By Peter Chawaga, Associate Editor, Water Online
Last month, residents of San Francisco were accosted by a smell that is all too familiar to certain wastewater treatment plants. The scent of rotten eggs wafted through the air.
“It sounds like a setup for a joke, but apparently more than 50 people on Wednesday really did report a mysterious and overpowering odor of rotten eggs across the city,” Curbed San Francisco reported.
Of course, the stench was not actually caused by rotten eggs, but rather an influx of sulfur.
“Sulfur’s in some of the most gut-wrenching stenches in the book,” according to a Forbes report on the outbreak. “Hydrogen sulfide, a compound of one sulfur atom and two hydrogen atoms (H2S), is the culprit when something reeks of ‘rotten egg’ … It doesn’t take many of these molecules to raise a stink.”
While there is still some mystery surrounding the unpleasant fumes in San Francisco, oftentimes these outbreaks can be traced back to aeration issues at wastewater treatment plants.
“What about the waste locations, like wastewater treatment plants, landfills, and composting facilities?” Forbes speculated. “With proper aeration, sulfur in waste can convert to compounds called sulfates. Sulfates don’t have the pungent aroma of rotten eggs or fetid feet. Without proper aeration, however, foul odors can crop up.”
Wastewater treatment operations face this problem in a range of severity and there are a few tactics for remediation, as Joel Bleth of Medora Corporation explained:
All organic material contains sulfur, a chemical element that is necessary to sustain life. Sulfur in the aerobic digestion process is converted to odorless sulfate in the presence of oxygen. Sulfur in anaerobic digestion becomes sulfide and exists in several forms, from hydrogen sulfide to mercaptins, or thiols. The odors associated with sulfides are equally as diverse, ranging from the smell of garlic to rotten eggs and worse. Wastewater treatment plant operators may rate the odors coming from their plants from mild to offensive, depending on the number of complaints received from nearby residents. Operators have several options for trying to deal with pond odors, from increasing the aeration to applying chemical to the water or perfume to the air.
If wastewater operations do need to improve their aeration to keep foul smells from bothering neighbors, it is important that they do their homework.
“As the main consumer of electricity in a wastewater treatment plant, the aeration system greatly influences the overall cost of operation, that in the longer-term by far exceed the initial investment cost,” technology provider Aerzen wrote in a white paper. “Several blower technologies can be chosen from and it therefore behooves the engineer to accurately evaluate the characteristics of the aeration blowers and carefully interpret some of the claims made by various manufacturers.”
Image credit: "San Francisco" Eli Goren © 2013, used under an Attribution 2.0 Generic license: https://creativecommons.org/licenses/by/2.0/.