Organoleptic Characterization and Concentration Profiles of Odorous Compounds in Raw Influent versus Secondary-Treated Municipal Wastewater | Aug-2026
Municipal wastewater contains a complex mixture of volatile and semi-volatile odorous compounds spanning reduced sulfur species, nitrogen-containing heterocycles and amines, halogenated solvents, monoaromatic hydrocarbons, and volatile fatty acids. This paper synthesizes quantitative concentration data for 19 key odorants in raw influent and secondary-treated effluent of municipal wastewater treatment plants (WWTPs) with organoleptic impact profiles generated by the MAMAY Organoleptic Digitizer 1.0. Concentration data are drawn primarily from Hwang et al. (1995) together with literature-derived removal efficiencies for compounds lacking paired secondary-effluent measurements; sensory impact is quantified in the proprietary unit val®. Total odor impact declined from 2271 val® in the raw influent to 976 val® in the secondary-treated effluent (≈57 % reduction). Reduced-sulfur compounds (hydrogen sulfide, methanethiol, dimethyl sulfide, dimethyl disulfide) were substantially attenuated, shifting the dominant sensory notes from “rotten eggs / sulfurous / vegetable” toward “fishy / chloroform / animalic / sweet.” Nitrogenous odorants, particularly indole, skatole and the low-molecular-weight amines, together with residual chloroform and monoaromatics, exhibited far lower removal and continued to dominate residual odor. These findings reconfirm that secondary biological treatment preferentially removes reduced-sulfur species while leaving a persistent mixed nitrogenous / halogenated / aromatic odor signature, with implications for effluent reuse, odor-control process selection, and the design of tertiary polishing steps.
Dr. Michael Zviely | MAMAY
Keywords: wastewater odor; hydrogen sulfide; methanethiol; indole; skatole; trimethylamine; chloroform; BTEX; volatile fatty acids; organoleptic digitizer; secondary treatment; val®
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