Poop, Loop, and the Things We Recoup
If you're like me, you've thought a lot about where things go when you flush the toilet.
If you're not like me and you're just wondering about it now for the first time - or maybe you've thought about it but never found an answer - that's fine. I'll tell you! If you live in and around Redmond, Bothell, or Woodinville, WA, everything you send down the drain eventually goes to the Brightwater Treatment Plant.
It's a relatively new (2011) wastewater treatment plant that features innovative integrated systems that turn stinky stuff into useful commodities, like energy and fertilizer.
Brightwater treats 25 million gallons of wastewater per day. This includes water from any flushing, handwashing, showering, dishwashing, and laundry you may be doing on any given day. It also includes certain kinds of industrial wastwater but it does not include stormwater or other kinds of runoff (which is water that falls on impervious surfaces when it rains, when sprinklers are on, etc).
After the water is treated at the plant, most of it flows 13 miles downhill to be dishcharged far out into Puget Sound. Before it's allowed to mix with water where our beloved orcas, seals, salmon, anemones, and other PNW marine life live, it must be treated to remove pathogens, solids, nutrients, and many other contaminants - including trash.
The treatment process! (Photo by Sejal Soni)
As you can see in the diagram above, water treatment happens in multiple phases (shown in blue). During preliminary treatment, large and small debris is removed from the influent. Much of this is trash that should not have been flushed - including "flushable" wipes and tampons!
For more on what you should and should not flush, check out the hilarious antics of The Roll Family:
These PSAs are both informative and hilarious! (Source: Queensland Urban Utilities)
After debris and trash are removed and trucked to a landfill, gravity and filtration are used to separate solids from water.
Bacteria and oxygen are introduced into aeration tanks so that the bacteria can consume poop and food that makes it down the drain. After this, teeny tiny membrane-thick straws suck up the water. The bacteria are too big and get stuck to the outside of the straws so all that gets through is water.
As you may have seen in the treatment process diagram, organic solids are removed from water at various stages in the process. These are made up of the bacteria that was introduced, bacteria and food bits that were screened out, any remaining sewage, and anything too big to pass through the membrane filter.
How to turn poop into plant food. (Photo by Sejal Soni)
What's a water treatment plant to do with all these biosolids? Some plants incinerate their solids and some send them to a landfill, but these options are kind of wasteful because these nutrient-rich biosolids make some pretty primo fertilizer.
At Brightwater, biosolids are dewatered even further by a gravity belt thickener and the addition of a polymer. After that biosolids are processed through anaerobic digestion. This kind of biological processing produces "biogas", which is mostly methane (AKA natural gas) and can be used to generate electricity. In fact, almost all of Brightwater's energy needs are met through the burning of this reclaimed resource!
The gravity belt thickener in action. It may not be pretty, but this is an important part of sustainable urban water infrastructure. (GIF by Sejal Soni)
With a bit more dewatering, the biosolids - which oddly enough resemble poop - can be sent off to farms to feed the crops. They are sold under the brand name Loop (does the blog title make sense yet?) because they close the nutrient cycle: plants use nutrients, people eat plants, people poop excess nutrients, nutrients get treated and go back to plants! Apparently, they work especially well on wheat.
Some of the clean water at the end of all these treatment processes is used to water the lawn of a nearby golf course and athletic fields. The rest goes out to sea!
Reclaimed water, energy, and fertilizer are valuable commodities that make this a sustainable process and show why wastewater treatment plants of the future are more accurately called Water Resource Recovery Plants!
Brightwater is a treatment plant, a resource recovery plant, and a public art museum. This is the clean effluent on its way to the Sound. (GIF by Sejal Soni)
Thanks for reading! All photos and GIFs are by Sejal Soni and may not be used without permission.
This display celebrates some of the pathogens that are commonly removed during wasewater treatment. (Photo by Sejal Soni)