Field Evaluation of Aerators in
Activated Sludge Systems
JOHN T. PFEFFER, Associate Professor
Department of Sanitary Engineering
University of Illinois
Urbana, Illinois
FRED C. HART, Marketing Engineer
Dorr-Oliver, Inc.
Stamford, Connecticut
LAWRENCE A. SCHMID, Assistant Professor
Civil Engineering Department
Kansas State University
Manhattan, Kansas
INTRODUCTION
Studies of aeration systems in the past five years have demonstrated a great
need for evaluation of aeration equipment operating under field conditions. Procedures have been developed for using clean water as standard test conditions.
Also, procedures for the evaluation of the systems under field conditions have
been developed (1). While performance data are readily available for aeration
systems under standard conditions, the translation of these data to field conditions
is one of the most perplexing problems in design of aeration systems.
Some designers have developed performance specifications for the aerators
operating in the field system. This has transferred the problem of equipment sizing from the designer to the supplier and has not solved the overall problem.
Benjes and McKinney (2) provided and example of a performance specification
and a field technique for evaluating the performance of the aerators in the operating environment of a complete-mix activated sludge system. A performance specification similar to the above was also written for the Topeka, Kansas, contract
stabilization plant. This specification required the satisfaction of a performance
test in the operating environment. The results of this testing provide important
factors to be considered in future evaluation and design.
This design and evaluation is unique since the contact stabilization system
studied presents a much different problem than a conventional activated sludge
plant. This is because of the different characteristics of the mixed liquors in the
contact and the reaeration portions of the process. The contact tank contained
2000-3000 mg/1 of suspended solids that are very active, i.e., a low degree of
stabilization of the organic material. The reaeration tank contained 6000-9000
mg/1 of a more stable sludge. The aerators are operating two different conditions.
BASIC THEORY
In order to develop the proper procedure for evaluation of aeration equipment,
it is necessary to have an understanding of the fundamental concepts of oxygen
transfer theory.
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