Madison, Wisconsin: Wisconsin Department of Natural Resources
The objective of this project was to demonstrate the feasibility of hypolimnetic aeration as a useful technique for lake restoration. In order to successfully evaluate hypolimnetic aeration, aerators were installed in two eutrophic lakes in central Wisconsin. The major component of the hypolimnetic aerator consisted of a 40-ft long, 18-inch diameter polyethylene tube with an internal longitudinal plate dividing the tube in half and twisted to form a helix. Compressed air or a combination of compressed air and liquid oxygen were supplied to the base of the unit and water was air lifted up the tube to enter a 4-ft by 4-ft by 8-ft bubble separation box at the surface of the lake, where the air bubbles were vented to the atmosphere. The bubble-free oxygenated water was returned to the hypolimnion via two 18-inch diameter flexible return tubes. An evaluation of the unit was completed in a eutrophic, clear, hard water lake (Mirror) in 1972 and 1973 and in a dystrophic soft water lake (Larson) in 1973. The initial studies indicated that all of the oxygen transfer from the compressor occurred in the bottom half of the unit, with further transfer occurring in the surface separation box as the water momentarily came into contact with the atmosphere.