Section 13. REFINERY WASTES
ACCELERATING THE DYNAMIC RESPONSE OF BACTERIAL
POPULATIONS IN ACTIVATED SLUDGE SYSTEMS
Curtis S. McDowell, Vice President
Thomas G. Zitrides, President
Polybac Corporation
Allentown, Pennsylvania 18103
INTRODUCTION
Most industrial biological wastewater treatment systems depend on "natural selection
processes" and the "ubiquity principle" to establish appropriate populations of microorganisms for degradation of organic wastewater contaminants. The dynamic response
of the populations selected in these systems, consequently, establishes the overall
stability and performance of these wastewater treatment systems in the face of changes
in strength and/or composition of the wastewater.
Since the variation in wastewater characteristics is generally beyond the control of
the operator, his control of the dynamic response of the biological system is, in many
cases, inadequate. The operator thus struggles, sometimes for weeks, to restore satisfactory treatment following upsets caused by variations in strength and/or composition of
the wastewater. In essence, the timeframe required for restoration of the appropriate
microbiological populations through natural selection and ubiquity is sometimes long
in relation to the time of response needed to protect the receiving waters from
contamination.
Recently, the apparent dynamic response of "natural populations" has been modified
significantly through the application of a spectrum of adapted, mutant microorganisms
to a full-scale operating activated sludge system. The improvement in dynamic response
as measured by improved performance and plant stabdity was significant in comparison
with a parallel operating control system. Thus, the operator has been given a new
method of exerting some control on the dynamic response of his treatment system.
The improvement in dynamic response generated through introduction of the adapted,
mutant microbes prompted development of a model. A model would facditate description of the impact and limitations of applying adapted, mutant bacteria to activated
sludge systems, in terms of conventional biological system kinetics. Model   development
was important, therefore, to future development of this new technique for enhancing
the performance of biological treatment systems.
This chapter presents a brief case history to dlustrate the impact that adapted, mutant
bacteria can have and summarizes progress to date on the development of a model.
ACCELERATED DYNAMIC RESPONSE-A CASE HISTORY
The impact which adapted, mutant bacteria can have on refinery activated sludge
systems is iUustrated by a test program conducted by Exxon, U.S.A. [Ij. Two identical
activated sludge systems operating in parallel at a sludge age of approximately 15 days
were used to demonstrate the efficacy of adding adapted, mutant microbes. One of
the two units (Figure 1) was treated with the adapted, mutant bacteria (Phenobac1^
while the other operated as a control unit.
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