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Bowie officials this week began upgrading the city's wastewater treatment plant to improve the quality of the water the plant discharges into the Patuxent River that eventually makes its way into Chesapeake Bay.

To comply with Maryland Department of the Environment regulations to reduce the level of nitrogen and phosphorus in water released from wastewater treatment plants, officials are installing an enhanced nutrient removal system to the plant, city public works director Jim Henrikson said.

The plant will add sand filters and an improved aeration system to cut nutrient levels to about half of the current average.

Bowie plant superintendent Christopher Bolander said high nutrient levels are the leading cause of algae blooms in the summer, depleting the oxygen in the water and causing fish kills.

The Bowie plant processes approximately two million gallons of wastewater a day, and its output averages six milligrams of nitrogen per liter, Bolander said.

"In the summertime it's usually lower, as low as three milligrams," he added. "Winter could be up to eight milligrams. This project will give us total nitrogen of three milligrams or less year round."

The plant also processes about .5 milligrams of phosphorus per liter a month, which the new system will cut to roughly .3 milligrams per liter a month, Bolander said.

The city's nitrogen levels are well below levels that could be toxic for swimming, said Beth McGee, a spokeswoman for the Chesapeake Bay Foundation. Ammonia, organic nitrogen, nitrites and nitrates comprise the total nitrogen released from the Bowie plant, Bolander said.

For the nitrogen levels to be toxic to humans, the ammonia levels alone would have to register between 30 to 60 milligrams per liter, McGee said.

In an effort to clean up the Chesapeake Bay, Maryland plants that process at least a half-million gallons of sewage a day are being required to reduce their nutrient discharges by October 2010.

A recent study by the Chesapeake Bay Foundation concludes that the same nutrient pollution that kills fish is responsible for increases in bacteria that are harmful to humans. A 2008 study by the U.S. Geological Survey looked at Mycroscystis algae blooms around the bay and found that almost a third of the blooms contained toxins in levels sufficient to make the water unsafe for children to swim in.

The $10.4 million project is mostly financed through "flush fees" collected from sewer uses through the Bay Restoration Fund. The $2.50 monthly fee, collected since 2004, will help to pay for upgrades at Maryland's 66 major treatment plants.

In Bowie, the fund will pay $8.2 million for the engineering and construction of the enhanced nutrient removal system, leaving the city to pay approximately $1.8 million for the upgrades.

The upgrades are expected to take 15 to 18 months to complete, Henrikson said.

The improvements at the plant will allow the city to keep pace with the latest technology in protecting the Bay and reducing the algae blooms that are devastating for fish, said Tiffany Wright, Bowie's watershed manager.

However, much work remains in educating residents about reducing pollutants found in storm water runoff, she added.

Wastewater treatment plants "are so regulated that they are of little effect on the bay," she said.

E-mail Andrea Noble at anoble@gazette.net.