Proximity to sewage and wastewater plants is often signaled by nuisance odors, the control of which is likened to peeling an onion: upon peeling and removing one layer, a second and then a third emerge with their own odoriferous presence.

A technique for identifying various odors, which run the gamut of burnt matches, rotten eggs, and fecal matter at these facilities, has been developed and tested by researchers from CH2M and University of California (Los Angeles).

An example of a wastewater odor wheel. (I.H. (Mel) Suffet et al.)

Field research is conducted with an “odor wheel” displaying public-friendly general descriptions of a range of smells on the outside and the chemical composition of the smelly agents on the inside. The team uses this wheel to ask the public about a bothersome stench, and captures and measure odors using plastic bags, metal containers, sorbent tubes, hand-held devices, and electronic noses. Both sensitive detection devices and human panels are enlisted in analyzing samples. A mass spectrometer helps identify the compounds that make up an offensive scent, while human odor panels determine how strong and offensive the smell is to people, based on their experience.

Once identified, the chemical and its aroma can be eliminated with scrubbers, biofilters or the introduction of masking chemicals.

Over the years, the most common stink — the odor of rotten eggs from hydrogen sulfide — has been mostly eliminated with chemical and biological odor control equipment. However, there are other culprits of concern, such as the odor of rotten vegetables derived from methyl mercaptan and dimethyl disulfide; the fecal odor of skatole and indole; and the pungent smell of ammonia.

Controlling these chemicals at their source is the cheapest remedy but that is not always possible. For instance, an odor from a chemical emitted by an industrial facility was not apparent until the compound reached a Philadelphia sewage treatment plant. The strong odor of dimethyl sulfide was only released when the chemical was exposed to oxygen and bacteria in the sewage treatment facility’s aeration tank.

The researchers are working to refine and standardize the technology to measure and control odors. Most of the samples must be brought to UCLA for analysis, but the technique is being expanded to other laboratories and is spreading throughout the industry as a viable alternative to traditional methods.

This research will be presented at the 253rd National Meeting & Exposition of the American Chemical Society in San Francisco, CA, held April 2-5, 2017.