And the Prize for Most Convincing Heaving Brown Mass Goes to ...

Not That Dirty: A Sample of Raw Sewage from West Point

Wastewater treatment is pretty awesome. And disgusting. Our last two trips in Seattle were to the West Sound Utility (WSU) Wastewater Treatment Plant (WWTP) and the West Point Treatment Plant. WSU, a small treatment plant with an average treatment capacity of 1.9 million gallons per day (MGD), located in Port Orchard on the Washington peninsula. West Point, on the other hand, has an average treatment capacity of 133 MGD and is the largest WWTP in the Pacific Northwest. Both WSU and West Point use essentially the same treatment process.

Large debris is screened from the waste stream as it enters the treatment plant and sent to a landfill. What may surprise you is the typical quality of the raw sewage. I want to be outraged at the wasted water, but our tour guide pointed out that most sewage lines are gravity drained and reducing the water content significantly may require pumping. What's a water-conscious engineer to think?

Activated Sludge Tank at WSU

After the large debris is removed, the wastewater flows through a series of sedimentation tanks, where heavy organic material sinks to the bottom, is removed from the waste stream and is sent to digester tanks. This heavy organic material is known as activated sludge, is highly microbial and pathogenic and just about as disgusting as you would imagine. The sludge was heaving like a monster from a science fiction movie. Some people get very excited about this sort of thing.

After the sedimentation tanks, the waste stream is sent to aeration and clarifier tanks where even more sludge is removed and sent to the digester tanks.

After leaving the clarifier tanks, the waste stream is chlorinated and dechlorinated, before it is discharged into the Puget Sound. Solids from the digester tanks are safe for use as soil additive.

The information presented on these tours was pretty complicated, so I hope I haven't oversimplified too much, gotten something wrong (or gone into too much detail).

Rocking the Hard Hat:
Joe, Ornwipa, Maggie, Casey, Dr. Heidi, Nate, and Rico

A note about the smell: while neither plant smelled like a field of roses, the smell wasn't that bad. Both locations are highly conscious of their neighbors and do a great job preventing odors from leaving the WWTP grounds. In any case, both plants smelled better than an Abercrombie and Fitch store.