A new method for evaluating nuisance of odorants by chemical and sensory analyses and the assessing of masked odors by olfactometry

The odor threshold concentration and the odor nuisance concentration of the nine persistent odorants at two wastewater treatment facilities were determined by Weber- Fechner curves for each odorant using dynamic olfactometry combined with the odor profile method. The odor threshold concentration results, representing each odorant's concentration at odor intensity of one (I = 1), were within range in the literature. The nuisance concentrations were determined by interpolation along the curves intersecting with the arbitrary odor intensity of three (I = 3). There is no reference that exists in the literature about determining odor nuisance concentrations for a complete set of odorants from any facility. The nuisance concentration results presented here are novel to odor control because they can provide information defining the nuisance odorant's isopleths in modeling and in designing effective odor control systems that avoid public nuisance. Dynamic olfactometry combined with the odor profile method was also used with actual foul air samples from different sources. When analyzed from raw to increased dilution, it was observed that the fecal and sulfur odors initially prominent (with no musty odors detected) gradually changed with increased dilution. Musty odors began to gradually appear while the fecal and sulfur odors became undetectable. We named this observation the "peeling of an onion effect". It is speculated that this occurs because the musty odors in the concentrated foul air sample are masked by the fecal and the sulfur odors.