Recirculation, Reaction Kinetics and
Effluent Quality in a Trickling
Filter Flow Model
B. ATKINSON, Assistant Professor of Chemical Engineering;
A. W. BUSCH, Associate Professor of Environmental Engineering;
G. S. DAWKINS, Associate Professor of Chemical Engineering.
Department of Chemical Engineering
Rice University
Houston,   Texas
SUMMARY
A mathematical analysis of a flow model for the biological oxidation
process carried out in a trickling filter is presented. The widely used residence time concept is shown to yield the same result, although the form of
the equation restricts its usefulness.
The result of the analysis is studied numerically and analytically for both
laminar and turbulent flow.
It is suggested that the utilization of turbulent fUm filters may result in a
substantial reduction in filter volume requirements.
INTRODUCTION
The trickling filter used for the biological treatment of organic bearing
waste waters represents an extremely complex system of mass transport and
reaction kinetics. However, since the process is essentiaUy controlled by the
liquid phase, a final solution to the problem seems ultimately assured.
For this paper, a simple model has been taken as a basis for mathematical analysis. This model is based on assumptions that are by no means recognized in practice, but it is pointed out that in the past these same assumptions
have been made without recognition and are implicit in the various discussions concerning trickling filter analysis. Thus the model presented provides
a basis for future work to determine the applicability of the assumptions upon
which it is based.
The need for a mechanistic approach to trickling filter analysis is most
apparent, and it is emphasized that an analysis based on a residence time
concept is extremely awkward to handle since it results in an infinite series.
In addition, the application of such a concept to a more complex model
would be very difficult.
DEFINITION OF THE FLOW MODEL
The model of the trickling filter process used in this analysis is that of
film flow in contact with a vertical wall. Figure 1 gives a diagramatic representation of the flow model. In order to make the analysis tractable it is
necessary to make certain qualifying assumptions in specifying the model.
These are listed below:
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