• Mechanical Axial Flow Pumps use a “top-down” approach to set up a circulation pattern. A floatation platform and frame support an electric motor, gearbox, drive shaft, and large propeller (6—15 foot diameter). The propeller is suspended just a few feet below the water surface. Its rotation “pushes” water from the lake surface downward, setting up a circulation pattern that prevents thermal stratification. Oxygen-poor water from the lake bottom is circulated to the lake surface, where oxygenation from the atmosphere can then occur. These systems are being utilized in several Illinois water supply reservoirs.

 

Other Systems

Other mechanical circulation systems include surface spray units, impeller-aspirators, and pump-and-cascade systems. While they do set up a circulation pattern in the water, they typically are not designed to destratify a lake. Hence, they probably have more applicability in non-stratified (shallow) lakes and ponds to enhance the water’s oxygen content.

• Surface Spray units consist of a float supporting an electric motor-driven impeller. The rapidly-turning impeller pulls water up a vertical tube and throws it out in an umbrella- or fountain-shaped spray a few to many feet above the lake surface. Atmospheric reaeration occurs in the sprayed water and at the agitated lake surface.

•Impeller-Aspirator systems consist of an electric motor-driven impeller at the bottom of a hollow shaft extending at an angle down into the water. The assembly floats on the lake surface. The rapidly- turning impeller draws air down the shaft and propels water and air bubbles into the lake. Aeration takes place through air bubble/water contact and at the agitated lake surface.