Odor Testing Meets Molecular Odor Analysis

Odor detection threshold determination following international standards, ASTM E679 and EN13725, is the primary odor parameter of choice used in odor assessments worldwide. While this is a tool that, when coupled with air dispersion modeling, provides an understanding of the first layer of odor impact in the community and is commonly used for odor regulation around the world, the assessment of odor threshold is only one parameter of odor. Odor intensity and characterization (odor profiling) provide more important information related to true receptor impact from the perspective of when these odors will be a nuisance. Odor profiling, through descriptive analysis, is a sensory science term used to describe methodologies utilizing a panel of trained assessors to identify and describe specific sensory attributes about a test sample (qualitative) and scaling the intensity of these attributes (quantitative). The food, beverage, and consumer product industries have formally use descriptive analysis to obtain critical information about the appearance, aroma, flavor, and texture of products for over 70 years. These methods can be used to document odor profiles of samples collected from facility odor sources. As described by other researchers, further considering odor descriptors with dilution methods will help to understand how the odor profile may change from the point of emission from the stack to point of impact at the stakeholder as it dilutes in the air. The odor profiles of odorous sources are the perceived response of a complex mixture of chemicals in the air. While hydrogen sulfide is targeted (as the Celebrity) in work at water resource recovery facilities, there are many other compounds present from multiple chemical families, e.g., organic sulfur compounds, organic acids, amines, VOCs. Many of these compounds (the entourage of the Celebrity) have extremely low odor thresholds below the low ppb levels of hydrogen sulfide. State-of-the-art molecular odor analysis by SIFT-MS provides quantification at these sub-ppb concentration levels utilizing the same samples submitted for odor perception evaluation. This combined analysis including odor threshold, odor intensity, odor descriptors, and molecular analysis on the same sample provide access to direct relationships not available before for a broad range of wastewater issues and studies. This paper will present examples comparing the full odor profiles from multiple emissions sources. Inlet and outlet sample comparisons show one case where odor descriptor profiles are similar even with reduction in odor threshold and molecular concentration values and in another case, odor descriptors shift significantly with lower reduction in odor threshold values. A review of odor characters and molecular concentrations of other samples show how data relationships provide a deeper understanding of the odor sources and thus provide direction for improving in odor impacts in the community.