New use for marsh pest

Sludge: Officials find that beds of menacing reeds make good filters for water treatment plants.

May 13, 2000|By Joel McCord | Joel McCord,SUN STAFF

BRIDGEVILLE, Del. -- In a field behind Town Hall, a sewer plant operator is using a reed reviled for taking over Chesapeake marshes to soak up sludge and cut costs.

Every couple of weeks, Phillip Mowbray, the plant operator, pumps about 6,000 gallons of sludge from his plant onto two beds of phragmites, the 10-foot-high green reeds with feathery brown top knots that are common to waterways throughout the world.

The sludge, mostly water, fills the 51-by-21-foot beds. The water soaks through six inches of sand and a layer of gravel to pipes that send it back to the beginning of the plant for more treatment, and the sludge is left behind to be soaked up by the phragmites.

Disposing of sludge is one of the most important parts of treating waste water, said Leonard Gold, an Easton-based consultant.

"If you can't manage the sludge, then you can't remove pollutants and you can't get the water clean," he said. "And the cleaner you make the water, the more sludge you generate."

Bridgeville, a town of about 13,000 on the way to Delaware's beach resorts, is among a growing number of municipalities -- four of them in Maryland -- to use the technique since it was imported from Germany about 25 years ago. Most of those towns are north of the Mason-Dixon Line, where winters are colder. The reeds must be cut down once a year, and it is best to do that when the sludge is frozen so crews can walk on it, not in it.

In conventional drying beds, the sludge is poured onto sand. The water drains through, and an inch-thick slab of sludge dries and cracks like a desert creek bed. Every two weeks, municipal crews have to pry the dried sludge from the sand with pitchforks and load it onto trucks to be hauled to a landfill or some other disposal facility.

Beds of phragmites -- known generically as reed beds -- need to be cleaned every seven or eight years. The annual harvest keeps taller reeds from falling over and taking up space reserved for sludge.

Mowbray figures that the low maintenance saves him $6,000 a year, and Jack Gallagher, a University of Delaware scientist studying phragmites, figures that it's a "useful purpose for a plant we consider to be a pest."

Phragmites have "a tendency to overcome more desirable marsh species," Gallagher said.

The reeds fill in small streams in the marsh with their roots and choke out other plants. They close off channels that juvenile fish and crabs use to get to protected areas to feed, and they eliminate places for waterfowl to take off and land.

Gallagher and his students at Delaware's Sea Grant campus at Lewes are trying to develop a variety of phragmites that will more efficiently soak up the sewage and allow the water to pass through.

"We want one that's not too tall and has a fair number of roots," he says. "And we want one that's identifiable so we can trace it."

A German company developed this method of using phragmites in the 1960s. Reed Bed Systems Inc. a New Jersey company, got exclusive licensing rights for the United States in the 1970s and began marketing it to municipalities in the 1980s.

"It's almost like creating compost," said Scott Davis, head of Reed Bed. The roots make a way for water to drain through the sand and gravel while feeding on bugs in the sludge, he said.

At least 60 municipal sewer plants nationwide use reed beds to treat sludge, most of them in the Northeast.

Denton, in Caroline County, installed 16 reed beds when it upgraded its sewer plant last fall and began pumping sludge into them this spring, making it the fourth municipality in Maryland to do so.

"We had been looking at different avenues to upgrade our wastewater treatment plant," said Terry Fearins, manager of the town of 3,000. "We didn't want to raise our costs, and the consultant told us [other methods] would cost $43,000 a year. And we had the land."

Denton spread its reed bed over 5 acres.

Reed beds seem to work for smaller municipalities, where treatment plants handle less than 2 million gallons of sewage a day -- Denton's plant is designed to handle 800,000 gallons a day and Bridgeville's 180,000 a day -- but experts say it would be a failure at larger plants because of the land required for the beds.

For example, Baltimore's Back River and Patapsco treatment plants handle more than 200 million gallons a day.

"If Denton's using 5 acres for its 800,000-gallon plant, you'd have to take over Druid Hill Park for reed beds in Baltimore," said Gold, the Easton consultant.

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