Application of the Continuous Culture
Theory to the Trickling Filter Process
BILLY H. KORNEGAY, Assistant Professor
School of Civil Engineering
Georgia Institute of Technology
Atlanta, Georgia
JOHN F. ANDREWS, Professor
Environmental Systems Engineering
Clemson University
Clemson, South Carolina
INTRODUCTION
The trickling filter, like other biological processes, depends upon the action of
microorganisms for the removal of organic waste. In spite of the differences in
geometrical design and physical operation between filters and other aerobic treatment processes the reactions involved are essentially the same and may be'represented by the general reaction equation:
Organisms + Substrate + Oxygen-
-New Cells + Metabolic
Waste Products
(1)
The above reaction occurs as the liquid waste stream flows over the filter media
where the organic waste products are adsorbed and subsequently oxidized by the
growth of microorganisms which are attached to the filter media. In view of the fact
that the microbial population of a trickhng filter is responsible for the ultimate
removal of these wastes, it should be possible to describe this removal in terms of
microbial growth by the theory of continuous culture of microorganisms.
The kinetics of fixed microbial films have been previously described by
Kornegay and Andrews (1) using the Monod (2) growth relation for single stage
reactors. This single stage model would certainly not be expected to describe the
substrate removal in trickling filters. However, the kinetic principles presented may
be extended to other reactor systems in which the predicted substrate removal and
residence time distributions more closely approximate those in actual filters. In view
of the experimental problems associated with packed towers and inclined plate reactors, a decision was made to use completely mixed, fixed-film reactors in series to
approximate the plug-flow conditions associated with the trickling filter. Therefore,
theoretical substrate removal equations were developed for both the plug flow and
series reactor models. This was done in order to choose a series reactor system which
would adequately approximate a plug flow model.
THEORY
Plug Flow Model
The trickhng filter is a multiphase, packed tower and as such must be treated in
a different manner than a suspended reactor system, which is normally considered to
be homogeneous. This requirement stems from three major facts previously reported
or observed for trickhng filters. First, the organisms and substrate do not occupy a
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