Patuxent test might help clean county wastewater Nitrogen removal would benefit bay

December 27, 1996|By Beth Reinhard | Beth Reinhard,SPECIAL TO THE SUN

A one-year experiment on the Little Patuxent River in Savage could help cut the amount of environmentally hazardous nitrogen that flows from Howard County into the Chesapeake Bay.

Since August, Little Patuxent Water Reclamation Plant has been studying better ways to cleanse wastewater from Columbia, Savage and North Laurel.

Although water discharged from the plant meets the state limit of 8 milligrams of nitrogen per liter, officials aim to reduce the proportion to 3 milligrams.

Last month, the state Board of Public Works granted the Howard County Department of Public Works $250,000 for the pilot project on biological nutrient removal. Howard County matched the money, for a total of $500,000.

Nitrogen fuels the growth of algae, which clogs waterways and depletes the oxygen supply.

"Nitrogen is like a fertilizer, and then you get weeds and other stuff that uses up the oxygen and fish can't breathe," said Bob Diaz, a project engineer at the county's Department of Public Works. "It's a vicious cycle."

Under the new process, bacteria in wastewater tanks are fed methanol to increase the conversion of nitrates to harmless nitrogen gas.

Said Daniel Ward, process control engineer at the plant: "The bacteria need food and oxygen to support themselves just like we do. The methanol is the food, and the oxygen is in the nitrates."

The nitrogen removal process being tested works like this: Dirty water collects in sewers and flows through steel bars to remove large solids such as sticks.

The water is pumped from underground sewer pipes into 600,000-gallon concrete tanks.

Water flows through sand to allow solid waste such as coffee grounds to settle to the bottom of the tanks. Solid waste goes through a separate process to become sludge, which farmers use as fertilizer.

Bacteria in the tanks convert the nitrogen to nitrates. Another kind of bacteria, which is fed methanol, converts nitrates to nitrogen gas, which rises into the air.

The water seeps through sand again and is disinfected with chlorine before it is dumped into the Little Patuxent River about four miles from the plant.

If the test using methanol is successful, Diaz said, it would cost millions of dollars to adjust the whole plant to the new system.

"They want pristine water, but there's only so much you can do until it gets to a point where it's very expensive," Diaz said.

The plant has had better luck removing phosphorus, another nutrient, from wastewater. Water discharged from the plant contains only .25 milligram of phosphorus per liter, below the state limit of 1 milligram per liter.

The eastern part of the county, including Ellicott City, Elkridge and Jessup, sends its wastewater to Patapsco Wastewater Treatment Plant in Baltimore.

Most residents in western Howard use septic tanks.

When Little Patuxent Water Reclamation Plant opened on 48 acres in Savage in 1965, it treated 1 million gallons per day and was mainly concerned with removing organic matter. Since then, Howard's growing population and increased efforts to remove pollutants from wastewater have led to about $100 million in renovations. The plant now treats 18 million gallons per day from 75 square miles in central Howard.

In 1994, the plant started using bacteria to remove nitrogen and phosphorus instead of using less efficient chemicals such as lime that generate solid waste.

"The process works a lot better than it did 15 years ago," Ward said.

Pub Date: 12/27/96

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