TESTING FOR OXYGEN TRANSFER EFFICIENCY
IN A FULL-SCALE DEEP TANK
R. Gary Gilbert, Senior Environmental Engineer
S. J. Chen, Manager
Research and Development Department
Kenics Corporation
North Andover, Massachusetts 01845
INTRODUCTION
Designer/Customer Concerns
During the past few years, claims made by aeration equipment manufacturers and
others concerning oxygen transfer testing and analysis for determination of equipment
efficiency have, at times, caused confusion and apprehension on the part of the designer
or customer evaluating a proposed aeration system.   The determination of oxygen transfer
efficiency at standard conditions probably has been the most controversial area with respect to the design and application of an aeration system.   Standard conditions are defined
as:   water temperature = 20 C and atmospheric pressure = 760 mm Hg.
The two major concerns in the determination of oxygen transfer efficiency for a specific
application are:   (a) testing procedures employed and methods of analysis used to interpret
the raw data, and (b) scale-up of the test results from the test facility to the operating
aeration system.
The purposes of this paper are to:   (a) present the test procedure used to evaluate
Kenics STATIC MIXER Aeration Systems, and (b) evaluate various data analysis methods
using the fundamental oxygen transfer theory.   The clean-water sodium sulfite reaeration
testing method is used.   Scale-up is not a problem because the Kenics test facility aerator
geometry can be arranged to model, on a full-scale basis, each particular application.
Fundamental Theory
The oxygen transfer mechanism in wastewater treatment is commonly based on the two-
film theory of mass transfer of oxygen from the gas phase to the liquid phase [1-3].
The basic equation which describes the oxygen transfer process is:
-^-= KLa (C*-C) (1)
dt
dC
where:     —— =   rate of oxygen transfer, mg/l/hr
dt
K[_a =   overaU oxygen transfer coefficient, hr"
C*   ■  dissolved oxygen saturation concentration, mg/1
C     ■   dissolved oxygen concentration at time t, mg/1.
KLa is the product of the liquid fUm coefficient (Kl) and the unit interfacial area (a)
available for oxygen transfer.   Since it is not possible to measure the interfacial area under
most testing conditions, the overall transfer coefficient is used.   Kl is the limiting mass
transfer factor.   Therefore, a mass balance of the liquid side of the reaction adequately
describes the true oxygen transfer rate.
In order to calculate the rate of oxygen transfer (dC/dt) for a submerged aeration system,
both the overall transfer coefficient (KLa) and dissolved oxygen saturation concentration
(C*) must be determined experimentally through aeration testing.   Both Kj^a and C* are
functions of the aeration equipment, tank geometry, air supply rate, and the physical and
chemical characteristics of the test water and air supply.
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