Potty Plant Tour

Last week, the local chapter of ASHRAE organized a tour of the Fairbanks Potty Plant.

One summer when I was an undergrad at Berkeley, I did an internship at San Francisco's main potty plant, the Southeast Water Pollution Control Plant, known at the Department of Public works by the catchy acronym of SEWPCP (or SEP, for Southeast Plant). I was interested to see how similar the Fairbanks plant was. Turns out, quite a bit, except that the parts that are outdoors at SEP are indoors in Fairbanks, because of course they would freeze if they were outdoors. San Francisco's other potty plant, the Oceanside Plant (OSP), is in a hoity-toity neighborhood and therefore also fully enclosed (in fact, mostly underground) so no wealthy people have to smell the potty plant.

Both cities treat both point (from a pipe, like sewage from homes and businesses) and non-point (storm runoff, which includes pollution from car tailpipes and the like) sources of pollution, so there is a big difference in treatment volume between the wet and dry seasons. Both cities utilize gravity as much as they can, so the potty plants are located at low-elevation locations. San Francisco has a ridge down the middle like a spine. The western drainage from the spine is both geographically smaller (about 1/4 of the city area), and far lower in population density. The Southeast Plant therefore treats the vast majority of the sewage. Its capacity is 250 Million Gallons per Day (MGD). The Oceanside Plant is 17 MGD. The Fairbanks plant is a wee bitty 8 MGD.

Another thing I recall about potty plant life is that every day around 5:20 p.m., a flood of sewage comes in... because all of the office workers go pee before they leave their offices for the day!

Here is a schematic of the Fairbanks potty plant:


The basic operation of all three potty plants is similar. The initial treatment is purely physical: a series of screens, ever decreasing in size, to remove all solids:


Then the fluid sewage is floated very slowly down a very shallow incline:

During this slow process, the lighter turds float to the top (scum), and the heavier turds sink to the bottom (sludge).

Then anaerobic bacteria are introduced to help break down the organic material. These bacteria apparently have a learning curve, and older bacteria are very valuable (like sourdough starter). Therefore, after the bacterial portion of treatment, some of the old bacteria are introduced back to the first step. Therefore, there are two poop lines: The Waste Activated Sludge (WAS, which gets disposed), and the Return Activated Sludge (RAS, which gets reintroduced).

After the anaerobic bacteria have done their thing, and the solids are removed, the remaining liquid is aerated to kill off the anaerobic bacteria, and feed the aerobic bacteria to continue the job:


After that, chlorine is added to kill the bacteria and stop the process. The Fairbanks plant makes their own chlorine from salt:


The solids (sludge) are then dewatered using centrifuges. The Fairbanks plant has this crazy horizontal one that apparently is quite finicky:


The operator who gave us the tour was very unimpressed with it, and told us that he would have preferred one of the simpler, more robust dewatering mechanisms currently on the market. The lesson I took from him was that, when it comes to sewage handling, and when it comes to the Arctic, it is best to follow the KISS principle.

The dewatered sludge is called "cake" in both San Francisco and Fairbanks, so that must be the term!


The SEP in San Francisco releases the treated effluent into the Bay. The OSP releases its effluent to the Ocean, off Ocean Beach. The Fairbanks potty plant releases it into the Tanana. The SEP has a team of biologists who sample the water and make observations about the sea life periodically. They have caught tiny sharks in the Bay! Whoda thunk?

Here are some other photos!

Here is a map of Fairbanks from pre-1971. There is no Parks Highway, and Geist Road is not connected to Chena Pump Road:


I lovelovelove these dial readouts:




I hope you don't think that makes me a strange engineer, when engineers are supposed to love everything high-tech. To me, they provide very reliable visual recordings that you can judge at a glance without having to click anything.

Here is where the turdy air gets vented:


There was a bird next up there in the eaves. What an extremely tolerant bird family!

One of three generators for backup power:


I don't recall what exactly this situation is. Look at that crazy coiled line!


Boiler for space heating:


This is what the corridors look like:


Some comedian employee must have painted this:


Boy, I would not like to be there alone at night!

And that concludes my potty plant report.

By the way, it smells every bit as horrible as you'd imagine! But it's super interesting, and I think everyone should know what it takes to support her or his life, from knowing where food comes from to where poop goes. It's all part of being a Fully Informed Person!