DUAL NONSTEADY-STATE EVALUATION OF
STATIC AERATORS TREATING PHARMACEUTICAL WASTE
James A. Mueller, Associate Professor
Environmental Engineering and Science Program
Manhattan College
Bronx, New York 10471
Richard Donahue, Senior Engineer
Merck and Company, Inc.
Rahway, New Jersey 07065
Russell Sullivan, Applications Engineer
Chemineer-Kenics, Inc.
North Andover, Massachusetts 01845
A bench scale activated sludge design study was conducted at the Merck & Co., Inc.
Stonewall Plant in Elkton, Virginia, from January 10, 1980 through May 30, 1980. The
purpose of this study was to define the design criteria for a new activated sludge system to
replace an existing activated sludge system and rock biofilters. The full scale aeration system
design was based on the bench scale oxygen utilization data and a series of bench scale
alpha and beta tests. An alpha value of 0.6 and a beta value of 0.95 were used for the full
scale plant where 1000 Kenics aerators will be installed during May and June 1982.
A wastewater treatment pilot plant containing static aerators was installed in Elkton
after the bench scale study was finished to provide confirmation of the full scale process
design and to generate enough sludge for thickening and dewatering studies. Pilot plant
operations began in January 1981. These facilities were used to perform oxygen transfer
tests to check the clean and process water oxygen transfer coefficients used to design the
Kenics static aeration system.
THEORY
The dual nonsteady state technique requires two consecutive nonsteady state aeration
tests to be conducted at different gas flows in an aeration tank having a constant oxygen
uptake rate [ll. For a completely mixed system such as the Merck plant, data collection
and analysis is relatively straightforward. A schematic of the technique with typical data
is shown in Figure 1. The equations describing the system are given below and yield estimates of the field oxygen transfer coefficients under both conditions as well as the oxygen
uptake rate and field saturation value in the aeration tank.
A nonsteady state differential equation is obtained from a mass balance on oxygen for
the completely mixed system shown in Figure 1.
dc C - C
— = K.aafC-ocf-C) -R ♦--  (1)
dt 'o
Nomenclature is described in the appendix. Substituting the steady state solution describing
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