Odorant prioritization of the odor nuisances from wastewater treatment plants needs to be targeted for removal from the minor contributors. The Concentration/Odor Threshold Concentration (C/OTC) ratio is known as the odor activity value. Higher C/OTC ratios indicate the odorants that are likely to pose the biggest odor nuisance at a given location. The OTC of nine odorants at two Wastewater Treatment Plants were determined based on the Odor Profile Method (OPM) and dilution method of dynamic olfactometry. Hydrogen sulfide (H<sub>2</sub>S), Methyl mercaptan (MM), Dimethyl sulfide (DMS), Dimethyl disulfide (DMDS), 2-Methylisoborneol (MIB), 2-Isopropyl-3-methoxypyrazine (IPMP), Indole, Skatole and Ammonia were studied. The OTC of IPMP - musty odor (0.02 ng/L in air), MM - rotten vegetable odor (0.2 ng/L in air), MIB - musty odor (0.1 ng/L in air), and skatole –fecal odor (0.3 ng/L in air) are quite low. The OTCs measured in this study were within the range in the literature. The results were comparable with the odor threshold concentration measured by the ASTM 679-04 method. High C/OTC ratios may not elicit the anticipated results from the OPM measurement of intensities of different odors, when the air samples contain mixtures of odorous compounds. The odors from multiple odorants may mask, blend or produce an integrated odor. After the primary odor is removed by dilution, other odors become apparent and subsequently need to be controlled. This is called the “Peeling of the Onion Effect” . Samples were studies at different locations at two wastewater treatment plants and upon dilution of the original odor, the fecal and rotten vegetable odors that were initially prominent decreased upon dilution. At the greatest dilutions, musty odors appeared and the fecal and rotten vegetable odors became undetectable (Peeling the Onion Effect). The OPM is able to determine the change of major odors during dilution and shows how the “Peeling of the Onion Effect” occurs with dilution. Thus, the OPM with dilution can correctly evaluate odor nuisances that neighbors to the wastewater treatment plant can observe upon dilution. Models of dilution of odors should be evaluated by this method. While the intensities of musty odors were not strong on-site within the wastewater treatment plant, the reason the musty odors could be observed as an off-site nuisance is by the “Peeling the Onion Effect." Modeling and treatment technology to control odors must consider this masking effect.

Determination of the primary odor nuisances from wastewater treatment plants

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.