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The next time you flush in the capital of United States, you may think about this: You — or, more precisely, when ever anyone flushes — will assist in generating clean energy.
D.C. Water, which also treats sewage from much of the Maryland and Northern Virginia suburbs, recently became the first utility in North America to make use of a Norwegian thermal hydrolysis system to transform the sludge left over from treated sewage into electrical energy.
Yes, to put it bluntly, the city’s sewage treatment plant is turning poop into power.
“It is an enormous deal on so many fronts,” D.C. Water General Manager George S. Hawkins stated after Wednesday’s official unveiling of the system. “It’s a public utility leading the world in innovation and technology. We have private and public water firms coming from all around the world to see this.”
However the Blue Plains Advanced Wastewater Treatment Plant, officials say, is the first in North America to do so using “pressure cooker” technology that can fit such a system in the relatively tight confines of an urban treatment plant. D.C. Water officials say it’s the biggest of its type on the planet.
Hawkins mentioned the system, which started producing electricity in September, will provide one-third of the 157-acre plant’s power, saving about $10 million yearly. Huge amounts of water and sewage need lots of energy to move via pipes and pumps, making D.C. Water the city’s largest consumer of electricity.
The utility expects to save an extra $2 million or so yearly on treatment chemicals and $11 million yearly in trucking expenses. Previously, the plant produced 1,200 tons of “Class B” biosolids every day, the industry term for the darkish gunk left over from treated sewage. That moist, smelly residue needed to be carried away in 60 truckloads every single day, traveling about seventy five miles to farms in Virginia. The new system produces about half as much of a cleaner “Class A” biosolid, which requires half the number of truck runs and smells less like poop and more like damp mulch.
The Class A compost-like substance may show up within the next year on the shelves of Home Depot as a soil nutrient for home gardens, officials said.
D.C. Water officials say the $470 million system, which took 4 years to construct, will end up paying for itself and shrink the plant’s overall carbon footprint by one-third.
At the dedication ceremony, officials from the U.S. Environmental Protection Agency and the U.S. Energy Department touted the system as an example of how localities can invest in infrastructure while conserving energy and cleaning the environment. Officials noted that water & sewer utilities account for 4% of the nation’s overall power usage, making them the biggest energy consumers in most communities.
“This is on the cusp of science, my friends,” D.C. Del. Eleanor Holmes Norton (D) informed the group of about a hundred local officials and utility employees. “This is the kind of magic that results when science is put to its twenty first century use.”
D.C. Mayor Muriel E. Bowser (D) said the system dovetails with the city’s sustainability efforts.
“We can not afford to have waste be just waste,” Bowser stated. “Every dollar spent to transform that waste into energy will help us to reach our goals.”
Here’s the way it works: Once you flush or send soapsuds down the drain, the contents travel via miles of pipe and finally reach Blue Plains, off Interstate 295 in Southwest Washington . There, what appears like brown, murky water flows by screens that remove debris and then sits to allow solids to settle. Then, enormous centrifuges spin off the water and focus the remaining poopy solids.
The liquid is sent off to be treated after which it returned to the Potomac River (yuck! and we thought only astronauts drank water purified from the piss), and the concentrated sludge is pumped into massive steel Cambi reactors, named for the Norwegian manufacturer. The reactors perform like pressure cookers, using 338-degree steam and pressure to cook the sludge. Then it gets pumped to another tank at a much lower pressure, which causes the cell walls of the unhealthful pathogens and other microbes to burst.
“We are not just burning up the bacteria,” Hawkins explained. “We completely destroy it.”
The sludge is then despatched into one of 4 “digesters” — concrete cylinder tanks as tall as eight-story buildings — that each hold 3.8 million gallons. There, it spends about three weeks as microbial bugs nibble at it. The bugs convert the organic matter into methane gas, which is cleaned and sent to a close-by building, where generators burn the methane gas and produce electricity. The entire system covers about 5 acres.
The key, Hawkins stated, is the Cambi pressure cookers that burn off a lot of the sludge, leaving less of it to be treated. That allowed D.C. Water to have only 4 monumental cylinder-like digester buildings instead of eight, which it didn’t have room for.
Hawkins lauded the group of local leaders for their support, saying that they and D.C. Water customers had made the venture possible.
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