Significance of
Transport Phenomena in
Biological Oxidation Processes
E. L. SWILLEY, USPHS Trainee
J. O. BRYANT, USPHS Trainee
A. W. BUSCH, Associate Professor of Environmental Engineering
Department of Chemical Engineering,
Rice University
Houston, Texas
INTRODUCTION
As process design requirements become more stringent, new concepts and
approaches based on combined mathematical and experimental elucidation of
process characteristics must be invoked. The description of mass, momentum,
and energy transport relationships offers a powerful methodology for analysis of
complex problems. This paper is intended to encourage interest in this approach
to the unit operations problems of environmental engineering.
Description and control of biological oxidation processes require knowledge
of two general aspects of a given reaction system: thermodynamic properties and
kinetic behavior. Thermodynamic properties define the equilibrium state of the
reaction and kinetic behavior establishes the rate at which the reaction proceeds
toward equilibrium. The rate processes which determine kinetic behavior include
not only thermochemical kinetics but also physical processes external to the
chemical reaction taking place. It is this latter aspect of systems behavior which
is discussed in this paper.
In biological unit operations many rate processes may be described by the
classical equations of momentum, mass, and energy transfer (1). That is to say,
many of the relevant rate processes may be classed as transport phenomena. The
transport equations may not usually be applied in a complete sense, but this paper
shows that consideration of certain simplified models can provide a great deal of
insight into, and feeling for, the more important mechanisms of a given reaction
system.
GENERALIZED AEROBIC SYSTEM
A generalized aerobic biochemical reaction process can be considered and
the component rate processes pointed out.   The final biochemical reaction is:
substrate + oxygen    ^-    products
The major processes involved in such a system are graphically represented
in Figure 1.   These are:
(a) Interphase transport of gaseous oxygen and solid phase substrate into solution (rates R^ and R4).
(b) Intraphase transport of dissolved oxygen and substrate to the vicinity of a
metabolizing organism (rates Rg and R5).
- 821  -