Nation's capital pioneers a poop-to-power system

Tanks dc water sewage powerDistrict of Columbia Water and Sewer AuthorityYou do not want to see what’s inside these tanks.

Any city’s sewer authority has to do a lot of dirty work, collecting and processing the waste that residents and visitors flush down toilets all over the city.

The Washington D.C. Water and Sewage Authority has a new treatment plant that will be taking that dirty work — at least, the solids collected as part of the process — and converting it into clean energy.

As The Washington Post notes, there are other energy utilities that generate power from sewage, but the new D.C. Water system uses a unique “pressure cooker” technology that lets them fit the plant into a small space, essential for such an operation in a city.

Officials say that the new treatment center at Blue Plains Advanced Wastewater Treatment Plant, which uses Norweigan thermal hydrolysis technology, is the first of its kind in North America and the largest of these facilities in the world.

And while it cost $US470 million to build, city officials say it will pay for itself.

That’s because the new system will save them $US10 million a year by leveraging the hidden energy stores of human waste to generate one-third of the plant’s overall power. The Blue Plains Plant, which uses an energy-intensive process to turn sewage into water clean enough to dump into the river and solids that used to be trucked out of the city, is currently the biggest electricity consumer in the city.

Now they will be able to sell those “biosolid products” as a “compost-like product” at Home Depot — no more trucking required.

The new facility will also save the plant $US2 million on treatment chemicals and $US11 million in the cost it takes to truck away the current “dark gunk left over from treated sewage,” according to the Post.

As the press release notes in delightful language, “The facilities include a dewatering building, 32 sleek thermal hydrolysis vessels, four concrete 80-foot high anaerobic digesters that hold 3.8 million gallons of solids each and three turbines the size of jet engines.”

The turbines are actually the same as the ones used in jet engines, according to D.C. Water. Jet engines. That’s what it takes.

Once the solids are processed, they’re put into “digesters” where bacteria eat them. The sellable biosolids are left behind, while the rest of the waste is converted to gas. It’s those jet turbines that turn the gas into useful energy.

Here are the details on how it works, which we pieced together from both D.C. Water and an infographic at the Post:

  1. You flush after you do your business. The total from around D.C. adds up to 370 million gallons of wastewater each and every day.
  2. After a journey through miles of pipe and sewers, everything that went down the drain arrives at the D.C. Water facility in Southwest D.C.
  3. Screens remove the debris from the system before the solids are separated from the liquids. (Stop flushing things down the toilet or the drain if they don’t belong there, grease included.)
  4. Liquids get treated, cleaned, and sent right back to the Potomac River.
  5. Solids get centrifuged to compress them into a thick mass of — well, you know. “Biosolids.”
  6. Sludge goes into a giant tank and then pumped into something called a “pulper.”
  7. After being pre-heated there, it gets sterilized in a reactor at a high temperature and pressure.
  8. Returning that mix immediately to regular pressure causes the cell walls of those biosolids to burst, which kills bacteria and makes everything digestible for microbes in the digesters.
  9. Those massive digesters convert solids into gas and then the turbines convert that into energy.
  10. The remaining solids “meet and exceed all EPA standards for soil production and use in both rural and urban settings.”

And the end result is pretty awesome: It will reduce emissions by 50,000 tons of CO2, which the water agency compares to removing 100 million car miles from the road.

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