The Proper Odor

Inspired by "The proper order" lists, we look at the order of a sewage treatment plant. From start to finish, the process is ripe with unique odors. We asked Southerly manager Christen Wood to describe the smells of a plant walk.
  1. "Like a forest"
    "There's quite a variety of scents around the plant. The first thing people will pass is 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."
  2. "Septic"
    "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 lids to keep it down, though, controlling the odor."
  3. "Unique, greasy"
    "As you 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."
  4. "Earthy"
    "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."
  5. Odorless
    "The effluent (treated water) is odor free by the time it leaves the south side of the plant and returns to the environment."
  6. "Fresh-cut grass"
    "Besides these, we also usually smell fresh cut grass and flowers in the landscaping during the summer. It's actually fairly pleasant!"