FIELD TESTING FOR OXYGEN TRANSFER AND MIXING IN
STATIC MIXER® AERATION SYSTEMS
R. Gary Gilbert, Technical Manager
Water and Wastewater Systems
Donald Libby, Senior Research Engineer
Kenics Corporation
North Andover, Massachusetts 01845
OXYGEN TRANSFER STUDIES
Introduction
Full-scale factory testing of static mixer aeration systems has been reported upon elsewhere [ 1,2]. The test facility consisted of a 38.5-ft-diameter tank containing 46 aerators.
Water depths to 30 ft were tested. It was believed that the factory test facility was of sufficient size to generate oxygen transfer data which could be used directly in design applications.
Scale-up of results from a test facility to the design application is one of the most important considerations in the evaluation of aeration equipment. Secondly, oxygen transfer
efficiency in terms of pounds of oxygen per horsepower hour is a required parameter for
evaluating operating cost of an aeration system. Scale-up factors and transfer efficiency cannot be accurately measured at the factory test facility. Therefore, field testing must be conducted to generate the necessary information.
Several field oxygen transfer tests were conducted at wastewater plants containing static
mixer aeration systems. The results of this field testing are compared with data from the
factory test facility for scale-up. Oxygen transfer efficiency was calculated from measured
electrical power consumption at two of the facilities tested.
Mixing studies were conducted at one of the facilities. Flow and nonflow stimulus-response testing was used to determine mixing characteristics. Dispersion characteristics and
aerator pumping rates are compared.
Description of Aeration Systems and Equipment
Clean water sodium sulfite reaeration testing was conducted at three industrial wastewater
treatment facilities using static mixer aeration systems in the activated sludge process. Table
I contains sizing information for each aeration system. Photographs of the aeration tanks
tested are shown in Figures 1 and 2. Two-phase flow through a clear 5-element aerator is
illustrated in Figure 3. Bubble formation and turbulence shown in Figure 3 are representative of conditions occurring in the aerators at the three aeration systems reported upon herein.
Hoffman Model 79104 centrifugal blowers supply air at all three wastewater treatment
facilities. Air flow measuring equipment is installed in the main header pipes supplying each
individual aeration tank tested.
Continuous-recording watt meters were installed on motor leads during testing of Plants
A and B. Oxygen transfer efficiency was determined directly from these data and the experimentally determined oxygen transfer rates. Dissolved oxygen (DO) measurements were
made by calibrated DO probes located at various depths throughout the aeration tanks.
The DO measurement system consists of an analyzer, agitator-equipped DO probes and
a recorder. The DO probes are temperature-compensated membrane electrode type containing
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