With a flick of a switch this fall, the Chesapeake Bay nutrient reduction effort got its single largest boost to date.

In late September, half the flow at the District of Columbia's massive Blue Plains Wastewater Treatment Plant - the largest such plant in the watershed - started getting Biological Nutrient Removal (BNR) treatment before being discharged into the Potomac River.

About 160 million gallons of wastewater will receive BNR treatment daily, and the process is expected to reduce nitrogen in the treated wastes by at least 40 percent - from about 14 parts per million to an annual average of 7.5 ppm.

That would remove about 3 million pounds of nitrogen from the Blue Plains discharge a year, or about 5 percent of the total nitrogen the Potomac annually sends into the Bay. Blue Plains is the largest plant in the world to attempt to use BNR technology.

"So far, the performance has been at least as good as we anticipated if not better," said Walter Bailey, Blue Plains operations manager. "We really haven't been surprised by anything."

In fact, the plant has been removing more than the targeted amount of nitrogen in its first weeks of operation. The annual 7.5 ppm discharge was based on reducing nitrogen in the discharge to 8.5 ppm during the winter, and 5.5 ppm in the summer.

For about two weeks in early November, Bailey said the nitrogen levels in the discharge were below 4 ppm. "We will not be able to achieve that kind of performance all winter, but we're encouraged that we have been able to get the amount of nitrogen that low," he said.

BNR uses naturally occurring bacteria in the wastes to convert ammonia nitrogen into inert nitrogen gas which is released harmlessly into the atmosphere. To make that possible at Blue Plains, methanol is added to the wastes as a source of carbon - or food - to stimulate activity by the bacteria.

Because the process relies on biological activity, it is expected to be more effective in the summer when temperatures are warmer - and the rate of biological activity faster - than in the winter.

So far in the tests, the rate of nitrogen removal has increased as more methanol is added to the wastewater. At times, with higher levels of methanol being added, the amount of nitrogen in the discharge has dipped to as low as 2 ppm.

Methanol is costly, though, and one of the things being learned during the pilot project is the optimal rate of methanol use.

"We're ecstatic because it shows it works, that it's something that really can be implemented on that large of a scale, and that for D.C., they should be able to meet their tributary strategy goals," said Allison Wiedeman, point source coordinator with the EPA's Bay Program Office.

The pilot project will continue for two years, after which a decision will be made whether to convert the other half of Blue Plains to BNR as well. If so, that would meet the District of Columbia's 40 percent nitrogen reduction goal.

The District and the states of Maryland, Pennsylvania and Virginia are in the process of writing and implementing tributary strategies aimed at reducing the amounts of nitrogen and phosphorus that enter the Bay 40 percent by the turn of the century.

The nutrients are blamed for worsening the Bay's water quality and habitats by stimulating the growth of large algae blooms. The blooms cloud the water, blocking sunlight to grasses that provide habitat for crabs and juvenile fish, and food for waterfowl. When algae die, they sink to the bottom and decompose in a process that depletes the water of oxygen needed by aquatic organisms.

Officials in the past have suggested that if the Blue Plains plant exceeds the 40 percent reduction goal - which the early data suggest is possible - it may open the potential for "trading" nutrient reductions with other wastewater treatment plants. In such a scenario, other wastewater plant operators could postpone upgrading their facilities with BNR by underwriting a portion of the Blue Plains operating costs.

The construction and operational costs for the two-year pilot project is $22 million, with the EPA paying about a third, and the District of Columbia and municipalities in Virginia and Maryland that send wastes to the plant contributing the rest.

After that, the annual operating costs for using BNR in both halves of the plant, much of which is purchasing methanol, is expected to be about $10 million a year.

More than 30 plants - mostly in Maryland - are implementing various types of BNR to help meet the nutrient reduction goal. But Blue Plains - which handles 16 percent of the wastewater for in the entire Bay watershed - is the largest plant to implement BNR in the world.

The BNR technology implemented at Blue Plains was aimed at removing nitrogen because past improvements at the plant had already reduced phosphorus discharges by about 97 percent.