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 <%=company%>, 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."
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.
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.
Edited by Ian Lisk