DC Water adopts Norway’s Cambi system for making power and fine fertilizer from sewage

This is a topic that one must approach delicately so as not to offend the reader's sensibilities, but since it is a matter of importance for which you may receive a bill for some portion of $470million, we start out with an analogy.

You need energy, so you eat. Through the miracle of digestion, your body sorts what you have eaten, say, a pastrami on rye with a glob of coleslaw and a dill pickle, and plucks out the nutrients — proteins, carbohydrates and sugars it needs to generate power. Then it jettisons the rest.

What your body jettisons disappears forever, carried along in a huge network of sewers to a plant in the southeastern corner of Washington.

Just like you, that plant needs energy. Through a miracle called thermal hydrolysis, it soon will be able to sort through what you have jettisoned and use it to generate electricity.

Yes, from poop will come power — 13 megawatts of it. Enough electricity to light about 10,500 homes.

Ben Franklin never dreamed of this one.

While Ben may have denounced the scheme as impossible sorcery, he also noted that a penny saved is a penny earned, so he might have been at least intrigued by this notion.More than a few pennies may be saved for the citizens of the District and for some Virginians and Marylanders. Those people — 2.2million of them — get a monthly bill for the privilege of sending their thoroughly digested nutritional intake to the plant in Southeast Washington operated by D.C. Water.

A chunk of that monthly bill is passed on to another local utility — Pepco. D.C. Water is the electricity company's No. 1 customer. By converting poop to power, the water company will cut its Pepco bill by about one third and reduce by half the cost of trucking treated waste elsewhere.

But enough about poop, a subject that makes many a reader a bit squeamish. Because we'd rather not drive you away from the description of a wholly remarkable plan that is very likely to affect your pocketbook, henceforth we will refer to the matter that flows through the sewage plant as "the product."In fact, you soon will learn, it is going to be turned into a genuine product. One with a price tag. One that you may buy back.

Think about it.

The product has shed the label "wastewater" to morph into something called "enriched water," a term laden with many more intriguing possibilities.

"It could be a game changer for energy," saidGeorge Hawkins, an environmentalist who became general manager of D.C. Water. "If we could turn every enriched-water facility in the United States into a power plant, it would become one of the largest sectors of clean energy that, at the moment, is relatively untapped."

What's nearing completion outside Hawkins's office window, however, is something never built on this scale anywhere in the world. A decade of study came first, and to see whether the system would work here, D.C. Water paid smaller European utilities that use the same process to modify their product so it more closely matched that which Washington produces.

"We're confident that this model will work," Hawkins said.

Something called theCambi, for the Norwegian company that builds it, sits at the heart of it.

When the product flows into the more than 150-acre plant known as Blue Plains, it goes through a couple of mesh filters to shed the debris swept up in the sewer system. Then it goes through a treatment process that turns it into what the Environmental Protection Agency categorizes as class B waste, enough to fill 60 big dump trucks with 1,600 tons of product every day.

And out the gate it goes, at a cost of $16million a year.

That will change in May and June, as D.C. Water begins a phase-in intended to get the new system into full service by January.

Here's how it works:

A centrifuge drains off the liquid, and then the screened product will flow into four pulpers, tall stainless steel vats that look like Gulliver's soda cans. Steam recycled from farther down the process is used to preheat it, and then it flows into one of the two dozen Cambis. They sit like a row of gleaming, blunt-nosed rockets, but they serve as pressure cookers.

The product is heated to more than 320 degrees under as much as 138 pounds of pressure for 22 minutes. Then it moves to a flash tank, where the temperature and pressure drop dramatically and a critical change takes place.

"Because of that pressure difference, the cells burst," said Chris Peot, director of resource recovery at D.C. Water.

When the cells burst, the methanogens can have their way with them.

That happens in the digesters. They are four huge concrete vats, 80 feet tall and 100 feet in diameter. Right now, their interiors are like vast cathedrals, with domed ceilings and a shaft of light glancing through a hole in the top.

Details here

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Taxonomy

• Combined Sewer
• Sewage