INFLUENCE OF BASIN GEOMETRY ON DIFFERENT GENERIC TYPES
OF AERATION EQUIPMENT
T. C. Rooney, Senior Research Manager
Rexnord Inc.
Milwaukee, Wisconsin 53214
N. A. Mignone, Marketing Group Manager
Envirex Inc.
Waukesha, Wisconsin 53186
INTRODUCTION
The relative oxygen transfer efficiency of different generic types of aeration devices
has been reported in many publications. Unfortunately a direct comparison has always
been difficult for two reasons: (a) The absence of a standardized test procedure which
would normalize all the known or suspected errors; and (b) A lack of understanding
regarding influence of basin geometry.
Rexnord Inc. and their wholly owned subsidiary, Envirex Inc., an industry leader in
screening, clarification and collection equipment, established an aeration development
program in the early '60s. The program included surveys by recognized authorities comparing the relative merits of the types of equipment and actual testing of the major
mechanical and diffused air devices on the market.
In order to satisfactorily evaluate each device, a standardized test procedure was developed. The galvanic dissolved oxygen probe developed by Mancy and Westgarth in
1961 was incorporated into the procedure which has remained basically unchanged for
more than thirteen years [ 1 ].
The acquisition of P.F.T. Co. by Rexnord in 1968 further added to the growing
aerator performance data. Both diffused air and aspirators were marketed by P.F.T. Co.
Testing up to 1969 was conducted in a full or half section of a 16 ft x 32 ft x 16
ft deep basin. This was thought to be representative of a 32 ft length of a 16 ft wide
tank for diffused air, and the 16 ft x 16 ft was adequate for most of the 3 to 7Vi hp
high and low-speed aerators purchased for testing.
It became apparent that extrapolating data from this smaller size could be completely
erroneous. Most of the efficiencies were well above what aeration systems were actually
accomplishing in wastewater treatment applications.
In order to properly evaluate equipment on a large scale, a one million gallon basin
was constructed in 1969. The basin measures 80 ft x 80 ft x 22 ft deep and can be
partitioned into 20 ft x 20 ft, 40 ft x 40 ft and 40 ft x 80 ft plan sections.
The first full scale basin geometry study was conducted using high-speed surface
aerators. The results were presented at the 28th Purdue Industrial Waste Conference [2],
High-speed aerators had been selected by Envirex Inc. as the first mechanical aeration
device to be tested, developed and marketed. The study was possible because a wide
range of unit sizes was available and could be installed and removed economically. Also,
because they were floating units, the water level could be easily varied.
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