Multi-Stage Biological Processes for
Waste Treatment
EUGENE P. WILLIMON, JR., Research Engineer
Deering Milliken Research Corporation
Spartanburg, South Carolina
JOHN F. ANDREWS, Professor
Environmental Systems Engineering
Clemson University
Clemson, South Carolina
INTRODUCTION
Biological processes for waste treatment have been operated as continuous
systems for many years. However, the theoretical analysis of continuous biological cultures has been developed since 1940, beginning with the studies of Monod
(1), Utenkov (2) and Malek (3). Since this early work, considerable attention has
been given to continuous culture, and symposia on the subject have been held in
Prague (1958 and 1962), in Chicago (1958), in Stockholm (1959), in London (1960
and 1964) and in Tokyo (1963).
The significance of multi-stage continuous culture theory has only recently
been recognized. Interest was shown in multi-stage systems at the 1962 Prague
symposium which included an important contribution by Herbert (4). This interest
resulted from basic studies of the fundamental principles of these systems, and
applications of these principles are gradually being made to fermentation and
waste treatment processes.
Several investigations (5, 6, 7) have indicated that the anaerobic digestion
process can be expressed in a simplified manner as three biological reactions oc-
curing in series, as shown in Figure 1. As is usually the case, optimum environmental conditions for the different organisms vary from group to group and species
to species. It appears then that the isolation of the biological reactions into
separate vessels would enable the environmental conditions to be varied in order
to maximize the rate of each reaction. It should be emphasized that the environmental conditions required for optimization of each stage are still largely unknown.
The purposes of this paper are to examine the use of multi-stage systems in
biological processes, including several multi-stage waste treatment processes, and
to discuss the results obtained in an exploratory study of multi-stage digestion.
APPLICATION OF MULTI-STAGE SYSTEMS TO BIOLOGICAL PROCESSES
Although most of the interest in multi-stage systems has developed in recent
years, it is interesting to note that Buhring (8) in 1929 patented a two vessel process for the cultivation of baker's yeast. In 1952 Malek (9)made use of the multistage process as a method of distributing a culture into several stages in order to
better determine the kinetics of the individual physiological states. Following
Malek's early work numerous applications of multi-stage theory have been reported
in several extensive reviews (10, 11, 12).
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