Poolandia

Today I had the opportunity to visit the Colombia Waste Water Treatment Center in Portland OR to learn where our poo goes when we flush the toilet.

What I learned is that Portland has over 2300 miles of sewage pipes and over 100 pumping stations that carry upwards of 25 billion gallons of wastewater to this treatment plant per year (this figure is actually half what it once was due to people’s efforts to disconnect their downspouts in Portland, and otherwise practice water conservation).  Of course, that sewage water is composed of 99% water and 1% guck… so everything that follows is only necessary because we dump our guck into what is otherwise clean drinking water in the first place, and then require all of these energy intensive processes in order to clean that very same water again!

Portland's "Big Pipe"

On average the plant we visited treats 70-75 million gallons per day.  This amount varies depending on the time of year , dropping down as low as 12 million gallons in the summer when the aquifers are low, and peaking at 450 million gallons per day during major rain events.

In fact, this record of 450 million gallons was only recently set, and Mike who gave us the tour sugggested that due to climate change, more major rain events such as this are occurring each year.

When a major rain event sends more water into the sewers than the system can allow, sewage water has to be dumped directly into the Columbia River without treatment!  Regulations allow the treatment plant to dump raw sewage into the river no more than 4 times per year… Ickk!

A “Big Pipe” is currently being built in Portland that will be able to store some of this excess sewage water during major rain events and reintroduce it into the treatment facility once the demand on the system has been reduced.

Maybe Video Games are Good for Something After All?

As it turns out, operating a sewage treatment plant is a lot like playing a video game… these days, everything is controlled on screens.

When Mike started working here 35 years ago, the controllers actually had to open and close valves such as these manually… but not any more.  On our entire tour we only say one controllers and he was sitting behind the screens.

The first stop for the wastewater is the primary treatment where sticks and stones are all filtered out with 1/8th inch metal grids.  Sand and smaller grit is separated by a centrifuge (centrifugal degritter).  All of these solids are then sent to the landfill.   The next step in the primary treatment is seperating out the corn… yeppp, that’s right… the treatment facility has to deal with TONNES of corn that pass through millions of Portlandian bowels each year without actually digesting.  The corn requires its own unique process in order to be extracted!

The Methane Digester uses bacteria in Anaerobic Conditions to Convert Solids into Energy which is then Sold

Next, the liquids are slowed down in a tank where 20-25% of the remaining solids settle to the bottom of the tank and create a sludge.  The sludge is sent to a methane digester.  The methane digestor uses anaerobic bacteria to digest the biomass and  produce 1.7 Megawatts of power.  Poo power!!!  Methane digesters are cool!   I wish I could say that this power was being used for the cause of world peace, but in fact much of this power is sold to a local roofing factory to make shingles with.  The wastewater treatment facility makes $25,000 per month from selling Methane.

The Wastewater sits anaerobic for 1 hour in the First Tank Before Entering the Second Tank Where Air is Added

The soluble particulate that can’t be settled out continues on to the secondary treatment .  Here, the treatment facility breeds over 22,000 lbs of bacteria, some of which are introduced to the wastewater here.  Once the bacteria are introduced, the wastewater passes through a slow moving tank for one hour where they are deprived of oxygen, killing off all of the unwanted filamentous bacteria.  The desired species of bacteria (Pseudomona and Nitrobactor) are able to essentially shutdown their life processes temporarily and survive this anaerobic stage.  Once the unwanted bacteria dies off, the surviving bacteria are then fed oxygen and they are HUNGRY little buggers, so they rapidly gobble up any solids remaining in the wastewater, and they also begin to breed like crazy.

You can see the wastewater moving from this slow moving anaerobic tank to the vigorously bubbling aerobic tank in the photos above. The compressors that are used to blow this air through the second tank  uses a massive amount of energy – about 40% of the energy required by the entire facility.

Now most of the solids have been removed, but the remaining bacteria still have to be removed from the process. The liquid enters a second settling tank where these bacteria sink to the bottom and form a sludge.  Some are cycled back to the start of the aerobic digester, but by now they have reproduced and so excess populations of these critters have to be removed or else their digestive activities become too vigorous.  The water in the settling tank is hot from all of this biological activity and makes a very cozy hangout spot for ducks and seagulls!

Sludge Cakes of Bacteria and Polymers from the Aerobic Process

The bacterial sludge from the aerobic process, and the bacterial sludge produced from the Methane Digester, are then seperated out from any existing water by introducing a polymer.  Sludge from the methane digester comes out brown and is fed back to the methane digester.  Sludge from the aerobic bacteria comes out black and is then passed through a fungal biofilter, before being applied to a field where they fully compost after 1-3 months.

Decomissioned Composting Facility

The facility used to compost the sludge fully before applying it to the soil, however this required massive woodchip inputs that the facility could no longer afford.

A Powerful Bleach called Hypochloride is Added

The final stage for the resulting water is a dose of a powerful bleach called hypochloride that is introduced to kill off any remaining pathogens.  The hypochloride is mostly removed before the end product is pumped into the Columbia River.  At this point the water must be at least as clean as the river itself.

This entire process at the treatment center costs $170,000 per month in energy alone.  I felt overwhelmed by the massive amount of infrastructure at this site… and all this simply to clean water that was already clean in the first place before we defecated in it!  While we walked though extensive underground corridors filled with pipes, pumps, concrete, computers, blinking lights, valves, funny smells, loud noises, and far more devices and energy intensive processes than I could possibly wrap my mind around. It all seemed like a nightmarish scene out of a Shawn Tan novel.

… and I just couldn’t help but to contrast it all to my simple little poo and  greywater buckets at home and think about how much more easier it all could be….