statistically different?

Are there testing standards?

Aren't the odor results subjective?

This paper presents the fundamental math concepts of olfactomatics and several calculation methods used to produce usable odor testing data. The “Laws of Olfactomatics” include the concepts of the “power law”, “best estimate threshold”, geometric progression of ascending concentration series, logarithmic transformations, statistical significance of transformed logarithms, dimensionless dilution ratios, pseudo-dimensions, dose-response function (persistency), and inputs/outputs of dispersion models.

Example calculations (practice problems) of odor testing are presented as well as example graphics used to illustrate odor testing results. This paper provides a thorough review of the necessary mathematical concepts that will be needed by the field practitioner, design engineer, treatment plant operator, and facility manager in order to understand and interpret odor data.

Frequently, odor testing is overlooked as a valuable tool for engineering and operations. This paper presents the tools for all practitioners to understand and use odor testing data successfully.

Document Type: Research Article


Publication date: January 1, 2000

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  • Proceedings of the Water Environment Federation is an archive of papers published in the proceedings of the annual Water Environment Federation® Technical Exhibition and Conference (WEFTEC® ) and specialty conferences held since the year 2000. These proceedings are not peer reviewed.

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