COMPUTER SIMULATION AND DESIGN OF
SEQUENCING BATCH BIOLOGICAL REACTORS
Robert L. Irvine, Associate Professor
Richard O. Richter, Graduate Student
Department of Civil Engineering
Notre Dame University
Notre Dame, Indiana 46556
INTRODUCTION
The national goal of the Federal Water Pollution Control Act Amendments of 1972
(PL 92-500) is that the discharge of all pollutants into navigatable waters be eliminated
by 1985 [1].   This goal would appear to be an expression of the attitude of Congress
towards pollution in general rather than a directive to eliminate the discharge of pollutants.   Indeed PL 92-500 sets a deadline of July 1, 1983 for point sources which requires
"best available technology economically achievable" for treatment works [2].   The implementation of such technology will not eliminate the discharge of all pollutants.   The time
period between July 1, 1983 and 1985 certainly is not sufficient to meet the national
goal stated; however, clear recognition of the need for a general national awareness in pollution abatement was crystallized in PL 92-500.
The art or science of pollution abatement technology has progressed rapidly during
the past two decades; yet, even with these advances we find technology that was developed
in the 1920s and 1930s carrying the major treatment burden of today.   Primary treatment remains virtually unchanged.   Secondary treatment centers around operational modifications of the biological process.   Tertiary treatment, while relatively new, employs the
early technology of water treatment plants.   Attention must be focused on that course
of action which will meet with the national goal stated by Congress.
Recognition has been given to many important problem areas.   More sophisticated control devices are being used to regulate new and existing treatment plants [3-9].   One
treatment plant operator making $8000/yr no longer has the sole responsibility of operating
a multimillion dollar treatment plant.   Further design approaches continue to assume
mixing patterns, which may or may not exist in reality, for the various operations and
processes within a treatment plant.   Variations in flow and overall waste concentration are
handled empirically and variations in waste type are often ignored.   Modifications in
treatment technology which effectively handle the uncertainty associated with mixing
patterns and waste variations will allow a major step forward in insuring the reliability
of treatment plant performance.   Then process control will approach its full potential
and the skilled operator will be able to apply his expertise.   Otherwise, the control devices and the operators will be too severely constrained by the limitations of the treatment system itself.
Without question, progress has been made in the area of mixing and waste variations.
Complete mixing has been assured in rapid mix tanks and many activated sludge tanks.
Flow variations are minimized or eliminated in many equalization tanks.   Sedimentation
tanks, however, are designed with far less than ideal flow patterns [10, 11].   Equalization
tanks do little more than shift peaks for wastes that have dramatic variations in waste
strength.   Because of these problems consistent and reliable performance of treatment
plants can be neither guaranteed nor expected without excessive expenditures and increased
operational complexity.
Perhaps fortuitously in this bicentennial year a look to the past once again uncovers
a treatment approach which may provide the direction necessary to minimize problems
of mixing and waste variations.   Early biological waste treatment plants employed fill
and draw reactors [12, 13].   While it was noted that these systems resulted in more
reliable treatment performance, the complexities of operation resulted in the development
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