Subsurface Aeration System For The
Activated Sludge Process
STEPHEN LABERIS, Product Development Engineer
S.J. CHEN, Manager
Research and Development
Kenics Corporation
Danvers, Massachusetts 01923
THE KENICS AERATOR CONCEPT
A new concept in subsurface compressed air aeration has been developed by Kenics
Corporation of Danvers, Massachusetts, which incorporates the now well-documented
STATIC MIXER ™ principle. The STATIC MIXER device is a motionless in-line mixer
which consists of a series of alternating right and left hand helical elements. The elements
are oriented such that the leading and trailing edges of consecutive elements are at right
angles, (Figure 1), and the entire string of elements is inserted into a pipe.
Figure I — Static mixer device.
The action of the mixer on an air-water stream is two-fold. Fluid shear disperses the air
into fine bubbles, and radial mixing provides complete contacting of air and water. This
combination of large interfacial area and high degree of turbulence results in high oxygen
transfer rates.
The KENICS AERATOR unit is a 12" diameter, 5 foot long STATIC MIXER unit
containing five helical elements. The aerator is oriented in a submerged, vertical position
just above the air inlet point (Figure 2).
Using 5/\s" orifices for air injection, the enhancement of oxygen transfer due to the
aerator has been determined (Figure 3). Thus it is possible to obtain the absorption
efficiency (percent oxygen transfer) of a fine bubble diffuser, with the trouble-free operation
of a coarse bubble diffuser.
The KENICS AERATOR unit functions as an air-lift pump providing circulation of
liquid from the bottom to the top of the basin. A surface jet then radiates outward from the
centerline of the unit, and provides oxygen-rich liquid to the most extreme areas. The
moving layers of liquid generate eddy currents in the liquid bulk, providing sufficient
velocities for solids suspension.
The oxygen transfer and mixing capabilities of the KENICS AERATOR unit are
summarized in Figures 4 and 5.
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