A UNIFIED APPROACH TO THE DESIGN AND OPERATION
OF THE ACTIVATED SLUDGE SYSTEM
Thomas M. Keinath, Associate Professor
Department of Environmental Systems Engineering
Clemson University
Clemson, South Carolina 29631
Mark D. Ryckman, Manager
Environmental Systems Engineering
D. W. Ryckman & Associates, Inc.
St. Louis, Missouri 63141
Caleb H. Dana, Environmental Engineer
Division of Water
U.S. Environmental Protection Agency, Region IV
Atlanta, Georgia 30306
David A. Hofer, Staff Engineer
Department of Public Works
New Castle County
Wilmington, Delaware 19803
INTRODUCTION
Advancements made by Dick [1-3] and Vesilind [4] with respect to the solids thickening function of final clarifiers in the activated sludge treatment system served to transform
existing system design methodologies to a rational basis.   Their developments, based on the
theoretical contributions of Coe and Clevenger [5], Kynch [6] and Yoshioka, et al. [7],
considered system interactions between the aeration basin and final clarifier.   The first objective of this chapter is to demonstrate how these developments, herein termed the settling
flux approach, can be adapted for evaluating economic trade-offs between alternative system designs and for establishing least-cost designs.
Although the settling flux approach is now occasionally employed for system design,
the technique has not yet been applied to system operation.   Accordingly, the second objective is to demonstrate that the settling flux approach also can be employed by treatment plant operators to monitor the operational state of an activated sludge system.
Biosolids inventory control decisions can thereby be made to (a) prevent system failure,
(b) to maximize overall treatment efficiency and (c) to minimize energy consumption and
the resultant costs of operation.   It will be shown that the settling flux approach is effective for making control decisions in response to both short-term (diurnal) and long-term
(seasonal or yearly) changes in the plant influent and system operational conditions.
While the unified systems approach, developed for designing and operating an activated
sludge treatment train, has been adapted for computer solution, only the methodology is
presented herein.   This permits the reader the opportunity to review the fundamental considerations and to appreciate the simplicity and versatility of this approach.
BACKGROUND
Only a brief introduction to the theory of thickening is included herein.   For a com-
prehensive treatment, the reader is referred to Dick [8] or Vesilind [9].   The basic activated
sludge system considered in this development is shown diagrammatically in Figure 1.
Biosolids Sedimentation
Biosolids that are introduced into a clarifier are transported to the bottom of two
velocity components (see Figure 2):   v, the grativational sedimentation component and
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