19    KINETIC ANALYSIS OF ROTATING BIOLOGICAL
CONTACTORS
TREATING HIGH STRENGTH WASTES
Mohamed F. Hamoda, Professor
Civil Engineering Department
Kuwait University
Kuwait
Francis Wilson, Senior Lecturer
Department of Civil Engineering
University of Canterbury
New Zealand
INTRODUCTION
There has been a growing interest in the application of biological fixed-film (attached growth)
processes, such as the rotating biological contactor (RBC), for the aerobic treatment of industrial
wastewaters. Stability and long retention of microorganisms in the RBC process proved to be advantageous.1 Although the RBC process has been extensively examined for municipal wastewater treatment applications,2 its performance during the treatment of high-strength industrial wastewaters has
not received equal attention. Process kinetics have yet to be determined under conditions of high
influent organic concentrations and long retention times encountered in such situations in order to
adequately design the RBC process.
Fixed-film systems, such as the RBC process, have traditionally been designed using empirical
relationships between the pollutant removal efficiency and hydraulic or organic loading rates. A more
adequate approach to the analysis of biological systems commonly involves biological removal kinetics combined with the proper hydraulic regime to yield equations describing system performance. In
fixed-film processes, however, mass transfer resistances associated with both the liquid phase (external mass transfer) and the biofilm (internal mass transfer) could result in significant concentration
gradients from bulk liquid to biofilm reaction sites, and may control system performance.3 Some
investigators4,5 have verified the importance of the liquid film in affecting removal rates in fixed-film
systems, while others6,7 emphasized the importance of the biofilm in controlling substrate removal
rates. Studies by Atkinson et al} and Williamson and McCarty9 have shown the importance of both
films in describing fixed-film removal kinetics.
The type of kinetics used to describe biological reaction rates within biofilms include both Monod10
and zero order kinetics.'' Results obtained by Shieh12 indicate that the observed reaction rate in a zero
order biofilm process is first order if external mass transfer is rate-limiting. The reaction order
changes from first order to half order when internal mass transfer becomes predominant. A comprehensive review of biofilm kinetics has been presented by Harremoes.'3
A number of models have been used to describe the RBC process. Komegay and Andrews7 proposed a model based on biological growth using Michaelis kinetics which neglects mass transfer
resistance. Grieves,14 however, has applied mass transfer resistances to the RBC process using both
first order and Michaelis kinetics for substrate utilization. Friedman15 has employed two models to
analyze RBC data, one of which is an empirical model assuming that substrate diffusion controls the
overall reaction rate while the other is a simple first-order model. A model which incorporates
simultaneous oxygen and substrate transport with both liquid and biofilm resistances was developed
and verified by Famularo et al}* A design model that utilizes the total organic loading concept was
presented by Kincannon and Stover17 with an analytical solution. Various analytical and graphical
methods for the design of the RBC process were discussed by Lumbers.18
In view of the literature findings, it is recognized that incorporation of mass transfer limitations,
substrate diffusion and oxygen diffusion with biochemical reactions is required in the formulation of
RBC kinetic models. These parameters may be very important in the overall performance of fixed-
44th Purdue Industrial Waste Conference Proceedings, © 1990 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Primed in U.S.A.
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