Patuxent water plant upgraded

August 09, 1994|By Erik Nelson | Erik Nelson,Sun Staff Writer

The county Public Works Department has coerced some microscopic help in the fight against pollution in the Patuxent River and the Chesapeake Bay.

Thanks to a $47 million upgrade of the county's Little Patuxent Water Reclamation Plant in Savage, county engineers are starving pollution-eating bacteria into consuming nitrates and breaking them into oxygen, which the organisms use, and nitrogen, which they release as a harmless gas.

"It's nothing other than that these microorganisms need oxygen," explained Daniel Ward, process control engineer for the bureau's Division of Water Reclamation. "If they're starving for regular oxygen, then they're going to take it from the nitrate."

A contractor put the finishing touches last month on the project, which began in 1991.

The upgrade increased the capacity of the plant from 15 million to 18 million gallons a day and improved the plant's sludge-handling capabilities in addition to refitting the plant's biological "reactor" to take more nitrogen from the effluent.

The problem with nitrogen, along with its nutrient cousin, phosphorus, is that it provides food for algae, which has been clogging the Patuxent River.

The algae block sunlight needed for vital ecological components such as river grass, which provide habitat and oxygen fish and other river creatures need to survive.

Nutrient levels in the Patuxent have been reduced in some areas by as much as 40 percent, according to a study released last year. Most of that improvement has been attributed to changes at other wastewater treatment plants such as the new process at the Little Patuxent plant.

Before the new process, effluent entering the plant averaged about 25 parts of nitrogen per million, and was pumped into the Little Patuxent at 16 parts per million.

With the new process, the effluent enters the river at about 7 parts per million, which is better than river water upstream, said Robert M. Beringer, chief of the Public Works Department's Bureau of Utilities.

"That's great," said Richard A. Eskin, chief of the Chesapeake Bay Coordination Division of the state Department of the Environment. "We were hoping for 8 and they've gotten lower than that."

Before the water gets to the new process, it has to do some traveling.

The Little Patuxent plant processes sewage from areas generally south of Route 108, except rural areas west of U.S. 29 and south of Route 32. Most households in Ellicott City and Elkridge are served by the Patapsco Wastewater Treatment Plant plant in Baltimore.

Columbia, Savage, North Laurel and Jessup send about 13 million gallons of sewage daily to the plant, where it is first screened to remove solids.

In other tanks, called clarifiers, solid particles are allowed to settle and be siphoned off.

All solid waste separated in those processes is removed as sludge, which is used as fertilizer for farming and land reclamation.

"In the old days, what they would do is just settle the solids and take the liquid and just pump it into the stream," Mr. Beringer said.

About 15 years ago, sewage treatment plants began using bacteria to feed on nutrients -- nitrogen and phosphorus -- that promote algae growth that damages waterways.

"They like oxygen and they like it wet," said Mr. Ward. The plant provides that environment by blowing air through pipes in the bottom of 600,000-gallon tanks called reactors. The frothy brown mixture is created much the same way beverages are carbonated, but with oxygen instead of carbon dioxide.

"It's like Perrier," Mr. Beringer said.

While that environment was just fine for getting bacteria such as Acinetobacter to remove phosphorus from the effluent, and other species to convert ammonia to nitrate, it didn't solve the problem of the leftover nitrate.

So in some of the 10 reactor tanks, there are no bubbles, and bacteria such as Nitrosonomas and Nitrobacter are forced to eat nitrates.

After the reactors, the effluent is put into a final clarifier tank, which allows the bloated, but still microscopic, bacteria to settle to the bottom and are pumped back to start again.

Some of the returning bacteria are diverted and disposed of with the sludge.

On average, the bacteria will go through the process twice a day for 12 days.

"You find a Howard County swimming pool that looks as clean as that water," said Mr. Beringer, walking toward tanks of clear water being chemically treated to remove chlorine -- the final stage of treatment to remove pathogens, which are disease-causing microrganisms.

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