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WEIRD: Making sense of the smells of wastewater treatment [#cwc5K]

If you thought the smell of victory was unique, you’ve never visited a wastewater treatment plant.

Our Southerly Wastewater Treatment Center is hosting the Clean Water Classic 5K run/walk for charity this Saturday, so all of our guests will have a chance to smell both. It has raised some questions.

“What does a sewage treatment plant smell like?”

So many factors can affect the answer on any given day, but we asked one of our operators what scents runners might encounter along the five-kilometer course. Here’s what she said.


“There’s quite a variety of scents around the plant. The first thing people will pass is our first-stage aeration. The ‘mixed liquor’ (the wastewater aerated to help microorganisms begin breaking down the waste) reminds me of the earthy smell a forest has after a thunderstorm.”

“Next, we’ll pass the gravity thickeners, which is where we separate the primary sludge (solid organic material settled from the wastewater). This is the most likely place to catch a whiff of the septic/sewage smell people expect. The tanks have lid to keep it down, though, controlling the odor.”

“As runners get closer to the northern end of the plant, we’ll be passing through the headworks area where the raw wastewater first enters Southerly. This is pure, untreated wastewater. It has a very unique odor, a mix of grease, industry, etc.”

“Then we’ll swing along the second stage aeration, back to the earthy smell of mixed liquor, but we also disinfect the almost fully treated water. You usually can’t smell much here, though.”

“The effluent (treated water) is odor free by the time it leaves the south side of the plant and returns to the environment.”

“Besides these, we also usually smell fresh cut grass and flowers in the landscaping during the summer. It’s actually fairly pleasant!”

Special thanks to Christen Wood for the descriptions and Karl Ellis for the photos.

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