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How Blue Plains works

Chief engineer calls it recycling on a ĎgrandĎ scale

(Published August 14, 2000)


Staff Writer

Back in the old days, big cities would build a sewer pipe right in the river and send all of the stuff they didnít want downstream ó out of sight and out of mind.

That was long before the modern environmental movement.

Nowadays the D.C. Water and Sewer Authority (WASA) does a lot more than that. When someone flushes a toilet, instead of just floating down the Potomac River, the sewage ends up at the Blue Plains Advanced Wastewater Treatment Plant.

Blue Plains Chief Engineer Mike Marcotte is responsible for cleaning up the more than three million gallons of water that enter the plant each day. He claims Blue Plainsí effluent ó the water that flows into the Potomac and eventually the Chesapeake Bay at the end of the treatment process ó is actually cleaner than the upstream water that is pumped into the cityís water system to be treated for drinking.

"If you put a glass of our effluent water and a glass of drinking water side by side, you couldnít physically tell the difference except for the chlorine in the drinking water," Marcotte says.

While working in a sewage treatment plant might not sound like a desirable line of work to most people, Marcotte says the plantís malodorous reputation is undeserved. Besides he says, referring to the smell, "Most people do get used to it."

"This is a great little business," Marcotte jokes. "Thereís not a lot of competition. Not a lot of people particularly want to do this job."

There has been a water treatment site at the eastern bank of the Potomac River since the 1930s, when the first set of round settling tanks were built to filter sewage before it went into the river. Today the plant uses a variety of methods to remove solid waste, organic waste and quantities of nitrogen and phosphorous that cause algae growth in the river and bay.

The journey begins at a series of machines that screen out the larger solid waste that makes its way into the sewers. The "screeners" dump the refuse into large piles full of used condoms, tampon applicators, plastic bags and other waste that is not biodegradable. Plant employees must then carefully shovel the trash into containers to avoid health hazards. "One thing you can do is pick up a hypodermic needle down here," Marcotte warns.

From there, the water heads over to a series of bacteria tanks. The bacteria work to "chew" on the organic wastes, especially urine. Keeping the bacteria alive and active requires care, Marcotte says. He notes that they regularly feed oxygen and methanol, which is a liquid form of carbon, into the tanks for this purpose.

After the bacteria do their work on the wastewater, huge settling tanks filter out the organic solid waste. The plantís oldest working parts are these round cement tanks and in order to refurbish the plant, some tanks are being periodically phased out.

That can be a challenge, though. The 2.5 million people whom the plant serves donít just stop flushing their toilets on weekends and holidays. Marcotte says that treatment plants are not something you can just shut down, making it difficult to do major improvements to the plantís constantly working machinery.

"Someone said that itís like reconstructing a 747 while itís in the air," says Marcotte, about WASAís ambitious plans to replace many of the plantís older components.

Once the solids are separated from the rest of the wastewater in the settling tanks, the liquid waste continues being cleaned and purified. Massive filters, similar to the ones used in swimming pools, filter even more impurities out. Then once it passes through that stage, the water is chlorinated in large "control pools."

The amounts of chlorine needed to disinfect the water are immense. Huge 90-ton tank cars arrive at the plant by rail. The tank cars are pressurized, so the chlorine remains in a liquid state, but Marcotte says it would turn to gas if exposed to the air and could be a major catastrophe. He says WASA is in the process of replacing liquid chlorine with concentrated bleach, which is safer to use.

At the end of the line, the chlorine is then taken out with various chemicals to make the water more hospitable to marine life, and then sent back into the river, Marcotte says. But once the water is cleaned, the waste treatment process at Blue Plains still isnít done. Thatís when WASA recycles the solid waste, which is the strongest-smelling part of the plant.

And just what does WASA do with the sludge thatís taken out of the sewage? First itís renamed "biosolids," the politically correct term, and then itís given to farmers who use it as fertilizer. The soft brown matter is 20 to 30 percent water but solid enough to work well in agricultural fields. Marcotte said 1,100 tons of the compost are trucked away every day, primarily to farms in Virginia.

Despite the irony that locally grown foods might have been fertilized with human waste, Marcotte says Blue Plains is beneficial because it puts its product back into the environment.

"This is really a grand recycling effort," he said, "because nothing is being wasted. The water is going back into the Potomac, and the solids are going back into the land."

Copyright 2000, The Common Denominator