• 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 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.
consist of a large electric pump that moves lake water to the top
of a ramp-like chute containing numerous baffles. The water cascades down
the ramp and falls back into the lake at a point located as far as
possible from the water inlet (to prevent recycling of just-pumped water).
Aeration occurs in the cascade chute and in the plunge pool as the
water flows away from the ramp.