From: Eng-Leong Foo 
Subject:      [IBS-GEN] wastewater treatment with duckweed

Source: http://www.wateronline.com/times/firms-and-faces/ff7031402.html


Wastewater Facility Using Duckweed Plants In Process Gets EPA Award

The U.S. Environmental Protection Agency has presented its 1996 Regional =
Operations and Maintenance Excellence award to the town of Laurel, =
Delaware for the retrofit of the municipality's wastewater treatment =
plant. The 0.5 mgd facility is owned and operated by the town and is =
primarily used for treating sanitary wastewater.=20

The advanced secondary treatment phase used at Laurel involves three =
biological lagoons, the first of which provides primary treatment with =
extensive aeration. The second is for anaerobic treatment. It is in the =
third lagoon, however, that a significant processing improvement =
developed by LEMNA USA, Inc. has been implemented. In this lagoon, =
lemnacea plants (duckweed) were introduced to create a floating blanket =
of vegetation that prevents sunlight from reaching the water. Allen =
Atkins, supervisor of public works for the town, explained that this =
"helps with the control of algae in our lagoon, and also helps remove =
other nutrients from the wastewater."=20

Because the duckweed blanket is composed of growing vegetation, periodic =
harvesting is carried out to remove dead plants. These are readily =
composted. Harvesting also ensures a continuing supply of new, young =
lemna plants which have been shown to be more effective in the nutrient =
removal process than the older ones.=20

A number of other significant steps were taken in this project to =
upgrade the plant and make it worthy of this important USEPA award. For =
instance, bacterial enzymes are being used to reduce sludge blankets, =
operator training has been given additional emphasis, and maintenance =
procedures have been reviewed and improved.=20

Edited by Ian Lisk